Air ring for controlling blown film thickness
AssigneeBattenfeld Gloucester Engineering Co., Inc.
InventorDavid J. Smith
Life of this patent
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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.
Claims12
An air ring for controlling gauge of blown plastic film 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) a flow path for cooling air between said plenum and said annular orifice;
- d) an electrical cartridge heater inserted in said air flow path;
- whereby the temperature of cooling air discharge against said extruded plastic tube can be locally varied.
In a system for producing blown plastic film, including an extruder, an annular die, and an air ring for discharging cooling air on an extruded plastic tube, a thickness measurement system, and a nip roll assembly, the improvement which comprises an air ring equipped with a plurality of electrical cartridge heaters for locally altering the temperature of cooling air discharged from the air ring onto the extruded plastic tube in response to film thickness measurements from said thickness measurement system, whereby the thickness of the resulting film can be locally altered.
Dependencies are inferred from the claim text.