US3526266A - Mold for the casting of metals - Google Patents

Description

Sept. 1, 1970 T. E. SNELLING 3,526,266

MOLD FOR THE CASTING OF METALS Original Filed July 13, 1965 2 Sheets-Sheet 1 THOMAS E. SNELL/N6 14 News Sept, 1, 1970 T. E. SNELLING MOLD FOR THE CASTING OF METALS Original Filed July 13, 1965 2 Sheets-Sheet 8 640 v 6. w ...n.

INVENTOQ. TIMOIJS BSA/ElL/NG United States Patent Ofiice 3,526,266 Patented Sept. 1, 1970 3,526,266 MOLD FOR THE CASTING F METALS Thomas E. Snelling, Rte. 2, Box 792, Boring, Oreg. 97009 Original application July 13, 1965, Ser. No. 471,679, now Patent No. 3,374,824. Divided and this application Mar. 13, 1968, Ser. No. 726,631

Int. Cl. B22c 9/04 US. Cl. 164349 Claims ABSTRACT OF THE DISCLOSURE A combination is provided of a sand mold and a pattern of porous plastic material thermally capable of forming vapor without substantially leaving a residue confined within a body of sand, the porous pattern having an entry portion adapted for receiving molten metal, the entry portion communicating with a hollow portion of the pattern that extends to one end of the pattern confined within the body of sand.

This is a division of application Ser. No. 471,679, filed July 13, 1965, now Pat. No. 3,374,824.

This invention relates to a method for casting metal shapes and, in particular, to a displacement method for casting molten metal. The invention also relates to molds therefor.

In recent years a new molding technique has been proposed by means of which metal shapes may be produced by utilizing patterns or forms of porous combustible material, e.g., foamed polystyrene, which are embedded or confined in sand and molten metal then poured via a sprue into the mold whereby the hot metal contacts the confined pattern or form, causes the porous material to combust and/or vaporize and be replaced by the metal which assumes substantially the configuration of the previously embedded form.

A patent covering this technique was awarded to Harold F. Shroyer (US. Pat. No. 2,830,343 granted Apr. 15, 1958) on A Cavityless Casting Mold and Method of Making Same. The process disclosed uses a pattern made of cellular material, such as expanded polystyrene, which is molded in a rammed green sand mold. Sodium silicate-bonded sand hardened by carbon dioxide injection may be employed or other sand molding techniques conventional in the art. After the pattern is embedded, a cope is provided having a multiplicity of vents therein, together with gate and riser means, which cope is placed in contact with the previously prepared mold with the gate disposed relative to the pattern, so that metal poured into the gate flows into the pattern and displaces it as the pattern material burns or vaporizes.

A development further to the Shroyer technique is described in US. Pat. No. 3,157,824 granted to Thomas R. Sm th on Nov. 24, 1964. The Smith process has as its aim to simplify molding practice by utilizing a simple container having bottom and side walls of a size sufficient to receive the combustible pattern and a suflicient volume of dry free-flowing sand to surround and support the pattern without using the conventional and often complicated flask equipment. According to the Smith patent, the combustible pattern is inserted in the aforementioned container with clean, unbonded sand poured about it and into all of the recesses and cavities of the pattern. Suitable risers and gates may be included with the pattern, the risers or gates being made of either combustible or non-combustible materials. The purpose of the unbonded sand is to provide a myriad of interstitial passageways to enable entrapped air and vapors of the combustible pattern to diffuse through the surrounding sand and out into the atmosphere. While the foregoing appeared to be an improvement over the bonded sand technique, it did not take care of all the problems pre sented by the cavityless technique of casting metals.

For example, it has been noted that as to some of the metals, such as aluminum, magnesium and alloys thereof, it was generally difiicult to obtain complete penetration of the molten metal throughout the pattern, so that in some instances, at distant points from the point of entry of the molten metal, some of the pattern material was not always displaced or burned away. The general indication was that as molten metal contacted the solid porous pat tern during gravity flow into the mold, some of the heat content of the moving front of metal would be dissipated in transit during the initial burning and/ or vaporization of the pattern material, whereby the moving front of molten metal would drop in temperature sufiiciently to cause at least partial solidification of the front before reaching the extremities of the pattern.

