Head for extrusion of a tubular parison formed of at least one layer of material

In a head for the extrusion of a tubular parison, formed of at least one layer of material useful for the purpose of forming hollow objects or tubular films, said head being an assembly of parts formed by a stack of internally circular annular flanges which are centered on the general axis of the head and are axially traversed with clearance by a torpedo having as an extension a mandrel support which serves to support and guide a mandrel, the assembly forming a tubular channel beyond said torpedo to accommodate the flow of material to be extruded, at least one annular passage formed between adjacent annular flanges and in open communication with said channel, the improvement comprising a ring mounted in each such annular passage in a manner adapted to oscillate about a point located generally on the central axis of the head, each such ring comprising on the one hand a lateral internal surface and an external surface in the form of concentric spherical zones which are centered on said axis and which abut on bearing surfaces of complementary configuration which are provided on the upper flange and on the lower flange, respectively, which frame said ring, and on the other hand an annular beveled surface connecting the lower edges of said internal and external surface of the ring, said beveled surface and said complementary surface of the lower flange which externally bound said respective annular passage make wide obtuse angles with one another at all normal operative positions of said ring and are steeply inclined toward said axis and toward the outlet end of the head.