| 摘要 |
PURPOSE:To variably control the cross sectional area of a parison in the peripheral direction thereof so as to obtain a desired wall thickness, in the blow molding of a thermoplastic resin, by providing a valve in the resin passage between a die and a core in a movable manner. CONSTITUTION:The thermoplastic resin melted and plasticized in an extruder flows between a valve 4 and core 2 through a resin passage 3 while distributed at the tapered part 4' having a circular cross sectional area of the valve 4 and reaches a tapered part 4'' having an oval cross sectional area. When the valve 4 moves downwardly and the base part of the oval tapered part 4'' is coincided with the lower end of the core 2, there is no change in the wall thickness of a molded parison in the peripheral diection thereof. When the valve 4 moves upwardly and the lower end surface of the oval tapered part 4'' is coincided with the lower end surface of the core 2, the wall thickness of the parison changes in the peripheral direction thereof and becomes max. In this case, the wall thickness of the parison is adjusted by the moving amount of the valve 4. |
