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Chapter XIV
COPPER-BASE ALLOYS
 

SELECTION OF ALLOY

COMPOSITION G

Composition G, or gunmetal, is a tin bronze which has good resistance to salt-water corrosion and to dezincification. These properties make it a useful alloy for castings required aboard ship. It is often used in valves and steam fittings.

COMPOSITION M

Composition M, or valve bronze, is a tin bronze to which lead has been added to improve the machinability. It can be used in place of Composition G if its lower strength is adequate.

HYDRAULIC BRONZE

This alloy, the familiar 85-5-5-5 alloy, is a leaded red brass, also known as ounce metal. It is a general-purpose alloy having good corrosion resistance. Castings subjected to hydraulic pressures up to 350 pounds can be made from this alloy.

MANGANESE BRONZE

Manganese bronze castings are strong, ductile, and are corrosion resistant to sea water, sea air, waste water, industrial wastes, and other corroding agents. Typical uses are in propeller hubs, propeller blades, engine framing, gun-mount castings, marine-engine pumps, valves, gears, and worm wheels. Manganese bronze has an excellent combination of corrosion resistance, strength, and ductility that makes it very useful for the various marine castings. It has the disadvantage of having a high solidification shrinkage and a comparatively high drossing tendency. These disadvantages, however, can be overcome by proper design and casting procedures.

YELLOW BRASS

Castings which are not subjected to air or water pressure but which require corrosion resistance are made from yellow brass. It is a general-purpose alloy used for fittings, name plates, and similar applications. Naval brass is a yellow brass which has a higher corrosion resistance than commercial yellow brass.

ALUMINUM BRONZE

Strength, hardness, ductility, and corrosion resistance for the properties which make

  aluminum bronze a desirable alloy for shipboard use. Higher strength and hardness can be obtained in some of the alloys by proper heat treatment. Typical uses are for worm gears, bearing sleeves, pinions, and propeller blades.

70-30 CUPRO-NICKEL

Cupro-nickel has an excellent resistance to salt water corrosion. Fittings such as couplings, tees, ells, pump bodies, and valve bodies are cast from this alloy.

NICKEL SILVER

Nickel silver provides good mechanical properties and excellent resistance to corrosion and tarnish. It has a pleasing white color that makes it useful where the appearance of the cast part is important.

HOW COPPER-BASE ALLOYS SOLIDIFY

Copper-base alloys solidify by the nucleation and growth of crystals as described in Chapter 1, "How Metals Solidify." There are two types of alloys so far as solidification is concerned: (1) those which have a short solidification range, and (2) those which have a long solidification range. A long solidification range means that an alloy solidifies slowly over a wide range of temperature. Ordinary solder is such an alloy, and solidification over a long range is shown by the fact that the alloy remains mushy for quite a while during solidification. Alloys with short solidification ranges do not show this mushy behavior. Manganese bronze, aluminum bronze, and the yellow brasses have a short solidification range, which cause their high solidification shrinkage. Composition G, Composition M, and hydraulic bronze have a long solidification range, which permits extensive growth of the dendrites. These alloys have a tendency toward interdendritic shrinkage and microporosity, with the result that piping in the riser is not so pronounced.

Solidification of all the alloys begins at the mold and core surfaces. The part of the alloy having the highest solidification temperature (the copper-rich material) solidifies first and a crystalline structure is formed. This is the exterior shell of the casting. As the molten metal continues to cool, the parts of the alloy with the lower freezing temperature will crystallize on the already-growing dendrites. This process continues until the metal is completely solid. The composition of the alloy within the

 

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dendrites will vary from the center to the outer edges. The center of the dendrite (first part to solidify) will have a composition corresponding to the high-freezing part of the alloy, while the outer parts of the dendrite will have a composition corresponding to the last part of the alloy to solidify. Any lead or other insoluble material in the alloy will be trapped between the dendrites. Failure to properly feed alloys having a long solidification range results in micro-porosity and leakage under pressure.

PATTERNS

Patterns for copper-base alloy castings should be constructed with the following points in mind:

(1) Patterns should be parted in such a manner that the important machined surfaces are in the drag.

(2) Heavy sections should be cored or altered in such a way that sections will be of uniform thickness or will be gradually tapered.

(3) Where there is a possibility of casting distortion, tie-bars or brackets should be placed on the pattern as required.

(4) Follow boards and "stop off" bracing should be used to avoid pattern breakage or warpage.

(5) Core boxes should be constructed to permit adequate venting of the cores.

(6) In constructing cylindrical bushings or circular patterns, annular risers should be made as part of the pattern.

(7) Parting lines should be made as even as possible. Flat-back patterns are preferred.

 

MOLDING AND COREMAKING

SAND MIXES

Various sand mixes and properties are given here as a guide for preparing sand for the different metals poured. As has been mentioned in Chapter 4, "Sands for Molds and Cores," the best properties for any sand mixture can only be obtained through proper mixing by the use of the sand muller. Also, the maintenance of properties of a sand mixture can be accomplished only through continuous and correct sand-testing procedures.

Most copper-base alloys will be cast in the all-purpose sand described in chapter 4. When time and materials are available, better results will be obtained by using the following recommended sand mixtures.

Compositions G and M. Sand used for these alloys should have properties within the following limits, depending on the size of the casting.

Grain Fineness
Number
100-140
Clay Content, percent 5 for synthetic sand to 20 for natural sand
Permeability, AFS units 10- 50
Green Compressive Strength, p.s.i. 4-9
Moisture, percent 5-6

The table of properties given below for hydraulic bronze can also be used as a guide for Compositions G and M.

For some types of work, a molasses water spray for the mold surface may be used. Facing sands are not generally used, but for heavy castings a plumbago coating may be used.

Hydraulic Bronze. Sand properties for castings of various weights and section thickness are given below:
 

Casting Weight,
pounds
Section Thickness,
inches
Permeability,
AFS units
Green Compressive
Strength, p.s.i.
Moisture,
percent
Up to 1 1/2 20 7 6.5
1 to 10 1 30 7 6.0
10 to 50 2 40 7 6.0
50 to 100 3 50 8 5.5
100 to 200 4 60 10 5.5
200 to 250 5 80 12 5.5

 
The preceding sand properties should be used as a guide in obtaining similar properties with the all-purpose sand.

Manganese Bronze. Sand which has too high a moisture content usually results in damaged

  castings. To overcome this condition, the sand should be worked with moisture content on the low side. This is a good general rule to follow when casting any alloy, because water is almost always harmful to any alloy.
 

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Typical properties of sand for manganese bronze are as follows:
Casting Weight,
pounds
Section Thickness,
inches
Permeability,
AFS units
Green Compressive
Strength, p.s.i.
1 to 100 1/4 to 3/4 20 8
Up to 250 3/4 to 1-1/4 40 8
500 1-1/4 to 1-3/4 60 10

 
Moisture contents of 5 to 6 percent are normally used for manganese bronze castings. Because of the high strength of manganese bronze, strong cores may be used with this alloy without causing excessive strains in the casting. A graphite core wash may be used to make core removal from the casting easier.

Yellow Brass. A sand having a permeability of 20, green strength of 7 p.s.i. and a moisture content of 6 percent is suitable for the majority of small castings made from yellow brass. Castings up to 50 pounds with wall thicknesses up to 1/2-inch can be made with sand having these properties.

Aluminum Bronze. Aluminum bronze alloys are difficult to cast in green sand molds because of the high drossing tendency of the alloys and the possibility of surface pinholes and porosity in the finished castings. The defects caused by high moisture in the green sand molds can be minimized by using dry sand molds. It is recommended that dry sand molds be used as described in chapter 4. Property ranges for sand mixtures are as follows:

Grain Fineness 100-160
Clay Content, percent 10-20
Permeability, AFS units 20-50
Green Compressive Strength, p.s.i. 5-12
Moisture, percent 3-6

Cupro-Nickel and Nickel Silver. The 70-30 cupro-nickel alloys and the nickel silver alloys should have a sand with a permeability between 40 and 60 and a moisture content between 4.5 and 5.5 percent. The sand grain size should be about 95 Fineness Number, with an 18 percent clay content. Nickel silvers are sensitive to gas from organic binders. Such binders, therefore, should not be used.

PROCEDURES

The procedures for coremaking, molding, and the use of washes are the same as the practices described in previous chapters. Certain procedures are repeated here to stress their importance to copper-base alloy castings.

Coremaking. Cores used in making copper-base alloy castings should be strong and well vented. Many of the castings are of such a design that considerable pressure is placed on

  the core during the pouring of the casting. Care must be taken, however, not to make the cores too hard or hot cracks and tears will result. Refer to Chapter 4, "Sands for Molds and Cores," for representative core mixes, and to Chapter 6, "Making Cores," for coremaking techniques.

Molding. Good molding practice as described in Chapter 5, "Making Molds," is the principal requirement when making molds for copper-base alloy castings. Extra precautions should be taken to ram the molds as uniformly as possible. Uneven ramming will cause localized hard spots and agitation of the molten metal at these points because of nonuniform permeability. In high-zinc alloys, this will cause zinc to boil out and produce rough surfaces at the areas of agitation. Alloys containing aluminum will form dross at these areas and the castings will be dirty.

Washes. Washes for copper-base alloy castings are used primarily to prevent metal penetration. The wash most generally used in plumbago. Molasses water is sometimes sprayed on the mold surface to provide a stronger bond in the surface sand. A typical molasses-water mix contains one part of molasses thoroughly mixed with 15 parts of water.

GATING

"Gating Principles," described in Chapter 7, "Gates, Risers, and Chills," should be used in the gating of Compositions G and M. Because these two alloys are tin bronzes and subject to interdendritic shrinkage, the gating system should be designed to make maximum use of directional solidification.

Heavy bushings, or "billets," can be cast by two methods to obtain directional solidification. They can be molded horizontally, as shown in figure 224, by using a thin gate to provide a choking action and causing the metal to enter the mold quietly. The mold should be tilted with the riser end lower during pouring to provide an uphill filling of the mold. The mold is then tilted with the riser up to provide maximum gravity feeding. A second method of gating bushings is to use a circular runner with pencil gates. This method, if used with a pouring temperature on the low side, will provide the best conditions for directional solidification. The cold metal will be at the bottom of the mold

 

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and the hottest metal at the top, where it will be available to feed solidification shrinkage. A third method may be used, which utilizes a tangential gate as shown in figure 225. This method permits the metal to enter the mold with the least amount of agitation, but is not so good for directional solidification of the metal.

A gating system that has proved successful for the production of valve bodies uses a sprue diameter of 1/2 inch or 5/8 inch, depending on the casting size. The runner is placed in the cope, and a reduction of at least 20 percent in cross-sectional area from the sprue to runner to gate is used.

Manganese bronze castings can be gated successfully by using a reverse horn gate into the riser and gating from the riser into the casting is illustrated in figure 226. When a number of small castings of manganese bronze or red brass are made in the same mold and gated from the same sprue and runner system, a gating system such as shown in figure 227 can be used. The runner is placed in the cope and the ingates in the drag. The castings are gated through small blind riser s. The dimensions indicated for the runner and ingates show the range in sizes that can be used and depend on the size of the castings.

Agate with a large cross section (as shown in figure 228) is used for thin castings made in nickel silver. This is a plate cast in nickel silver. Notice the many ingates to permit rapid filling of the mold and also the large size of the runner. The gating system should also give uniform distribution of the metal in the mold. A gating system which resulted in a defective cupro-nickel check valve is shown in figure 229. The improved method of gating that produced a pressure-tight casting is shown in figure 230.

RISERING

Risering of copper-base alloy castings follows the same principles as described in Chapter 7, "Gates, Risers, and Chills." Castings made from Composition G, Composition M, and hydraulic bronze may give some difficulties in feeding because of their long solidification ranges that permit strong dendritic growth and make feeding of heavy sections difficult. Risers for these alloys will have to be made larger to obtain proper feeding. In connection with the risering of these alloys, it is only through experience and records of successful risering practice that correct risering procedures can be developed.

The correct placement of risers as well as the correct size is important. Good and bad risering practices are shown in figures 231, 232, 233, and 234. Figure 231 shows a globe valve

  that was poured without risers on the flange sections. Porosity in the casting caused low physical properties. A revised procedure is shown in figure 232. Notice that risers were used on all of the flange sections. This risering arrangement resulted in a casting with greatly improved physical properties because of the improved soundness. Similarly, the lack of risers on a high-pressure elbow, as shown in figure 233, resulted in microshrinkage in the flange section with low physical properties. The revised risering system shown in figure 234 resulted in improved physical properties in the casting.

Risers for nickel silver and cupro-nickel alloys must be large to provide enough molten metal to feed heavy sections and to compensate for the high solidification shrinkage. An example of a suitable riser is shown in figure 235. The casting is a 4-inch check valve body cast in cupro-nickel.

CHILLS

The use of chills to aid in directional solidification is described in Chapter 7, "Gates, Risers, and Chills." The procedures are generally the same for all copper-base alloy castings. Alloys having a long solidification range (such as G metal, M metal, and hydraulic bronze) require a stronger chilling action than the metals with shorter solidification ranges (manganese bronze, aluminum bronze, and yellow brass). Stronger chilling action means that if two identical castings are made, one with a long solidification-range alloy and one with a short solidification-range alloy, the long solidification-range alloy will require larger chills or chills with higher heat capacity in order to obtain the same amount of directional solidification as the short solidification-range alloy.

Recent studies have shown that special chills may be used to produce strong directional solidification in G metal. The chills used are wedge-shaped, as shown in figures 236 and 237. Their use is recommended to produce the desired directional solidification in G-metal castings. The size of the tapered chills must conform to the size of the casting. Chills 24 inches long were cut into two 12-inch pieces to prevent warping of the chills. Fifteen-inch chills were used in one piece. A general idea of the placing of the chills for flat castings can be obtained from figure 236. Figure 237 shows the use of chills on a bushing casting. Notice that the casting was top poured. The chills should not extend to the riser, because this would cause heat extraction from the riser and nullify the desired directional solidification. It is suggested that records be kept on the use of chills of this type so that effective use can be made of experience gained with their use.

 

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VENTING

Venting procedures used for other metals and alloys are applicable to copper-base alloys.

MELTING

Copper-base alloys can be melted in any of the melting units that are to be found aboard repair ships. The melting procedures for all the units are essentially the same. Oil-fired furnaces require closer attention during melting because of the need for maintaining the proper furnace atmosphere.

When melting copper-base alloys, it is important to develop some means of determining the quality of the melt. This is best done by the use of a fracture test. Refer to Chapter 21, "Process Control," for details on developing a fracture test.

OIL-FIRED CRUCIBLE FURNACES

Any copper-base alloys that are melted in an oil-fired crucible furnace should be melted under a slightly oxidizing atmosphere. This means that at all times there must be a slight excess of air in the combustion chamber. An easy method for checking the nature of the furnace atmosphere is to hold a piece of cold zinc in the furnace atmosphere for 2 or 3 seconds. If the zinc shows a black carbon deposit when it is removed, the atmosphere is strongly reducing and more air is required. If the zinc is straw colored, the atmosphere is slightly reducing. If the zinc remains clean, the atmosphere is oxidizing. It is good practice to check the furnace atmosphere before any metal has been charged into the crucible.

General Procedure. When charging a crucible, the remelt material such as gates, riser s, sprues, and scrap castings should be charged first. Ingot material may be charged on top if there is sufficient room in the crucible. Under no circumstances should any of the charge material extend above the crucible. Such conditions will permit direct flame impingement with resulting high oxidation losses and gas pick up by the metal. If the crucible is not large enough to accommodate the entire charge, the first part of the charge should be melted and the remainder added after the initial meltdown. Any ingot material that is added to the melt should be thoroughly dried and preheated.

No fluxes, glass-slag covers, or charcoal should be used at any time during melting. Experience has shown that any of these practices may lead to poor quality metal.

  Procedure for Tin-Bronzes. Melting should be done under oxidizing conditions as described under "General Procedure." The melt should be superheated only 25° to 50°F. above the pouring temperature and thoroughly skimmed before removal from the furnace. The melt is skimmed again if it is transferred to a pouring ladle. The melt is then flushed by plunging a piece of zinc (4 ounces for each 100 pounds of melt) deep below the surface of the melt. A phosphorizer or a pair of refractory-coated tongs are used for this purpose. Extreme care should be taken to insure that any tools used for this purpose are thoroughly dry. Moisture on the tools not only causes undesirable gassing of the metal, but also causes severe splashing of metal with danger to personnel.

The melt is allowed to stand for 2 or 3 minutes and come into equilibrium with the surrounding atmosphere. It is then deoxidized by plunging phosphor-copper into the melt (2 to 3 ounces for each 100 pounds of melt). The same precautions must be observed as when flushing with zinc. The melt is then ready for pouring into the molds.

Procedure for Manganese Bronzes and Yellow Brasses. The melt should be brought up to a temperature of about 1,800°F. to 2,000°F. in a slightly oxidizing atmosphere, the temperature at which the flaring of zinc occurs, and allowed to flare for a few minutes under a good ventilating system. The purpose of the flaring is to flush the melt with the aid of the escaping zinc vapor. Under normal operation, a flaring period of 3 to 5 minutes will result in a zinc loss of approximately one percent. Care should be taken not to overheat these alloys, because the zinc loss and resulting zinc fume will be a serious health hazard. After the flaring is finished, the melt should be skimmed. The crucible is then removed from the furnace and the melt skimmed again or, if the melt is poured into a ladle, it is skimmed after the transfer. Enough zinc should then be added to replace that lost by flaring. The melt should be allowed to cool to the desired temperature and poured.

Procedure for Aluminum and Silicon Bronzes. These two alloys are also melted under oxidizing conditions. The control of the furnace atmosphere is more critical than for the previously described alloys. Aluminum and silicon oxidize very easily and form dross and surface films. Therefore, the atmosphere must not have too much excess air or the dross- formation and oxidation losses will be high. The melt should be superheated at least 25 to 50°F. above the pouring temperature and skimmed before removal from the furnace.

If any zinc additions are required, they are added at this time. The melt is then allowed to cool to the desired temperature and poured.

 

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Procedure for Cupro-Nickel. Electronickel, electrolytic copper, 97 percent metallic silicon, and low-carbon ferromanganese are used in making up charges of cupro-nickel. Nickel-copper shot is used to make nickel additions to the base charge. Up to 50 percent remelt in the form of gates and risers can be used in the charge. This scrap should be clean. Borings and turnings should not be used.

The meltdown procedure is the same for all types of equipment available aboard ship. The nickel, copper, and iron are charged first and melted down. With the oil-fired furnace, an oxidizing atmosphere should be maintained. The melt is then deliberately oxidized with 1-1/4 ounces of nickel oxide or 3-1/2 ounces of copper oxide for each 100 pounds of virgin metal. This addition may be placed in a paper bag and stirred vigorously into the melt. If the scrap is heavily oxidized, this procedure is not necessary. After the deliberate oxidation treatment, the remelt scrap is added, melted down, and the heat brought to the desired temperature. Manganese and silicon additions are made as part of the deoxidation practice.

If the charge consists of new metal, 1-1/4 pounds of manganese and 9 ounces of silicon should be added for each 100 pounds of new metal. Final deoxidation is made with 0.025 to 0.05 percent of magnesium.

Procedure for Nickel Silver. Charges for nickel silver can be made from virgin metals such as electro-nickel, ingot copper, tin, lead, and zinc; 50-50 nickel-copper alloy, ingot copper, tin, lead, and zinc; from commercially prepared ingot.

For a virgin metal heat, the copper is charged first, the zinc next, and the nickel last. Remelt may be added on top or added to the heat as it settles during melting. In crucible melting, a charcoal or glass-slag cover may be used. The heat is brought to the desired temperature and the remainder of the zinc is added and stirred into the melt. The lead is then added, followed by the tin. All additions should be thoroughly stirred into the melt. The heat is then ready for deoxidation.

The recommended deoxidation practice for nickel silver is to add 0.10 percent of manganese (1-1/2 ounces for each 100 pounds of melt) 5 to 7 minutes before pouring. This is followed by 0.05 percent of magnesium (3/4 ounce for each 100 pounds of melt) 3 to 5 minutes before pouring, and 0.02 percent of phosphorus, as 15 percent phosphorcopper (2 ounces for each 100 pounds of melt) immediately before pouring. The phosphorus deoxidation may be done in the pouring ladle. If phosphorus is used, a check should be maintained on the scrap, if at all

  possible, to make sure there is not a buildup of phosphorus in the circulating scrap.

INDIRECT ELECTRIC-ARC FURNACE AND RESISTOR FURNACE

The melting procedures in these furnaces are the same as far as the handling of the melt is concerned. The indirect electric-arc furnace requires much closer control than the resistor furnace. Poor arc characteristics in the indirect-arc furnace will cause a highly reducing atmosphere that causes silicon to be picked up from the furnace lining and contaminate the melt. The furnace must be maintained in proper condition at all times when melting copper-base alloys. Refer to Chapter 8, "Description and Operation of Melting Furnaces." A smoky operation is sure to be reducing and will produce metal of low quality.

A factor that is of major importance in both types of furnaces is the proper drying of linings and patches. Copper-base alloys are very easily gassed and moisture in the lining is a major source of gassing troubles.

General Procedure. Any scrap material charged into the indirect electric-arc or resistor furnaces should be as free as possible of dirt and sand. Preferably all scrap should be sand blasted to clean it. Sand in particular will cause a slag blanket that will increase the melting time and make handling of the heat more difficult. Heavy pieces of scrap should be charged to the rear of the barrel with ingots on top and close to the arc.

Additions of zinc, tin, and lead should be made as new metals in the order mentioned approximately 3 to 5 minutes prior to tapping. The additions should compensate for any shortages in the desired analysis and any melting losses of zinc and lead. One quarter of one percent (0.25 percent) of the total charge for zinc and lead is usually sufficient to compensate for melting losses.

When melting tin bronzes, aluminum bronzes, or silicon bronzes in these furnaces, it is important to maintain the proper amount of oxygen in the bath in order to prevent gassiness caused by hydrogen. Opening of the charging door or blowing of air into the furnace is poor practice because this causes increased electrode consumption. A better method of obtaining oxygen in the melt is to use copper oxide.

Deoxidation Procedures. These are the same as described under the procedure for the oil-fired crucible furnace.

 

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ELECTRIC INDUCTION FURNACE

The melting procedure is essentially a crucible process. The heat is generated entirely in the charge itself, melting is rapid, and there is only a slight loss of the oxidizable elements. Furthermore, on account of the rapidity of operation, preliminary bath analyses are not usually made. The charge is preferably made up of carefully selected scrap and alloys of an average composition to produce as nearly as possible the composition desired in the finished metal. Final additions are made to deoxidize the metal or to adjust composition, as for the other melting methods just described.

General Procedure. The heavy scrap is charged first and as much of the charge as possible is packed into the furnace. The current is turned on and, as soon as a pool of molten metal has formed in the bottom, the charge sinks and additional scrap is introduced until the entire charge has been added. The charge should always be made in such manner that the scrap is free to slide down into the bath. If the pieces of the charge bridge over during melting and do not fall readily into the molten pool, the scrap must be carefully moved to relieve this condition. Rough poking of the charge must be avoided at all times, however, because of danger or damaging the furnace lining. Bridging is not serious if carefully handled but, if allowed to go uncorrected, overheating of the small pool of metal may damage the lining seriously and will have an undesirable effect on the composition of the metal. The molten metal in the crucible below the bridged charge will become highly superheated with a resulting loss in the lower melting metals such as zinc and lead. There is no way of determining the metal loss when such a condition occurs. When loosening the bridged charge material, extreme caution should be observed, and the charge should never be forced down into the crucible in an effort to loosen the bridge. Forcing the charge may result in a cracked or broken crucible with a resulting run-out of molten metal and damage to the furnace coil.

Safety precautions should always be observed when holding or melting molten metals. Protective eye and face shields and safety clothing should be worn at all times.

The compactness of the charge in the furnace has an important influence on the speed of melting. The best charge is a cylindrical piece of metal slightly smaller in diameter than the furnace lining. This will draw very close to the full current capacity of the equipment. Two or three large pieces with considerable space between them will not draw maximum current because the air cannot be heated by induction. The charge should not be so tightly packed that

  it cracks the crucible or lining when it expands during heating.

As soon as the charge is completely melted and refining or superheating operations finished, further necessary additions of alloys or deoxidizers are made. The furnace is then tilted to pour the metal over the lip. If the entire heat is poured into a large receiving ladle, the power is turned off before tilting. If, however, the metal is taken out in small quantities in hand ladles, reduced power may be kept on while pouring. This maintains the temperature of the bath and facilitates slag separation by keeping it stirred to the back of the bath. When the heat is poured, the furnace is scraped clean of adhering slag and metal and is then ready for the next charge.

It is important that only similar metals be melted in the same lining or crucible. When melting cast iron or steel, the lining absorbs iron. Brass or bronze melted in the same lining will become contaminated with iron. The reverse will also be true. Cast iron or steel can become contaminated with copper, tin, or zinc. If it ever becomes necessary to melt different metals in the same furnace, a wash heat similar in composition to the next heat planned can be used to cleanse the crucible. It is always better practice to have separate furnaces or crucibles for different types of metals that may be required.

Most metals have a tendency to absorb gas and oxidize upon heating. Gas absorption and oxidation increase with time and temperature, with the largest increase occurring at the melting point of the metal, and continuing to increase as the temperature increases. The possibilities of gas absorption in induction-melted heats are less than for other types of furnaces because combustion products are absent. Nevertheless, to minimize hydrogen pickup it is important that metals be melted as rapidly as possible and be held no longer than necessary in the molten state after the desired temperature is attained.

By selective arrangement of the charge, melting time and metal loss can be kept at a minimum. The usual procedure when using new virgin metals is to charge the base metal or the higher melting metals first. Best results are obtained when the crucible is filled to capacity with the larger pieces placed on the bottom. If scrap makes up a proportion of the charge, it may be added with the base metal. Otherwise, it should be charged after the base metal is melted to cut down metal loss and prevent overheating. Scrap melts faster because it usually has a lower melting point than the pure base metal and also has greater electrical resistance. Alloying additions should be made

 

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gradually in amounts small enough to allow rapid solution.

Alloying. Elements may be added as commercially pure metals or as master alloys (hardeners). The lower melting metals used for alloying present little difficulty because they are molten at temperatures near those of the base metals. However, such metals as iron, manganese, silicon, nickel, and copper present a problem because of their relatively high melting points. In most cases, it is undesirable to heat the base metals to temperatures necessary to effect rapid solution of the higher melting metals. For this reason, master alloys with their lower melting ranges are used. Because of the ease with which castings can be made from prealloyed ingots of the proper composition, it is a good idea to obtain special ingots of the compositions that will probably be needed.

