A screw extruder for processing melts of synthetic plastic materials or synthetic
plastic material in powder or granulated form to effect mixing, kneading and homogenizing of the material and causing chemical reactions thereof comprises a long main conveyor screw and a short auxiliary screw parallel thereto and disposed in the feed zone of the casing of the extruder. The screws are unidirectionally rotated in tight engagement with each other.
Single screw extruder if suitably dimensioned are generally quite satisfactory for carrying out the hereinbefore referred to procedural steps. In fact, the kneading action of single- screw extruders in many instances is superior to that of twin screw extruder the screw elements of which mesh though not with a tight profile. However, single- screw screw extruders have inherently certain disadvantages. The dwell time of the material within the extruder cannot be kept constant within a narrow range and such constancy of the dwell time is very important for most of the processing operations which are to be carried out in the extruders. Moreover, a positive and uniform flow of the material to be processed through treatment zones of the extruder cannot be reliably obtained with single- screw screw extruders, especially if quantity processing is to be carried out.
It is a broad object of the invention to provide a novel and improved single screw extruder of the general kind above referred to which has all the aforepointed out advantages of twin screw extruder in which the two screws are unidirectionally rotated and engage each other with a tight profile or engagement without being as complex and hence as expensive as the now known twin- screw screw extruders.