Injection moulding of hollow thermoplastic components with gas injection

摘要

Hollow thermoplastic components are made by injecting polymer from an extruder into the cavity of a mould (1, 2) and subsequently and/or simultaneously injecting a pressurised fluid, esp. a gas, through an injection nozzle (5) which protrudes into the cavity. The molten polymer is distributed round the mould walls to form the material and releasing the fluid pressure, the mould is opened and the component (8) is removed. Before closing the mould in preparation for the next cycle the injection nozzle (5) is cooled. Pref. cooling can take place by allowing the pressurising gas (G) to flow through the injection nozzle (5) while the mould is open. The gas is cooled due to expansion in the nozzle (5). In addition or alternatively cooling jets (6) blow on the nozzle (5), pref. automatically, after the mould has been opened.