US3426834A

US3426834A - Expendable pattern for precision investment casting

Info

Publication number: US3426834A
Application number: US623743A
Authority: US
Inventors: Louis J Jacobs; Bela Klaudinyi; Robert Earl Fisher
Original assignee: S Obermayer Co
Current assignee: S Obermayer Co
Priority date: 1967-03-16
Filing date: 1967-03-16
Publication date: 1969-02-11
Anticipated expiration: 1986-02-11

Description

Feb. 11, 1969 J JACOBS ET AL 3,426,834

EXPENDABLE PATTERN FOR PRECISION INVESTMENT CASTING Filed March 16, 1967 PREPARATION OF PLAsTIC PATTERN APPLICATION OF Q\\\ PLAsTIC FILM I DRYING OF PLASTIC FILM I /4- APPLICATI N OF REFRACTORIY COATING 30 DRYING OF AD REFRACTORY COATING 34fi I INvEsTMENT OF j i PATTERN IN REFRACTORY MOLD BODY POURING OF MOLTEN METAL CHARGE INTO MOLD BODY TO DISPLACE I PLASTIC PATTERN I 22 LCOOLING OF CASTINFI N I REMOVAL OF CASTING FROM REFRACTORY MOLD l/I/VEA/TORS LOU/S J. JACOBS ROBE/PT E. F/SHEI? BEL/1 KLAUO/NY/ United States Patent 3,426,834 EXPENDABLE PATTERN FOR PRECISION INVESTMENT CASTING Louis J. Jacobs and Bela Klaudinyi, Chicago, and

Robert Earl Fisher, Clarendon Hills, Ill., assignors to The S. Obermayer Company, a corporation of Ohio Filed Mar. 16, 1967, Ser. No. 623,743

U.S. Cl. 164-235 12 Claims Int. Cl. B22c 7/00, 9/12, 1/22 ABSTRACT OF THE DISCLOSURE Improved coating techniques including compositions and methods for preparing expendable patterns to be used in full mold casting processes and including applying to casting-defining surfaces of a combustible foamed plastic pattern a rapidly drying two-coat envelope system to provide castings having superior surface characteristics, the first coating comprising an organic film-forming preparation applied as a non-aqueous coating composition, and the second coating of the system comprising a refractory shell applied from a slurry. In preferred embodiments of the invention a non-flammable, volatile vehicle is used as a carrier in the refractory slurry.

This invention relates to improved precision casting methods of the type utilizing investment molding techniques. More particularly, the invention is directed to a lost pattern" process of the type known in the art as a full mold casting process.

Casting processes of the type in which the present invention finds utility do not use a conventional mold cavity, but a mold which has invested or embedded therewithin an expendable pattern which is destroyable in the mold, the pattern being in shape an exact replica of the intended casting and including all recesses, apertures, and other declivities and surface configurations. The expendable, destructible pattern is accessible through a gate to a poured molten casting charge which effects rapid and complete combustion or gasification of the pattern so that the molten charge replaces the embedded pattern in the mold and solidifies therein into the intended casting, assuming the exact shape of the replaced and varnished pattern. A detailed disclosure of the general techniques involved is found in Harold F. Shroyer U.S. Patent No. 2,830,343 and the entire disclosure of that patent is hereby specifically incorporated herein by reference to the extent that it is not inconsistent with the subject invention.

The present invention is also to be distinguished from traditional prior art molding and casting procedures wherein a permanent pattern is used to form the mold cavity in split mold assemblies. The use of such divided molds requires tolerances which are much wider than those feasible when one part molds are used. These tolerances are further undesirably increased when the pattern is drawn from the mold. Consequently, castings made in a mold cavity formed by means of an expendable pattern, in a one-part flask, can be made with marked reductions in tolerances and with greater accuracy and detail. Moreover, the use of a single cavity or a full mold casting technique eliminates mold joints and associated grinding and finishing operations. Flashes are completely eliminated, and there is an overall marked improvement in precision, and accuracy.

In full mold processes of the type described in the above referred to U.S. patent, lost patterns or forms of foamed plastic are used in the casting process, the pattern being imbedded in a one-part molding box in a mold body comprising granular refractory or ceramic material such as quartz, silicates, sillimanite, sand, fire brick, alumina, in combination with suitable bonding agents. Widely used systems include molding sands containing cold setting binders, furan resins in combination with quartz sand, and sand mixes used for CO setting.

