US3254379A - Expendable molding shape for precision casting - Google Patents

Description

A. P. POE 3,254,379

EXPENDABLE MOLDING SHAPE FOR PRECISION CASTING June 7, 1966 3 Sheets-Sheet 1 Original Filed Aug. 19, 1960 INVENTOR 144F250 Poe M W ATTORNEYS June 7, 1966 v A. P. POE 3,254,379

EXPENDABLE MOLDING SHAPE FOR PRECISION CASTING Original Filed Aug. 19, 1960 5 She r-s-S'nnet 2 INVENTOR flF/as'a R Pa:

zfojad L 42 ATTORNEYS A. P. POE 3,254,379

EXPENDABLE MOLDING SHAPE FOR PRECISION CASTING June 7, 1966 15 Sheets-Sheet 3 Original Filed Aug. 19, 1960 ATTORNEYS United States Patent This application is a division of my U. S. application Serial No. 50,756, filed August 19, 1960, now Patent No. 3,114,948, dated December 24, 1963.'

This invention relates to the art of precision casting and in particular to precision casting molds and a method of making them.

Following World War H, the application of precision casting to industrial purposes received a great deal of attention because of its success in the wartime production of parts difiicult to fabricate by other methods. While this process of casting, which is also known as the lost wax or investment casting process, has been used for many years in the dental and jewelry field, new techniques and materials were devised to make it applicable to a wide range of metals for the production of precise complicated shapes heretofore not possible by conventional casting procedures.

In the foregoing process, expendable patterns of the desired configuration are produced from waxes or plastics that will melt, vaporize or burn completely without leaving a residue. The patterns are made by the injection of the pattern material into metal dies. The patterns are then removed and assembled as clusters with gates and risers of expendable metal in the form of a tree, with the branches forming branch gates on which the patterns are mounted and the trunk serving as the runner leading from the riser at the base.

After the patterns have been mounted, in one method the tree is dipped or sprayed with a slurry of fine refractory powder and dried. However, depending upon the type of investment used, the patterns need not be coated. The tree with the coated patterns is then attached to a flat plate by molten wax or similar expendable material and a heat-resistant metal flask open at both ends brought down over the tree and also sealed to the plate. The space remaining in the flask is filled with a slurry of refractory material, such as plaster of Paris, as in the case of non-ferrous metals, such as aluminum, copper and their respective alloys. For alloys of higher melting points, silica generally forms the base of the mold and the binding agent is frequently organic silica formed by the hydrolysis of ethyl silicate. Thereafter, the filled molds are subjected to deaeration, either by vibration or by subjecting the slurry to a vacuum.

After the mold has adequately set, the expendable material, e.g. wax, is sometimes first melted out in a lowtemperature oven and the mold later fired at a temperature as high as 2000 F. or the mold with the patterns intact thereafter heated to temperatures as high as 2000 F., depending on the investment material employed, and the expendable material burned or vaporized leaving clean cavities in the mold. After the mold has been due to the decrease of free space of manipulation. The

nature of the process previously and hereafter described required the use of expensive quantities and types of material as well as flask rims in order to provide the necessary mechanical strength, heat sink and resistance to thermal shock.

In addition, time was required in setting up the metal flask around the tree for receiving the investment' Also, because of the mold shape, penetration of the heat was slow and generally 8 to 16 hour heating cycles were required from the time the mold was placed in the furnace to remove the expendable patterns to the time the metal was cast into it. Because the entire runner and gate system of expendable material was bulky and had to be melted out before the patterns and their gates were removed, the mold was likely to crack due to the expansion stresses set up by the runner and sprue, thus adversely afiecting the casting. Moreover, after casting and solidification, care had to be exercised to remove the casting while minimizing damage to the re-usable alloy flask. Furthermore, because ofthe tree-like nature of the runner and gating system, the cast shapes clustered and attached thereto were oriented in so many different directions that degating was rendered difiicult with conventional cut-oif machines, whereby free hand fixed-wheel cutting had to be resorted to which was frequently dangerous.

