Abstract:
A journal bearing element for use in forming a roller cone bit coupled to a bearing shaft to prevent circumferential sliding. Also included are material compositions of the journal bearing element. A journal bearing element is fixed in place relative to a head section and comprised of dense high purity powdered metal alloys with uniform micro-structure. A preferred material is comprised of a metal made of a carbon content of about 2.3% by weight, chromium of about 14% by weight, vanadium of about 9% by weight, and molybdenum at about 1% by weight.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 60/949,756, filed Jul. 13, 2007, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    This disclosure relates to a journal bearing for a roller cone bit. Specifically, it concerns a set of bearing element materials, a method of manufacturing the bearing elements, and a manner of securing these bearing elements to a roller cone bit. 
         [0004]    2. Description of Prior Art 
         [0005]    Drill bits used in drilling of subterranean well bores typically comprise drag bits and roller cone bits. Roller cone bits typically comprise a body having legs extending downward and a head bearing extending from the leg towards the axis of the bit body. Frusto-conically shaped roller cones are rotatably mounted on each of these journals and are included with cutting teeth on the outer surface of these cones. Because of the high stresses incurred during drilling operations, the bearing mating surfaces within the bit require a bearing material or a surface treatment to sustain the loads and extend the bit life. 
         [0006]      FIG. 1  provides in a side cross-sectional view an example of a portion of a roller cone drill bit  10 . In this embodiment, the roller cone  12  mates with the head portion  14 . A set of balls  16  is provided in an annular opening formed between the cone  12  and the head  14  and serves as a cone-retention system. A secondary purpose of the balls  16  is to provide a rolling surface for facilitating rotation of the cone  12 . Cone bearing surface  13  mates against and rotatably slides about head bearing surface  15 . The respective surfaces ( 13 ,  15 ) must accommodate the high stress during the respective loading and rotation of these elements. 
         [0007]    Traditionally, a journal bearing element  18  is disposed in a recess  19  circumferentially formed within the head section  14 . The journal bearing element  18  accommodates the cone  12  rotation and the forces that the cone  12  may exert on the head section  14 . The material used in forming the journal bearing element  18  varies; some are hard substances while others are soft, such as bronze and beryllium copper. In  FIG. 2 , an example of a journal bearing element  18  is illustrated in a perspective view. The journal bearing element  18  is not a continuous ring but includes a separation  20  along the circumference of the journal bearing element  18 . The separation  20  allows the journal bearing element  18  to be temporarily deformed during installation so it can be placed in the recess  19 . Thus, should the journal bearing element  18  become galled and adhere to either one of the cone bearing surface  13  or the head bearing surface in the recess  19 ; the cone  12  can still rotate relative to the head  14  because one of the two bearing surfaces ( 13 , 19 ) is still rotatable. While the embodiment of  FIG. 1  does provide some redundancy in situations where seizing may occur between the journal bearing element  18  and one of the opposing surfaces ( 13 ,  19 ), journal bearing element  18  addition complicates the design with regards to tolerances. The invention described herein provides increased bearing precision and wear resistance over that of the prior art. 
       SUMMARY OF INVENTION 
       [0008]    The disclosure herein provides embodiments of a journal bearing for use in a roller cone bit and includes a manner of attaching a journal bearing element onto the head section of a drill bit. The journal bearing element included herein may prevent rotation of the journal bearing element. For example, when the bearing is used in conjunction with a roller cone, the sliding surfaces will be on the outer circumference of the journal bearing element and the inner surface of the roller cone. Methods of adhering the journal bearing element to the head include welding, brazing, gluing, the use of pins or dowels, an interference or press fit, splines transverse to the journal bearing circumference, and keys or key ways formed for insertion between the journal bearing element and the head section. In one embodiment, the journal bearing element is fixed in place relative to the head section and may optionally be comprised of dense high purity powdered metal alloys with uniform micro-structure. These powdered metal alloys may optionally be of a class that contains vanadium. A second optional class of materials would include a cobalt-chromium-tungsten alloy with high carbon content. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a cross-sectional view of a portion of a roller cone bit. 
           [0011]      FIG. 2  is a view of a journal bearing element with a single separation. 
           [0012]      FIG. 3  is a sectional view of a bit body head section. 
           [0013]      FIG. 4  is a perspective view of an embodiment of a journal bearing portion of a head section consistent with the present disclosure. 
