Abstract: This invention describes a process for orienting and drawing multiple-layer thermoplastic materials, in particular of a tubular type, wherein

Abstract: A process for orienting and drawing multiple-layer thermoplastic materials, in particular of a tubular type, wherein a tube exiting from a heating tunnel is brought up to an orienting temperature of a first material having the highest orienting temperature, while the material of the remaining layers is still in a plastic state. The first material is subjected to a first partial drawing process, while the remaining layers plastically deform to follow its expansion. The temperature of the tube is dropped to the orienting temperature of a second layer and a second layer is drawn, while at the same time continuing to draw the previous layer. Steps of dropping the temperature and drawing the second layer are repeated for the subsequent layers, until the maximum allowable degree of drawing is achieved for each layer.

Abstract: The die includes a central core and an annular ring arranged around the core, so as to define an annular slit for extruding a material, as well as a multiple number of inserts peripherally arranged around the ring and mechanically tied to the same, and device for heating the inserts independently from each other, so as to be able to change by thermal deformation of the inserts, the thickness of the annular slit. The inserts are radially arranged around the ring and attached to the structure of the machine on the inner side, next to the ring, while their free opposite extremities are free to radially slide so as to expand toward the out. Devices mechanically tie the inserts to the ring and devices heat and/or cool the inserts.

Abstract: A plant for the production of plastic tubular films with a biaxial orientation, includes one or more extruders to feed the molten polymer to an extrusion head; an annular drawplate for extruding a tube; an orientation station in which the tube is heated, expanded by an air bubble and simultaneously stretched in an axial direction. Elements are provided, for compensating the volume of inflation air so as to maintain a constant pressure inside the tube during the orienting process. To this end at least one of the pairs of rollers that feed and pick-up the tube is mobile in a direction parallel to the axis of the tube, and elements are provided to command the shifting of the pair of rollers depending on the diameter of the tube measured during the orienting phase.