Until I made my invention, no method was available which eflectively utilized the investment casting process to its fullest economic advantage.

An object of my invention is to provide a novel method of preparing precision casting molds.

Another object is to provide a disposable molding support of substantially planar configuration having associated therewith a runner and gate system adapted to receive in cooperation therewith precision molded expendable patterns of a particular shape preliminary to the preparation of precision casting molds.

The invention also provides as an object a disposable molding shape of substantially planar configuration formed from a web or film of expendable material having molded thereon raised areas and sections conforming to a runner and gate system.

These and other objects will be apparent from the disclosure and the appended claims taken in conjunction with the drawing, wherein:

FIG. 1 is illustrative of a disposable pattern support of substantially planar configuration formed from a film' of plastic material, such' as styrene plastic, showing raised areas conforming to a runner and gate system;

FIG. 2 is a fragmentary section of a pattern support of the type illustrated in FIG. 1 showing in more detail the configuration of the elements making up the runner and gate system;

FIG. 3 depicts another embodiment of a disposable pattern support formed of a film of plastic material having printed thereon the outline of a tree conforming to a runner and gate system;

FIG. 4 shows in partial section the pattern support of FIG. 1 and also indicates partially in dotted lines a rectangular molding frame held on top of the peripheral margin of the support for receiving and confining a molding material in the production of a mold;

FIG. 5 depicts a preferred embodiment of a rectangular pattern support similar to FIG. 1 but in the form of a disposable flask or [tray with a corner thereof broken away to show more clearly the peripheral configuration of the support;

FIG. 5A is a fragmentary representation of a corner of a flask-like support similar to FIG. 5 but showing in combination therewith a reinforcing rim for strengthening the mold produced therefrom;

FIGS. 6A and 6B show in cross section two means of connecting the sprue portion of an expendable pattern to the planar support;

FIG. 7 is a partial representation of the drag portion of the precision casting mold produced from the disposable support of either FIG. 4 or FIGS. 8 and 8A are illustrative of a completed precision casting mold comprising a heat resistant ceramic or glass plate as the cope in contact with the surface of the drag portion of the mold in which the drag portion may be reinforced with a metal rim;

FIG. 9 depicts the final casting, including the runner and gate system, produced from the mold of the type shown in FIG. 8;

FIG. shows another embodiment of a disposable support of substantially planar configuration in the form of a disc having molded therein radially extending runners attached to a central sprue adapted for the production of precision centrifugal casting molds of the type shown in FIG. 11;

FIGS. 11 and 12 depict a composite centrifugal casting mold comprising a cope portion and a drag portion provided by the invention; and

FIG. 13 shows the cope portion of a rectangular mold in which the runner and gate system is permanently formed and adapted to conform with a disposable flat support of the type shown in FIG. 3.

As a preferred embodiment of my invention, I fabricate a precision casting mold by first forming a thin disposable support of substantially planar configuration simulating a tree adapted to receive precision molded expendable patterns. The tree outline is made to simulate a central gate runner extending from a sprue with branch gates projecting transversely therefrom in substantially the same plane. A plurality of expendable precision molded patterns are provided, each having a gate stem by means of which the patterns are mounted in spacial relationship along the branch gates, the points of contact between the gate stem and the branch gates lying substantially in the same plane.

The somewhat planar arrangement of the patterns greatly facilitates the production of the mold. By confining the pattern support peripherally, the slurry of molding material can be poured easily on to the support, deaerated by vibration or by vacuum and then allowed to set or cure about the patterns and the expendable material -thereafter destructively removed by combustion. The resulting precision casting mold has a flat configuration compared to the more conventional precision casting mold and it is'this mold configuration which lends itself readily to large scale and efficient production techniques. Because of this configuration, a rapid expulsion of the expendable material is possible in a very short time without adversely affecting the mold structure.