           [0014]      FIG. 5  is a view of a journal bearing element as embodied in the present disclosure. 
           [0015]      FIG. 6  is a perspective view of an embodiment of a journal bearing element coupled to a journal. 
           [0016]      FIG. 7  is a perspective partial sectional view of the embodiment of  FIG. 6 . 
           [0017]      FIG. 8  is a perspective partial sectional view of a journal bearing element coupled to a journal. 
           [0018]      FIG. 9  is a perspective partial sectional view of a journal bearing element coupled to a journal. 
           [0019]      FIG. 10  is a sectional view of a bit body head section. 
       
    
    
       [0020]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0021]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0022]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
         [0023]      FIG. 3  is a partial sectional view of an earth-boring bit  21  having a journal bearing element  28  as described herein. While  FIG. 3  only illustrates a single section, the bit  21  may comprise two or more sections welded together to form the composite bit  21 . The earth-boring bit  21  has bit body  23  with a threaded upper portion  25  for connecting to a drill string member (not shown) and a leg section  22  having a cutting cone  41  attached thereon. A fluid passage  27  directs drilling fluid to a nozzle (not shown) that impinges drilling fluid against the borehole bottom to flush cuttings to the surface of the earth. A pressure compensating lubrication system  31  may optionally be contained within each section of the bit  21 . A lubrication passage  33  extends downwardly to a ball plug  35 , which is secured to the body  21  by a plug weld  37 . A third lubrication passage (not shown) carries lubricant to a bearing surface between a bearing shaft  39 , which is cantilevered downwardly and inwardly from an outer and lower region of the body  23  of the bit  21 . The ball plug  37  retains a series of ball bearings  40  rotatably secured to the cutter cone  41  and to the bearing shaft  39 . Dispersed in the cutter cone  41  are a plurality of rows of earth disintegrating cutting elements or teeth  42  securable by interference fit in mating holes of the cutter cone  41 . An elastomeric O-ring seal  43  is received within a recess  44  formed in the journal bearing shaft  39 . 
         [0024]      FIG. 4  provides a perspective view of an embodiment of a portion of the earth boring bit  21  of  FIG. 3 .  FIG. 4  illustrates in more detail an example of a journal bearing portion of the leg section  22  in accordance with the present disclosure. The leg section  22  is shown in perspective view having the bearing shaft  39  which comprises a base for the cutter cone  41 . The bearing shaft  39  includes a journal section  26  having a recess  44  circumscribing the outer circumference of the bearing shaft  39 . The recess  44  includes a bearing surface  47  ( FIG. 3 ) on its lower surface formed to receive a journal bearing element  28  thereon. Adjacent the journal section  26  is a ball race  30  formed to receive the ball bearings  40  connecting the leg section  22  to the cutter cone  41 . In this embodiment, the journal bearing element  28  is a cylindrical body having an inner surface  48  ( FIG. 3 ) that couples with the bearing surface  47 . First and second lateral sides ( 45 ,  46 ) extend from the inner surface  48  and terminate at an outer surface  49 . At least one separation  32  is shown along the circumference of the journal bearing element  28 . 
         [0025]    The journal bearing element  28  may be affixed to the journal section  26  by means of brazing, gluing, soldering, or welding either individually or in combination with other coupling means as illustrated in  FIG. 5 . Optionally, the journal bearing element  28  may comprise multiple sections or members. Each individual member is curvilinear and having a radius of curvature that circumscribes the bearing shaft  39  when the members are arranged around the bearing surface of the bearing shaft  39 . Within the scope of this disclosure, the term coupling means joining the journal bearing element  28  to a bearing shaft  39  where some or no degrees of freedom exist between the element  28  and the bearing shaft  39 . Thus coupling includes preventing the journal bearing element  28  from sliding within the recess  44  circumferentially around the bearing shaft  39  but yet allowing the journal bearing element  28  to be removed from the bearing shaft  39 . Coupling also includes preventing relative sliding but allowing axial movement as well as totally affixing the journal bearing element  28  to the bearing shaft. Coupling a single member of a multi-member journal bearing element  28  to the bearing surface  47  within the recess  44  precludes the other members from sliding when adjacent members abut at a split section  32 . Optionally, the journal bearing element  28 , or the individual members, may also be coupled to prevent sliding in a lateral direction 
         [0026]      FIG. 6  illustrates an alternative coupling element embodiment for coupling a journal bearing element  28   a  to the bearing shaft  39 ; in this embodiment a dowel  34  is inserted through a bore  62  formed in the journal bearing element  28 . Illustrated in a perspective partial sectional view in  FIG. 7 , the bore  62  through the journal bearing element  28  registers with a corresponding bore  60  formed through the bearing surface  47  on the journal section  26 .  FIG. 9  is a perspective partial sectional view of a coupling device comprising a key  36  that couples the journal bearing element  28  to the journal section  26 . The key  36  is inserted into a passage formed by aligning a channel  56  in the journal bearing element  28  with a channel  54  formed in the journal section  26 . 
