GB774184A - Improvements in or relating to moulds for metal casting - Google Patents

Abstract

A moulding process comprises investing a pattern with two different refractory mixes, one of which is formed into a layer in contact with the pattern and the other is formed as a backing to said layer, the layer in contact with the pattern being composed of a highly refractory aggregate and a lower alkyl silicate containing sufficient aqueous acid to hydrolyse the same, and the backing consisting of a normal foundry type silica core sand and any desired binder, and when the alkyl silicate has set by hydrolysis and gelling of the binder, igniting said layer to burn off the alcohol released in the hydrolysis. The backing layer may be bound with sodium silicate and hardened by CO2 gas, and the lower alkyl silicate is preferably ethyl ortho-silicate. In one method a pattern is encased by a layer of plaster or modelling clay and sand-sodium silicate mix rammed thereabout and hardened by CO2 gas. The backing is removed, the plaster or clay stripped from the pattern, the backing replaced and the space formerly occupied by the plaster or clay filled with the acidified ethyl silicate refractory mix. In a modification the sand-sodium silicate mix is rammed about an oversize pattern which is then replaced by the original pattern and the space between the latter and the hardened mix filled with the facing layer. After ignition of the alcohol the moulds may be baked. The mix for the facing layer may be as described in the parent Specification.