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United States Patent 4052038
Douris , ê et al. October 4, 1977

Screw extruder for thermoplastics synthetic materials or elastomers

Brand October 4, 1977

Abstract

A screw extruder for thermoplastics synthetic materials or elastomers having a screw rotating in a cylinder wherein the screw has a mixing part having a plurality of first grooves at an upstream position thereof inclined in the direction of feed, a plurality of second grooves at a position downstream of the first grooves and also inclined in the direction of feed and a grooveless portion between said first grooves and said second grooves, and the cylinder has a mixing part which surrounds said grooveless portion of the mixing part of the screw and has third grooves therein which extend axially or are inclined in the direction of feed, the number of said first grooves, said third grooves and said second grooves differing. Preferably the number of grooves diminishes in the feed direction that is to say the number of said first grooves exceeds the number of said third grooves and the number of said third grooves exceeds the number of said second grooves. The transitions of said third grooves to the cylinder bore are preferably gradual transitions.