Method in manufacturing a heat insulated tube and a device in extruders for manufacturing the tube

In an extruder having an angle extruder die defining a passage for prefabricated tubing having an insulating layer and overlying sheath, the improvement comprising sleeve means projecting from said angle extruder die coaxially with said passage and forming an extension of the passage at the outlet of the angle extruder die and corrugation means at the downstream end of said sleeve, said means together extruding and then corrugating the sheath onto said insulating layer, said corrugation means comprising chill molds forming said sheath under the influence of negative pressure.

Method for manufacturing a heat insulated tube including an inner tube for conducting fluid, a heat insulating layer enclosing said inner tube, and a sheath covering the heat insulating layer, comprising the steps of feeding the inner tube and the insulating layer axially through an angle extruder, extruding the sheath from the angle extruder around the heat insulating layer radially spaced therefrom, maintaining the sheath spaced from the insulating layer when moving together with said layer and said inner tube, over an initial distance from the angle extruder, and compressing the heat insulating layer against the inner tube at the end of said initial distance, where the sheath is contacted with the heat insulating layer, and then forming said sheath against chill molds under the influence of negative pressure for imparting a corrugated shape to the sheath.