Plastic Sheet and Blown Film Extrusion

Flat plastic comes from an extruder in two ways. Sheet too thick to blow is pushed through a wide slit die and pulled through chill rolls, which cool it and set its thickness and surface. Thin film is blown: a tube is extruded upwards from a ring die, inflated by air into a tall bubble that stretches it both ways, cooled, flattened by nip rolls into lay-flat tube, and wound or slit. Bags are cut and heat-sealed from the lay-flat tube; wrap is slit film.