Patent GB-755035-A (GB)
Title: Extrusion of plastic materials
IPC: B29C48/19
Filed: 1954-02-10
Abstract: <PICT:0755035/IV(a)/1> <PICT:0755035/IV(a)/2> Apparatus for making extruded products of thermoplastic material comprises a conduit member having a passage adapted to conduct thermoplastic material in a temporarily heatliquefied condition from the barrel of an extruder towards a die orifice, a number of auxiliary inlets to the passage arranged across its width, and means for injecting additional thermoplastic material in a temporarily heatliquefied condition through the inlets into the stream of material moving from the extruder barrel to the die orifice.  As shown in Fig. 1, comminuted thermoplastic material is fed continuously into the hopper 13 and is forced by screw 11 through the cylinder 12 heated by the element 14. The material, in a heated, highly plastic or molten condition, emerges from the cylinder 12 at a uniform rate and travels under pressure through a passage 16 formed in a block 17, then through a passage 18 in a block 19, and finally through a passage 22 in a die 23.  The cross-section of the passage is as shown at 18 in Fig. 2, so that the stream of material passing through it is in sheet form. Heat is supplied to blocks 17 and 19 and to die 23 by means of conventional strip heaters (not shown) and the highly plastic sheet emerging from the die 23 is rapidly cooled.  The block 19 is provided with a number of cylindrical injection passages 24 terminating in tubular injection tips 26.  The outer ends of some of the tips 26 are flush with the walls of the passage 18 while other tips extend for varying distances into the passage.  The injection passages 24, in operation, receive thermoplastic material which is different in composition, colour or other characteristic from the material fed through the passage 16. This different material is supplied by means of an extrusion screw 27 (Fig. 2), operating in a cylinder block 28 provided with heating means 29, a feed hopper 30 and a flanged heated coupling 31 which is attached to the block 19 in alignment with the open end of a tubular sleeve 32 mounted for rotation in a cylindrical bore 33 in the block 19.  Secured to the other end of the sleeve 32, and closing that end, is a shaft 34 on which is keyed a pulley 35 (or gearing) adapted to be driven so as to rotate the shaft and sleeve. The sleeve 32 is provided with a number of arcuate apertures 36, adapted to be aligned with the injection passages 24 during the rotation of the sleeve, so that during each rotation of the sleeve 32 the apertures 36 connect each passage 24 for only part of the time with the hot, highly plastic or molten material under pressure in the sleeve, thereby causing the material to be injected intermittently into the main stream of material moving from the passage 16 past the tips 26.  Since the apertures 36 are staggered around the circumference of the sleeve 32, these injections take place at different times during the rotation of the sleeve and, since the tips 26 are located at different levels with respect to the passage 18, the injections are made at different levels in the main stream of material.  In this manner an ornamental effect can be produced in the finished sheet, which may be made of a rigid, light-coloured or colourless transparent material having spaced discrete masses of darker coloured rigid material distributed at different levels throughout it.  The sleeve 32 is preferably rotated continuously and may also have a reciprocating axial movement.  The apertures in the sleeve may be slots and/or round holes.  The rate of injection from each auxiliary injection passage 24 may vary cyclically, the cycle consisting of a gradual rise from zero to a maximum, a gradual fall from the maximum to zero, and a dwell at zero.  On the other hand, where irregularly patterned materials are required, the movement of the sleeve may be intermittent, and/or the rate of injection at one injection point may vary according to a different cycle from that at another injection point.  The thermoplastic materials which may be used include the cellulose esters of the lower aliphati acids, cellulose nitrates, cellulose ethers such as ethyl or benzyl cellulose, extrudable polyamides such as nylon; polyesters such as polyethylene adipate or terephthalate, resinous vinyl or vinylidene polymers, e.g. polymeric methyl or ethyl methacrylate, polystyrene or polyvinyl chloride or acetate, copolymers of vinyl acetate and chloride and polymers and copolymers of vinylidene chloride.