| abstract |
In the casting or extrusion of ceramic building units such as bricks there is interposed between the mould or die and the mouldable ceramic material a film comprising an aqueous solution of a surface active agent and an alkali, and/or there are incorporated in the material prior to casting or extrusion a water-soluble surface active agent and water-soluble alkaline material. The surface active agent is preferably anionic, e.g. sodium alkyl aryl sulphonate. Water soluble phosphates as carbonates e.g. of sodium or mixtures thereof, are suitable for the alkaline material. Anti-corrosive, e.g. sodium bichromate, may be added; also anti-bacterial substances, e.g. copper sulphate, to inhibit rotting of conveyer belts. Inert extenders e.g. sodium sulphate, may be added. For treatment of mouldable material in an extrusion machine, a suitable strength of solution is 1 lb. of the mixture of 8-10 gallons of water, for 24,000 lb. material. The strength of a solution first incorporated is material to be moulded varies with the material and is generally 1 lb. in 100 gallons for 5000 lb. A specific example of a suitable mixture is 12 1/2 % sodium alkyl aryl; 40% Na3PO4; 35% Na2CO3; 10% Na2SO4; 1% CuSO4; 1% sodium benzoate and 1/2 % colouring matter. |