The present invention relates to a mechanism in a plastic injection machine and the mechanism ensures the screw rod to be precisely moved together with the open and close of the molds.
A conventional plastic injection molding machine for manufacturing products having screw holes generally employs a gear system for controlling a screw rod moving into or removing from the cavity between two molds. The gear system is controlled by electric control system. The gear system including too many gears which is a load of maintenance. The gear system is difficult to precisely move the screw rod relative the molds so that the depth of the screw rod in the cavity cannot be obtained the same each time when the plastic material is injected into the cavity. The screw hole of the products could be damaged if the screw rod cannot be removed from the molds in stable. The gear system is activated after the movement of the molds is finished so that it prolongs the period of the complete process.
In accordance with one aspect of the present invention, there is provided a plastic injection molding machine which comprises a position block on the upper mold and a slide member on the lower mold. A pin is inserted in the position block and the movable member. A rod extends through the slide member so that the top end of the rod is inserted in the cavity when the pin is inserted in the slide member. Two side members each have threaded semi-circular recesses which are engaged with a threaded section on the rod so that when the rod is rotated by a motor, the rod is smoothly removed from the cavity.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.