US Patent 7594529 Investment casting process

A method for the production of a shell mould. The method comprises the sequential steps of:(i) dipping a preformed expendable pattern into a slurry of refractory particles and colloidal liquid binder whereby to form a coating layer on said pattern,(ii) depositing particles of refractory material onto said coating, and(iii) drying,steps (i) to (iii) being repeated as often as required to produce a shell mould having a primary coating layer and at least one secondary coating layer, characterised in that during at least one performance of step (ii) a gel-forming material is also deposited onto the coating layer formed in step (i).