GB768232A - Precision moulds for casting metals using polysilicate binders - Google Patents

Abstract

A binder for refractory material used for making moulds or cores for precision casting is prepared by hydrolysing ethyl silicate in the presence of a stable silica sol. The ethyl silicate may be tetra-ethoxy silane, or the product obtained by reacting silicon tetrachloride with ethyl alcohol as described in Specification 290,717 [Class 2 (ii)], or the product described in Specification 674,137, [Group IV (b)]. A suitable ethyl silicate is available under the Registered Trade Mark "Silester." Hydrolysis is preferably effected in acid conditions, but may be carried out under basic condition or by emulsifying the ethyl silicate with the silica sol. The silica sol may be prepared by reacting a water-soluble inorganic silicate, e.g. sodium silicate with an ion-exchange resin. Suitable silica sols are available under the Registered Trade Mark "Syton." Refractories specified are silica, sillimanite, calcined kaolin, fireclay grog, zircon and zirconia (in which materials the lime, magnesia and alkali content must not exceed 4 per cent). In examples, the binding agent is made by (1) adding ethyl silicate to a solution of silica sol, hydrochloric acid and ethyl alcohol, and adding further silicate 1 hour after mixing; (2), (3) adding to hydrochloric acid solution, silica sol, ethyl alcohol and finally ethyl silicate; (4 to 6) adding to silica sol, hydrochloric acid, then ethyl alcohol and finally ethyl silicate: the respective binders are then mixed with (3 to 5) a mixture of equal parts by weight of zircon sand and calcined kaolin, or (6) fireclay grog, to form mould investment slurries.