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United States Patent 4802140
Douris , ê et al.

Method and molding screw for injection molding

Dowling January 31, 1989

Abstract

This invention relates to a method and molding screw for injection molding. The molding screw has a fixed inner screw mounted within a rotatable and reciprocally movable outer screw. The outer screw is continuously rotated throughout the injection cycle to counter the back flow of melt material around the screw, subject the melt material surrounding the inner screw to a vigorous mixing action, add additional thrust to inject the melt material into the mold, and return the outer screw to its initial starting position. A rod-type electrical heater is internally positioned in the fixed screw to maintain the temperature throughout the melt material surrounding the inner screw at a substantially constant value which is substantially equal to the barrel temperature.