PROCEDURES FOR MELTING BRONZES

G Bronze. The nominal composition of this bronze is 88 percent copper, 8 percent tin, and 4 percent zinc. A slightly oxidizing atmosphere is preferred during melting.

The copper is melted and heated to approximately 2,000°F. Tin is then added. In adding the zinc, the power should be turned down, the melt cooled nearly to freezing, and the zinc held beneath the surface of the bath with an iron rod to prevent excessive loss. It is customary to add from 2 to 5 percent more zinc than is desired in the final composition to compensate for loss by oxidation. The melt should be superheated 75°F. above the desired pouring temperature. Before pouring, the bronze should be skimmed and deoxidized with or 3 ounces of 15 percent phosphor-copper per 100 pounds of metal and stirred well. The pouring range of this alloy is between 2,000°F. and 2,200°F., depending upon the section size of the casting, thin sections requiring hotter metal.

M Bronze. This alloy has a nominal composition of 88 percent copper, 6.5 percent tin, 1.5 percent lead, and 4 percent zinc. The melting procedure is the same as that for G bronze. Lead is added after the tin, and the melt should be stirred thoroughly by an acceptable stirring rod. The deoxidation practice and pouring range for this bronze are the same as for Corn-position G.

Manganese Bronze. The nominal chemical composition of this alloy is 58 percent copper, 1.0 percent aluminum, 0.5 percent manganese, 1.0 per cent iron, 0.50 percent tin, and remainder zinc. The manganese, iron, and aluminum are most easily added as master alloys. When the copper is at approximately 2,000°F., the copper - manganese, iron, and aluminum master alloys

  are added. The metal should then be allowed to cool sufficiently to dissolve the zinc without flaring. The zinc loss is about 1 percent. The metal should be poured between 1,900° and 1,975°F., depending upon the size of the casting.

TEMPERATURE CONTROL

Temperatures should be measured with immersion-type pyrometers. The instruments should be maintained in proper operating condition. The immersion end of the pyrometer should be cleaned of any adhering metal or dross before taking readings. The power should preferably be shut off when taking a temperature reading in an induction furnace. Otherwise, a faulty reading may be obtained.

As an emergency measure, the power input for the electrical furnaces may be used for estimating temperatures of the melt if adequate records have been kept on previous heats. Temperatures obtained with the pyrometer and the power input of the furnace should be recorded for various heats and used as a reference in estimating temperatures. This should not be made a general practice but should be used only in an emergency when no pyrometer is available.

POURING

Copper-base alloys require the same precautions in pouring as do any of the other alloys handled aboard repair ships. The high-zinc alloys, aluminum bronze, and silicon bronze in particular, require added attention to pouring techniques. Any agitation of these alloys will result in poor castings. High-zinc alloys will lose zinc in the form of zinc vapor if agitation occurs during pouring. Agitation of aluminum bronze during pouring produces dross, which is trapped to produce defective castings. Silicon bronzes form a skin that if agitated during pouring, will act similar to dross and result in a defective casting.

In the pouring of copper-base castings, extreme care should be taken to prevent agitation of the molten metal and to insure a quiet stream of metal entering the casting. Refer to Chapter 9, "Pouring Castings," for information on proper pouring techniques.

Typical pouring temperatures for the various alloys are listed in table 25. It must be remembered that these temperatures are suggested pouring temperatures, and actual experience aboard ship may indicate that pouring temperatures different from those listed are more satisfactory. This is one of the reasons why it is helpful to keep records of castings made aboard ship and to record information such as the pouring temperatures used.

 

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TABLE 25. TYPICAL POURING TEMPERATURES FOR COPPER-BASE ALLOYS

Alloy Average Section Size of Casting
Light,
less than
1/2 inch
Medium,
1/2 to 1-1/2
inches
Heavy,
over 1-1/2
inches
Composition G
Composition M
Hydraulic bronze
2200°F. 2150°F. 2050°F.
Yellow brass
Naval brass
Commercial brass
Manganese bronze
2000°F. 1900°F. 1850 °F.
Aluminum bronze 2300°F. 2200°F. 2100°F.
Silicon bronze 2200°F. 2100°F. 2050°F.
Cupro-Nickel 2800°F. 2700°F. 2650°F.
Nickel Silver 2500°F. 2400°F. 2350°F.

CLEANING

Copper-base alloy castings do not present any problems in cleaning. Any sand adhering to the casting can be easily removed with a wire brush or by grit or sand blasting.

CAUSES AND CURES FOR COMMON CASTING DEFECTS IN COPPER-BASE CASTINGS

Copper-base alloy castings develop the same defects as other types of castings. For descriptions of these defects and their cures, see Chapter 11, "Causes and Cures For Casting Defects."

METAL COMPOSITION

There are various elements that, either by their presence alone or because of an excess, are detrimental to the physical properties of copper-base alloy castings.

Iron can be tolerated up to 0.25 percent in tin bronze and red brass. A higher iron content causes harder and more brittle alloys and hard spots. Large amounts of iron in manganese bronze reduce corrosion resistance.

Sulfur in small quantities has little effect on the strength of red brass or tin bronze. Too much sulfur decreases fluidity, produces excessive dross, and may cause dirty castings.

  Phosphorus in excess increases the fluidity and may result in severe metal penetration into the sand. In aluminum bronze, it produces embrittlement.

Antimony in excess of specification requirements usually results in a weakened alloy. In excess of 0.1 percent in yellow brass it causes hot shortness.

Zinc in excess of specification requirements produces hardness and brittleness in manganese bronze.

Aluminum is detrimental to red brass and sometimes causes lead sweat. Its presence should be avoided for pressure castings. In combination with lead, it weakens tin bronze.

Silicon in excess of 0.05 percent causes embrittlement in aluminum bronze. In combination with lead it weakens tin bronze.

In short, use the specified compositions. Deviations from them are an invitation to trouble. Remember that the specifications have been worked out over many years.

POURING

Metal that has been poured too hot may produce cracks in the side walls of castings. This crack can be orange, yellow, or golden red in color and will leak under pressure. Such a crack is a good indication that the metal was poured approximately 200°F. above the proper pouring temperature.

Improperly dried ladles or furnace linings cause their own type of porosity in copper-base castings. Holes caused by improperly dried ladles will have a color ranging from orange to yellow and will be associated with a gray to yellow crystalline fracture of the casting in the vicinity of the holes. The casting will generally leak under pressure. The cure for this type of defect is to dry the ladles, crucibles, and linings thoroughly before use.

Dross inclusions in copper-base castings have the appearance of fins when occurring in side walls and have a red and green color when fractured. Proper skimming of the ladle followed by complete filling of the sprue with a steady uninterrupted stream of metal are the cures for this defect.

MELTING PRACTICE

Gas holes in castings are usually caused by a reducing atmosphere instead of a correct oxidizing atmosphere. Hydrogen is dissolved by the metal under reducing conditions and produces the gas holes during the solidification

 

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process. The defects may occur as rounded gas holes or may be present as microporosity. Melts that are gassy will not shrink normally in a riser or sprue. This is illustrated in figure Z38. Note that the gassy metal has a dome shaped surface (sample on left), while the gas-free metal showed a conventional pipe. If the metal isn't fed from the riser, there must be holes or porosity in the casting. Remember that all of these alloys shrink when they solidify. Gas holes in copper-base castings will be colored brown, red, orange, or yellow gold.

An evenly distributed porous structure is caused by overheating and soaking the metal for too long a time. It is a type of gas defect that is usually associated with correct shrinkage in the sprue and riser, followed by the ejection of a small globule of metal. The correct pouring temperature and proper temperature control are the cures for this defect.

MISCELLANEOUS

Veining in copper-base castings is usually caused when the lower melting constituent of the alloy penetrates into cracks that have occurred in weak cores. The casting may show a porous structure in the vicinity of the veining. This defect is usually caused by a core mix with a low hot strength and can be cured by using a core mix with a higher hot strength. This usually can be obtained with additions of clay, silica flour, or iron oxide.

Tin sweat is a defect that is found in high-tin copper-base alloys. A high gas content in the melt causes pressure that forces the low melting-point tin-rich part of the alloy to the outside of the casting through interdendritic spaces. The "sweated" metal occurs as small droplets on the surface of the casting. Correct melting practice and proper degassing procedures are the cures for this defect.

WELDING AND BRAZING

Copper-base alloys have a very high heat conductivity. As a result, brazing of these alloys is difficult and should be done only by trained personnel. When repairs by welding or brazing are required, refer to the "General

  Specifications for Ships of The United States Navy," Section S9-1, "Welding," for general guidance.

SUMMARY

Copper-base castings make up a major part of the foundry work that is done aboard repair ships. It is necessary for molders to become familiar and proficient with castings made from these alloys. Various castings made from these alloys are very often repeaters and the maintaining of records on sand and core mixes used, gating and risering arrangements, and any measures taken to correct specific defects will prove helpful in reducing the time required to produce a good casting.

The important points to consider in melting copper-base alloys are as follows:

1. Use clean uncontaminated crucibles.

2. Use clean uncontaminated melting stock.

3. Melt under oxidizing conditions.

4. Melt rapidly.

5. Do not use excessive superheat. Heat only as hot as necessary.

6. Do not hold the metal at high temperatures.

7. Pour the casting as soon as possible after the metal is melted.

8. Skim carefully and avoid agitation.

9. Allow metal to cool to pouring temperatures in the open air. Do not use cold metal additions to reduce the temperature.

10. Use a properly maintained and calibrated pyrometer.

11. Use deoxidizers only in recommended amounts.

12. Do not agitate or stir the melt immediately before pouring.

 

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Figure 224. Horizontal holding of a bushing.
Figure 224. Horizontal holding of a bushing.

Figure 226. Gating a manganese bronze casting.
Figure 226. Gating a manganese bronze casting.

Figure 228. Gating for a thin nickel-silver casting.
Figure 228. Gating for a thin nickel-silver casting.

 

Figure 225. Vertical molding of a bushing.
Figure 225. Vertical molding of a bushing.

Figure 227. Gating a number of small castings in manganese bronze or red brass.
Figure 227. Gating a number of small castings in manganese bronze or red brass.

Figure 229. Poor gating system for a cupro-nickel check valve.
Figure 229. Poor gating system for a cupro-nickel check valve.

 

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Figure 230. Improved gating that produced a pressure-tight casting.
Figure 230. Improved gating that produced a pressure-tight casting.

Figure 231. Globe valve - poor risering practice.
Figure 231. Globe valve - poor risering practice.

 

Figure 232. Globe valve - improved risering practice.
Figure 232. Globe valve - improved risering practice.

Figure 233. High pressure elbow - poor risering practice.
Figure 233. High pressure elbow - poor risering practice.

 

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Figure 234. High pressure elbow - improved risering practice.
Figure 234. High pressure elbow - improved risering practice.

Figure 235. Risers for a cupro-nickel valve body.
Figure 235. Risers for a cupro-nickel valve body.

 

Figure 236. Tapered chills on a flat G metal casting.
Figure 236. Tapered chills on a flat G metal casting.

Figure 237. Tapered chills on a G metal bushing.
Figure 237. Tapered chills on a G metal bushing.

Figure 238. Examples of gassy and gas-free metal.
Figure 238. Examples of gassy and gas-free metal.

452605 0-58-14

 

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Chapter XV
ALUMINUM-BASE ALLOYS
 
The two principal aluminum alloys; used for making castings for shipboard use are the aluminum-silicon alloys and the aluminum-copper alloys. An aluminum-zinc alloy is also available. Refer to table 2, Chapter 13, "Compositions of Castings."

Aluminum-base alloys are used because of their light weight, good corrosion resistance, good machinability, and each castability. Their particular characteristics that affect foundry practice are:

1. Light weight and high shrinkage call for well-vented and permeable molds that are rammed fairly soft to vent gases and give little resistance to contraction of the casting.

2. Ease of absorption of hydrogen requires proper melting practice (oxidizing atmosphere) and close control of moisture in all forms.

3. Ease of reaction with oxygen promotes a dross or scum that must be properly removed and must be minimized by proper gating and pouring practice.

4. Gas absorption calls for pouring at the lowest possible temperature.

ALUMINUM SILICON

The aluminum- silicon alloys have very good casting properties. The fluidity (castability) increases as the silicon is increased. The tendency to hot tearing (which is characteristic of many aluminum alloys) is reduced by the silicon additions. These alloys are well suited for castings which must be pressure tight. Corrosion resistance is very good. The aluminum-silicon alloys do not machine as easily as some of the other aluminum alloys; carbide tools are recommended for the alloys with high silicon content. These alloys have been generally replaced with aluminum-silicon-magnesium alloys or aluminum-silicon-copper-magnesium alloys.

ALUMINUM COPPER

The addition of copper to aluminum increases its strength and hardness. These are the main advantages of the aluminum-copper alloys. The disadvantages of these alloys is that they are more susceptible to hot tearing and that they have a relatively low resistance to

  corrosion. Machinability of the aluminum-copper alloys is good. These alloys have been generally replaced by the aluminum-silicon-copper alloys.

ALUMINUM ZINC

This alloy has high strength and ductility without heat treatment. However, these properties can be improved by room-temperature aging or by heat treatment. Its machining properties are good. It is somewhat more difficult to cast than are the aluminum-silicon or the aluminum-copper alloys.

ALUMINUM MAGNESIUM

This alloy has the best strength and corrosion resistance of any aluminum alloy when properly cast and heat treated. Heat treatment of the 10 percent magnesium alloy is mandatory but the 7 percent magnesium alloy is used as cast. These alloys are difficult to cast properly.

HOW ALUMINUM SOLIDIFIES

Aluminum solidifies in the manner described in Chapter 1, "How Metals Solidify." Its solidification shrinkage is high. Solidification starts at the mold and core surfaces and proceeds inward. Aluminum, however, is an excellent conductor of heat. Within a short time after a casting is poured, all of the molten metal has cooled to near the solidification temperature. Nucleation and growth of crystals then start throughout the melt and solidification is rapid. This makes it difficult to feed a casting. Large risers and strong directional solidification are needed. The addition of copper and silicon to aluminum (as in the alloys mentioned) increases the fluidity and makes feeding easier. The aluminum-zinc alloy has a greater shrinkage than the aluminum-silicon or aluminum-copper alloys. For easiest castability, use the aluminum-silicon alloys, if they are otherwise suitable for the purpose intended.

PATTERNS

Patterns used in making molds for aluminum castings are the same as for other metals. Patterns should be checked to make sure that any section junctions are properly blended as shown in figure 17, Chapter 2, "Designing a

 

228
 
Casting." Blending of junctions is especially necessary in aluminum-alloy castings because they are highly susceptible to hot tearing.

MOLDING AND COREMAKING

Molding and coremaking procedures are generally the same as for other metals. See Chapter 5, "Making Molds," and Chapter 6, "Making Cores."

SAND MIXES

Aluminum-alloy castings can be made in either a natural sand (such as Albany sand) or in a synthetic sand. Synthetic sand will usually produce a sounder casting, but the natural sand will usually give a smoother casting surface. Properties of a typical natural sand for aluminum are as follows:

Green Compressive Strength, p.s.i. 6-8
Permeability, AFS units 5-15
Clay Content, percent 15-22
Grain Fineness Number 210-260
Moisture Content, percent 6-7

A sand of this type must be properly reconditioned and the moisture content closely controlled. Negligence will lead to blows and gas porosity. Although one advantage of a natural sand is that it can be reconditioned by shoveling, the use of a sand muller will give more uniform mixing and extend the quality and use-full life of the sand.

Synthetic sands used for aluminum-alloy castings should have properties in the ranges listed as follows:

Green Compressive Strength, p.s.i. 6-10
Permeability, AFS units 25-120
Clay Content, percent 4-10
Grain Fineness Number 70-160
Moisture Content, percent 3-5

This type of synthetic sand must be reconditioned with a sand muller in order to obtain the best properties. Manual conditioning of synthetic sand is not recommended.

PROCEDURES

Coremaking. Coremaking for aluminum castings follows the same techniques as used for other metals except that a minimum amount of binder should be used to give the weakest core that can be handled. Binders should also be maintained at the proper amount to prevent any excessive gas generation. Aluminum and its alloys are sensitive to gas pickup. The cores, therefore, should be thoroughly dried and well vented to prevent any defects from moisture.

  Molding. Because aluminum has a density approximately one-third that of bras s, cast iron, or steel, it creates a much lower pressure than the other metals against the mold wall. Because of this, the mold can be rammed lighter. Light ramming is particularly important when casting the aluminum alloys that are hot-short or susceptible to hot tearing. Light ramming permits the casting to contract more easily and avoids hot tear s. The placing of gates and risers must also be planned so that they do not hinder the contraction of the casting while it is cooling.

Washes. Refractory washes and sprays may be used on mold and core surfaces, but any organic materials should be avoided because they are sources of gas. Commercial washes of alcohol and clay are generally used on cores. Even though these washes contain alcohol as the liquid, the cores should preferably be dried in the core oven after they have been coated.

GATING

Aluminum and its alloys have the disadvantage that they form dross (metal oxides or scum) if they are agitated when molten. To eliminate or minimize drossing, the gating system must be designed to conduct the molten metal to the mold cavity as quietly as possible and with as little agitation as possible.

For small castings, the casting should be gated with a singe gate on one side. Larger, simple shaped castings and castings of complicated shapes will have to be gated from more than one side with multiple gating systems. However, it must be remembered that the metal must be poured hotter with the multiple gating system to prevent cold shuts and laps in the larger castings.

Studies in recent years have shown that if the sprue and gating system can be filled quickly, sucking in of air and the resulting formation of dross can be minimized or even eliminated. It is also necessary to avoid abrupt changes in the direction or cross-sectional area of the gating system. This principle seems to be violated at the junction of the sprue and runner, but this is necessary in order to distribute the metal and to reduce its velocity.

The best results can generally be obtained from a sprue that has a reduction in cross-sectional area of 3 to 1. In other words, the top of the sprue has an area three times larger than the bottom of the sprue. Sometimes a square or rectangular sprue may reduce turbulence more than a round sprue, but this must be determined by experiment. Usually a reduction of turbulence at the start of the pouring operation is obtained by the choking action at the base

 

229
 
of the sprue and rapid filling of the gating system. Two sprue-base designs have been developed to reduce turbulence and aspiration of air caused by the abrupt change in direction at the base of the sprue. The first is known as the enlargement type of sprue-base design, and the second as the well type.

The enlargement type of sprue base is shown in figure 239. The runner is enlarged below the base of the sprue. This arrangement reduces the velocity of the molten metal as it passes from the sprue to the runner. The diameter of the enlargement should be approximately 2-1/2 times the width of the runner. This type of sprue base is most effective with a narrow deep runner.

The well-type sprue base is shown in figure 240. The best results with this design were obtained when the area of the well was approximately five times the area of the sprue base and its depth was about two times the depth of the runner. This type of sprue base is most effective with wide shallow runners and with square runner s.

In the runners and gates, turbulence can be avoided by rounding the corners with as large a radius as possible. As each gate is passed, the cross- sectional area of the runner should be reduced by the area of the gate passed. For example, if the runner ahead of the first gate is 1/2 x 1 inch (0.5 square inch) and the first gate is 1/2 x 1/4 inch (0.125 square inch), the runner past the first gate should be 0.5 minus 0.125 or 0.375 square inch (say, 3/8 x 1 inch). This type of gating will keep the runner system full of molten metal and distribute it uniformly to the mold. If the runner system is not reduced in area as described, the gates farthest from the sprue will carry most of the metal. As general practice, or as a starting point for planning the gating system, the total area of the gates should be equal to (or slightly larger than) the cross-sectional area of the runner between the first gate and the sprue. The cross-sectional area of the runner between the sprue and the first gate should be two to three times greater than the cross-sectional area of the small end of the sprue.

The relationship between the cross-sectional areas of the gating system is called the gating ratio, and is expressed as three numbers. As an example, a gating ratio of 1:4:4 means that the area of the gates is the same as the area of the runner, and the area of all the runners (or all the gates) is four times as large as the cross-sectional area of the small end of the sprues.

The size and location of gates is determined by the size of the casting, wall thickness, and weather it is a flat plate or chunky. For general

  usage, the following may be used in locating gates: (1) the width of the gate should be approximately three times the thickness of the gate, (2) the thickness of the gate at the mold cavity should be slightly smaller than the thickness of the casting at that point, (3) the gate should be slightly longer than it is wide, and (4) the spaces between the gate s should be approximately twice the width of the gates. This information is given to show good gating procedure. The rules are not hard and fast, but the molder should have a good reason for changing them.

Large castings should be gated at the bottom to insure a minimum of turbulence. In small castings where the drop from the parting line to the drag side of the mold is four inches or less, parting-line gates may be used.

The runner should be in the drag and gates in the cope. The gating system will fill with metal before flowing into the mold cavity, trapping the dross against the cope surface, and result in more uniform distribution of metal. Wide flat runners and ingates provide more cope surface for the trapping of dross. This is the major difference between gates for light and heavy metals.

Risers. Aluminum alloys have a high solidification shrinkage and must be risered properly to prevent any defects due to shrinkage. Riser s should be used to obtain directional solidification as much as possible. Gating through risers so as to have the last and hottest metal in the riser should be used wherever possible. Refer to Chapter 7, "Gates, Risers, and Chills."

Chills. Strong directional solidification is difficult to obtain in aluminum alloys without the use of chills. The tendency for solidification to start throughout the metal makes proper feeding difficult. Chills must often be used to obtain satisfactory directional solidification.

External chills for aluminum castings can be made from cast iron, bronze, copper, or steel. They should be clean. Chills are occasionally coated with plumbago, lampblack, red oxide, or other compounds to prevent the cast metals from sticking to them, but this procedure is generally not necessary. Organic coatings should never be used on chills for aluminum alloys. The chills should be absolutely dry (and preferably warm) before being set in the mold.

Vents. Aluminum is approximately one-third the weight of cast iron, steel, or bronze. This low density makes it more difficult for aluminum to drive mold gases or air from the mold cavity. The mold, therefore, must be thoroughly vented to permit easier escape of the

 

230
 
gases. This is the reason that molding sands for aluminum must have a high permeability.

MELTING

TYPE OF FURNACE

Aluminum and its alloys can be melted only in the oil-fired crucible furnace, or high-frequency induction furnace. The oil-fired furnace has the disadvantage of exposing the molten aluminum to the products of combustion in the furnace atmosphere. Close control and constant attention are required during melting in these units.

PROCEDURE

Charges for aluminum heats should be made of ingot material and foundry remelt. Machine turnings and borings should not be used. It is difficult to clean turnings and borings so as to remove any oil, and the large surface area of the chips causes high oxidation losses. If turnings and borings must be used, they should be thoroughly cleaned, melted down, and poured into ingots, and then the ingots used as charge material. Such a procedure will reduce the gas content of the material and eliminate the large amount of dross which would result from direct use of the turnings.

Oil-Fired Crucible Furnace. Aluminum alloys can be melted in graphite or silicon carbide crucibles. The crucibles must be kept clean to avoid contamination. Sometimes cast iron pots are used, but they require a refractory wash to prevent pickup of iron by the aluminum. The pots must be thoroughly cleaned before the protective coating is applied. A coating for iron pots can be made from seven pounds of whiting mixed with one gallon of water. A small amount of sodium silicate may be added to provide a better bond. The pot should be heated to a temperature slightly above the boiling point of water and the wash applied. Care must be taken in charging these pots in order to avoid chipping of the coating; which will expose the iron.

The metal charge should not extend above the top of the crucible. Such charging practice will result in high oxidation losses and severe drossing. It is better to melt down a partially filled crucible and then charge the remainder of the cold metal.

The furnace atmosphere should be slightly oxidizing to prevent excessive absorption of gases by the melt. Hydrogen is the gas that is most harmful to aluminum. Hydrogen is dissolved by the aluminum and produces gas defects if it is not removed or permitted to

  escape. Oxygen combines with aluminum to form the familiar dross which is easily removed.

High-Frequency Induction Furnace. Melting practice in the high-frequency induction furnace is essentially the same as that described for the oil-fired furnace. Temperature control is much easier with an induction furnace because the temperature will rise only slightly after the power has been shut off.

TEMPERATURE CONTROL

The temperature of molten aluminum cannot be determined by visual observation, as is sometimes done with iron and steel. It is necessary to use an immersion pyrometer for temperature readings. Without a pyrometer, overheating would probably result and produce a gassy heat or a casting having a very coarse grain structure. Remember that a melt of aluminum alloy that is overheated is usually permanently damaged. Merely cooling the metal back to the proper temperature will not correct the damage.

An immersion Chromel-Alumel pyrometer is satisfactory for temperature measurements in molten aluminum. The thermocouple should be protected with a cast iron tube coated with the same wash as described for iron melting pots. If temperatures are to be taken in the ladle, an open-end thermocouple should be made from 8-gage asbestos-covered Chrome Alumel wires. While the thermocouple is in the melt, it should be moved with a slow circular motion.

DEGASSING

Because aluminum and its alloys absorb gases so readily, the proper removal of gases is an important step in preventing defective castings. Degassing of aluminum can be accomplished with gaseous fluxes.

Aluminum should be degassed with dry nitrogen. Chlorine, either solid or gaseous, should not be used in shipboard foundries. A carbon or graphite pipe is connected to the tank of compressed gas with suitable rubber hoses. When the metal temperature reaches about 1,250°F., the gas should be turned on and the preheated tube inserted in the metal to the bottom of the crucible. The flow of gas should be adjusted to produce a gentle roll on the surface of the metal. Fluxing times should be from 10 to 15 minutes for a 100-pound heat. (Differences in size of heat will not change the fluxing time appreciably.) Temperature control will generally require the fuel to be shut off as soon as the charge has melted. The metal temperature should never be allowed to go over 1,400°F. After the fluxing operation, the surface of the melt should be skimmed and the metal poured.

 

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POURING

The pouring temperature and method of pouring determine whether a properly melted heat and a properly made mold will produce a good casting. Aluminum and its alloys should be poured at as low a temperature as possible without causing misruns. For any given alloy, the pouring temperature will determine whether a casting will have a fine grain structure and good properties or a coarse grain structure and lower properties. A high pouring temperature will tend to give a large grain size, and a low pouring temperature will tend to give a small grain size. The pouring temperature will vary between 1,240°F. and 1,400°F., depending on the alloy and section size of the casting. If a casting poured at 1,400° F., misruns, the gating should be revised to allow faster pouring.

Because aluminum absorbs gases easily, pouring should be done with the lip of the ladle as close as possible to the sprue of the mold. The stream of molten metal should be kept as large as possible (as large a stream as the sprue will handle). A thin stream or trickle of molten metal from a ladle that is held high above the mold will cause a gas pickup and unnecessary agitation of the metal.

