US2476726A - Method for making molds - Google Patents

Description

July 19, 1949. Y G HAAS 2,476,726

METHOD FOR MAKING MOLDS Filed Oct. 1, 1945 @JY 6245/052 H445.

INVENTOR.

Bmx/WM ATTORNEYS.

Patentedjuly 19, 1949 stares METHOD FR '-1 1r. MOLDS 6 Claims. (CH. 22h-193) This invention relates to a method for making molds, and particularly molds for casting ferrous or non-ferrous metals, plastics, glass and like materials. 'Ihe molds with which this invention is concerned are of the type in which a single article is cast and the mold then destroyed, for example a sand mold, as distinguished from the permanent type of mold which may be formed from metal and which may lbe used repeatedly to produce lange numbers of castings.

Heretofore, there have been certain hard and fast limitations in foundry practice and other molding arts with respect to the shapes which could be cast or molded in a mold cavity formed v l entirely in a ller.

Articles having hooked contours, overhanging or underlying projections and the like can only be molded by conventional methods if the hooked part or the projection can be located at the parting plane of the mold or if a separate insert, such as a baked sand core, is set into the ask in a position to define a part of the molding cavity. Consequently, it is conventional practice to either mold a blank of the general contour desired, and then machine or otherwise iinish the blank to produce the hooked contours, etc., which are desired, or to employ separate cores or inserts in the mold. Both of these practices are expensive and often times may not be practical.

Further limitations of convention-a1 molding practice are that the article which is molded has a rough surface, cannot be made accurately to the desired size Within low tolerance limits, and its minimum wall thickness must be quite heavy. compared to wall thicknesses for similar objects fabricated from rolled metal stock such as plate or sheet metal. The latter limitation results from the inability to obtain a good continuous casting of lesser thickness, and not from lack of strength of thin cast sections.

It is the primary object of this invention to provide a method for making a mold which is simple, inexpensive, and adapted to quantity production, and which overcomes the aforementioned limitations and permits mold cavities to be formed around a single pattern, for faithful and accurate reproductions of contours heretofore found impractical or very expensive.

A further object is to provide a method for making molds from which can be cast or molded articles which are characterized by smooth sur-- faces, thin cross-sections and accurate dimensions and contours.

A further object of the invention is to provide a quick and inexpensive method for forming molds having cavities of intricate or irregular contours.

Other objects will be apparent from the description and appended claims.

In the drawing:

Fig. 1 is a face view of the drag of a molding ask in which a pattern, illustrated in crosssection, is applied for the purpose of forming a mold cavity.

Fig. 2 is a transverse sectional view taken on line 2 2 of Fig. 1. y

Fig. 3 is a transverse' sectional view of another type of molding pattern which may be used according to my invention.

Referring to the drawing, which illustrates the preferred embodiment of the invention applied in the casting of metal articles, the numeral .it designates the drag andthe numeral I2 the cope of a conventional molding flask. Each mold part contains filler material ift, such as sand. in which :an impression or cavity of the article to be cast can -be formed.

A pattern it is utilized to outline the molding cavity. As in conventional practice, the pattern is positioned by means of an arbor iii or other support in proper relation to the parting plane between the drag and the cope While the filler id is compacted therearound in the drag and cope. In this case, however, the pattern i6 is formed, at least in part, of flexible' material. rather than from wood or' other rigid material as is conventional. The particular material of which the pattern is formed may vary, and among the materials which are suitable are rubber, synthetic rubber, exible plastic such as vinyl copolymer resins, and gelatin compounds. The materials enumerated are illustrative of those which are applicable, and not limiting. The pattern It has been illustrated as provided with longitudinally spaced iianges or projections 2li, and with circumferentially spaced projections 22 and hook shaped projections 2t so arranged that there is no position in which the pattern can be located in the flask to permit free withdrawal thereof from the mold.

In the condition illustrated, a mold for the accurate reproduction in a casting of the pattern contour can be produced by the following method. The sand or other ller material is wel] moistened, is firmly packed around the pattern or model, and is provided with a suit-able pouring opening or gate. The flask so prepared is then chilled until the ller in the cope and drag is frozen solid. Thereupon the drag and cope may be separated and the iiexible pattern or model 24, and by the withdrawn. Such withdrawal is accommodated by the flexibility of the projections 22 and rigidity of the frozen filler, and does not disturb or damage the contour of the molding cavity. The moisture content of the filler must be adequate to insure the desired solid freezing of the filler in casting metals, and should preferably not exceed the minimum to any extent which would entail substantial expension incident to freezing. I have found that where the filler is molders sand, and the moistening agent is water, best results are obtained when the moisture content of the filler is in the range between 10% and 12%. However, the operative range is much wider, so that a moisture content of around may be feasible in some cases depending in part on the fineness of the sand or filler. There is a much greater latitude as to maximum moisture content, so that a solid ice filler, i. e., ali-liquid mold, might even be feasible in some cases.

