Abstract: This invention relates to a process for making a tubular structure formed by a film of extruded synthetic matter whose walls are at least partially perforated, including the steps of extruding from an annular die a tubular film having gaps or voids obtained in manner known per se by teeth which temporarily obturate the outlet of said die, and extruding and forming the film on leaving the die after flow of matter in the plastic state, upstream of the die, in a ring-shaped passage of which the outlet constitutes the die, this passage being of constant thickness equal to the width of the extrusion slot and consequently to the final thickness of the film, the flow of plastic material in this ring-shaped passage causing an effect of lamination of the matter ensuring dimensional stability, particularly the thickness of the film obtained at the outlet of the die, and in particular avoiding the formation of excess thickness or surface roughness on the film thus extruded.

Abstract: The present invention relates to a process for extruding a thermoplastic sheath in the form of a tubular film provided with perforations and to a device for carrying out the process, according to which the extruded film passes over a skirt through which are blown jets of hot air provoking the perforation and formation of openings in the film; in the areas where the film is not to be perforated, air jets are also blown through channels of smaller width, therefore with a reduced pressure, so that the jets do not provoke the perforation of the film but form an air-cushion facilitating the flow of the film on the skirt; the channels are supplied from a pneumatic chamber with interposition of a rotary distributor formed by a ring made of graphite or self-lubricating material. The invention is applicable to the manufacture of partially perforated tubular films with a view to making packings.

Abstract: A relative nutational movement is provided between a member carrying teeth or other radial projections and a member against which these projections bear, these two members being just downstream of an annular extrusion gap that produces a plastic tube which is slit by the teeth or other projections passing through the tube wall in succession and bearing against the backing member. As it comes out from the slitting or punching produced by these members, the tubular material is stretched to and over a mandrel and cooled there to produce a tubular netting or a perforated sheath. Either the toothed member or the backing member may be fixed while the other is moved in a movement of nutation and the toothed member may have externally or internally directed teeth.

Abstract: Apparatus is provided for preparing perforated seamless tubular films of preferably thermoplastic material by passing an extruded tubular film over a perforated wall of a chamber connected to a constant pressure compressed air source.In the apparatus compressed air from the chamber is allowed to pass periodically out of a first series of openings in the perforated wall, the openings being periodically closed either by axially displacing a plate to block said openings, or by rotating a subadjacent chamber itself provided with a second series of openings, whereby said first and second series of openings are periodically aligned.