US2420851A - Method of making patterns and use thereof - Google Patents

Description

y 20, 1947- E. H. ZAHN :rm. 2,420,851

OF MAKING PATTERNS AND USE THEREOF Filed Julw B. 1943 Patented May 20, 1947 lKETHOD OF MAKING PATTERNS AND USE THEREOF Eric H. Zahn,

Feagin, New York, N.

Laboratories, Inc., New York, N.

tion of New York Pound Ridge, and My Chester Y., asslgnors to Austcnal Y., a corpora- Application July 8, 1943, Serial No. 493,828

Claims. 1

Our present invention relates generally to the casting art, and has particular reference to certain improved procedures to be employed in the production of cast articles having hollow interiors.

While our invention is not necessarily restricted to the casting of any particular type of hollow article. nor to the material of which such casting is to be made. it is primarily useful in the production of cast metallic articles of relatively intricate configuration in which the hollow interior is of irregular shape. especially articles of relatively small size and accurate dimensions. The mechanical arts abound with illustrations of these types of articles. but for the purposes of the present disclosure we have chosen to allude to surgical appliances intended for permanent implantation in the body to reinforce or replace portions of the skeleton structure. As a specific example we have depicted in the accompanying drawings an artificial member designed for surgical attachment to the upper end of the shaft of the human femur or hip-bone to serve as a permanent replacement for the head portion of the bone. Despite the fact that such an article has unique curvatures and certain relatively critical dimensions, and the interior of the article is quite irregular in shape and has numerous "under-cut" portions, the present invention permits items of this irregular character to be produced in finished form. in commercial quantities. by the employment of pure casting procedures. Usually the casting is made of a non-corrodible heat-resistant alloy, such as chromium-cobalt-molybdenum alloy. and is carried out at high temperatures in molds of suitable refractory character.

The ultimate casting need not necessarily be made in a one-piece mold. but the advantages of the present invention and its potential usefulness for a variety of purposes will be best appreciated by describing its applicability to the creation of such molds.

In the formation of a refractory mold of onepiece chari-cter. it is conventional practice to make a pattern of destructible material (such'as wax, for example) which is a replica of the de sired article. This pattern is invested in the mold material and then destroyed (for example, by melting the wax). thereby leaving a corresponding mold cavity in which the ultimate article may be cast. It is among the objects of the present invention to provide an improved method of making a self-sustaining casting pattern composed entirely of destructible pattern material which is a replica of an article having an irregularly M 2 shaped hollow interior. More particularly, the present method is one which permits such dcstructible patterns to be manufactured in commercial quantities by means of casting operations.

By the term "destructible material," as used herein and in the appended claims, we intend to refer generally to the types of materials which are customarily employed for making patterns which are to be invested in mold material and then :iestroyed. Theoretically. there is no known material which is not destructible." but the present use of this term is intended to signify a susceptibility to destruction by relatively simple commercial procedures such as a heat-treatment which either melts the material or burns or volatilizes or otherwise breaks it down. or a treatment with a liquid which has a dissolving or equivalent chemical effect upon the material. Various substances which have this type of "desructibility will be illustratlvely specified hereinafter.

Another object of our invention is to provide an improved method of utilizing a model of the ultimate desired article for the general purpose of making a cored mold, and for the specific purpose of making a cored mold of sectional character in which destructible patterns of the type hercinbeiore referred to may be made.

In accordance with our invention, we first form a core of destructible material conforming in shape and size to the hollow interior of the desired article, and then form the desired pattern around this core, the pattern being composed entirely of differentially destructible material. We then destroy the core to eliminate it from the pattern. By the term "differentially destructible" we allude to the employment of two different materials each of which is destructible by some type of destructive action to which the other is immune. Thus, example. by the destructive action of a solvent in which the pattern material is insoluble. A convenient and preferred procedure involves the formation of the core and the surrounding pattern of waxes or equivalent materials of meltable character, the melting temperature of the core being suiiiciently below the melting temperature of the pattern so that the core elimination may be enected by subjecting it to the lower temperature.

We achieve these general objects and advantages in the manner illustratively exemplified in the accompanying drawings in which:

Figure 1 is a perspective view of a core whose formation is one of the first steps involved in carrying out the present process:

Figure 2 is a diagrammatic cross-sectional view the core elimination may be eifected. for

through a sectional casting mold in which the core of Figure l is employed;

Figure 3 is a cross-sectional view taken substantially along the line 3-4 of Figure 2;

Figure 4 is a cross-sectional view of the intermediate product resulting from the employment of themold ofFigures2and3;

Figure 5 is a cross-sectional view of the destructible pattern which is produced by eliminating the core from the assembly of Figure 4;

Figure 6 is a diagrammatic cross-sectional view through a one-piece refractory mold in which the pattern of Figure 5 has been invested and from which it has thereupon been eliminated; and

Figure 7 is a perspective view of the ultimate article which is cast in the mold of Figure 6.

