1. Field of the Invention
This invention relates to the field of apparatus and methods for rotating substantially cylindrical objects, particularly drill pipe, drill collars, casing, etc. The word "cylindrical" is employed in this specification in its ordinary or common sense, namely to define objects which have a circular or substantially circular exterior cross-sectional shape.
2. Description of Prior Art
In making joints between sections of the drill pipe used in drilling oil wells, and in disconnecting such joints, it is conventional practice to spin the drill pipe (rotate the same about the longitudinal axis thereof) by the following method: A length of chain is wrapped a number of times around the drill pipe, and one end of the chain is pulled. The chain then disengages the pipe and becomes a very dangerous moving object which may effect injury to the workmen. Because of such danger, because of the slowness of the operation, and because of other factors, large numbers of prior-art workers have attempted to provide automatic apparatus which will do the job successfully, rapidly, etc. The results of such prior-art efforts have not achieved widespread commercial success, so that the above-indicated archaic method of spinning pipe prevails to this day.
Prior-art U.S. patents for effecting spinning or rotation of drill pipe, etc., and which are known to applicant, are the following: Nos. 1,639,710; 1,760,167; 1,805,007; 1,925,970; 2,450,934; 2,460,671; 2,523,159; 2,544,639; 2,573,212; 2,615,681; 2,650,070; 2,741,460; 2,746,329; 2,760,392; 2,784,626; 2,862,690; 2,928,301; 3,061,011; and 3,308,691.
Some of the above-specified patents provide intermediate members between the chain (or other drive means) and the pipe to be spun, which is highly undesirable for reasons including (among others) excessive wear on such intermediate members. The remaining patents effect direct engagement between a chain or a belt and the exterior cylindrical surface of the pipe to be spun. The chains employed are frequently in the nature of bicycle chains, ordinary link-chains, etc., which often have teeth thereon disposed to bite into the pipe surface. For various reasons, including excessive wear, injury to the pipe, unsatisfactory operation, etc., all of such chains and belts have proved to be unsatisfactory.
There has been known for decades a type of chain termed a "silent chain", and it has had wide application in industry. However, to the best knowledge of applicant, no prior-art worker has employed a silent chain for the direct frictional gripping (under pressure) and then spinning of a drill pipe or other cylindrical object. One prior-art worker has, as taught by U.S. No. 2,353,642, employed a silent chain to turn non-cylindrical objects, namely nuts and bolts, the relationship being such that the individual links of the chain fit against the faces of a nut or a bolt head (whether it be square or hexagonal). The indicated prior-art patent did not suggest, or provide any means to achieve, frictional gripping of a cylindrical object to be rotated.
The prior-art apparatus and methods known to applicant are also deficient in other major respects. These frequently include (for example): (1) mounting the chain completely around the pipe, so that the chain must be broken prior to each spinning operation, (2) mounting the chain-drive motor and sprocket by means of a weak spring, instead of fixedly in any adjusted position, so that inadequate chain tension was developed, (3) mounting the chain on only three sprockets, which were so located that the chain tension created large torques tending to open the jaws and permit release of the pipe, (4) requiring some locking-connector means to lock the jaws closed, and which must be connected and disconnected between spinning operations, (5) requiring pipe-engaging teeth on the chains, which teeth wore the pipe excessively and also prevented desirable clutching action from occurring when the joint seated, (6) failing to compensate properly for the tendency of the spinning apparatus to rotate when the joint seats, (7) failing to grip a sufficiently large proportion of the pipe circumference, (8) failing to adequately control and equalize the jaw-closing mechanisms, (9) failing to compensate for depletion of air in the pneumatic supply, and (10) failing to generate sufficient torque.