In carrying my invention into practice, I prefer to use a preformed styrene film or sheet as the pattern support material. In one embodiment, the preform may take the rectangular configuration shown in FIG. 1. The support may be vacuum formed into a female mold or over a male die which incorporates a runner and gate system of the type shown in FIG. 1, which shows a styrene support 1 so produced comprising central runner 2 with branch gates 3 projecting transversely therefrom in substantially the same plane as the styrene film or sheet, runner 2 beginning at the molded-in convex portion 4 and terminating at 5. Convex portion 4 provides the feeder well or sprue to runner 2 in the mold producedfrom the preform. If desired, indexing means may be provided near the four corners of the pattern support so as to produce indexing means in the drag portion of the precision casting mold to cooperate with indexing means in the cope portion of the mold. It will be appreciated that the pattern support may be employed in producing the cope portion of the mold.

In other words, the invention may be applied in the production of either the cope or the drag portions of the mold.

The shell-like preform must be strong enough to support expendable patterns and be smooth and flat enough on the parting face of the investment so that the mold thus produced, whether cope or drag, will make a tight enough seal with the corresponding drag or cope portion of the mold or with the surface of another similar mold in instances where molds are stacked together of gang pouring of metal.

A feature of this preform is that a runner and gating system can be easily simulated by having molded or formed in it raised areas and sections such as 2 and 3 in FIGS. 1 and 2, which will produce in the reverse similar depressions in the face of the investment cast against it, thereby providing channels and risers for the metal to flow to the casting cavity.

The gates formed in the plastic sheet may be punched with holes to receive the gate stems provided on each wax or plastic expendable pattern. This is shown in FIG. 4 which depicts in partial section the preform pat tern support 1 with pattern 7 (shown in more detail in FIG. 2) plugged into holes 8 via gate stem 6 arranged along branch gates 3. The preform support of FIG. 4 is shown relative to a molding frame 9, phantomly indicated in dotted line, positioned on the peripheral margin of the preform and adapted for receiving the molding material.

The mounting of the pattern on the support is illustrated in cross section in FIGS. 6A and 6B, FIG. 6A shows stem portion 10 of the pattern fitted into hole 8 in branch gate 3 via reduced end portion 11 of the sprue. Or the pattern may be Welded or bonded to the gate as in FIG. 6B which shows stem-portion 12 of a wax pattern which is caused to melt superficially by heating its end on a hot plate or by other suitable means and then bonded to gate 3 at its end and by excess wax at 13 as shown. This is also in FIG. 2. This latter means of bonding would have particular use where a flat pattern support of expendable material is used such as shown in FIG. 3. Instead of indicating the runner and gate system as raised areas as shown in FIG. 1, the outline may be printed as shown in dotted line wherein 14 simulates the runner and 15 the branch gates. As stated hereinbefore, indexing means may be provided to insure matching of the cope and the drag elements of the precision casting mold.

. Where the thin support of FIG. 3 is utilized, then the cope element of the mold should make allowances for the feed-in runner provided for the pattern. The cope configuration of the type shown in FIG. 13 would be used in which runner 14 and branch gates 15 indented therein would be designed to coincide with those of FIG. 3. By placing the cope on top of the drag mold with the runner and gate side of the cope in contact with the mold surface in register with the spaced cavities of the drag mold, metal poured through sprue hole 17 will flow along the runner and the gates into the cavities of the mold.

In preparing the preform from expendable sheet material, I prefer for production convenience to produce it in the shape of a tray or flask 18 with side walls 19, 20, 21 and 22 shown in FIG. 5, the bottom of the tray having the same configuration as that shown in FIG. 1, that is having molded therein raised areas and sections simulating a runner and gate system of a tree. In effect, the tray of FIG. 5 becomes an expendable tray for confining the molding material therein. The tray for production purposes, is peripherially indented at the bottom at 23 as shown in FIG. 5 so as to provide internally thereof a peripheral shelf 23a. The peripheral indent enables the trays to be nested one on top of the other with mounted patterns therein ready for use. As shown in FIG. 5A, the peripheral shelf 23a is adapted to receive a metal retaining ring 23b, if desired, to become part of and reinforce the mold produced from the tray.