The article I 0 which we have chosen to illustrate (Figure 7) is a hollow artificial femur head, but it will be understood that this item is merely an illustrative example of a wide variety of different articles which may be produced by the practice of the present invention. It should also be mentioned that the article II as illustrated herein is not intended to be an absolutely accurate representation 01 the surgical appliance, numerous contour and other details having been omitted for the sake of simplicity.

The article III has a substantially cylindrical stem portion Ii merging with an oblique neck I 2 upon which a substantially spherical head II is formed. The stem II is ultimately intended to be secured by any suitable technique of bone surgery to the shaft portion of the femur which is to be re-built, while the rounded head it is intended to establish a pivotal relationship within the corresponding socket of the aoetabulum. At the Junction of the neck I: with the stem p rtion ii there are irregular protuberances (indicated generally by the reference numeral M) which correspond to the eminences normally present on a natural femur (known as trochanters) for muscle-attachment purposes. In the artificial device, these protuberances ll may be provided with loops or the like to facilitate suturing.

For the sake of lightness in weight, the artificial appliance is made substantially hollow as indicated in Figure '7. being in eilect a mere shell of suitable material (such as an alloy of the character hereinbefore mentioned) whose strength. stability, chemical resistance and other properties are adequate for the purpose. The opening in the end of the head It, formed there by virtue of the corresponding eLLension ll (see Figure 1), is sealed up by means of a plug or the like which may be welded into position during the final manui'acturing stages.

In carrying out our invention, we first form a core I! (Figure 1) which conforms in shape and size to the interior cavity within the item II. This core is composed of destructible material, and it is provided with extensions I I at its opposite ends to permit it to be properly positioned within a sectional mold such as that shown in Figures 2 and 3. v

This mold is composed of two or more separable complementary sections (such as the four sections l1 herein illustrated by way of example), these sections being provided with special openings which accommodate the extensions I l, as shown, and provided with a casting cavity I. which conforms in shape and size to the external characteristics of the desired article. The mold is composed of some suitable permanent material, such as metal. and may be of any conventional structural character provided with positioning lugs 4 and the like (not shown) to facilitate the assembly and disassembly of the mold sections. A sprue or sprues are formed in a suitable locality to permit the introduction of the material which is to be cast around the core l5.

Into this mold we introduce a material which is of differential destructibility with respect to the core i5, and the ultimate result is a castin as shown in Figure 4 in which the core 1.5 is embedded. The cast body It is a replica of the item I0, and by now destroying the core I! to eliminate it from the surrounding material a body of the character shown in Figure 5 is produced. This body is identical in shape. size. and contour details with the item I 0, except that it is composed entirely oi destructible pattern material.

This destructible pattern is then invested in mold material 20 (see Figure 6) which may be, for example, of refractory composition. After the mold material has set, the pattern i5 is destroyed and eliminated, thereby leaving a casting cavity ii of corresponding contour and shape. In accomplishing this result, the pattern It is preliminarily associated with a suitable projecting portion or portions of like destructible material so as to form the sprue opening I! in the mold 20. It is through this opening, and such other openings as may be provided for the same purpose. that the material of the pattern It, when destroyed, is allowed to escape. For example, if the pattern is of meltable material, its elimination from the mold 20 would be accomplished by subjecting it to heat and allowing the molten pattern material to flow out through the opening 22.

The opening 22 serves also as a passage-way for the introduction of the ultimate metallic material of which the final casting is to be made. If the casting is to be composed of a chromiumcobalt-molybdenum alloy, for example, the mold 20 is usually predicated to a temperature of about 2000 F., and the molten alloy is usually heated to a temperature of about 2800' F., and is introduced into the mold 20 under pressure. Ultimately, the mold II is destroyed to free the casting which has been formed within it.

In forming the cored mold of Figures 2 and 3, we prefer to employ the following procedure. A solid model is first made either of wood, ivory, metal, or any other desired composition. which conforms in external shape and size to the ex-- ternal characteristics of the desired article. This model has the external appearance, when first formed, of the structure shown in Figure 4 of the present drawings. It is employed in any conventional or suitable manner to form the complementary mold sections i1 and in achieving this result it may be desirable, for example, to employ the procedure described and illustrated in Patent No. 2,308,516. The model is then altered, by carving or whittling it down, or otherwise reducing and changing its shape and possibly adding locating tabs or the like, so that it ultimately appears like the item shown in Figure 1 of the present drawings. Its body portion now conforms in shape and size to the hollow interior of the desired article. This altered model is then utilized in any suitable or desired manner to form another set of separable complementary mold sections (not shown) which are also composed of metal or equivalent permanent material. and in forming these mold section. the procedure illustrated and described in Patent No. 2,806,516 may be employed. if desired. The

model has then iuliilled its functions and m y bedlsposed of.