This was particularly the case in large castings, especially casting having somewhat irregularly shaped crosssections as generally exists in statuaries of modern de sign.

It is thus the object of my invention to provide an improved method for casting molten metals utilizing a sand-molded pattern of fugitive material, which pattern is adapted to be displaced completely by hot molten metal, whereby the resulting casting is substantially an exact replica of the pattern.

Another object is to provide the combination of a sand mold and a pattern of fugitive material embedded therein, the pattern being adapted to be completely displaced by molten metal.

These and other objects will more clearly appear when taken in conjunction with the following disclosure and the accompanying drawings, wherein:

FIGS. 1A to 1D shows progressively one method of casting molten metal using my invention concept;

FIG. 2 is illustrative of a mold containing a plastic tree-like form with the gate of the tree serving as the means for feeding metal into laterally extending patterns;

FIGS. 3 and 4 are illustrative of casting techniques using a pattern of fugitive material in which the resulting castings are incomplete;

FIGS. 5 and 6 are illustrative of a casting method provided by the invention as applied to fairly large castings of irregular shapes; and

' FIGS. 7 to 9 are illustrative of a method for producing hollow metal castings.

Stating it broadly, the invention comprises providing a form of desired shape of porous material combustible Without leaving a residue such as foam polystyrene or foam polyurethane plastic, the form having an entry portion which communicates with a hollow portion that extends to one end remote therefrom; confining the form in a sand mold with the entry portion of the form adapted at the surface of the mold to receive molten metal; pouring molten metal via the entry portion into the hollow of said form whereby to establish immediately a reservoir of hot metal within the combustible form remote from the entry portion; and continuing the pouring of said metal to fill up said hollow, while the molten metal vaporizes and replaces the embedded form from within as the metal rises to the entry portion at the surface of the mold.

In other words, by constructing the pattern or the form with a passage way within it by which the molten metal can be made to fall unhindered to the bottom of the pattern or form without substantially losing any heat during its travel to the bottom, the molten metal accumulates as a reservoir and displaces the foam plastic at the bottom,

while new hot metal continues to be poured into the pattern or form to displace additional foam material from the bottom to the top of the mold. FIGS. 1A to 1D which illustrate the casting of a simple shape, such as a cylinder, show progressively what happens during the casting of the metal. Referring to FIG. 1A, a hollow cylindrical pattern is shown embedded in a loose dry pack of sand 11, the cylinder having a substantially centrally located passageway 12 having an entry portion 13 at or near the surface of the mold, the passageway extending to the bottom of the pattern.

A steady stream of hot metal 14 is poured as shown in FIG. 1A which metal immediately passes unhindered to the bottom of the mold without substantially losing its heat and starts to displace the foam plastic material from the bottom up. As the reservoir of hot metal rises as shown in FIG. IE, it is continually being added to by new hot metal so that vaporization of the foam plastic continues unhindered further up the pattern as shown in FIGS. 1C and 1D. In this way all parts of the cavity formed by the pattern is efiiciently filled with metal which assumes the exact shape of the resulting object being cast.

In effect, this technique is akin to the bottom pour method of casting metal but differs in calling for the requirements shown in FIGS. 1A to 1D, in that the previous techniques did not work too successfully for light metals, such as aluminum, in instances where solid form plastic patterns were employed as shown in FIG. 3. There a foam plastic pattern 15 is shown completely embedded in sand 16 and connected at its bottom to a hollow gate 17 and runner 18. As metal is poured into the gate to the bottom of the mold, it contacts the pattern at 19 and begins to vaporize the plastic material in front of it. As will be appreciated, the moving front of molten -:metal loses heat which is abstracted by virtue of the relatively high heat of vaporation of the plastic material. As the metal displaces the plastic, the vapor diffuses through the forms and out to the atmosphere. As the metal rises to the top of the mold, it is cooled to such an extent that it fails to fill out the toe of the casting completely as shown by the frozen front of metal 20'. The same thing occurs in the case of the simple downward flow of metal shown in FIG. 4. Since the moving front of metal 21 must penetrate the complete cross-section of the porous plastic material during its downward course, the front is subjected to considerable cooling so that it fails to fill out the toe of the casting completely as shown by the frozen front of metal 22 and the unconsumed portion of pattern 23.

