Patent Application
20160115739
The present invention relates in general to earth boring drill bits, and in particular to an air flow bypass for use with a lubricator compensator in sealed bearing drill bits.
Earth penetrating tools include the rotatable cutter-type earth boring drill bit, such as a rolling cone rock bit. Rolling cone earth boring bits have a bit body with an upper end adapted for connection to a drill string and typically three bit legs which extend downward from the body. Depending from the lower portion of the bit body are a plurality of support arms, typically three in number. A bearing shaft extends inward and downward from each bit leg. A conventional rock bit bearing shaft is cylindrical and rotatably receives a cutter cone. The cutter cone is generally mounted on each bearing shaft and supported rotatably on bearings acting between the spindle and the inside of a spindle-receiving cavity in each cutter cone. The cutter cones have teeth or compacts on their exteriors for disintegrating earth formations as the cones rotate on the bearing shafts. One or more fluid nozzles are often formed on the underside of the bit body. The nozzles are typically positioned to direct drilling fluid passing downwardly from the drill string toward the bottom of the borehole being drilled. Drilling fluid washes away material removed from the bottom of the borehole and cleanses the cutter cones, carrying the cuttings and other debris radially outward and then upward within an annulus defined between the drill bit and the wall of the borehole.
There are several varieties of bearing systems used to support the cutter cones. These bearing systems typically consist of a combination of radial and thrust bearings that may be either sealed and lubricated, or unsealed and open to the drilling fluid, such as air. Contact wear surfaces for bearing shafts may consist of wear-resistant metals or non-metals such as tungsten carbide. In sealed bearing drill bits, seals which are placed across gaps between the cutter cones and respective bearing shafts to prevents debris from contaminating the bearing and also block the lubricant from leaking to the exterior. Various types of seals have been used, including elastomeric seals and metal-to-metal face seals. Open bearing drill bits operate without a seal, and often pass drilling fluids through the cutter bearings for cooling and lubrication. Open bearings often have ports to force drilling fluid through the bearing system to lubricate and cool bearing wear surfaces. In some instances air may be used for the drilling fluid and driven through the bearing to cool and to lubricate the bearings.
When operated in a borehole filled with liquid, hydrostatic pressure acts on the drill bit as a result of the weight of the column of drilling fluid. Temperature increases in the lubricant from heat transfer as the bit is lowered into the well and due to friction heat while rotating causes expansion of the lubricant. A sealed, grease-lubricated bearing drill bit contains a lubricant reservoir in the bit body that supplies lubricant to the bearing shafts. Each bearing shaft has a pressure compensation system that is mounted in the lubricant reservoirs in the bit body. Sealed bearing drill bits commonly use lubrication systems that include a lubricant pressure compensator to limit the pressure differential between the lubricant and the pressure in the borehole. A typical lubricant compensator includes a flexible diaphragm or a spring biased piston separating a lubricant reservoir and the lubricant from the borehole fluid. The diaphragm or spring biased piston moves in response to the pressure differential across it tending to equalize the pressure differential between the lubricant reservoir pressure and the borehole fluid pressure. A lubricant flow passage extends from the reservoir of the compensator to an exterior portion of the bearing shaft. The pressure compensation system has a communication port that communicates with the hydrostatic pressure on the exterior to equalize the pressure on the exterior with lubricant pressure in the passages and clearances within the drill bit. The viscous lubricant creates hydrodynamic lift as the cone rotates on the bearing shaft so that the load is partially supported by lubricant fluid film and partially by surface asperity to surface asperity contact.
Sealed bearing drill bit failures typically occur due to cutter bearing seals wearing until damaged and then the bearings fail before the cutting structure wears out. It is desired to extend the life of sealed bearing drill bits beyond the life of the seals.
