HOLLOW INJECTION-MOLDING METHOD AND PRESSURIZED FLUID INTRODUCING AND DISCHARGING APPARATUS THEREFOR

摘要

The invention relates to a hollow injection-molding method of forming a hollow portion in molten resin in a mold cavity by introducing a pressurized fluid, and also to a pressurized fluid introducing and discharging apparatus therefor, and has an object of eliminating the backflow of the molten resin to a pressurized fluid passage and surly introducing and rapidly discharging the pressurized fluid. A gap between a cylindrical sleeve and a shaft core inserted into the sleeve is used as the pressurized fluid passage. The front end of the shaft core is projected into a mold so as to be beyond the sleeve, and the projection portion of the shaft core is used as a guide face. By sliding the shaft core, the state of an opening portion of the pressurized fluid passage in the side of the mold is changed from a narrowed state where the pressurized fluid can pass through the opening portion but the molten resin cannot enter the opening portion, to a widened state or vice versa. The width of the opening portion of the pressurized fluid passage in the side of the mold is changed by sliding the shaft core, whereby the backflow of the molten resin is prevented from occurring and the pressurized fluid can be rapidly discharged. The provision of the guide face allows the pressurized fluid to be surely introduced.