The expendable patterns have ordinarily been fabricated from foamed plastics, foamed polystyrene being a preferred material. Other suitable foamed plastics include polyethylene, polypropylene, and other synthetic resins, all acceptable materials having in common the property of combustibility with relatively low ash. In elfect, the expendable pattern must be readily gasifiable or otherwise removable rapidly upon the introduction of the molten casting charge. In the practice of the casting system described, the patterns for pouring basins, ingate and feeder systems, and for templates may also be conveniently made of foamed plastic.

The form or pattern may be prepared by any of several techniques, these including but not being limited to the cutting or machining of patterns from blocks of foamed plastic, and the forming of patterns directly from foamable compositions in special metal molds to provide unitary patterns as well as parts of or separate elements of composite or cluster patterns. Patterns may be fabricated by adhesively joining or by cementing together separate expanded plastic elements.

The finished coated pattern is surrounded in a conventional manner with a refractory material such as sand, the latter being compacted or packed about the pattern by jolting, vibrating, pressing or ramming, in a manner well known in the art. Ingate systems, which may if preferred be foamed with the pattern in a single operation, may be positioned in the flask and within the refractory material at the same time, a sprue being permitted to extend through a wall of the refractory mold so as to facilitate the escape of the destructible pattern material. The main refractory mold may be formed about the pattern in any suitable manner, and hence, the procedure for forming the mold will not be described in further detail. With the pattern in place within the molding box, the molten casting charge is poured effecting a complete burning of the embedded form or pattern and replacing that form in the resulting cavity in the molding box and faithfully reproducing the exact physical form of the pattern.

The prior art procedures and techniques utilizing the full rnold casting process do not meet the demanding standards of precision castings. It is obvious that the final casting can be no better than the destroyable foamed plastic pattern, and in many cases the expanded plastic has an undesirably rough surface, this roughness being associated either with the inherent physical structure of the foamed mass, or being due, at least in part, to cutting or machining operations. In practice, it is sometimes not possible properly to compact the sand or other refractory granular material to a uniform density completely around and in firm contact with the polystyrene pattern. The above described conditions cause rough casting surfaces or castings which have excessive burn on where the casting metal or other molten casting material has penetrated and caused the porous sand to sinter to the casting surface.

Various types of compositions have been proposed for coating the plastic pattern. These coatings have been applied by spraying, painting, or dipping, the coatings themselves include alcohol or water base core washes or slurries consisting of fine refractory particles, suspension agents, and binders. Other film forming compositions which have been used include aqueous solutions of water soluble alkyl celluloses such as methyl cellulose. While the use of these prior art coating compositions has to some extent eliminated burn-on, and while the coatings have had some beneficial effect on the cast-defining surface of the plastic pattern, none of these prior art materials or techniques constitutes a complete or satisfactory solution to the problems involved. Moreover, the core washes and coatings utilizing aqueous systems require long drying time. As much as four hours or longer drying time is necessary between each application of coating. It is, therefore, the aim of the present invention to provide improved coatings and an improved coating system for vaporizable, fusible, combustible or otherwise destructible foamed plastic patterns, to obviate the many shortcomings of prior art compositions and materials.

It is a principal object of this invention to provide methods and compositions for applying improved coatings to casting surfaces of expendable plastic patterns.

It is a related object of the invention to provide an improved coating system for covering rough surfaces and surface blemishes of expendable patterns fabricated from foamed or expanded plastics to render the casting surfaces of these patterns extremely smooth, without the costly delays associated with prior art slow drying coatings.

A further object of the invention is to provide a twocoat or dual coating system for treating casting surfaces of expendable foamed plastic patterns in a full mold casting process.

A related object of the invention is to provide a coating system for expendable plastic patterns in which the coatings or facings comprise a first coating of an organic film-forming material, applied from a non-aqueous system, and a second coating which is applied over the first coating and which comprises a strong refractory envelope applied as a slurry using a halogenated solvent system.

It is still a further object of the invention to provide a coating system for application to expendable foamed plastic patterns whereupon upon removal of the ultimate casting from the mold, that casting may be readily cleaned.

