| 摘要 |
<p>A lifting head having a gate arm (47), and a latch arm (63), pivotally secured to a frame (11). A clamping block (83), also mounted on the frame, is movable between a retracted position away from the drill collar and an extended position against the drill collar. A plurality of gripping inserts (95,97) are located on the clamping block and on the gate arm. Each insert has a body and a plurality of teeth (103). The bodies of the inserts may be vertical or angled, but the teeth of the inserts are angled with respect to the longitudinal axis of the drill collar. This allows the inserts to grip the drill collar, even if the lifting head grips the collar at a place having a spiral groove. </p> |
