Tong assembly for drill pipes

Claim 1

A tong assembly for selectively gripping and releasing a drill pipe, comprising: an annular mounting element for positioning adjacent a drill pipe and having a central aperture capable of receiving a drill pipe without contact, said element having a coaxial shaft extension at one end adapted to be threadedly secured to a power swivel of a drilling apparatus, three pivotal members on the side of said annular mounting element remote from said coaxial shaft extension, said members spaced axially at approximately 120* in the annular mounting element and each pivotal member adapted to rotate about a pivot axis in a plane normal to the axis of said drill pipe, each pivotal member having a pipe-gripping portion spaced from its pivot axis and moveable toward and in contact with said drill pipe when said pivot member rotates in one direction with respect to said annular mounting element and moves away from said drill pipe when the pivotal member rotates in the other direction with respect to said annular mounting element, an annular inertial element loosely retained in said annular mounting element and capable of movement with respect to each of said pivotal members, a part of each of said pivotal members projecting generally away from the pipe gripping portion through an opening in said inertial element whereby a sudden change in the rotational velocity of the annular mounting element results in a relative rotational movement between the annular mounting element and the inertial element thereby urging said part of each of said pivotal members to move tangentially about the pivot axis of the respective pivotal member.