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United States Patent 4900156
Douris , ê et al. February 13, 1990

Twin screw extruder with thread-free mixing zones

Bauer February 13, 1990

Abstract

Apparatus for mixing material in a twin screw extruder by longitudinally advancing material by the interengaging threads of two screws in the housing of a twin screw extruder such that a plurality of separate streams of material are advanced by the threads of the screws, combining the separate streams of material in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement around one of the screws, and thereafter dividing the combined stream back into separate streams downstream of the thread-free zone. In the thread-free zone, a baffle element is mounted on the shaft of one of the screws, the baffle element being of conical shape and increasing uniformly in diameter in the direction of advance of the product. The smaller end of the baffle element has a diameter which is substantially equal to the inner diameter of the threads of the associated screw and the larger end has a diameter which is substantially equal to the outer diameter of the threads of the screw. The shaft of the other screw supports a cylindrical sleeve in the thread-free zone.