Patent GB-644994-A (GB)
Title: Investment compositions for the production of refractory molds and method of preparation
IPC: B22C1/16
Filed: 1946-12-18
Abstract: An investment composition for the production of refractory moulds for the precision casting of metals comprises an aqueous slurry of particles of a refractory substance, a low temperature bonding agent comprising a resin of a low degree of polymerization which bonds the refractory particles at a low temperature and which in the presence of a catalyst is polymerized to such an extent that the composition is set, a catalyst to effect the polymerization of said resin, and a high temperature bonding agent which effects bonding of the particles when the set refractory is subjected to the high temperature. Phosphoric acid or one of its acid salts is specified as a higher temperature bonding agent, and serves also as a catalyst for the resin.  Polybasic acids of elements of the 5th, 6th or 8th group of the Periodic Table, or soluble salts thereof such as ammonium silicate, vanadate or tungstate are also suitable.  The refractory particles may be oxides, nitrides or carbides, e.g. silica, magnesia, zirconia, zirkonite, ferrosilicon, carborundum.  The refractory structure bound at 20-60 DEG  C. by the resin is then heated to 250-1000 DEG  C. to bring about high temperature bonding, and at the same time the resin is decomposed to CO2, CO, and carbon.  The resin is present in amount 1/2 to 30 per cent, preferably 2 to 15 per cent based on the refractory.  In examples: (1) a water soluble melamine-urea-formaldehyde condensate is added to a dispersion of silica flour in aqueous phosphoric acid solution and the slurry poured into a flask of wax patterns.  After the mixture has set, the wax is melted out at 80 DEG  C., which sets the resin further and the flask is then gradually heated to 850 DEG  C.  The mould is used for making steel castings; (2) the method of example (1) is repeated, using melamine formaldehyde resin and polystyrene patterns; (3) a urea formaldehyde resin is used in a process as in example 1; (4) silica flour is dispersed in a mixture of phosphoric acid and ammonia of pH2, and urea-formaldehyde resin is used; (5) ammonium dihydrogen phosphate is used to prepare the silica dispersion; (6) the process of example 2 is repeated with different proportion.  Other suitable resins are furane- and phenol-formaldehyde condensation products.ALSO:An investment composition for the production of refractory moulds for the precision casting of metals comprises an aqueous slurry of particles of a refractory substance, a low temperature bonding agent comprising a resin of a low degree of polymerization which bonds the refractory particles at a low temperature and which in the presence of a catalyst is polymerized to such an extent that the composition is set, a catalyst to effect the polymerization of said resin, and a high temperature bonding agent which effects bonding of the particles when the set refractory is subjected to the high temperature.  Phosphoric acid or one of its acid salts is specified as a higher temperature bonding agent and p serves also as a catalyst for the resin.  Polybasic acids of elements of the 5th, 6th or 8th group of the Periodic Table, or soluble salts thereof such as ammonium silicate, vanadate or tungstate are also suitable.  The refractory particles may be of oxides, nitrides or carbides, e.g. silica, magnesia, zirconia, zirkonite, ferrosilicon, carborundum.  The refractory structure bound at 20-60 DEG  C. by the resin is then heated to 250-1000 DEG  C. to bring about high temperature bonding, and at the same time the resin is decomposed to CO2, CO, and carbon.  The resin is present in amount 1/2 to 30 per cent, preferably 2 to 15 per cent based on the refractory.  In examples: (1) a water soluble melamine-urea-formaldehyde condensate is added to a dispersion of silica flour in aqueous phosphoric acid solution and the slurry poured into a flask of wax patterns.  After the mixture has set, the wax is melted out at 80 DEG  C., which sets the resin further and the flask is then gradually heated to 850 DEG C.  The mould is used for making steel castings; (2) the method of example (1) is repeated using melamine formaldehyde resin and polystyrene patterns; (3) a urea formaldehyde resin is used in a process as in Example (1); (4) silica flour is dispersed in a mixture of phosphoric acid and ammonia of pH2, and urea-formaldehyde resin is used; (5) ammonium dihydrogen phosphate is used to prepare the silica dispersion; (6) the process of example (2) is repeated with different proportion.  Other suitable resins are furane- and phenol-formaldehyde condensation products.