A jaw adapter for use in a pivoting jaw power tong having a cage plate designed to house a pivoting jaw member. The jaw adapter includes an adapter body shaped to fit between the cages plates of a pivoting jaw power tong. The adapter body further includes a pin assembly for engaging at least one of the cage plates, and the adapter body still further includes a sliding jaw passage. A jaw assembly is then positioned within the sliding jaw passage.

BACKGROUND OF INVENTION 
     The present invention relates to power tongs used to apply torque to tubular members in the oil exploration/production industry. In particular, the present invention deals with a novel device for converting a pivoting jaw power tong into a sliding jaw power tong. 
     Both pivoting jaw and sliding jaw power tongs are well known in the art. An example of a pivoting jaw power tong can be seen in U.S. Pat. No. 4,350,062 to Farr et al, which is incorporated by reference herein. FIG. 1 illustrates the basic components of a pivoting jaw power tong  1 . A tong body  2  will enclose a ring gear  3  which will have a cam surface  4 . Positioned within ring gear  3  are the pivoting jaws  5 . Pivoting jaws  5  are pivotally attached between an upper and lower tong cage plate (not shown) by pivot pin  7 . A roller  6  on pivoting jaws  5  will engage cam surface  4  on ring gear  3 . As is well known in the art, the rotation of ring gear  3  will cause different sections of cam surface  4  to either push roller  6  toward tubular  100  (and thus cause the jaws to grip the tubular) or allow roller  6  to move away from tubular  100  (causing the jaws to release the tubular). 
     An example of a sliding jaw power tong may be seen in U.S. Pat. No. 5,435,213 to Buck which is incorporated by reference herein. A sliding jaw power tong has a tong body and ring gear structure similar to a pivoting jaw power tong, but the jaw is not pinned to the cage plates. A pocket for housing the sliding jaw is formed in the cage plates and the sliding jaw is moved radially toward the tubular by way of the ring gear's cam surfaces acting on the sliding jaws' rollers. 
     One advantage which pivoting jaw power tongs have relative to the sliding jaw variety is that pivoting jaw power tongs have a somewhat smaller overall diameter. This smaller diameter is a result of pivoting type jaws needing less radial distance within the ring gear to open and receive a tubular than is the case with sliding jaw power tongs. However, pivoting jaws also have certain disadvantages compared to sliding jaws. Generally both pivoting jaw and sliding jaw power tongs are designed to grip a range of standard tubular diameters with varying jaw sizes designed for each standard tubular diameter. For example, a 14″ power tong will typically accommodate different jaw sizes for the gripping of 14″ diameter down to 5″ diameter tubulars. Nevertheless, because of the pivoting geometry of the pivoting jaw power tongs, these power tongs tend to grip out of tolerance tubulars with a less uniform load than sliding jaw power tongs, thereby causing damaging slippage between the jaws and the tubular. For certain types of tubulars such as well casing and production tubing, this is not a significant problem because these tubulars generally manufactured and maintained within relatively tight tolerances (e.g. +/−{fraction (1/32)}″). However, with other tubulars such as drill pipe, the tool joint of the tubular can vary significantly in diameter (e.g. ¼″) and such relatively large variations in diameter can cause a tubular to not be reliably gripped by pivoting jaw tongs. 
     Because sliding jaws move on a straight radial path toward and away from the tubular, this type of power tong can grip the tubular with an equally uniformly applied load over a wider range of radial distances. Thus, the wider variance in diameters found in drill pipe does not adversely effect the gripping ability of sliding jaw power tongs. 
     Additionally, there will be occasions in tubular handling operations when only a pivoting jaw tong is available and large tolerance tubulars must be manipulated with that power tong. It would be a significant advantage if there was a quick and economical manner of converting a pivoting jaw power tong into a sliding jaw power tong. 
