Patent ID: 6783344
Filing Date: 2004-08-31
Classification: B29C

Abstract:
A device for controlling the thickness profile in the production of blown film, comprising a blown film extruder with a blow head for producing a film tube;a main cooling ring for supplying a main cooling gas stream, said main cooling ring arranged above and in the direction of production behind the blow head; said main cooling ring comprises annular nozzles which are arranged in two different planes, said nozzles fixed in section or which can be adjusted to a fixed section; said nozzles being directed in the direction of production, the first of the nozzles having a smaller diameter than the second of said nozzles, with the first nozzle being arranged underneath and in the direction of production before the second nozzle; an additional cooling ring arranged outside the main cooling ring, said additional cooling ring supplying separate additional cooling gas streams; the additional cooling ring arranged adjacent the blow head of the blown film extruder underneath and in the direction of production before the main cooling ring; at least one blower arranged outside the additional cooling ring and a number of volume flow rate control elements and supply lines corresponding to the number of additional cooling gas streams coupled between said at least one blower and said additional cooling ring; a measuring and controlling device for controlling the thickness profile of the blown film, said measuring and controlling device measuring the film thickness at a film tube above and in the direction of production behind a freezing zone across the circumference, and individually controlling the additional cooling gas streams as a function of the measured film thicknesses, the additional cooling ring arranged adjacent the blow head of the blown film extruder underneath the main cooling ring.