CLEANING

Aluminum-alloy castings are easy to clean. Burn-in is absent and any loosely adhering sand can be easily removed with a wire brush. Gates and risers can be removed with hack saws, band saws, or by chipping hammers. When using chipping hammers, the cutting should be done slightly away from the surface of the casting to prevent breaking into the casting. The remainder of the metal can then be removed by grinding. After any cutting operation for the removal of gates and risers, grinding is used for a rough finish. Final finishing can be done with a single deep-cut coarse curved-tooth file.

Grit or sand blasting is useful for cleaning up the casting surface and gives it a pleasing appearance. Unsoundness that may be present just below the surface of the casting is usually revealed by a blasting operation. Grit or sand blasting is also useful for removing minor surface roughness and burrs from a casting.

CAUSES AND CURES FOR COMMON DEFECTS IN ALUMINUM CASTINGS

Aluminum castings are subject to the defects described in Chapter 11, "Causes and Cures for Common Casting Defects."

  METAL COMPOSITION

An embrittled and coarse grain structure is produced in aluminum alloys by iron contamination. A structure of this type can be seen in the fracture of a casting shown in figure 241. An increase in iron content is usually due to improperly coated melting tools and iron melting pots. This defect can be remedied only by proper coating of the molding tools and melting pots with a protective wash.

Aluminum-copper alloys cannot tolerate magnesium contamination, aluminum-silicon alloys cannot tolerate iron or magnesium and aluminum-magnesium alloys cannot tolerate copper, iron, or silicon. The contaminating elements result in embrittlement and lowering of physical properties. Aboard ship, where chemical analyses are not available, proper scrap segregation is the only way of preventing contamination from harmful elements.

POURING

Dross inclusions are caused by poor pouring practice or poor gating practice. Such a defect is shown in figure 205,Chapter 11, "Causes and Cures for Common Casting Defects." This type of inclusion can be eliminated by using a proper pouring and gating technique as described under the section, "Pouring," in this chapter. Thorough skimming of the melt must also be a part of the pouring practice. Gas trapped in the stream of molten metal during pouring will cause porosity and can be corrected only by proper pouring technique.

MELTING

Pinhole porosity in aluminum castings is caused by poor melting practice. This type of defect is common and shows up as very small gas holes that are scattered through the casting. They may or may not show up on the casting surface. Porosity of this nature can be cured only by correct melting practice. In the case of an oil-fired furnace, a slightly oxidizing atmosphere must be used. Melting tools must be clean and dry to prevent any pickup of moisture by the melt. Degassing procedures must be used to remove any gases which are dissolved in the melt.

MISCELLANEOUS

Excessive moisture in the molding sand will cause porosity in aluminum castings. This defect can be easily identified because it occurs just below the surface of the casting and on all surfaces. Such porosity is shown in figure 242. The cure for this defect is to use the correct moisture content in the molding sand. This can be done only through proper testing procedures.

 

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The causes of hot cracks in aluminum alloys are described in Chapter 11, "Causes and Cures for Casting Defects." Because some of the aluminum alloys are so likely to hot tear and hot crack, special precautions must be taken to reduce the resistance of the mold so as to permit free contraction of the casting.

WELDING AND BRAZING

When used with the proper welding rods and fluxes, oxyacetylene, oxyhydrogen, carbon-arc, and metallic-arc welding can be done on aluminum-alloy castings. When repairs or other welding are required, refer to the "General Specifications for Ships of the United

  States Navy," section S9-1, "Welding," for general guidance.

SUMMARY

The light-weight and good corrosion resistance of aluminum alloys make them ideal for certain applications aboard ships. The production of aluminum castings is not easy, because dross forms and gases are absorbed readily by molten aluminum. Careful attention to the melting and molding procedures are necessary for the production of good castings. Variations in sand properties, superheating, and pouring temperatures must be maintained more closely than for the other metals cast aboard ship.

 

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Figure 239. Enlargement-type sprue base.
Figure 239. Enlargement-type sprue base.

Figure 240. Well-type sprue base.
Figure 240. Well-type sprue base.

Figure 241. Coarse-grained structure. (Caused by iron contamination)
Figure 241. Coarse-grained structure. (Caused by iron contamination)

 

Figure 242. Porosity. (Caused by excessive moisture in the sand)
Figure 242. Porosity. (Caused by excessive moisture in the sand)

 

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Chapter XVI
NICKEL-BASE ALLOYS
 

SELECTION OF ALLOYS

The nickel-base alloys available for use aboard ship are Monel and modified S-Monel. Nickel-base alloys are used mainly because of their excellent corrosion resistance and strength, even at high temperatures. They have a pleasing appearance and are heavy.

Peculiarities of nickel-base alloys which influence foundry practice are:

1. High melting temperatures require hard well-rammed molds made on sturdy patterns.

2. Nickel is poisoned by sulfur.

3. Gas is absorbed during poor melting practice or by overheating during melting and causes defective castings.

4. The molten metal is hotter than it looks.

5. Risers develop a deep pipe, so they must be large.

MONEL

Castings requiring a medium strength, high elongation, and extra-high corrosion resistance are made from Monel. High-pressure valves, pump impellers, pumps, bushings, and fittings are typical parts cast in Monel.

MODIFIED S-MONEL

This alloy has a high hardness that is retained up to 1,000°F. It has excellent resistance to galling and seizing. Modified S-Monel is useful under conditions where there is very poor lubrication. Refer to the table in chapter 13, for the actual alloy compositions.

HOW NICKEL-BASE ALLOYS SOLIDIFY

Nickel-base alloys solidify with a high shrinkage and have a narrow solidification range. Risers show the deep pipe which is characteristic of this type of solidification. Large risers are usually required to supply the molten metal necessary to make the casting sound.

 

PATTERNS

Patterns for nickel-base-alloy castings require rugged construction. The molds are rammed hard (similar to molds for steel castings). Solidly built patterns are required to insure castings which are true to pattern.

Shrinkage allowances vary for the type of alloy cast and the casting design. Monel and Modified S-Monel have a shrinkage of 1/4 inch per foot when unrestricted. The shrinkage may be as little as 1/8 inch per foot in heavily cored castings or in castings of intricate design.

MOLDING AND CORE MAKING

Generally, the sand and core practices for nickel-base alloys are similar to those for steel castings.

SAND MIXES

Sands for Monel and modified S-Monel should have a high permeability and low clay content. Organic binders should be kept to a minimum. The all-purpose sand described in Chapter 4, "Sands for Molds and Cores" is satisfactory for use with these nickel-base alloys.

PROCEDURES

Molding. Molding practices for nickel-base alloys are the same as for steel. The molds should be rammed hard to provide a surface that will resist the erosive action of the molten metal at the high pouring temperatures.

Dried, oil-bonded sand molds should be used for Monel and modified S-Monel castings weighing more than 15 pounds. Smaller castings are made in skin-dried or green sand molds.

Coremaking. Pure silica sand with linseed oil binders should be used for cores. The cores should be well vented and have good collapsibility. Core practice for nickel-base castings should follow the practices used for copper-base alloy castings.

Washes. Either graphite or silica-flour washes can be used for cores.

GATING

Gating for the nickel-base alloys should permit rapid filling of the mold without erosion of the mold surface or exposure of the mold to

 

236
 
radiated heat from the molten metal for longer than absolutely needed. Gating practices similar to those used for steel castings are best for nickel-base castings.

RISERING

Riser s for nickel-base alloys must be large in order to provide enough molten metal to feed heavy sections and to compensate for the high solidification shrinkage. Risers must be located properly to obtain complete feeding of heavy sections. The gating and risering arrangement shown in figure 243 resulted in shrinkage porosity in the section marked A-A. A change in the gating as shown in figure 244 permitted proper feeding of all the heavy sections from the risers and produced a sound casting. Notice the deep piping in the risers in figure 244. Refer to Chapter 7, "Gates, Risers, and Chills," for details of proper gating and risering practice.

CHILLS

Chills should be used as needed to obtain directional solidification and to insure soundness in heavy sections. See Chapter 7, "Gates, Risers, and Chills."

VENTING

Because high pouring temperatures are required for nickel-base alloys, liberal venting of molds and cores is necessary. Cores in particular should be well vented because some of the nickel-base alloys are sensitive to the gases generated by organic core binders (linseed oil).

MELTING

TYPE OF FURNACE

Nickel-base alloys can be melted in oil fired crucible furnaces, indirect-arc furnaces, resistance furnaces, and induction furnaces. Fuel in oil-fired crucible furnaces may damage the alloys because of the sulfur content or the possibility of producing a reducing atmosphere. See Chapter 8," Description and Operation of Melting Furnaces," and manufacturer's literature for operating procedures for the various furnace s.

PROCEDURE

The charge for Monel or modified S-Monel is made up from Monel block and remelt scrap in the form of gates and risers. The Monel block is 2 inches x 2 inches x 4 inches and weighs about 6 to 8 pounds. Remelt scrap should be free of all sand and foreign materials. Sandblasting should be used to make sure it is cleaned

  properly. Machine-shop borings and turnings should not be used at all. Sulfurized oils and lead oxides used for machine lubrication cannot be removed satisfactorily and are likely to cause contamination of the melt. Up to 40 percent remelt scrap is used in normal operation, but as much as 50 percent can be used. Electrolytic nickel and nickel shot are available for adjustments of nickel content. Manganese is added as 80 percent ferromanganese and silicon as 95 percent metallic silicon.

The procedures for all types of equipment are the same as far as the actual meltdown is concerned. In oil-fired crucible furnaces, clay-graphite crucibles should be used and an oxidizing atmosphere maintained in the furnace. If the crucible is closed with a clean cover, no slag is needed. A lead-free glass slag may be used in the crucible instead of a cover.

The charge of Monel block and scrap is melted down and brought to a temperature about 50° to 75°F. above the desired pouring temperature. The major additions of manganese and silicon are made as part of the deoxidation practice.

TEMPERATURE CONTROL

The nickel-base alloys are sensitive to the proper pouring temperature. The surface appearance of the melt is deceptive when trying to judge temperature. Usually the metal is much hotter than it appears. Any unnecessary superheating of these alloys results in gas absorption.

Temperature control should be maintained with the use of properly operating pyrometers. The surface of the melt should be clear of slag before temperature readings are taken with an optical or immersion pyrometer.

DEOXIDATION

Three to 5minutes before the heat is ready to pour, manganese is added as 80 percent ferromanganese and is followed by the silicon addition of 95 percent metallic silicon. Final de-oxidation is accomplished with 0.1 percent of magnesium, which is plunged below the surface of the melt with a pair of tongs, or with a specially made rod. This causes a vigorous reaction and proper safety precautions should be observed. If the magnesium burns on the surface, it is ineffective as a deoxidizer.

POURING

Nickel-base alloys should be poured as rapidly as possible in order to fill the mold quickly and to prevent chilling of the molten metal. A pouring basin should be used and kept full at all times during the pouring of the casting.

 

237
 
Pouring temperatures for Monel are between 2,700°F. and 2,850°F., depending on the size and section thickness of the casting. Modified S-Monel is poured between 2,650°F. and 2,800°F.

Haphazard pouring may cause slag or sand to flow into the mold with the stream of molten metal. The ladle should be skimmed of all slag, or a skimming rod should be used to keep the slag from entering the sprue. The mold should be rammed hard around the sprue to prevent sand erosion.

CLEANING

Nickel-base alloy castings usually come free from the mold easily and wire brushing is the only cleaning necessary. Grit or sand blasting can be used to give a better surface.

CAUSES AND CURES FOR COMMON CASTING DEFECTS IN NICKEL-BASE ALLOY CASTINGS

Nickel-base alloy castings are susceptible to all of the various defects described in Chapter 11, "Causes and Cures for Common Casting Defects." There are, however, some defects that are particularly apt to occur in nickel-base alloys, such as gas contamination.

METAL COMPOSITION

The carbon content of Monel and modified S-Monel must be kept low. Carbon in excess of the very small amounts that these alloys can tolerate will be precipitated as free graphite and cause intercrystalline brittleness. Sulfur causes hot shortness in nickel-base alloys and

  makes them susceptible to hot tearing. Modified S-Monel cannot tolerate any lead. Lead in the presence of silicon (which is an alloying element in modified S-Monel) causes a coarse grain structure and cracking.

MELTING PRACTICE

Nickel-base alloys are especially sensitive to gas absorption and will develop porosity and gas holes if proper attention is not paid to melting practice. Proper temperature control should be maintained to prevent the possibility of excessive superheating which will increase the susceptibility to pick up of gas. Pouring ladles and any other pouring equipment should be thoroughly dried to prevent moisture pick up from these sources.

WELDING AND BRAZING

Nickel-base alloys may be welded by metallic arc, electric resistance, oxyacetylene, and atomic hydrogen processes. When repairs or other welding are required, refer to the general "Specifications for Ships of the United States Navy," Section S9-1, "Welding," for general guidance.

SUMMARY

The high melting point of nickel-base alloys, combined with their sensitivity to absorption of gases, makes the proper control of all foundry procedures mandatory for the production of good castings. Proper temperature control by the use of pyrometers cannot be stressed too strongly. Determination of metal temperature by visual observation is at best a gamble and should never be used.

 

238
 

Figure 243. Poor gating and risering practice for a nickel-base alloy casting.
Figure 243. Poor gating and risering practice for a nickel-base alloy casting.

Figure 244. Improved gating and risering for nickel-base alloy casting.
Figure 244. Improved gating and risering for nickel-base alloy casting.

 

239
 
Chapter XVII
CAST IRON
 
Cast iron has many properties that make it a good alloy for castings. Gray cast iron has: (1) excellent castability, (2) good machinability, (3) good water resistance, (4) high damping capacity, (5) high compressive strength, (6) good tensile strength, and (7) good yield strength. Its two major disadvantages are: (1) low impact strength, and (2) low ductility.

The unique feature of cast iron is its high carbon content. In gray iron, the casting has been cooled in the mold at a rate which allows graphite flakes to precipitate. These graphite flakes act as built-in "cushions" in the metal and as lubricants during machining or when the casting is subjected to wear. The metal is called "gray" iron because the graphite flakes impart a gray color to a fractured surface. Although the graphite flakes impart many desirable features to gray iron, they also make it brittle and reduce its strength.

In white cast iron, the casting has been cooled so that no graphite flakes are formed. The high carbon content shows up in hard massive particles of chilled iron (cementite), which make the iron act much as high-speed steel.

Excellent castability enables cast iron to be cast into very thin sections without any particular difficulty. High machinability permits fast and easy machining without the difficulties encountered with many other metals. Wear resistance permits the use of cast iron in moving and rubbing parts without any special treatment. A high damping capacity means that cast iron is capable of absorbing vibrations. This makes it useful for machine bases and tool holders. High compressive strength permits it to withstand heavy loads. Good tensile and yield strengths enable cast iron to withstand normal stresses required of engineering materials. However, cast iron cannot be subjected to sudden blows and it will not stretch like steel when an overload is applied.

White cast iron, on the other hand, is almost impossible to machine or saw because of its very high hardness. It is highly useful where a very hard material is needed to resist wear, but is more brittle than gray cast iron.

SELECTION OF ALLOYS

Cast iron is a general name given to a group of alloys rather than a name for one particular alloy. It is primarily an alloy of iron with carbon and silicon. By changing the

  amounts of carbon, silicon, and other alloying elements, it is possible to produce a series of alloys with a wide range of properties.

Carbon is the most important alloy in cast iron. The total amount of carbon and its condition are the major factors that determine the properties of the iron. The presence of other elements (such as silicon and phosphorus) affect the solubility of carbon in iron. The eutectic composition of carbon and iron (the mixture with the lowest melting point) has 4.3 percent carbon. Silicon and phosphorus each reduce the amount of carbon required to form the eutectic mixture by approximately one -third of one percent of carbon for each one percent of silicon or phosphorus in the iron. From this has developed the term "carbon equivalent" that is used to express the composition of the cast iron with respect to its carbon content.

The carbon equivalent is determined by using the following equation: carbon equivalent, % = total carbon, % + 1/3 (silicon, % + phosphorus, %).

Cast irons that have a carbon equivalent greater than 4.3 percent may have a coarse open-grained structure with large amounts of "kish" graphite (graphite that floats free of the metal during pouring and solidification). Cast irons that have a carbon equivalent less than the eutectic amount will have finer graphite flakes and a more dense grain structure.

Cast irons are more sensitive to section size than most other casting alloys. This is caused by the great effect that cooling rates have on the formation of graphite flakes.

It is important to realize that the properties and strength of cast iron can be affected greatly by cooling rate. For example, if an iron is poured into a casting with variable wall thickness, a high-strength iron might be obtained in 2-inch walls and brittle unmachinable white iron in 1/4 inch walls and at edges where the cooling rate is high.

REGULAR GRAY IRON

Regular or ordinary gray iron is often used for space-filling castings where high strength or ductility are not needed. It also finds considerable use in castings that serve as replaceable wearing parts. Typical examples are cylinder blocks, heads, piston rings, and cylinder liners for internal-combustion engines.

 

240
 
Ordinary cast irons have a tensile strength varying from 18,000 p.s.i. to 24,000 p.s.i. Typical compositions and mechanical properties
 
  obtained from various section sizes are listed in table 26.
TABLE 26. TYPICAL COMPOSITIONS OF ORDINARY GRAY CAST IRON
Composition, percent Wall
Thickness,
inch
Tensile
Strength,
p.s.i.
Brinell
Hardness
T.C. Si P S Mn
3.50
to
3.80
2.40
to
2.60
0.20
max
0.15
max
0.50
to
0.70
Up to
1/2
22,000 to
26,000
160 to
190
3.40
to
3.60
2.30
to
2.50
0.20
max
0.15
max
0.50
to
0.80
1/2
to
1
18,000 to
24,000
160 to
180
3.10
to
3.30
2.20
to
2.40
0.20
max
0.15
max
0.50
to
0.80
Over
1
18,000 to
22,000
130 to
170

 

HIGH-STRENGTH GRAY IRON

Castings requiring a higher strength than ordinary gray cast iron but no other improvements in properties can be made from an iron having the following typical analysis:
Total carbon 3.30 - 3.35 percent
Manganese 0.80 percent

 
Silicon 2.00 percent
Phosphorus 0.20 percent
Sulfur 0.12 percent

An iron made with this analysis would have an average tensile strength of 34,000 to 40,000 p.s.i. in a 1.2-inch-diameter bar. Typical compositions of high strength gray cast iron are listed in table 27.
 

TABLE 27. TYPICAL COMPOSITIONS OF HIGH-STRENGTH GRAY CAST IRON
Composition, percent Wall
Thickness,
inch
Tensile
Strength,
p.s.i.
Brinell
Hardness
T.C. Si P S Mn
3.10
to
3.30
2.00
to
3.30
0.20
max
0.12
max
0.45
to
0.70
Up to
1/2
36,000 to
40,000
180 to
230
3.00
to
3.25
1.80
to
2.10
0.20
max
0.12
max
0.45
to
0.70
1/2
to
1
35,000 to
39,000
205 to
230
2.80
to
3.10
1.60
to
2.00
0.20
max
0.12
max
0.45
to
0.70
Over
1
35,000 to
38,000
180 to
220

 
As a general rule, the higher the tensile strength of a gray iron, the greater will be the shrinkage during solidification and the poorer the machinability. Tensile strengths of at least 50,000 p.s.i. are readily obtainable in gray iron by proper selection of the carbon and silicon contents and by alloying. As a general rule, for tensile strength over 45,000 p.s.i., the   carbon content of the iron should not exceed 3.10 percent and the silicon content should not exceed 2.00 percent. Useful combinations of alloying additions to increase the strength of such irons are: (1) 1 percent of nickel and (2) 1 percent of nickel with 0.50 percent of molybdenum or chromium.
 

241
 
SCALE AND CORROSION-RESISTANT GRAY IRON

Ordinary and high-strength gray cast irons sometimes are not satisfactory where high temperatures will be encountered continuously. When heated, these irons have a tendency to scale or warp and to "grow." In simple words, "casting growth" means that when unalloyed cast irons are heated to high temperatures for a long time, they increase in size. To provide a casting material that will have the properties of gray iron and be more useful at high temperatures, the alloyed cast irons known as scale and corrosion-resistant gray cast irons have been developed.

Two analyses for these irons are given in the Navy Specifications:
MIL-G-858
Class 1 Class 2
Total carbon 2.60-3.00 2.60-3.00
Manganese 1.0-1.5 0.8-1.3
Silicon 1.25-2.20 1.25-2.20
Copper 5.5-7.5 0.50
Nickel 13.0-17.5 18.0-22.0
Chromium 1.8-3.5 1.75-3.50

In addition to scale resistance at high temperatures, these irons are resistant to corrosion by acid, caustic, and salt solutions. They are, however, low-strength irons having a tensile strength of only about 25,000 p.s.i.

WHITE CAST IRON

Cast irons in this classification are not provided for in Navy Specifications. However, information is supplied as background material in case the occasion should ever arise for their use.

A white cast iron gets its name from the fact that a newly fractured surface has a white metallic appearance. A white cast iron is obtained by: (1) severe chilling of a low-carbon low-silicon iron, (2) addition of elements (especially chromium) that will prevent the formation of free graphite, or (3) by a composition that will produce a white iron when poured into a sand mold. Malleable iron in the as-cast condition is an example of the last method.

HOW GRAY CAST IRONS SOLIDIFY

Gray cast irons solidify generally the same as other eutectic alloys. Solidification starts

  with the growth of dendrites as described in Chapter 1, "How Metals Solidify." The first dendrites to form in gray cast iron are austenite because austenite is the constituent having the highest melting point and at this temperature ferrite cannot exist. As the austenite dendrites grow, they contain some dissolved carbon and the melt surrounding them changes in composition until it reaches the eutectic composition. In turn, the remaining liquid starts to solidify. Up to this point, the solidification is the same as for a normal eutectic alloy.

As the eutectic starts to solidify, however, another process begins. This is the nucleation and growth of the graphite flakes. The growth of graphite flakes starts at nuclei different from those that initiate the growth of the dendrites. The graphite flakes continue to grow so long as there is liquid eutectic around the flakes. This shows the importance of cooling rate to gray cast iron. The slower the cooling, the longer it takes for solidification, and graphite flakes can become quite large. A faster cooling rate means a shorter solidification time and smaller graphite flakes. Once the eutectic mixture has solidified, the structure of the graphite flakes is established. No further change in the pattern of the graphite flakes occurs as the iron cools to room temperature.

PATTERNS

Section thickness plays an important part in gray iron castings. There are limiting wall thicknesses below which a chilled structure (white iron) will be produced. Chill can be removed by annealing, but other physical properties are also reduced. The limiting wall thickness for ordinary gray iron is 1/8 inch, and for high-strength gray iron 3/8 inch. Patterns should be checked to determine that sections are not thinner than these limits.

As will all cast metals, gray iron is also sensitive to abrupt changes in section size and to sharp corners. Patterns should be checked for proper blending of unequal sections and for proper filleting of junctions. Refer to Chapter 2, "Designing a Casting."

The shrinkage allowance for gray cast iron is 1/8 inch per foot and pattern draft is 1/16 inch per foot. Machining allowances and approximate tolerances in the as-cast condition for various sizes of castings are listed in table 28.

452605 0-58-15

 

242
 
TABLE 28. MACHINING ALLOWANCES AND AS-CAST TOLERANCES FOR GRAY IRON
Approximate
Length of Casting,
inches
Machining Allowance,
inch
Approximate
As-Cast Tolerance,
inch
Up to 8 1/8 1/16
Up to 14 5/32 3/32
Up to 18 3/16 1/8
Up to 24 1/4 5/32
Up to 30 5/16 3/16
Over 30 3/8 to 1/2 1/4

 

This table is to serve only as a guide. Information of this type is best determined by experience. Refer to Chapter 3, "Patternmaking," for information on repair and storage of patterns.

MOLDING AND COREMAKING

Molding and coremaking procedures for gray iron are the same as for other metals as

  described in Chapter 5, "Making Molds," and Chapter 6, "Making Cores."

SAND MIXES

Various sand mixes that may be used for gray iron castings are listed in table 9, Chapter 4, "Sands for Molds and Cores." Core mixes are listed in table 14 of the same chapter. Typical properties of gray iron sands and the types of castings poured in these sands are listed in table 29.

 

TABLE 29. TYPICAL PROPERTIES AND USES OF GRAY IRON SANDS
Moisture,
percent
Green Compressive
Strength, p.s.i.
Permeability,
AFS units
Type of Casting
4.5 9 28 Piston rings
4.5-5.5 10-12 20-25 Small
5-6 9-12 50-60 Medium
5.7 9 55 Machinery parts up to 300 pounds
7 9 50 20 to 50 pounds
9 8 63 High-pressure pipe fittings
9.6 9 20 200 to 500 pounds

 

PROCEDURES

Coremaking and Molding. Cores and molds for cast iron present no unusual problems. Cores and molds must, however, be rammed firmly and uniformly to resist the high temperatures at which cast iron is poured. The quality of the surface finish is determined mainly by the fineness of the sand. The finer the sand, the better will be the surface finish of the casting.

Cores for cast iron should be well vented, and core vents should connect with vents in the mold. Because of the high heat content of the molten iron, it is important that cores be well baked to avoid core blows in the casting from gas generated in the core.

  Green-sand molds are used for iron castings. Skin-dried or completely dried molds are rarely required. Sea coal (ground bituminous coal) in amounts of 1 to 6 percent of the weight of the sand, is almost always added to molding sands for gray iron. The sea coal generates a controlled amount of gas when the casting is poured. This gas forms a film over the surface of the mold and helps to give a better surface finish of the casting. It also has a cushioning effect which helps to prevent sand expansion defects.

Washes. Iron castings do not usually require that molds or cores be protected with a wash if the sand is fine enough. It a coarse sand must be used, a silica wash can be applied to the mold as described in chapter 4. Another variation that gives an excellent surface finish

 

243
 
is to rub or brush dry powdered graphite onto the surface of the mold or core.

Gating. The good castability and fluidity of gray cast irons permit the use of gating systems that seem small in comparison with the gating of other metals. Gating systems for gray iron castings can use the same ideas as described in Chapter 7, "Gates, Risers, and Chills," except that they can be made quite small in cross section. Experience and the use of properly kept records are the best sources of information for selecting a gating system for iron castings.

There are two ingates that have proven useful in the casting of flat castings in gray cast iron. These ingates are the knife gate shown in figure 245 and the lap gate illustrated in figure 246. Both gates permit the molten metal to enter the casting through a thin gate. The cross-sectional area of gates of this type is the same as for conventional ingates, but they have the advantages of filling the casting more uniformly and are e easily removed by simply breaking them off. As part of the gating system for gray cast iron, it is good practice to include a strainer core or whirl gate in the system to remove dirt and slag.

RISERING

As for other metals, the size of riser for a particular casting depends on the thickness of the section that must be fed and the type of iron being poured. Generally the same practices as described in Chapter 7, "Gates, Risers, and Chills," may be followed. A rule-of-thumb for gray iron is that the cross sectional area of the riser should be about 80 percent of the cross- sectional area of section that must be fed.