     SUMMARY OF INVENTION 
     The present invention provides a jaw adapter for use in a pivoting jaw power tong having a cage plate designed to house a pivoting jaw member. The jaw adapter includes an adapter body shaped to fit between the cages plates of the pivoting jaw power tong. The adapter body further includes a pin assembly for engaging at least one of the cage plates, and the adapter body still further includes a sliding jaw passage. A jaw assembly is positioned within the sliding jaw passage. 
     The present invention also includes a method of converting a pivoting jaw power tong into a sliding jaw power tong. The method comprises the steps of: a) providing a pivoting jaw power tong; b) removing the pivoting jaw from the power tong; and c) positioning a sliding jaw adapter within the power tong. The sliding jaw adapter includes an adapter body shaped to fit between the cages plates of the pivoting jaw power tong. The adapter body further includes a pin assembly for engaging at least one of the cage plates, and the adapter body still further includes a sliding jaw passage. A jaw assembly is then positioned within the sliding jaw passage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of the ring gear and jaws of a prior art pivoting jaw power tong. 
     FIG. 2 is a top view of the ring gear and sliding jaw adapter of the present invention. 
     FIG. 3 is an exploded view of the cage plates, ring gear, and sliding jaw adapter of the present invention on one side of the ring gear and a conventional pivoting jaw on the other side. 
     FIG. 4 is an exploded view of the sliding jaw adapter of the present invention positioned within the power tong of FIG.  1 . 
     FIG. 5 is a perspective view illustrating the jaw member and pusher utilized in the present invention. 
     FIG. 6 is a sectional view of the sliding jaw adapter of the present invention. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     While FIG. 2 shows the present invention, sliding jaw adapter  20 , positioned within a power tong, FIG. 3 more clearly shows how jaw adapter  20  will be positioned relative to the upper and lower cages plates  8   a  and  8   b  and ring gear  3 . For the sake of comparison, FIG. 3 also shows a prior art pivoting jaw member  5 . However, it will be understood that the power tong will be operating either with two prior art pivoting jaw members  5  or, in accordance with the present invention, will have both pivoting jaw members  5  replaced with jaw adapters  20 . As is well known in the art, cage plates  8   a  and  8   b  will be held together at the proper spacing by way of spacers  9  and spacer bolts  11  inserted therethrough. It can be seen from FIG. 3 how the pivot pin  7  extending from the bottom of top cage plate  8   a  would extend through pivot pin aperture  13  on pivoting jaw  5  such that cam surface  4   a  (on ring gear  3 ) would act against roller  6  to pivot pivoting jaw  5  on pivot pin  7 . 
     The specific details of jaw adapter  20 's construction are best seen in the exploded view of FIG.  4 . Jaw adapter  20  will generally comprise an adapter body  22  formed by an upper half  22   a  and a lower half  22   b . Formed though the mid-portion of adapter body  22  will be a jaw passage  35 . Sized to slide within jaw passage  35  will be pusher  30 . Pusher  30  will have a rounded rear surface similar to conventional jaw member  40 . Also like conventional jaw members, pusher  30  will include an open section  33  and pin apertures  34 . A conventional roller  31  will fit within open section  33  and be rotatively pinned into place by roller pin  32 . The design of roller  31  and pin  32  may be any convention type, with one example being disclosed in U.S. Pat. No. 5,819,605 to Buck et al., which is incorporated by reference herein. 
