Patent ID: 6123536
Filing Date: 2000-09-26
Classification: B29C

Abstract:
A plant for the production of plastic tubular films with a biaxial orientation, which comprises in series:an extrusion station, an orientation station and a stabilization station;the extrusion station comprisingat least one extruder for feeding molten polymer to an extrusion head;said extrusion head being equipped with an annular drawplate for extruding a tube;the orientation station comprisinga pair of feeding rollers for feeding the tube to a heating zone;air injection means, positioned downstream of the pair of feeding rollers, for injecting an air bubble into the tube so as to expand and simultaneously stretch said tube in an axial direction;means for compensating the volume of injected air so as to maintain a constant pressure inside the tube;a pair of traction rollers positioned downstream of said heating zone for squashing the stretched tube into a flattened film, and delivering said flattened film to the stabilization station;at least one of said pair of rollers being mobile in a direction parallel to the axis of the tube;said pair of traction rollers being mounted on a series of threaded shafts parallel to the direction of forward motion of the tube;sensor means for measuring the diameter of the tube and for controlling rotation of the threaded shafts in response to a signal generated by said sensor means;the stabilization station comprisinga pair of feed rollers for feeding the flattened film to a heating station;air injector means, positioned downstream of said pair of feed rollers, for injecting air into the film;a pair of traction rollers positioned downstream of said heating station for squashing the flattened film; andshifting means for moving at least one of the pair of feed or traction rollers in said stabilization station, along the longitudinal axis of the flattened film so as to compensate for changes of air volume contained inside the film.