GB777967A - A method and apparatus for providing a permeable tube with an impermeable lining - Google Patents

Abstract

<PICT:0777967/III/1> <PICT:0777967/III/2> In a process for providing a permeable tube with an impermeable inner lining integral therewith thermoplastic material is passed through the walls of the tube as it is continuously advanced and is extruded as a ring within the tube while blocking off that portion of the tube through the walls of which thermoplastic material has not yet been passed, the permeable tube is closed some distance beyond that at which the thermoplastic material is extruded so as to form a closed tube section, air is directed under pressure into the centre of the permeable tube within the ring of thermoplastic material, thereby expanding the ring to form an interior impermeable lining forced into contact with the interior of the tube so that it adheres thereto and becomes integral therewith. As shown in Fig. 1 a tube of flexible permeable material is drawn from a reel 1 between rollers 3 and opened by passing over a tubular cylindrical former. It then is passed between an assembly 20 serving as a mandrel and members 10, 11 bolted together and mounted on a base member. After receiving a coating of thermoplastic material is passes between rollers 7 and is wound on a reel 8. Compressed air, for removing dust, is introduced at the inlet 14 and is passed to a chamber 18, through apertures 19 to an annular chamber 21, through apertures to a chamber 22 and through a filter 23 to a chamber 24 connected by apertures 25 and chamber 26 to suction outlet 15. The tube is gripped between rollers 39, 40 and is passed over openings 28 fed from a pipe 16 connected to an extrusion device E with thermoplastic material at a suitable temperature. The material is passed through the tube through openings 29 to channels 32 between a guiding die 31 and a surrounding ring and to channels 33 within the die. The tube is passed between rolls 41, 42 and the squeezed out material passes through openings to the main stream. The tube is passed over rotary toothed wheels 44 which perforate the surface, and over compressed air inlet 17 which supplies air to an annular chamber 34 connected by ducts to a ring 35 in the die, supplying channels 36, and to a central opening 37, supplying duct 38. Air from the ducts blows the tubes 48, 49 of thermoplastic material on to the inner surface of the tube of permeable material in layers. If the tube is rigid the squeezing device grips without deforming the tube and part of the device is rotatably driven to advance the tube. A piston may be used to grasp the tubes and advance with them. Heating means 45, 46 are provided to maintain the thermoplastic material at the required temperature. The material can be used for impermeable packing bags.