Injection mould of foam plastics

摘要

Components are moulded from a foamable molten plastic and a foaming agent, e.g. granular polypropylene or polystyrene sprayed with azobisformamide. The pressure exerted on the mixture is higher than the blowing pressure of the foaming agent. The mixture is maintained in liquid state until it has reached the injection mould and the foaming process is controlled to produce components of high cellular quality. The liquid mixture is placed in a mould cavity at a pressure above that necessary for foaming and the temperature is increased to that necessary for foaming. After the mould is filled the pressure is reduced to a value equal to the blowing pressure.