IE38545B1 - Improvements in and relating to a method and apparatus for the production and accurate internal calibration of extruded thermiplastic tubular mouldings - Google Patents

Abstract

1456222 Extruding tube N G PETZETAKIS M G PETZETAKIS and I DIAPOULIS 29 Nov 1973 [29 Nov 1972 2 Dec 1972 9 March 1973] 55522/73 Heading B5A A thermoplastics, or natural or synthetic rubber tube 3, Fig. 1, is extruded from the can extrusion head 1 and drawn around an internal sizing mandrel 4 along which its passage is facilitated by a layer of hydraulic lubricant, (is) entrained by the tube 3 from an annular space 9, between the head 1 and mandrel 4, containing the lubricant at a pressure which does not inflate the tube 3, the layer of lubricant, Fig. 3 (not shown), being of progressively decreasing thickness and increasing pressure along the mandrel, produced by radially inwardly directed forces acting on the tube. The radial forces may be produced by cooling of the tube 3, by a widened portion of the mandrel, or by the pressure at extrusion of a further layer around the tube 3. The tube may be of circular or elliptical section. The lubricant 14 is introduced gravitationally from a reservoir 11, at atmospheric pressure, or vacuum, and via lines 7 in the Fig. 1 embodiment, to the space 9. Lubricant may be leaked from the space 9, via pressure relief boxes 12, as shown in Fig. 9. In the Fig. 1 embodiment, the tube 3 is not stretched in being drawn around the mandrel 4, which is cylindrical, and through a cooling means 8 comprising sequential chambers 13, at different temperatures, producing the radial forces on the tube by shrinkage thereof. In the Fig. 4 embodiment, the extruded tube is cooled to a biaxial stretching temperature during passage through a first heat exchanger 8, around an upstream cylindrical portion 4a of the mandrel which is internally cooled. Biaxial stretching is effected around a conically widened part 4b of the mandrel followed by cooling during passage through a second cooling heat exchanger around a cylindrical mandrel part 4c. The radial forces on the tube are produced by the stretching at 4b, and cooling at 4c. Lubricant may also be supplied between the mandrel parts 4a and 4b. In the Fig. 9 embodiment, the extruded tube comprises an internal extruded layer passing around a cylindrical mandrel 4 with lubricant supplied to the chamber 9, and the mandrel 4 being cooled by coolant circulated via passages 20, 21. circumferential, and/or crossed, and/or parallel filamentary reinforcements 19, are applied at 18 prior to extrusion therearound at die 16 of an external layer, at a pressure producing the radial force on the layer 3. [GB1456222A]