1. Technical Field
The present invention relates in general to rock drill bits and, in particular, to an improved system, method, and apparatus for conformal bearings in rock drill bits.
2. Description of the Related Art
Rolling cone earth boring bits have a bit body that typically has three bit legs which extend downward from the body. A bearing pin extends inward and downward from each bit leg. A conventional rock: bit bearing pin is cylindrical and rotatably receives a cone. There are several varieties of bearing systems used to support the cone. These bearing systems typically consist of a combination of radial and thrust bearings that may be either scaled and lubricated or unsealed and open to the drilling fluid. The contacting wear surfaces may consist of wear-resistant metals or non-metals such as tungsten carbide and/or diamond, and may engage through sliding and/or rolling. Open bearings may contain ports to force drilling fluid through the bearing system to lubricate and cool the wear surfaces.
The cones have teeth or compacts on their exteriors for disintegrating earth formations as the cones rotate on the bearing pins. A sealed, grease-lubricated bearing drill bit contains a lubricant reservoir in the bit body that supplies lubricant to the bearing pins. A seal prevents debris from contaminating the bearing and also blocks the lubricant from leaking to the exterior. When operated in a borehole filled with liquid, hydrostatic pressure acts on the drill bit as a result of the weight of the column of drilling fluid. Each bearing pin has a pressure compensation system that is mounted in the lubricant reservoirs in the bit body. A lubricant passage extends from the reservoir of the compensator to an exterior portion of the bearing pin. The pressure compensation system has a communication port that communicates with the hydrostatic pressure on the exterior to equalize the pressure on the exterior with lubricant pressure in the passages and clearances within the drill bit. The viscous lubricant creates hydrodynamic lift as the cone rotates on the bearing pin so that the load is partially supported by lubricant fluid film and partially by surface asperity to surface asperity contact.
A polycrystalline diamond compact (PDC) bearing is a type of open bearing system. The bearing pin and cone contain discreet PDC elements placed in a circumferential array on the radial bearing and in a planar array on the thrust bearing. The PDC elements on the cone slidingly engage the PDC elements on the bearing pin. Drilling fluid is driven through the bearing to cool and to lubricate the bearing. In this type of bearing system, load is supported almost entirely by surface asperity contact. Drill bits of this nature operate under extreme conditions. Very heavy weights are imposed on the drill bit to facilitate the cutting action, and friction causes the drill bit to generate heat. In addition, the temperatures in the well can be several hundred degrees Fahrenheit. Improvements in cutting structure have allowed drill bits to operate effectively for much longer periods of time than in the past. Engineers involved in rock bit design continually seek improvements to the bearings to avoid bearing failure before the cutting structure wears out.
In conventional bits (
There has been a variety of patented proposals to address this issue. For example, U.S. Pat. No. 4,403,812 discloses the use of an elastomeric suspension around the ball bearing race to take up bearing play. This compliant suspension allows the bearing elements to self-align. Other techniques have called for pre-wearing the bearings to increase surface contact area, and modifying the PDC element size and shape. Although each of these designs is workable, an improved solution that overcomes the limitations of the prior art would be desirable.
Embodiments of a system, method, and apparatus for rock drilling bit comprises improved radial bearings that maximize the contact area between the journal and cone bearings and, thus, maximizes load support. The radius of curvature of the journal and cone bearing are matched or conformed to greatly increase the apparent contact surface area on the pressure side of the bearing. The conformal radial bearing matches the journal and cone bearing radius on the bearing pressure side. This design reduces thermal fatigue cracks compared to conventional, completely cylindrical designs. The conformal journal surfaces may be formed on the main journal bearing, the pilot pin radial bearing, or both surfaces. In addition, diamond inlays or particles may be located on the bearing surfaces of the cone, the bearing pin, or both components.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
Referring to
A cone 23 rotatably mounts on bearing pin 17. Cone 23 has a plurality of protruding teeth 25 or compacts (not shown). Cone 23 has a cavity 27 that is slightly larger in diameter than the outer diameters of bearing pin 17. Cone 23 has a back face 29 that is located adjacent, but not touching, last machined surface 19. If the bearing type is a sealed, lubricated bearing, a seal 31 is located in a seal cavity adjacent to the back face 29. Seal 31 may be of a variety of types, and in this embodiment is shown to be as an o-ring. Seal 31 engages a gland or area of bearing pin 17 adjacent to last machined surface 19. Other types of seals such as dual seals, seals with non-circular cross-sectional shapes, etc., also may be used.
Cone 23 may be retained in more than one manner. In the embodiment shown, cone 23 is retained on bearing pin 17 by a plurality of balls 33 that engage a mating annular recess formed in cone cavity 27 and on bearing pin 17. Balls 33 lock cone 23 to bearing pin 17 and are inserted through a ball passage 35 during assembly after cone 23 is placed on bearing pin 17. Ball passage 35 extends to the exterior of bit leg 15 and may be plugged as shown after balls 33 are installed.
A portion of cavity 27 slidingly engages journal surfaces 18 and 22. In one embodiment, the outer end of journal surface 18 is considered to be at the junction with the gland area engaged by seal 31, and the inner end of journal surface 18 is considered to be at the junction with the groove or race for balls 33. Journal surfaces 18 and 22 serve as a journal bearing for loads imposed along the axis of bit 11.
In sealed, lubricated bearings, a first lubricant port 37 is located on an exterior portion of journal surface 18 of bearing pin 17. In one embodiment, first port 37 is located on the upper or unloaded side of journal surface 18 of bearing pin 17 between balls 33 and seal 31. When viewed from nose 21 (
Lubricant reservoir 41 may be of a variety of types. In one embodiment, an elastomeric diaphragm 43 separates lubricant in lubricant reservoir 41 from a communication port 45 that leads to the exterior of bit body 13. Communication port 45 communicates the hydrostatic pressure on the exterior of bit 11 with pressure compensator 43 to reduce and preferably equalize the pressure differential between the lubricant and the hydrostatic pressure on the exterior.
The precise positioning between bearing pin 17 and cone 23 varies as the drill bit 11 is loaded during service, thereby creating eccentricity. The eccentricity is a result of the difference between the outer diameter of journal surfaces 18 and 22 and the inner diameter of cone cavity 27.
Under load, there is a difference between axis 16 (
Even though annular clearance 51 is very small, it is required to allow assembly of cone 23 on bearing pin 17 and to allow for differences in thermal expansion during service. The annular space 51 has a largest width or clearance point 51a at approximately 0° (i.e., top dead center). A minimum width or clearance span 51b extends on both sides of a position at approximately 180° due to the downward force imposed on the bit during drilling.
Assuming cone 23 rotates clockwise in
In one embodiment, the invention comprises an earth boring bit 11 (
Optionally, the invention may further comprise a material 42 (
As shown in
In the illustrated embodiment of
The cylindrical cavity 27 defines a maximum potential contact area having an angular span of approximately 180° as shown in
In alternate embodiments (e.g.,
In another embodiment, the zero clearance conforming bearing surfaces are created in combination with spherical bearing surface curvature to further increase bearing contact area under conditions when the cone misaligns on the bearing pin.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.