Abstract: A flexible die head for continuously extruding pipe may have a flexible ring mandrel (112). A second, open end (120) of the ring mandrel (112) near the die exit may be continuously and resiliently formed to a non-circular shape whilst extruding the pipe so as to provide an extrudate profile to counter slump in plastic pipe forming. Symmetric and asymmetric shapes may be formed by the ring mandrel (112). The second end (120) may be flexed or otherwise distorted by use of a flexing means (122). The ring mandrel (112) may also be necked in a circumferential portion to order to further improve the forming of non-circular shapes.

Abstract: A method of modifying compressive strains in formation of a pipe ring groove (16), in which a differential temperature profile is established across the pipe wall in a narrow bending locus (l3) corresponding to the ring groove position, and the material is bent to form the ring groove. The temperature differential creates a differential in elastic modulus between the inner and outer surfaces of the pipe material, modifying the strain induced in inner concave and outer convex surfaces of the ring groove during the bending step.

Abstract: A continuous process and apparatus for producing oriented plastic tube comprising the steps of extrusion, temperature conditioning, diametrical expansion and cooling, characterized by the step of inducing axial draw of the tube between first and second haul-off means located upstream of the expansion step.