Extrusion of laminate pipes.

摘要

An extrusion assembly for extrusion of a triple walled pipe comprises a first extrusion apparatus for extruding an inner layer of the pipe, which inner layer is of plastics material, which first extrusion apparatus comprises an extruder (24) having an extrusion sleeve (302) and an extrusion die (304) disposed substantially coaxially within the extrusion sleeve (302), which extrusion sleeve (302) and extrusion die (304) together define, at an axial end of the extrusion sleeve, a first, annular, exit orifice (322) for the plastics material which is to provide the inner layer of the pipe, a shaping sleeve (600) surrounding and substantially coaxial with the extruder (24) of the first extrusion apparatus, which shaping sleeve (600) has a first axial end adapted to receive a U-section form metallic layer, the shaping sleeve being capable of shaping the U-section form metallic layer passing through it into a tubular configuration, means (301) for welding the metallic layer of tubular configuration to provide a metal tube (40) defining a metallic layer of the pipe, means (342) for supplying a pressurized gas downstream of the first, annular exit orifice (322) whereby extruded plastics material emerging from the said first exit orifice (322) is forced against an internal surface of the metal tube (40) to provide the inner layer of the pipe, and a second extrusion apparatus (22) for extruding an outer layer of the pipe, which outer layer is of plastics material and is disposed radially outwardly of the metallic layer of the pipe, which extrusion apparatus comprises a body part (370) and a supply channel (334) within the body part (370) for supplying plastics material and terminating in a second exit orifice (346), surrounding the metal tube (40), for the plastics material which is to provide the outer layer of the pipe, which extrusion assembly has positioning means selected from at least one of, (a) an essentially annular section recess (336) in the body part (370) of the second extrusion apparatus (22) which recess is capable of receiving a second axial end (352) of the shaping sleeve (600) remote from the said first axial end, which allows accurate positioning of the shaping sleeve (600) relative to the first and second extrusion apparatuses, and (b) a universal joint (11) to which the extruder (24) of the first extrusion apparatus is connected, which connection allows accurate positioning of the said first exit orifice (322) of the first extrusion apparatus relative to the said second exit orifice (346) of the second extrusion apparatus (22).