Patent GB-636947-A (GB)
Title: Patterns for the production of refractory molds and compositions therefor
IPC: B22C7/02
Filed: 1946-12-18
Abstract: A pattern for use in making metal-casting moulds is made from low molecular weight polystyrene or low molecular weight polymethylmethacrylate, the molecular weight being between 5000 and 40,000.  It is stated that it is known to make the patterns from commercial resins of high molecular weight (more than 200,000).  The pattern may contain a plasticizer, e.g. dioctylphthalate, diphenyl or naphthalene, and fillers such as carbon black or wood flour.  The low molecular weight compounds may be prepared by adding a chain-transfer agent such as carbon tetrachloride or dodecyl mercaptan to the polymerizing system. Thus, a mixture of styrene monomer, carbon tetrachloride and benzoyl peroxide is heated, and the resulting polymer isolated from the reaction mixture and dried.  The mixture may contain also water and a suspension stabilizer, e.g. gelatin or polyvinyl alcohol.  The Specification as open to inspection under Sect. 91 states also that the pattern may be made from other (low molecular weight) materials, viz.: (a) vinyl resins in general, such as polyvinyl acetate, butyral and carbazole; (b) co-polymers of styrene with other monomers; (c) polyethyl methacrylate and polycyclohexyl methacrylate; (d) polyethylene; and (e) cellulose derivatives such as cellulose acetate, acetate butyrate and acetate propionate.  The Specification states also that it is known to make the patterns from commercial high molecular weight cellulose acetate, ethyl cellulose, polyacrylates and polystyrene.  This subject-matter does not appear in the Specification as accepted.ALSO:An alloy comprises 3.9 to 4.3 per cent aluminium, 0.3 per cent copper, 0.03 to 0.06 per cent magnesium, 0.075 per cent iron, 0.003 per cent lead, 0.003 per cent cadmium, 0.001 per cent tin and the remainder zinc.ALSO:Relates to patterns or replicas for use in making refractory moulds by casting an investment of refractory composition about a pattern and firing the assembly after the investment has hardened. According to the invention the pattern consists essentially of low molecular weight polystyrene or low molecular weight polymethylmethacrylate, the molecular weight being between 5,000 and 40,000.  It is stated that it is known to make the patterns from commercial resins of high molecular weight (more than 200,000).  When the assembly of investment and pattern is fired the pattern is burnt out.  The pattern may contain a plasticizer, e.g. dioctylphthalate, diphenyl or naphthalene, and fillers such as carbon black or wood flour, and may be made by injection-moulding or compression-moulding. The refractory investment material may be an aqueous slurry of sand, lime, silica, zirconia or alumina or mixtures thereof, and a binding agent.  Such material is described in Specification 644,944.  In making the mould the pattern is mounted by means of wax, a flask is placed over the mounted pattern, and the investment material is poured in and left at room temperature or heated slightly until it has hardened.  Then the flask is placed in an oven to fire the mould and burn out the pattern.  The Specification as open to inspection under Sect. 91 states also that the pattern may be made from other (low molecular weight) materials, viz.:-(a) Vinyl resins in general, such as polyvinyl acetate, butyral and carbazole; (b) co-polymers of styrene with other monomers; (c) polyethyl methacrylate and polycyclohexyl methacrylate; (d) polyethylene; (e) cellulose derivatives such as cellulose acetate, acetate butyrate and acetate propionate.  The Specification states also that it is known to make the patterns from commercial high molecular weight cellulose acetate, ethyl cellulose, polyacrylates and polystyrene.  This subject-matter does not appear in the Specification as accepted.