US3648757A - Method of making centrifugal casting mold - Google Patents

Abstract

A method of making a multilayer mold for centrifugally casting generally cylindrical bodies such as iron pipe. The mold includes a tapered bore within a low-stress metal sleeve surrounded by and mechanically locked to an outer sleeve or layer constructed of a metal having high heat conducting and dissipating qualities.

Description

llnited @tnten Willinglinm nten'l 51 Mar. l4, W72

[54] METHUD 01F MAKING ClENTRllFlJGAllL CASTIIING MUM) [72] Inventor: l-llnrold 1E. Willinglnarn, Sky Drive, An-

niston, Ala. 3620] [22] Filed: Jan. 119, 11970 [21] Appl. No.: 3,660

Related US. Application Data [63] Continuation-impart of Ser. No. 669,048, Sept. 20,

1967, abandoned.

{52] US. (II ..164l/138, 164/72, 164/100, 164/76, 164/14, 29/5273, 29/DIG. 5

[51] Int. Cl ..lB22c 11/00, B220 3/00 [58] Field oliSearch ..204/6, 9; 29/5271, 527.3, 29/DIG. 5, DIG. 8, DIG. 12; 164/23, 33, 72, 76, 98,

[56] References Cited UNITED STATES PATENTS Tanner ..204/ 6 2,699,413 1/1955 Lindbom ..204/6 3,083,424 4/1963 Bauer 29/5273 X 3,186,678 6/1965 Keating 164/14 X 3,401,736 9/1968 Tameichi lmagawa ..l64/l38 X 3,450,189 6/1969 MacDonald ..164/l38 X Primary Examiner-John F. Campbell Assistant Examiner-Donald C. Reiley Att0rneyA. Yates Dowell and A. Yates Dowell, Jr.

[5 7] ABSTRACT A method of making a multilayer mold for centrifugally casting generally cylindrical bodies such as iron pipe. The mold includes a tapered bore within a low-stress metal sleeve surrounded by and mechanically locked to an outer sleeve or layer constructed of a metal having high heat conducting and dissipating qualities.

10 Claims, 1111 Drawing Figures 7 PATENTEDMAR 14 972 3, 648 7'57" SHEET 2 [IF 3 /9 FT W Un 7 4 5 4 Cay PATENTEDHARM I972 3,648,757

SHEET .3 OF 3 INVENTOR HAROLD E W/ZZ/NGI/AM m m 7 47,4: 441 [0A i MlETllllUiU Gil MAKING CIENTIIIFIIGAL CAETING MOLD CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the making of cylindrical bodies and particularly to the method of making molds used in the centrifugal casting of iron pipe. The mold includes a plurality of layers of different materials and has an axial bore tapered substantially the full length of the mold.

2. Description of the Prior Art The art of casting metals is very old in recorded history and many methods and theories have been practiced, including in the centrifugal casting of iron pipe. The basic method of making a mold for the centrifugal casting of iron pipe has remained substantially unchanged in the industry for many years. This method has been to provide a cylindrical member which initially is roughly formed by casting and then by heat treatment and forging is formed roughly into the desired external configuration and preferably with a bore extending axially of the member. The forging improves the quality of the mold by compacting the molecules of metal. The bore, which usually is from 2 to 15 inches in diameter, is then machined to the external diameter of the pipe to be molded and is provided with a constant taper of approximately 0.003 inch per linear foot along the entire length of the mold which generally is approximately 5 to 20 feet in length. The bore normally is machined by using a boring bar which is inserted in one end of the bore and advanced to the opposite end while gradually increasing the diameter in accordance with the desired taper.

This has been a particularly difficult and costly machine operation since the taper must be constant and must be concentric about the longitudinal axis in order for the cast pipe to be removed from the mold. The casting, forging and subsequent machine operations have induced internal stresses within the mold and after being placed in service these stresses have been subjected to molten metal such as iron at a temperature of approximately 2,500 F. which causes heat cracks and ruptures and eventually renders the molds unserviceable. After the heat cracks have opened sufficiently to render the mold unserviceable, it has been necessary to remove the mold from service and rebore the opening to the next larger size of pipe before the mold could be used again. The number of times that the opening can be rebored is limited by the wall thickness of the mold, as well as the fact that the molecules of metal tend to align themselves along the metal faults or stresses so that once a crack or fissure begins it will continue to enlarge until the mold is useless.