The ordinary gray cast irons with a tensile strength of less than 25,000 p.s.i. can often be cast without risers. In such irons, the high carbon content (over 3.40 percent) often produces sufficient graphite flakes to offset most of the normal solidification shrinkage of iron. Indeed, if the gating system is selected carefully, sounder castings of ordinary gray iron can often be made without risers than with risers. However, this practice is not recommended. As the carbon content and silicon content of gray iron are decreased (tensile strength increased), larger risers become necessary; but even in the highest-strength gray irons, smaller risers are required than for almost any other metal. White cast iron, on the other hand, does not have the offsetting advantage of graphite formation and require s the large riser s typical of steel practice.

A gating and risering system that is useful in industry uses a shrink-bob riser and a whirl

  gate. It is a modification of the simple but good system of gating through the riser.

Figure 247 illustrates a good type of riser for a casting that is cast in both the cope and the drag. The risering of a casting that is molded in the drag is shown in figure 248. A cope casting is risered as shown in figure 249. The plan view of all three risers is the same and is shown in figure 250. Notice that for all three systems of risers, the top of the riser must be a minimum distance of four inches above the uppermost part of the casting.

The runner is usually rectangular in cross section but has a slight taper. It is slightly curved and enters the riser tangentially to provide a swirling motion of the flowing metal. In all three cases of casting location in the mold, the runner is in the drag. The ingates for all three casting locations are made to conform with the casting position. In other words, if the casting is in the cope, the ingate is in the cope and if the casting is in the drag, the ingate is in the drag. The cross section of the ingate can be either square or round.

The riser size is the same as previously mentioned. The cross-sectional area of the riser should be about 80 percent of the cross-sectional area to be fed. This type of riser must have what is called the drag portion of the shrink bob. This is as important as the other dimensions of the riser to obtain good feeding. The drag part of the shrink bob is important because the part of the riser next to the ingate must be kept molten to permit proper feeding. The drag part of the riser heats the sand in this area and keeps the metal in a molten condition for a longer period of time. If the drag part of the riser is omitted or is too shallow, the last metal to solidify will be well up in the cope section of the riser and will be unable to perform its function of feeding the casting.

Proper feeding of gray iron castings with this system can best be assured by using the sizes of risers, runners, and ingates listed in table 30. As mentioned before, the exact size of riser, runner, and ingate is determined by the casting size and the type of iron poured. The use of records that show successful gating and risering systems is invaluable in rigging new castings.

CHILLS

In the manufacture of gray iron castings, it is usually not necessary to use chills to promote directional solidification. The desired degree of directionality can usually be obtained by intelligent use of a gating and risering system. The use of chills can be dangerous.

 

244
 
TABLE 30. PRINCIPAL DIMENSIONS OF GRAY IRON GATING AND RISERING SYSTEM
Size of Casting,
pounds
Riser Diameter,
inches
Depth of Riser
Below Neck A,
inches*
Runner Size,
inch
Ingate Size,
inch
Lightest castings
that require
feeding - under
50
2 2-1/4
3/8 wider on top than bottom
1
1/4
1/2 to 3/4 square
2-1/2 2-1/4 13/16 to 7/8
diameter round
50 to 400 3 2-3/4
1/2 wider on top than bottom
1
3/8
1 to 1-1/4 square
3-1/2 2-3/4 1-3/16 to 1-7/16
diameter round
4 3-1/4
4-1/2 3-1/4
*Refer to figures 239, 240, and 241.
 
If chills are necessary, they must be used cautiously with gray iron castings. Chills must be located with the understanding that there is a possibility of producing chilled or white iron in that section. If the casting can be annealed to remove chill, this is not too important. If the casting cannot be annealed, this situation is very important and considerable thought must be given to the size and location of chills. The use of chills on thin sections is particularly risky. Thin sections solidify rapidly, even with only the sand mold surrounding them, and in some cases may result in chilled iron. If the chilled portions are in an unstressed location or where no machining is to be done, it is probable that the chills will cause little or no harm.

Chills are highly useful when it is desired to produce a cast iron part entirely or partly of white iron. Because chills speed the cooling rate, they promote the formation of white iron. For example, assume that a gray iron casting is desired with a white iron section to resist wear at some point. An iron or steel external chill with a thickness about twice that of the casting can be inserted in the mold (or rammed up against the pattern) at the place the white iron is desired. The iron should be cast directly against the chill, which should be free of all rust and dirt, warm, and coated with a thin mixture of plumbago and fire clay in water. The coating must be dried before the casting is poured.

VENTING

Cast iron is not particularly susceptible to damage by gases other than water vapor and is heavy enough to displace most mold gases if

  they are given a reasonable chance to escape. High spots on a casting should be vented by using a hacksaw blade passed through the mold. This is good practice with all metals.

MELTING

The electric indirect-arc furnace, electric-resistor furnace, and electric induction furnace are all capable of melting cast iron. In an emergency, an oil-fired crucible furnace can be used to melt the high-carbon, high-silicon cast irons. This practice, however, is slow and permits only one or two heats per crucible and results in reduced refractory life in the furnace. Because of its high pouring temperature, cast iron is difficult to melt in an oil-fired crucible furnace. Electric methods should be used whenever possible.

ELECTRIC INDIRECT-ARC FURNACE

Charging. After the furnace has been preheated in accordance with instructions in the manufacturer's manual, the shell should be rotated until it is 45° down either front or rear from the top center position. The charging position should be varied from time to time to prevent excessive wear on one section of the lining. The ideal method of charging is to have the furnace door in the top-center position. The carbons should be moved back until they are flush with the furnace wall to prevent damage during the charging period.

Foundry returns (gates and risers) should be charged first and should be free of sand. Sand causes a slag blanket to form on the surface

 

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of the molten metal during the melting cycle. This insulates the bath from the heat generated by the arc and makes it difficult to reach and to determine the desired tapping temperature. Usually, heavy pieces should be charged first. If cast iron or steel borings are used, they should be added next because they will filter down through the scrap, give a more compact charge, and will be free from direct contact with the arc. Additions of nickel, chromium, molybdenum, and vanadium may now be made. If charged on top (close to the arc), some loss of the finer alloys may occur because of "blowing-out" by the arc. Pig iron should be charged next and steel scrap on top (closest to the arc). Ferromanganese and ferrosilicon should not be added with the charge, but should be added to the molten bath before tapping.

Charging should be accomplished as quickly as possible to prevent excessive loss of heat from the lining. It is not good practice to exceed the rated capacity of the furnace. Lastly, the furnace door should be closed and clamped securely.

Working the Heat. The charge should be observed periodically during the melting cycle through glasses with a No. 12 lens. The angle of rock should be increased steadily as the pool of molten metal collects under the arc. As melting proceeds, the melted metal will wash over the rest of the charge until it is entirely melted.

Ferromanganese and ferrosilicon should be added through the spout in the order mentioned about 3 to 5 minutes before tapping. The bath should not be superheated from 2,700°F. to 2,800°F. to permit good separation of slag from the metal. The metal can be cooled in the furnace or tapped and cooled in the ladle to the desired pouring temperature. The temperature of the molten bath maybe estimated rather closely from the kwhr input. However, sufficient data must be collected before this is possible.

A typical operating log for a few cast iron heats is shown in figure 251. Notice that the kwhr input decreases slightly with each consecutive use of a barrel because of the heat retained by the lining. Another rough method for determining the temperature of the bath is to work a 1/2 inch-diameter soft-iron rod in the molten bath for a period of 15 to 20 seconds. If the tip sparkles, the temperature is approximately 2,700°F. Should the tip melt in that period, the bath is 2,800°F. or higher and the iron should be tapped. The iron rod should be bent and care taken to avoid striking the electrodes. The behavior of the molten bath gives an indication of the proper tapping temperature. A bubbling action can be observed at approximately 2,800°F.

  Prior to tapping, a chill-test specimen should be poured and fractured to determine if the heat has the desired characteristics. If the chill depth is too great, the chill characteristics can be adjusted by the addition of graphite, ferrosilicon, or other graphitizing inoculants to the bath or ladle. The effective use of this fracture test requires experience in order to judge the relationship between the depth of chill and the carbon equivalent of any heat as it applies to the controlling section thickness of the casting to be poured. The use of a chill test is described later in this chapter.

Slag is objectionable in this type of furnace because it serves as an insulating blanket between the arc and the surface of the bath and it reflects an abnormal amount of heat to the refractories above the slag. Under these conditions, the refractories start to melt, more slag is formed, and the entire lining can be melted out rather quickly. Melting of the lining is shown by a "runny" appearance of the refractory. When this occurs, the power should be shut off, the door removed, and clean dry sand spread over the slag to thicken it. The slag should then be pulled from the furnace and operations resumed.

Tapping. The furnace should be operated at reduced input (just sufficient to maintain the temperature of the bath) throughout the tapping period. The "Automatic Rock" switch should be placed in the "off" position and the furnace should be operated by the portable push-button station during pouring. If the entire heat is to be tapped into one ladle, ladle inoculations of ferrosilicon, graphite, ferronickel, or proprietary inoculants may be used. If the heat is to be shanked, ladle inoculants may cause nonuniformity of composition unless the weight of metal tapped can be weighed separately.

There should be no delay in tapping once the proper temperature has been reached. If a slight delay is unavoidable, the arc and the "Automatic Rock" switch should be shut off. The temperature of the bath will not fall or rise appreciably during the first few minutes. If a longer period of delay is necessary, the furnace should be operated intermittently at reduced input and at full rock in order to maintain the desired temperature. A well dried and preheated ladle should always be used for tapping.

ELECTRIC-RESISTOR FURNACE

Melting of cast iron in an electric-resistor furnace follows the same practice as described for the electric indirect-arc furnace.

ELECTRIC-INDUCTION FURNACE

The procedure for melting gray cast iron in the electric induction furnace is a simple

 

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operation. Refer to Chapter 8, "Description and Operation of Melting Furnaces," for the proper charging procedure and handling of the heat. The sequence of charging and alloy additions are the same as for the electric indirect-arc furnace.

TEMPERATURE CONTROL

The melting and tapping temperatures of cast irons are too high to permit the use of the type of immersion pyrometers used aboard repair ships. The optical pyrometer should be used to determine the temperature of the molten metal and readings must be taken on the clean metal surface. The surface of the metal bath should be as free of slag as possible. Otherwise, a false reading will be obtained.

Tapping temperatures may be estimated from the kwhr input and the time at the particular power input. Estimations of this type can be made only after considerable experience with the particular melting unit used and comparison of the power input with actual pyrometer temperatures. This type of procedure should be relief upon only as an emergency measure. Pyrometer readings are the only reliable indications of the true temperatures of the molten metal.

A common error with an optical pyrometer is to focus the instrument on the brightest portion of the metal. This is usually slag or an iron oxide and will give a temperature reading that is too high. Sighting the pyrometer into an enclosed chamber will also give a high reading. For consistent and dependable results, focus the instrument on metal in the open end of the furnace on the darkest portion of the metal.

LADLE TREATMENT

Inoculants such as ferrosilicon, graphite, or other commercial materials are added to the melt to obtain better properties in the base iron or to obtain the proper carbon equivalent. The chill-test as a melting control is discussed in the following section and described in Chapter 21, "Process Control."

The addition of the inoculant should be made in the stream of molten metal if a small ladle is used, or to the heat in the furnace if the entire heat is to be tapped at one time. The ladle addition to the stream of metal is a tricky process because the amount of metal tapped into a ladle can only be estimated. Small additions that are weighed out beforehand and added gradually to the molten metal stream are the easiest to make. The purpose of adding the inoculant to the metal stream is to assure good mixing with the molten metal. If the addition is placed in the bottom of the ladle before the iron is

  tapped, the addition is likely to fuse to the ladle lining and its effectiveness is reduced. Likewise, if the addition is made to the top of the metal bath after the ladle has been filled, intimate mixing is impossible and effectiveness of the inoculant is again reduced.

The inoculant should be thoroughly dry before adding it to the molten metal. Moisture in an inoculant causes severe boiling and spattering of the molten metal. The size of the inoculant is important in its effectiveness. If the material is too fine and powdery, it will be blown away during the ladle-filling operation and recovery is r educed. If the material is too coarse, it will not dissolve readily and will be carried into the casting as undissolved particles.

USE OF CHILL TEST AS A MELTING CONTROL

One of the major problems in selecting, melting, and controlling gray iron is to avoid the formation of hard white iron (chill) in thin sections and on edges and corners of castings. Fortunately, however, a rapid chill test can be made while the iron is still in the furnace.

Assume that it is desired to pour a certain iron into a 1/4 inch wall without danger of forming white iron. A logical test is to make a small test specimen 1/4 inch thick, pour it with the iron, cool it, and break it to examine the fracture. If white iron (chill) is present, it will be easy to see on the fractured face. Such a test can be made rapidly while the iron is still in the furnace and while there is still time to adjust the composition.

A test such as that above, however, would be restricted to one wall thickness (1/4 inch). A more versatile and universal test would be to pour a wedge (say, 4 inches long and with a triangular cross section tapering from 3/4 inch down to a knife edge). This wedge can then be broken through the middle. The triangular area of the fracture gives important information. The knife edge of the wedge will be white except for the very soft irons. The 3/4 inch base will be gray, except for the very strong irons. Most irons will have intermediate degrees of chill. By measuring across the wedge at the zone of chill depth, one has a direct measure of the thinnest casting that can be poured gray without chill.

Thus, the wedge test when fractured gives a measure of the chilling tendency of the iron. Ordinary low-strength irons will have low chill depths. High-strength irons will have high chill depths.

The wedge can be poured in green sand, but if used often can conveniently be poured in

 

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oil-sand cores made up ahead of time. The wedge does not have to be cooled slowly. As soon as it is solid, it can be shaken out of the mold, quenched in water, broken, and examined.

Intelligent and informative use of a chill test for iron depends upon experience gained in making a number of tests and examining the castings that result.

If chill depth of a chill test is too deep, the most rapid and satisfactory correction can be made by adding ferrosilicon to the melt. Graphite additions will serve the same purpose, but graphite is usually difficult to put in solution in iron.

If the chill depth is too low, the carbon and silicon content of the iron are probably too high. These elements cannot be readily removed from the iron, but they can be reduced by dilution if steel is added to the melt in the furnace. Another method to increase chill depth is to add up to 1 percent chromium or 1 percent molybdenum to the iron. If a totally white iron is desired, up to 4 percent chromium or nickel can be added to the iron in the furnace.

POURING

Pouring practices for gray cast iron are the same as for other metals as described in Chapter 9, "Pouring Castings." Proper skimming before and during the pouring operation are particularly important with cast iron. A small amount of slag passing into the mold usually results in a scrapped casting. It is best to use a pouring basin for cast iron. The high temperatures of molten cast iron tend to burn out the binder in pouring cups, cut into the top of the mold, and wash loose sand particles into the casting.

As with all metals, the castings should be poured at the lowest temperature that will permit complete filling of the mold. For thin and intricate castings, the pouring temperature may be as high as 2,600°F., but a good molding sand and good mold are required under these conditions to obtain a reasonably clean casting finish and freedom from trapped dirt. For fairly chunky castings with a 2 inch wall, the pouring temperature can be as low as 2,350°F. with excellent results. Because of its lower carbon and silicon contents, white iron castings must be poured slightly hotter (say, 50°F. to 100°F.) than gray iron. Even so, the white iron will not reproduce the pattern detail as well as gray iron.

CLEANING

Gray iron castings usually shake out of a mold easily and sand adherence is not a problem.

  Any sand sticking to the casting after shakeout can be removed with a wire brush or by sand blasting.

Gates on gray iron castings are normally small enough that the gates and risers can be smacked off easily with a hammer. If there is any doubt as to whether a gate or riser will break cleanly without damaging the casting, the gate or riser should be notched before attempting to knock it off. The remaining stub on the casting can be easily ground to the casting surface. A stand or portable grinder can be used, depending on the size of the casting.

CAUSES AND CURES FOR COMMON DEFECTS IN IRON CASTINGS

Gray iron castings can have the same defects as other types of cast metals. Refer to Chapter 11, "Causes and Cures for Common Casting Defects." There are some that are especially apt to occur in gray iron castings and are discussed in this section.

METAL COMPOSITION

The proper control of chemical analysis is important in the production of gray cast iron. Information given here can only serve as a rule - of-thumb method for recognizing the effects of the various elements.

The chill test is invaluable in determining if a particular heat is going to have the desired properties. A high carbon content, a high silicon content, or a combination of both will result in a weak iron. Small additions of some of the carbide-stabilizing elements (chromium or molybdenum) can be made to correct such a condition. A heat that reveals too strong a chill in the chill test can usually be corrected by additions of ferrosilicon.

Severe and unexplainable chilling of a test specimen or a casting may be traced to contamination by tellurium. There are tellurium mold washes that produce a severe chilling action. Their use should be avoided unless the molder is absolutely certain as to their use and results. If the charge is contaminated with tellurium, a faint odor of garlic maybe detected when the charge becomes molten. Such a heat should be scrapped unless it can be used for castings that require chilled iron. If it is necessary to anneal an iron casting that contains chill or hard areas, a temperature of about 1,700°F. is required for at least several hours and the casting must be cooled slowly in the furnace to at least 1,200°F.

 

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POURING

A particular defect known as a cold shot may be found in gray iron castings. This defect is caused by a small amount of molten metal entering the gating system or mold cavity and solidifying in the form of a small ball. This condition usually takes place if the man pouring the metal starts to pour, for some reason must stop momentarily, and then resumes pouring. The cold shot occurs because the small globule of metal is highly chilled and cannot dissolve or fuse with the molten metal entering the mold. The cure for this defect is to fill the gating system as rapidly as possible and to keep a steady uninterrupted stream of metal flowing into the mold.

MELTING PRACTICE

It is hard to damage gray iron by improper melting in the furnaces used aboard ship. The greatest source of trouble will be from overheating of the metal which will increase the loss of carbon, silicon, and manganese from the iron. Contamination of the charge or melt with phosphorus or sulfur in excess of specified maximums will cause defective castings.

Excessive carbon pickup by the iron can occur in an arc furnace if the arc is permitted to run smoky for a long time. This is bad practice with any metal. However, gray iron is less likely than any other metal to be damaged by such practices. It is almost certain that any melting practice that will damage gray iron even slightly will be impossible for any other metal.

MISCELLANEOUS

Cast iron is particularly susceptible to damage from water vapor released from damp linings or ladles. Damp linings will cause the iron to pick up gas which is rejected as blows or pinholes when the casting solidifies.

  Hard cores will restrict contraction of the iron and may cause cracks. It is sometimes advisable to dig out cores before the casting is shaken out of the sand.

Because of its high pouring temperature, gray iron is rough on sand. For smooth castings, it is necessary to use a fine sand bonded with high-fusion clay or bentonite or to use a suitable mold wash.

WELDING AND BRAZING

Welding of iron castings is a difficult procedure and unless done properly usually results in a cracked casting. White iron castings are more likely to crack than gray iron when welded. Iron castings of any type should be preheated to at least 700°F. for welding or brazing. Under such conditions, excellent and dependable repairs can be made by brazing. If repairs by welding or brazing are required, refer to the "General Specifications for Ships of the United States Navy," Section S9-1, "Welding," for general guidance.

SUMMARY

Gray cast iron is a casting alloy that has a wide range of good properties that make it highly desirable as an engineering material. It is particularly adapted to structural castings of intricate design requiring thin sections. Gray iron is one of the easiest metals to cast.

Aboard repair ships, the determination of the composition of the iron is impossible. The use of the chill test and records of successful gating and risering systems are indispensable in producing good castings.

 

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Figure 245. Knife gate.
Figure 245. Knife gate.

Figure 246. Lap gate.
Figure 246. Lap gate.

 

Figure 247. Riser for a gray iron casting molded in the cope and drag.
Figure 247. Riser for a gray iron casting molded in the cope and drag.

Figure 248. Riser for a gray iron casting molded in the drag.
Figure 248. Riser for a gray iron casting molded in the drag.

 

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Figure 249. Riser for a gray iron casting molded in the cope.
Figure 249. Riser for a gray iron casting molded in the cope.

 

Figure 250. Plan view of runner, riser, and ingate.
Figure 250. Plan view of runner, riser, and ingate.


 

Figure 251. Operating log for cast iron heats.
Figure 251. Operating log for cast iron heats.

 

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Chapter XVIII
STEEL
 
Steel is an iron-base alloy fairly low in carbon content. All of the carbon in steel is dissolved in the iron so that no carbon is present as graphite.

The outstanding characteristics of steel castings are their high strength and toughness. With steel, it is possible to make castings stronger and tougher than with any other common casting alloy. Steel retains its high strength even up to fairly high temperatures but can become quite brittle as low temperatures.

The main disadvantages of steel as a casting alloy are: (1) it melts at a high temperature, (2) has a high shrinkage during solidification, and (3) is difficult to cast. Except for specially alloyed grades, steel will rust or corrode and is magnetic. As a general rule, low-carbon unalloyed steel is harder to cast than high-carbon or alloyed grades.

SELECTION OF ALLOYS

The proper grade of steel for a casting is usually designated on the blueprint which accompanies the work order. When the blueprints are not available or when the casting must be made from broken parts, the intended use of the

  casting is the best basis for determining the proper steel. Steels generally used aboard ship can be divided into three general classes: (1) unalloyed steels, (2) low-alloy steels, and (3) corrosion-resistant steels.

UNALLOYED STEELS

Unalloyed steels (plain carbon steels) are those which contain carbon and manganese as the principal alloying elements. Other elements are present in small amounts carried over from the customary steelmaking operations. The elements normally found in plain carbon-steel castings are as follows:

Element Percent
Carbon 0.05 to about 0.90
Manganese 0.50 to 1.00
Silicon 0.20 to 0.75
Phosphorus 0.05 maximum
Sulfur 0.06 maximum

The unalloyed steels can be further subdivided into low, medium and high-carbon steels. Table 31 lists the ranges of composition and mechanical properties (after normalizing) of three classes of plain carbon steel.
 

TABLE 31. COMPOSITION AND PROPERTIES OF PLAIN CARBON STEELS
Low Carbon Medium Carbon High Carbon
Composition
Carbon, percent 0.09-0.20 0.20-0.40 0.10-0.90
Manganese, percent 0.50-1.00 0.50-1.00 0.50-1.00
Silicon, percent 0.20-0.75 0.20-0.75 0.20-0.75
Phosphorus, percent 0.05 max 0.05 max 0.05 max
Sulfur, percent 0.06 max 0.06 max 0.06 max
Physical Properties
Tensile Strength, p.s.i. 42,000-70,000 60,000-80,000 70,000-120,000
Yield Strength, p.s.i. 20,000-38,000 30,000-40,000 35,000-70,000
Elongation in 2 Inches, percent 36-22 30-20 26-30

 
High-carbon unalloyed steel is used where parts are subject to high stresses and surface wear (such as in hawse pipes, chain pipes, and engine guides). Low-carbon unalloyed steel is used where strength is not of prime importance but where welding may be necessary.   LOW-ALLOY STEELS

Alloy steels contain either unusually large amounts of the common elements or fairly large amounts of special elements. These changes from the composition of plain carbon steel are

 

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made to obtain special properties (usually for higher strength). In the low-alloy steels, manganese may be used up to 3.00 percent and silicon up to 2.75 percent, with copper, nickel, molybdenum, and chromium in varying amounts. The total content of special materials added to low-alloy steels is usually less than 8 percent.

CORROSION-RESISTANT STEELS

Steels in this group are highly alloyed and are used where high resistance to chemical or salt-water corrosion or good strength at high temperatures is necessary. A typical corrosion-resistant steel has a low carbon content and additions of 18 percent chromium and 8 percent nickel. This steel is commonly called 18-8 stainless steel. The alloying elements are added to obtain particular properties, which vary with the element added, the amount of the element, and combinations of several elements.

HOW STEELS SOLIDIFY

Steels solidify by the nucleation of crystals at the mold wall and growth of crystals in the molten metal as described in Chapter 1, "How Metals Solidify." The amounts of carbon and other elements affect the method of solidification of the steel.

Figure 252 can be used to illustrate how a steel solidifies. The composition of a steel is represented by the vertical lines. Any steel above the temperature line marked "Liquidus" is entirely molten. Any steel below the line marked "Solidus" is entirely solid. At temperatures between the liquidus and solidus, the steel is mushy. Consider a steel containing 0.20 percent carbon that has been heated to 2,900°F. The intersection of the vertical line (0.20 percent carbon) and the horizontal line (2,900°F.) is above the liquidus line, so the steel is entirely molten. As the steel cools, its composition does not change, so this steel is always represented by the vertical line marked 0.20 percent carbon. When the steel cools to 2,775°F., it reaches the liquidus and the first crystals (dendrites) start to solidify. Solidification continues until the temperature reaches the solidus at 2,715°F. At this temperature, the steel is completely solid. Thus, a steel containing 0.20 percent carbon solidifies over a 60°F. range of temperature. Figure 252 shows that with 0.10 percent carbon, the solidification range would be about 70°F.; with 0.30 percent carbon, the range is about 90°F.; and with 0.60 percent carbon, the range is about 160°F.

Except for very low carbon contents, an increase in the carbon content of steel causes it to solidify at a lower temperature and over a wider range of temperature. Laboratory studies

  have shown that actual solidification for a 0.05 to 0.10 percent carbon steel takes approximately 40 minutes for a square bar, 8 inches by 8 inches. A similar casting of 0.25 to 0.30 carbon steel takes approximately 45 minutes to solidify, and a 0.55 to 0.60 percent carbon steel takes approximately 50 minutes. The longer solidification times of the medium and high-carbon steels permit dendrites to grow farther into the liquid metal and make proper feeding of these castings more difficult. The low-carbon steels, which have a short solidification time, do not have as much growth of dendrites and so are more easily fed to produce sound castings.

PATTERNS

Molds for steel castings must be rammed quite hard to withstand the erosive action of the stream of molten metal and to bear the weight of the casting. The patterns must be sturdy to stand the impact during molding. Any patterns which are to be used repeatedly should be made of aluminum or some other easily worked metal. Many times a wood pattern will be satisfactory if the areas of high impact and wear on a pattern are protected by using metal inserts. However, many accurate steel castings have been made with soft wood patterns.

If a pattern is designed so that hard ramming of the mold makes it difficult to draw, the draft (taper) of the pattern should be checked and increased if necessary. It must be remembered that the harder a mold is rammed, the more draft is required to permit proper drawing of the pattern.