A related object of the invention is to provide a coating system for expendable foamed polystyrene patterns, the system including an organic facing applied directly to the plastic pattern and a second, refractory facing imparting a smooth surface texture to the pattern and, ultimately, smooth surface characteristics to the ultimate casting.

It is an important feature of this invention that the improved facings allow the foundry man to obtain greater metallurgical control and improved strength and fatigue resistance of castings made in accordance with the full mold process.

Another object of the invention is to provide a foundry facing material which is premixed and in liquid form and which may be applied to patterns without running or dripping.

Still another object of the invention is to provide a water resistant, non-hygroscopic coating for foamed plastic expendable patterns, which coating provides a hard smooth moisture repellent envelope or sheath of unusual strength and hardness and resisting cuts and erosion during use.

Additional objects and aims of the invention include the following:

To provide a refractory pattern-facing material in which the solvent is readily volatilized and is of a relatively high specific gravity and of a relatively low toxicity; to provide a refractory facing coating composition consisting of a dispersion of refractory material, which dispersion is relatively stable without excessive settling or phase separation; to provide a pattern facing system which forms a smooth facing of suflicient strength to resist the erosive action of molten metals during the casting process; to provide a refractory facing which acts as an effective barrier to prevent metal of the casting from fusing with the sand or foundry forms during the casting operation; to provide a two-coat pattern facing material which will produce castings having a smooth surface to obviate the need for chipping operations and grinding; to provide a plastic pattern facing material which can be applied by spraying, swabbing, or dipping and which may then be subsequently dried readily, rapidly, and conveniently; to provide a system of pattern facing compositions in which the solvents are highly volatile and vaporize shortly after application of the coatings to the plastic pattern; and to provide an ultimate facing material for expendable foamed plastic patterns in which the surface produced is hard and smooth.

More specifically, it is an object of this invention to produce improved expendable foamed plastic patterns in which the casting surfaces are coated with a two-coat system requiring little drying time and including a film forming organic foundry facing which is of low ash, high strength, and which is elastic and nonporous and produces an extremely smooth textured surface on the foamed pattern. A second coating material comprising an inorganic foundry facing is then applied to and reproduces the smooth surface pattern contours of the organic film. It is an important feature of the invention that both facing materials air dry rapidly and have suflicient physical strength so that chills or insulators may be applied to control cooling and to produce the desired quality casting.

Other objects and advantages of this invention will more fully appear from the following detailed description of the invention in conjunction with the accompanying drawing, in which:

FIGURE 1 is a somewhat schematic sectional view of a destructible pattern invested in a refractory mold and provided with the dual coating system in accordance with the invention; and

FIGURE 2 is a flow diagram of the process embodying the practice of this invention.

Referring more particularly to the drawing, a pattern 10 to be cast is shown invested in a refractory mold 12 within a metallic container or flask 14 supported on a base plate 16. The pattern 10 itself is formed of a foamed plastic which is vaporizable, fusible, combustible, or otherwise destructible, and which leaves substantially no residue or ash. While foamed polystyrene patterns are preferred, other thermoplastic materials such as resinous polymerized derivatives of acrylic acid and resinous polymerized derivatives of methacrylic acid may be used.

The expendable pattern may be formed in any preferred manner such as through a casting process. Alternatively, the pattern may be machined or carved, and may be either a single body or a composite body built from separate pieces. In the case of foamed polystyrene or polyethylene, a preferred density for the plastic material is in the range of about 2 pounds per cubic foot. Pattern material of substantially greater density will not readily burn or volatilize away when contacted by the molten casting charge, and if the density of the pattern is too low, the pattern lacks adequate strength to withstand handling and molding pressures and other stresses. B-lock expanded polystyrene may be shaped by conventional hand or machine operations to provide the desired pattern. Alternatively, the polystyrene may be obtained in a non-expanded state and thereafter extruded into dies and foamed in the desired form. Only one master die or pattern forming mold is required to produce many thousands of expendable foamed polystyrene patterns.

Referring further to FIGURE 1, a gating portion having a pouring basin part 22 at its outer end is attached to the pattern, the gating portions and the basin preferably being formed of a material similar to that of pattern 10.

The term pattern" as used herein refers to individual expendable patterns formed of the plastic material or combinations of such patterns or clusters consisting of two or more individual patterns, in accordance with conventional investment casting techniques. After cleaning the pattern and making any necessary corrections and modifications, the pattern is ready for further treatment, in accordance with the teachings of this invention.

