Air ring for controlling blown film thickness provided with individual heat conducting segments

A system for producing blown plastic film, comprising:

• an extruder, an annular die, a thickness measurement system and means for discharging cooling air-on an extruded plastic tube which includes-a plurality of segments for guiding the cooling air on the extruded plastic tube;
• each segment guiding cooling air to a certain section of the circumference of the extruded plastic tube;
• and
• heating means for individually and selectively heating said segments such that the temperature of cooling air discharge against said extruded plastic tube can be locally varied by heating different segments with different intensity.

A method for producing blown plastic film comprising:

• extruding plastic molt through an annular die;
• measuring the thickness of the extruded plastic film and discharging cooling air on an extruded plastic tube;
• and
• passing different quantities of the cooling air by different segments which guide the cooling air on sections of the circumference of the extruded plastic tube;
• whereby the temperature of the segments is controlled individually and selectively based on the measurement of the thickness of the extruded plastic film so that the temperature of cooling air discharge against said extruded plastic tube is locally varied by heating different segments with different intensity.