Extrusion of seamless tubing

摘要

Apparatus is described for the production of seamless tubular film by continuously extruding hot thermoplastic material through an annular die, inflating the extruded tubing to form a tubular film of predetermined diameter and blowing a cooling gas against the outer surface of the tubing from a supply chamber for cooling gas having an outlet, the walls whereof define an annular passageway for the cooling gas, which passageway is coaxial with the die and arranged to direct the gas against said surface as an annular stream, the apparatus being characterized in that the passageway is adjustable in width. As shown in Fig. 2, which illustrates an apparatus described (apart from the means for adjusting the width of the passageway) in Specification 854,368, the means for adjusting the width of the annular passageway 29 for directing a stream of cooling air on to the outer surface of the extruded tubing 16 comprise a bevelled flexible annular member 42 supported on a number of studs 43 disposed at uniformly spaced intervals all round the lower annular member or ring 21, each stud being threaded on a corresponding adjusting screw 44 mounted in ring 21. For rotating screws 44 so as to raise or lower the studs 43 there are provided a series of radial shafts 46, mounted in lugs 47, 48 and having at their inner ends bevel gear wheels 49 adapted to engage bevel gear wheels 51 fixed to the lower ends of the screws 44. In this manner one part of the flexible member 42 may be raised and another lowered so as to obtain any desired pattern of flow of the cooling air against the tubing 16 to compensate for non-uniformity of air flow round the passageway 29. The bevelled upper surface of the flexible member 42 is parallel to the bevelled adjacent surface 52 of the upper ring 19, the angle of these bevels being such that the stream of air emerging from the passage 29 has a component directed along the line of movement of the extruded tubing 16 as well as radially towards the surface of the tubing. The inner side 53 of the flexible member 42 is cylindrical and adapted to be a close sliding fit on the outer surface of a cylindrical sleeve 54 projecting upwards from the lower ring 21. The supply chamber 18 may be rotated to and fro or, if desired, continually in one direction by means of a motor, reduction gear and belt. As shown in Fig. 4, the lower ring 121, which is otherwise identical with ring 21, has an upwardly directed inner cylinder flange 122, which is internally threaded to receive an externally threaded annular member 123 having a flanged rim 124, the upper surface of which is bevelled parallel to the adjacent bevelled surface 52 of the upper ring 19. Thus the upper surface of the rim 124 and the surface 52 constitute the walls of an annular passage 126 for discharging cooling air on to the tubing 16 at the same angle as in the apparatus shown in Fig. 2. The width of this passage 126 is constant around its circumference and may be adjusted by rotating the threaded spacing member 123 by means of a tool inserted in holes 127 to move the member up or down. Leakage of air between the flange 122 and the member 123 is prevented by means of the resilient sealing ring 128.