Apparatus for the extrusion of tubular thermo-plastic film

Claim 1

In an apparatus for forming tubular thermoplastic film comprising extruder means; annular extrusion die means, adapted in combination to extrude a seamless tube of thermoplastic film; pinch rollers spaced downstream from said annular extrusion die adapted to flatten said tube; and means for introducing a fluid under pressure into said tube to biaxially expand said tube and reduce the wall thickness thereof; the improvement which comprises a configuration imposition assembly disposed concentric to said extruded tube downstream of and adjacent to said annular die, which assembly comprises a series of spaced pairs of diverging aperture row means directed toward said extruded tubing, means for forcing a fluid through said apertures toward said extruded tubing thereby creating a suction and thus drawing said extruded tubing toward said assembly, said configuration imposition assembly further comprising a plurality of vertically spaced-apart individual plenum chambers, said aperture row means being further characterized by being detachably connected to said individual plenum chambers, and a common chamber formed by superposed individual plenum chambers for feeding said fluid under pressure into said individual plenum chambers.