Method and device for injection moulding of plastic articles made of thermoplastic material

摘要

Injection molding of large foamed thermoplastic plastic components comprises adding melt at screw flight and holding constant difference between melt and blowing agent pressures. A fluid blowing agent (4) is added to a thermoplastic melt (1) in an injection molding unit cylinder (3) in the region of the screw flight (7) and the mixture is injected into a tool cavity (8). During fluid addition either: (a) the pressure difference (deltap) between fluid pressure (pF) and melt pressure (pS) remains constant; (b) a volumetric metering or control of fluid addition occurs; (c) a constant pressure difference is maintained by volumetric metering and/or control of fluid addition. An Independent claim is made for the process equipment which has an arrangement (11) for injecting fluid (4) into melt close to the screw flight (7) and either: (a) pressure measuring equipment (12,13,14) for determining both melt and fluid pressures and pressure difference or (b) equipment for measuring and/or metering the volume of added fluid.