Release of blowing gas in injection moulding of hollow articles

摘要

Hollow thermoplastic articles (6) are made by injecting melt into the cavity of a mould (1, 2) and simultaneously and/or subsequently injecting a pressurised fluid through one or more nozzles (5). After cooling the fluid pressure is released through one or more pressure release nozzles (7) which are separate from the fluid injection nozzles (5). Pref. the pressure release nozzle (7) is positioned away from the injection nozzle (5) and can be moved so that it is only introduced when the article has partially hardened. A short pressure pulse is pref. used to ensure that the nozzle is clear. The nozzle is pref. adjustable to give a gap of /= 0.1 mm. The released nitrogen gas can be collected in a vessel (8) and reused.