Patent Application
20070045008
This invention relates in general to rotating cone earth boring bits, and in particular to a bit having a magnetic metal face bearing seal.
One type of earth boring bit has at least one rotatable cone, typically three. The cones are mounted on depending bearing sections. As the bit body is rotated about the bit axis, each cone rotates about its bearing pin axis. A lubricant chamber supplies lubricant to the bearing spaces between the cone and the bearing pin. A seal adjacent the mouth of the cone seals lubricant from leakage to the exterior as well as sealing bore hole drilling fluid from entering the lubricant chamber.
One type of seal employs metal faces in sliding contact with each other. One of the metal faces is pressed against the other by an elastomeric energizer ring. While successful, some axial play occurs between the bearing pin and the cone, particularly after the bit has been drilling for an extended time. This fluctuating axial play will cause the energizing force supplied by the elastomeric energizing ring to also fluctuate, contributing to leakage and seal failure.
Metal face seals having magnets are commercially available for general industrial applications. These magnets are mounted to one of the seal members to attract the opposite seal member. Applicant is not aware of any earth-boring bits utilizing magnetic metal face seals.
In this invention, the earth boring drill bit seal assembly has a rotating and a non rotating seal member, each having metal face in sliding engagement with the other. A magnet is carried by one of the seal members to attract the other seal member into dynamic sealing engagement. In one embodiment, the magnet is mounted to the face of the non rotating member. An elastomeric seal seals debris and drilling fluid from contact with the magnet.
In one embodiment, the magnet is recessed from the seal face so that it will not contact the metal seal face of the other member. In another embodiment, the magnet has a face mounted flush with the metal seal face. A coating is applied to the face of the magnet as well as to the seal face of the member to which the magnet is mounted. This coating is of a hardened wear-resistant material such as diamond or diamond like carbon coating. In that embodiment, the coated face of the magnet slidingly engages the opposite metal face.
In still another embodiment, the seal assembly includes a conventional, elastomeric energizer ring. The energizer ring creates a force component that is coaxial with the bearing pin axis to force the rotating seal member against the non rotating seal member. A magnet is used in conjunction with the energizer ring for maintaining the seal members in engagement with each other should the force of the energizing ring drop below a desired amount. That embodiment also may employ a backup elastomer to block drilling fluid and debris from contact with the energizer ring as well as the magnet.
Referring to
A cone 21 mounts to each bearing pin 19 for rotation relative to bearing pin 19. Cone 21 has cutting elements 23, which may be either tungsten carbide inserts as shown or machined steel teeth. In this embodiment, cone 21 has a bearing sleeve 25 that is press-fitted within its cavity for forming a journal bearing with bearing pin 19. Alternately, the bearing surface within cone 21 could be integrally formed with cone 21. Cone 21 is locked to bearing pin 19 in this embodiment by a plurality of balls 21 to reduce axial movement or play of cone 21 on bearing pin 19.
A lubricant chamber 29 holds viscous grease that is dispensed through lubricant passages 31 to the spaces in and surrounding bearing sleeve 25 on bearing pin 19. Normally, each bit leg 17 has one of the lubricant chambers 29. A drilling fluid passage 35 extends through body 15 for pumping drilling fluid or mud downward and out nozzles (not shown) at the lower end of body 15. Drilling fluid flows around cones 21 and back up the borehole. A pressure compensator 37 is mounted in lubricant chamber 29. Compensator 37 includes an elastomer that seals between the grease in lubricant chamber 29 and drilling fluid on the exterior of bit 11. Compensator 37 also tends to equalize the pressures on the exterior and the interior of lubricant chamber 29.
Cone 21 has a back face 39 that defines an annular mouth or entrance to its cavity. Back face 39 is closely spaced, but not touching a last machined surface 41 formed at the junction of bearing pin 19 and bit leg 17. A small clearance exists between back face 39 and last machined surface 41. A seal assembly 42 is located in the mouth of cone 21 adjacent back face 39 for sealing the mouth of cone 21 to bearing pin 19.
A carrier ring 47 is located in the gland between surfaces 43 and 45. Carrier ring 47 is a rigid ring, preferably formed of a nonmagnetic metal material in this embodiment. Carrier ring 47 has a non rotating seal face 49 that engages in dynamic sliding contact with a rotating seal face 51. Rotating seal face 51 is located on an end of bearing sleeve 25 in this embodiment and thus rotates with cone 21. Carrier ring 47 has an outer diameter portion 53 that is spaced radially inward from cone gland 43 by a clearance. Carrier ring 47 has an inner diameter portion 55 that is spaced radially outward by a clearance from bearing pin gland surface 45.
A recess 57 is formed in the forward facing end of carrier ring 47 adjacent seal face 49. In this embodiment, recess 57 is annular and extends from inner diameter portion 55 outward to about half the thickness of carrier ring 47. An annular magnet 59 is secured within recess 57 by suitable means, such as an adhesive. Magnet 59 is a strong permanent magnet and may be of a variety of conventional materials. Magnet 59 has a face 61 that is recessed rearward from rotating seal face 51, providing a clearance. Magnet face 61 is thus not in sliding contact with rotating seal face 51 in this embodiment. Although described as annular, magnet 59 could alternately comprise a plurality of circular disks or cylindrical rods spaced circumferentially apart from each other around carrier ring 47. Bearing sleeve 25 is of a ferrous material. Thus, magnet 59 is attracted to it and has sufficient strength to maintain seal face 49 in dynamic contact with bearing sleeve 25 at a desired force or pressure.
Carrier ring 47 has a groove 63 formed in its inner diameter portion 55 that contains a seal ring 65. Seal ring 65 is deformed against bearing pin gland surface 45 to prevent rotation of carrier ring 47 but allow some radial play relative to the axis of bearing pin 19. Also, seal ring 65 seals against the entry of cuttings, debris and drilling fluid into contact with magnet 59. In this embodiment, seal ring 65 does not provide any energizing force tending to force seal face 49 against seal face 51.
Lubricant is contained within the lubricant chamber 29 (
In the operation of the embodiment of
Although magnet 59 has been shown mounted to carrier ring 47, it could alternately be mounted in a recess in bearing sleeve 25 for rotation with bearing sleeve 25. In that instance, bearing sleeve 25, or at least a portion of it, would be of a non magnetic material, and carrier ring 47, or at least a portion of it, would be of a ferrous metal.
In the embodiments of
Referring to
A magnet 79 is mounted to carrier ring 73. Magnet 79, similar to magnet 59, may be annular or it may comprise a plurality of circular disks or cylindrical rods spaced around carrier ring 73. Magnet 79 in this embodiment is recessed as in the embodiment of
The invention has significant advantages. The magnet provides a retentive force that maintains the seal faces in dynamic sliding engagement with each other. The retentive force causes the carrier ring to move axially slightly in unison with any axial play of the cone, thus maintaining sealing engagement even though axial play becomes significant. The magnet can be combined with a conventional energizer elastomer that provides the primary energizing force, with the magnet providing the secondary backup force in the event that the elastomer begins to fail to achieve the desired contact pressure of the seal faces.
While the invention has been shown in only a few of its forms, it should apparent to those skilled in the art that it is not so limited but it is susceptible to various changes without departing from the scope of the invention.
