PROCESS AND APPARATUS FOR GAS-ASSISTED INJECTION MOULDING PROCESS WITH EXPULSION OF PLASTICS MATERIAL

摘要

The present invention relates to a process for injection moulding a hollow plastics article. The process includes the step of injecting a quantity of molten plastics material (20) into a mould cavity (25) to fill fully the mould cavity; and injecting pressurised fluid (31) into the plastics material in the mould cavity. At least one valve (29) is opened to allow a portion of the molten plastics material in the mould cavity to be expelled into at least one secondary cavity (26) coupled to the mould cavity, sufficient plastics material being expelled to fill the at least one secondary cavity. The remaining plastics material in the mould cavity is permitted to solidify and the fluid is exhausted from the mould cavity. The plastics article is then removed from the mould. The process includes determining when the step of filling full the mould cavity is at or near completion, and initiating the step of injecting pressurised fluid in response to that determination.