APPARATUS FOR PRODUCING MULTI-WALLED THERMOPLASTIC TUBING

摘要

In an apparatus for producing multi-walled thermoplastic tubing in which the inner and outer tubing walls (33 and 26 respectively) are continuously formed by extrusion one within the other, the inner tube (33) being urged outwardly into pressing engagement with the outer tube (26), the mechanism for urging the inner tube outwardly into securement with the outer tube comprises a mandrel (70) mounted coaxially with the die (25) for extruding the inner tube and on the downstream side of it. The mandrel has an outer surface providing a tapered end portion (72) positioned to receive the inner tube as it is extruded, and a generally cylindrical portion (71) positoned to urge the inner tube into securement with the outer tube. To prevent sticking of the thermoplastic material to the mandrel, the outer surface of the mandrel is maintained at a temperature lower than the molding temperature and is transverseiy ribbed (73).