Method and apparatus for injection molding foamed plastic articles

Claim 1

PROCESS FOR MOLDING FOAMED THERMOPLASTIC ARTICLES WHICH COMPRISES THE STEPS OF (A) MELTING A MIXTURE OF A BLOWING AGENT AND A FOAMABLE THERMOPLASTIC MATERIAL IN AN EXTRUDER AT A TEMPERATURE ABOVE THE FOAMING TEMPERATURE OF SAID BLOWING AGENT AND AT A PRESSURE ABOVE THE FOAMING PRESSURE THEREOF; (B) EXTRUDING THE RESULTING MOLTEN MIXTURE INTO AN EXPANDING ACCUMULATION ZONE WHILE MAINTAINING SAID MIXTURE THEREIN IN THE MOLTEN TATE AND AT A PRESSURE ABOVE THE FOAMING PRESSURE THEREOF; (C) ESTABLISHING COMMUNICATION BETWEEN SAID ACCUMULATION ZONE AND A MOLD MAINTAINED AT A PRESSURE NO GREATER THAN THE FOAMING PRESSURE OF SAID MOLTEN MIXTURE; (D) RAPIDLY FORCING SAID MOLTEN MIXTURE FROM SAID ACCUMULATION ZONE INTO SAID MOLD WHEREBY THE PRESSURE DIFFERENTIAL BETWEEN SAID ACCUMULATION ZONE AND SAID MOLD CAUSES SAID MIXTURE TO RAPIDLY EXPAND IN SAID MOLD.