Patent Application
20120160561
The present invention relates generally to rock bit drilling tools, and more specifically concerns roller cone drilling tools and the bearing system used within such roller cone drilling tools.
Reference is made to the following prior art references: Neilson U.S. Pat. No. 4,178,045; Highsmith U.S. Pat. No. 4,200,343; Koskie U.S. Pat. No. 4,209,890; Dysart U.S. Pat. No. 4,249,622; Dysart U.S. Pat. No. 4,981,182; Chavez U.S. Pat. No. 4,955,440; Dysart U.S. Pat. No. 5,027,911; and Dysart U.S. Pat. No. 5,513,715. The disclosures of each of the foregoing references are hereby incorporated by reference.
In an embodiment, a drill tool comprises: a bit body; at least one bearing shaft extending from the bit body; a cone mounted for rotation on the bearing shaft; a first sealing system comprising a first annular seal gland formed in a cylindrical surface of the cone and a seal ring retained within the first annular seal gland and compressed against a cylindrical surface of the bearing shaft; a second sealing system comprising a second annular seal gland formed in a radial surface of the cone and sealing member (such as, for example, a Belleville spring) retained within the second annular seal gland and compressed against a radial surface surrounding the bearing shaft; and a set of non-pressure compensated lubrication channels configured to supply lubricant to an interstitial volume defined between the cone and bearing shaft, the lubricant retained within the interstitial volume by the first and second sealing systems, the lubrication channels further supporting open air circulation through the bearing when the sealing systems fail and lubricant is lost.
In another embodiment, a method for rock drilling comprises: providing a non-pressure compensated rock drill bit with a bearing sealed to contain lubricant; using the rock drill bit in an initial drilling mode with the lubricant supporting bearing operation; continuing the initial drilling mode until seal failure and loss of the bearing lubricant; and further using the rock drill bit in a secondary drilling mode, after loss of bearing lubricant, with an open air circulation supporting bearing operation.
Reference is now made to
The head 10 of the bit includes a downwardly and inwardly extending bearing shaft 12. A cutting cone 14 is rotatably mounted on the bearing shaft 12. The bearing system for the head and cone assembly that is used in roller cone rock bits to rotatably support the cone 14 on the bearing shaft 12 typically employs either rollers as the load carrying element (a roller bearing system) or a journal as the load carrying element (a friction bearing system).
The bearing system for the head and cone assembly of the bit is lubricated and sealed from the external environment by the annular seals. An interstitial volume within the bearing system is defined between the cone 14 and the bearing shaft 12, and this volume is filled with a lubricant (typically, grease). The lubricant is provided to the interstitial volume through a series of lubricant channels 28. The illustrated bit is of the type which does not include a pressure compensator coupled in fluid communication with the series of lubricant channels 28. Thus, an upper end 36 of the lubricant channel 28 is open, or alternatively is temporarily sealed at a location adjacent an inner air flow chamber 35. The temporary seal may take the form of any suitable isolation structure 37 such as, for example, a check valve, a one-way valve, a one-way membrane, or the like. The lubricant is retained within the bearing system in the region of the cones by a sealing system 32 provided between the base of the cone 14 and the base of the bearing shaft 12.
The first roller bearing (main roller bearing) 16 is defined by an outer cylindrical surface on the bearing shaft 12 and a set of roller bearings provided within an annular roller raceway in the cone 14. The second roller bearing 22 is defined by an inner cylindrical surface on the cone 14 and a set of roller bearings provided within an annular roller raceway in the shaft 12. The first radial friction (thrust) bearing 24 of the bearing system is defined between the first and second roller bearings 16 and 22 by a first radial surface on the bearing shaft 12 and a second radial surface on the cone 14. The second radial friction (thrust) bearing 26 of the bearing system is adjacent the second roller bearing 22 at the axis of rotation for the cone and is defined by a third radial surface on the bearing shaft 12 and a fourth radial surface on the cone 14.
Reference is now made to
Lubricant (such as grease) is provided in the interstitial volume that is defined between the cone and shaft at the first roller bearing 16, the second roller bearing 22, the ball bearings 18, the surfaces of the first radial friction bearing 24 and the surfaces of the second radial friction bearing 26. The sealing system 32 with the o-ring type seal member 50 positioned in the seal gland 52 functions to retain the lubricant within the lubrication system and specifically between the opposed surfaces of the bearing system.
