GB770527A - Refractory moulds for investment casting - Google Patents

Abstract

A lost wax moulding process comprises coating a wax or other expendable pattern with a finely divided refractory filler suspended in a liquid binder, dusting a relatively coarse refractory onto the coated pattern, then carrying out at least once the sequence of covering the coated pattern with acid hydrolysed methyl or ethyl silicate solution, the solution being prepared by using only HC1 for the acid to promote hydrolysis and not having any refractory material suspended in it, followed by dusting the coated pattern with a relatively coarse refractory. The coating is then allowed to dry and the mould body formed by investment with a powdered refractory which may be suspended in a suitable bonding liquid. The initial coating may be 200 mesh silica flint or zirconium silicate in a binder prepared from sodium silicate or potassium silicate, with or without hydrochloric acid, together with a wetting agent such as a soap solution and if desired a film forming agent such as ammonium or sodium alginate or alginic acid. Other compositions may be bound with ethyl silicate. One specific example quoted comprises 200 mesh alumina cement, a solution of dioctyl or dinonyl sodium sulphosuccinate, water and 2 ethyl hexanol. The relatively coarse refractory may be fireclay grog, calcined kaolin, or zirconium silicate. The acid hydrolysed solution is preferably ethyl silicate, and specific examples of solutions and methods of preparation are quoted. The body of the mould may be of fireclay p grog, sillimanite, mullite, calcined kaolin, zirconium silicate, zirconia, silica, or alumina, and binders therefore may be hydrolysed ethyl silicate solutions, or the acid reaction products obtained from the reaction of sodium silicate solution with a dilute mineral acid such as nitric acid. Alternatively, the body of the mould may be a mixture of alumina and Portland cement bound with water. Specifications 290,717 [Class 22], 650,532, 674,137 and 678,035 are referred to.