Patent Publication Number: US-6220374-B1

Title: Rotary cone drill bit with enhanced thrust bearing flange

Description:
RELATED APPLICATIONS 
     This application claims the benefit of previously filed provisional application U.S. Ser. No. 60/072,488, filed Jan. 26, 1998, entitled Rotary Cone Drill Bit with Enhanced Thrust Bearing Flange. 
     This application is related to co-pending application U.S. Ser. No. 09/237,133, filed Jan. 25, 1999, entitled Rotary Cone Drill Bit with Enhanced Journal Bushing. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to rotary cone drill bits and more specifically to a rotary cone drill bit with an enhanced thrust bearing flange. 
     BACKGROUND OF THE INVENTION 
     Various types of rotary drill bits or rock bits may be used to form a borehole in the earth. Examples of such rock bits include roller cone bits or rotary cone bits used in drilling oil and gas wells. A typical roller cone bit comprises a bit body with an upper portion adapted for connection to a drill string. A plurality of support arms, typically three, depend from the lower portion of the bit body with each support arm having a spindle or journal protruding radially inward and downward with respect to a projected rotational axis of the bit body. 
     A cutter cone assembly is generally mounted on each spindle or journal. Each cutter cone typically has a opening at its base, and a cavity extending from the base almost to the tip of the cutter cone. The cavity is formed such that it conforms with the associated journal. The cutter cone is supported rotatably on bearings acting between the exterior of the journal and the interior of the cutter cone assembly. The bearings in a typical rotary cone drill bit are heavily loaded during downhole drilling operations. In such drilling operations, the drill bit is rotated in a borehole, which causes the associate cutter cone assemblies to rotate on their respective journals. The drill bit typically operates at a low speed with heavy weight applied to the bit. This produces a high load on the associated bearings. 
     The drill bit typically includes a journal bushing. The journal bushing is positioned around the journal, and between the journal and the cutter cone assembly. The journal bushing is used to bear some of the forces transmitted between the journal and the cutter cone assembly, and to facilitate the rotation of the cutter cone assembly about the journal. 
     The journal also typically includes a thrust flange. The top of the thrust flange typically bears the load applied to the journal that is generally parallel to the axis of the journal about which the cutter cone rotates. Such forces are applied to the journal by the cutter cone assembly, and to the cutter cone assembly by the borehole wall. A thrust washer or bushing may be placed between the thrust flange and the cutter cone assembly to help bear this load. In addition, the thrust flange may also be used to contain the ball bearings. In such a situation, the thrust flange also must bear the load applied by the ball bearings when forces are acting to pull the cutter cone assembly off of its respective journal. 
     SUMMARY OF THE INVENTION 
     In accordance with teachings of the present invention, a roller cone drill bit having support arms with a spindle or journal extending from each support arm, and a respective cutter cone assembly rotatably mounted thereon is provided with an improved thrust flange. 
     The present invention allows the load-bearing capabilities of a drill bit thrust flange to be increased. The invention utilizes an enhanced thrust flange that is larger than the inside diameter of an associated drill bit journal bushing. The thrust flange may extend past the inside diameter of the journal bushing up to a distance equal to two times the thickness of the journal bushing. The invention may also utilize a thrust washer that is disposed adjacent the thrust flange to assist in bearing loads applied to the thrust flange. 
     Technical advantages of the present invention include an increased load carrying capacity of the thrust flange. This increased capacity improves the performance of the drill bit, and increases the drill bit&#39;s useful life by reducing the unit loading on its load-bearing surfaces. Another technical advantage of the present invention is that the enhanced thrust flange aids in maintaining the axis of the cutter cone concentric with the axis of the journal. This decreases wear on the drill bit, and thus increases its useful life. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and its advantages, reference is now made to the following brief description, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which: 
     FIG. 1 is a schematic drawing in elevation showing one type of rotary cone drill bit with support arms that may be used in conjunction with cutter cone assemblies formed in accordance with teachings of the present invention; 
     FIG. 2 is a schematic drawing in section and in elevation with portions broken away showing another type of rotary cone drill bit disposed at a downhole location in a borehole with the drill bit having support arms that may be used in conjunction with cutter cone assemblies formed in accordance with teachings of the present invention; 
     FIG. 3 is a schematic drawing in section with portions broken away showing portions of a typical rotary cone drill bit having a support arm with a journal extending therefrom, and showing a cutter cone assembly rotatably mounted on the journal; 
     FIG. 4 is a schematic drawing in section with portions broken away of a rotary cone drill bit support arm having a journal extending therefrom with an enhanced thrust flange formed adjacent to one end of the journal, and with a cutter cone assembly rotatably mounted on journal; 
     FIG. 5 is a schematic drawing showing a plan view of a thrust washer which may be satisfactorily used in conjunction with the present invention; and 
     FIG. 6 is a drawing in section taken along lines  6 — 6  of FIG.  5 . 
