| 摘要 |
In a pivoting jaw power tong, each primary camming surface of the rotary gea r has a substantially linear rather than curved configuration. Each primary camming surface forms an acute angle with a radial line extending from the rotary gear centerline to the point where the primary camming surface transitions to its associated neutral recess. Accordingly, the radial distance to a point on any of the primary camming surfaces reduces linearly with increased distance from the neutral recess. Rotation of the rotary gear in either direction away from the neutral position thus results in a linearly progressive reduction in the distance from the center of rotation to the points where the pivoting jaws' cam followers contact the camming surfaces, thus increasing the force exerted by the dies of the jaws upon a tubular disposed within the jaws. This camming surface geometry allows the power tong to automatically adjust for wear in the mechanism such that the contact force between the rollers and the camming surfaces, and the gripping force applied by the dies, will be substantially uniform.
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