| 摘要 |
<p>Pipe tongs for casings in boreholes consits of a housing complete with axial entry and radial recess adapted to the casing dia. and encloses a power rotated rim gear with associated radial recess and ramp cams allocated to the hinged tong jaws. The forces operating between the cams and jaw guide rollers can be reduced to the minimum amount required to rotate the casing and at the same time. produce a radially operative contact pressure on the jaws. Levers inserted between the jaws and their holders should reinforce the contact or clamping effect, and each cam should have a flat centering curve and a tensioning curve at a much steeper slope than the first curve run.</p> |
