Abstract: Method in extruding a double-walled plastic tube by using plastic materials of different colors for the inner layer and the outer layer, a portion of the material for the inner layer being diverted to form a longitudinal strip of the outer layer on the outside surface of the tube. The invention also relates to an extrusion tool for working the method, wherein an element (21) is provided inside the tool to divert material from a passage (19) for material for the inner layer to a passage (16) for material for the outer layer.

Abstract: Method in manufacturing a heat insulated tube includes a tube (17) for conducting fluid and a sheath (12) enclosing said tube, a heat insulating material (15) being disposed between the fluid tube and the sheath. The sheath is being extruded in an angle extruder die (10) while the fluid tube and the heat insulating material enclosing said tube are being fed axially through the angle extruder die as the sheath is being extruded around the heat insulating material. Then the sheath (12) extruded from the angle extruder die is kept spaced from the heat insulating material (15) enclosing the fluid tube (17), over an initial length of the axial movement thereof up to chains of chill molds (13) for imparting to the sheath a corrugated shape by forming the sheath against the chains of chill molds under the influence of negative pressure. The invention also relates to a device in extruders having an angle extruder die (10) for the manufacture of the heat insulated tube.

Abstract: A method of forming a hole in a plastic pipe feeds a plastic layer for the plastic pipe from a nozzle about a mandrel into chill moulds being displaced along an elongated mould cavity about the mandrel formed by the chill moulds. All of the plastic layer is pressed into the chill moulds with a pressure medium between the mandrel and all of an inner surface of the plastic layer for forming the plastic pipe therefrom. Only portions of the plastic layer of the plastic pipe are then subjected to a local pressure difference exceeding the breaking limit of the plastic layer between the inner surface and an opposite, outer surface of the plastic layer at least in part from a flowing medium for forming a hole in the plastic layer of the plastic pipe, the flowing medium being one of a gas and a liquid and flowing from the mandrel at a pressure higher than that of the pressure medium pressing the plastic layer of the plastic pipe.

Abstract: A sleeve joint for plastic-sheathed insulated pipes, comprising an oversized joint sleeve of plastic material overlapping the ends of the sheaths of connected pipes with a gap provided between the sleeve and said ends. Spacer means are located in the gap at either end. A circumferential groove is provided in the respective sheath outside of the gap. A fillet weld of a plastic material fills up the groove and the gap opening, and covers the sleeve end face.

Abstract: Method in extruding a double-walled plastic tube by using plastic materials of different colors for the inner layer and the outer layer, a portion of the material for the inner layer being diverted to form a longitudinal strip of the outer layer on the outside surface of the tube. The invention also relates to an extrusion tool for working the method, wherein an element (21) is provided inside the tool to divert material from a passage (19) for material for the inner layer to a passage (16) for material for the outer layer.