| 摘要 |
A torque-reduction and/or protection device for use in a drill string comprises a generally cylindrical body (10) including a mandrel portion (18) and a rotatable collar (20) mounted on the mandrel portion between first and second shoulders (22, 24), one of which is defined by a ring member (24) secured to said body after the collar has been located. A low friction bearing is provided between the collar and the mandrel including at least one of the following on the bearing surfaces of each of the collar and mandrel: low friction alloy coating; low friction ceramic coating; low friction alloy insert; low friction ceramic insert; magnetic elements. The collar has a low friction coating (30) on its outer surface comprising a composite coating having an inner layer of hard low friction material and an outer coating of relatively softer low friction material. The device may be incorporated into a sub but is preferably incorporated in a tool joint of a length of drill pipe. |
