GB190318764A - Improvements in the Production of Moulds for Castings - Google Patents

Abstract

18,764. K³ller, M. Aug. 31. Moulding.-Moulds for undercut and complicated objects such as busts are made without the use of elastic patterns. In forming a mould for such an object, the pattern is coated with a plastic mass which contains an elastic and a binding medium, so that it is elastic before it hardens, and can thus be stripped from the pattern. The hardening may be assisted by heat. A sand mould is formed by placing a sand box over the pattern after it has been coated with the elastic material, and ramming in sand, the lower half of the pattern being supported by being embedded in sand. After the sand mould is thus formed, the plastic mass is stripped from the pattern and placed therein to harden. The plastic mass is made by mixing sand, infusorial earth, fireclay, wood, coal-dust, tow-waste, or molasses &c. with a binding-medium such as plaster of Paris, resin, glycerine, dextrin, or gum arabic, and adding the mixture to a solution of an elastic material such as glue, gelatine, agar-agar, carragheen, caoutchouc or gutta-percha, starch, &c. In order to render the mould insoluble, some substance which acts upon the elastic substance such as alum, chromates or formalin, is added to the mass. For producing porosity, the elastic substance may afterwards be removed by burning or glowing, or by treatment with acids or other dissolving-agents. For large numbers of similar articles, a plaster of Paris mould is first formed in which moulds of the elastic material are moulded. A divided pattern is used, and the lower half is supported in a bed of clay or similar material, while the upper half is coated with a layer of clay. A cap of porous material, or of perforated metal, is placed over the layer of clay. The model is then inverted, and the remaining half is coated with a layer of clay surmounted by a cap, the two caps being formed with interlocking lugs and grooves. Each half of the model with the layer of clay and cap is placed in an inverted position, and a layer of plaster of Paris spread on the upturned part, so that when turned over each half of the model with the clay and cap is supported by a bed of plaster of Paris. When the clay is removed, a mould is left in which the elastic material may be moulded. The core is formed in the usual way. The thin layer forming the mould may be placed in a sand bed instead of a cap. An elastic or fusible pattern may be used round which a plaster of Paris mould is formed, the pattern being removed or melted out.