GB1486016A - Method of and apparatus for treating the outer surface and inner surface of a pipe of a thermoplastic resinous material produced by extrusion - Google Patents

Abstract

1486016 Smoothing extruded plastics tube MITSUI PETROCHEMICAL INDUSTRIES Ltd 20 Sept 1974 [26 Sept 1973 (2)] 41123/74 Heading B5A The interior and exterior surfaces of a pipe 10, Fig. 2, of thermoplastics material which is produced by extrusion from a die 11 followed by passage through an external sizing die 20, are rendered smoother by passing a gas which is inert to the thermoplastics into the interior of the pipe as it extrudes from the extrusion die, i.e. to reduce oxidation of the material, and applying a lubricant to the exterior of the pipe from annular grooves 27 at the upstream end of the sizing die 20. Biaxially oriented bottles may be continuously produced by leading the tube from the sizing die, Fig. 1 (not shown), through a cooling tank and then through a furnace in which it is heated to below its crystalline melting point and then axially stretched in being drawn through a draw cone by alternately acting blow moulds which close upon the pipe and effect blowing as they move away from the draw cone, the blown bottles then proceeding to a finishing station. The material is preferably a highly crystalline polymer of a mono-α-olefin having a carbon number of up to 6, such as ethylene polymers of high density, isotactic polypropylene, poly-4- methyl-1-pentene, or polybutene-1. The inert gas may be nitrogen, carbon dioxide, or helium, and the lubricant may be wax, silicone oil, or soap water, or preferably a surface active agent which is removed from the pipe in passing through a water cooling tank which follows the sizing die. The sizing die, Figs. 2 and 3, is connected at 21 to a vacuum source, and the lubricant is supplied to the annular grooves 27 at the upstream end of the die from an outlet 23 of a pipe 22, via a recess 24 and downwardly extending groove 26 in the upstream end face 29 of the die. The extrusion may be effected from an axially fed die head, Fig. 4 (not shown), comprising a radially adjustable outer die and an inner mandrel supported by a spider which has an upstream projecting portion around which the material from the extruder flows, with the inert gas being delivered by passages through the mandrel and spider, from a valve controlled inert gas supply source. Alternatively, Fig. 5, extrusion may be effected from a cross-head die head into which material from the extruder is admitted from a passage 54, to flow to the extrusion passage 34 via a threaded portion 36a of the mandrel 36, the inert gas being delivered from a source 41 and valve 43, to a mandrel passage 40, either via a lateral inlet 40a to a torpedo passage 40c, or via an end inlet upon removal of a plug 56.