Apparatus for producing thermoplastic tubing

Abstract

In apparatus for producing corrugated thermoplastic tubing and which comprises a pair of complementary upper and lower mold assemblies each having an endless array of articulately interconnected mold blocks which are driven along a forward run and back along a return run, the mold blocks co-operatively interengaging in pairs along said forward run to form an axially extending tubular mold tunnel, there is disposed at the entrance to the tunnel an extrusion head having an inner core member and an outer member which surrounds the core member and is spaced therefrom to define therebetween an annular passage terminating in an annular orifice and through which the tubing of thermoplastic material is extruded for expansion by blow molding within the tubular mold tunnel, the annular orifice having portions of increased width in axial alignment with the locations of interengagement between the mold blocks of the mold assemblies in the forward runs thereof, thereby to provide the tubing with thickened portions at these otherwise weak locations. In each mold block passages extend between the bases of the troughs of the corrugations and the exterior of the mold block, these passages which communicate with the base of each trough throughout the length thereof serving to permit the escape of any atmospheric air which is trapped by the tubing in the troughs during the blow molding thereof.