     FIG. 7 shows a journal bushing including a split to aid in placement over the journal. 
     FIG. 8 shows a section taken along lines  8 — 8  of FIG.  7 . 
     FIG. 9 shows a journal bushing comprising two semi-circle halves. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGS. 1-6 of the drawings, in which like numerals refer to like parts. 
     FIG. 1 illustrates various aspects of a rotary cone drill bit indicated generally at  510  of the type used in drilling a borehole in the earth. Drill bit  510  may also be referred to as a “roller cone rock bit” or “rotary rock bit.” With rotary cone drill bit  510 , cutting action occurs as cone-shaped cutters, indicated generally at  540 , are rolled around the bottom of a borehole (not expressly shown) by the rotation of a drill string (not expressly shown) attached to drill bit  510 . Cutter cone assemblies  540  may also be referred to as “rotary cone cutters” or “roller cone cutters.” Cutter cone assemblies  540  may be modified so that they may be used in conjunction with the present invention, as described below in conjunction with FIG.  4 . 
     Rotary cone drill bit  510  includes bit body  512  having a tapered, externally threaded upper portion  530  which is adapted to be secured to the lower end of a drill string. Depending from body  512  are three support arms  514 . Only two support arms  514  are visible in FIG.  1 . Each support arm  514  preferably includes a spindle or journal (not explicitly shown) formed integral with the respective support arm  514 . Each cutter cone assembly  540  is rotatably mounted on a respective journal. The journals are preferably angled downwardly and inwardly with respect to bit body  512  and exterior surface  516  of the respective support arm  514 . As drill bit  510  is rotated, cutter cone assemblies  540  engage the bottom of the borehole. For some applications, the journals may also be tilted at an angle of zero to three or four degrees in the direction of rotation of drill bit  510 . 
     FIG. 2 is an isometric drawing of a rotary cone drill bit, indicated generally at  610 , attached to a drill string  700  and disposed in borehole  710 . Examples of such drill bits and their associated bit body, support arms and cutter cone assemblies are shown in U.S. Pat. No. 5,439,067 entitled Rock Bit With Enhanced Fluid Return Area, and U.S. Pat. No. 5,439,068 entitled Modular Rotary Drill Bit. These patents provide additional information concerning the manufacture and assembly of unitary bit bodies, support arms and cutter cone assemblies which are satisfactory for use with the present invention. 
     Drill bit  610  includes one piece or unitary body  612  with upper portion  630  having a threaded connection adapted to secure drill bit  610  with the lower end of drill string  700 . Three support arms  614  are preferably attached to and extend longitudinally from bit body  612  opposite from upper portion  630 . Only two support arms  614  are shown in FIG.  2 . Each support arm  614  preferably includes a respective cutter cone assembly  640 . Cutter cone assemblies  640  extend generally downwardly and inwardly from respective support arms  614 . Cutter cone assemblies  640  may be modified so that they may be used in conjunction with the present invention, as described below in conjunction with FIG.  4 . 
     Bit body  612  includes lower portion  616  having a generally convex exterior surface  618  formed thereon. The dimensions of convex surface  618  and the location of cutter cone assemblies  640  are selected to optimize fluid flow between lower portion  616  of bit body  612  and cutter cone assemblies  640 . The location of each cutter cone assembly  640  relative to lower portion  616  may be varied by adjusting the length of support arms  614  and the spacing of support arms  614  on the exterior of bit body  612 . 
     Referring now to FIG. 3, a schematic drawing shows portions of a typical rotary cone drill bit  10  having a support arm with a journal or spindle  20  extending therefrom, and showing a cutter cone assembly  40  rotatably mounted on journal  20 . Journal  20  fits within a cavity formed in cutter cone  40 , and is mounted such that it may rotate about the longitudinal axis  80  of journal  20 . 
