GB577373A - Improvements in or relating to the moulding of thermosetting materials - Google Patents

Abstract

577,373. Injection-moulding thermosetting material. GOLDHARD, F. K., and PRENN, D. D. June 29, 1944, No. 12420. [Class 87 (ii)] The material is preheated throughout its mass before the injection operation to a temperature near the softening point but below the polymerization point, is maintained constantly below such polymerization point up to the time of leaving the injection feed passage, and is then heated above the polymerization point as it passes from the passage to enter the mould cavities. The apparatus shown comprises an injection cylinder 1, in which a passage 3 connects with a heating chamber 4 provided with electrodes 5, 6 for dielectric high-frequency heating. The cylinder 1 is maintained at a constant temperature by heating elements 9, thermostatically controlled. The injection nozzle 11, the temperature of which is similarly controlled, is cooled, especially during and after the injection operation, by liquid circulating in a space 12. With this arrangement, the plastic material, preheated throughout to a temperature near the softening point, is maintained below the polymerization temperature whilst in the injection cylinder and nozzle. As it passes through the sprue 13, which is heated electrically or otherwise by a device 14, or when it reaches the mould 18, the material is heated above the polymerization point. All or most of the heat required for polymerization may be imparted by the sprue channel, and a slight excess of heat may be applied in the sprue, during the injection stroke only, the excess being provided to replace heat losses in the mould.