| 摘要 |
PROBLEM TO BE SOLVED: To provide a back flow preventing device and a method for operating an injection device, in which resin is prevented from being moved by suck back and seal is surely performed. SOLUTION: The back flow preventing device is equipped with a metering part, a screw head, a first resin flow path formed in a first ring, a second resin flow path formed in a second ring which is adjoined to the first ring and is relatively provided freely rockingly, a driving means which selectively rotates a screw in the direction of one hand and in the direction of the other hand and a controlling device. Such a rocking regulating means is formed between the first and second rings that when the screw is rotated in the direction of one hand, the first and second resin flow paths are communicated and further when the screw is rotated in the direction of the other hand, the first and second resin flow paths are not communicated and seal is performed. The controlling device is equipped with a treatment means of pressure drop of resin for lowering the pressure of resin in the front of the screw head before seal is begun after a measuring process is completed.
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