Abstract: A method and a device for extrusion of plastic tubes with use of a screw extruder which has a tube molding head comprising an external stationary nozzle and a mandrel which is supported against the nozzle head by the aid of ribs. The plastic material is made to rotate by the mandrel rotating about its axis and by the aid of inclined ribs that are attached to the nozzle wall or the mandrel. Then the edges of the screw line shaped cuts occuring due to said ribs are made to join together in a subsequent tool member. The apparatus comprises a screw extruder with a tube molding head comprising of an external stationary nozzle with a passage corresponding to the external contour of said tube, and a mandrel the cross section of which corresponds to the internal contour of said tube. The mandrel is rotatably, and the spokes or ribs are inclined or extend along a screw line and are attached to said mandrel or in the external mould member.

Abstract: An extruder assembly (1) for extruding round, cylindrical plastic pipe having a smooth inner pipe wall and a ribbed or ridged outer pipe wall, comprising a feed screw (2) for transporting and softening the plastic material (4), and an annular nozzle having a central mandrel (6). The mandrel constitutes a cylindrical, coaxial extension of the feed screw. The mold part (8) of the nozzle is provided with one or more parallel, helical grooves (14) with the spiral extending in the direction of rotation of the screw and mandrel, and the mold part (8) is provided with a lubricating device (17) for lubricating the molding surface of the mold part. A calibrating device (27) with helical grooves (28) is provided downstream of the annular nozzle.