Patent ID: 7255025

Claim:
A power tong comprising: (a) a ring gear having a central pipe-containing region accessible through a throat opening in the side of the ring gear and having an inner surface facing such central region; (b) a camming surface formed on the inner surface of the ring gear; (c) twin C-shaped cage plates with outer surfaces rotationally mounted with respect to the ring gear on opposite sides of the ring gear, said cage plates having a gap formed therein that is of a size and position, when aligned, that corresponds with the throat opening and central pipe-containing region in the ring gear, said cage plates being free to rotate with respect to the ring gear, but being constrained to maintain a center of rotation corresponding to the center of the ring gear; (d) pipe receiving jaw means mounted between said cage plates and positioned to receive pipe that has passed through the throat in the ring gear to be positioned centrally within the ring gear; (e) a sliding jaw assembly having upper and lower retaining portions slideably engaged with the gap in the upper and lower cage plates to maintain the sliding jaw assembly in a central, position within said throat and between said cage plates, said assembly carrying a sliding jaw mounted between the upper and lower retaining portions, said sliding jaw being dimensioned to fit within and pass through the throat in the ring gear to advance to a pipe-engaging position where it will bear against a pipe held in position by the pipe receiving jaw means, the radial dimension of the sliding jaw assembly being sufficiently limited so that, once the sliding jaw advances to a pipe engaging position rotation of the ring gear becomes possible; (f) a cam follower mounted within the sliding jaw assembly, positioned to contact and advance along the camming surface when the sliding jaw is in said pipe-engaging position, forcing the sliding jaw, together with the outer retaining portions of the sliding jaw assembly to move inwardly within the gap in the cage plates when the ring gear is initially rotated with respect to the drill pipe and the cage plates whereby the inwardly directed force developed by the camming surface will cause the sliding jaw to bear tightly against pipe contained within the tong, thereby engaging the ring gear with said pipe.