We then have available two sectional casting molds of permanent character which may be used repeatedly. One of them permits the production oi cores as shown in Figure 1. The other is illustrated in Figures 2 and 3 and is used repeatcdly in the manner herein described to produce pattern-core assemblies as shown in Fisure 4. Obviously, if desired. the mold which forms the core I! may be constructed with a multiplicity of casting cavities so that a plurailty'oi cores may be produced at the same time. The mold of Figures 2 and 3 may also be constructed, if desired, with a series or separate casting cavities, preferably communicating with one another, so that a plurality of destructible patterns may be formed in one operation.

The materials of which the core and pattern are made may be of various types. For example, they may be so chosen as to have difierentlal characteristics of solubility. Thus, the core might be of water-soluble (or water-dispersable) material while the pattern material is insoluble in water. Among the water-soluble or -dispersabls materials of which the core could be composed are certain oi the polyhydric alcohol esters such as di-glycol stearate, di-ethylene-glycol monostearate, glyceryl tartrate, or the like; or certain dehydrated condensed glycols such as the polyglycols; or certain of the polyallrylene oxides (currently available under the name "carbowax"): or acetamide. To any selected one or more oi these materials polyvinyl alcohol might well be added to impart greater strength.

Among other materials of water-soluble character which might be employed to form the core are numerous salts which are very soluble in hot solutions and less soluble in cold solutions, and which are adapted to take up water or crystallisation. For example, salts such as sodium thiosulphate; magnesium chloride, sodium bichromate, and ammonium aluminum sulphate are oi this type and have been found satisfactory in forming strong cores with smooth surfaces. The cores may be i'ormed by crystallization from hot supersaturated solutions of the salts, e. g., by introducing such hot solutions into the core molds and allowing the crystalline hydrate to term as cooling proceeds. Calcium chloride is typical oi another kind of salt which could be used in much the same manner, except that calcium chloride takes up alcohol of crystallization to form a crystalline water-soluble cor material. Accordingly, the use of salts ior the present purpose is not necessarily restricted to water solutions but may involve alcohol solutions as well, or water-alcohol solutions.

with a core 0! this type. susceptible to destruc tion and elimination by subjection to an aqueous treatment, any of a large group of materials, insoluble in or immune to water, might be emlayed for the outer pattern. For example, any or the commonly-employed wax mixtures could be used. such as a mixture of carnauba, candelila, and beeswax, with or without peraflin: or a mixture or the foregoing with polymeriaed terpene: or a mixture or oarnauba, paraiiin. and polybutene. Other possible materials are acrylic resin, or polystyrene resin, or mixtures at these substances with other resins, waxes, or the like. In 'each case. the pattern material is or moldable (i. a, eastable) character, and is destruotible to permit its ultimate elimination from the one- 6 piece mold in which it is to be invested. For example, it wax mixtures are employed, they can be eliminated by the dissolving action 01' a suitable solvent, or by melting them or by other means; and ii acrylic or polystyrene resins or the like are employed, they can be eliminated by the destructive burning or decomposing action oi heat, or by other means.

Most of the foregoing illustratlvely specified pattern materials are not soluble in ethyl alcohol, hence an alternative way oi carrying out the process may reside in using any 0! these materials to form a pattern which is cast around a core composed of a material which will yield to the dissolving action oi ethyl alcohol. Among such alcohol-soluble materials, suitable for the present purpose, might be mentioned sorbitol lactate, sorbitol dl-stearabc, polyvinyl acetate resin, acetamide, or the like.

Another way of providing for the desired diiierential destructibility oi the core and pattern materials is to compose the core of a relatively lowmelting-point substance. For example. it the outer pattern is formed of one or the conventionally-employed wax mixtures it may have a melting point 01' approximately 76 C. In the case of carnauba wax mixtures the melting point might be approximately 83'-86 C. The core might then be composed, for example, oi any of the following illustrative materials:

Yellow beeswax, which melts at 61' (3.,

Cocoa butter, which melts at 3045 C.,

Di-glycol stearate, which melts at 53 C.,

Levulinic acid, which melts at 33' C.,

Bomyl acetate, which melts at 29' C.,

Tetrachloro (l, 2, 3, 4) benzene, which melts at or of any other suitable material having a melting temperature appreciably lower than that oi the pattern material, care being taken, of course. when the pattern material is formed around the core, that the latter is adequately pre-chilled or otherwise guarded against destruction at this stage or the process. Ultimately, the destruction of the core and its consequent elimination from the pattern may then be accomplished by merely subjecting it under controlled conditions (e. g., in a water bath or the like) to the lower temperature.

