Process to control the bubble diameter of an inflated flattened tubular film having a vertical middle line, between feeding and nip rollers

摘要

Lay-flat tubular film(1) is fed upwards from feed rolls(6), inflated with a constant air or gas pressure to form a bubble(7,8) and heated before being flattened again. Pressure, maintained by introducing water(20) or another fluid with a different boiling point into the tube above the feed rolls and heating the fluid above its boiling point until a predetermined pressure is created inside bubble. An Independent claim is made for the process plant which includes a radiation heater(21) above the feed roll pair(6) for heating a fluid in the base of the bubble(8) and a control unit(31) for switching the heater on and off when the bubble diameter or flat breadth deviates from a specified range.