In the twin screw extruder the interengaging threads of the two screws in the housing of the twin screw extruder longitudinally advance the material in a plurality of separate streams and these separate streams of material are combined in a thread-free zone of the screws in which the passage area for the streams of material undergoes uniform reduction and lateral displacement for confinement around one of the screws whereafter the combined stream is divided back into separate streams downstream of the thread-free zone.
    The twin screw extruder as constructed according to the invention carries out a unique method in which material is longitudinally advanced by the interengaging threads of the two screws in the form of a plurality of separate streams of material as shown in FIG. 2. In the thread-free zone of the screws, the separate streams of material are combined and the combination takes place in the uniformly reducing passage area 14 between the conical baffle element 10 and the sleeve 11, such that the combined stream has been laterally displaced around sleeve 11 wherefrom the material is thereafter divided from the combined stream back into the separate streams downstream of the thread-free zone. As shown in FIG. 1, the successive combining and dividing of the material takes place in alternation between the screws by placing the conical baffle elements 10 and the sleeves 11 in alternation on the different screws.
    A twin screw extruder comprising a housing, two extruder screws supported in said housing for rotation in the same direction about parallel, longitudinal axes of rotation, each of said screws including a shaft and a screw section having threads secured on the associated shaft for rotation therewith, the threads of the screw section of one shaft interengaging with the threads of the screw section of the other shaft to advance a product longitudinally along the screws, the threads of said screw section having inner and outer diameters, said screws including adjoining sections devoid of said screw sections to define a zone free of threads, one of said shafts including a cylindrical section in said zone free of threads and a baffle element on the other of said shafts in the zone free of threads, said baffle element being of conical shape which increases uniformly in diameter in the direction of advance of the product, said baffle element having one end of smaller diameter which is substantially equal to the inner diameter of the threads of said screw section and a seciond end of larger diameter which is substantially equal to the outer diameter of the threads of said screw section.
    twin screw extruder as claimed in claim 1 wherein said baffle element has a length between 0.5 and 1 times the outer diameter of the threads of said screw section, a plurality of thread-free zones being arranged in longitudinally spaced relation along said screws.
    Twin screw extruder