Patent ID: 7806674

Claim:
An air ring for controlling gauge of blown plastic film of an extruded plastic tube comprising: a) a generally annular plenum; b) an annular orifice for discharging cooling air against an extruded plastic tube passing through the air ring; c) an air flow path for cooling air between said plenum and said annular orifice, said air flow path being segmented along a circumference of the annular plenum by a plurality of segments each having an upper surface and a lower surface, said segments including a material with high heat conductivity, each segment having axially directed grooves formed in one of said upper and lower surfaces to form a grooved side, with said grooves guiding the air from the annular plenum to the orifice; and d) each of said segments having an integrated heating element for individually and selectively heating said segments of the air flow path such that the temperature of cooling air discharged against said extruded plastic tube can be locally varied, said heating element being adjacent to a side of said segment opposite said grooved side and heating the air as the air flows through said grooves.