GB1291997A - Method and apparatus for extrusion of synthetic resinous materials - Google Patents

Abstract

1291997 Screw mixers DOW CHEMICAL CO 30 Oct 1969 53246/69 Heading B1C [Also in Division B5] Fibrous reinforced plastics material is delivered with decreased surging, and decreased breakage of fibrous reinforcement, through a heated screw extrusion or injection barrel incorporating a screw which is of decreasing compression at least at the feed end thereof and at a downstream location where the material is heated and is molten. Figs. 2-4 (not shown) respectively illustrate screw configurations in which the decreased compression is obtained by a pitch which progressively increases to the screw discharge end, a root diameter which progressively decreases to a constant diameter prior to the discharge end, and a land width which progressively decreases in width to the discharge end. In the Fig. 1 embodiment of extrusion apparatus the extruder barrel 19 is heated by means 25 in two heating zones, and a hopper 32 at a feed inlet port 30 is supplied with material from a liquid supply 16 and/or through a control valve 14 of a supply hopper 12. The fibrous reinforcement, as 10 to 15 weight per cent of the plastics, is preferably metal, or glass fibres as roving or chopped strand, and may be fed to the hopper 32 as a mixture with particulate plastics from the hopper 12, or in a separate stream from the particulate resin and which may comprise continuous filament which is broken within the barrel. A fibre reinforced strand 35 issuing from the orifice 34 of a die 22 is cooled by means 36 prior to comminution between co-operating elements 38, 39. The resins may comprise glass fibre reinforced polystyrene or styrene-acrylonitrile. Calcium carbonate or titanium oxide particulate filters may be employed with other specified additives. Preferably the screws comprise a pitch to overall diameter ratio of at least 0.4, and preferably of 0.5 increasing to unity or 2.5 at the discharge end. In the Fig. 5 embodiment of injection apparatus, the screw 70 which is selectively axially positionable, increases in pitch to the termination thereof adjacent an unflighted mixing head 72, within a barrel 63 heated by means 67 and supplied with thermoplastic or thermosetting plastics and reinforcement from sources 78, 79. The screw 70 is simultaneously rotated and retracted in the barrel 63 with a nozzle valve 82 closed and after locating a mould 84 against the nozzle 81, the valve 82 is opened and the screw 70 advanced to fill the cavity 86.