It is apparent that by using a pattern having a hollow portion to receive molten metal as shown in FIGS. 1A to ID, a cast article of good fidelity is obtainable by utilizing the process of the invention. As stated hereinbefore, the foregoing technique is particularly applicable to the casting of light metals such as aluminum, magnesium and alloys thereof which, because of their low specific gravity, have inadequate penetrating power to displace the plastic pattern completely. However, I find the invention applicable to even the denser metals, such as copper and copper-base alloys, iron and iron-base alloys, nickel and nickel-base alloys and the like, particularly in the production of castings having intricate surface designs. Since it is important that the molten metal be fluid in order to insure high fidelity in the final casting, my method insures delivery of hot fluid metal to the extremities of the pattern before substantial cooling of the metal occurs.

In utilizing the invention in producing a plurality of castings having the same canfiguration, the embodiment illustrated in FIG. 2 may be employed. There a hollow foam passageway 25 is shown having a plurality of molded shapes 26 laterally attached to the hollow gate or passageway. It will be noted that as the reservoir of hot metal 27 rises and displaces the foam plastic of the hollow gate and penetrates each of the molded shapes, fresh hot metal is continually being fed at each level so that reproducible castings, such as hardware parts, e.g., brass valves, valve handles, fittings, and the like, are obtained.

I find that my invention is particularly advantageous in the production of large castings having an irregular cross-section requiring the handling of a large mass of molten metal. Normally, in casting large shapes utilizing a solid foam pattern of fugitive material, because of the large mass of molten metal involved, erosion of the pattern adjacent the sand interface may occur prematurely as the molten metal penetrates downwardly into the pattern. In addition, in its downward course, the metal is also being subjected to substantial cooling. I find that with my invention I can substantially avoid this problem by designing the passageway entering the pattern so that it broadens and increases in volume as it approaches the bottom of the mold.

As illustrative of the foregoing, reference is made to FIG. 5, which is representative of a composite mold for casting a large irregularly shaped object, for example a modern piece of sculpture. A plastic pattern or form 28 is shown of irregular shape supported in position by sand packed around it, the pattern having associated therewith an entry portion 29 which leads into a hollow portion 30 which increases in volume as it projects toward the bottom of the pattern. The pattern is recessed at 31 and has inwardly projecting shoulders at 32, 33, 34 etc., and an extending portion 35, all of which must be reproduced with the desired fidelity. As the stream of molten metal 36 is poured through the entry portion 29, it immediately flows to the bottom of the pattern and forms a hot reservoir of molten metal 37 which rises upwardly and gradually displaces the foam plastic material which vaporizes and diffuses through the interstices of the sand.

In instances Where a large passage or hollow is desirable in the pattern employed in the production of certain castings, the passage is first machined and the opening then plugged with a similar disposible material to prevent sand from penetrating the cavity. FIG. 6 shows such a pattern 38 having the shape of an owl embedded in the inverted position in sand. As will be noted, the pattern has a large hollow or passage 39 which extends from below the entry portion or gate 40 to the head 41 of the owl. A plug 42 of foam plastic is provided to close ofi the opening at the foot of the owl-shaped pattern. Openings 43 and 44 are provided in the head corresponding to the eyes, the openings being occupied by sand when the pattern is embedded as shown. When molten metal is poured in the gate or entry portion 40, the plug 42 is burned away, thus allowing the molten metal to flow immediately into the hollow of the pattern and gradually displace it as the hot reservoir of metal arises to the top of the pattern.

An advantageous feature of the invention is the application of the novel technique in the production of hollow intricate castings of the type shown in FIG. 7. The cross-section there shown may comprise hollow rectangular segments joined together to form the configuration illustrated; The shape may be produced by joining together rectangular slabs of foam plastic material using conventional plastic adhesives, such as epoxy resins, or the like, as the cementing means. Before the last slab is cemented in place, the hollow 46 of the pattern is filled with sand 47 and the pattern then assembled with hollow gate and riser means 48, 49, respectively, of foam plastic material, the gate 48 being connected to the pattern at several levels via runners 50, 51 and 52, and the riser 49 likewise connected to the pattern via runners 53, 54 and 55. The gate and riser are connected together via a hollow bridge 56 of foam plastic so that metal 57 poured into gate 48 immediately flows via the bridge to hollow riser 49 whereby to create a reservoir of hot metal 58 which rises in both the gate and the riser to displace by vaporization the foam plastic material and feed fresh molten metal to the pattern via the runners as shown. In order to illustrate clearly the fiow paths of metal to the various parts'of the pattern, the cross-section of the various elements -of the pattern has been left unshaded. After the casting has solidified, the runners are cut away and removed with the gate and riser system. A hole is drilled into the hollow casting, the sand removed therefrom and the hole, if desired, thereafter plugged and finished to conform to the surface of the casting.

