Abstract:
The present invention provides a jaw assembly and die insert for use in conventional power tongs, back-up power tongs, and similar tools. The die insert has a rear surface having a plurality of splines extending outwardly from the rear surface and forming a plurality of grooves between the splines. The die also has a front surface adapted to grip a tubular member and a keyway formed on the rear surface. A mating jaw member is provided which also has a front face of splines and grooves with a keyway which aligns with the die&#39;s keyway when the die is inserted into the jaw. A key is inserted into this combined keyway to prevent vertical forces from drawing the die out of the jaw member.

Description:
This is a continuation-in-part of Ser. No. 08/805,422 filed Feb. 25, 1997 now U.S. Pat. No. 5,911,796. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to tools used in the in the oil and gas drilling industry to grip and rotate tubular members such as drill pipe. More particularly, the present invention relates to the jaw assembly, which is the component of such tools actually coming into contact with the tubular. 
     In the oil and gas drilling industry, a certain class of machines known as power tongs are employed to grip and rotate drill pipe and other tubular members in the process of making up or breaking apart the joints on a string of tubulars. Typically, when a tubular joint is be made up or broken apart, back-up power tongs will grip the tubular on one side of the joint and power tongs will grip the tubular on the opposite side of the joint. The power tongs are used to apply torque to one tubular while the back-up power tongs (hereinafter referred to simply as back-up tongs) are used to hold the other tubular stationary against rotation. Both the back-up tongs and the power tongs must have a means to securely grip the tubular when large torque loads are being applied. One such gripping means is a jaw member having a concave shaped die insert such as seen in U.S. Pat. No. 4,576,067 to Buck. The die insert may have a knurled surface in order to better grip the tubular. However, the die must be easily replaceable in the jaw member because the knurled surface is eventually worn smooth during use and loses its gripping characteristics. While being replaceable, the dies must also be able to transfer large torque loads between the jaw member and the tubular without the die breaking its mounting in the jaw member. One successful solution to this problem is disclosed in U.S. Pat. No. 4,576,067 to Buck where the jaw member and die have a plurality splines and grooves that interlock lock the jaw member and die together. 
     However, the torque load imparting a force transverse to the splines and grooves is not the only force acting on the die. In certain situations, a vertical force parallel to the spline and grooves is exerted on the dies. To resist this vertical force, the prior art typically employed some type of retaining screw. If the vertical force becomes great enough, the retaining screw fails and the die is displaced from the jaw. What is needed in the art is an improved method of making the die secure in the jaw member from vertical displacement. 
     SUMMARY OF INVENTION 
     The present invention provides a jaw assembly and die insert for use in conventional power tongs, back-up power tongs, and similar tools. The die insert has a rear surface having a plurality of splines extending outwardly from the rear surface and forming a plurality of grooves between the splines. The die also has a front surface adapted to grip a tubular member and a keyway formed on the rear surface. A mating jaw member is provided which also has a front face of splines and grooves with a keyway which aligns with the die&#39;s keyway when the die is inserted into the jaw member. A key is inserted into this combined keyway to prevent vertical forces from drawing the die out of the jaw member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art jaw assembly. 
     FIG. 2 is a top view of the same prior art jaw assembly. 
     FIG. 3 is a top view of the interior of a prior art power tong illustrating the placement of the jaw assemblies. 
     FIG. 4 is a top view of the interior of a prior art back-up power tong illustrating the placement of the jaw assemblies. 
     FIG. 5 is a side view illustrating the typical combined use of power tongs and back-up power tongs. 
     FIG. 6 is an exploded view of the jaw assembly of the present invention. 
     FIG. 7 is a rear perspective view of a die insert of the present invention. 
     FIG. 8 is an exploded view of an alternate jaw assembly of the present invention. 
     FIG. 9 is a perspective view of a jaw member which comprises a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The prior art jaw assembly and die insert are depicted in FIGS. 1 and 2 and are explained thoroughly in U.S. Pat. No. 4,576,067 to Buck which is incorporated by reference herein. The jaw member  40  has a pin aperture  42  for pinning jaw member  40  into the power tongs  30  (seen in FIG. 3) or back-up tongs  34  (seen in FIG.  4 ). The jaw member  40  further has a concave surface with a plurality of splines  44  and grooves  45  which matingly engage corresponding splines  46  and grooves  47  in die  41 . Die  41  may slide into position in jaw member  40  and is retained in the downward direction by lip  48  which is formed at the bottom of the concave surface of jaw member  40 . To secure die  41  from sliding upward and out of jaw member  40 , retaining screw  43  is threaded into aperture  49  and the head of retaining screw  43  overlaps die  41  in order to prevent upward movement of die  41 . 
