Abstract: An apparatus for the manufacture of corrugated tubing of thermoplastic including a shaping path adjoining the head of an extruder, composed of a guide arranged in a frame structure, along which guide mold halves closed together in pairs as annular molds are advanced in close succession, said mold halves being provided on a lower side thereof with racks, at least one drive pinion arranged in the initial part of the shaping path for meshing with the racks of the mold halves as the same are pushed along the path, and an outlet, following the shaping path, in which the mold halves are separated from one another and are transferred to mutually separate return paths, on which they are shunted back by a conveyor to the inlet.

Abstract: Pipe made from thermoplastic polymeric material and including a transversely corrugated outer wall and a smooth inner wall of constant diameter fusion welded to the inner crests of the corrugations of the outer wall is produced by an improved method involving simultaneous extrusion of two tubes, blow molding of the outer wall and fusion of the two walls while the inner wall is supported by an internal shaping and cooling mandrel. Even when the polymeric material is polyvinyl chloride, good fusion welds and lack of brittleness are achieved by the manner in which extrusion is carried out, control of the location at which the fusion welds are established, and the extrusion formulation. The finished pipe is characterized by the fact that, when the fusion welded areas have been cut for inspection, no line of demarcation between the materials of the two walls can be observed.

Abstract: Pipe made from thermoplastic polymeric material and comprising a transversely corrugated outer wall and a smooth inner wall of constant diameter fusion welded to the inner crests of the corrugations of the outer wall is produced by an improved method involving simultaneous extrusion of two tubes, blow molding of the outer wall and fusion of the two walls while the inner wall is supported by an internal shaping and cooling mandrel. Even when the polymeric material is polyvinyl chloride, good fusion welds and lack of brittleness are achieved by the manner in which extrusion is carried out, control of the location at which the fusion welds are established, and the extrusion formulation. The finished pipe is characterized by the fact that, when the fusion welded areas have been cut for inspection, no line of demarcation between the materials of the two walls can be observed.