The sealing system 32 further comprises an additional sealing member 56. In one embodiment, the additional sealing member 56 is a Belleville ring type seal member positioned in a seal gland 58 between the cutter cone 14 and the bearing shaft 12 to retain lubricant and exclude external debris. A radial sealing surface 60 is provided on the head circumferentially surrounding the base of the bearing shaft 12. The annular seal gland 58 is formed including a radial sealing surface 74 at the base of the cone 14. The gland 58 and sealing surface 60 align with each other when the cutting cone 14 is rotatably positioned on the bearing shaft 12. The Belleville ring type seal member is compressed between the surface(s) of the gland 58 and the sealing surface 60, and functions to retain lubricant within the bearing system. The sealing member 56 also prevents materials in the well bore (such as drilling debris) from entering into the bearing system.
A cylindrical sealing surface 62 is provided on the head 10 adjacent the radial sealing surface 60. The surfaces 60 and 62 circumferentially surround the base of the bearing shaft 12, and in a preferred implementation are offset from the base of the bearing shaft by a radial surface 64. A corner 66 is provided by the intersection of the surfaces 60 and 62. The cylindrical sealing surface 62 has a diameter substantially equal to an inner diameter of the sealing member 56 (for example, the Belleville ring type seal member) such that the inner circumferential surface 70 (see,
A cylindrical surface 72 is provided on the cone 14 adjacent the radial sealing surface 74. A corner 76 is provided by the intersection of the surfaces 72 and 74. The cylindrical surface 72 has a diameter larger than an outer diameter of the sealing member 56 (Belleville ring type seal member). As the sealing member (Belleville ring type seal member) 56 is compressed, this permits movement of the seal member 56 along the radial sealing surface 74 until the outer circumferential surface 78 (see,
Reference is now made to
The roller cone rock bit has a preferred use as a mining bit, for example in the preparation of blast holes. The bit has a sealed bearing but because it is not used at great drill depths there is no need for a pressure compensation system. The bit utilizes two independent seals in the area of the base of each bearing shaft. The first seal is provided by the o-ring or other elastomeric seal and the second seal is provided by the Belleville ring. In an alternative embodiment, the sealing member 56 may comprise another ring shaped sealing structure such as a fine mesh screen, having for example a shape similar to that of the Belleville spring, capable of limiting the influx of fine drilling particles into the area of the elastomeric seal. The o-ring primarily functions to retain grease (and may additionally function to keep debris from reaching the bearing). The Belleville ring or alternative mesh ring structure primarily functions to keep debris (such as dust particles) from reaching the o-ring (and may additionally function to retain grease).
A preferred operation of the bit is as follows. During an initial drilling mode, the bit utilizes a lubricated bearing supported by operation of the o-ring seal and the Belleville ring seal. After a period of time drilling in this initial mode, the seals will fail and the grease within the bearing will be evacuated. Operation of the bit then moves to a secondary drilling mode where the bit utilizes an open air circulation bearing. Open air circulation is supported because there is no pressure compensation system included on the bit to block fluid (air) circulation through the lubricant channels 28 and to the bearing. After a period of time drilling in this secondary mode, the roller bearings will fail. The bit will then need to be replaced, and may be repaired by replacing the roller/friction bearings and recharging the lubrication system. However, the air circulation in the secondary drilling mode provides for an extended operating use of the bit after seal failure.
An alternative embodiment additionally uses the isolation structure 37 (providing a barrier such as a breakable membrane, a breakable plug, or a one way valve) deployed at or near the upper end of lubricant channel 28 in the region 36. The purpose of this isolation structure 37 is to limit the erosion or premature displacement of the lubricant or grease column prior to the failure of the primary seals. The isolation structure 37 may be fixed in place through the use of adhesive, press fit, threads, snap rings, or other methods known in the art. This isolation structure 37 acts to isolate the air flow through the inner air flow chamber 35 of the bit from the lubricant or grease volume within channel 28 while the annular cone seals are effective. When the annular seals fail, pressure from the air flow within inner air flow chamber 35 overcomes the resistance of the isolation structure 37 to allow air flow to incept or accelerate the evacuation of grease or lubricant from the bearing system, thus ultimately converting the bearing system from grease lubrication to air lubrication (through open air circulation).
It should be noted that each of the three bearings on a leg of the bit act independently and that the failure of one primary set of seals and the conversion of that bearing on one leg to an air lubricated bearing may precede in time the failure of one or both of the other bearings on other legs of the bit.
Although preferred embodiments of the method and apparatus of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.