     The two sections of adapter body  22  will be held in alignment by pins  53   a  engaging apertures  53   b  which are formed in both upper half  22   a  and lower half  22   b . A pair of body connecting bolts  23  will pass through apertures  24  and hold upper and lower adapter body halves  22   a  and  22   b  securely in together. Adapter body  22  will include a spacer groove  28  to accommodate the spacer tubes  9  (FIG. 3) running between upper and lower cage plate  8   a  and  8   b . There will also be a pair of lifting rings  51   a  engaging ring apertures  51   b  and which will provide a convenient handhold for the heavy metal adapters. The outer top surface of both adapter body halves  22   a  and  22   b  will include a retaining spring  50  positioned in a retaining spring groove  52  and attached at one end by spring bolt  44   b . Retaining spring  50  will attach to spring bolt  44   a  on jaw member  40  and bias jaw member  40  toward the rear of adapter body  22  as is explained in greater detail below. Finally, a locking pin  27  is intended to pass through upper cage plate  8   a  and engage locking pin aperture  26 . The combination of locking pin  27  and pivot pin  7  (see FIG. 3) will hold adapter  20  firmly against rotation. Locking pin  27  and locking pin aperture  26  form but one type of locking pin assembly. Those skilled in the art will undoubtedly methods of securing adapter  20  against rotation relative to the cages plates and all such methods are intended to come within the definition of “locking pin assembly.” 
     A more detailed view of the mechanical relationship between pusher  30  and jaw member  40  may be seen in FIGS. 5 and 6. A front view of pusher  30  is seen in FIG.  5 . In this embodiment, pusher  30  is formed with an front face  36  which is complementary to the rear face  46  of jaw member  40 . Jaw member  40  may be any conventional power tong jaw such as seen in U.S. Pat. No. 5,911,786 to Buck which is incorporated by reference herein. Jaw member  40  (absent a roller or roller pin) will slide into passage  35  of adapter body  20  and abut up against the front face of pusher  30  as suggested in the cross-sectional view of FIG.  6 . The spring pin  44   a  on jaw member  40  will engage retainer spring  50  and serve to bias jaw member  40  rearward against the front face  36  of pusher  30 . It can be seen that pusher  30  acts as a reducer in power tongs which would normally be too large to accommodate jaw member  40 . For example, if the power tong is a 14″ diameter power tong and jaw member  40  an 8⅝″ jaw (i.e designed to grip 8⅝″ tubulars), jaw member  40  would be too small to properly operate in the power tong without special modification. However, by positioning pusher  30  between the ring gear cam surfaces and jaw member  40 , pusher  30  effectively reduces the size of jaw members which can be utilized in the power tong. 
     FIG. 3 illustrates how sliding jaw adapter  20  will replace pivoting jaw  5  in a conventional pivoting jaw power tong. After pivot pin  7  is removed, pivoting jaws  5  may then be slid to the central throat opening of ring gear  3  and lifted out of the power tong. Thereafter, sliding jaw adapters  20  are positioned in place between the cages plates and then pivot pin  7  will be repositioned such that it extends through pivot pin aperture  25  on sliding jaw adapter  20 . Locking pin  27  will extend through upper cage plate  8   a  to engage locking aperture  26  on sliding jaw adapter  20 . At this point, sliding jaw adapter  20  is securely fixed between upper and lower cages plate  8   a  and  8   b . FIG. 2 illustrates sliding jaw adapters  20  positioned within the power tong which previously housed the conventional pivoting jaws  5  seen in FIG.  1 . FIG. 2 also shows a much smaller diameter, low tolerance, tubular member  110  which pivoting jaws  5  could not have properly gripped. However, the jaw members  40  positioned within adapter body  22  are able to effectively grip smaller diameter tubular  110 . As ring gear  3  rotates, roller  31  on pusher  30  will travel up positive cam surface  4  on ring gear  3 . This naturally will cause pusher  30  to move jaw member  40  toward and eventually into engagement with tubular  110 . Just as clearly, when ring gear  3  rotates in the opposite direction, roller  31  will travel back to a neutral part of cam surface  4  and retainer springs  50  (FIG. 4) will pull jaw member  40  back away from and out of engagement with tubular  110 . It will be noted that during the entire travel of jaw member  40 , adapter body  22  did not move as it is held in place by pivot pin  7  and locking pin  27 . 
     While the present invention has been described in terms of specific embodiments, those skilled in the art will recognize many variations and modifications which are with the scope of the present invention. All such variations and modifications are intended to come within the scope of the following claims.