Patent GB-649770-A (GB)
Title: Patterns for the production of refractory molds and compositions therefor
IPC: B22C7/02
Filed: 1946-12-18
Abstract: A combustible pattern, for use in the production of a refractory mould for casting metals, is moulded from a homogeneous mixture of a mouldable synthetic organic plastic material and a finely-divided polysaccharose filler, the proportion of plastic material to filler by weight being within the range 1 : 3 to 6 : 1 and the pattern on combustion leaving not more than 2 per cent by weight (based on the plastic material plus filler) of a fluffy powdery ash.  The plastic material may be polyvinyl acetate, butyrate or formal, polystyrene, polymethylmethacrylate, cellulose acetate or acetobutyrate, ethyl cellulose or starch acetate.  The polysaccharose filler may be wood flour, cork, cotton flock, cotton linters, paper pulp, shredded pulp, lignin flour, cotton cord, vegetable fibres, nut shell flours, cellulose, starch or modified starch.  The composition may contain also a plasticizer, such as castor oil, camphor, dibutyl or dioctyl phthalate, tricresyl phosphate or octyl or dilauryl sebacate; a water-repellant, such as an oil or a wax; and a combustion accelerator such as nitroglycerin, nitroglycol, nitrobenzene, nitrocellulose or ammonium nitrate.  The Specification as open to inspection under Sect. 91 contains also the following matter:-(a) A pattern mix is made by ball milling 17 gr. of cellulose acetate and 83 gr. of wood flour and compression-moulding 12 gr. of this mix at 200 DEG  C. and 20,000 lbs. per square inch for 4 minutes.  (2) The filler may be sulphur. (3) The water-repellant may be soap.  This subject-matter does not appear in the Specification as accepted.ALSO:Relates to a combustible pattern for use in the production of a refractory mould for casting metals, the mould being made by casting a refractory composition about the pattern and, after the composition has set, firing the assembly to burn out the pattern. The Specification states that it is known to make such a pattern from cellulose acetate, ethyl cellulose, polystyrene, polyacrylates and wax.  According to the invention the pattern is moulded from a homogeneous mixture of a mouldable synthetic organic plastic material and a finely-divided polysaccharose filler, the proportion of plastic material to filler by weight being within the range 1 : 3 to 6 : 1 and the pattern on combustion leaving not more than 2 per cent by weight (based on the plastic material plus filler) of a fluffy powdery ash.  The plastic material may be polyvinyl acetate, butyrate or formal, polystyrene, polymethylmethacrylate, cellulose acetate or acetobutyrate, ethyl cellulose or starch acetate.  The polysaccharose filler may be wood flour, cork, cotton flock, cotton linters, paper pulp. shredded pulp, lignin flour, cotton cord, vegetable fibres, nut shell flours, cellulose, starch or modified starch.  The composition may contain also a plasticizer, such as castor oil, camphor, dibutyl or dioctyl phthalate, tricresyl phosphate or octyl or dilauryl sebacate; a water-repellent, such as an oil or a wax; and a combustion accelerator such as nitroglycerin, nitroglycol, nitrobenzene, nitrocellulose or ammonium nitrate.  The pattern may be made by casting, compression-moulding or injection-moulding.  When the pattern is made by injection-moulding, the mould may be made of steel or stainless steel and the interior surface thereof may be highly polished or chromium-plated.  A pattern thus made may be mounted by means of wax in a flask, an aqueous slurry of one or more highly-refractory materials, with or without a binder, is poured into the flask, and the slurry is allowed to set at room temperature or slightly heated for this purpose.  Then the filled flask is placed in an oven and fired to bake the mould and burn out the pattern.  The residue of ash may be removed by an air jet. A pattern made by compression-moulding from a mix including polyvinyl acetate and shredded sulphite pulp may, before mounting in a flask, be sprayed with a solution of polystyrene in benzene, to reduce the swelling of the pattern in the slurry.  For the same reason a pattern made by injection-moulding from a mix including polymethylmethacrylate powder and wood flour may be sprayed with a solution of nitrocellulose in acetone containing paraffin wax.  The Specification as open to inspection under Sect. 91 contains also the following matter: (a) a pattern mix is made by ball milling 17 gr. of cellulose acetate and 83 gr. of wood flour and compression-moulding 12 gr. of this mix at 200 DEG  C. and 20,000 lbs. per square inch for 4 minutes; (2) the filler may be sulphur; (3) the water-repellent may be soap.  This subject-matter does not appear in the Specification as accepted.