| 摘要 |
<p>A power tong includes a frame and a pipegripping mechanism associated with a throat at one end of the frame. Power is transmitted to the pipe-gripping mechanism from a power unit through a drive train. The pipe-gripping mechanism cooperates with the throat to receive a pipe section to be rotated and includes a partial ring rotatably mounted within the frame and having an opening which may be aligned with the throat. The ring may be rotated in either direction by the power unit. Mounted on the tong is a die carrier which is rotatable relative to the ring. Link members are pivotally mounted on the die carrier and include dies positioned to grip the external surface of the pipe section. The link members are arranged to cooperate via cam followers with arcuate cam surfaces on the ring so that, when the ring is rotated relative to the die carrier, the dies are moved into engagement with the pipe section. After the movable dies have engaged the pipe section, further relative movement between the ring and the die carrier is prevented and the pipe section is therefore rotated. The cam angle between lines extending from the position of a cam follower on a cam surface when the dies grip the pipe to the center of rotation of the partial ring and to the center of the circle defined by the cam surface is about 1/2 to 5-1/2 degrees.</p> |