MOLDING AND COREMAKING

SAND MIXES

Sands for molds and cores must be highly refractory in order to resist the intense heat of molten steel. The sand mixes must have good permeability. The binder must not burn out too readily but at the same time cannot have such a high hot strength that defective castings are produced. The synthetic all-purpose sand described in Chapter 4, "Sands for Molds and Cores," has the properties required for a good sand for steel castings and should be used aboard repair ships and at advanced bases for this purpose. Refer to chapter 4, table 8 for typical molding sand mixes, and table 13 for typical core-sand mixes for steel castings.

PROCEDURES

The procedures for molding and coremaking as applied to steel castings are generally the same as for other types of castings. For general

 

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procedures, refer to Chapter 5, "Making Molds," and Chapter 6, "Making Cores."

Coremaking for steel castings requires a slight change in practice as compared to the coremaking practices for other metals. Cores must be rammed harder than usual to provide the strength that is required to resist the weight of steel. Hard ramming is also necessary to make the surface resistant to the eroding action of molten steel. Erosion of sand from cores is more of a problem in steel castings than in other metals because the molten steel burns out the binder quickly and sand is easily washed away.

All cores require adequate internal support but cores for steel castings require increased internal support for additional strength because of the high temperatures involved. Internal support for smaller cores is usually by means of reinforcing wires. Larger cores require arbors.

Steel castings hot tear easily if the cores do not have good collapsibility. To avoid this cause of hot tearing, large cores are often hollowed out or the center parts are filled with some soft material that will let the core collapse as the metal contracts around it.

Molding requirements for steel castings are similar to those for core making. Ramming of the mold must be harder than for other types of metals to withstand the weight of steel and provide a surface that will resist the eroding action of molten steel. Steel castings are often so large that the sand must have high strength or be reinforced to support its own weight and maintain dimensions of the mold.

Steel castings can be made in green-sand molds or in dry-sand molds, or in intermediate types such as skin-dried or air-dried molds. The type of casting determines the type of mold to use. Green-sand molds offer little resistance to the contraction of the casting but are relatively weak. However, they are used successfully for many types of steel castings. Dry-sand molds are stronger, and are used in special cases. Molds which have had the surface dried about 1/2 inch deep with a torch are excellent for most general-purpose work.

If a skin-dried or air-dried mold is used for steel and the casting cracks, try a green-sand mold. If the mold deforms or does not hold the steel, try a dry-sand mold.

Washes are extremely useful on molds and cores for steel castings. Without a wash, the molten steel will often penetrate the sand and cause rough "burned-on" surfaces. Washes on a mold or core should be thin and uniform. If a wash is put on a hot core after removal from

  the core oven, the wash will usually dry properly. A core that is coated with a wash after it has cooled should be returned to the core oven for drying.

When applying a wash to the mold, particular attention should be paid to the coating of deep pockets. Many times a careless application of a wash in a pocket will result in a heavy coating in that area or a thick coating of wash at the bottom of the pocket. Washes applied in this way result in areas of high moisture concentration, which in turn are likely to cause defects. Washes should be applied as uniformly and as thinly as possible and must be dried before use.

GATING

Steel castings are gated according to the principles discussed in Chapter 7, "Gates, Risers, and Chills." The gating of steel castings varies a great deal and it is difficult to provide a basic gating system that can apply to steel castings in general. A few suggested gating sizes are given, but they should be taken only as a starting point for determining the proper gating system. Records of successful steel casting gating systems should be used to determine gating systems for new or unfamiliar castings.

The use of a single ingate is to be avoided because it produces a jet effect in the molten metal stream entering the mold; mold erosion results. Likewise, the gating system should not produce an appreciable drop of the molten steel into the mold cavity. This also produces severe mold erosion.

The use of splash cores at the base of the sprues to prevent erosion is advisable also. If the metal must fall far in the sprue, the entire gating system may be made profitably out of cores that are rammed in the mold. Mold washes on the runners and ingates may also be used to reduce the erosive action of molten steel.

RISERING

The risering of steel castings has been based primarily on experience. However, a great deal of information has been developed recently through research and proved through application to production castings. Much of this information is beyond the scope of this manual.

CHILLS

Because of its high shrinkage during solidification, steel must freeze progressively toward a riser. This is called directional solidification. One way to encourage directional solidification is to pour the metal through the riser and use risers that are large enough to

 

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stay fluid while the casting is solidifying. Sometimes, however, the part of the casting farthest from the riser still cools too slowly. When this happens, external chills can be used to speed up the freezing of the metal farthest from the riser. The use of chills for this purpose was discussed in detail in Chapter 7, "Gates, Risers, and Chills." Chills are used more extensively with steel castings than with any other common casting alloy.

Whenever chills are used, they must be clean and dry. External chills are usually coated with plumbago or clay and then thoroughly dried before use. Refer to chapter 7 for special precautions in the use of chills.

External chills used with steel castings should have tapered edges as shown in figure 253. A straight chill causes a sharp change in solidification characteristics at the edge of the chill and often causes a hot tear.

VENTING

Because steel is poured at higher temperatures than other metals, a greater volume of gas must be removed from the mold. Thorough venting of molds for steel is necessary to prevent defects caused by trapped air or gas.

MELTING

TYPES OF FURNACES

Steel can be melted in either an indirect-arc furnace, resistor furnace or induction furnace. These three units are particularly adapted to the melting of steel because of their ability to melt rapidly and to reach high temperatures. For details on furnace operation see Chapter 8, "Description and Operation of Melting Furnaces." Oil-fired crucible furnaces are not satisfactory for melting steel because they will not reach the melting temperature of steel.

PROCEDURE

Indirect-Arc Furnace. The indirect-arc furnace is somewhat difficult to use for melting steel and requires the constant attention of the operator throughout the melting operation. Operation and control of the furnace are described in Chapter 8, "Description and Operation of Melting Furnaces."

Charging. The charging precautions described in chapter 8 should be followed in the charging of steel. After the furnace has been properly preheated, the shell should be rotated until it is 45° down either front or rear from the top center position. The charging position

  should be varied from time to time to prevent excessive wear on one section of the lining. The ideal method of charging is to have the furnace door in the top center position. The electrodes should be moved back until they are flush with the furnace wall to prevent damage during the charging period.

Heavy pieces should be charged first but should be avoided when possible because they prolong the melting time. Foundry returns (gates and risers) should be charged next and should be as free as possible from sand. Excessive sand causes a slag blanket to form on the surface of the molten metal during the melting cycle. This insulates the bath from the heat generated by the arc and makes it difficult to reach or determine the desired tapping temperature. Steel borings should be added after the returns. They will filter down through the scrap, make the charge more compact, and be away from direct contact with the arc. Structural steel scrap should be charged last (on top). Alloys of nickel and molybdenum may be added to the cold charge. (Alloys that oxidize rapidly, such as chromium, manganese, and silicon, are added just before tapping.) Any alloys of fine size should be charged so that they are not near the arc. This will prevent losses due to "blowing-out" by the arc.

Working the Heat. There are two distinct methods for making steel in the indirect-arc furnace. One is the dead-melting method and the other is the boiling method. The boiling method more nearly approaches the methods developed for commercial steel-melting furnaces and is the recommended method. Up to the time the charge is completely melted, the procedure is the same for both methods.

The metal should be melted as fast as possible and the furnace brought to full rock quickly. In the dead-melting method, additions of ferromanganese and ferrosilicon should be made as soon as the last piece of steel melts. The arc should not be broken and the rocking motion of the barrel should not be changed when making the additions. The alloys should be sized 'so that they can be charged without difficulty. After the additions have been made, the heat will be almost at the tapping temperature and provisions should be made for tapping shortly thereafter (approximately 5 minutes). The bath should be watched carefully during this stage because the temperature of the molten metal is approaching the fusion point of the furnace lining. If the lining shows any indication of "running," or if a thick slag blanket forms on the surface of the bath, the heat should be tapped immediately.

The dead-melting method described in the preceding paragraph frequently results in

 

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porosity as a casting defect. The porosity is produced by gases present in the charge and absorbed during melting.

When using the boiling method (the recommended method), as soon as the charge is completely molten, 2 percent of iron ore should be added to the charge, which has previously been calculated to melt down at 0.25percent carbon. As soon as the iron ore melts, an immediate reaction takes place between the carbon in the steel and the iron oxide in the ore. This reaction produces carbon monoxide gas. Hydrogen and nitrogen pass into the bubbles of carbon monoxide and are removed from the steel. The carbon monoxide formed in the steel burns to carbon dioxide at the furnace door. As soon as the reaction subsides (which can be determined by the force and brilliance of the flame at the furnace door), the furnace should be rolled so that all excess slag is drained off. At the time the ore is added, the power is reduced approximately one-third and is kept reduced during the balance of the heat. After all the excess slag has been removed, the addition of ferrosilicon and ferromanganese should be made at once followed by any ferrochrome required and the heat tapped within two or three minutes.

The ore addition may be reduced to 1 percent if very rusty scrap is used. This practice of using rusty scrap should be avoided except in an emergency. Larger additions of ferromanganese will have to be made because of the oxidized condition of the bath if rusty scrap is used.

After making several heats of steel by the boiling method, an experienced operator should have no difficulty in controlling composition. Making steel in this manner results in sound castings, but the handling of the s lag is a greater problem than with the dead-melting method.

Temperature Control. Proper temperature control for the production of good castings cannot be overemphasized. The proper pouring temperature is determined by the composition of the metal being poured and the size and nature of the casting. A heavily cored mold or one having thin sections will require a higher pouring temperature than other types of castings. Castings with heavy sections require lower pouring temperatures to minimize the attack of the steel on the sand molds and cores.

When melting steel, the optical pyrometer is the best instrument available for shipboard use to determine the temperature of the molten metal. It must be remembered when using the optical pyrometer that the surface of the bath must be free of any slag and the reading must be taken on the surface of the metal. If there is any smoke or fumes in the furnace, an

  erroneous reading will result. For proper operation of the optical pyrometer, see Chapter 9, "Pouring Castings."

Melting records are useful for estimating the temperature of the bath should an emergency arise because of lack of an optical pyrometer. If accurate melting records are kept to show the power input and optical-pyrometer readings once the charge has become molten, the temperature of the bath in later heats can be estimated from the power input. This procedure is strictly for emergency use and should not be used as standard practice.

Another method useful for determining the proper tapping temperature is to use steel rods. A 5/16-inch diameter rod is cut off to make a blunt end. The rod is then immersed in the steel bath for a short period of time. If the bath is at the proper temperature, the rod will have a rounded end when it is drawn out. The appearance of the rod before and after immersion is shown in figure 254. Considerable skill is required for this test.

De-oxidation and Tapping. The tapping temperature for steel is preferably between 3,0000 and 3,100°F. The molten metal should not be held in the furnace any longer than necessary. Holding of the heat in the furnace makes possible the absorption of gases by the melt.

The furnace should be tapped into a well-dried and heated ladle. The ladle lining should be red hot before it is used. When the ladle is half full, the necessary de-oxidizers should be added to "kill" the heat. Additions of calcium-silicon-manganese (Ca-Si-Mn) and aluminum give satisfactory results.

Care must be taken to make certain that the additions are effective. De-oxidizers which are not completely dissolved in the metal or which become trapped in slag are ineffective and result in an incompletely de-oxidized or "wild" heat.

PROCEDURE FOR RESISTOR FURNACE

The mechanical operation of the resistor furnace is the same as for the indirect-arc furnace. Charging is carried out with the same precautions as for the indirect-arc furnace described in Chapter 8, "Description and Operation of Melting Furnaces." For a detailed description of the operation of the resistor furnace, also see chapter 8.

The dead-melting method of making steel is used in the resistor-type furnace. The working, melting, and tapping of the heat are the same as for the indirect-arc furnace. The power input should be maintained constant during

 

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the melting cycle and tapping. For a 500-pound capacity furnace, this is 150 k.w.

PROCEDURE FOR CORELESS INDUCTION FURNACE

The dead-melting method may be used with this furnace but does not consistently produce sound castings. It is recommended that the following practice be used for melting all grades of carbon and low-alloy steel.

Charging. The initial charge is made up of gates, risers, and steel scrap. A mixture of 50 percent gates and risers and 50 percent steel scrap makes a satisfactory initial charge. Old castings, if used, should be considered as gates and risers.

The charge is made by placing about 10 percent of steel scrap on the furnace bottom. On top of this, 3 or 4 percent of iron ore is added and then the remainder of the plate scrap. Gates and risers are charged last. Careful handling of the charge material should be followed as standard practice to prevent any damage to the furnace lining.

Working the Heat. As the initial charge melts down, any remaining charge material can be added to the molten metal. Any material added to molten metal should be completely dry. As soon as melting is completed and a temperature of about 3,000°F. is reached, 1-1/2 to 2 percent of pig iron is added. Before being added, the pig iron should be placed on top of the furnace for four or five minutes to warm and to dry. When added, the pig iron should be held under the surface of the bath with a steel rod. The addition of carbon from the pig iron will react with the oxides in the molten metal to produce a boil that will serve to flush out undesirable gases.

After the boil has subsided, ferro-manganese and ferro-silicon should be added. When they are completely dissolved, the heat should be tapped. If the entire heat is to be tapped into one ladle, the power should be shut off and should remain off. If the heat is to be tapped into several ladles, the power should be shut off as soon as the ferro-manganese and ferro-silicon have dissolved. The slag will come to the surface where it can be skimmed off. As soon as the slag is removed, reduced power should be turned on again and allowed to remain on during the tapping of the furnace. POURING DURING TAPPING SHOULD BE AS FAST AS POSSIBLE.

TEMPERATURE CONTROL

Properly calibrated optical pyrometers should be used to obtain temperatures of the

  molten bath during the melting operation. It is advisable to take numerous temperature readings during the superheating of the melt. The induction furnace produces a very rapid rate of energy input to the melt and this may result in overheating of the metal. Power should be reduced as the desired temperature is approached and an attempt made to reach the final temperature gradually.

DE-OXIDATION

The final de-oxidizers should be added in the ladle when the heat is tapped into one large ladle. When tapped into small ladles, aluminum (2 ounces per 100 pounds of melt) may be added in the furnace with a small extra addition in the small ladle. Power must be turned off and tapping must be rapid after the aluminum is added to the furnace.

POURING

Separate pouring cups or basins are necessary when pouring steel castings. A pouring cup cut into the top of the mold at the sprue does not have the necessary properties to resist the erosive action of the stream of molten steel. Pouring cups or basins for steel should be made from sand with extra binders (core oil or clay), baked, and coated with a refractory wash.

Steel should be poured as rapidly as possible without causing defects such as swells or shifts. These may be caused by excessively high pouring rates. When determining how fast a casting is to be poured, consideration must be given to the structure of the mold. A simple mold without cores can be poured much faster than a heavily cored mold requiring a more extensive gating system. For large steel castings, an average speed of pouring which results in metal rise in the mold of 1 inch per second is satisfactory.

CLEANING

Wire brushing and sand blasting are the best ways to remove adhering sand from steel castings. If sand adheres tightly to the casting, it can usually be removed with a chipping hammer. Many surface defects can be removed by chipping and grinding.

For Grade B and carbon-molybdenum steel, flame cutting with the oxyacetylene, oxyhydrogen, or oxypropane torch is the best method for removing gates and risers. Thorough cleaning is very important to facilitate starting the cut and to insure a uniform cut. The gates and risers should be cut about 3/16 or 3/8 inch from the casting. The remaining stub is then removed

 

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by grinding or by the use of power chipping hammers.

The gates and risers of stainless steel castings cannot be removed by flame cutting. They must be removed by mechanical means, such as sawing, chipping, shearing, or an abrasive cutoff wheel, or by melting off with the electric arc from a welding machine. In melt-in off, care must be taken to leave a stub of 1/4 to 1/2 inch on the casting.

If castings show a tendency to crack during cutting, risers should be removed while the castings are at a temperature over 400°F. For risers larger than 6 inches in diameter, it is well to preheat to 700°F. or higher. The heat may be that remaining in the casting from the mold, or it may be obtained by heating in a furnace.

CAUSES AND CURES FOR COMMON DEFECTS IN STEEL CASTINGS

The casting defects described in Chapter 11, "Causes and Cures for Casting Defects," are generally applicable to steel castings. Defects that pertain particularly to steel castings are described here.

Metal Composition. The control of sulfur and phosphorus content is important in steel castings because an excess of either element harms strength and toughness of the castings.

Sulfur should be kept below the upper limit stated in the specifications (0.06 percent). At this low level, manganese is able to combine with the sulfur and form manganese sulfide, which is not harmful to steel castings. An excess of sulfur will result in "hot shortness," which is brittleness at high temperatures. High sulfur, free machining, and screw stock should not be used in the charge. All sheared ship plate from GSSO will be accompanied by certified analyses. These analyses should be checked for sulfur content. An excess of phosphorus produces a similar effect, but the brittleness occurs at room temperature and is known as "cold shortness."

Pouring. Defects caused by pouring steel castings are generally the same as for other metals. Reference should be made to the section, "Pouring," Chapter 11, "Causes and Cures for Common Casting Defects."

Skimming is particularly important in the pouring of steel castings. Small amounts of slag that get into the mold will be found as isolated inclusions that form weak spots in the casting (nonmetallic inclusions), or as stringers of

  solidified slag that completely cross a section and make the casting useless. Therefore, extreme care should be taken to remove all slag from the metal surface before it is poured.

Melting practice. Excessive superheating of steel can be a major contributing factor to casting defects. Excessive superheating causes severe oxidation of the melt and the formation of iron oxide. Iron oxide entering the mold can react with carbon to produce gases that cause blows or porosity. Iron oxide can also combine with the molding sand and produce slag inclusions or cause a hard glassy surface of slag to adhere to the casting.

Miscellaneous. Steel castings are very susceptible to hot tearing (as has been mentioned in other parts of this chapter). The direct cause of hot tearing must be determined before corrective measures can be taken. Refer to the "Summary," Chapter 11, "Causes and Cures for Common Casting Defects," for the various causes.

It is important to have the proper degree of collapsibility in cores and molding sand to prevent hot tears. Large cores should be hollowed out before use to provide easier collapsibility.

The design of the casting should not be overlooked as a cause of hot tears. A small change in design can often prevent hot tearing and save a lot of extra work.

WELDING AND BRAZING

Repairs to steel casting by welding and brazing are not difficult but should be made only by qualified personnel. When repairs by welding are required, refer to the "General Specifications for Ships of the United States Navy," Section S9-1, "Welding," for general guidance.

SUMMARY

The production of good castings from steel is more difficult than from other cast metals because of the high temperatures involved. Melting control must be more rigid to prevent an oxidized heat or severe slagging of the furnace lining and its ruin. Sand properties must be controlled much closer than for other metals. In general, for repair ship work, the molder must be more alert to the possibility of defects and take immediate corrective measures while he is going through the various procedures for making a steel casting.

452605 0-58-16

 

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Figure 252. Iron-carbon diagram.
Figure 252. Iron-carbon diagram.

Figure 253. Tapered chill.
Figure 253. Tapered chill.

 

Figure 254. Steel rods used for determining
the pouring temperature of steel.
Figure 254. Steel rods used for determining the pouring temperature of steel.

(A) Is a sheared end of the rod before immersion in the molten steel.
(B) Is the rounded end of the rod, showing how the molten steel melts the end of the rod at the correct pouring temperature.
 

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Chapter XIX
COPPER
 
Copper castings are not included in the Navy Specifications. Many times, however, the need arises for castings of this type. The following information is given as a guide for the production of these castings.

SELECTION OF METAL

Copper castings may be required where unusually high electrical or heat conductivity is needed. The addition of alloying elements to copper reduces its electrical conductivity. The effect of small amounts of various elements on the electrical conductivity of copper is illustrated in figure 255. The conductivities are compared to a specially prepared standard whose conductivity is taken as 100 percent. Notice the drastic reduction in conductivity with very small additions of phosphorus, silicon, or iron. Even brass and bronze castings have a lower electrical conductivity than pure copper.

Castings that must have an electrical conductivity greater than 80 percent must be made from electrolytic copper. Where strength is required and electrical conductivity may be as low as 50 percent, castings can be made from beryllium-nickel-copper (0.5 beryllium, 2.0 nickel, balance, copper) or chromium-silicon-copper alloys (0.08 silicon, 0.80 chromium, balance, copper). Heat treatment of these alloys is required to obtain their best properties.

HOW COPPER SOLIDIFIES

Copper solidifies by the nucleation and growth of crystals as described in Chapter 1, "How Metals Solidify." High-conductivity copper is a pure metal so far as foundry metals are concerned and solidifies at a single temperature instead of over a range of temperature as for most metals. Low-alloy copper has a very narrow solidification range. Because of their narrow solidification range, high-conductivity copper solidifies with strong piping characteristics and requires large risers.

PATTERNS

Pattern practice for copper castings is the same as for copper-base alloys. Refer to Chapter 14, "Copper-Base Alloys." Deep pockets should be avoided because it is hard to make such areas free of defects.

 

MOLDING AND COREMAKING

The molding and coremaking practices for copper castings are generally the same as for copper-base alloys.

SAND MIXES

Molding sands that are used for copper-base castings can be used for copper castings. However, the use of organic additives in molding sands for copper castings should be kept as low as possible. Organic additives (seacoal, wood, flour, etc.) are likely to generate large amounts of gas, which the copper absorbs readily.

PROCEDURES

Coremaking procedures for copper castings are in general the same as those described in Chapter 6, "Making Cores." Cores should have a high permeability and very good collapsibility.

Oil or cereal binders are usually used. Clay up to 15 percent may also be used as a binder. Regardless of which type of binder is used, it should be kept low. Use only enough binder to hold the core together. Physical strength of the cores is obtained by using core arbors and reinforcing wires. Strong, hard cores should not be used.

Molding procedures are also the same as for copper-base alloy castings. To reduce the possibility of porosity in copper castings, the molds should be skin dried or completely dried. Dry-sand mold s are preferred for large castings.

Washes are not used on molds or cores for high-conductivity-copper castings. If a better casting surface is desired, the mold can be dusted with finely powdered graphite. Excess graphite should be carefully removed.

GATING

Top-pouring systems are preferred to establish proper temperature gradients and to obtain good directional solidification. If size or design do not permit top gating and pouring of castings, the best gating system obtainable should be used. In all cases, the gating system must establish proper temperature gradients for strong directional solidification. In this respect, the gating of copper castings is similar to that for steel.

 

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RISERING

Because of the short solidification range of high-conductivity copper, it is often difficult to design risers that will feed the casting correctly. The risers are larger than those used for copper-base alloys. Each casting presents its own problem, but it is suggested that risers comparable in size to those for steel castings be used as a starting point.

CHILLS

Because strong directional solidification is necessary for producing good copper castings, chills should be used to help accomplish it. Chill practice, as described in Chapter 14, "Copper-Base Alloys," can be used as a guide. In this respect, too, copper castings are similar to steel in behavior.

VENTING

Copper in the molten stage absorbs gases readily. Molds should be thoroughly vented to provide easy escape for air or gases that may be generated in the mold.

MELTING

The melting procedure for copper is similar to that for copper-base alloys. The same routine can be followed but much closer control of the heat is necessary.

TYPE OF FURNACE

All of the melting units aboard repair ships can be used for melting copper. The oil-fired crucible furnace is the poorest melting unit because of the difficulty of maintaining close control over the furnace atmosphere and because it is slow.

PROCEDURE

The charge should consist of electrolytic copper, copper wire, bus bar stock, and gates and risers from other high-conductivity castings.

HIGH-CONDUCTIVITY

Gates and risers may be used up to 50 percent of the charge. SCRAP METAL SHOULD NEVER BE USED IN THE CHARGE FOR HIGH-CONDUCTIVITY-COPPER CASTINGS. If the alloyed compositions are to be melted, the alloy additions are made with high-purity master alloys. All melting should be done under slightly oxidizing conditions. Melting should be as fast as possible so that little gas is picked up.

  Where the heat is to be poured from the melting crucible (such as those used in the oil fired crucible furnace) 1/3 to 2/3 of the final weight is charged into the crucible. This may be electrolytic copper or returns. It is melted down and black copper oxide (1/2 pound per 100 pounds of melt) added and stirred into the melt. The balance of the charge is then melted, skimmed, deoxidized, and poured.

The procedure for electric melting furnaces is the same, except for the copper oxide addition. This addition is made in the bottom of the pouring ladle before filling it. The ladle is skimmed, the melt deoxidized in the ladle, and the molten metal poured.

TEMPERATURE CONTROL

Temperature control is important when melting high-conductivity copper because copper absorbs gas readily. The amount of gas dissolved increases very rapidly with increasing temperature and makes the problem of gas removal much more difficult. Control should be maintained with a properly calibrated immersion pyrometer. The metal should be melted fast with no overheating.

DEOXIDATION

Deoxidation is done in the melting crucible in the case of oil-fired crucible furnaces, or in the pouring ladle for the other types of furnaces. Deoxidation is usually done with 2 ounces of 15 percent phos-copper per 100 pounds of melt. For the alloyed compositions, deoxidation can be done by adding 1 percent of 2 percent lithium copper. If possible, this should be followed by bubbling dry nitrogen gas through the melt for approximately three minutes. This can be done with a stainless steel tube that is perforated in the immersion end of the tube.

As a check on a heat to determine whether it is properly deoxidized, the following test may be used. Before pouring a casting, a small sample approximately 2 inches high and 2 inches in diameter should be poured in a dry core -sand mold. If the heat is properly deoxidized, the sample will show a strong pipe as shown in figure 256. If it solidifies with a flat surface, or with a slight pipe as illustrated in figure 257, it requires further deoxidation. A puffed-up surface on the sample indicates a badly gassed heat, as shown in figure 258. Notice the gas holes in figure 257.

POURING

Pouring of copper castings should be done as quickly as possible to prevent cooling of the melt and occurrence of defects such as laps and

 

261
 
cold shuts. Pouring temperatures range from 2,100°F. to 2,160°F. The castings should preferably be poured on the high side of this range. Pour fast and with the lip of the ladle close to the sprue. The most common defect that is encountered from pouring practice is the cold shut, caused by too low a pouring temperature. As mentioned previously, copper castings should be poured fairly hot, but the metal should not be overheated so that it absorbs gas.

CLEANING

Sand adherence is not a problem with copper castings. Sand can be easily removed by wire brushing and sandblasting. Gates and risers must be removed by cutting, usually by sawing. The castings should be permitted to cool in the mold to room temperature when high conductivity is required.

CAUSES AND CURES FOR COMMON CASTING DEFECTS IN COPPER

The defects described in Chapter 11, "Causes and Cures for Common Casting Defects," apply generally to copper castings. There are some that occur more frequently in high-conductivity-copper castings and will be discussed here.

  METAL COMPOSITION

The principal defect caused by improper metal composition would not be called a casting defect, but can render a copper casting unfit for its intended service. This defect is the reduction of electrical conductivity. The use of phosphorus as a deoxidizer is particularly important. Phosphorus that dissolves in copper because of large additions for deoxidation causes a big reduction in electrical conductivity. Phosphorus is the worst offender in this respect (as shown in figure 255), but is still commonly used as a deoxidizer (as phos-copper).

