Process and apparatus for injection moulding and mouldings produced thereby

摘要

The invention provides a process and apparatus for producing an injection moulding of plastics material. The process comprises introducing the plastics material in the form of a molten stream into a mould space, measuring a quantity of a non-plastics fluid by filling a chamber with the fluid and holding the fluid in the chamber under pressure, said measured quantity being sufficient to achieve an intended weight reduction in the resultant injection moulding and to create a required internal pressure in the moulding to be formed, injecting the fluid into the stream of plastics material, injection of the fluid commencing as soon as the stream of plastics material has passed the position at which the fluid is injected and the fluid creating a fluid containing cavity or core in the plastics material continuing to inject the pressurized fluid at a controlled rate whereby the fluid containing cavity or core extends with the plastics material as the plastics material continues to flow through the mould space, and after the supply of plastics material is terminated maintaining a pressure within the fluid containing cavity or core to hold the plastics material positively against the mould surfaces as the plastics material solidifies and cools until the moulding can itself sustain the form dictated by the mould surfaces.