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United States Patent 5288223
Douris , ê et al.

Three stage intermixing feed screw for polymers

Toro February 22, 1994

Abstract

A polymer-extruder screw has a mixing section with relatively deep channels between flight lands at a proximal end, progressively shallower channels with a progressively larger screw core of a central transition section, and finally a metering section having a plurality of at least three pressure channels juxtaposed helically between flight lands having channel interruptions comprised of helical inclines and constant-radii tops in helical progression to a distal end of the extruder screw where the pressure channels end with equal depth at an interface with a metering gate of an extruder. The pressure channels can be symmetrical or asymmetrical in angles of incline and decline at opposite helical sides of the channel interruptions for optimizing channel depths, for positioning of maximum channel depths in relation to tops of channel interruptions, for equalizing channel depths at the distal end of the extruder screw and for optimizing incline and decline advantages for polymers with different characteristics. Helical degrees of channel-interruption cycles can be different for different polymers. The screw core in the mixing section can be graduated in diameter and distance between flight lands can be designed as required for different polymers.