The molds thus far described normally are used in two forms of casting machines. The first form of casting machine is known as a "captive machine and includes one or two molds at a single station where an operator both pours and extracts cast pipe in accordance with his skill and experience. This machine has the advantage of increasing mold life since the operator can remove the pipe promptly when it solidifies, thereby avoiding the deteriorating effect of prolonged heat; however, it has the disadvantage of a reduced production rate. The second form of casting machine is known as an over and under" machine and includes a plurality of molds mounted for travel from station to station. At one station molten metal is poured into the mold as it rotates and thereafter the mold is moved to another station where the pipe is withdrawn. This machine has the advantage of an increased production rate but the molds do not last as long due to the prolonged high heat.

In both of these machines, a slurry of water and diatomaceous earth normally is sprayed in a light coating inside the mold. The slurry serves as an insulator to reduce thermal shock on the mold caused by the molten metal and to prevent too rapid heat transfer and cooling of the metal which results in a chill as well as serving as a release agent after the pipe has solidified.

Due to the complexity of the machining operation that is required to produce a mold, a substantial length of time is required between the receipt of an order and the time it can be delivered by a manufacturer. Also once a mold has served in useful life, its only value is scrap metal which is practically worthless.

Some efforts have been made to improve molds utilized in the centrifugal casting of pipe, such as a mold having multiple layers of materials with different heat expansion qualities, as exemplified by the patent to Pohl US. Pat. No. 2,147,350, and the combination of an electroplated core and a strengthening member is described in the patent to Laukel U.S. Pat. No. 1,845,502. The formation of a sleeve on a mandrel by electrodeposition per se is well known, as disclosed in the patent to Grant US. Pat. No. 2,613,178; however, this sleeve was not intended for use as a mold but only as a finished pipe. These devices are substantially different from the present inventive concept and have not been satisfactory because of the separation of layers due to heat expansion and contraction, as well as for other reasons, including the fact that the method of mak ing these prior molds is entirely different.

SUMMARY OF THE INVENTION The present invention is a method of making a centrifugal mold by providing a body having external dimensions of the exact configuration of the pipe to be molded and thereafter forming a sleeve or layer on said body by the electrodeposition of metals which produces a low-stress sleeve, and thereafter providing a strengthening member or outer layer about the sleeve which will be mechanically locked thereto in such a manner that the layers cannot become separated and the in terface between such layers will be in contact with each other so that heat equilibrium will be established by substantially balancing the heat input from the molten'iron with the dissipation and radiation lost through the outer layer. If desired, a sleeve having a first layer of a hard, relatively expensive lowstress material such as nickel, cobalt or the like may be electrodeposited on the body, and then an intermediate layer of a more plentiful, relatively soft low-stress material such as copper or the like may be electrodeposited on the first layer. Thereafter, a strengthening member or outer layer of a material which is compatible with at least the intermediate layer is provided in any desired manner, as by pouring molten material around such sleeve.

It is an object of the invention to provide a method of making a permanent type centrifugal mold constructed of multiple layers of materials having different heat expansion and dissipation qualities which are locked together mechanically and at least one layer is constructed in a manner to avoid internal stresses.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation of a mandrel on which the mold of the present invention is formed.

FIG. 2 is a diagrammatic section illustrating the mandrel within an electrodeposit bath in which a first layer will be electrodeposited on the mandrel.

FIG. 3 is an enlarged fragmentary detailed section illustrating the structure of the electrodeposited layer.

FIG. I is a vertical section illustrating the casting of a min forcing outer layer about the electrodeposited layer.

FIG. is a section on the line 5-5 ofFlG. 4.

FIG. 6 is a section of the mold of the present invention in use.

FIG. 7 is a section on the line 7-7 of .FIG. 6.

FIG. ft is an enlarged fragmentary detailed section of one end of the mold.

FIG. 9 is an enlarged fragmentary section of a mandrel having multiple layers of material electrodeposited thereon.

layer.

FIG. 11 is a section on the line Iii-11 ofFlG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With continued reference to the drawings a mandrel is provided by machining a body 11 (shown in phantom in FIG. 1) to the exact configuration of the external surface of the pipe to be molded. The body is provided with an extension 12 at each end which can be mounted in the jaws of a lathe or grinder so that the body can be machined. The machining of the body along the exterior surface is relatively simple and a desired taper can be imparted along the entire length of the body by the utilization of conventional machine shop practices. The mandrel is constructed of a material which will not warp when heated or which has been annealed prior to the machining process to relieve any internal stress so that the mandrel will remain true. 7

After the mandrel has been machined to the desired configuration a coating 13 of a relatively low melting point metal or alloy such as tin or lead is applied to the outer surface of the mandrel to a thickness of approximately 0.0005 inch. This coating 13 can be applied in any desired manner, as by electroplating, hot dipping or the like.

