GB429220A - Process for the preliminary treatment of smooth cast pieces, in particular, centrifugally cast tubes manufactured in chilled moulds, for coatings of paint and other coatings - Google Patents

Abstract

In a process of treating smooth castings to enable them to receive a coating of paint, tar, &c. an intermediate coating of sintering material is applied and burnt on before the application of the paint &c. The sintering material may be applied to castings which have already been produced or may be applied during their manufacture in chilled moulds. Materials suitable for the intermediate coating are stone powder, cement or a pulverised preliminary product thereof, founder's black, pebble powder, or phosphorus salts, which, at high temperatures, become sintered or combine with the hot shell of the casting. The material may be applied to a rotating centrifugal mould before the commencement of the casting or during the casting, or may be applied to the casting itself whilst it is still glowing immediately after removal from the chilled mould, by means of sifting or blowing apparatus. Alternatively the material may be applied to the casting during its passage through an annealing furnace or immediately after it has left the annealing furnace, or by means of a separate furnace. When applied during or after annealing the nature of the material may be adapted to each temperature zone of the annealing furnace, e.g. pure pebble powder at high temperatures and a mixture of fluxes such as fluorspar, borax, boric acid, &c. at low temperatures. A phosphate layer may be applied to the casting either additionally to or alternatively with the sintered material either by sintering a pulverized phosphorus compound at the necessary temperature, or by dipping the casting in a hot water bath in which phosphorus salts are dissolved. The salts may be added to a hot water tempering bath used for the casting.ALSO:In a process of treating smooth castings to enable them to receive a coating of paint, tar, &c. an intermediate coating of sintering material is applied and burnt on before the application of the paint &c. The sintering material may be applied to castings which have already been produced or may be applied during their manufacture in chilled moulds. Materials suitable for the intermediate coating are stone powder, cement or a pulverized preliminary product thereof, founder's black, pebble powder, or phosphorus salts, which, at high temperatures, become sintered or combine with the hot shell of the casting. The material may be applied to a rotating centrifugal mould before the commencement of the casting or during the casting, or may be applied to the casting itself whilst it is still glowing immediately after removal from the chilled mould, by means of sifting or blowing apparatus. Alternatively the material may be applied to the casting during its passage through an annealing furnace or immediately after it has left the annealing furnace, or by means of a separate furnace. When applied during or after annealing the nature of the material may be adapted to each temperature zone of the annealing furnace, e.g. pure pebble powder at high temperatures and a mixture of fluxes such as fluorspar, borax, boric acid, &c. at low temperatures. A phosphate layer may be applied to the casting either additionally to or instead of the sintered material either by sintering a pulverized phosphorus compound at the necessary temperature, or by dipping the casting in a hot water bath in which phosphorus salts are dissolved. The salts may be added to a hot water tempering bath used for the casting.