Abstract: Apparatus for producing plastic film, of the type in which molten plastic is extruded through an annular die to form a tubular bubble which is expanded by air blown into the bubble, and a collapsing frame for forming the bubble into a flat tube prior to passing the tube through a nip formed between rollers, in which opposed, converging reaches of endless belts are used for the collapsing. The belts have their upstream ends held by a pair of first rollers spaced apart on opposite sides of the bubble, and have their downstream ends held by a pair of nip rollers which hold the belts together to form a nip for the collapsed tube. Pulleys and a belt, or gears, are provided which rotatably interconnect the pinch rollers and ensure that the belts entering the nip travel at the same surface speed.

Abstract: A bubble guide unit according to the present invention comprises two concentric frames, at least one of which rotates relative to the other, through which the film bubble passes. At least four bubble guiding rods are arranged symmetrically to each pivotally engage one frame at one end and to freely engage the other frame near its other end. Freely engage here means that the other end of each rod is free to pivot to some extent as well as to move in the direction of its length beyond the pivoting point and back. This is most easily accomplished by a pivoting ring through which the rod passes or, less elegantly, by a fixed ring having an aperture larger than the rod diameter.