| 摘要 |
APPARATUS FOR COOLING A TUBULAR PLASTIC FILMS Apparatus for cooling tubular plastic films extruded from a film blowing head comprises air cooling means consisting of co-axial pipes extending axially through the film blowing head to supply the cooling and inflating air and to withdraw the same from the inflated parison and vertically spaced apart inner cooling rings disposed substantially concentrically to the axis of the parison downstream of the annular extrusion die orifice of the blowing head. The inner cooling rings together with annular members define nozzle gaps and have air guiding surfaces, which face the wall of the parison and are convexly curved in a longitudinal section of the inner cooling rings and during the operation of the apparatus are swept by the cooling air blown out of said nozzle gaps. The cooling air blown out of said nozzle gaps flows approximately parallel or at an acute angle to the direction of travel of the parison. Said cooling means also comprise outer cooling means, which concentrically surround the extruded parison and comprise an outer cooling ring defining an annular nozzle gap, which is adjacent to and downstream of the annular extrusion die orifice and serves to blow air in a direction which is approximately parallel to the direction of travel of the parison. An apertured baffle plate or shield is provided, which surrounds the parison below its expanding portion adjacent to the downstream end of the cooling path defined by the inner cooling rings. In an axial projection on the inflated parison, said baffle plate or shield covers at least the inner part of the inflated parison. The baffle plate or shield has an annular inner edge, which together with the wall of the parison defines an annular gap. The inner cooling rings concentrically surround the tube serving to withdraw the cooling and inflating air. The inside diameter of the lowermost internal cooling ring is substantially as large as the diameter of the annular extrusion die orifice. The diameters of the inner cooling rings above said lowermost inner cooling ring progressively decrease in an upward direction so that the parison will assume an upwardly tapering, frustoconical shape having a small included angle before it is inflated. |
