The thickness distribution of blown film is conventionally controlled by either changing the temperature or the velocity of the cooling air. This technique cannot be used for the double bubble process, where the film is cooled by water before being reheated and blown up in a second step. A new technique to alter the localized gap of the flow channel at the exit of the die has been developed. It can be used to control the thickness over the circumference of the blown film for both the conventional and double bubble process. The technology is explained and initial test results achieved are presented herein.
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