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United States Patent 4770539
Douris , ê et al. September 13, 1988

Barrier screw

Heathe September 13, 1988

Abstract

The present invention relates to a barrier screw having improved solids conveying capability. The barrier screw comprises a feed zone having a helical primary flight defining a solid material feed path, a transition zone for converting the solid material into molten material having a solids channel and a melt channel, and a metering zone for mixing molten plastic material from the melt path. In the feed zone, the helical flight defining the feed path is characterized by a substantially constant leading edge pitch and a trailing edge pitch which causes the thickness of the flight to increase as one moves along the screw barrel toward the beginning of the melt channel in the transition zone.