| 摘要 |
PURPOSE:To enable the back pressure of the injecting material in a heating cylinder to be heightened by a method in which in purging operation, the nozzle of the heating cylinder is brought into contact with the opening part of a connecting path, moving said nozzle from an injection molding position, and the injecting material in the heating cylinder is discharged through the connecting path. CONSTITUTION:Moving a heating cylinder 14 from an injection molding position, a nozzle 16 is brought into touch with a nozzle bush 34 of a nozzle closing device 18. At this state, purging operation is carried out. While the pressure of resin material having been injected into a horizontal hole 26 from the nozzle 16 is low, the injecting material is obstructed to flow by a shut off pin 48, and when the pressure of the injecting material becomes large, the shut off pin 48 is elevated against the energizing force of a compressed coil spring 56 and is retracted, and the resin material is allowed to flow out, whereby the pressure of the resin material injected from the nozzle 16, accordingly the back pressure of the resin material in the heating cylinder 14 is always kept in the pressure equal to or larger than a constant value. Therefore, the replacement of the old material with a new material may be sufficiently and effectively carried out. |