Other types of hollow bodies which may be produced in accordance with the invention are shown in FIGS. 8 and 9. In FIG. 8, a cross-section of a polyhedron is shown embedded in a sand mold, the polyhedron being similarly constructed from shaped slabs of foam plastic which are attached together by a plastic adhesive-The cavity of the polyhedron, however, is filled with coated sand, for example, with sand coated with a curable phenolic resin. The pattern 60 with the contained coated sand is embedded in the mold as shown and has an entry portion or gate 61 associated with the top thereof through which metal is poured. As the molten metal displaces and vaporizes the foam plastic portions of the pattern, heat is transferred to the interior of the casting causing the phenolic coating to cure and fuse together the coated particles which are retained within the casting as a part thereof. FIG. 9 shows the production of a hollow conical shape, with the hollow thereof filled with dry sand. A filling cup 62 is employed as a basin to contain hot metal fed to it, which hot metal flows through gates 63, 64 and thence into the pattern as shown which is displaced by the molten metal. After the casting has solidified, the sprues formed by gates 63, 64 are cut away and holes drilled in the space formerly occupied by the sprues for the purpose of removing the dry sand from the mold.

As has been stated hereinbefore, I have found the above-mentioned improvements particularly advantageous in the casting of shapes from aluminum, magnesium and alloys thereof. Because of the low density of such metals and alloys and the generally lower pouring temperatures occasioned by the use of such metals, difliculties are presented in the casting of items where there is a high ratio of surface area to weight due to the rapidity with which the metal is cooled down in the mold. Thus, the invention provides means by which molds containing plastic foam patterns may be charged with molten metal in such a way as to provide a fresh hot metal interface to the foam material with minimum in-transit cooling, as compared to the previously employed method where the front of the molten metal had to traverse substantial thickness of foam material with consequent under-cooling, before reaching its final destination in the mold. Thus, by having passageways within the foam material to conduct the molten metal rapidly to its destination, under-cooling by virtue of the latent heat of vaporization of the foam plastic is substantially minimized.

Of course, similar advantages can be obtained in the casting of the heavier metals, such as copper and copperbase, iron and iron-base, nickel and nickel-base alloys and other metals. For example, foam densities of 2 pounds per cubic foot or less have, according to the Shroyer Pat. No. 2,830,343 been employed for such metals. As will be appreciated, unless considerable precautions are taken, such low-density foams may be subject to distortion and crushing during the ramming operations necessitated by use of the green sand molding technique. On the other hand, if much denser foams are employed, even the heavier metals may tend to under-cool due to the considerable amount of foam material to vaporize, thereby resulting in castings of inferior quality. Thus, by allowing for passageways in the foam pattern assembly, for example within the pattern itself, and/ or via the gates, runners or risers attached to the pattern, denser and stronger foam 6 patterns may be employed, even in situations involving the use of green sand molding techniques and the casting of heavier metals.

Examples of metals which can be cast utilizing my improved process including the pouring temperatures are: aluminum which may be cast at a temperature varying from 1550" F. to 1850 F.; copper and manganese-bronze at a pouring temperature of about 2200 F.; tin and tinbase alloys at a pouring temperature of about 1000 F., and iron and steel at a pouring temperature of about 3000 F.

Examples of foam or expanded plastic which may be employed in carrying out my invention are urethane, polystyrene, polyethylene, cellulose acetate, and the like.

I prefer to use the rigid foam type, although in certain applications the flexible or semi-rigid foams may be employed. The expanded plastic may be either an open or closed cell structure.

Generally speaking, the density of the foam plastic employed in carrying out the invention may range from about 1 pound per cubic foot to about 10 pounds per cubic foot. I have found it advantageous to work over the range of about 1.5 pounds to about 8 pounds per cubic foot. I prefer to work at the lower range of densities in casting the light metals, such as aluminum, and at the higher range when working with the denser metals, such as iron, iron-base alloys, copper and copper-base alloys and the like.