It is an essential and critical feature of the present invention that two separate and distinct coatings or films are applied to the expendable pattern. The first of these coatings or facings 30 is a completely organic composition which is conveniently applied to the pattern by spraying, brushing, or dipping to produce a smooth, non porous facing or envelope. The second facing or coating 34 is a slurry composition including highly refractory materials and is applied directly to the organic foundry shell or facing 30 which encloses the plastic pattern 10. Both facings air dry rapidly to provide solvent-free films and the refractory facing 34 covers the smooth primer coating 30 to provide a strong refractory envelope which is markedly resistant to the penetration of the molten casting charge. Upon removal of the casting from the mold, the former is readily cleaned, the cleaning operation being greatly simplified as compared with the steps required when prior art pattern coatings are used. In the paragraphs below, the nature of the present invention will be more completely set forth and the invention itself will be described with reference to illustrative examples, these being provided for the purposes of disclosure and not in any limiting sense.

EXAMPLE 1 The following formulation indicates, for a preferred composition, the preferred ranges of concentration for each of the various components in the unique, completely organic facing material which is applied directly to the expendable plastic pattern. Unless otherwise indicated, all parts listed are by Weight.

Preferred Ingredients: concentration ranges Methanol 20-80 Glycerine 5.0- Isopropanol or ethanol 20-80 Ethylacetate 0-10 Nitrocellulose 1-50 Melamine resin 1-50 EXAMPLE 2 A typical composition of the organic facing material is 58.6% methanol, 11.3% glycerine, 13.9% isopropanol, 1.7% ethylacetate, 10.3% nitrocellulose, and 4.2% melamine resin, all percentages being by weight.

EXAMPLE 3 The following is an example of a suitable procedure for preparing the organic foundry facing compositions described above. The nitrocellulose is dissolved in the methanol in a jacketed vessel provided with an agitator and the mixture heated to a temperature in the range of from about 80 to 140 F. The melamine resin and the glycerine are then incorporated in the mix which then appears to undergo a polymerization process to form a smooth, elastic, resin solution. After cooling the reaction mixture to about 70 F., the ethylacetate and isopropanol are added. Dyes, surfactants, defoamers, and other additives in relatively small concentrations may also be added to alter the color or the consistency or to reduce air entrainment. The resulting finished product may then be removed and stored until needed.

The pattern primer coating or organic foundry facing film has unique and valuable properties, and is markedly superior to coating compositions which have heretofore been used. For example, the primer film of the invention readily adheres to the foamed polystyrene; it does not shrink, peel, or crack upon drying; it is sufiiciently elastic to permit handling or the polystyrene patterns without fracture of the film; it does not dissolve the polystyrene or solvate the surface to any objectionable extent; and the final film has very low permeability and is insoluble in the halogenated non-flammable carriers which are used in applying the second film, that is, the inorganic foundry facing.

The foamed plastic pattern with its smoothing protective organic film is treated with a second coating composition of the coating system of the invention. The second coating or facing composition comprises a slurry including a vehicle, a suspending agent, a binder, and an inorganic refractory material such as zircon flour, silica flour, mica, or graphite. The refractory facing is applied over the organic facing, the organic film or skin serving as a barrier to protect the pattern.

Preferred formulations for the refractory coating composition are set forth in the examples below.

In non-aqueous solvent systems preferred carriers for the refractory compositions are organic vehicles of relatively high specific gravity such as halogenated solvents, e.g., methylene chloride. Alcoholic and mixed alcoholwater systems may also be used. In these systems ethyl and isopropyl alcohols are preferred.

EXAMPLE 6 Within the broader range of weight compositions indicated in Examples 4 and 5 above, the following specific composition represents a preferred formulation.

