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United States Patent 4994223
Douris , ê et al.

Extruder screw and method for the extrusion of thermally sensitive thermoplastic materials

Hestehave , Ê et al. February 19, 1991

Abstract

An extruder screw and a method for extrusion to achieve high output rates with thermally sensitive plastic materials and without thermal degradation problems involving the use of a single flight metering type extruder screw having an initial feed zone, distal metering zone, and a transition zone interconnecting the feed and metering zones. In particular, improvements in the extrusion of thermally sensitive plastics such as PVC are achieved through use of a compression ratio of approximately 2:1, a constant lead and pitch, and a proportioning of the length of the feed zone, transition zone, and metering zone relative to the total length of the zones of 27-33%, 23-25%, and 45-48%, respectively. To achieve cooler and more uniform mixing with rigid PVC, polyethylene and like materials, an improved arrangement for using rings of mixing pins is provided.