Rock-bit seals with asymmetric contact profiles
Sealing arrangements for a rotary cone rock-bit comprising a leg extending from a bit body and a cone rotatably mounted to the leg. A seal is disposed radially between the cone and the leg. A footprint defines an area of contact between the seal and the leg. Compression of the seal generates a contact pressure between the seal and the leg. An axial centerline evenly bisects the footprint into a mud side and a grease side. A contact pressure profile defines the contact pressure over the footprint, wherein the contact pressure on the mud side of the footprint is greater than the contact pressure on the grease side of the footprint.
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BACKGROUNDThe present invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits. More particularly, the present invention relates to seal rings for use in rotary cone rock bits. Still more particularly, the present invention relates to journal bearing seal rings used to isolate a lubricated bearing area from abrasive wellbore fluids.
Rock bits are employed for drilling wells in subterranean formations for oil, gas, geothermal steam, minerals, and the like. Such drill bits commonly have a body connected to a drill string and three cutter cones mounted on the body. The cutter cones are rotatably mounted on steel journals or pins integral with the bit body at its lower end. A lubricated bearing is often used to support rotation of the cutter cone about the journal pins. Journal bearing seal rings are used to isolate the lubricated bearing from abrasive fluids moving through the well.
Journal bearing seal rings are often constructed from an elastomer or rubber material and have a symmetric axial cross-sectional geometry. The particular geometric configuration of the seal surfaces produces a given amount of seal deflection that defines the degree of contact pressure or “squeeze” applied by the dynamic and static seal surfaces against respective journal bearing and cone surfaces.
The contact pressure generated by the journal bearing seal ring is the force that protects the journal bearing from wellbore fluids. Failure of the journal bearing seal ring can allow wellbore fluids to contaminate the journal bearing and can lead to failure of the bearing. Once the bearing fails, or becomes severely worn, the cutter cone may no longer operate properly and the drill bit will have to be replaced. Replacement of a drill bit can be a time consuming process, because it requires a cessation of drilling operations and removal of the entire drill string from the wellbore. Therefore, any improvement that maximizes the life of a drill bit is beneficial.
Conventional journal bearing seals perform best within a narrow range of contact pressures and fluid conditions. Because the seal bears against a rotating surface between the seal and the leg, lubricant is often used to decrease the friction forces in this sealing area. If the contact pressure is too high, lubricant will not be able to reach the sealing interfaces and the heat generated by sliding contact of the seal and the leg will increase. If the contact pressure is too low, abrasive particles can enter the sealing interfaces and increase wear of both the seal and the leg. In either condition, the life of the seal will be greatly reduced over a seal operating with proper lubrication and without abrasive particles.
Thus, there remains a need to develop journal bearing seal rings that overcome some of the foregoing difficulties while providing more advantageous overall results.
SUMMARY OF THE PREFERRED EMBODIMENTSThe embodiments of the present invention are directed toward sealing arrangements for a rotary cone rock-bit comprising a leg extending from a bit body and a cone rotatably mounted to the leg. A seal is disposed radially between the cone and the leg. A footprint defines an area of contact between the seal and the leg. Compression of the seal generates a contact pressure between the seal and the leg. An axial centerline evenly bisects the footprint into a mud side and a grease side. A contact pressure profile defines the contact pressure over the footprint, wherein the contact pressure on the mud side of the footprint is greater than the contact pressure on the grease side of the footprint.
In certain embodiments, a bit for drilling a borehole into earthen formations comprises a a journal shaft extending from a bit body and a rolling cone cutter mounted on the journal shaft and being adapted to rotate about a cone axis. A seal gland is formed by the shaft and the cone and comprises a first seal engaging surface on the shaft and a second seal engaging surface on the cone. An annular seal is disposed in the gland. The annular seal comprises a radially inner surface sealingly engaging the first seal engaging surface and a radially outer seal surface sealingly engaging the second seal engaging surface. A seal footprint on one of the seal engaging surfaces is defined by the portion of the seal contacting the one seal engaging surface. The footprint has a footprint length measured axially relative to the cone axis and being bisected by a footprint centerline that is perpendicular to the cone axis. The seal creates a pressure profile on one of the seal engaging surface axially along the footprint, the pressure profile being asymmetric relative to the centerline.
Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGSFor a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:
FIGS. 5A-B through 9A-B are partial cross-sectional views of and contact pressure profiles generated by radial seals that have asymmetric external features;
FIGS. 10A-B through 12A-B are partial cross-sectional views of and contact pressure profiles generated by radial seals that have asymmetric internal features;
FIGS. 13A-B through 22A-B are partial cross-sectional views of and contact pressure profiles generated by radial seals that have a combination of internal and external asymmetrical features;
FIGS. 23A-B through 26A-B are partial cross-sectional views of and contact pressure profiles generated by radial seals having multiple material interfaces;
FIGS. 27A-B through 31A-B are partial cross-sectional views of and contact pressure profiles generated by symmetrical radial seals disposed within asymmetrical seal glands.
Referring now to
Cuter cone 11 comprises an inner cavity with a cylindrical bearing surface 21. Bearing surface 21 interfaces with bearing surface 17 to form the journal bearing that supports rotation of cutter cone 11. The bit may also comprise ball bearings 24 that carry thrust loads tending to remove cone 11 from the journal pin 16 and thereby retain the cone on the journal pin.
Grease, or another appropriate lubricant, lubricates the bearing surfaces between the journal pin 16 and the cone 11. A supply of grease is provided by a grease reservoir in cavity 29. Grease is supplied to the bearing surfaces through lubricant passages 31 and 32. Grease is retained in the bearings by a radial seal 33 between cone 11 and journal pin 16. A pressure compensation subassembly, including bellows 37, is included in the grease reservoir in cavity 29, and acts to maintain the pressure of the grease within a desired pressure range.
Referring now to
Referring now to
Radial seal 40 thus provides a distribution of sealing contact pressure along sealing surface 54 that is symmetric about centerline 58. Seals that generate a symmetrical contact pressure distribution, such as seal 40, perform best within a narrow range of contact pressures. If the contact pressure is too high, lubricant will not be able to reach the sealing interfaces and the heat generated by sliding contact of the seal and the cone will increase. Similarly, if the contact pressure is too low, abrasive particles can enter the sealing interfaces and increase wear of both the seal and the cone. In either condition, the life of the seal will be greatly reduced over a seal operating with proper lubrication and without abrasive particles.
Referring now to
Referring now to
The area under contact pressure profile curve 110 represents the total contact pressure applied to the seal. The asymmetric contact pressure profile created by seal 80 results in a the area under curve 110 on abrasive-side 112 being greater than the area under curve 110 on the lubricant-side 114. In some embodiments, the area under curve 110 on the lubricant-side is 95% of the area under curve 110 on abrasive-side 114. In some embodiments, the area under curve 110 on the lubricant-side is 75% of the area under curve 110 on abrasive-side 114. The asymmetrical contact pressure profile curve 110 translates into less contact pressure on lubricant-side 114 and more contact pressure on abrasive-side 112. The asymmetrical distribution encourages increased lubrication and reduced interaction with abrasive particles.
The peak contact pressure 116 on abrasive-side 112 is also higher than the peak contact pressure 118 on lubricant-side 114. The highest peak contact pressure may indicate the interface between the abrasive fluids and the lubricating fluids. By shifting the highest peak contact pressure toward abrasive-side 112, less of footprint 96 is exposed to abrasive fluids.
Thus, the asymmetrical contact pressure profile 110 has a peak contact pressure point 116 that is shifted toward abrasive side 104, causing a sharp increase in contact pressure on the abrasive side and a more gradual increase in contact pressure on lubricant side 106. The high contact pressure on abrasive side 104 acts to prevent abrasive particles from entering the sealing interface. The lower contact pressure profile on lubricant side 106 allows lubricants to more easily enter the sealing interface.
