Patent GB-749813-A (GB)
Title: A casting mold and pattern and process
IPC: B22C9/04
Filed: 1951-10-15
Abstract: 749,813. Moulding - processes ; patterns. BEAN & CO., M. Oct. 15, 1951 [Dec. 4, 1950], No. 23971/51. Drawings to Specification. Class 83 (1). Mould materials; moulds.-In a process of making moulds, a wastable pattern which will retain its form at room temperature is invested with a mixture of refractory granular material and a heat-destructible bonding material, the resulting mass is subjected to conditions adapted first to convert it into a rigid cohesive mould and then to convert the pattern into a readily disintegrable material, and finally removing the pattern material and cleaning the mould by a stream of fluid. As applied to making a mould for casting ferrous or other high-melting alloy &c., e.g. a tyre-mould of grey iron, a negative is made by moulding a flexible resilient plastic; e.g. elastic gel of vinyl chloride with tri-cresyl phosphate or other plasticizer or a synthetic rubber which will vulcanize at room temperature, over the article or model, and from this a positive is made of plaster, with or without a filler, e.g. as in Specification 530,778, [Group V]. This positive is invested with dry sand, the grains of which have been coated with thermo-setting resin. The sand may be coated by mixing it with 1 to 4 per cent each of phenol formaldehyde resin and of a volatile solvent until the sand is again dry and free flowing. If desired fine sand passing 140 to 200 mesh to the inch may be poured first over the damp pattern, the excess being poured back. Then 70 or 50 mesh sand is poured in and the whole vibrated and heated. To prevent distortion in use, wood flour may be added to the sand, or steel reinforcements inserted, but preferably the mould thickness is increased sufficiently to resist distortion. Other binders which bond at a lower temperature may also be added in some cases. In a modification the pattern is sprayed with a slurry of fine resincoated sand and water, or of fine sand, powdered and liquid phenolic resins in equal amounts, water and, if desired, clay. In this case the wet pattern is preferably first surface-dried with acetone and coated by spraying-on a solution of collodion or of potash soap followed by finelypowdered graphite, red iron oxide, alumina or aluminium or other material desired to form the surface of the mould. The subsequent sand investment should be poured in while the sprayed coating is still wet. The mould is dried in circulated air at 400-475‹ F. for 3 to 12 hours. The pattern is then broken up and removed in pieces or removed by soaking in water and directing a jet of air or water thereon. Stainless steel strips, sheet metal, wire, screwthreaded or other inserts may be partly embedded in the pattern so as to be transferred to the sand mould and thus to the iron tyre mould or other casting. A mould-part made in this way may be associated with other mouldparts, and cores made in any way, and with chills, inserts &c. and be invested with green sand or other refractory. In a further modification the pattern may be of paraffin wax or lowmelting-point alloy. A suitable plaster comprises 40 parts moulding plaster, 50 of sand passing 50 mesh, and 10 of talc with, optionally ¢ part each of sodium silicate and Portland cement and ¢ to 2 parts of calcium sulphate dihydrate. Steel reinforcements may be used and auxiliary binders and other mouldmaterials, e.g. urea formaldehyde resin and wood flour may be added. Dielectric baking may be used. U.S.A. Specifications 2,349,806, 2,391,855, 2,402,528, 2,435,643 and 2,531,496 also are referred to.