Patent GB-1025815-A (GB)
Title: Improvements in or relating to refractory moulds
IPC: B22C1/20
Filed: 1964-10-16
Abstract: In the production of a refractory mould by mixing a particulate refractory material and a binder, the refractory material which may be silica, alumina, mullite, calcined clay, sillimanite or zirconia is coated with a layer of a nitrogenous organic base or an alkali metal or alkaline earth metal salt thereof, the base or the salt having from 4-22 carbon atoms, preferably 8-22, and a vapour pressure of less than 10 mm. of Hg at temperatures of less than 100 DEG  F. and having an m.p. of from 70 DEG  F. to 160 DEG  F.  The binder is a solution of a prehydrolysed alkyl silicate and it is mixed with the refractory to form a slurry which is used to invest a pattern, which is removed after the slurry has gelled, to form the mould.  The mould may be fired, e.g. at a temperature up to 2000 DEG  F., to form a ceramic bond and give the mould more strength. The refractory is coated by treating it with the base (or the salt) dissolved in a solvent, e.g. a low mol. wt. alcohol, a cetone or methyl ethyl ketone, and the solution may contain 1-25% by weight of the amine, and the amount of amine used is from 0.1% to 2% by weight of the refractory, the preferred range being 0.3 to 0.7%.  After the grains have been treated, e.g. by spraying while mixing or tumbling, the solvent is evaporated to leave a coating on the grains, the moisture or solvent content of the so-coated refractory preferably being less than 5% by weight. Many suitable coating materials are indicated in the Specification but those preferred are diethylene triamine, dodecylamine actadecyl - amine, and the amines R-NH.CH2.CH2.CH2.NH2 where R is an alkyl group derived from a fatty acid.  The coating layer on the particles may be a monomolecular layer.  The preferred binder is a prehydrolysed ethyl silicate which may if desired only be partially prehydrolysed.ALSO:In the production of a refractory mould by mixing a particulate refractory material and a binder, the particulate refractory material which may be silica, alumina, millite, calcined clay, sillimanite or zirconia, is coated with a layer of nitrogenous organic base or an alkalimetal or alkaline earth metal salt thereof, the base of the salt having from 4-22 carbon atoms, preferably 8-22 and a vapour pressure of less than 10 mm of Hg at temperatures of less than 100 DEG F. and having a mp. of from 70 DEG F. to 160 DEG F.  The binder may be a solution of a prehydrolysed alkyl silicate.  The refractory is coated by treating it with the base (or the salt) dissolved in a solvent e.g. a low mol wt. alcohol, acetone, or methyl ethyl ketone, and the solution may contain 1-25% by weight of the amine and the amount of amine used is from 0.1% to 2% by weight of the refractory the preferred range being 0.3 to 0.7%. After the grains have been treated e.g. by spraying while mixing or tumbling, the solvent is evaporated to leave a coating on the grains, the moisture or solvent content of the so-coated refractory being less that 5% by weight.  Many suitable coating materials are indicated in the Specification but those preferred are diethylene triamine, dodecylamine, octadecylamine, and the amines R-NH-CH2 . CH2 . CH2-NH2 where R is an alkyl group derived from a fatty acid.  The coating layer on the particles may be a monomolecular layer.  The preferred binder is a prehydrolysed ethyl silicate, which may if desired only be partially prehydrolysed.