An important feature of the foregoing embodiment is that the disposable flask or pattern support starts its useful life as a tray to receive the freshly made expendable patterns immediately after removal from the injection mold. In the pattern room the patterns are mounted within the tray (as in FIG. 4) which later becomes the mold flask. As they are required, the pattern-filled trays are then transported to the molding line. Here each tray is placed on a smooth flat sup-porting surface. As the flask passes along the molding line it is filled with automatically measured and mixed molding plaster. The Weight of the plaster mixture causes the bottom of the thin plastic flask to conform to the smooth flat supporting surface. The flask is then covered and agitated mechanically to deaerate the mixture. The flask then passes to a setting station. After initial setting (chemical) is complete, the mold is set aside for the 'burnout treatment. Where a molding frame such as shown in FIG. 4 is used, the set mold is extracted therefrom by a vacuum extractor head or removed by gently-rapping, the mold frame being provided with a slight draft to effect release.

The set mold is placed on a grid at the receiving end of a firing oven. As soon as the cnveyor carries the mold to an area of sufficiently high temperature in the oven, the plastic pattern support ignites and is completely .consumed. Because the pattern support is thin, the mold is not subjected to any amount of expansion stresses of the support which normally cause stress cracking of the mold. The mold continues to dry and purge itself of the expendable patterns it contains.

After the burn-out is complete, the drag element or cope of the plaster mold will have the configuration shown partially in FIG. 7 comprising feeder well or sprue 24, runner 25 and branch gates 26. The precision molded cavities 27 project inward from the branch gates as shown.

In preparing the mold for casting, a composite is formed as 'shown in FIGS. 8 and 8A comprising drag element 28 with cope element 29 formed of a plate of heat and shock resistant insulating material, such as ceramic, fused silica foam, fused silica glass known by the trademark Pyroceram and other similar heat and shock resistant insulating material. Cope 29 is provided with an opening which registers with the well in the drag, e.g. well 24 in FIG. 7. It is adapted to receive ceramic sleeve 30 or other sprue material through which the metal is poured. line 861-80, after casting metal in the mold, runner 31 is shown of the metal cast with branch-gates 32 extending therefrom and the precision metal castings 33 connected therealong. The mold is also shown provided with a metal rim 34 for use where the mold is employed in the casting of high melting alloys, e.g. alloy steels or heat resistant alloys in which heat shock at above 2000 F. might present a problem.

The precision casting cluster produced from the mold of the type shown in FIG. 8 is shown in FIG. 9 as com: prising sprue 35, runner 36, branch gates 37 and the desired precision cast articles 38 projecting from the gates. It will be noted that except for the sprue, the runner, branch gates and the individual castings form a simple geometry in that they all lie substantially in the same plane.

One of the advantages of using a precision casting mold substantially of flat or thin configuration is its adaptability to gang pouring. Instead of having a Well 24 as shown in FIG. 7, the well may take the form of a In the cross-section taken along the most mold element would have a blind sprue hole similar to wall 24 of FIG. 7. By this means a number of thin mold elements, such containing a single plane of cavities, would be stacked, weighted or clamped, and poured economically. After pouring and cooling the stack mold would be moved to the break-out station. Here the mold sprue or riser would be out through at each asbestos separator. The stack would then be reduced to its single plane elements (as in FIG. 9) for quick and easy break out and casting cut-off. From here the castings would be processed the same as conventional plaster mold or in vestment castings.

