Air ring for controlling blown film thickness
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United States of America Patent
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Feb 22, 1994
Grant Date -
N/A
app pub date -
Mar 25, 1991
filing date -
Mar 25, 1991
priority date (Note) -
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Abstract
Apparatus and method are described for controlling thickness of plastic films produced by the blown film process. The apparatus is an air cooling ring modified to include devices for locally modifying the temperature of the air discharged from the air ring onto the blown bubble. Local variations in the temperature of the cooling air applied to the surface of the bubble result in variations in the bubble cooling rate and viscosity, with consequent variations in thinning during transverse bubble expansion. The method includes controlling the location and extent of local temperature variation applied to the bubble in response to comparison of measured film thickness with a desired film thickness.
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