When the coating has cooled the mandrel is placed in an electroplating tank 14 where a substantial thickness of a lowstress material such as nickel, copper, cobalt or the like is electrodeposited on the coating 13. A low-stress material as used herein is defined as a metal which is capable of being formed about the mandrel without internal stresses which cause a weakening along predetermined lines. It has been found that the coating 13 includes a series of microscopic hills and valleys and that the electrodeposited particles build up at a faster rate on the hills or projections than in the valleys or depressions. This phenomena causes the electrodeposited material to be built up of a series of knobs or nodes which continue to grow and spread until they join together in the valleys. These knobs or nodes combine with adjacent knobs or nodes to form trees" and appreciably extend the outer surface of the electrodeposited material, as illustrated in FIG. 3.

The size of the trees can be controlled in several different ways, for example, by roughening the outer surface of the coating by rubbing with an abrasive material such as fine emery cloth or the like, sprinkling impurities such as fine sand or grit onto the mandrel during the plating process, or by increasing the voltage applied between the anode and the cathode for a short period of time during the initial phase of the plating process. The increase in voltage will cause portions of the electrodeposited material to burn and the trees will grow from the burned" areas after the current is again reduced to normal. The electrodepositing process continues until a sleeve or layer 15 is formed on the mandrel 10. The sleeve may be of any desired thickness although a thickness of three-sixteenths to three-eighths inch has been found satisfactory.

In order to strengthen the sleeve 15 after it has been completed, the mandrel is removed from the tank 14 and the ends are machined to remove material electrodeposited on the ends of the mandrel. The mandrel with the sleeve thereon then is placed within a form 16 which functions as a mold. The electroplated sleeve 15 is retained in fixed position within the form 16 by a plurality of set screws 17 disposed radially about the form I6 and along the length thereof. The screws 17 extend inwardly to engage the sleeve 15 and firmly fix such sleeve in position. Thereafter a molten metal having high heat conduction and radiation qualities such as aluminum, magnesium or the like 18 is poured within the form 16 and allowed to harden to form an outer layer. The metal l8 must be compatible with the low-stress material of the sleeve 15 so that it will bond to such sleeve in intimate heat exchange relationship. The molten metal 18 will flow around the trees" of the sleeve 15 and in direct contact therewith so that after the molten metal has hardened the trees" will mechanically lock the layers together. Also, due to the roughness of the "trees" the total surface area of the interface between the layers will be substantially more than twice the surface of a smooth sleeve and the area of contact for transmitting heat from one layer to another will be correspondingly greater.

After the outer layer has hardened the assembly is removed from the form 16 and the exterior of the outer layer is machined to a desired diameter. A pair of wear-resistant shoes or bands 19 are placed about the exterior of the outer layer in any desired manner and such shoes are adapted to be engaged and supported by drive wheels 20 and idler wheels 21 of a casting machine 22. Such drive wheels are mounted on a common axle 23 supported by pillow blocks 24 on a table 25 and the axle 23 is adapted to be driven by a sprocket 26 from any suitable source of power (not shown).

When the mold has been completed, it is heated to a temperature sufficient to melt the coating 13 and the mandrel is withdrawn from the mold. Any excess coating material is removed from the mandrel as well as the bore of the mold by following standard machine shop practices. The mandrel then can be used to make another mold or can be stored for future use.

In order to cast pipe by centrifugal action a circular steel flange 27 is mounted on one end of a mold to act as a gate or dam to retain molten casting metal within the mold while the mold is spinning and the casting metal is still fluid or in a plastic state. At the opposite or bell end of the mold a shell core 28 of any desired material such as molded resin sand is provided having a flange 29 at one end in engagement with the mold, and such core has a forwardly extending reduced portion 30 which is spaced from and generally complementary to the bell end of the mold so that when molten metal is poured into the mold such metal will flow into the area between the mold and the reduced portion 30 to form the bell of the pipe.

The shell core 28 is expended with each pipe cast and must be replaced with a new shell core before a new pipe is cast. It is noted that a permanent metal core has been successfully substituted in experiments conducted in making pipe with the present mold.

