| 摘要 |
An active jaw for a power tong is provided with an upper cam and a lower cam which are shaped so that rotation of the rotary relative to the active jaw in either sense from a first position results in the active jaw being applied to a pipe via a roller. The active jaw can be released by reversing the direction of rotation of the rotary. A peg may be used to limit movement of the active jaw relative to the rotary to prevent the active jaw being reapplied to the pipe. Pipes of different diameters may be gripped by using rollers of different diameters and, optionally, different active jaws shaped to grip the pipe. In a second embodiment a brake band acts on a drum which supports the active jaw. When the rotary is started the active jaw is restrained from rotation. This relative movement applies the dies on the active jaw to the pipe. Further rotation of the rotary then overcomes the braking force and the rotary, drum and active jaw rotate in unison. An adjustable bolt is provided to prevent the active jaw being reapplied when the rotary is reversed.
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