DIES FOR THE EXTRUSION OF EXPANDED PLASTICS MATERIALS AND EXTRUSION USING SUCH DIES

摘要

1399654 Extrusion dies OMEGA PLASTICS Ltd 28 March 1973 [30 March 1972] 15143/72 Heading B5A An extrusion die which enables foamed polystyrene sheeting having a thickness of less than 0À010 inch and a weight of less than 30 grams per square metre to be formed, comprises a torpedo which is held to the die body by a perforated breaker plate 9 and which includes aligned bores 24, 25 that co-operate with a bore 26 in the outer ring of an air spacing ring 8 and with a bore 27 in a tube 28 to allow pressure air to pass through the die and inflate the extruded tube. The torpedo comprises a bullet-shaped upstream part 17 and a downstream part 18 which are screw-threaded together and to the breakerplate 9. The latter comprises two rings of perforations 30. Immediately downstream of the breaker-plate 9, the torpedo and die body 1 taper towards each other, i.e. 31, 32, to form a throat section 33. Further downstream the torpedo tapers more than the body to form a section 35 which increases in radial width in a downstream direction. Passage of molten polystyrene which includes a blowing agent, through the throat section 33 and section 35 gives rise to a turbulence which together with passage through the breaker-plate 9 destroys the rotational motion of the material due to the screw (40, Fig. 2). The torpedo includes an extension which carries an adjustable sleeve 19 which has a lip 20 which co-operates with a lip 14 of the die body to define an annular die outlet. The extruded tube is passed through a collapsing screen 48 of rollers, a set of draw-off rollers 49 which roll the tube flat and an edge slitter 50 to a wind-up station 51. The extrusion die is also provided with a wire screen filter pack 5 and is surrounded by a cooling water jacket to provide a die body temperature of 260- 280‹ F.