The invention is also applicable to the production of centrifugal precision casting molds; In this case the disposable preform pattern support (e.g. of styrene sheet) would be produced as a circular disc 39 depicted at FIG. 10 with a convex portion 40 located centrally thereon for molding in reverse a well 40a (FIG. 12) with feeding branch gates 41 extending radially therefrom to which the expendable patterns would be connected in the manner previously described herein. As in the case of the preform shown in FIG. 1, the circular preform would be supported within a molding tray such as 9 shown in FIG. 4 except the tray would have a circular rim adapted to lie on top of the peripheral margin of preform 39. The drag or cope mold element produced therefrom would then be combined with a circular cope or drag, whatever the case may be, having a sprue hole located centrally therein in register with wall 40a of the drag element. Such a mold combination is shown in FIG. 11 as comprising in'this instance cope 42 of a plate of heat and shock resistant insulating material, e.g. fused silica foam, on top of and in register with drag element 43, the cope having associated with its sprue hole sleeve element 44 into which molten metal would be poured.

Other details of the moldof FIG. 11 are indicated in the partial cross section of FIG. 12 which shows cope 42 with sleeve 44 extending into it in register with well 40a in drag mold element 43. One of the gates 41 is shown' cast against the rim in situ.

As has been stated hereinbefore, the invention is particularly adapted to automatic or semi-automatic molding techniques based on the use of calcium sulphate plasters or other similar molding materials used for non-ferrous castingsf On the other hand, ferrous castings present problems because of the high fusion temperatures of the ferrous alloys and require the use of mold materials that retain chemical stability at elevated temperatures. Molds for ferrous investment castings are usually based on silica in some form. Silica is a stable, cheap and plentiful refractory material. However, to use silica in its common form, natural or crushed sand, requires the use of bonding agents which are not cheap. However, excellent refractory molds may be made from silica without binder additions provided: (1) that the silica be crushed to a particle size range and to a particle configuration that will allow intimate particle interlock, and (2) that the silica is dispersed in a liquid which will allow the particle interlock to develop slowly by the process of sedimentation. The first condition is met by crushing high quality white silica to a particle size encompassing approximately to 300 mesh sizes. The liquid requirement is met with water modified by the addition of a small quantity of vitreous sodium phosphate to reduce the rate of particle fallout to that'which allows such sedimentation to occur. Unfortunately, the proper rate of solids sedimentation is slow. A conventional investment casting' tion, another 24 hours of air drying is required before the mold can be placed in the burnout furnace. It is evident that to utilize this material a considerable number of expensive flasks would be required if a reasonable daily casting volume is desired. The disadvantages which attach to the use of this molding system in investment casting are these: (a) the lack of chemical setting creates a storage problem, (b) the necessity for decantation makes necessary extensive flask preparation in the form of waterproof flask extension liners, and (c) the relatively high thermal conductivity of pure silica causes rapid heat penetration which in turn causes wax expansion to occur before the gating system can cope with wax drainage. This condition gives rise to serious cavity cracking with heavy casting losses. Thus, even though this mold material is initially cheap and is capable of producing excellent cast surfaces, the material is not a particularly desirable one for conventional investment casting processing. The preformed disposable flask support of the type shown in FIG. obviates for the most part the disadvantages enumerated in that (a) while the storage problem during settling is still present, it does not tie up expensive alloy flasks; (b) no preparation of flasks is required; and (c) the mold morphology and open gate and runner system tend to minimize the cracking tendency. The use of the sedimentation system is then highly compatible with the features of the invention and makes possible lower production cost and higher quality castings in the ferrous alloys as simple as those in the non-ferrous groups.