Ingredients: Parts by weight 400 mesh zircon 60.25 200 mesh muscovite mica 2.5 Methyl methacrylate binder 1.0 Lithium hydroxy stearate 2.0

Methylene chloride (halogenated solvent) 34.2

Other voltatile, solvents of low toxicity and relatively high density may be substituted for the methylene chloride. Suitable solvents include the fluorine and chlorine substituted hydrocarbons sold under the trademarks Freon and Genetron, ethylene chloride, trichloro-trifiuoro methane, trichloroethane, methyl chloroform, tetraohloroethane, dichlorotetrafiuoroethane, triohlorofluoromethane and trichloromethane. While carbon tetrachloride has many of the required physical properties, its high toxicity dictates against its general use. Two or more solvents may be combined to obtain the desired system parameters, including volatility and flash point characteristics. Organic solvent carrier systems useful in the refractory slur- 'be used.

EXAMPLE 7 Finely ground crystalline graphite or silica may be used in place of the zircon and muscovite mica.

Methylene chloride (halogenated solvent) 34.2

Silica may be substituted for all or part of the graphite.

In the above examples, aluminum octoate may be substituted for some or all of the lithium hydroxy stearate. Also, other suspension agents including alkaline earth metal salts and aluminum salts of fatty acids may be used. Typical examples are magnesium and calcium oleate and aluminum palmitate. Organic resins and polymers are also useful.

It has been found advantageous in compounding specific coating compositions of the invention to include a relatively small amount of a binder or adhesive to impart film forming properties to the coating composition and to increase the adhesion of the coating to the organic facing, and ultimately to the mold body. A preferred binder is a thermo-plastic high molecular weight resin having a relatively high softening point and good mechanical strength and hardness. The acrylic resins are particularly suitable, and methylmethacrylate resin is a preferred composition. This resin has a specific gravity of 1.19 and a softening point of 239 F. Other acrylic resins including ethyl and butyl methacrylates may be used. Still other thermoplastic resins which find utility in the practice of the invention are such materials as polyvinyl chloride, vinylidene chloride, polyvinyl alcohol and polyvinyl acetate. Thermosetting resins such as phenol formaldehyde and melamine formaldehyde resins may be used. The binders may be used singly or in any preferred combination. The concentration of the resin binder is not critical but ordinarily not more than by weight is employed. As little as about 0.5% by weight of the binder in the coating composition imparts the desirable property of adhesion.

Refractory materials suitable for use in the practice of the present invention include zircon (zirconium dioxide and zirconium silicate), aluminum silicate (sillimanite and mullite), mica, vermiculite, graphite, silica and the like. A refractory-containing coating of the type described above is disclosed in United States patent application Ser. No. 378,988, that application being assigned to the same assignee as is the instant application. To the extent that the above-referred to application is not inconsistent herewith, it is specifically incorporated herein by reference.

The pattern-encasing organic facings of the invention are unaffected by and are relatively inert with respect to halogenated solvents, alcohols or water. While refractory coatings based on halogenated solvent systems such as those described in Examples 6 and 7 are preferred, alcoholic, aqueous or mixed alcoholic and aqueous vehicle systems may be used, as illustrated in Examples 8 and 9.

EXAMPLE 8 Ingredients: Parts by weight Zircon flour, silica flour, graphite flour 1 70 Refractories, individually or in combination.

8 EXAMPLE 9 Ingredients: Parts by weight Zircon flour, silica flour, graphite flour 1 50-60 Vinsol resin (binder) 0.5-1.5 Bentonite (suspending agent) 0.5-2.0 Alcohol 30-40 Refractories, individually or in combination.

In the above formulations clays such as bentonite are preferred bodying agents. Starches such as dextrin and resins such as vinsol resins are auxiliary agents found useful in imparting desired adhesive and bonding properties to the coating slurries.

EXAMPLE 10 The following is an example of the method of formulating and mixing the refractory foundry facing compositions. While the method is described with reference to the formulation illustrated in Example 6, in the light of the present disclosure it will be apparent what if any modifications must be introduced in different formulations. For best results, it is important that the lithium hydroxy stearate be mixed and dispersed through the methylene chloride solvent phase in a separate operation, to produce a uniformly defined dispersion. Proper dispersion is ensured by passing the mixture through a colloid mill or homogenizer. About one-fourth of the total methylene chloride is used in this initial operation. The methyl methacrylate resin is then dissolved in the lithium hydroxy stearate suspension. Finally the balance of the methylene chloride and the muscovite mica and the zircon are added and the entire mixture agitated in a vessel, using a propeller-type mixer. The resulting liquid product is ready for use or may be diluted to a preferred consistency suitable for the specific method of application selected. Application may be by spraying, brushing, or dipping, an important or usual property of the coating composition being that it does not tend to drip or run.