Some of the performance advantages of seal 80 can be seen by comparing the contact pressure distribution shown in
Generation of a desirable contact pressure distribution profile is not limited to seals similar to seal 80, but may be achieved a variety of seal configurations. As illustrated by seal 80, the external geometry of the seal and/or the geometry of the internal material interface may be asymmetric. Non-composite and single material seals may also be used. The sealing surfaces on either, or both, the cone and the leg may also be shaped so as to generate an asymmetric contact pressure distribution. Further, the asymmetric contact pressure distribution is not limited to that shown in
FIGS. 5A-B through 31A-B illustrate a variety of sealing arrangements that provide asymmetrical contact pressure distributions. FIGS. 5A-B through 9A-B illustrate radial seals that have asymmetric external features. FIGS. 10A-B through 12A-B illustrate radial seals that have asymmetric internal features. FIGS. 13A-B through 22A-B illustrate radial seals that have a combination of internal and external asymmetrical features. FIGS. 23A-B through 26A-B illustrate radial seals having multiple asymmetrical material interfaces. FIGS. 27A-B through 31A-B illustrate symmetrical radial seals disposed within asymmetrical seal glands.
Referring now to FIGS. 5A-B through 9A-B,
Referring now to
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FIGS. 1A-B through 12A-B illustrate radial seals that have asymmetric internal features. Referring now to FIGS. 10A-B through 12A-B,
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FIGS. 13A-B through 22A-B illustrate radial seals that have a combination of internal and external asymmetrical features.
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FIGS. 23A-B through 26A-B illustrate radial seals having multiple asymmetrical material interfaces formed between a plurality of component material layers.
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FIGS. 27A-B through 31A-B illustrate radial seals disposed within asymmetrical seal glands. The radial seals are shown as being symmetrical seals but could also be asymmetrical seals, such as those described above.
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An asymmetrical contact pressure profile may also be generated by an o-ring type seal. Referring now to
Referring now to
In each of these seal designs, the portion of the seal that has material removed is oriented toward the mud-side of the dynamic sealing surface. The removed material creates a stress concentration that generates a peak in the contact force on the dynamic sealing surface toward the mud-side of the seal. Although the features of
While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting by size, shape and/or directionality of the rotating body against the stationary body. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
Claims
1. A rotary cone rock-bit comprising
- a bit body;
- a leg extending from said bit body;
- a cone rotatably mounted to said leg;
- a first seal disposed radially between said cone and said leg;
- a footprint defining an area of contact between said first seal and said leg, wherein compression of said first seal generates a contact pressure between said first seal and said leg;
- an axial centerline that evenly bisects said footprint into a mud side and a grease side; and
- a contact pressure profile defining the contact pressure over said footprint, wherein the contact pressure on the mud side of said footprint is greater than the contact pressure on the grease side of said footprint.
2. The rotary cone rock-bit of claim 1 wherein the contact pressure on the grease side of said footprint is less than 95% of the contact pressure on the mud side of said footprint.
3. The rotary cone rock-bit of claim 1 wherein the contact pressure on the grease side of said footprint is less than 75% of the contact pressure on the mud side of said footprint.
4. The rotary cone rock-bit of claim 1 wherein the maximum contact pressure is on the mud side of said footprint.
5. The rotary cone rock-bit of claim 1 wherein said first seal further comprises:
- a body constructed from a first resilient material; and
- a first end portion constructed from a second resilient material, wherein said first end portion is connected to said body along a first interface.
6. The rotary cone rock-bit of claim 5 wherein said first end portion has an asymmetrical outer surface arranged such that a greater volume of the second resilient material is disposed on the mud side of said seal.
7. The rotary cone rock-bit of claim 1 further comprising a second seal disposed radially between said cone and said leg, wherein said second seal is adjacent to and on the mud side of said first seal.
8. A bit for drilling a borehole into earthen formations, the bit comprising:
- a bit body;
- a journal shaft extending from said bit body;
- a rolling cone cutter mounted on said journal shaft and being adapted to rotate about a cone axis;
- a seal gland between said shaft and said cone and comprising a first seal engaging surface on said shaft and a second seal engaging surface on said cone;
- an annular seal disposed in said gland, said annular seal comprising: a radially inner surface sealingly engaging said first seal engaging surface; a radially outer seal surface sealingly engaging said second seal engaging surface; and
- a seal footprint on one of said seal engaging surfaces, said footprint being defined by the portion of said seal contacting said one seal engaging surface, said footprint having a footprint length measured axially relative to said cone axis and being bisected by a footprint centerline that is perpendicular to said cone axis;
- wherein said seal creates a pressure profile on one of said seal engaging surface axially along said footprint, said pressure profile being asymmetric relative to said centerline.