     A series of ball bearings  30  are disposed between journal  20  and cutter cone  40  to hold cutter cone  40  onto journal  20 , and to facilitate rotation of cutter cone  40  about journal  20 . Ball bearings  30  are positioned between an arm ball race  22  formed in journal  20  and a cone ball race  42  formed in cutter cone  40 . Arm ball race  22  and cone ball race  42  are both annular grooves. The radius of cone ball race  42  is typically closer to the ball bearing radius than the radius of arm ball race  22 . With such a configuration, arm ball race  22  is primarily loaded along a surface  24 . Surface  24  is approximately the top half of arm ball race  22 , as shown in FIG.  3 . Any forces that tend to pull cutter cone  40  off journal  20  are taken up by journal  20  along surface  24 . 
     The portion of journal  20  that extends over ball bearings  30  is a thrust flange  28 . Thrust surface  26  of thrust flange  28  aids in bearing the load placed on journal  20  by surface  46  of cutter cone  40 . In the prior art, the diameter of thrust flange  28  typically extends no further than the diameter of a journal bearing surface  21  of journal  20 . A thrust washer or bushing  50  may be positioned between thrust surface  26  of thrust flange  28  and surface  46  of cone  40 . The outside diameter of thrust washer  50  may be larger than the diameter of thrust flange  28 . Alternatively, surface  26  of thrust flange  28  may directly contact surface  46 . This is typically referred to as “flange contact.” 
     A journal bushing  60  is positioned between journal  20  and cone  40 . In the prior art, the inside diameter of bushing  60  is generally equal to or greater than the outside diameter of thrust washer  50  and the diameter of thrust flange  28 . Journal bushing  60  is separated from ball bearing  30  by a bearing flange  45 . Bearing flange  45  prevents the movement of journal bushing  60  towards ball bearings  30 . Drill bit  10  also includes a elastomeric seal  70  that is used to prevent debris from entering the gap between journal  20  and cone  40 . Seal  70  is disposed in an annular groove  72  formed in the interior surface of cutter cone  40 . 
     The present invention teaches extending thrust flange  28  out past journal bearing surface  21  in order to increase the support for thrust washer  50  and/or surface  46  of cutter cone  40 . Journal bushing  60  and elastomeric seal  70  will remain substantially the same as shown in FIG.  3 . In addition, the same ball bearings  30  may be used. A portion of a rotary cone drill bit  110  incorporating teachings of the present invention is shown in FIG.  4 . 
     Referring now to FIG. 4, journal  120  includes an enhanced thrust flange  128  having a diameter larger than the diameter of thrust flange  28  of FIG.  3 . The increased diameter of thrust flange  128  is larger than the diameter of journal  120  at a journal bearing surface  121 . In addition, because of the increased diameter of thrust flange  128 , thrust washer  150  may be larger than thrust washer  50  of FIG. 3, and have more support from the enlarged thrust surface  126  of thrust flange  128 . For example, the outside diameter of thrust washer  150  may be approximately equal to the inside diameter of cutter cone  40  adjacent thrust washer  150 , as shown in FIG.  4 . One example of a thrust washer  350  suitable for use with the present invention is shown in FIGS. 5 and 6. 
     Utilizing a larger thrust washer  150  and a larger thrust flange  128  increases the area of contact between journal  120  and cutter cone  40 , thus reducing the unit loading on the interface of surfaces  46  and  126 . The size of surface  24  is also increased, thus decreasing the unit loading on the interface of thrust flange  128  and ball bearings  30 . The extension of thrust flange  128  also improves the stability of cutter cone  40  by helping to prevent the rocking or wobbling of cutter cone  40  on journal  120 . By decreasing the unit loading and increasing the stability of drill bit  110 , better performance is obtained from drill bit  110 . 
     In one embodiment of the present invention, the diameter of thrust flange  128  may be 0.100 inches larger than the outside diameter of journal  120  at journal bearing surface  121 . However, other appropriate dimensions may be utilized, and such dimensions will vary depending on the overall size of the drill bit. One limiting factor for the diameter of thrust flange  128  will be the inside diameter of cutter cone  40  adjacent thrust flange  128 . 
     FIG. 7 is a schematic drawing showing a journal bushing  60 . Journal bushing  60  may be split at point  702 . Such a split is made to allow the expansion of journal bushing  60  for placement around a journal. 
     FIG. 8 shows a cross section of FIG. 7 along lines  8 — 8 . 
     For some applications, it may be desirable to have a two-piece journal bushing, as shown in FIG.  9 . As shown, this embodiment includes a second split  704  located approximately opposite first split  702 . Such a configuration is particularly useful when the journal bushing is made out of material that is not flexible or does not return to its desired shape after being placed around the journal. 
     Although the present invention has been described by several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompasses such changes and modifications as fall within the scope of the present appended claims.