In each case, a number of types of powdered or ground tillers may be used in either the core matcrial or the pattern material or both. Such fillers might consist, for example, of acrylic or vinyl resins, or simple inorganic or organic compounds and waxes, and it properly chosen they serve to decrease shrinkage of the core or pattern, a the case may be, and help to produce more accurate results.

It will be understood, of course, that the invention is not restricted to the use of the particular materials mentioned merely by way of example, ".0? to the particular modes of core or pattern destruction described. The core may be destroyed and thus eliminated from the pattern by any suitable or desired procedure so long as it leaves the destructlble pattern it let for its contemplated subsequent investment: and the destruction of the pattern to eliminate it from the mold material in which it is invested may similerly be accomplished by any suitable or desired means. The important i'eature oi the invention resides in the proper selection of the destructible materials employed to form the core and pattern, wherebythestepsottheentireprocessmaybe 2,42o,ss1

7 satisfactorily carried out, as described, in a wholly feasible and commercially utillzable manner.

In general it will be understood that the details herein described and illustrated are intended to be merely illustrative in character, and that the present process may be applied to a large variety of different purposes, and may readily be modified in numerous ways by those skilled in the art without departure from the spirit and scope of the invention as expressed in the appended claims,

Having thus described our invention and illustrated its use, what we claim as new and desire to secure by Letters Patent is:

1. A method of making a cast metallic article having a hollow interior, which consists in forming a core of destructible material conforming to said hollow interior, casting differentially destructible material around said core to form a destructible pattern which is a replica of the desired article, destroying the core to eliminate it from said pattern, said core elimination bein effected by subjecting it to a destructive action to which the pattern material is immune, investing the resultant hollow pattern in refractory mold material and then destroying it to eliminate it and thereby leave a corresponding mold cavity in the refractory material, and casting the desired metallic article in said cavity.

2. A method of making a cast metallic article having a hollow interior, which consists in forming a core of destructlble material conforming to said hollow interior, casting differentially destructible wax material around said core to form a destructible wax pattern which is a replica of the desired article, destroying the core to eliminate it from said pattern, said core elimination being affected by subjecting it to a destructive action to which the wax pattern material is immune, investing the resultant hollow wax pattern in refractory mold material and then destroying it to eliminate it and thereby leave a corresponding mold cavity in the refractory material, and casting the desired metallic article in said cavity.

3. A method of making a cast metallic article having a hollow interior, which consists in forming a core of destructible material conforming to said hollow interior, casting differentially destructible material around said core to form a destructible pattern which is a replica of the desired article, destroying the core to eliminate it from said pattern, said core elimination being effected by subjecting it to the destructive action of a solvent in which the pattern material is insoluble, investing the resulting hollow pattern in refractory mold material and then destroying it 8 to eliminate it and thereby leave a corresponding mold cavity in the refractory material, and casting the desired metallic article in said cavity.

4. A method of making a cast metallic article having a hollow interior, which consists in forming a core of destructlble material conforming to said hollow interior, casting differentially destruetible material around said core to form a destructible pattern which is a replica of the desired article, destroying the core to eliminate it from said pattern, said core elimination being effected by subjecting it to a destructive heat treatment to which the pattern material is immune, investing the resultant hollow pattern in refractory mold material and then destroying it to eliminate it and thereby leave a corresponding mold cavity in the refractory material, and casting the desired metallic article in said cavity.

5. A method of making a cast metallic article having a hollow interior, which consists in forming a core of destructible material conforming to said hollow interior, casting differentially destructible material around said core to form a destruotible pattern which is a replica of the desired article. destroying the core to eliminate it from said pattern, said core being composed of a material which melts at a temperature below the melting temperature of the pattern material, and said core elimination being effected by melting it at said lower temperature, investing the resultant hollow pattern in refractory mold material and then destroying it to eliminate it and thereby-leave a corresponding mold cavity in the refractory material, and casting the desired metallic article in said cavity.

- ERIC H. ZAHN.

ROY CHESTER FEAGIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,017,218 Marcus Oct. 15, 1935 1,384,123 Lougheed Jan. 4, 1921 1,421,988 Richards July 4, 1922 1,666,840 Diliman Dec. 22, 1925 1,554,597 Alden Sept. 22, 1925 1,697,438 Wagenhorst Jan. 1, 1929 FOREIGN PATENTS Number Country Date 151 Great Britain 1869

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