     Die  41  typically has a gripping surface  64 , which is shown in FIG. 1 as being formed from a pattern of raised metal teeth  65 . Each of the teeth  65  will include peak  66  which will be the first part of the teeth  65  to contact and bite into the tubular member being gripped. Between the peaks  66  of teeth  65  are depressions or valleys. The gripping surface  64  seen in FIG. 1 includes horizontal depressions  67  and vertical depressions  68 . However, the depressions need not be horizontal and vertical or run perpendicular to one another. It is only necessary that the depressions substantially surround teeth  65  in order to form peaks  66 . This allows the peaks  66  to bite into a tubular and for teeth  65  to resist slipping between die  41  and the tubular in the horizontal direction, the vertical direction, or any other direction. 
     Teeth  65  with peaks  66  should be distinguished from other prior art gripping surfaces such as that disclosed in U.S. Pat. No. 2,656,751 to Johnson, which is incorporated by reference herein. Johnson discloses a pipe wrench having jaws with ridges running parallel to the long axis of the pipe being gripped. The ridges will resist slippage between the wrench and pipe when torque is applied. However, if an axial force is applied to the wrench, the ridges will be prone to slipping along the surface of the pipe. This slipping will occur because the ridges are continuous along the axial direction in which the force is applied. Therefore, the ridges cannot bite into the pipe in a manner to prevent slippage in the axial direction. 
     Nor should only the gripping surface  64  as shown in FIG. 1 be considered teeth with peaks and depressions. Co-pending application Ser. No. 09/267,174 to Daniel Bangert, filed on Mar. 12, 1999, discloses a gripping surface formed of granular particles. The granular particles are also intended to be considered as teeth having peaks and depressions between adjacent particles. 
     The manner in which jaw members  40  are used in power tongs  30  and back-up tongs  34 , as well as the main components of a typical prior art power tongs  30  and back-up tongs  34 , are seen in FIGS. 3 and 4, respectively. FIG. 3 illustrates power tongs  30  which are intended to grasp a tubular  60  in jaw members  40  and rotate the jaw members  40  and tubular  60  by way of a ring gear  50 . The back-up tongs  34  seen in FIG. 4 illustrate how back-up tongs are not designed to rotate the tubular  60 , but rather to simply securely grasp the tubular  60  and hold it against rotation. FIG.  5  depicts how power tongs  30  are used in combination with back-up tongs  34  in order to make up or break apart a tubular joint  51 . The frames of power tongs  30  and back-up tongs  34  are joined and maintained in alignment by guide legs  38 . Typically the guide legs  38  are coupled with some type of resilient means, such as a heavy tension spring  55 , which allows some relative movement between back-up tongs  34  and power tongs  30 . However, because of the substantial weight of the back-up tongs  34 , these springs must have considerable rigidity and only large forces will induce relative movement between power tongs  30  and back-up tongs  34 . 
     In operation as shown in FIG. 5, the combination of tongs  30  and  34  will be positioned on the tubular string such that the joint  51  connecting the tubulars is between back-up tongs  34  and power tongs  30 . In this manner, back-up tongs  34  may hold the lower tubular  52  immobile while power tongs  30  apply torque to the upper tubular  53  in order to make up or break apart the joint  51 . It will be understood that as the joint is being made up, the distance between the tubulars decreases as the threaded portions of joint  51  come together. This causes an upward vertical force on the jaw members  40  in back-up tongs  34  and a downward vertical force on the jaw members  40  in power tongs  30 . Conversely, when joint  51  is being broken apart, tubulars  53  and  52  move apart causing a downward force on the jaw members  40  of back-up tongs  34  and an upward force on the jaw members  40  of power tongs  30 . Additionally, other circumstances may impart vertical forces to the power tongs  30  and back-up tongs  34 . For example, the drill string may inadvertently be slightly raised or lowered while the tongs are gripping a tubular. Because the dies  41  have gripping surfaces  64  formed from teeth  65  with peaks  66 , gripping surface  64  will be capable of preventing vertical slipping between the tubular member and the jaw members  40 . 
     However, these vertical forces on the jaw members  40  are often sufficient to over stress the retaining screw  43  securing die  41 , causing retaining screw  43  to fail and die  41  to be lifted from jaw member  40 . While the spring devices  55  on guide legs  38  will allow some displacement between the tongs, these spring devices are typically so rigid that retaining screw  43  will fail prior to the spring devices being displace any appreciable distance. 