MELTING PRACTICE

Gassy melts caused by poor melting practice produce badly gassed copper castings. Close control over the furnace atmosphere (by maintaining slightly oxidizing conditions) and proper deoxidation measures are the only way to avoid gassy melts and defective castings.

SUMMARY

The information given in this chapter is given as a starting point for personnel who may be required to make copper castings. The production of castings of this type is not in great demand. Copper castings are not strong and, because they are difficult to cast, should be used only when specifically needed for their high electrical conductivity.

 

262
 

Figure 255. The effect of various elements on the electrical conductivity of copper.
Figure 255. The effect of various elements on the electrical conductivity of copper.

Figure 256. Properly deoxidized copper sample.
Figure 256. Properly deoxidized copper sample.

 

Figure 257. Partially deoxidized copper sample.
Figure 257. Partially deoxidized copper sample.

Figure 258. Gassy copper sample.
Figure 258. Gassy copper sample.

 

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Chapter XX
BABBITTING WITH TIN-BASE BEARING METAL
 

Bearing metals must have certain special properties: (l) the ability to retain an oil film, (2) resistance to scoring and galling, (3) the ability to imbed foreign particles in themselves, and (4) the ability to deform within very slight limits.

The ability of a bearing material to retain an oil film on its surface is necessary for proper lubrication of the moving part in the assembly. Failure of the bearing material to retain an oil film or lack of its ability to re-establish the oil film when it is broken causes premature breakdown of the bearing.

Because shafts and bearings are not perfectly smooth, there are instances when there is metal-to-metal contact. Foreign particles in the lubricant cause a momentary breakdown of the oil film and permit metal-to-metal contact. Also, many bearings start under a load that causes a momentary metal-to-metal contact. During momentary periods of metal-to-metal contact, severe seizure or galling can occur between the surfaces in contact. It is during this critical period that resistance to seizure and galling is necessary.

Foreign particles (such as dirt or metal filings) are always present in a lubrication system. When these particles reach the bearing, it must have the ability to embed the particles in the bearing material. Lack of ability to do this can lead to serious damage or failure of the bearing assembly.

Perfect alignment of a bearing and shaft is impossible for normal equipment. The ability to deform is necessary in a bearing material to permit it to conform with slight misalignments in bearing and shaft assemblies. This property permits bearings to be "worked-in" to obtain good operation of the shaft and bearing.

SELECTION OF ALLOYS

There are several types of castable bearing materials that are in use for machinery applications. They are: (l) tin-base babbitts, (2) lead-base babbitts, (3) cadmium-base alloys, and (4) copper -lead alloys. The tin-base babbitts are the only ones covered in the Specifications and will be discussed here.

Tin-base babbitts contain 80 to 90 percent tin and are alloyed with copper and antimony. The alloying elements are added to increase the hardness of the babbitt. The bearing properties

  of tin-base babbitts are excellent. Their strength decreases as they get hotter.

PREPARATION OF BEARINGS

The proper cleaning of the shell cannot be stressed too strongly in bearing preparation. No matter how well the other operations may be conducted, an improperly cleaned shell will result in bearing failure.

REMOVAL OF OLD BABBITT

In the preparation of the bearing shell for rebabbitting, all old babbitt should be machined out of the bearing. Dirt and other foreign matter can be removed from the shell by warming it. Be careful to avoid overheating or the subsequent tinning will be difficult. Machining of the shell should be the last step in the mechanical cleaning of the shell. The finish cut should leave a fine machine-tool finish and the base metal of the shell should be completely exposed. No old babbit should be left on the shell.

CLEANING

Oil or grease should be removed by first washing in a degreasing solvent. The use of a vapor degreaser is recommended if available. An alternative method is to completely immerse the shell in a boiling alkaline-cleaner solution (4 to 6 ounces of Oakite in one gallon of water) or a lye solution (6 ounces of lye to one gallon water) for 20 minutes. The shell then should be washed in boiling water. Any oxide film deposited during the degreasing and washing operations should be removed by pickling the shell in a 25 percent hydrochloric acid solution (l part HCl to 3 parts water). The shell should then be washed again in boiling water. During the cleaning operation, the shell should be handled with a pair of clean, grease-free tongs. Holes through the shell should be plugged with dry asbestos or magnesia. Surfaces which are not to be tinned should be coated with fire clay wash.

FLUXING

After cleaning thoroughly and pickling, the surface to be babbitted should be fluxed either by dipping or swabbing. A suitable flux can be prepared by mixing equal parts by weight of zinc chloride and water. A flux may also be made by mixing 11 parts of commercial grades of zinc chloride with 1 part of granulated ammonium chloride (sal ammoniac). Boiling water should

 

264
 
be stirred into this mixture until a hydrometer reading of 52° Baume is reached.

It is important that freshly prepared flux be used. Oil or weak flux will not properly clean the surface.

TINNING

Procedures. Bronze and steel shells should be coated with a thin layer of tin before babbitting. Tin will aid in producing a strong bond between the babbitt and shell. After the shell has been fluxed, it should be dipped in a bath of pure tin maintained at a temperature of 570° to 580°F. The bearing shell is dipped into the bath and held there for 55 seconds. The shell is then removed and inspected for flaws. Those areas which have not been adequately coated should be scraped, refluxed, and retinned. As soon as an adequate coat of solder is assured, the bearing shell should be set in the jig and mandrel for immediate pouring.

Jig and Mandrel Assembly. Figure 259 shows a simple jig for use in babbitting bearings. Before tinning, the two halves of the bearing are wired together with l/8 to l/4 inch-thick spacer pieces of metal wrapped with asbestos paper between them. A center core or mandrel of steel of the correct diameter is bolted to the base plate. Steel tubing or pipe thoroughly cleaned is satisfactory. The mandrel should be 3/8 to 3/4 inch smaller in diameter than the diameter of the finished bearing to allow for peening and subsequent machining. A cross-bar is bolted to the top of the mandrel after the bearing is set in place and wooden wedges are driven between the crossbar and the pouring lip to hold the bearing and lip in place during pouring. While the bearing shell is being cleaned, fluxed, and tinned, the mandrel must also be prepared for pouring.

PREHEATING

The mandrel should be preheated with a torch to at least 600°F. This reduces the chilling effect of the mandrel, permits solidification to start at the bearing shell and progress toward the mandrel, and prevents the babbitt from pulling away from the bearing shell during solidification.

Care must be taken also that no moisture remains on the bearing shell. Moisture will cause the hot babbitt to spatter dangerously and will cause porosity in the liner.

As soon as the mandrel has been thoroughly preheated and the bearing tinned, the bearing is set in the jig and centered. The pouring lip is set in place and the crossbar bolted in place and wedges driven in. The jig assembly should

  be carefully checked for leaks and made tight with calking clay or putty to prevent metal loss during pouring.

MELTING

Melting of any of the tin-base antifriction metals can be accomplished in a pressed steel, cast steel, or cast iron pot.

EQUIPMENT

Melting is done by means of an ordinary oil or gas torch or by a burner specially designed for the purpose. A muffle-type furnace may also be used for melting these metals.

PROCEDURE

A sufficient quantity of the proper grade of ingot should be charged in the pot and the heat applied slowly so that the melting does not take place too fast. As soon as the babbitt begins to melt, the surface may be covered with powdered charcoal. This will protect the metal from the air and retard the formation of oxides and accumulation of dross. Care must be taken to remove the charcoal before pouring to prevent it from becoming trapped in the babbitt during pouring.

When the bars or ingots are all melted, the bath should be stirred with a motion from bottom to top (not circular). No splashing should be permitted.

TEMPERATURE CONTROL

The quality of the babbitted bearing depends mainly upon the temperature at which the metal is poured. Too high a pouring temperature will increase the amount of shrinkage during solidification and this will create more severe shrinkage stresses. A high pouring temperature will heat up the bearing and mandrel and tend to keep metal in the "mushy" state for too long a time. The shrinkage stresses may produce cracks which will cause bearing failure during service. The temperature needed at the end of melting will depend on the distance from the melting position to the point of pouring. Generally, 675°F. to 690°F. is the best pouring temperature for Grade 2. An immersion-type pyrometer should be used in all cases to control the temperature of the bath and of pouring.

POURING

The babbitt should be poured as soon as possible after the assembly is ready. Good bonding of the babbitt to the shell will not be obtained if the tin bond has become solid. Pouring

 

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must be accomplished while the tinned surface on the shell is still hot.

LADLES

The size of the ladle and quantity of metal melted should be governed by the size of the bearing to be babbitted. More metal should always be melted than is actually required because the excess can be pigged and remelted. The ladle or ladles should always be large enough to hold more metal than required for the pour. Twice the amount of babbitt required should be melted to prevent shilling of the metal in the ladle. If an insufficient amount of metal is poured into the cavity, subsequent addition of metal will produce a defective bearing because the second metal will not bond with the originally poured metal that has solidified.

When a single ladle of sufficient size is not available, two ladles may be used if the contents of both are poured into the bearing at the same time. If there is insufficient room for both ladles over the pouring jig, the contents of one ladle may be poured directly into the bearing, while the metal from the second ladle is being poured into the first.

SKIMMING

A bottom-pour or self -skimming type of ladle is preferred because it prevents dross, dirt, oxides, or other impurities from entering the mold. If such a ladle is not available, a lip-pour ladle may be used. When using a lip-pour ladle, careful attention must be given to skimming of the surface of the molten metal to produce a bright surface free from oxides. Any scum which forms on the top of the molten metal must be pushed back from the lip with a wood or metal rod.

The metal should be stirred thoroughly and poured slowly and steadily in a thin stream. A fast heavy stream fills the opening too rapidly to allow the necessary escape of air and causes it to be trapped as bubbles or seams in the lining. A slow steady stream will prevent this.

Solidification shrinkage will take place in antifriction tin-base babbitts as in other casting metals. During pouring, the chilling action of the steel mandrel and the bearing shell will usually cause solidification to start before the mold is filled. Liquid and solidification shrinkage will take place in the first metal to enter the mold as soon as the freezing temperature is reached. Because the babbitt is generally poured slowly, automatic feeding will take place (the early shrinkage of the solidifying metal is compensated for by metal added during pouring). The amount of feeding is dependent upon the temperature of the metal, rate of pouring, and the thickness of sections involved.

  PUDDLING

Pouring should be continued until the bearing cavity is filled to the top. The elimination of gas and air from the bearing is of vital importance. This is usually accomplished by thorough puddling of the metal during pouring. Generally, a flat steel rod 3/8 inch by 1/16 inch in cross section which has been previously preheated by immersing the rod in the molten babbitt is used. As soon as the first metal is poured, the puddling or churning should be started. This action, which permits efficient feeding, should be continued throughout pouring. Molten babbitt should be added as contraction occur s until the mold has been completely filled. Immediately after pouring is completed, cooling of the bearing should be started with a water spray. A circular spray jig made from a piece of pipe is ideal for this purpose.

POST POURING OPERATION

When the babbitt has solidified, it will be seen that the sides of the shell have been drawn together by the contraction of the lining. The shell may be returned to its original dimensions by peening the inner surface of the lining. The spacers are removed from between the shells and the halves separated by sawing through the babbitt on each side.

FINISHING OF BEARING

The bearings are then set up for machining to the correct dimensions. After machining, the bearing should be carefully fitted to the shaft whenever possible. This is done by coating the shaft with blue chalk and setting the bearing in place. High spots as indicated by the adherence of chalk to the babbitt are scraped off and the operation repeated until a close fit is obtained with maximum contact with the shaft.

BEARING FAILURES

Checked, cracked, or crumbling bearings were probably improperly bonded or poured at too high a temperature, thus causing high contraction stresses to occur during cooling. The proper relation between the temperatures of the metal, mandrel, and bearing shell is an important factor in producing sound babbitted bearings.

The presence of air pockets in the lining or between lining and shell can quickly produce bearing failure. Oil will collect in these pockets and prevent uniform transfer of heat to the shell. A hot spot can develop and progress until the bearing metal is hot enough to melt.

 

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A properly cast babbitt liner with a homogeneous structure will give good service. During the running in of a bearing, the load and vibration will cause the metal to pack, closing any minute voids and making the metal more dense. This close structure will give the maximum bearing life.

An outline of the preceding procedures is also contained in paragraph 43-36, Chapter 43 of the Bureau of Ships Manual. The "United States Naval Engineering Experiment Station Report C-3230-B," dated 6 May 1949, recommends the use of a wood mandrel and wood

  riser. Heating of the mandrel and puddling are not required with this method.

SUMMARY

The production of good bonds in tin-base babbitts depends on: (l) proper cleaning of the shell, (2) correct tinning temperature, (3) proper time of immersion for the tinning operation, (4) correct pouring temperature, and (5) rapid cooling of the bearing when pouring is finished. Strict control of these steps is necessary for the production of good tin-base babbitt bearings.

 

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Figure 259. Jig for babbitting bearings.
Figure 259. Jig for babbitting bearings.

 

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Chapter XXI
PROCESS CONTROL
 
The ability to make good castings depends on experience. To make the most of experience, it is necessary to keep written records of what has been done. A manual such as this one could not have been written unless many people had made many castings and kept records of what they did. Good records contain information that enable a molder to produce a better casting without repeatedly going through the trial-and-error routine.

Some persons may believe that the keeping of records and their use in repair ship work is a waste of time and not worthwhile. Inspection of repair ship foundries has shown that the foundries with the best reputation for producing good castings are those that keep foundry records and refer to them continually when making new castings.

SAND

Sand records should include three types of information: (l) the properties of sand as it is received by the repair ship foundry, (2)day-today test results on the properties of sand mixtures prepared for particular alloys (gray iron, copper base, etc.), and (3) the properties of sand mixtures used successfully for making a particular casting. Records of the properties of sand received from a source of supply indicate the uniformity of the sand supplied. Many times, the sand-grain distribution or the clay content of a sand will change over a period of time because of some change in the supplier's source. A change in these properties can affect the castings made in that sand. The only way to check this as a possible source of trouble is to have records of the properties of each lot of sand received.

Day-to-day testing and recording of sand properties provides the molder with an up-to-date record of his molding sand. Any change in properties will be shown by routine tests. For example, a buildup of clay content or an increase in fines will result in a decrease in permeability and gas defects can be expected if corrective measures are not taken.

A record of sand properties applying to a particular type of casting provides information for repeated production of the same casting or similar castings. Such information can save a lot of time, which may be extremely valuable in an emergency.

 

MOLDING

Records should be kept of successful gating and risering arrangements for various castings. Photographs or simple snap shots are very helpful for showing gating and risering of loose patterns. Any information pertaining to the method of ramming the mold (whether it was rammed hard or soft), any additives used, venting, size of flask, and depth of flask are items of information that should be included in records of this kind. They are all helpful in determining the causes of various defects. It is a bad practice to depend on memory when correcting casting defects. Some defects may be very apparent, while others may be caused by factors that are not self-evident to the molder.

Gating and risering arrangements are particularly important for future work that may be done. By far the best method of recording a gating and risering system is to make a simple sketch or photograph with pertinent notes and dimensions. Very often, when a new casting is to be made, the gating and risering arrangement will be determined by a guess. If the guess is good, a good casting is the result; bad guess-scrap casting. The records might not show a casting identical in design or size to the one under consideration but good records will often give information that will take the guesswork out of the gating and risering of the new casting.

MELTING

The purpose of melting records is to supply information that permits day-to-day control when melting various metals. Records should contain such information as the type of alloy melted, size of the heat, how it was charged (all or in parts), when alloy additions were made, time to melt-down, holding time, and in the case of electrical melting equipment, the power input during various periods of the melting cycle.

Any control tests that are available for determining melt characteristics should be used as a routine test. Results of these tests should be incorporated as part of the melting record. If a melter is to make effective use of a control test, he must use it repeatedly to become familiar with it, and must have records to show him what the test means in terms of metal quality.

The chill test for gray cast iron is discussed in Chapter 17, "Cast Iron." The results of routine chill tests can be compared with casting

 

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defects that may be caused by poor melting practice, or with machining characteristics. After some experience is obtained in its use, a heat that would produce an iron hard to machine can be corrected before being poured into the mold.

Heats of many metals can also be checked by means of a fracture test. A trial heat can be melted under different conditions varying from strongly oxidizing to strongly reducing. A test sample can be poured when the melt has become stabilized under each condition. the test samples are then fractured and the fractured surface examined. This group of samples will then be a set of comparison standards that will be useful for showing the particular conditions under which other heats of the same alloy have been melted. If clear lacquer is applied to the fractured surface, the fractured sample can be used for a long time. Another procedure which is less satisfactory is to set up a record that describes the character of the various types of fractures. This should include the comparative grain size, color, and whether the fracture was light and solid or whether it had an open structure.

 

INSPECTION AND TEST

For inspection and test requirements refer to the "General Specifications for Ships of the United States Navy," Section S-l-0, "Castings." Inspection and tests required therein shall be performed within the capabilities of the inspection and test equipment available. Refer to the specification numbers in the material specifications. These cover detailed inspection requirements.

SUMMARY

Good records are not only a means of control for producing sand of uniform properties and melts of good quality, they are also the best source of information for inexperienced personnel. It is true that a molder can learn by experience, that is, by making molds, but he can learn still more in less time by profiting from someone else's work. This information can be obtained only from properly kept records. Records should also contain methods that resulted in poor results so that such errors may be avoided in future work.

 

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FOUNDRY TERMINOLOGY
 

A.

Abrasion. Wearing away of material at its surface because of the cutting action of solids.

Abrasives. Materials for grinding, polishing, cleaning, etc., bonded to form wheels, bricks, and files, or applied to paper and cloth by means of glue. Natural abrasives include emery, corundum, garnet, sand, etc. Main manufactured abrasives are silicon carbide and aluminum oxide. Metallic shot and grit also are used as abrasives in cleaning castings.

Acetylene. A colorless, tasteless gas composed of carbon and hydrogen and used for welding and cutting operations in combination with oxygen. It is really generated by action of water on calcium carbide.

Acid. With reference to refractories, those materials high in silica or in minerals chemically similar to silica and low in bases such as lime or magnesia.

Acid lining. In a melting furnace, the lining composed of materials that have an acid reaction in the melting process - either sand, siliceous rock, or silica bricks.

Acid brittleness. Brittleness induced in steel when pickling (cleaning) in dilute acid to remove scale, or during electroplating; commonly attributed to absorption of hydrogen. Also commonly called hydrogen brittleness.

Acid refractories. Ceramic materials of high melting point consisting largely of silica.

Acid steel. Steel melted in a furnace that has an acid bottom and lining, under a slag that is mainly siliceous.

Aerator. A machine for fluffing or decreasing density of sand and for cooling sand by mixing with air.

Age hardening. An aging process that increases hardness and strength and ordinarily decreases ductility, usually following rapid cooling or cold working. See AGING.

Agglomeration (flocculation). Gathering together of small particles into larger particles in a liquid medium; usually used in connection with fineness test of clay or foundry sand.

Aging. In an alloy, a change in properties that generally occurs slowly at atmospheric

  temperature and more rapidly at higher temperatures. See AGE HARDENING, PRECIPITATION HARDENING.

Air compressor. Machine to buildup air pressure to operate pneumatic tools and other equipment.

Air control equipment. Device for regulating volume, pressure, or weight of air.

Air drying. Surface drying of cores in open air before baking in an oven; also applies to molds which air dry when left open, thus causing crumbling or crushing when metal is poured; a core or mold dried in air without application of heat.

Air-dried strength. Compressive, shear, tensile, or transverse strength of a sand mixture after being air dried at room temperature.

Air furnace. Reverberatory-type furnace in which metal is melted by the flame from fuel burning at one end of the hearth, passing over the bath toward the stack at the other end of the hearth; heat is also reflected from the roof and side walls.

Air hammer. Chipping tool operated by corn-pressed air.

Air hoist. Lifting device operated by compressed air.

Air hole. A cavity in a casting, caused by air or gas trapped in the metal during solidification. More commonly called "gas hole."

Alkali metals. Metals in Group IA of the periodic system, including lithium, sodium, potassium, rubidium, cesium, and francium.

Alkaline earth metals. Metals in Group IIA of the periodic system, including calcium, strontium, barium, and radium.

Allotropy. Occurrence of an element in two or more forms. For example, carbon occurs in nature as the hard crystalline diamond, soft flaky crystalline graphite, and amorphous coal (lamp black).

Alloy. A substance having metallic properties and composed of two or more chemical elements, of which at least one is a metal.

Alloying elements. Chemical elements constituting an alloy; in steels, usually limited to metallic elements added to modify the

 

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A.-Continued

properties of the steel; chromium, nickel, molybdenum are examples.

Alpha iron. The form of iron that is stable below 1670°F. See TRANSFORMATION TEMPERATURE.

Alumel. A nickel-base alloy containing about 2.5 percent Mn, 2 percent Al, and 1 percent Si, used chiefly as a part of pyrometric thermocouples.

Anchor. Appliance for holding cores in place in molds.

Annealing. A process involving heating and cooling, usually applied to cause softening. The term also applies to treatments intended to alter mechanical or physical properties, produce a definite microstructure, or remove gases. Any process of annealing will usually reduce stresses, but if the treatment is applied for the sole purpose of such relief, it should be designated as stress relieving.

Annealing pots. Iron containers in which castings are packed for protection against the furnace atmosphere during annealing.

Arbors. Metal shapes embedded in and used to support cores.

Arc welding. Welding accomplished by using an electric arc that may be formed between a metal or carbon electrode and the metal being welded; between two separate electrodes, as in atomic hydrogen welding; or between the two separate pieces being welded as in flash welding.

Arrestor, dust. Equipment for removing dust from air.

Artificial aging. An aging treatment above room temperature. See PRECIPITATION HEAT TREATMENT.

Artificial sand. Product resulting from crushing a rock to the size of sand grains.

Asbestos. Hydrated magnesium silicate often used for insulation of risers, thus keeping metal molten for feeding purposes.

Austenite. Solid solution in which gamma iron is the solvent, the non-magnetic form of iron found in 18-8 stainless steels.

Austenitizing. Process of forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing).

 

B.

Back draft. A reverse taper which prevents removal of a pattern from the mold.

Backing board. A second bottom board on which molds are opened.

Backing plate. See BACKING BOARD.

Backing sand. Reconditioned sand used for ramming main part of mold or loose molding sand used to support green cores while baking.

Bail. Hoop or connection between the crane hook and ladle.

Baked core. A sand core which has been heated.

Baked permeability. The property of a molded mass of sand which allows gases to pass through it after the sand mass is baked above 230°F. and cooled to room temperature.

Baked strength. The compressive, shear, tensile, or transverse strength of a sand mixture when baked at a temperature above 230°F. and then cooled to room temperature.

Balanced core. One with the core-print portion so shaped and dimensioned that it will overbalance that part of the core extending into the mold cavity.

Band, inside. A steel frame placed inside a removable flask to reinforce the sand.

Band, snap flask. See JACKET, MOLD.

Band saw. A saw in the form of an endless steel belt which runs over a pulley.

Bars. Ribs of metal or wood placed across the cope portion of a flask. Sometimes called "cleats."

Base permeability. That physical property which permits gas to pass through packed dry sand grains containing no clay or other bonding substance.

Basic. A chemical term which refers to a material which gives an alkaline reaction. In refractories, the chemical opposite of acid. See ACID.

Basic lining. In a melting furnace, the inner lining composed of materials that have a basic reaction in the melting process. Crushed b u r n e d dolomite, magnesite, magnesite bricks, and basic slag are examples.

 

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B. Continued

Basic pig iron. A special high-phosphorus (2.0 to 2.5 percent), low-sulfur (0.08 percent), low-silicon (0.80 percent) pig iron made for the basic open hearth process for steelmaking.

Basic refractory materials. Bodies containing basic oxides which react with acids to form salts. Magnesia and lime are examples.

Basic steel. Steel melted in a furnace that has a basic bottom and lining, and under a slag that is predominantly basic.

Bath. Molten metal contained in hearth of furnace during melting process.

Battens. Wooden bars or strips fastened to patterns for rigidity or to prevent distortion during ramming of the mold.

Baume. A measure of specific gravity of liquids and solutions reduced to a simple scale of numbers.

Bauxite. An ore of aluminum consisting of moderately pure hydrated alumina, Al2O3.2H2O.

Bayberry wax. Wax made from bayberries, used for coating patterns.

Beam and sling. Tackle used in conjunction with a crane for turning over the cope or drag of a mold prior to assembly.

Bedding a core. Resting an irregular-shaped core on a bed of sand for drying.

Bed-in. Method whereby drag may be rammed in the pit or flask without necessity of rolling over; process used for production of heavy castings.

Bellows. A bag like hand-operated air blowing device for removing loose sand or dirt from molds or parting sand from patterns.

Bench molder. A craftsman who makes molds for smaller type castings, working at the molder's bench only.

Bentonite. A colloidal clay derived from volcanic ash and employed as a binder in connection with synthetic and silica sands, or added to ordinary natural (clay-bonded) sands where extra dry strength is required; found in South Dakota and Wyoming, also in Africa and India. (Western bentonites are sodium bentonites; southern bentonites are calcium bentonites. Their properties are slightly different.)*


  Binary alloy. An alloy containing two principal elements.

Binder. Material to hold sand grains together in molds or cores, such as cereal, pitch, resin, oil, sulfite by-product, etc.

Black lead. A form of graphite used for coating green sand molds and cores, applied as a water suspension to skin-dried molds (in some cases brushed on dry).

Black wash. Graphite applied as a water suspension to mold and core; it is customary to add a bonding agent such as bentonite, fire-clay, dextrin, molasses, etc.

Blacking. A thin facing of carbonaceous materials, such as graphite or powdered charcoal, used to finish mold surfaces and protect the sand from the hot metal.

Blacking hole s. Irregular - shaped surface cavities containing carbonaceous matter, sometimes found in defective castings.

Blacking scab. A casting defect formed by blacking flaking off because of sand expansion and being retained in or on the surface of the metal.

Blast cleaning. Removal of sand or oxide scale from castings by the impact of sand, metal shot, or grit projected by means of air, water, or centrifugal pressure. See BLASTING.

Blasting. A process for cleaning or finishing metal objects by use of air blast that blows abrasive particles against the surfaces of the work pieces. Small, irregular particles of steel are used as the abrasive in grit blasting, sand in sand blasting, and steel balls in shot blasting. See BLAST CLEANING.

Bleeder. A defect wherein a casting lacks completeness because of molten metal draining or leaking out of some part of the mold cavity after pouring has stopped.

Bleeding. See SLUSH CASTING.

Blended molding sands. Mixtures of molding sands made to produce desirable sand properties.

Blind riser. A riser which does not break through the top of the cope, and is entirely surrounded by sand; often combined with whirl gates, together forming an efficient method of gating and feeding a casting.

*Grim, Ralph E.; Clay Mineralogy; McGraw-Hill Book Company, Inc.; New York (1953).

452605 0 - 58 - 17

 

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B. Continued

Blister. A shallow blow with a thin film of iron over it appearing on the surface of a casting.

Blow. Forcing of air into the molten metal due to insufficient venting.

Blower. Machine for supplying air under pressure to the melting unit.

Blow gun. Valve and nozzle attached to a corn-pressed air line to blow loose sand or dirt from a mold or pattern; used also to apply wet blacking.

Blowhole. Irregular - shaped cavities with smooth walls produced in a casting when gas trapped while the mold is being filled or evolved during solidification of the metal fails to escape and is held in pockets.

Blows. Rounded cavities, that may be spherical, flattened, or elongated, in a casting caused by the generation or accumulation of gas or entrapped air.

Bond, bonding substance, or bonding agent. Any material other than water which, when added to foundry sands, imparts strength to them.

Bond strength. Property of a foundry sand by virtue of which it offers resistance to deformation and holds together.

Bonding clay. Any clay suitable for use as a bonding material.

Boss. A projection on a casting that can be used for various purposes, such as drilling and tapping holes for bolts.

Bot. A cone-shaped lump of clay attached to the end of an iron or wooden "bot stick" used to close the taphole of a furnace.

Bot stick. An iron rod, with a loop or long wooden handle at one end and a small round disk at the other, to receive the clay for botting off when the ladle is sufficiently full.

Bottom board. A flat base of wood or metal for holding the flask in making sand molds.

Bottom running or pouring. Filling of a mold from the bottom by means of gates from the runner.

Box. See FLASK.

Brass. Copper-base metal with zinc as the major alloying element.

  Brazing. Joining metals by melting of nonferrous alloys that have melting points above 800°F. but lower than those of the metals being joined. This may be accomplished by means of a torch (torch brazing), in a furnace (furnace brazing), or by dipping in a molten flux bath (dip or flux brazing). The filler metal is ordinarily in rod form in torch brazing; whereas in furnace and dip brazing the work material is first assembled and the filler metal may then be applied as wire, washers, clips, bands, or may be integrally bonded.

Breeze. Coke or coal screenings.

Bridging. Local freezing across a mold before the metal solidifies. Also locking a part of the charge in the crucible above the molten metal while melting.

Brinell hardness. The hardness of a metal tested by measuring the diameter of the impression made by a ball of given diameter applied under a known load. Values are expressed in Brinell hardness numbers.

British thermal unit (B. t. u.). The quantity of heat required to raise the temperature of 1 lb of water 1°F.; a unit of heat measurement.

Bronze. Copper-base metals with tin as the major alloying element.

Buckle. An indentation in a casting resulting from expansion of the sand.

Built-up plate. A pattern plate with the cope pattern mounted on or attached to one side and the drag pattern on the other. See MATCHPLATE.

Bull ladle. A large ladle for carrying molten metal, has a shank and two handles, and may have a geared wheel for tilting.

Burned sand. Sand in which the binder has been destroyed by the heat of the metal.

Burning in. Rough surface of a casting due to metal penetrating into the sand.

Burnt. Term applied to a solid metal permanently damaged by having been heated to a temperature close to the melting point. Damage is caused by severe oxidation.

Burnt-on sand. A phrase developed through common usage and indicating metal penetration into sand resulting in a mixture of sand and metal adhering to the surface of the casting. Properly called metal penetration.

Butt rammer. The flat end of the molder's rammer.

 

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C.

Calcium carbide. A grayish-black, hard, crystalline substance made in the electric furnace by fusing lime and coke. Addition of water to calcium carbide forms acetylene and a residue of slaked lime.

Carbide. A compound of carbon with one metallic element. (If more than one metallic element is involved, the plural "carbides" is used.)

Carbonaceous. A material containing much car - bon. Examples are coal, coke, charcoal, and graphite.

Carbon equivalent. A relationship of the total carbon, silicon, and phosphorus content in a gray iron expressed by the formula
C.E. = T.C.% + (Si% + P%)/3

Carbonization. Coking or driving off the volatile matter from carbon-containing materials such as coal and wood. (Do not confuse this term with carburization.)

Carbon steel. Steel that owes its properties chiefly to the presence of carbon without substantial amounts of other alloying elements; also termed "ordinary steel," "straight carbon steel," and "plain carbon steel."

Casting (noun). Metal object cast to the required shape as distinct from one shaped by a mechanical process.

Casting (verb). Act of pouring molten metal into a mold.

Casting, open sand (noun). Casting poured into an uncovered mold.

Casting ladle. A crucible or iron vessel lined with refractory material for conveying molten metal from the furnace and pouring it into the mold.

Casting stress. Residual stresses resulting from the cooling of a casting.

Cast iron. Essentially an alloy of iron, carbon, and silicon in which the carbon is present in excess of the amount which can be retained in solid solution in austenite at the eutectic temperature. That is, some carbon is pre sent as graphite flakes, as in gray cast iron, iron carbide, or in white cast iron. When cast iron contains a specially added element or elements in amounts sufficient to produce a measurable modification of the physical properties of the section under consideration, it is called alloy cast iron. Silicon, manganese, sulfur, and phosphorus, as

  normally obtained from raw materials, are not considered as alloy additions.

Cast steel. Any object shaped by pouring molten steel into molds.

Cast structure. The structure (on a macroscopic or microscopic scale) of a cast alloy that consists of cored dendrites and, in some alloys, a network of other constituents.

Cementite. A compound of iron and carbon known as "iron carbide" which has the approximate chemical formula Fe3C.

Centerline. Well-defined gage line placed on the work to serve as a basis from which dimensions are to be measured.

Centrifugal casting. A casting technique in which a casting is produced by rotation of the mold during solidification of the casting; unusually sound castings may be produced by action of centrifugal force pressing toward the outside of the mold.

Chamfer. To bevel a sharp edge by machining or other methods.

Chamotte. Coarsely graded refractory molding material, prepared from calcined clay and ground firebrick mulled with raw clay.

Chaplets. Metallic supports or spacers used in molds to maintain cores in their proper position during the casting process; not used when a pattern has a core print which serves the same purpose.

Charcoal. Used in pulverized form as dry blacking, or in suspension with clay, as black wash.

Charge. A given weight of metal introduced into the furnace; the metal that is to be melted.

Cheeks. Intermediate sections of a flask that are inserted between cope and drag to decrease the difficulty of molding unusual shapes or to fill a need for more than one parting line.

Chill. A piece of metal or other material with high heat capacity and conductivity inserted in the mold to hasten solidification of heavy sections and introduce desired directional cooling.

Chill-cast pig. Pig iron cast into metal molds or chills.

Chilled iron. Cast iron in which sufficient combined carbon is retained to form a mottled or white structure. These conditions result

 

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C. Continued

from accelerated cooling that prevents normal graphitization in those areas.

Chipping. Removal of fins and other excess metal from castings by means of chisels and other suitable tools.

Chipping-out. The process of removing slag and refuse attached to the lining of a furnace after a heat has been run.

Clamp-off. An indentation in the casting surface caused by displacement of sand in the mold.

Clays. Hydrous silicates of alumina, more or less mixed with mineral impurities and colored by presence of metallic oxides and organic matter. Pure clay is an earth which possesses sufficient ductility and cohesion when kneaded with water to form a paste capable of being fashioned by hand and when suitably burned is capable of resisting intense heat.

Clay substance (AFS clay). Clay portion of foundry sand which when suspended in water fails to settle 1 in. per min and which consists of particles less than 20 microns (0.02 mm or 0.0008 in.) in diameter.

Clay wash. A mixture of clay and water for coating Baggers and the inside of flasks.

Cleaner. A tool of thin steel or brass, 16 to 18 in. long; one extremity has a bent spatula blade; the other, a short blade bent on the flat to a right angle. It is used for smoothing the molded surfaces and removing loose sand; also called a slick.

Coal dust. Used largely in green sand molding compositions for cast iron. A bituminous type of coal is selected with a high percentage of volatile matter, crushed to various grades (coarse to super fine) and additions of 5 to 10 percent added to the facing sand. Also called sea coal.

Cold short. A characteristic of metals that causes them to be brittle at ordinary or low temperatures.

Cold shot. Small globule of metal embedded in but not entirely fused with the casting; a casting defect. (Sometimes confused with cold shut.)

Cold shut. A casting defect caused by imperfect fusing of molten metal coming together from opposite directions in a mold.

  Collapsibility. The tendency of a sand mixture to break down under the conditions of casting. A necessary property to prevent hot tears in castings.

Colloids, colloidal material. Finely divided material less than 0.5 micron (0.00002 in.) in size, gelatinous, highly absorbent and sticky when moistened. Clays are colloids.

Columnar structure. A coarse structure of parallel columns of grains caused by highly directional solidification resulting f r o m sharp thermal gradients.

Combination core box. A core box that may be altered to form a core of another shape.

Combined carbon. Carbon in iron and steel which is joined chemically with other elements; not in the free state as graphitic carbon.

Combined water. Water in mineral matter which is chemically combined and driven off only at temperatures above 230°F.

Combustion. Chemical change as a result of the combination of the combustible constituents of the fuel with oxygen to produce heat.

Compressive strength (sand). Maximum stress in compression which a sand mixture is capable of withstanding.

Compressive strength. Maximum stress that a material subjected to compression can withstand.

Continuous phase. In alloys containing more than one phase, the phase that forms the matrix or background in which the other phase or phases are present as isolated units. For example, in a concrete aggregate, the cement paste is the continuous phase and the gravel is a discontinuous phase.

Contraction cracks. A crack formed by the metal being restricted while it is contracting in the mold; may occur during solidification (called a hot tear).

Contraction rule. A scale divided in excess of standard measurements, used by pattern-makers to avoid calculations for shrinkage. (Usually called a shrink rule.)

Controlled cooling. A process of cooling from an elevated temperature in a predetermined manner to avoid hardening, cracking, or internal damage or to produce a desired microstructure.

 

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Cooling stresses. Stresses developed by uneven contraction or external constraint of metal during cooling after pouring.

Cope. Upper or topmost section of a flask, mold, or pattern.

Core. A preformed baked sand or green sand aggregate inserted in a mold to shape the interior, or that part of a casting which cannot be shaped by the pattern.

Core-blowing machine. A machine for making cores by blowing sand into the core box.

Core box. Wood or metal structure, the cavity of which has the shape of the core to be made.

Core cavity. The interior form of a core box that gives shape to the core.

Core compound. A commercial mixture which when mixed with sand supplies the binding material needed in making cores.

Core driers. Sand or metal supports used to keep cores in shape while being baked.

Core frame. Frame of skeleton construction used in forming cores.

Core irons. Bars of iron embedded in a core to strengthen it (core rods or core wires).

Core maker. A craftsman skilled in the production of cores for foundry use.

Core marker. A core print shaped or arranged so that the core will register correctly in the mold.

Core oil. Linseed or other oil used as a core binder.

Core ovens. Low-temperature ovens used for baking cores.

Core paste. A prepared adhesive for joining sections of cores.

Core plates. Heat resistant plates used to support cores while being baked.

Core print. A projection on a pattern which forms an impression in the sand of the mold into which the core is laid.

Core raise. A casting defect caused by a core moving toward the cope surface of a mold, causing a variation in wall thickness.

  Core sand. Sand free from clay; nearly pure silica.

Core shift. A variation from specified dimensions of a cored section due to a change in position of the core or misalignment of cores in assembling.

Coring. Variable composition in solid-solution dendrites; the center of the dendrite is richer in one element.

Cover core. A core set in place during the ramming of a mold to cover and complete a cavity partly formed by the withdrawal of a loose part of the pattern.

Critical points. Temperatures at which changes in the phase of a metal take place. They are determined by liberation of heat when the metal is cooled and by absorption of heat when the metal is heated, thus resulting in halts or arrests on the cooling or heating curves.

Crossbar. Wood or metal bar placed in a cope to give greater anchorage to the sand.

Cross section. A view of the interior of an object that is represented as being cut in two, the cut surface presenting the cross section of the object.

Crucible. A ceramic pot or receptacle made of graphite and clay, or clay and other refractory material, used in melting of metal; sometimes applied to pots made of cast iron, cast steel, wrought steel, or silicon carbide.

Crush. An indentation in the casting surface due to displacement of sand in the mold.

Cupping. The tendency of tangential sawed boards to curl away from the heart of the tree.

Cuts. Defects in a casting resulting from erosion of the sand by metal flowing over the mold or cored surface.

Cutting over. Turning over sand by shovel or otherwise to obtain a uniform mixture.

D.

Damping capacity. Ability of a metal to absorb vibrations.

Daubing. Filling cracks in cores, or plastering linings to fill cracks.

Decarburization. Loss of carbon from the surface of a ferrous alloy as a result of heating in a medium that reacts with the carbon.

452605 0-58-18

 

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D. continued

Deformation (sand). Change in a linear dimension of a sand mixture as a result of stress.

Dendrite. A crystal formed usually by solidification and characterized by a treelike pattern composed of many branches; also termed "pine tree" and "fir tree" crystal.

Dezincification. Corrosion of an alloy containing zinc (usually brass)involving loss of zinc and a surface residue or deposit of one or more active components (usually copper).

Diffusion. Movement of atoms within a solution. The net movement is usually in the direction from regions of high concentration towards regions of low concentration in order to achieve homogeneity of the solution. The solution may be a liquid, solid, or gas.

Dispersion (deflocculation). Separation or scattering of fine particles in a liquid; usually used in connection with the fineness test of clay.

Distribution (sand). Variation in particle sizes of foundry sand as indicated by a screen analysis.

Dowel. A pin used on the joint between sections of parted patterns or core boxes to assure correct alignment.

Draft, pattern. Taper on vertical surfaces in a pattern to allow easy withdrawal of pattern from a sand mold.

Drag. Lower or bottom section of a mold or pattern.

Drawback. Section of a mold lifted away on a plate or arbor to facilitate removal of the pattern.

Draw bar. A bar used for lifting the pattern from the sand of the mold.

Draw peg. A wooden peg used for drawing patterns.

Drawing. Removing pattern from mold.

Draw plate. A plate attached to a pattern to make drawing of pattern from sand easier.

Drop. A defect in a casting when a portion of the sand drops from the cope.

Drop core. A type of core used in forming comparatively small openings above or below the parting; the print is so shaped that the core is easily dropped into place.

  Dross. Metal oxides in or on molten metal.

Dry fineness. The fineness of a sample of foundry sand from which the clay has not been removed and which has been dried at 221° to 230°F.

Dry permeability. The property of a molded mass of sand that permits passage of gases resulting during pouring of molten metal into a mold after the sand is dried at 221° to 230°F. (105° to 110°C.) and cooled to room temperature.

Dry sand mold. A mold which has been baked before being filled with liquid metal.

Dry strength, dry bond strength. Compressive, shear tensile, or transverse strength of a sand mixture which has been dried at 221° to 230°F. and cooled to room temperature.

Ductility. The property permitting permanent deformation in a material by stress without rupture. A ductile metal is one that bends easily. Ductile is the opposite of brittle.

Durability (sand). Rate of deterioration of a sand in use, due to dehydration of its contained clay.

E.

Elastic limit. The greatest stress which a material can withstand without permanent deformation.

Elongation. Amount of permanent extension in the vicinity of the fracture in the tensile test; usually expressed as a percentage of original gage length, as 25 percent in 2 in. Simply, the amount that a metal will stretch before it breaks.

Erosion scab. A casting defect occurring where the metal has been agitated, boiled, or has partially eroded away the sand, leaving a solid mass of sand and metal at that particular spot.

Etching. In metallography, the process of revealing structural details by preferential attack of reagents on a metal surface.

Eutectic or eutectic alloy. An alloy that melts at a lower temperature than neighboring corn-positions. For example, ordinary solders, made up of a tin and lead combination, are eutectic alloys that melt at a lower temperature than either lead or tin alone.

Eutectoid reaction. A reaction of a solid that forms two new solid phases (in a binary alloy

 

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system) during cooling. In ferrous alloys, the product of the eutectoid reaction is pearlite.

Eutectoid steel. A steel of eutectoid composition. This composition in pure iron-carbon alloys is 0.80 percent C., but variations from this composition are found in commercial steels and particularly in alloy steels, in which the carbon content of the eutectoid usually is lower.

Expansion (sand). The increase in volume which a sand undergoes when heated.

Expansion scab. A casting defect; rough thin layers of metal partially separated from the body of the casting by a thin layer of sand and held in place by a thin vein of metal.

F.

Facing, facing material. Coating material applied to the surface of a mold to protect the sand from the heat of the molten metal. See MOLD WASH.

Facing sand. Specially prepared molding sand used in the mold next to the pattern to produce a smooth casting surface.

False cheek. A cheek used in making a three-part mold in a two-part flask.

False cope. Temporary cope used only in forming the parting; a part of the finished mold.

Fatigue. Tendency for a metal to break under repeated stressing considerably below the ultimate tensile strength.

Fatigue crack. A fracture starting from a nucleus where there is a concentration of stress. The surface is smooth and frequently shows concentric (sea shell) markings with a nucleus as a center.

Fatigue limit. Maximum stress that a metal will withstand without failure for a specified large number of cycles of stress.

Feeder, feeder head. A reservoir of molten metal to make up for the contraction of metal as it solidifies. Molten metal flowing from the feed head, also known as a riser, minimizes voids in the casting.

Feeding. The passage of liquid metal from the riser to the casting.

  Ferrite. Solid solution in which alpha iron is the solvent.

Ferroalloys. Alloys of iron and some other element or elements.

Ferroboron. An alloy of iron and boron containing about 10 percent boron.

Ferrochromium. An alloy of iron and chromium available in several grades containing from 66 to 72 percent chromium and from 0.06 to 7 percent carbon.

Ferromanganese. Iron-manganese alloys containing more than 30 percent manganese.

Ferromolybdenum. An alloy of iron and molybdenum containing 58 to 64 percent molybdenum.

Ferrophosphorus. Alloy of iron and phosphorus for the addition of phosphorus to steel.

Ferrosilicon. Alloy of iron and silicon for adding silicon to iron and steel.

Ferrotitanium. An alloy of iron and titanium available in several grades containing from 17 to 38 percent titanium.

Ferrous. Alloys in which the main metal is iron.

Ferrovanadium. Alloy of iron and vanadium containing 35 to 40 percent vanadium.

Fillet. Concave corner at the inter section of surfaces.

Fin. A thin projection of metal attached to the casting.

Fineness (sand). An indication of the grain-size distribution of a sand. See GRAIN FINENESS NUMBER.

Fines. In a molding sand, those sand grains smaller than the predominating grain size. Material remaining on 200 and 270-mesh sieves and on the pan in testing for grain size and distribution.

Fine silt. Sand particles less than 20 microns in diameter (0.02 mm or 0.0008 in.). This is included in AFS clay and by itself has very little plasticity or stickiness when wet.

Finish allowance. Amount of stock left on the surface of a casting for machine finish.

Finish mark. A symbol (finish mark) appearing on the line of a drawing that represents a surface of the casting to be machine finished.

 

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Fire brick. Brick made from highly refractory clays and used in lining furnaces.

Fire clay. A clay with a fusion temperature of not less than 2,770°F.

Flask. A metal or wood box without top or bottom; used to hold the sand in which a mold is formed; usually consists of two parts, cope and drag. Remains on mold during pouring.

Flask pins. Pins used to assure proper alignment of the cope and drag of the mold during ramming and after the pattern is withdrawn.

Flowability. The property of a foundry sand mixture which enables it to fill pattern recesses and to move in any direction against pattern surfaces under pressure.

Fluidity. Ability of molten metal to flow and reproduce detail of the mold.

Fluorspar. Commercial grade of calcium fluoride (CaF2).

Flux. Material added to metal charges during melting to form a slag.

Fluxing. Applying a solid or gaseous material to molten metal in order to remove oxide dross and other foreign materials, or a cover slag to protect the melt from oxidizing.

Follow board. A board which conforms to the pattern and locates the parting surface of the drag.

Fusion. Melting. Also used to designate a casting defect caused when molding sand softens and sticks to the casting to give a rough glossy appearance.

Fusion point. Temperature at which a material melts.

G.

Gaggers. Metal pieces used to reinforce and support sand in deep pockets of molds.

Gamma iron. The form of iron stable between l,670° and 2,550°F.

Ganister. A siliceous material used as a refractory, particularly for furnace linings.

Gas holes. Rounded or elongated cavities in a casting, caused by the generation or accumulation of gas or trapped air.

  Gate. End of the runner where metal enters the casting; sometimes applied to the entire assembly of connected channels, to the pattern parts which form them or to the metal which fills them; sometimes restricted to mean the first or main channel.

Gated patterns. Patterns with gates or channels attached.

Grain fineness number (AFS). An arbitrary number used to designate the grain fineness of sand. It is calculated from the screen analysis and is essentially the "average" grain size. The higher the number, the finer the sand.

Grain (sand). The granular material of sand left after removing the clay substance in accordance with the AFS fineness test.

Grains. Individual crystals in metals.

Grain refiner. Any material added to a liquid metal for producing a finer grain size in the casting.

Graphite. A soft form of carbon existing as flat hexagonal crystals and black with a metallic luster. It is used for crucibles, foundry facings, lubricants, etc. Graphite occurs naturally and is also made artificially by passing alternating current through a mixture of petroleum and coal tar pitch.

Graphitizing, graphitization. A heating and cooling process by which the combined carbon in cast iron or steel is transformed to graphite or free carbon. See TEMPER CARBON.

Gravity segregation. Variable composition caused by the settling of the heavier constituents where the constituents are insoluble or only partially soluble.

Gray cast iron. Cast iron which contains a relatively large percentage of its carbon in the form of graphite and substantially all of the remainder of the carbon in the form of eutectoid carbide. Such material has a gray fracture.

Green permeability. The ability of a molded mass of sand in its tempered condition to permit gases to pass through it.

Green sand. Molding sand tempered with water.

Green sand mold. A mold of prepared molding sand in the moist tempered condition.

Green strength. Tempered compressive, shear, tensile, or transverse strength of a tempered sand mixture.

 

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Grinding. Removing excess materials, such as gates and fins, from castings by means of an abrasive grinding wheel.

H.

Hardness (sand). Resistance of a sand mixture to deformation in a small area.

Head. Riser. Also refers to the pressure exerted by the molten metal.

Heap sand. Green sand usually prepared on the foundry floor.

Heat. Metal obtained from one period of melting in a furnace.

Holding furnace. A furnace for maintaining molten metal from a melting furnace at the right casting temperature, or provide a mixing reservoir for metals from a number of heats.

Homogenization. Prolonged heating in the solid solution region to correct the microsegregation of constituents by diffusion.

Horn gate. A semicircular gate to convey molten metal over or under certain parts of a casting so that it will enter the mold at or near its center.

Hot deformation (sand). The change in length or shape of a mass of sand when pressure is applied while the sand is hot.

Hot permeability (sand). The ability of a hot molded mixture of sand to pass gas or air through it.

Hot shortness. Brittleness is hot metal.

Hot spruing. Removing gates from castings before the metal has completely cooled.

Hot strength (sand). Compressive, shear, tensile, or transverse strength of a sand mixture determined by any temperature above room temperature.

Hot tear. Fracture caused by stresses acting on a casting during solidification after pouring and while still hot.

Hypereutectoid steel. A steel containing more than the eutectoid percentage of carbon. See EUTECTOID STEEL.

Hypoeutectoid steel. A steel containing less than the eutectoid percentage of carbon. See EUTECTOID STEEL.

 

I.

Impact strength. The ability to withstand a sudden load or shock.

Inclusions. Particles of impurities (usually microscopic particles of oxides, sulfides, silicates, and such) that are held in a casting mechanically or are formed during solidification.

Induction heating. Process of heating by electrical induction.

Ingate. The part of the gating system connecting the mold cavity to the runner.

Inhibitor. (l) A material such as fluoride, boric acid or sulfur used to prevent burning of molten magnesium alloys or for restraining an undesirable chemical reaction. (2) An agent added to pickling solutions to minimize corrosion.

Inoculant. Material which is added to molten cast iron to modify the structure and change the physical and mechanical properties to a degree not explained on the basis of the change in composition.

Inoculation. Addition to molten metal of substances designed to form nuclei for crystallization.

Internal stresses. A system of forces existing within a part.

Inverse chill. This, also known as reverse chill, internal chill, and inverted chill in gray cast iron, is the condition in a casting where the interior is mottled or white, while the outer sections are gray.

Iron, malleable. See MALLEABLE CAST IRON.

J.

Jacket. A wooden or metal form or box which is slipped onto a mold to support the sides of the mold during pouring.

Jig. A device arranged so that it will expedite and improve the accuracy of a hand or machine operation.

K.

Killed steel. Steel deoxidized with a strong deoxidizing agent such as silicon or aluminum to reduce the oxygen content to a minimum so that no reaction occurs between carbon and oxygen during solidification.

 

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Kiln-drying. Artificial drying of lumber by placing it in a specially designed furnace called a kiln.

Kish. Free graphite which has separated from molten iron.

Knockout. Operation of removing sand cores from castings or castings from a mold.

L.

Ladles. Metal receptacles lined with refractories and used for transporting and pouring molten metal.

Layout board. A board on which a pattern layout is made.

Ledeburite. Cementite-austenite eutectic structure.

Life (of sand). See DURABILITY.

Light metals. Metals and alloys that have a low specific gravity, such as beryllium, magnesium, and aluminum.

Liquid contraction. Shrinkage occurring in metal in the liquid state as it cools.

Liquidus. The temperature at which freezing begins during cooling or melting is completed during heating. The lowest temperature at which a metal is completely molten.

Loam. A mixture of sand, silt, and clay that is about 50 percent sand and 50 percent silt and clay.

Loam molds. Molds of bricks, plates, and other sections covered with loam to give the form of the castings desired.

Loose piece. Part of a pattern that is removed from the mold after the body of the main pattern is drawn.

Low-heat-duty clay. A refractory clay which fuses between 2768° and 2894°F.

Lute. (l) Fire clay used to seal cracks. (2) To seal with clay or other plastic material.

M.

Machinability. The relative ease with which a metal can be sawed, drilled, turned, or otherwise cut.

  Machine finish. Turning or cutting metal to produce a finished surface.

Macroscopic. Visible either with the naked eye or under low magnification up to about ten diameters.

Macrostructure. Structure of metals as revealed by macroscopic examination.

Malleable cast iron. The product obtained by heat treatment of white cast iron which converts substantially all of the combined carbon into nodules of graphite. Differs from gray cast iron because it contains nodules of graphite instead of flakes.

Malleability. The property of being permanently deformed by compression without rupture.