Urethane foam is particularly advantageous in that it can be produced with a wide variety of properties and characteristics. It can have open or closed cells and vary in density from less than one to over 30 pounds per cubic foot. Urethane shapes can be produced by foaming in place. Polystyrene can be foamed in place or shapes produced by using a charge of small beads which are heated in a suitable mold and allowed to expand up to thirty times their original volume. The density of the resulting foam is controlled by the amount of beads charged in the molds and can be varied from about 1.5 to 10 pounds per cubic foot and higher. A major advantage of the bead material is the simplicity of the foaming process which permits the foundry to produce foamed shapes economically in its own plant where large quantities are required. Where small quantities of castings are involved, it would be economical to use expanded polyurethane as suit molds for the patterns may be made of wood.

The expandable bead method has the advantage in that automatic molding machines may be employed in massproducing economically many patterns, such as would be required in the production of standard hardware fittings. In producing tailer-made patterns, polystyrene foams are readily available and can be easily worked without special tools, and can be glued together by light aerosol spraying with certain plastic solvents.

In cutting foam plastics to the desired shapes, generally a rough surface is exposed which usually leaves its imprint upon the surface of the casting produced. In some instances such a surface may be desirable where an object of art is produced having a textured surface. On the other hand, where a rough surface might be undesirable, the carved pattern to be duplicated may be coated with wax or sprayed with a plastic solution to provide a smooth membrane to cover the rough surface. Where the particular pattern is machine-molded from beads, extra fine bead sizes may be employed to avoid the formation of a rough textured surface on the pattern and consequently on the resulting casting produced therefrom.

While dry sand may be preferred as a molding material, it will be appreciated that other methods of sand molding may be employed in carrying out the invention. I prefer dry sand for the reason that it enables the setting up of a continuous mold preparation and casting line without requiring any mold baking time. In packing the sand about the pattern, vibration devices may be employed. The term sand as employed herein may include any particulate material that can be used in mold preparation. For example, in the casting of copper shapes, I may desire to use finely-divided hard carbon particles because of their fairly high heat of conductivity.

The material employed for the pattern is one that upon being contacted by hot molten metal is easily displaced and leaves the confines of the mold as a vapor substantially without leaving a residue. The term vapor as employed herein is meant to include escaping gaseous prod,- ucts formed either as a result of partial or full combustion of the pattern or as a result of the thermal conversion of the plastic into its corresponding vapor.

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 the appended claims.

What is claimed is:

1. The combination of a sand mold and a pattern of porous plastic matrial thermally capable of forming vapor without substantially leaving a residue confined within a body of sand, said porous pattern being embedded in sand and having an entry portion adapted for receiving molten metal, said entry portion communicating with a hollow portion of said pattern that extends to one end of said pattern remote from said entry portion, such that molten metal poured into said mold via said entry portion flows into the hollow portion of the embedded pattern whereby to establish immediately a reservoir of hot metal within the pattern which displaces the embedded porous pattern as the molten metal rises to the entry portion.

2. The combination of claim 1, wherein the porous pattern has a density of about 1 to 10 pounds per cubic foot.

3.,The combination of claim 1, wherein said pattern is a main pattern and has a plurality of smaller patterns projecting laterally from said main pattern from the top to the bottom thereof.

4. The combination of claim 1, wherein the pattern of plastic material has an irregular cross section, and wherein the hollow portion of the pattern broadens in size as it extends to the bottom of the pattern remote from said entry portion.

5. The combination of claim 1, wherein the pattern has an intricate shape and has a completely enclosed hollow filled with sand, said pattern having associated and embedded with it a hollow gate and riser system of said porous plastic material connected to the bottom portion of said pattern, said gate and riser having runners of said porous plastic material extending laterally to difierent levels of said pattern.

References Cited UNITED STATES PATENTS 2,793,412 5/1957 Lashbrook 16434 3,249,972 5/1966 Watts at al 164-350X FOREIGN PATENTS 1,115,559 1956 France.

475,566 1936 Great Britain.

J. SPENCER OVERHOLSER, Primary Examiner U.S. Cl. X.R. 164-34

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