     To overcome these disadvantages in the art, FIG. 6 illustrates a novel jaw assembly which retains a die insert securely against far higher vertical loads than the prior art jaw assembly described above. Jaw assembly  1  will include jaw member  2  and removably insertable die  3 . Jaw member  2  will have pinning aperture  15  through which pin  17  will be inserted to secure jaw assembly  1  in power tongs  30 , back-up tongs  34  or other tools where jaw assemblies are employed. Jaw member  2  has a front surface  18  with splines  13  and grooves  14  formed thereon. As best seen in FIG. 7, rear surface  20  of die  3  also has splines  4  and grooves  5 . When die  3  is inserted in jaw member  2 , jaw member splines  13  and grooves  14  will mesh with die grooves  5  and splines  4  and will prevent lateral movement between jaw member  2  and die  3 . Jaw assembly  1  further includes die retention clips  8  which have front edges  12  and retaining screw apertures  9   a . It will be understood that when die  3  is inserted into jaw member  2 , front edges  12  of retention clips  8  will engage die retaining channels  6  of die  3 . When screws are threaded through apertures  9   a  in to apertures  9  in jaw member  2 , die  3  will be held against forward and vertical movement within jaw member  2 . It should be noted that there will be some variation in size and shape of the jaw assemblies  1  depending the size of pipe they are designed to grip and the type of tool in which they are to be used. Not all jaw assemblies  1  will require retention clips  8  if the size and amount of curvature in a particular jaw assembly is sufficient to prevent die  3  from moving forward out of jaw member  2 . However, the embodiments of jaw assembly  1  illustrated herein all require retention clips  8 . 
     Still viewing FIG. 6, it can be seen that jaw member  2  has a keyway  16  formed laterally across front surface  18 . As best seen if FIG. 7, die  3  has a corresponding keyway  7  formed across its back surface  20 . When die  3  is inserted into jaw member  2 , keyways  16  and  7  will be aligned such that key  11  (FIG. 6) may be inserted in keyways  16  and  7 . Key  11  may be formed of steel or any other material flexible enough to be inserted into the key yet hard enough to not seriously deform under the vertical forces encountered. By employing this key and keyway configuration, any vertical force tending to lift die  3  out of jaw member  2  will be resisted by the entire length of key  11  as opposed to merely the retaining screws found in the prior art. This key and keyway configuration allows die  3  to resist many times more vertical force than the prior art retaining screws were able to withstand. While key  11  in FIG. 6 is shown as a length of material having a square cross-section, any cross-sectional shape of key that will securely engage keyways  16  and  7  may be utilized. Furthermore, keyway  16  need not span the entire distance across the front surface  18  of jaw member  2 , but could span less than the entire distance as long as a suitable provision is made for pulling key  11  out of the keyway rather than driving key  11  out the side opposite insertion as envisioned in the embodiment of FIG.  6 . 
     An alternate embodiment of the present invention is shown in FIG.  8 . Here jaw member  2  has a keyway  16  beginning in a first side  21  of jaw member  2  and extending through jaw member  2  to a second side  22  (hidden from view in FIG.  8 ). As suggested by the straight key  11 , keyway  16  does not follow the concave shape of front surface  18 , but rather travels on a straight line through jaw member  2 . As seen in FIG. 8, this results in keyway  16  intersecting front surface  18  only along that portion of front surface  18  with the deepest concave curvature. While this embodiment illustrates a friction pin type key  11 , it will be understood that a threaded key  110  as shown in FIG. 8 could also be employed if keyway  16  was threaded. Still other types of keys  11  could be used in place of friction pin key  11  or threaded key  110 . 
     A third embodiment of the present invention is seen in FIG.  9  and illustrates an alternative method of forming a key  11 . In this embodiment, jaw member splines  13  have discrete key extensions  25  formed approximate to the midpoint of each spline  13 . Of course, less than all splines  13  could be provided with extensions  25 . Nor do the extensions need to be at the midpoint of the spline as long as the corresponding keyway  7  on die  3  is positioned at the same level as key extensions  25 . As best seen in FIG. 7, keyway  7  may be formed by cutting not just the splines  4  extending from rear surface  20 , but also cutting a short distance into rear surface  20  itself. This produces upper and lower keyway shoulders  10  between which key extensions  25  become engaged. To install this embodiment of die  3  in jaw member  2 , the retention clips  8  are removed and die  3  is placed against jaw member  2  such that key extensions  25  rest between keyway shoulders  10 . Retention clips  8  are then attached to jaw member  2  securing die  3  in jaw member  2  and thereby securing key extensions  25  between keyway shoulders  10 . It will be understood that a jaw member  2  having keyway extensions must be mated with dies  3  having keyway shoulders cut therein. Otherwise dies  3  will not fit closely enough against jaw members  2  in order that retention clips  8  may be properly attached between dies  3  and jaw members  2 . 
     Finally, while many parts of the present invention have been described in terms of specific embodiments, it is anticipated that still further alterations and modifications thereof will no doubt become apparent to those skilled in the art. For example, while not shown in the drawings, the term jaw member is intended to include slips, elevators or other holding devices used in the oil and gas industry for suspending and lifting tubular members. Conventional slips or elevators could be adapted to the present invention by being manufactured with a removable die as the gripping surface. The slip or elevator body would be formed with a concave surface having splines and grooves similar to the jaw member  2  seen in FIG.  9 . Dies  3  could then be removably inserted in the elevator or slip and later replaced when the die gripping surface became excessively worn. This example is just one possible modification of the present invention and it is intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention.