Abstract: This invention is directed to a lubricating arrangement for a plastic extruder (1) for production of cylindrical plastic tubes with a smooth inner surface. The plastic extruder (1) includes a mandrel which consists of a die core (6) which is a cylindrical coaxial extension of an extruder screw (2). Die core (6) rotates together with said screw, and a stationary external die member (7). The lubricating arrangement is located in the external die portion for lubricating its forming surface. The lubricating arrangement has a plurality of radially directed plugs (11, 11', 17, 17'), each plug engaged in a bore (10) in the external die member. The inner end of the plug lies in the die surface. Lubricating ducts (13) are provided to the bore which are connected with a source of a lubricant, which supplies a lubricant under pressure.

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.