US 3635280 A
Combustible patterns of expanded polystyrene, carved to complex forms by the tape-controlled milling of two or more self-aligning parts, resist displacement from each other as sand is packed within and around them. Tongue-and-groove joints, formed on the mating surfaces of the parts, locate and align the parts and prevent their displacement more surely than adhesives, which tend to cause inclusions and voids in the casting. Adhesive may be coated on the tongue-and-groove parts only, leaving adjacent margins of the mating surfaces free from adhesive; and the exterior surfaces of the assembled pattern may be coated with a noncombustible ceramic coating. The marginal spacing of the adhesive inward from such coating permits quick dispersion of the adhesive when the molten metal is cast.
Description (OCR text may contain errors)
United States Patent Parsons 51 Jan. 18, 1972 FOREIGN PATENTS OR APPLICATIONS 1,220,970 7/l 966 Germany 164/34 Primary ExaminerRobert D. Baldwin Att0rneyJerome A. Gross  ABSTRACT Combustible patterns of expanded polystyrene, carved to complex forms by the tape-controlled milling of two or more self-aligning parts, resist displacement from each other as sand is packed within and around them. Tongue-ancl-groove joints, formed on the mating surfaces of the parts, locate and align the parts and prevent their displacement more surely than adhesives, which tend to cause inclusions and voids in the casting. Adhesive may be coated on the tongue-and-groove parts only, leaving adjacent margins of the mating surfaces free from adhesive; and the exterior surfaces of the assembled pattern may be coated with a noncombustible ceramic coating. The marginal spacing of the adhesive inward from such coating permits quick dispersion of the adhesive when the molten metal is cast.
4 Claims, 2 Drawing Figures r I r i I"; I/1i; 52
PATENTED JAN 1 a 1972 J OHM AQ N @%%A 1 SELF-ALIGNED MULTIPART COMBUSTIBLE CASTING PATTERN AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This invention relates to the making of combustible patterns for castings, using materials such as expanded polystyrene; and particularly to the secure alignment of such patterns assembled of several parts. To minimize the problem of alignment, l assemble such patterns of preferably only two parts, each carved to a complex shape according to the method dis- .closed in my copending application, Ser. No. 867,980, filed Oct. 20, 1969, entitled Use of Tape Controlled Milling Machines to Carve Combustible Casting Patterns, of which this application is a continuation-in-part.
Some pattern forms, such as hollow boxlike objects having substantial wall portions on six sides, cannot be carved integrally. If patterns are made to such forms by gluing together boards of low-density polystyrene material, in much the same manner as wooden patterns have been made, there is a serious danger that insufficient adhesion will result in displacement of the pattern parts as the sand is packed within and around the pattern. Such displacement is not likely to be discovered until after the casting has been poured and the pattern burned away.
Expanded polystyrene pattern material is not readily adhered by known adhesives; and as a further complication, the amount of adhesive must be minimized. Conventional adhesives do not vaporize at the same low temperature as the expanded polystyrene material. When the molten metal is cast, the adhesive present must be harmlessly dispersed through it, otherwise voids in the casting may result. Dispersion of the adhesives is interfered with whenever there is contact between the adhesive and a noncombustible coating material which is conventionally sprayed onto the exterior surfaces of polystyrene patterns.
Heretofore, there has been no satisfactory solution of the problem as to how to avoid displacement of pattern parts when the sand is packed; and the use of adhesives has added its own complications to the problem. Such use of adhesive is shown in US. Pat. No. 2,830,343 to Shroyer, which also discloses doweling or wiring the pattern parts together.
SUMMARY OF THE INVENTION A principal purpose of the present invention is to provide self-aligning multipart combustible patterns, which will resist the forces of packing sand into and around them. Further purposes are to provide securely assembled mullipart patterns with a minimum of adhesive, located spacedly away from noncombustible coatings, so that the adhesive will be quickly dispersed within the molten metal and cause no defects in the casting.
l accomplish these purposes by a method in which two or more parts are formed to shapes which when assembled will make up the desired pattern form. The parts having mating surfaces carved with interfitting portions, which locate and align the parts with the mating surfaces in contact with each other. The alignment is so positive and strong that forces encountered in foundry practices, particularly forces attendant to packing sand in and about the pattern, are resisted by the interfitting parts, without danger of misaligning them. Where adhesive is to be used, I apply it only to the interfitting tongueand-groove portions, leaving margins of the mating surfaces without any adhesive coating; and I form the tongue-andgroove portions to negative tolerances so that excess adhesive will not penetrate into the margins of the mating surfaces. Thereafter when a noncombustible coating is applied to the exterior surfaces, the adhesive will be so spaced inwardly of the coating as to avoid adhesion to the coating; when the pattern is subjected to a charge of molten metal, the small quanti ty of adhesive will be harmlessly dispersed through the metal.
BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:
FIG. 1 is a perspective view, partly broken away, of two pattern parts, carved of combustible pattern material, having the tongue-and-groove interfitting alignment means of the present invention.
FIG. 2 is an enlarged fragmentary cross section of an assembled pattern, with molding sand packed thereabout, including adhesive within the tongueand-groove mating parts only.
DESCRIPTION OF THE PREFERRED EMBODIMENT Intricate pattern forms may, according to the present invention, be made up of only two pattern parts, each carved from a block of expanded polystyrene material, using a tape-controlled milling machine in the manner described in my copending application referred to hereinabove. Two such pattern parts are shown in FIG. I, the lower part being generally designated 10 and the upper part being generally designated 11. Unlike the somewhat similar parts carved as described in said copending application, the lower and upper parts 10, II have integral interfitting provisions, hereinafter described. Each part 10, 11 is formed to an open boxlike shape with vertical sidewalls and vertical webs in alignment with each other. Thus, the vertical walls of the lower pattern part 10 have inner surfaces 12 and outer surfaces 13 parallel thereto, carved to be in alignment with the inner surfaces 14 and outer surfaces 15 of the upper pattern part 11. Similarly, vertical webs formed within the lower pattern part 10 have parallel opposite web wall surfaces 16, 17; and the corresponding webs in the upper pattern part 12 have opposite wall surfaces 18, 19 in alignment therewith.
Connecting the upper edges of the wall surfaces 12, 13, I6, 17 of the lower pattern part 10 is a mating surface generally designated 21; a corresponding mating surface 22 connects the lower edges of the walls l4, 15, 18, 19 of the upper pattern part 11. Midway between the opposed wall surfaces, there is carved on the mating surface 21, an upwardly projecting continuous interfit provision. The preferred interfit provision is a tongue generally designated 23, having beveled side surfaces 24 and a horizontal top surface 25. Between the tongue 23 and the inner and outer wall surfaces 12, 13 horizontal marginal portions 26 are provided, to fit tightly against similar marginal portions on the upper pattern part 12, as will be described. These marginal portions also provide a spacing between an adhesive coating 28 which may be applied onto the tongue 23, and a noncombustible coating, hereafter described, to be applied to the wall surfaces 12, 13.
Similarly, the corresponding mating surface 22 of the upper pattern part 11 has a continuous groove 31 which receives and mates with the tongue 23. The groove 31 has beveled sidewalls 32 and a horizontal top wall 33. Like the tongue 23 on the lower pattern part 10, the groove 31 is located spacedly between the inner and outer walls 14, 15 of the upper pattern part 11, leaving marginal portions 35. On assembly, these abut snugly against the marginal portions 26 of the mating surface 21 of the lower pattern part 10, without any adhesive therebetween.
As shown in the enlarged fragmentary view FIG. 2, the tongue 23 and groove 31 are formed to negative tolerances. The result is that space is provided for the flow of any excess adhesive. In FIG. 2 such excess adhesive from the coating 28 is shown as accumulated in the space at the top of the tongue 23.
The width of the abutting marginal portions 26, 35 is such as to prevent inflow to the adhesive coating 28 of a noncombustible coating 37 sprayed on the pattern walls after assembly, as hereinafter described. When the lower and upper pattern parts 10, 11 are carved from billets of expanded polystyrene material consisting essentially of self-adhered expanded beads, the width of each of the marginal portions 26, 35 is preferably at least three times that of an expanded bead. Thus, when the beads of material are cut by the milling cutter, at least two uncut beads will separate the spray coating 37 from the adhesive 28.
A spray coating of noncombustible material, usually a ceramic in a partially evaporable carrier, is conventionally applied to the exterior surfaces of polystyrene combustible patterns. When the casting is made, the noncombustible material in effect lines the molding sand as the combustible pattern is burned away. Such a coating 37 is applied to the wall surfaces of the pattern parts 11, 12 and covers the junctures of the mating surfaces 21, 22.
While expanded polystyrene material is not readily adhered by adhesives, such adhesives cannot be used in large quantities. Their vaporization temperatures are higher than that of the polystyrene. If not quickly dispersed throughout the charge of molten metal, they may form inclusions within the castings, resulting in voids.
To disperse the adhesive material harmlessly throughout the molten metal, it is important that the adhesive 28 should not adhere to the sprayed on noncombustible coating 37. In the present invention, such adherence is prevented by the spacing, inwardly of the coating 37, which is provided by the marginal portions 26, 35. Squeeze-out of the adhesive into these margins is avoided by fonning the tongue 23 and groove 31 to negative tolerances.
Even without use of any adhesive, the pattern parts 10, 11 are self-aligning and resist the lateral forces, such as those applied in packing sand 36 preparatory to casting. Thus, whether or not any such adhesive coating 28 is used, the lower and upper pattern parts 10, 11 are placed together in a large box, or flask of molding sand; and, with access through pattern openings generally designated 38 in the bottom wall 39 of the lower casting part and in the top wall 40 of the upper casting part 11, sand 36 is packed, by hand, in place against the opposite pattern walls l2, 13, 14, as shown in FIG. 2. Were it not for the interfitting tongue 23 and groove 31, the lower casting part 10 and upper casting part 11 would be likely to be dislodged out of the alignment, regardless whether adhesive was employed. The interfitting tongue and groove, 23, 31 not only positively locates the lower and upper parts 10, 11 in alignment, but holds them in alignment and resists the lateral forces attendant to packing sand within and about them. Thereafter when the casting is poured, if any adhesive has been used on the tongue 23, it will be quickly and readily dispersed in the charge of molten metal. None will be in contact with the noncombustible coating 37 and hence none will be retained by the coating.
Using the method of the present invention, there is no limit on the number of parts to be fonned and so assembled to make up the desired pattern form. The use of a tape-controlled milling machine to carve the complex pattern parts 11, 12 makes it possible to minimize the number of such parts, while the interfitting tongue 23 and groove 31 are integrally carved as part of the program of the machine. The result is sound castings, formed without glue inclusions, made from patterns whose complex shape involves no danger of displacement as the molding sand is packed.
1. A self-aligned multipart combustible pattern for foundry use, comprising a plurality of pattern parts formed of material of a type which is combustible under a charge of molten metal,
said plurality of parts having mating surfaces and being formed to shapes which, when assembled at such mating surfaces, make up a desired pattern form having shaped exterior surfaces,
at least one of said plurality of parts having opposed wall surfaces terminating in one of said mating surfaces,
tongue-and-groove means formed on the said mating surfaces and spaced inward of the opposed wall surfaces of said one part, whereby to provide marginal mating surface portions therebetween,
an adhesive coating joining the tongue-and-groove means,
the said marginal mating surface portions being free of said adhesive coating, and a noncombustible coating on said extenor surfaces and covering the junctures thereat of said marginal mating surface portions, whereby the spacing of the said adhesive coating from the noncombustible coating avoids retention of the adhesive when the assembled pattern is subjected to a charge of molten metal. 2. A self-aligned multipart combustible pattern as defined in claim 1, wherein the tongue-and-groove means is formed to negative tolerances, whereby to provide space for the flow of adhesive and thereby maintain the said marginal portions free of adhesive. 3. A self-aligned multipart combustible pattern as defined in claim 1, wherein the material from which the pattern parts are formed consists of self-adhered beads of expanded polystyrene, and in which the marginal portions of the mating surfaces have a width at least three times the diameter of such beads. 4. The method of making a multipart self-aligned combustible pattern for foundry use, comprising the steps of forming from expanded plastic material, of a type which is combustible under a charge of molten metal, a plurality of pattern parts having mating surfaces and being so shaped as, when assembled, will make up the desired pattern form, while so forming the parts, forming on their said mating surfaces tongue-and-groove interfitting portions leaving marginal portions of the mating surfaces thereadjacent, coating an adhesive on said interfitting portions only, superposing the plurality of parts upon each other whereby the interfitting portions locate and align the parts in the desired form and the marginal portions abut each other without any adhesive therebetween, and coating the exterior surfaces of the assembled pattern parts with a noncombustible coating, whereby the marginal portions establish a spacing between the adhesive on the interfitting portions and the noncombustible coating.