In a very short time (ordinarily less than one minute) after application of the coating to the pattern, the coating is dry and the pattern may be placed in the refractory mold. Upon final removal of the casting, the casting is easily cleaned, the refractory coating providing an effective casting and mold separation interface.

Metal chills or insulators, as required, can be set in place on the outer surface of the inorganic refractory facing While the latter is still wet. Such chills and insulators are conventionally used to control the metallurgical quality of the castings by regulating the rate of solidification of the casting to produce the desired grain structure, to reduce stresses, and to improve strength and fatigue resistance. The entire assemblage of coated pattern, chills and insulators is positioned in the foundry flask. Sand, crushed brick, or other suitable refractory fill materials are placed in the flask to hold the pattern and its associated elements firmly in place during the pouring operation. Alternatively, conventional molding sand may be rammed around or compacted against the assembly. If preferred, chemical setting sands may be used. When the double-coated expanded plastic pattern is properly encased in the mold, the molten casting charge is poured, entering the mold and taking the place of the foamed plastic pattern and solidifying in the cavity formerly occupied by the pattern.

It has been found that castings produced in accordance with the practice of this invention have surfaces which faithfully reproduce the form of the pattern and its outer surface texture. That is, as a result of using the improved coating system of the invention, the finished casting possesses excellent surface smoothness and detail and require little, if any finishing operations. The highly desired and long sought surface characteristics of castings produced in accordance with the practice of the invention resulting from the novel two-coat system including an organic coat or skin, which covers the normally rough texture of the foamed plastic, and a refractory shell or coating applied to the smooth-textured organic film, that film being non-porous and insoluble in the vehicle used in applying the inorganic refractory coating composition.

The interface between the organic foundry facing 30 and the inorganic coating 34 is a smooth, unbroken regular surface enveloping the entire pattern. Thus, when the molten casting charge is poured into the mold cavity and the plastic pattern and the organic foundry facing film are completely volatilized, the molten metal solidifies against the smooth inorganic refractory facing which, in effect, lines the refractory mold. The resulting casting reproduces the smooth surface exactly to provide a superior casting surface finish. It has been found that cleaning time and cleaning costs are much lower than for castings produced using conventional full mold process techniques.

The solidfied casting is easily removed from the flask, the sand readily shaking from the flask, and the casting and chills and/or insulators used being separated and recovered for subsequent reuse. The casting is then prepared for shipment or use by removal of the gate and riser, in the usual manner. Little, if any, additional cleaning or grinding is necessary. The chills and insulators may be returned to the molding station and the sand recycled for subsequent casting operations.

It will be apparent from the foregoing that the present invention provides easily applied and rapidly drying new and improved coating systems and compositions for use in the preparation of expendable foamed plastic patterns useful in precision casting procedures of full mold casting type processes. 'While the present invention has been described with reference to chemicals and chemical compositions, the invention may be considered to include important physical concepts as well. That is, the invention is characterized by the deposition of a two-coat system which encases or encapsulates an expendable combustible or vol-atilizable pattern, each of the two coatings or films of the system serving a well-defined specific role in the overall combination.

The term consisting essentially of as used in the definition of the ingredients present in the composition claimed is intended to exclude the presence of other materials in such amounts as to interfere substantially with the properties and characteristics possessed by the compositions set forth, but to permit the presence of other materials in such amounts as not substantially to affect the properties and characteristics adversely.

In the light of the present disclosure and teachings, those skilled in the art will know or be able to deduce with confidence the applicablity of other known materials as well as the applicability of newly developed commercial materials as yet unknown. It is, therefore, intended that the present embodiments be considered in all respects as illustrative and not restrictive. To the extent changes and modifications are within the scope of the appended claims, they are to be considered a part of this invention.

What is claimed is:

1. An expendable single-use pattern for precision investment casting, said pattern comprising an organic polymer combustible substantially without residue and having casting-defining surfaces thereof enveloped in a two-layer protective film system,

a first film of said system comprising a sealing and smoothing organic facing consisting 'of solids deposited on said pattern upon coating said surfaces with a solution comprising approximately 1 to 100 parts by weight of a nonaqueous volatile solvent and approximately 1 to 50 parts by weight of organic, film-forming resinous solute, and

a second film applied as a coating to said first film and comprising a slurry consisting essentially of finely divided refractory material, a volatile fluid carrier, a suspending agent, and a binding agent, defining a refractory shell on said pattern.