Malleabilizing. Process of annealing white cast iron in such a way that the combined carbon is wholly or partly transformed to graphitic or free carbon or, in some instances, part of the carbon is removed completely. See TEMPER CARBON.

Marking a core. Shaping the core and its print so that the core cannot be misplaced in the mold.

Martensite. An unstable constituent often formed in quenched steel. Martensite is the hardest structure formed when steels are quenched.

Mass hardness. A condition in which the entire casting is hard and unmachinable.

Master pattern. A pattern with a special contraction allowance in its construction; used for making castings that are to be employed as patterns in production work.

Matched parting. A projection on the parting surface of the cope half of a pattern and a corresponding depression in the surface of the drag.

Match plate. A plate on which patterns split along the parting line are mounted back to back with the gating system to form a complete pattern unit.

Mechanical properties. The properties of a metal which determine its behavior under load. For example, strength.

Melting loss. Loss of metal in the charge during melting.

Melting rate. The tonnage of metal melted per hour.

 

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Metal penetration. A casting defect resulting from metal filling the voids between the sand grains.

Metallography. The science of the constitution and structure of metals and alloys as revealed by the microscope.

Microporosity. Extremely fine porosity caused in castings by shrinkage or gas evolution.

Microshrinkage. Very finely divided shrinkage cavities seen only by use of the microscope.

Microstructure. The structure of polished and etched metal as revealed by the microscope.

Misch metal. An alloy of rare earth metals containing about 50 percent cerium with 50 percent lanthanum, neodymium, and similar elements.

Misrun. Cast metal that was poured so cold that it solidified before filling the mold completely.

Modification. Treatment of aluminum-silicon alloys in the molten state with a small percentage of an alkaline metal or salt such as sodium fluoride to develop maximum mechanical properties in the metal.

Modulus of elasticity. The ratio of stress to the corresponding strain within the limit of elasticity of a material, a measure of the stiffness of a material. A high modulus of elasticity indicates a stiff metal that deforms little under load.

Moisture. Water which can be driven off of sand by heating at 221° to 230°F.

Mold. The form (usually made of sand) which contains the cavity into which molten metal is poured.

Mold board. Board on which the pattern is placed to make the mold.

Mold cavity. Impression left in the sand by a pattern.

Mold clamps. Devices used to hold or lock cope and drag together.

Mold shift. A casting defect which results when a casting does not match at parting lines.

Mold wash. Usually an emulsion of water and various compounds, such as graphite or silica flour; used to coat the face of the cavity in the mold. See FACING.

  Mold weights. Weights placed on top of molds to withstand internal pressure during pouring.

Molder's rule. A scale used in making patterns for casting; the graduations are expanded to allow for contraction of the metal being cast. See PATTERNMAKER'S SHRINKAGE.

Molding, bench. Making sand molds from loose or production patterns at a bench not equipped with air or hydraulic action.

Molding, floor. Making sand molds from loose or production patterns of such size that they cannot be satisfactorily handled on a bench or molding machine; the equipment is located on the floor during the entire operation of making the mold.

Molding machine. May refer to squeezer or jolt squeezer machines on which one operator makes the entire mold, or to similar or larger machines including jolt-squeeze-strippers, and jolt and jolt-rollover-pattern draw machines on which cope and drag halves of molds are made.

Molding material. Substance that is suitable for making molds into which molten metal can be cast.

Molding sand. Sand containing sufficient refractory clay substance to bond strongly when rammed to the degree required.

Mottled cast iron. Cast iron which consists of a mixture of variable proportions of gray cast iron and white cast iron; such a material has a mottled fracture.

Muller. A machine for mixing foundry sand, in which driven rolls knead the sand mixture against suitable plates.

Multiple mold. A composite mold made up of stacked sections. Each section produces a complete casting and is poured from a single down gate.

N.

Naturally bonded molding sand. A sand containing sufficient bonding material for molding purposes in the "as-mined" condition.

Neutral refractory. A refractory material which is neither definitely acid nor definitely basic. The term is merely relative in most cases, since at high temperature, such a material will usually react chemically with a strong base functioning as a weak acid, or with a strong acid functioning as a weak base.

 

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Chrome refractories are the most nearly neutral of all commonly used refractory materials. Alumina (A12O3) is also nearly neutral and often serves as a neutral refractory.

Nodular iron. Cast iron which has all or part of its graphitic carbon content in the nodular or spherulitic form as cast. In nodular iron, the graphite is in tighter balls than in malleable iron. Nodular iron does not require heat treatment to produce graphite but malleable iron always requires heat treatment.

Nonferrous. Alloys in which the predominant metal is not iron.

Normalizing. A process in which a ferrous alloy is heated to a suitable temperature above the transformation range and cooled in still air at room temperature.

Normal segregation. Concentration of alloying constituents that have low melting points in those portions of a casting that solidify last.

Nucleus. The first particle of a new phase. The first solid material to form during the solidification of molten metal, occurring in a very microscopic size.

O.

Off-Grade metal. Metal whose composition does not meet the specification.

Open hearth furnace. A furnace for melting metal. The bath is heated by hot gases over the surface of the metal and by radiation from the roof. The preheating of air in a separate checker work distinguishes this furnace from an air furnace or reverberatory furnace.

Operating stress. The stress or load placed on a metal or structure during service.

Optical pyrometer. A temperature measuring device through which the observer sights the heated object and compares its brightness with that of an electrically heated filament whose brightness can be regulated.

Optimum moisture. The moisture content which results in the maximum development of any property of a sand mixture.

Overaging. Aging under conditions of time and temperature greater than that required to obtain maximum strength.

  Overhang. The extension of the end surface of the cope half of a core print beyond that of the drag in order to provide clearance for the closing of the mold.

Overheated. A term applied when, after exposure to an excessively high temperature, a metal develops an undesirably coarse grain structure but is not permanently damaged. Unlike burnt structure, the structure produced by overheating can be corrected by suitable heat treatment, by mechanical work, or by a combination of the two.

Oxidation. Any reaction where an element reacts with oxygen.

P.

Packing or packing material. Sand, gravel, mill scale, or other similar material used to support castings to prevent warpage during annealing.

Pad. Shallow projection on a casting, usually added to provide a taper that will benefit directional solidification.

Parted pattern. Pattern made in two or more parts.

Parting. The separation between the cope and drag portions of mold or flask in sand casting.

Parting compound. A material dusted or sprayed on patterns to prevent adherence of sand. It is also used on the drag surface of a mold at the parting line.

Parting line. A line on a pattern or casting corresponding to the separation between the cope and drag portions of a sand mold.

Parting sand. Finely ground sand for dusting on surfaces that are to be separated when making a sand mold.

Pattern. A form of wood, metal, or other materials around which sand is packed to make a mold for casting metals.

Pattern board. Board having a true surface upon which the pattern is laid for ramming of the drag.

Pattern checking. Verifying dimensions of a pattern with those of the drawing.

Pattern layout. Full-sized drawing of a pattern showing its arrangement and structural features.

 

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Pattern coating. Coating material applied to wood patterns to protect them against moisture and abrasion of molding sand.

Pattern letters and figures. Identifying symbols fastened to a pattern as a means for keeping a record of the pattern and for the identification of the casting.

Pattern members. Components parts of a pattern.

Pattern plates. Straight flat plates of metal or other material on which patterns are mounted.

Patternmaker's shrinkage. Shrinkage allowance made on patterns to allow for the change in dimensions as the solidified casting cools in the mold from freezing temperature of the metal to room temperature. Pattern is made larger by the amount of shrinkage characteristic of the particular metal in the casting. Rules or scales are available for use. See MOLDER'S RULE.

Plaster pattern. A pattern made from plaster of Paris.

Pattern record card. A filing card giving description, location in storage, and movement of a pattern.

Pearlite. Laminated mixture of ferrite and iron carbide in the microstructure of iron and steel.

Pearlitic malleable cast iron. The product obtained by a heat treatment of white cast iron which converts some of the combined carbon into graphite nodules but which leaves a significant amount of combined carbon in the product.

Peen. Rounded or wedge-shaped end of a tool used to ram sand into a mold. It is also the act of ramming sand or surface working metals.

Peg gate. A round gate leading from a pouring basin in the cope to a basin in the drag.

Penetration, metal. A casting defect in which it appears as if the metal has filled the voids between the sand grains without displacing them.

Permanent mold. A metal mold, usually refractory coated, used for production of many castings of the same form; liquid metal is poured in by gravity; not an ingot mold.

  Permeability (sand). A property which permits gas to pass through a molded mass of sand.

Phase diagram. A graph showing the equilibrium temperatures and composition of phases and reactions in an alloy system.

Phosphorus. A chemical element; symbol is P.

Photomicrograph. A photographic reproduction of any object magnified more than 10 times. The term micrograph may be used.

Pickle. Chemical or electrochemical removal of surface oxides from metal surfaces to clean them; usually done with acids.

Pig. An ingot of virgin or secondary metal to be remelted.

Pig bed. Small excavation or open mold in the floor of the foundry to hold excess metal.

Pig iron. Iron produced by the reduction of iron ore in a blast furnace; contains silicon, manganese, sulfur, and phosphorus.

Pinhole porosity. Small holes scattered through a casting.

Pipe. A cavity formed by contraction of metal during solidification of the last portion of liquid metal in a riser. It is usually carrot shaped.

Plumbago. Graphite in powdered form. Plumbago crucibles are made from plumbago plus clay.

Porosity. Unsoundness in cast metals. The term is used generally and applies to all types of cavities (shrinkage, gas, etc.).

Porosity (sand). Volume of the pore spaces or voids in a sand.

Pot. A vessel for holding molten metal.

Poured short. Casting which lacks completeness because the mold was not filled.

Pouring. Transfer of molten metal from ladle to molds.

Pouring basin. A cup may be cut in the cope or a preformed receptacle placed on top of the cope to hold molten metal prior to its entrance into the gate.

Precipitation hardening. A process for hardening an alloy; a constituent precipitates from a supersaturated solid solution. See AGE HARDENING and AGING.

 

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Precipitation heat treatment. In nonferrous metallurgy, any of the various aging treatments conducted at elevated temperatures to improve certain mechanical properties through precipitation from solid solution. See AGING.

Pressure tight. A term that describes a casting free from porosity of the type that would permit leaking.

Primary crystals. The first crystals that form in a molten alloy during cooling.

Proportional limit. The greatest stress (load) which a material can stand and still return to its original dimensions when the load is removed.

Pull cracks. Cracks in a casting caused by contraction, generally associated with stresses due to the irregular shape of the casting. See HOT TEAR.

Pull down. A buckle in the cope; sometimes severe enough to cause a scab.

Push-up. An indentation in the casting surface because of displacement of sand in the mold.

Pyrometer. An instrument used for measuring temperatures.

Pyrometer tube. A metal, ceramic or carbon tube sealed at one end and containing the thermocouple for measurement of temperatures, used as protection for the thermocouple.

Q.

Quench hardening. Process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and cooling at a rate sufficient to increase the hardness.

Quenching. A process of rapid cooling from an elevated temperature by contact with liquids, gases, or solids.

Quenching crack. A fracture resulting from thermal stresses induced during rapid cooling or quenching. Frequently encountered in alloys that have been overheated and are "hot short."

R.

Radioactive metals. A group of metals with high atomic weights and with atomic nuclei

  that decompose slowly giving off continual radiations of positively charged alpha particles (which are relatively slow), negatively charged beta particles (which are faster and lighter), and gamma rays. The gamma rays are similar to X-rays but are more penetrating and are used for radiography of very thick sections. Bombardment by neutrons can make any metal radioactive. Small concentrations of such metals are used as "tracers" in the study of diffusion and other phenomena.

Radiography. A nondestructive method of examination in which metal objects are exposed to a beam of X-ray or gamma radiation. Differences in metal thickness, caused by internal defects or inclusions, are seen in the image either on a fluorescent screen or on photographic film placed behind the object.

Ram. To pack the sand in a mold.

Rammer, air. A pneumatic tool used for packing sand around a pattern.

Rammer, hand. A wooden tool with a round mallet-shaped head at one end and a wedge-shaped head at the other, used to pack sand around the pattern when making a mold.

Ramming. The operation of packing sand around a pattern in a flask to form a mold.

Ram-off. A casting defect resulting when a section of the mold is forced away from the pattern by ramming after the sand has conformed to the pattern.

Rapping. Knocking or jarring the pattern to loosen it from the sand in the mold before withdrawing the pattern.

Rapping plate. A metal plate attached to a pattern to prevent injury to the pattern and to assist in loosening it from the sand.

Rat. A lump on the surface of a casting caused by a portion of the mold face sticking to the pattern.

Rat-tail. A casting defect caused by a minor buckle in the sand mold, occurs as a small irregular line or lines.

Rebonded sands. Used or reclaimed molding sand restored to usable condition by the addition of a new bonding material.

Reclamation, sand. See SAND RECLAMATION.

Recuperator. Equipment for recovering heat from hot gases and using it for the preheating of incoming fuel or air.

 

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R. Continued

Red shortness. Brittleness in hot metal.

Refractory (noun). A heat-resistant material (usually nonmetallic) used for furnace linings and such.

Refractory (adj.). The quality of resisting heat.

Refractory clay. A clay which fuses at 2890°F. or higher.

Residual stress. See CASTING STRESS and STRESS.

Retained strength. Compressive, shear, tensile, or transverse strength of a sand mixture after being subjected to a cycle of heating and cooling which approximate s foundry practice.

Reverberatory furnace. A furnace with a vaulted ceiling that deflects the flame and heat toward the hearth or to the surface of the charge to be melted.

Riddle. Screen or sieve operated manually or by power for removing large particles of sand

or foreign material from foundry sand.

Riddled sand. Sand that has been passed through a riddle or screen.

Riser. A reservoir designed to supply molten metal to compensate for shrinkage of a casting during solidification.

Rockwell hardness. The hardness value of a metal as determined by measuring the depth of penetration of a 1/16 inch steel ball ("B" scale) or a diamond point ("C" scale) using a specified load.

Rolling over. The operation of reversing the position of a flask in which the drag part of the pattern has been rammed with the parting surface downward.

Rollover board. A wood or metal plate on which the pattern is laid top face downward for ramming the drag half mold; the plate and half mold are turned over together before the cope is rammed.

Runner. A channel through which molten metal is passed from one receptacle to another; in a mold, the portion of the gate assembly that connects the down gate or sprue with the ingate.

Runner box. Device for distributing molten metal around a mold by dividing it into several streams.

  Runner riser. A channel which permits flow of molten metal to the ingates and also acts as a reservoir to feed the casting.

Runout. A casting defect where a casting lacks completeness due to molten metal draining or leaking out of some part of the mold cavity during pouring; escape of molten metal from a furnace, mold, or melting crucible.

S.

Sag. A decrease in metal thickness in a casting caused by settling of the cope or core.

Sand. A loose material consisting of small but easily distinguishable grains, usually of quartz from the disintegration of rock. When used as a molding material, the grains should pass a No. 6 and be retained on a No. 270 sieve. Sometimes used to designate a sand-clay mixture appearing naturally in proper proportions for molding.

Sand, bank. Sand from a bank or pit usually low in clay content.

Sandblast. Sand driven by a blast of compressed air and used to clean castings.

Sand burning. Formation of a hard glassy surface on a sand casting by reactions between the sand of the mold and the hot metal or metallic oxides.

Sand castings. Metal castings poured in sand molds.

Sand control. Procedure where various properties of foundry sand (such as fineness, permeability, green strength, and moisture content) are adjusted to obtain castings free from blows, scabs, veins, and similar defects.

Sand cut. Erosion of sand from the mold surfaces by running metal.

Sand cutting. Preparing sand for molding, either by hand or by a machine.

Sand holes. Cavities of irregular shape and size; the inner surfaces plainly show the imprint of a granular material.

Sand reclamation. Processing of used foundry sand, normally wasted, by thermal or hydraulic methods so that it may be used in place of new sand.

Sand tempering. Adding sufficient moisture to sand to make it satisfactory for molding purposes.

 

288
 

S. Continued

Scab. A defect on the surface of a casting; usually appears as a rough mass of metal attached to the normal surface of the casting and often contains sand; caused by generation of gas in the mold, poor ramming, or high expansion of the sand when heated.

Scarfing. Cutting off surface areas, such as gates and risers, from castings by using a gas torch.

Scrap. Material unsuitable for direct use but usable for reprocessing; metal to be remelted. Includes sprues, gates, risers, defective castings, and scrapped machinery.

Screen. Perforated metal placed between the gate and the runner of a mold to minimize the possibility of oxides passing through into the casting.

Sea coal. Finely ground soft coal often mixed with molding sand. See COAL DUST.

Seam. A surface defect on a casting; related to, but of lesser degree than, a coldshut.

Season cracking. Stress-corrosion cracking of copper-base alloys; involves residual stresses and specific corrosive agents (usually ammonia or compounds of ammonia).

Sectional core. A core made in two or more parts and pasted or wired together.

Segregation. In a casting, concentration of alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid. Microsegregation refers to normal segregation on a microscopic scale where material rich in the alloying element freezes in successive layers on the dendrites (coring). Macrosegregation refers to gross differences in concentration (for example, from one area of a casting to another).

Selective heating. A process by which only certain portions of a casting are heated in a way that will produce desired properties after cooling.

Selective quenching. A process by which only certain portions of a casting are quenched.

Semi steel. Incorrect name sometimes mistakenly used for high-strength gray iron made from a charge containing considerable steel scrap.

  Semikilled steel. Steel incompletely deoxidized to permit evolution of sufficient carbon monoxide to offset solidification shrinkage.

Shakeout. The operation of removing castings from the mold.

Shank. The handle of a ladle. (The metal form that holds the ladle.)

Sharp sand. A sand that is substantially free of bond. The term has no reference to the grain shape.

Shear strength. Maximum shear stress which a sand mixture is capable of developing.

Shift. A casting defect caused by mismatch of cope and drag.

Shrink rule. See MOLDER'S RULE.

Shrinkage cavity. A void left in cast metals as a result of solidification shrinkage and the progressive freezing of metal toward the center.

Shrinkage, patternmaker 's. Shrinkage allowance on patterns to compensate contraction when the solidified casting cools in the mold from the freezing temperature to room temperature.

Shrinkage cracks. Cracks that form in metal as a result of the pulling apart of grains by thermal contraction before complete solidification.

Silica. The hard mineral part of natural sand. Chemical formula SiO2.

Silicious clay. A clay containing a high percentage of silica.

Silt. Very fine particles that pass a No. 270 sieve, but which are not plastic nor sticky when wet.

Sintering point. The temperature at which the molding material begins to adhere to the casting.

Sizing. Primary coating of thin glue applied to end-grain wood to seal the pores.

Skeleton pattern. A framework representing the interior and exterior form and the metal thickness of the required casting; not a solid pattern.

Skimgate. See SCREEN.

Skimmer. A tool for removing scum and dross from molten metal.

 

289
 

S. Continued

Skimming. Holding back or removing the dirt, slag, or scum in the molten metal before or during pouring to prevent it from entering the mold.

Skin. A thin surface layer that is different from the main mass of an object in composition, structure, or other characteristics.

Skin-drying. Drying of the surface of the mold by direct application of heat.

Skull. A film of metal or dross remaining in a pouring vessel after the metal has been poured.

Slab core. Flat plain core.

Slag. A nonmetallic covering which forms on the molten metal as a result of the impurities contained in the original charge, ash from the fuel, and silica and clay eroded from the refractory lining. It is skimmed off prior to tapping of the heat.

Slip jacket. A frame to place around a snap-flask mold after the flask is removed.

Slick, slicker, smoother. A tool used for mending and smoothing the surfaces of a mold.

Slurry. A thin flowable mixture of clay or bentonite in water; used to fill cracks in linings or to fill joints in cores.

Slush casting. A casting made from an alloy that has a low melting point and freezes over a wide range of temperature. The metal is poured into the mold and brought into contact with all surfaces so as to form an inner shell of frozen metal. Then the excess metal is poured out. Castings that consist of completely enclosed shells maybe made by using a definite quantity of metal and a closed mold.

Snap flask. A flask used for small work; differs from the ordinary flask in that it has hinges and latches or some other device so that it can be opened or held together as desired.

Soaking. Prolonged heating of metal at a selected temperature.

Soda ash. Commercial sodium carbonate.

Soldier s. Thin pieces of wood used to strengthen a body of sand or to hold it in place.

Solid contraction. Shrinkage occurring in metal in the solid state as it cools from the solidus temperature to room temperature.

  Strain. The change in dimension of a structure. Strain may be caused by stress, or strain may cause stress. Usually expressed in inches per inch.

Stress. The load applied to or existing in a structure; usually expressed in pounds per square inch (p.s.i.).

Superheating. Heating a molten metal to a temperature above its melting point.

Superimposed core. A core placed on a pattern and rammed up with it.

Swab. A sponge or piece of waste, hemp, or other material used in dampening sand around a pattern before withdrawing it. Sometimes used in blacking molds which might be broken by a brush.

Sweep. A board having the profile of the desired mold; when revolved around a stake or spindle, it produces the outline of the mold.

Sweep-work. Molds made of pieces of patterns and sweeps instead of patterns.

Swell. A casting defect consisting of an increase in metal thickness because of the displacement of sand by metal pressure.

Synthetic molding sand. Any sand compounded from selected individual materials which when mixed together produce a mixture having the proper physical properties from which to make foundry molds.

T.

Tally mark. A mark or combination of marks indicating the correct location of a loose piece of a pattern or core box.

Tapping. Opening the hole at the spout to permit molten metal to run from the furnace. It also applies to tilting a furnace to pour molten metal.

Temper (verb). (l) Mixing sand with sufficient water to develop desired molding properties. (2) Reheating of a quenched casting to reduce internal stresses and reduce hardness.

Temper (noun). The moisture content of a sand at which any desired property is obtained; for example, temper with respect to green compressive strength, permeability, retained compressive strength, etc.

Temper carbon. The free or graphitic carbon that precipitates during the graphitizing or malleableizing of white cast iron.

 

290
 

T. Continued

Temper water. Water added to molding sand to give proper molding consistency.

Tempering sand. Dampening and cutting over or otherwise mixing sand to produce uniform distribution of moisture.

Template. Thin piece of material with the edge contour made in reverse to the surface to be formed or checked.

Temporary pattern. A pattern used to produce one or two castings and made economically as the case will permit.

Tensile. Pertains to pulling of a structure as compared with pushing it (compression) or twisting it (torsion).

Tensile strength. Maximum pulling stress (load) which a material is capable of withstanding. (Also known as ultimate strength.)

Ternary alloy. An alloy that contains three principal elements.

Test bar. A specimen having standard dimensions designed to permit determination of mechanical properties of the metal from which it was poured.

Thermal contraction, The decrease in length accompanying a change of temperature.

Thermal expansion. The increase in length accompanying a change of temperature.

Thermal stresses. Stresses resulting from nonuniform distribution of temperature.

Thermit reactions. Heat-producing processes in which finely divided aluminum powder is used to reduce metal oxides to free metals.

Thermocouple. A device for measuring temperatures by the use of two dissimilar metals in contact; the junction of these metals gives a measurable voltage change with changes in temperature that is recorded and read on a meter.

Tie piece (bar). Bar or piece built into a pattern and made a part of the casting to prevent distortion caused by uneven contraction between separated members.

Tilting furnace. A melting furnace that can be tilted to pour out the molten metal.

Tin sweat. Beads of tin-rich low-melting phase that are found on the surface of bronze casting s when the molt en metal contains hydrogen.

  Top board. A wooden board which is used on the cope half of the mold to permit squeezing of the mold.

Transfer ladle. A ladle that may be supported on a monorail or carried in a shank and is used to transfer metal from melting furnace to holding furnace.

Transformation range or transformation temperature range. The temperature or range of temperatures at which metals undergo phase changes while still solid. The existence of these ranges and different phases make it possible to harden or soften iron, steel, and some nonferrous alloys almost at will by proper selection of heat treatment.

Transverse strength. The load required to break a test specimen that is supported at both ends and loaded in a direction perpendicular to the longitudinal axis.

Trimming. Removing fins and gates from castings.

Trowel. A tool for slicking, patching, and finishing a mold.

Tucking. Pressing sand with the fingers under flask bars, around gagger s, and other places where the rammer does not give the desired density.

Tumbling. Cleaning castings by rotation in a cylinder in the presence of cleaning materials.

Tumbling barrels. Rotating barrels in which castings are cleaned; also called rolling barrels and rattlers.

U.

Ultimate strength. See TENSILE STRENGTH.

Undercut. Part of a mold requiring a drawback. See DRAWBACK.

Upset. Frame to increase the depth of a flask.

V.

Vents A small opening in a mold to permit escape of gases when pouring metal.

Vent wire. A wire used to make vents or small holes in the mold to allow gas to escape.

Vibrator. A device operated by compressed air or electricity for loosening and withdrawing patterns from a mold.

 

291
 

V. Continued

Virgin metal. Metal obtained directly from the ore rather than by remelting.

Vitrification point. The temperature at which clays reach the condition of maximum density and shrinkage when heated.

W.

Warm strength (of a core). Strength of a core at temperatures of 150° to 300°F.

Warpage. Deformation other than contraction that develops in a casting between solidification and room temperature; also, distortion of a board through the absorption or expulsion of moisture.

Wash. Defect in a casting resulting from erosion of the sand by metal flowing over the mold or core surface.

Wax. Class of substances of plant, animal, or mineral origin, insoluble in water, partly soluble in alcohol, and miscible in all proportions with oils and fats. Common waxes are beeswax, paraffin wax, ozokerite, ceresin, and carnauba. Mixtures are formed into rods and sheets and used for forming vents in cores and molds.

Weak sand. Sand lacking the proper amount of clay or bond.

Web. A plate or thin member lying between heavier members.

Welding. A process used to join metals by the application of heat. Welding requires that

  the parent metals be melted. This distinguishes welding from brazing.

Welding stress. Stress resulting from localized heating and cooling of metal during welding.

Whirl gate. A gate or sprue arranged to introduce metal into a mold tangentially, thereby imparting a swirling motion.

White cast iron. Cast iron in which substantially all the carbon is present in the form of iron carbide. Such a material has a white fracture.

Wood's metal. A low-melting alloy containing 25 percent lead, 12.5 percent tin, 50 percent bismuth, and 12.5 percent cadmium, melting temperature is 154.4°F.

Workable moisture. The range of moisture content within which the sand fills, rams, draws, and dries to produce a satisfactory mold; also the range in which the sand does not dry out too fast to mold and patch.

Working face. Surface of a piece of material that has been planed true and that is to be used as a basis for the dressing of other surfaces.

X.

X-ray. Form of radiant energy with extremely short wavelength which has the ability to penetrate materials that absorb or reflect ordinary light.

Y.

Yield strength. See PROPORTIONAL LIMIT.

U. S. GOVERNMENT PRINTING OFFICE: 1958 0-452605

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