In order to better appreciate the invention, the following example is given:

EXAMPLE 1 In producing a precision cast chuck for us as an element in canning machinery indicated by the numeral 7 in FIG. 2 from a beryllium-copper alloy, a disposable support of the type shown in FIG. 1 was vacuum formed from a thin polystyrene sheet onto a metal male mold to produce a runner and gate system of the type illustrated. A plurality of expend-able patterns of the shape 7 shown in FIG. 2 were injection molded in accordance with conventional practice, each of the patterns having a cylindrical gate stem 6. The patterns were then cemented by means of a cement consisting of a solvent and a polystyrene material and the patterns mounted thereon similarly to the illustration shown in FIG. 2. The support and the mounted patterns were surrounded by a molding frame like frame 9 in FIG. 4. A plaster mix comprising calcium sulfate, asbestos fiber, an accelerator and silica and water was then prepared and poured into the molding frame and allowed to stand until the plaster had set, for example 8 to 15 minute's.

The set mold was removed from the molding frame by slightly tapping the frame to dislodge it and the mold then placed cavity side down in the burn-out oven and the temperature raised to approximately 1400 F. in about the first one-third of the heating cycle. The heating cycle was completed in the short time of three hours and the mold removed and sent to the casting station. The mold may be cooled down or' used hot, depending on the casting shape and the alloy.

A cope comprising a plate of cellular glass (known in the trade as Foamglas) is applied to the mold by clamping it hydraulically and an asbestos sleeve inserted into the sprue hole of the cope (as in FIG. 8) for receiving the molten beryllium copper alloy. Sufficient of the alloy which was melted down in a crucible furnace was poured into the sleeve until the metal filled the sprue. After the metal solidified, the cope was removed and the drag portion of the mold broken away from the casting which appeared like that shown in FIG. 9 except that the castings had the shape shown by the element 7 of FIG. 2. The castings which were distributed in the same plane were easily removed by a cut-off machine. Inspection 8 showed the castings to be of high quality, the internal bores being particularly smooth and precise.

While it is preferred to make disposable pattern supports from thin plastic sheets (e.g. polystyrene), it will be appreciated that other disposable material may be employed, such as low ash paper of suflicient stiffness to support the patterns. The paper pattern support may be waxed to render it hydrophobic or otherwise treated so it does not soften and collapse when in contact with a wet molding mixture. Or the disposable pattern support might constitute a very low melting eutectic alloy such as Woods metal or similar alloy. An example of such an alloy is one containing 52% Bi, 32% Pb and 16% Sn which melts at C., i.e. below the boiling point of water. A pattern support made of such an alloy would be disposed of or removed by low temperature heating, for example, heating on a hot plate and the mold with the patterns thereafter subjected to burn-out in a furnace in the usual manner.

In the case of a styrene or wax support and patterns, besides removing the expendable materials by heat, they may be removed chemically by solution in methyl ethyl ketone, trichloroethylene or other suitable organic solvent. Whichever method is used, the expendable material is deemed to be destructively removed whether it be removed by combustion at elevated temperatures, by melting, by means of a solvent, or by any other means that does not adversely affect the mold structure.

Preferably, the disposable pattern support is preformed to include raised areas which simulate a runner and gate system in the form of a tree. However, in the preformed state, the pattern support and the tree are substantially planar in configuration, although in the reverse the support provides a feeder gate system for feeding metal to the precision-formed cavities. Broadly, the tree by itself may constitute the support or be associated with the pattern support in other ways. For example, as shown in FIG. 3, it may be printed in outline form on the flat support sheet, the tree outline conforming substantially to an actual runner and gate system in the cope portion of the mold so that when expendable patterns are mounted on the support, the cavities formed therefrom will be opposite and in cooperative relationship with the runner and gate system in the cope. Altematively, a template may be used in arranging the patterns on the first support in tree- :like distribution, the template conforming to the runner and gate system on the cope. Thus, in speaking of a pattern .support having associated therewith a tree for locating expendable patterns thereon, it is meant to include the foregoing methods and other methods which will effect the desired result.

The expendable patterns attached to the support may be made from plastics such as styrene or nylon, rigid polyethylene and the like, or from waxes. Examples of waxes which have been found particularly useful are those of the proprietary synthetic types of high surface tension.