A novel lubricant compensator with an air flow bypass for sealed bearing drill bits is disclosed. An earth boring drill bit has a bit body and downwardly extending legs. Bearing pins or shafts extend inward and downward for mounting rotary cutters. Seals are provided between the bearing shafts and the cutters. Lubricant flow passages extend from an interior cavity of the bit body, through the legs and the bearing shafts, and into the spaces located between the bearing shafts and the cutters. A lubricant compensator extends from the flow passage into the cavity with an open end in which a piston is secured, biased to apply pressure to lubricant located within the flow passages. The compensator has an elongate tube with an inward end disposed within the flow passage and having a section for receiving the piston when lubricant is expelled from within the tube. Perforations extend through the sidewall of the tube, spaced apart from the end by the cavity, in fluid communication with the flow passages.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which
The compensator 32 has preferably cylindrical shape, tubular body defined by a tube 42. The compensator tube 42 has opposite end portions define by an open end 48 and a closed end 50. The open end 48 is disposed in the interior cavity 30 and has apertures preferably defined by perforations 44 which extend circumferentially around the tube 42, adjacent to the open end 48. The crimped opening in the open end 48 of the tube 42 and the perforations 44 are both in fluid communication with the interior cavity 30, and provide fluid communication between the interior cavity 30 and an interior of the tube 42 at the tube end section defined by the open end 48. The closed end 50 is disposed to extend into the lubricant bore 34 and has apertures 46 preferably defined by perforations which extend circumferentially around the tube 42, spaced apart from the closed end 50 by a section 52. The section 52 preferably has a tubular shaped interior profile which is sized of a diameter and with a longitudinal length for receiving a piston 54, such that the piston 54 is disposed aside of the apertures 46 such that fluid flow from the open end 42 and the perforations 44 to the apertures 46 is not prevented by the piston 54, as shown in
The piston 54 is slidably disposed within the tube 42 and has a piston seal 56 preferably provided by an O-ring. A groove circumferentially extends around the piston 54 and, in combination with the interior surface of the tube 42, defines a seal gland for receiving the piston seal 56. A coil spring 58 provides a bias member disposed between the piston 54 and the open end of the tube 42. The open end 48 of the tube 42 is preferably crimped to define a retainer member 60 for securing piston 54 and the coil spring 58 within the tube 42. A flange 62 preferably extends circumferentially around an intermediate portion of the tube 42, located between the open end 48 and the closed end 50. The perforations 44 are preferably disposed between the open end 48 and the shoulder 62 and provide fluid communication between the lubricant bore 34 and the interior of the tube 42. The apertures 46 are preferably disposed between the closed end 50 and the shoulder 62 and provide fluid communication between the lubricant bore 34 and the interior of the tube 42. The flange 62 is preferably welded at the opening of the lubricant bore 34 to the compensator tube 42 to the bit body 14. A recess 66 may be provided to countersink the outward opening of the lubricant bore, or the flow chamber 34 for receiving the flange 62. The flange 62 is preferably continuously extending about a periphery of the compensator tube 42, but in some embodiments may be provide by tabs which protrude radially outward from an exteriors surface of the tube. When the flange 62 does not continuously extend about a circumference of the tube 42, a seal 64 may be provided by an O-ring for sealing between the exterior of the tube 42 and the lubricant bore 34. The seal 64 may be omitted when the weld between the flange 62 and the opening of the lubricant bore 34 provide a fluid tight seal.
The bearing shaft 18 provides a spindle on which the rotary cutter 20 is rotatably mounted. The shaft 18 preferably has a main portion 70 and a pilot portion 72. The outer bearings 74 are provided on the main portion 72, preferably provided by roller bearings Inner bearings 76 are provided on the pilot portion 72 of the shaft 18, preferably provided by roller bearings. Ball bearings 78 lock the cutters 20 onto the bearing shafts 18 in conventional fashion, with a ball plug 82 welded into the ball port 78 to retain the ball bearings 78 between the bearing races of the shaft 18 and the cutter 20. The ball plug 82 has a tapered portion 84 for fluid to flow from the flow passage 36 to the flow passage 38 in the ball port 80. A thrust bearing 86 is located at the outward end of the bearing shaft 18. An intermediate space 88 is located between the bearing shaft 18 and the cutter 20, provided by clearances between the shaft 18 and the cutter 20. The outer bearings 74, the inner bearings 76, the ball bearings 78 and the thrust bearing 86 are located within the intermediate space 88. A seal 90 extends between the bearing shaft 18 and the cutter 20 to seal the intermediate space 88 located there-between. The seal 90 may be provided by an elastomeric member, such as an O-ring, a metal-to-metal seal, or other type seals, such as oval or flat seals preferably formed of an elastomer.
The drill bit 12 is initially operated in sealed bearing mode shown in
The drilling fluid is preferably air, but other water based or oil based drilling fluids may be used as well. It should be noted that the cross-sectional areas of the lubricant bore 34, the flow passages 36 and 38, and the compensator tube 42 are sized for passing an adequate amount of the drilling fluids to provide proper cooling of the bit 12. The cross-sectional area of the lubricant bore is preferably sized to provide the annular space 40 with sufficient size for passing the proper amount of drilling fluids. Similarly, the open end 48 in combination with the perforations 44 and the apertures 46 are sized for passing this flow of drilling fluids without excessive pressure losses.
The present invention provides advantages of an earth boring drill bit which is first operable in a sealed bearing mode. Once the seals fail, the bit is operated in open bearing mode using the drilling fluids for cooling the drill bit. Air is preferably used as the drilling fluid, but water based and oil based drilling fluids may be used as well.
Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
