Abstract: A mixing element for a screw extruder comprises an element including opposing lobes and a central portion having common opposing broad surfaces; one lobe broad surface being formed into a taper. The elements may be used individually or combined in blocks, with the elements of a block oriented in various combinations. The blocks may comprise two or more elements. The tapered lobes provided reduced pressure and temperature of the process as compared to prior art mixing elements. Also, more graduated control over temperature and pressure are provided according to the value of the taper magnitude, the number of elements used in a process and the relative lobe orientations in a machine.

Abstract: A single flighted multi-screw conveying bushing that has only one helical screw element extending the length of the bushing. The bushing has a cross-section shape that has a segmented circular base and a lobe extending from the base. The lobe has a truncated crest that is sized to have a circumferential angle of from 15.degree. to 30.degree. and preferably from 22.degree. to 24.degree.. Also, a twin screw extruder having a pair of side by side drive shafts with at least two of the single flighted screw bushings mounted end to end on each shaft.