Fault-free blown film tubing prodn. - using machine with extruding nozzle and air cooling system fitted with circumferential gauges connected to computer to correct deviations

摘要

A procedure operates a film system, which has a blowing head with annular gap for extruding thermoplastic tubing, a means of inflating the tubing, a cooling system for the outside, and a lay-flat device for the blown film. The annular gap has at least one adjustable lip with its individually adjustable elements distributed uniformly round the circumference for segmental correction of the film thickness. The outer cooling system applies cooling air with regulators round the extruded tubing to provide segmental adjustment of the cooling air draughts. This cooling system also has a wobbler plate type adjustable component by which any lack of truth of the centre of the ring nozzle can be regulated. The adjustable features for segmentally correcting thickness deviations, the correcting features for the cooling air, and the adjustments for the wobbler type component are all connected to a computer to minimise tolerances in the section of the film. A device measures the film thickness directly or indirectly and acts on the regulating features according to the readings obtd. The effects of the system are (a) to minimise the tolerances in thickness across the section of the film (b) to regulate errors in centring the annular nozzle gap (c) to superimpose a periodic thickness error of set magnitude on the film, where the error is continuous or periodically fluctuating at a given angular speed, and (d) to rectify the periodic errors in thickness and to allow (a) and (b) to be effected without interruption. ADVANTAGE - The system virtually eliminates faults from the prodn. The film produced is free from `barrel' effects and can be reeled completely cylindrically.