2. A pattern as set forth in claim 1 wherein said solvent phase of said film-forming coating solution comprises approximately 20 to parts by weight methanol, 5 to 25 parts by weight glycerol, 20 to 80 parts by weight of an alcohol selected from the group consisting of ethanol, isopropanol, and mixtures thereof, and up to about 10 parts by weight ethylacetate, and wherein said solute comprises approximately 1 to 50 parts by weight nitro-cellulose and 1 to 50 parts by weight melamine resin.

3. A pattern as set forth in claim 1 wherein said refractory slurry comprises from about 40 to about parts by weight of finely divided refractory material, from about 0.5 to about 5 parts by weight of binder, from about 0.5 to about 5 parts by weight of suspending agent, and from about 20 to about 50 parts by weight of fluid carrier.

4. A pattern as set forth in claim 1 wherein said solvent phase of said film-forming coating solution comprises approximately 20 to 80 parts by weight methanol, 5 to 25 parts by weight glycerol, 20 to 80 parts by weight of an alcohol selected from the group consisting of ethanol, isopropanol, and mixtures thereof, and up to about 10 parts by weight ethylacetate, and wherein said solute comprises approximately 1 to 50 parts by weight nitrocellulose and approximately 1 to 50 parts by weight melamine resin, and wherein said slurry comprises from about 40 to about 90 parts by weight of finely divided refractory material, from about 0.5 to about 5 parts by Weight of binder, from about 0.5 to about 5 parts by weight of suspending agent, and from about 20 to about 50 parts by weight of fluid carrier.

5. A pattern as set forth in claim 4 wherein said finely divided refractory material is selected from the group consisting of zircon, mica, silica, graphite, aluminum silicates, vermiculite and mixtures thereof,

said binder is selected from the group consisting of thermo-plastic resins, thermosetting resins, and mixtures thereof,

said suspending agent is selected from the group consisting of lithium hydroxy stearate, aluminum octoate, alkaline earth metal salts, aluminum salts of fatty acids, organic resins and polymers, and mixtures thereof,

and wherein said carrier includes at least one halogenated hydrocarbon.

6. A pattern as set forth in claim 1 wherein said refractory slurry comprises from about 20 to about 70 parts by weight of finely divided refractory material, from about 0.5 to about 2 parts by weight of suspending agent, from about 0.2 to about 1 part by weight of binder, and from about 40 to about 50 parts by weight of water.

7. A pattern as set forth in claim 1 wherein said refractory slurry comprises from about 50 to about 60 parts by weight of finely divided refractory material, from about 0.5 to about 1.5 parts by weight of binder, from about 0.5 to about 2 parts by weight of suspending agent, and from about 30 to about 40 parts by weight of alcohol.

8. A pattern as set forth in claim 1 wherein said fluid carrier includes at least one halogenated hydrocarbon.

9. A pattern as set forth in claim 3 wherein said fluid carrier includes at least one halogenated hydrocarbon.

10. A pattern as set forth in claim 4 wherein said fluid carrier includes at least one halogenated hydrocarbon.

11. A pattern as set forth in claim 6 wherein said suspending agent is bentonite and said binder is dextrin.

12. A pattern as set forth in claim 7 wherein said 1 1 1 2 binder is vinsol resin and said suspending agent is ben- 3,270,382 9/1966 Emblem et a1 164--26 tonite. 3,339,620 9/ 1967 Krzyzanowski et al. 164-34 X References Cited UNITED STATES PATENTS I. SPENCER OVERHOLSER, Primary Examiner.

5 EUGENE MAR, Assistant Examiner.

2,441,695 5/1948 Feagin et a1. 16426 2,818,619 1/1958 Bradley et a1. 164-35 X US. Cl. X.R. 2,991,267 7/1961 Bean 16443 X 34 43, 45

3,169,288 2/1965 Dewey 16434 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,426,834 February 11, 1969 Louis J. Jacobs et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1 line 44, "varnished" should read vanished Column 6, line 10, "or should read of Column 9, line 2, "resulting" should read result Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents