Patent ID: 6875002

Claim:
An external stabilizer arrangement employed in a plastic film blowing apparatus in which a tubular die, fed with a supply of molten thermoplastic polymer, extrudes a tube of the molten polymer and which injects air into said extruded tube to inflate the tube and expand the tube into a film of a desired thickness, aid wherein means are positioned above said die for drawing the tube vertically upward along a vertical axis and collapsing and flattening the film; and winding the flattened film onto a mandrel; the external stabilizer arrangement comprising an upper frame having a rotary member having an opening through which said extruded tube passes, and structure for rotatably supporting said rotary member; a lower frame that is suspended from the rotary member of said upper frame, and being positioned such that the lower frame surrounds the extruded tube above the die to keep the tube aligned in a predetermined path as the tube is drawn upwards, and comprising a plurality of arms arranged on said lower frame so as to define an iris aperture having a diameter, wherein each of said arms includes a channel for coolant flow with a portion of said arm being in contact with the extruded tube; wherein said upper frame includes means for rotating said rotary member and said lower frame over a predetermined are in respect to the axis of said extruded tube, such that the angular positions of the portions of the arms that contact the tube change as the tube passes vertically through the external stabilizer, without changing the diameter of the aperture, so as to compensate for gauge variation in the film.