While the cope portion of the mold is preferably made from heat and shock resistant silica glass, other types of insulating materials may be used, such as glass foam plate, alumina plate and asbestos.

The investment employed in making the mold may comprise any of the compositions used heretofore in investment mold casting, such as calcium sulfate bonded materials for non-ferrous alloys, certain phosphate bonded materials for ferrous and non-ferrous alloys, and silicate bonded materials also for ferrous and non ferrous alloys.

My invention is applicable generally to castable ferrous and non-ferrous alloys.

It is apparent from the description that the invention provides many advantages over the invest-ment casting techniques heretofore employed. By using disposable pattern supports of the flask type shown in FIG. 5, i.e. with peripheral side walls for containing and confining the mold material, the low cost makes possible the use of investments requiring longer curing times. Since no flasks would be tied up in the process, once the process of mold preparation gets underway, high cost saving will result. Because the disposable flask-like pattern support will be thin and very light, mold weight is maintained at a minimum. Thus, the flask type support shown in FIG. provides low cost because of its inexpensiveness, because of the type and amount of materials required for the support and because of its method of manufacture.

Generally speaking, the advantages include the marked reduction in time of mold preparation including burn-out time (reduced more than one third), the applicability of automatic techniques for mold preparation, the applicability of the thin molds to gang pouring, etc. Since there is no flask to salvage and return to the system, mold breakout can be rapid since the mold is in effect a laminated composite, i.e., cope and drag, wherein the drag is separated from the cope and broken away from the casting. Moreover, since the castings in the drag mold lie in approximately the same plane, degating is greatly simplified by using a simple series of straight cut-off wheel strokes. As stated hereinbefore, this simple geometry lends itself to the safe chop-stroke type of abrasive cutting with much greater safety to the operator.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

What is claimed is:

1. An expendable molding shape for use in the preparaconforming substantially to the plane of the sheet, anda plurality of expendable precision molded patterns each having a stem, each of said patterns being mounted at the terminus of its stem to said raised areas defined by said gates, said patterns extending outwardly from said raised areas, the points of contact between the stems of the patterns and the raised areas lying substantially in the same plane.

2. The expendable molding shape of claim 1, wherein the expendable material is a sheet of plastic.

3. The expendable molding shape of claim 2, wherein the periphery of the molding shape has a retaining rim integral therewith of said expendable material.

References Cited by the Examiner UNITED STATES PATENTS 535,510 3/1895 Schwan 22162 1,349,829 8/ 1920 Gibson 22158 1,626,224 4/1927 Campbell 22158 1,744,571 1/1930 Papazian. 1,752,040 3/ 1930 Travt. 2,461,416 2/1949 Erdle et al. 22158 2,513,212 6/1950 Saives 2297 J. SPENCER OVERHOLSER, Primary Examiner.

M. U. LYONS, Examiner.

R. D. BALDWIN, Assistant Examiner.

Claims (1)

1. AN EXPENDABLE MOLDING SHAPE FOR USE IN THE PREPARATION OF A PRECISION CASTING MOLD WHICH COMPRISES, A PATTERN SUPPORT COMPRISING A SHEET OF EXPENDABLE MATERIAL HAVING FORMED AS RAISED AREAS THEREON AN OUTLINE OF A TREE SIMULATING A RUNNER AND A SYSTEM OF GATES CONFORMING SUBSTANTIALLY TO THE PLANE OF THE SHEET, AND A PLURALITY OF EXPENDABLE PRECISION MOLDED PATTERNS EACH HAVING A STEM, EACH OF SAID PATTERNS BEING MOUNTED AT THE TERMINUS OF ITS STEM TO SAID RAISED AREAS DEFINED BY SAID GATES, SAID PATTERNS EXTENDING OUTWARDLY FROM SAID RAISED AREAS, THE POINTS OF CONTACT BETWEEN THE STEMS OF THE PATTERNS AND THE RAISED AREAS LYING SUBSTANTIALLY IN THE SAME PLANE.

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