Mold for hollow injection molding.

摘要

A mold for hollow injection molding has an inlet (10) for admitting a fluid (930) into the molten resin when injected to form an interior hollow in the molded product. The inlet is opened and closed by retraction and advancement of a movable pin (121) having at least a portion to fill the inlet (10) and close it. When the inlet is closed, while the resin is being injected, the pin (121) has a portion which projects out of the inlet (10) into the space (2) where the resin is injected. When the inlet is opened, the retraction of the pin (121) leaves a short passageway in the injected resin leading from the fluid inlet (10) for flow thereinto of the hollow-forming fluid. Preferably, the pin is stepped with an inlet-closing large rear portion and a smaller projecting forward portion which is located in and has an annular clearance with the inlet when it is open. The pin may be detachably connected to a movable plunger (12), operated by fluid (50) or spring pressure, to enable replacement by pins of different lengths, sizes, etc.