EXTRUDER OF TUBULAR PLASTIC

PROBLEM TO BE SOLVED: To produce a double layer tubular plastic without causing the deviation of a thickness by an extruder. SOLUTION: The extruder is provided with an extrusion cylinder 7, an extrusion screw 8 with a first screw 8a formed at its periphery, a mandrel 9 with a second screw 9a formed at its periphery, a nozzle die 11 installed at the front edge of the extrusion cylinder and a core die 12 attached at the front edge of the mandrel. A first plastic material and a second plastic material are melted by the rotation of the extrusion screw, and subsequently extruded as the double layer plastic, wherein the first plastic material is fed between the extrusion cylinder and the extrusion screw, and the second plastic material is fed between the extrusion screw and the mandrel. The second screw may be formed at the inner periphery of the extrusion screw. Neither galling nor firing occurs between the extrusion screw and the mandrel since the melted second plastic intervenes between the extrusion screw and the mandrel as if it were a lubricant. COPYRIGHT: (C)2010,JPO&INPIT