Patent GB-1494684-A (GB)
Title: Apparatus for the production of a double-walled plastics pipe or conduit
IPC: B29C48/09
Filed: 1975-02-11
Abstract: 1494684 Moulding double walled pipes F KIRCHNER and H KIRCHNER [trading as FRANKISCHE ISOLIERROHRUND METALLWAREN-WERKE Gebr KIRCHNER] 11 Feb 1975 5822/75 Heading B5A [Also in Division F2] A plastics tube 4 comprises an external helically, or annularly corrugated wall, and an internal wall fused thereto and which is cylindrical, or has axially extending corrugations. The walls may be of the same or different thicknesses, or material. The tube is made by extruding tubes for each wall, from sequential extrusion passages 7, 8, into a moving cavity defined between opposed endless moving chains of mould halves 2, 3. The outer wall is corrugated by being urged into contact with grooves of the cavity by pressurized air admitted, through a passage 16 of the mandrel of the upstream passage, to a space sealed by a widened downstream end of an extension 12 of the mandrel which contacts the corrugation crests, and air within the corrugation troughs escaping around the seal is vented, prior to application of the inner wall to the outer in the cavity, by a passage or passages 17 extending through the mandrel extension 12 to atmosphere, or to a source of suction. The seal may be effected across a minimum of two corrugation crests. Escape of pressurized air along helical corrugations may be prevented by gaps provided in the cavity grooves. The inner wall may be applied to the outer by pressurized air, when the outlet of passage 8 may be axially directed, or may be applied by only a widened downstream extension 15 of the mandrel of passage 8, e.g. for application of an axially corrugated inner wall using a similarly shaped extrusion passage and mandrel extension. The venting may produce atmospheric pressure, or a slight vacuum, in the corrugation valleys. The grooves of the mould cavity may be evacuated by vents to the exterior. The outlets of both or one of the passages 7, 8, may be oriented radially outwardly, or axially or, particularly with the downstream passage 8, conically at an included angle of 20 degrees to assist application of the inner wall to the outer. If the outer diameter of the outlet of passage 8 is substantially that of the internal corrugation crests, a vent passage may open into an annular groove intermediate the ends of the seal. Where the inner wall is applied to the outer by internal air pressure, the outlet of passage 8 may be axially directed or, as in the embodiment, the inner wall may be guided into contact with the outer wall by a widened downstream extension 15 of the mandrel 14 of passage 8, with pressure air maintaining the contact being admitted between the downstream end of the mandrel extension 15 and a sealing member 20, via a passage extending through a rod 19 supporting the member 20. In the embodiment, the vent passage or passages 17, open at a downstream face 13 of the extension 12 and the seal is effected across four corrugation crests by the extension 12. The air pressure upstream of member 20 may be lower than that upstream of the seal of extension 12, and each air pressure and temperature may be independently controlled. A plurality of independently controlled and axially spaced vent passages may also be provided. The inner and outer walls may be extruded from the same, or different extrusion sources whose rate of extrusion may be independently, or interdependently controlled.