Patent Application
20080245577
1. Technical Field
The present invention relates in general to roller cone drill bits and, in particular, to an improved system, method, and apparatus for an earth boring bit having curved thrust faces between a thrust washer, bearing head and a cone.
2. Description of the Related Art
One type of earth boring bit for drilling oil and gas wells has a bit body with at least one roller cone. Each cone is mounted on a cylindrical bearing head that depends downward and inward from a bit leg of the bit body. Annular thrust faces are formed on the bearing head and in the cone cavity for reacting against downward thrust. The thrust face of the bearing head is in a plane that is perpendicular to an axis of the bearing head. Likewise, the thrust face of the cone is formed in a plane that is perpendicular to the rotational axis of the cone. Initially, the thrust faces are parallel to each other. Lubricant is supplied from a lubricant reservoir to the spaces between the bearing head and the cone.
While the bit is drilling, the thrust faces typically do not run precisely parallel to each other. The bearing head deflects slightly because it is cantilevered from the bit leg. Also, because of tolerances between the cylindrical portions of the cone and the bearing head, the cone can tilt slightly relative to the bearing head (i.e., axial rotation). This slight misalignment of the cone axis relative to the bearing head axis results in a circumferentially converging-diverging space between the thrust faces. This bearing misalignment concentrates thrust bearing contact loads, which is detrimental to the performance and life of the components. Thus, an improved solution that overcomes these problems would be desirable.
One embodiment of a system, method, and apparatus for a roller cone bit utilizes a thrust washer between the cone and the head. As the roller cone bit is drilling, there is radial rotation between the head and the cone. Due to clearance in the bearing and interaction between the cone and the earthen formation, there also can be slight axial rotation (i.e., cone tilting) between the head and cone with respect to the head axis.
A thrust washer constructed in accordance with the present invention and located between the thrust surfaces of the head and the cone allows for the required radial rotation between the cone and thrust washer during drilling operations. However, the thrust washer accommodates the axial rotation between the cone and the head. The mating thrust surfaces or faces between the thrust washer and the head are contoured to allow the thrust washer to rotate axially with the cone. For example, the head may comprise a concave thrust surface while the thrust surface of the thrust washer has a complementary convex shape. This configuration results in more bearing contact between the thrust washer and the cone. The thrust washer may be formed from a variety of bearing materials, or a combination of materials such as 440C, bronze, carbide, diamond, etc. The radial rotation between the thrust washer and head may be prevented with the use of a pin, dowel, etc., extending therebetween.
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
Each bearing head 19 has a cylindrical surface 21 that is concentric with a bearing head axis 23. In the illustrated embodiment, the radially inward end of bearing head 19 has a nose 25. Nose 25 also is cylindrical but has a smaller diameter than bearing surface 21. An annular bearing head thrust face 27 is formed on a shoulder that circumscribes nose 25. As shown in
Each roller cone 29 has a plurality of cutting elements 35 on its exterior. Cutting elements 35 may be tungsten carbide inserts press-fitted into holes in the body of cone 29. Alternately, cutting elements 35 could be teeth milled into the exterior surface of the body of cone 29. Cone 29 is retained conventionally on bearing head 19, which in this example is by a plurality of balls 37. Balls 37 engage mating grooves formed in cone 29 and on bearing head 19. Lubricant passages 39 supply lubricant or grease to the spaces between cylindrical surfaces 21, 31 and between thrust faces 27 and 33. A pressure compensator 41 reduces the pressure differential between the lubricant within passages 39 and drilling fluid pressure on the exterior of bit 11.
As best shown in
The thrust washer 51 permits radial rotation (see arrow 55) between the cone 29 and the thrust washer 51, and accommodates axial rotation (see arrow 57) between the cone 29 and the head 19 with respect to the bearing head axis 23. The thrust washer 51 does not permit or restrict the axial rotation 57 between the head 19 and cone 29. If the thrust washer 51 is pinned 65 to the head 19 and there is a spherical radius 59 on the head 19 and thrust washer 51, the thrust washer 51 will stay aligned with the cone 29 and “tilt” relative to the head 19. The pin 65 restricts the thrust washer 51 from radial rotation 55 relative to the head 19. There is sufficient clearance between the pin 65 and hole in the thrust washer 51 to allow a limited amount of axial rotation 57. This allows the thrust washer 51 to rotate 57 and align with the cone thrust surface 33, maintaining maximum contact area.
In one embodiment, the thrust faces 53, 27 of the thrust washer 51 and the bearing head 19 are non-orthogonally contoured and complementary in shape. In another embodiment, the thrust faces 63, 33 of the thrust washer 51 and the roller cone 29 are non-orthogonally contoured and complementary in shape. In still other embodiments, both thrust faces 53, 63 of the thrust washer 51 and the thrust faces 27, 33 of both head 19 and roller cone 29 are non-orthogonally contoured and complementary in shape. In any of these embodiments, the contoured thrust faces that are selected may be formed on a spherical radius 59 such as the one illustrated in
In one embodiment, the thrust face 53 of the thrust washer 51 is convex, and the thrust face 27 of the bearing head 19 is concave (see, e.g.,
In still other embodiments, the thrust washer 51 may be formed from one of a variety of bearing materials, or a combination of materials such as 440C, other stainless steel materials, bronze, carbide, carbide-containing materials, diamond, etc. Radial rotation between the thrust washer 51 and head 19 or cone 29 may be prevented with the use of a pin 65, dowel, etc., extending therebetween.
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.