The metal or other material to be molded may be poured through the pouring opening and into the molding cavity as in conventional practice. In cases of flasks whose filler comprises sand having a moisture content in the range indicated above as being preferred, the pouring operation may occur either while the filler is still frozen or after it has been permitted to thaw or dry. If the metal is poured while the filler is still at or near freezing temperature, as is necessary where the nller has a high moisture content, the metal will set up immediately upon contacting the surface of the mold cavity and before gases are formed which would tend to form gas pockets in the casting surface if setting of the metal at the cavity surfaces was not substantially instantaneous. In other words. when the filler is frozen or is at a near freezing temperature, the metal will lie quietly against the cavity wall as it sets to provide a dense, continuous, smooth casting surface. On the other hand. if the operation of pouring the metal` is delayed until after the mold nller has thawed and dried, surface pockets and roughness due to gas formation prior to setting of the metal will be experienced. Likewise, the minimum thickness or section in which the cast article can be molded successfully is consistent with conventional standards if the mold is at or near usual room temperature; whereas sections substantially thinner than are now conventionally feasible, for instance thicknesses of V8" or less, may be cast if the metal is poured while the mold is at or near a freezing temperature.

The finished casting produced from a frozen mold is also characterized by high accuracy as respects its size, so that low tolerance limits can be held successfully. In this respect the order of the accuracy obtainable is comparable to that heretofore obtainable only by the use of permanent, i. e. all metal, molds. All of these favorable results are obtainable at reasonable cost, the expense being substantially less than conventional practices entailing the use of baked sand inserts, andthe labor requirements being very little more than those pertaining in using molds with simple cavities formed entirely of green sand by the .use of wood patterns.

A further advantage of this invention is that many items now required to be cast in multiplepart flasks can be cast in one-piece flasks, since .the removal of the pattern or model from the mold cavity is no longer a problem as is the case in conventional practice using rigid patterns.

The pattern it may be made in various ways. Thus, as illustrated in Figs. 1 and 2, it may comprise a rigid core or body 2l and a sheath 2l of flexible material encircling the .sore and having the projections 2li, 22, 24 formed therein. The flexible material may be permanently bonded to the core 28, in which case the sheath 30 might be dispensed with so that only the projections are formed of the flexible material. In many instances it will be desirable to make the pattern with its rigid and flexible parts separable. This will accommodate removal of the pattern by first removing the core thereof, while the flexible sheath remains in place, and thenprogressively stripping the sheath from the mold filler in an action similar to removing a glove from the wearers hand, thus utilizing the 'nexibility of the pattern sheath to its maximum advantage. For example, where pattern projections are of thin section and provided with one or more bends, the separable pattern will facilitate the stripping action. The sheath 30 will then desirably be of very thin section.

Another alternative is to make the complete pattern from flexible material, as shown in Fig. 3. Still another alternative is illustrated in Fig. 3 and entails the incorporation of a reinforcement 32 in a projection which might otherwise be subject to being deformed incident to the packing of the ller in preparing the mold. This reenforcement may be made of sheet metal, wire, cloth, screen wire or any suitable material giving the required reinforcing action without rigidifying the projection to the extent of nullifying the property of flexibility required to strip it from the frozen mold without damage to the latter.

The invention has been described and illustrated as applied to the making of molds for use in casting metals; but the invention is not limited thereto. and may be applied to the making of molds for all types of plastic materials, such as glass and synthetic resins, etc.

I claim:

l. The method of making a mold having a cavity in which metal may be cast, comprising the steps of compacting a moistened normally fluent filler around and in contact with a exible pattern in a separable multi-part molding flask, chilling the moistened filler to temporarily solidify the same in compacted form around said pattern, and separating the flask parts and removing the pattern from the nller without disturbing the compacted form thereof while the filler remains solid.

2. The method of casting metal, comprising the steps of compacting moistened sand around and in`contact with a flexible pattern, freezing and temporarily solidifying said moistened sand while said pattern remains imbedded therein, removing the pattern from the frozen sand to provide a casting cavity, and then pouring molten metal into said cavity.

3. The method of making a mold for casting metal, including the steps of freezing and temporarily solidifying a moistened flask filler around and in contact with a pattern having a contoured flexible sheath, and removing the pattern while the filler remains in frozen solid condition by flexing the sheath contour portions.

4. The method of casting metal, consisting of the steps of compacting moistened sand in a flask around and in contact with a pattern having a flexible contoured sheath and a core ntting removably in said sheath, freezing and temporarily solidifying said sand while said pattern remains in situ, and then successively withdrawing said pattern core, flexing and stripping said pattern sheath from said frozen sand to provide a casting cavity, and pouring molten metal into said cavity.

5. The method of making a mold for casting metal, comprising the steps of freezing and temporarily solidifying a normally fluent mold material against a pattern having a flexible contour-dening portion contacting said mold material, and removing the pattern from the mold material without disturbing the pattern-engaging surface thereof while the latter remains in solid condition by flexing the exible portion of said pattern.

6. The method of casting metal, comprising the steps of compacting a moistened 1111er of the type which is uent when dry within a ask around a pattern having flexible contour-dening projections contacting said 1111er, freezing said ller to solid state around said pattern, removing said pattern while said ller remains frozen to provide a casting cavity, and pouring molten metal into said cavity to form and set a metal casting whereby said filler is heated and dried.

GUY CASPER HAAS.

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

UNITED STATES PATENTS in the OTHER REFERENCES Modern Core Practices and Theories, by Dietert; published, 1942, by the American Foundrymens Association, Chicago, Ill.; `page 76.

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