Hollow plastic component manufacture involves melt injection into a first cavity, then removal of non-solidified melt to a secondary cavity by pressure reduction

摘要

A main cavity(3) is filled with plasticized plastic which is then cooled so that the outer surface solidifies to form a shell. Pressure in the first cavity is then reduced below atmospheric and the still fluid plastic inside the solidified shell is extracted from the cavity. An Independent claim is also included for the process equipment which comprises a molding tool with a main cavity having a first connection(1) to an extruder and a second connection(5) to a vacuum pump(10) for extraction of plastic from the cavity. A vent(14) into the main cavity enables a pressure balance to be achieved. Preferred Features: The main cavity is connected to a secondary cavity(7) via the first connection which includes a closure valve(6). Pressure in the secondary cavity may be reduced either by a vacuum pump connected to the cavity or by varying the volume of the cavity. Cavity volume change can be effected by movement of a piston or screw in the secondary cavity or in a connection to it. After extracting melt from the main cavity positive pressure is applied via the vent to stabilize the hollow chamber in the molding.