With reference to FIGS. 9-11, a modified form of mold is provided in which an inner layer 15 of a hard relatively expensive material, such as nickel, cobalt or the like having lowstress characteristics, is electrodeposited on the coating 13. This inner layer may be of any desired thickness although a thickness of one-sixteenth to one-eighth inch is believed to be satisfactory. Thereafter an intermediate layer 15 of a less expensive low-stress material such as copper or the like which is compatible with the material of the inner layer is electrodeposited on the outer surface of such inner layer. During the electrodeposition process of the intermediate layer, the material will form first on the peaks of the nodules or nodes or the inner layer and will continue the growth of the trees. Since the materials of the inner layer and the intermediate layer are compatible, an integral bond will be effected so that the layers will be permanently locked together. If desired either the intermediate layer 15 or the metal of the outer layer 18 may be alloyed to provide metals having similar properties of heat conduction and radiation, as well as thermal expansion.

If desired the bore of the mold may be blasted with an abrasive and thereafter a layer of high melting point metal with a low coefficient of friction, such as chromium, may be elec trodeposited on such bore. The chromium layer aids in the withdrawal of finished pipe from the mold and tends to reduce the effect of thermal shock when the molten metal is introduced into the mold.

After all of the necessary appendages have been added to the mold, such mold is dynamically balanced to avoid excessive vibration during the casting of the pipe. When a pipe is to be cast it is necessary to initially heat the mold to a temperature of approximately 750 F. so that when molten metal is poured into the mold such metal will not cool too rapidly,

which would result in a chill causing the pipe to be brittle. Chilled pipe is unacceptable because of its tendency to shatter throughout its structure when struck by a cutting tool, as well as losses through breakage during handling and transporting of the pipe. The multilayer mold, by the nature of its construction, controls the rate at which the mold absorbs heat from the molten metal being cast, which in turn controls the quality of the pipe. By slowing down the heat absorption rate of the mold the pipe cools more slowly and does not chill at the interface between the mold and the metal being cast. This causes the molten metal to cool to the graphitic stage rather than the carbide stage.

The multilayer mold contains certain features of heat absorption, conduction and radiation which endow the mold with a regulated conductivity of heat transfer from high to low temperature areas of the mold and establish an equilibrium of heat at approximately 750 F. No attempt will be made to explain the phenomenon of heat conduction which is not entirely understood even to this day. But the basic laws which govern the phenomenon are believed to be consistent with classical thermodynamics. While heat conduction is commonly interpreted as a simple molecular interchange of kinetic energy within a mass, far more problems have arisen from the transfer of heat across interfaces of solids in contact. The nature of surface layers, films and imperfections of contact influence the ability of heat to move through these interfaces more than conduction in the molecular mass. Also, it is a known fact that as the temperature rises, nickel, copper and cobalt become less efficient as heat conductors, while aluminum and magnesium become more efficient. Advantage was taken of these facts in the design of the multilayer mold in regulating heat absorption in the mold, maintaining a heat equilibrium in the mold, and dissipating heat through the radiating surface at the required rate to maintain desirable levels of casting and cooling temperatures in the mold during operation. If desired, the absorption of heat by the mold from the molten iron and the radiation and dissipation of heat from the outer surface can be closely controlled by providing cooling fins on the mold or directing a flow of air or liquid against the rotating mold in accordance with standard foundry practices.

It is noted that the thickness of the metal layers comprising the multilayer mold may be varied to accommodate a variety of conditions governing heat transfer rates, mechanical strength, number and quality of interfaces between layers, all of which when combined will establish a practical solution to both heat transfer problems in the mold and the quality ofpipe being cast.

Due to the construction of the mold, the metal of the outer layer will not alloy or mix with the metal of the inner layer or layers. Accordingly, when the mold has served its useful life, it can be heated to a temperature sufficient to melt the outer layer which can then be used as the outer layer of another mold. When a single inner layer has been used, the removal of the outer layer leaves the inner layer in substantially a pure state which can then be cut into small pieces and placed in the electrodeposition tank to be used to make another inner layer. When an intermediate layer has been used to form a sleeve, such sleeve is heated to the melting point of one of the metals to cause separation thereof. Thereafter both metals can be returned to the electrodeposition tanks for reuse. By reusing the materials of the mold the value remains substantially constant.

It will be apparent that a relatively simple economical method of making a permanent centrifugal casting mold has been provided in which a mandrel of a desired size and configuration is formed and which can be used repeatedly for making molds of the same size. Since the initial mandrel can be reused, the difficult operation of machining the bore is eliminated and, therefore, a mold can be produced in a much shorter time than is currently possible, and such mold not only will have a longer useful life but the material of the mold can be reused to orm subsequent molds. By using the present method the time between the ordering of the mold and delivery thereof is substantially reduced and, therefore, it is unnecessary for the pipe producing foundry to carry such a large inventory of molds.

lclaim:

l. A method of making a multilayer mold for centrifugally casting elongated generally cylindrical bodies comprising the steps of: machining a mandrel to substantially the same configuration as the exterior of the elongated cylindrical body to be cast, coating said mandrel with a metal having a relatively low melting point, electrodepositing at least one thickness of a low-stress material on said coating to form a first layer, placing said mandrel and said first layer within a form, pouring a molten metal having high heat conduction and radiation qualities into said form and about said first layer to form a second layer in direct engagement with the first layer, permitting said second layer to harden, removing said form, heating said coating of metal having a low melting point to melt the same, and removing said mandrel from said mold.

