Abstract: For the production of extrudates such as profiles or granules, pulverulent or finely divided ultra-high molecular weight polyethylene is processed on single screw extruders. By the use of a screw with a specific geometry, thermal degradation of the polymer into low molecular weight products is avoided. Furthermore, profiles are obtained which have perfect surfaces, are free of voids and pores, and have no internal stresses.

Abstract: In a method for heated tool butt welding of pipe consisting of a thermoplastic material by placing or pressing the surfaces to be joined of the pipes to be welded into contact with a heated tool to form an inner weld bead at each end to be joined, subsequently heating the surfaces at a reduced contact pressure to the welding temperature and fitting the surfaces together under pressure after having removed the heated tool, the improvement for minimizing the formation of a protrusion within the resultant pipes which comprises pressing an elastic insert against the inner weld bead while joining said surfaces of said pipe together.