The interaction of one screw on the complimenting extrudate to the degree that it becomes necessary to provide a means to reduce the equivalent screw displacement. Without the addition of a means to disrupt the pumping capability of this extruder, relatively little mechanical energy is converted into heat. The equivalent displacement of the co-rotating twin screw extruder can be reduced in one of two ways: alteration of the flight pitch, or a decrease of the pumping or conveying capability of extruder. The screw pitch on the kneading zone may be reduced by about one-third from the screw pitch of the feed zone. Most frequently, however, shearlocks or kneading elements are added to separate the screw segments at specific points in the kneading zone.