2. The method of claim l in which said mandrel has a predetermined taper.

3. The method of claim 1 including the additional step of roughening said coating prior to electrodeposition so that the metal being electrodeposi'ted will develop nodular growths which will extend the surface area of the first layer.

4. The method of claim 1 including the step of providing means for firmly fixing said first layer within said form.

5. The method of claim 1 including the additional step of machining the exterior of said second layer to a desired configuration.

6. .The method of claim 5 including the additional step of providing wear-resistant bands on the exterior of said second layer.

7. The method of claim 1 in which the material of said first layer is chosen from nickel, copper and cobalt and the material of said second layer is chosen from aluminum and magnesiurn.

8. The method of making a multilayer mold for centrifugally casting elongated generally cylindrical bodies comprising the steps of: machining a mandrel to substantially the same configuration as the exterior of the elongated cylindrical body, coating said mandrel with a metal having a low melting point, roughening said coating, electrodepositing a substantial thickness of nickel on said coating to form a first layer, said nickel forming nodular growths which extend the total surface area of said first layer, placing said mandrel and said first layer in a form, providing a plurality of spaced attaching means for rigidly mounting said first layer within said form, introducing a metal in molten condition into said form and in direct engagement with said first layer, permitting said molten metal to harden and provide an integral second layer, said second layer being mechanically locked to said first layer by said nodular growths, removing said form, heating said coating of metal having a low melting point to melt the same, and removing said mandrel from said first layer.

9. The method of claim 8 including the additional step of plating the interior of said mold with a layer of metal having a high melting point and a low coefficient of friction.

M). The method of claim 8 including the additional step of electrodepositing an intermediate layer of copper on said first layer.

Claims (10)

1. A method of making a multilayer mold for centrifugally casting elongated generally cylindrical bodies comprising the steps of: machining a mandrel to substantially the same configuration as the exterior of the elongated cylindrical body to be cast, coating said mandrel with a metal having a relatively low melting point, electrodepositing at least one thickness of a low-stress material on said coating to form a first layer, placing said mandrel and said first layer within a form, pouring a molten metal having high heat conduction and radiation qualities into said form and about said first layer to form a second layer in direct engagement with the first layer, permitting said second layer to harden, removing said form, heating said coating of metal having a low melting point to melt the same, and removing said mandrel from said mold.

2. The method of claim 1 in which said mandrel has a predetermined taper.

3. The method of claim 1 including the additional step of roughening said coating prior to electrodeposition so that the metal being electrodeposited will develop nodular growths which will extend the surface area of the first layer.

4. The method of claim 1 including the step of providing means for firmly fixing said first layer within said form.

5. The method of claim 1 including the additional step of machining the exterior of said second layer to a desired configuration.

6. The method of claim 5 including the additional step of providing wear-resistant bands on the exterior of said second layer.

7. The method of claim 1 in which the material of said first layer is chosen from nickel, copper and cobalt and the material of said second layer is chosen from aluminum and magnesium.

8. The method of making a multilayer mold for centrifugally casting elongated generally cylindrical bodies comprising the steps of: machining a mandrel to substantially the same configuration as the exterior of the elongated cylindrical body, coating said mandrel with a metal having a low melting point, roughening said coating, electrodepositing a substantial thickness of nickel on said coating to form a first layer, said nickel forming nodular growths which extend the total surface area of said first layer, placing said mandrel and said first layer in a form, providing a plurality of spaced attaching means for rigidly mounting said first layer within said form, introducing a metal in molten condition into said form and in direct engagement with said first layer, permitting said molten metal to harden and provide an integral second layer, said second layer being mechanically locked to said first layer by said nodular growths, removing said form, heating said coating of metal having a low melting point to melt the same, and removing said mandrel from said first layer.

9. The method of claim 8 including the additional step of plating the interior of said mold with a layer of metal having a high melting point and a low coefficient of friction.

10. The method of claim 8 including the additional step of electrodepositing an intermediate layer of copper on said first layer.

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