9. The drill bit of claim 8 wherein said seal divides a lubricant side from a drilling fluid side, and wherein said pressure profile includes a maximum pressure peak located on said drilling fluid side.
10. The drill bit of claim 9 wherein a curve representing the pressure profile on the lubricant side defines an area that is less than 95% of an area defined by a curve representing the pressure profile on the frilling fluid side.
11. The drill bit of claim 9 wherein a curve representing the pressure profile on the lubricant side defines an area that is less than 75% of an area defined by a curve representing the pressure profile on the frilling fluid side.
12. The drill bit of claim 8 wherein said seal further comprises:
- a body constructed from a first resilient material; and
- a first end portion constructed from a second resilient material, wherein said first end portion is connected to said body along a first interface.
13. The drill bit of claim 12 wherein said first end portion has an asymmetrical outer surface arranged such that a greater volume of the second resilient material is disposed on the drilling fluid side of said centerline.
14. The drill bit of claim 12 wherein the first interface is asymmetric.
15. The drill bit of claim 8 wherein said seal creates a pressure profile on said second seal engaging surface.
16. A rotary cone rock-bit seal comprising:
- a first seal in contact with a rotating surface along a first footprint;
- a first centerline through the midpoint of the first footprint, wherein said first centerline divides said first seal into a drilling fluid side and a lubricant side; and
- a first contact pressure profile formed between said first seal and the rotating surface, wherein said first contact pressure profile is asymmetric about said first centerline.
17. The rotary cone rock-bit of claim 16 wherein said first contact pressure profile on the drilling fluid side of said first seal defines an area larger than an area defined by said first contact pressure profile on the lubricant side of said first seal.
18. The rotary cone rock-bit of claim 16 wherein said first contact pressure profile comprises a peak contact pressure that is located on the drilling fluid side of said first centerline.
19. The rotary cone rock-bit seal of claim 16 wherein said first seal is constructed of a resilient material, wherein a majority of the resilient material is located on the drilling fluid side of said first seal.
20. The rotary cone rock-bit seal of claim 16 wherein said first seal is constructed of a first material and a second material bonded along a boundary that is asymmetric about the first centerline.
21. The rotary cone rock-bit seal of claim 16 wherein said first seal has an asymmetric surface profile in contact with the rotating surface.
22. The rotary cone rock-bit seal of claim 16 further comprising:
- a second seal in contact with a rotating surface along a second footprint, wherein said second seal is adjacent to the drilling fluid side of said first seal;
- a second centerline through the midpoint of the second footprint, wherein said second centerline divides said second seal into a drilling fluid side and a lubricant side; and
- a second contact pressure profile formed between said second seal and the rotating surface.
23. The rotary cone rock-bit seal of claim 22 wherein said second contact pressure profile is asymmetric about said second centerline.
24. The rotary cone rock-bit of claim 23 wherein said second contact pressure profile on the drilling fluid side of said second seal defines an area larger than an area defined by said second contact pressure profile on the lubricant side of said second seal.
25. The rotary cone rock-bit of claim 23 wherein said second contact pressure profile comprises a peak contact pressure that is located on the drilling fluid side of said second centerline.
26. The rotary cone rock-bit seal of claim 23 wherein said second seal is constructed of a resilient material, wherein a majority of the resilient material is located on the drilling fluid side of said second seal.
27. The rotary cone rock-bit seal of claim 23 wherein said second seal is constructed of a first material and a second material bonded along a boundary that is asymmetric about the second centerline.
28. The rotary cone rock-bit seal of claim 22 wherein said second contact pressure profile is symmetric about said second centerline.
Type: Application
Filed: Sep 28, 2004
Publication Date: Mar 30, 2006
Applicant: Smith International, Inc. (Houston, TX)
Inventors: Sudarsanam Chellappa (Houston, TX), Zhou Yong (Spring, TX)
Application Number: 10/951,383
International Classification: E21B 10/00 (20060101);