Sequential co-injection unit adapted for structural foam molding

Claim 1

A single screw, single nozzle injection unit for sequential injection of unfoamed and foamed plastics melts to a mold for forming skin covered foamed plastics articles which comprises a housing having a cylindrical bore, an elongated screw rotatably mounted in said bore, a means feeding plastics material to said bore at one end of said screw, a gas inlet feeding foaming agent to said bore intermediate the ends of said screw, a seal radiating from said screw intermediate the ends thereof defining an extrusion gap communicating with said gas inlet, said screw having helical vanes mating with said bore and varying root diameters along the length thereof, said root diameters cooperating with said vanes to provide a feed zone advancing plastics material from the one end of the screw, a compression zone for compressing and plasticizing the material, a first pumping zone for extruding the material through said gap, a gas well zone for mixing the plastics material extruded from the gap with gas from said gas inlet, a second pumping zone advancing the gas and plastics material, and a mixing zone forming a gas foamed plastics material, a first port communicating with said first pumping zone, a second port communicating with said mixing zone, a first injector communicating with said first port, a second injector communicating with said second port, a nozzle, a valve selectively joining said injectors with said nozzle, injector heads for forcing the plastics material from the injectors to the valve, and an actuator for the valve to first join the first injector with the nozzle for feed of skin melt material to the mold, for next joining the second injector with the nozzle for feed or foamed melt material to the mold and for next sealing the nozzle from both injectors to allow solidification of the melt material in the mold.