Patent ID: 7387050

Claim:
A rotational unit for a torque tong, comprising: a fixed part; and a rotary part designed to grip a pipe to be rotated, said rotary part comprising: at least one movable gripping jaw arranged to be moved into engagement with the pipe; toothing arranged to engage at least one chain, the toothing including teeth, said at least one chain being operatively connected to an actuator in order to move the at least one chain and so impart rotary movement to the rotary part; and an opening at a periphery thereof for introduction of a pipe, wherein the at least one chain extends across a sector of a circle larger than the opening, thus ensuring that the at least one chain and the toothing on the rotary part are engaged at all times, the opening is arranged to be kept open during the rotation of the rotary part, and a rectilinear distance over which the at least one chain extends between the teeth of the toothing located closest to and on either side of the opening is equivalent to a whole number of teeth, wherein the distribution of the teeth on the rotary part is defined by: t 2 · 1 sin ⁢ ⁢ ( 2 · π - α 2 · N 2 ⁢ ) = 0 ( 1 ) 2 · a ⁢ ⁢ sin ⁢ ⁢ ( N 1 · t 2 · r ) - α = 0 ( 2 ) in which: t is the chain pitch, in mm, N 1 is the number of teeth that will fit between the two teeth nearest the opening, N 2 is the number of teeth along the curved section of the rotary part 40, α is the angle (in radians) between the teeth nearest the opening, and r is the radius of the rotary part at the at least one chain, the radius being the distance from a center of the rotary part to a center of the chain.