Patent Application
20100071960
1. Technical Field
The present invention relates in general to roller cone rock bits and, in particular, to an improved system, method and apparatus for a composite seal gland insert for enhancing the seal between the bearing pins and the roller cones on a roller cone rock bit.
2. Description of the Related Art
In roller cone rock bits, wear of the elastomer rotary bearing seals between the bearing pins and the roller cones is a primary cause of seal failure. Elastomer seals in current roller cone bits typically run in glands made up by opposing recesses that are formed on the bearing pin and on the inner surface of the cone. Wear occurs on both the elastomer seal itself and on the steel gland counter face surfaces that are in sliding contact with the elastomer seal. However, the majority of the wear typically occurs on the elastomer seal surface. The loss of seal radial cross-section as well as the loss of the seal contacting surface design geometry reduces sealing efficiency as there is a reduction in overall sealing pressure and a change in the distribution of the sealing pressure on the contacting surfaces. Consequently, there is an increased probability of drilling fluid ingress into the bearing, which leads to rapid bearing failure. An improved solution that overcomes the limitations and problems of prior art designs would be desirable.
Embodiments of a system, method, and apparatus for a composite seal gland insert in a roller cone rock bit are disclosed. Wear of the elastomer seal is reduced by reducing the friction between the seal and mating gland surface. In one embodiment, the steel seal gland surface is supplemented with the seal gland insert. The insert comprises a polymer composite sleeve containing one or more constituents that function to significantly lower the friction compared to direct engagement with the steel seal gland. The seal gland insert may comprise a thermoplastic polymer such as polyetheretherketone (PEEK) or a polyimide. Preferably, the polymer material contains a reinforcing material such as carbon fiber. Also, preferably the polymer contains a low friction additive such as polytetrafluorethylene (PTFE), which is impregnated into the composite material.
In one embodiment, a fluid lubricant film is provided between the elastomeric seal and the composite gland for initial operation. Subsequently, during operation, the grease or lubricant of the bit will enter the spaces between the elastomeric seal and the composite gland. In one embodiment, the outer surface of the composite gland insert is profiled with a grooved pattern against which the elastomer seal runs. The insert is installed over the pin and one surface is located against the last machined surface of the leg. A static seal, which may comprise an additional elastomeric o-ring seal, may be used beneath the gland insert to provide a pressure seal between the insert and the pin. Alternatively, a suitable adhesive may be used to retain the gland insert in the desired position. The adhesive may provide the pressure seal between the insert and the pin. If desired, a mechanical anti-rotation device also may be used to inhibit rotation of the gland insert.
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 are attained and can be understood in more detail, a 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. However, 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
In one embodiment, bearing pin 17 has a main journal surface 18 and a nose 21 having a smaller diameter than surface 18 that is formed on its inner end. Nose 21 also has a pilot pin radial bearing surface 22 that is parallel to surface 18 relative to axis 16. In another embodiment (e.g., for larger diameter bits), roller bearings may be used instead of journal bearings. The invention is well suited for both types of applications.
A roller cone 23 is rotatably mounted to bearing pin 17. Cone 23 has a plurality of protruding cutting elements 25. Cone 23 has a cavity 27 that is slightly larger than the outer diameters of bearing pin 17. 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 the roller 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.
In the embodiment shown, 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 a junction with the gland area engaged by a seal assembly 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. Again, other types of drill bits may utilize roller bearings instead of journal bearing surfaces and are readily configured for the invention.
In a sealed lubricated bearings embodiment, a lubricant port 37 is located on an exterior portion of journal surface 18 of bearing pin 17. The port 37 is connected to a passage 39 via ball passage 35. Passage 39 leads to a lubricant reservoir 41 that contains a lubricant. 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.
Cone 23 also has a back face 29 that is located adjacent, but not touching, last machined surface 19. A seal assembly 31 is located in a seal cavity adjacent to the back face 29. As shown in the embodiment of
The seal assembly 31 also comprises a gland insert 55 that is a ring located in the gland 51 between the dynamic seal 53 and the bearing pin 17. In other embodiments, however, the positions may be reversed such that the gland insert 55 engages only the cone 23 and the dynamic seal 53 engages the bearing pin 17. In some embodiments, the gland insert 55 engages the last machined surface 19, and no portion of the gland insert 55 engages the roller cone 23. Dynamic seal 53 engages gland 51 in sliding or dynamic engagement in all of the embodiments. Gland insert 55 is generally rectangular in cross-section in this embodiment and has a beveled corner on its outer edge that engages the rounded intersection of last machined surface 19 and bearing pin 17.
The gland insert may comprise a polymer composite sleeve that reduces wear of the elastomer seal by reducing the friction between it and the mating gland surface. The gland insert may contain one or more constituents that function to significantly lower the friction compared to direct engagement with the steel seal gland. The term “composite” is used herein to mean a polymer material containing a reinforcing material that is dispersed through at least a part thereof and structurally joined with the polymeric material. For example, composite gland insert 55 may comprise a thermoplastic polymer such as polyetheretherketone (PEEK) or a polyimide as the matrix material. The reinforcing material 56 (
Composite gland insert 55 must be capable of withstanding the elevated temperatures that occur during drilling. Typically, dynamic seal 53 is of a rubber-based material that may withstand about 375 degrees F. without significant degradation. Preferably composite gland insert 55 is capable of withstanding about 400-500 degrees F. without significant degradation. Gland insert 55 is much harder and less resilient than composite dynamic seal 53. For example, the tensile strength in teems of pounds per square inch of gland insert 55 may be ten times or more greater than the tensile strength of dynamic seal 53. The inner diameter of gland insert 55 is preferably only slightly greater than the outer diameter of journal 18, for example about 0.002 to 0.005 inch. Consequently, gland insert 55 may be considered to be rigidly mounted on journal 18 so that it is not axially movable relative to journal 18.
In still other embodiments, the surface of gland insert 55 that engages dynamic seal 53, which is the outer diameter of insert 55 in this example, is profiled to enhance lubrication. As illustrated in
Adhesive, if employed, may serve also to prevent gland insert 55 from rotating around journal 18. Alternately, a mechanical anti-rotation device 65 (e.g., a pin, as shown in
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.
| Number | Date | Country | |
|---|---|---|---|
| 61099657 | Sep 2008 | US |