         [0027]    Another coupling device embodiment is presented in perspective partial sectional view in  FIG. 8 . In this embodiment, a raised profile  38  having a semi-circular cross section is provided on the journal bearing element  28  inner circumference that protrudes into a similarly shaped indentation  52  on the journal section  26  outer circumference. Engaging the profile  38  with the indentation  52  couples the journal bearing element  28  with the journal section  26  to prevent circumferential sliding of the journal bearing element  28  over the journal section  26 . The profile  38  and indentation  52  of  FIG. 8  are not limited to semi-circular embodiments, but can include rectangular, triangular, elliptical, and other shapes. It should be pointed out that coupling the journal bearing element  28  to the journal section  26  may allow lateral tilting of the journal bearing element  28  with respect to the journal section  26 . For example, although coupled, one of the first lateral side  45  or second lateral side  46  may experience radial movement away from the journal section  26 . The coupling devices described herein can be disposed proximate or at the first and second lateral sides ( 45 ,  46 ) of the journal bearing element  28 . Optionally, a substantial portion of the indentation/profile, channel/key, and bore/dowel configurations may reside between the first and second lateral sides ( 45 ,  46 ). 
         [0028]      FIG. 5  provides a view of an embodiment of a multi-section journal bearing element  28 . In this embodiment, the journal bearing element  28  comprises three sections abutted at split sections  32 . Thus coupling at least one of the sections to a corresponding bearing shaft  39  prevents the remaining sections from circumferential sliding. Optionally, the use of silver plating on the inner circumference of a corresponding cone may be employed with the journal bearing element  28  described herein. 
         [0029]    An optional embodiment of a journal bearing element  28   a  is provided in a side sectional view in  FIG. 10 . The journal bearing element  28   a  illustrated comprises a single circular member and mates over the journal section  26  outer diameter rather than in a recess. The bearing  28   a  is installed on the bit  21  by slipping it over the free end of the bearing shaft  39  and sliding the journal bearing element  28   a  adjacent the journal bearing surface  47 . The journal bearing element  28   a  can be coupled to the journal section  26  in any of the above described manners. 
         [0030]    The material used in making the journal bearing element  28  of the present device may be any suitable material; examples of materials include steels, stainless steels, and hard metal alloys including various Stellite® alloys. A material formed using a powdered metal manufacturing technique may be used for the journal bearing element  28 . For example, a high vanadium content stainless steel powder could be used in conjunction with a powdered metal manufacturing technique to form a suitable bearing element. One specific example of this is an alloy referred to herein as S90V®, the alloy has carbon with a content of about 2.3% by weight of the alloy, a chromium content of about 14% by weight of the alloy, a vanadium content of about 9% by weight of the alloy, and molybdenum content of about 1% by weight of the alloy. Additionally, AISI 440C chemistries could be used to form a suitable head bearing element. For the purposes of the present disclosure, high vanadium content includes a composition, such as metal or metal powders having about 3% by weight or more of vanadium. Alternative values for vanadium content include 4%, 5%, 6%, 7%, 8% by weight, and all values of weight percentages between. 
         [0031]    Another set of powered metal alloys for use in making the journal bearing herein described includes a cobalt-chromium-tungsten-carbon alloy. Optionally, the alloy may have a carbon content of about 1.2% by weight or greater. 
         [0032]    The powder compositions described herein may utilize “master melt” compositions wherein all particles have essentially the same chemistry. Using a solid state consolidation technique, such as sintered-hot-isostatic-pressing, maintains homogeneity of the final product thereby producing a solid material without voids. 
         [0033]    Other bit components could be made from the compositions described herein. Those components include any load bearing surface within the roller cone bit including thrust surfaces; additionally, pilot pin elements could also be manufactured using the compositions cited herein.