Shale diverting means for a sealed bearing drill bit

Abstract: Sealed bearing rotary cone drill bits are subject to seal wear from detritus or debris generated during operation of the drill bit in a borehole. The debris invades the seal gland area resulting in premature cone bearing failure. A shale burn plug (38) secured in the leg back face (17) and positioned between the base of the rotary cone (30) and the leg back face has a shale or detritus diverting ridge (41) formed in the face (40) of the plug. Additionally, the burn plug is energized to urge the ridged face of the burn plug against the base of the rotary cone; the ridge (41) being non-radially oriented to divert debris away from the seal gland (21).

Description: This invention relates to a sealed bearing rotary cone drill bit of the type as described in the preamble of claim 1. It has long been recognized in the drill bit industry that the longevity of sealed bearing rotary cone drill bits is greatly increased if debris is prevented from entering the bearings associated with each of the rotary cones rotatably retained on legs of a drill bit. Drill bits used in carrying out rotary drilling have been subject to destruction by erosion caused by the abrasive effect of the materials present in the drilling method. Fluid circulation is employed primarily to circulate or flush the debris or cuttings from the well bore. In actual practice, mud and solids from the circulating fluid and from the earthen formation pack onto certain portions of the bit structure and this packed material flows or extrudes and moves relative to certain portions of the bit. Since great pressures are utilized in the drilling operations, the movement or flow of this packed material has adverse effects on the bit structure and, in particular, the seal cavity, seal and bearings associated with each rotary cone of the bit. The sealed bearing rotary cone drill bit of the type as described in the preamble of claim 1 is known from US-A-4 515 228. This drill bit has an air protected seal ring which is used to seal lubricant between the bearing channel and the cone. The air passage for cooling the seal ring includes an annular groove formed into the cone exterior of the seal ring. This annular groove is opened to the outside by an exit port. An air groove scraper is mounted in the exit port so that the scraper extends into the annular groove. The scraper has a pair of flat sides which deflect the air and rock particles from the angular groove to the exit port. The arrangement of the flat sides of the scraper with respect to the rotational axis of the channel bearing is not described to be critical while the flat sides appear to converge towards each other in a direction facing away from the rotational axis of the channel. Outside the flat sides the scraper is generally cylindrical and is inserted and mounted in a mating drilled hole in the leg. US-A-2,960,313 describes a deflecting post or pin in a leg back face to mechanically deflect mud and fluid material from a path that normally results in wear and destruction of a roller bit. The end of the pin is adjacent a cone back face; the pin serving to deflect detritus or debris as it invades the space between the cone back face and the leg back face. The pin is fixed in the leg back face and has an exposed cylindrical end that terminates in a flat surface, the flat surface paralleling the rotary cone back face. The deflecting post, while it is somewhat effective in intercepting the flow of debris, has a circular shape which can divert debris and fluid towards a seal cavity, thus allowing some debris to enter this cavity. US-A-3,013,621 describes a means for deflecting abrasive particles or cuttings from the space formed between a leg back face and a conical cutter. An overlay of hardened material is welded to the leg back face at an angle to a radial plane extending from a journal center line. The abrasive material metallurgically attached to the leg back face serves to scrape or divert debris away from rotary cone bearings to prevent the debris from destroying the bearing during operation of the bit in a borehole. The raised hardened material applied to the leg back face is less effective when the cone axially oscillates (on its journal) away from the leg back face during operation of the bit in a borehole. The present invention as claimed in claim 1 has an advantage over these prior art mechanisms in that the debris deflecting device is resiliently biased so that the shale burn plug face remains in constant contact with the cone back face, thereby providing a more reliable and effective means to deflect the debris away from the seal cavities during operation of the drill bit in a borehole. Moreover, the shale burn plug is provided with a raised ridge in the face of the energized shale burn plug to more effectively divert debris from the seal cavity associated with each of the rotary cones. The features and advantages of this invention are achieved by providing a sealed bearing rotary cone drill bit having a body having a first pin end and a second cutting end. A downwardly extending leg has an outer surface and a journal bearing integrally formed with the leg and projecting inwardly therefrom. An annular shoulder is formed at the juncture of the journal bearing and the leg. A cutter cone is mounted for rotation on the journal bearing. The cone has an annular end face that is adjacent to the shoulder formed on the leg. The shoulder and the end face of the cone are normal to a rotary axis of the cone and have clearance therebetween. The leg also has at least one aperture that is laterally spaced from the leg outer surface. At least one debris deflecting plug is retained within the aperture. A deflecting face of the plug is adjacent the annular face of the cone and forms a debris deflecting ridge. The debris deflecting plug is positioned in the aperture to orient the debris deflecting ridge on the face of the plug such that debris is deflected away from the clearance space formed between the leg and the cone. A means is provided for energizing the debris deflecting plug to urge the ridge of the plug against the annular face of the cone. The debris deflecting shale burn plug has a ridge that may be oriented to deflect debris away from the space formed between the leg back face and the rear surface of the rotary cone. An advantage to the present invention over the prior art is the means whereby the shale burn plug is energized to assure contact of the plug against the back face of the rotary cone. The above noted features and advantages of the present invention will be more fully understood upon a study of the following description of preferred embodiments in conjunction with the detailed drawings wherein: FIGURE 1 is a perspective view of a sealed bearing rotary cone rock bit; FIGURE 2 is a partially broken away and sectioned view of the lower end of a leg of a rock bit illustrating a rotary cone mounted to a journal extending from the leg; FIGURE 3 is a fragmentary view taken through 3-3 of FIGURE 2 illustrating the leg back face and cone with a debris deflecting shale burn plug mounted within the leg back face; FIGURE 4 is an enlargement of a segment of FIGURE 3 emphasizing the protruding detent that is aligned with a slot formed in the leg back face to prevent rotation of the shale burn plug; FIGURE 5 is a cross section through a journal bearing illustrating an alternate shale burn plug; and FIGURE 6 is a cross sectional view taken through 8-8 of FIGURE 5 illustrating the energized rectangularly shaped shale burn plug. With reference now to FIGURE 1, the sealed bearing rotary cone rock bit generally designated as 10 comprises a rock bit body 12 with a pin end 11 and a cutting end generally designated as 26. Each cone 28 making up the cutting end 26 is attached to a leg 14 that terminates in a shirttail portion 16. Each of the cones has, for example, a multiplicity of equally spaced tungsten carbide cutter inserts 29 interference fitted within insert holes formed in the cone bodies 28. A lubricant reservoir generally designated as 180 is provided in each of the legs 14 to supply lubricant to bearing surfaces formed between the rotary cones and their respective journals. Three or more nozzles 13 communicate with a chamber formed inside the bit body 12 (not shown). The chamber receives drilling fluid or "mud" through the pin end 11. The fluid then is directed out through the nozzles during bit operation. FIGURE 2 illustrates a leg 14 of the rock bit with a cone 28 mounted on a journal bearing 18. A plurality of cone retention balls 20 are confined within a bearing race 19 formed in the journal and a race 27 formed inside the cone. An O-ring seal 22 is retained within a seal gland 21 formed in the mouth of the cone. The seal 22 serves to retain grease within the bearings formed between the cone and the journal and also serves to prevent detritus from entering past the seal gland 21 into the bearing cavities between the cone and the journal. Leg 14 has, at the cutting end 26 of the rock bit, a shirttail 16 and a leg back face 17. The leg back face 17 has an annular shoulder at the juncture of the journal bearing 18 and the leg. The cone has an annular end face 30 that is spaced from and adjacent to an annular shoulder on the leg back face 17. As heretofore mentioned debris tends to pack into the annular space formed between the cone back face 30 and the leg back face 17. The debris eventually packs in and works its way into the seal bearings while the bit operates in a borehole (not shown). A debris deflecting plug or shale burn plug generally designated as 38 is slideably retained within a burn plug retention aperture 36 formed in the leg shoulder or back face 17. The shale burn plug 38 is preferably fabricated from cemented tungsten carbide (WC). The aperture 36 is sufficiently deep to retain, for example, an elastomeric material or a leaf or coil spring 44. The preferred elastomeric material (a highly saturated nitrile compound or rubber) bottoms out in the aperture 36 and is pressed against the base 37 of the plug body 39. The exposed plug face 40 has, for example, a ridge 41 formed on the shale burn plug body 39. A detent pin 42 is an integral part, for example, of the plug body 39 and is aligned with a detent recess 43 formed in the leg back face 17. (See Figs. 3 and 4). The top of the shale burn plug (the side adjacent the cone) surface 40 may be coated with a harder more abrasive resistant material such as diamond to prevent surface wear. Referring now to FIGURES 3 and 4, the plug body 39 is slideably engaged with an aperture 36 formed in leg back face 17. The alignment pin or detent 42 is engaged with the detent recess 43 in such a manner as to align the ridge 41 in a non-radial direction for most advantageously deflecting detritus 23 as it enters the space formed between the cone and the leg back face. A recess 45 is also formed in the leg recess to provide a depression surrounding the burn plug 38 to accumulate and direct debris toward impact with the deflecting ridge formed in the top face 40 of the plug body. Additionally, there may be a pair of shale burn plugs 38 to provide a redundant detritus diverting means. There may be as many as three shale burn plugs 38, circumferentially aligned or not aligned as the case may be (different radial distances from the journal axis) to deflect debris as it enters the space formed between the leg back face and the cone back face 17 and 30. Debris that may be missed by a first shale burn plug 38 is picked up by a backup shale burn plug 38. The angle of the ridge 41 may, of course, be varied to best deflect debris or detritus as it enters the space between the cone and the leg. A second alternative embodiment is illustrated with reference to figures 5 and 6 wherein a rectangularly-shaped shale burn plug 238 is slideably retained within a complementary rectangularly-shaped aperture 236 formed in leg back face 217. The shale burn plug 238 is urged against the cone back face by, for example, a rubber spring 244 placed between the bottom of the aperture 236 and the base 237 of the body 239 of the shale burn plug 238. The face of the rectangular burn plug 238 is urged against the cone back face 230, thus accommodating for any axial oscillations of the cone on the journal bearing 218. The rectangular slot 236 in the leg back face is oriented obliquely with respect to a radial line emanating from the journal axis. Thus, the edge of the plug inserted in the hole forms a non-radial ridge that deflects debris as it enters the space formed between the leg back face 217 and the cone back face 230. The angled orientation of the burn plug 238 may be varied to best deflect detritus from the space between leg and cone. It is important to maintain contact of the face 240 with the cone back face 230 to most effectively prevent debris from entering the journal bearings formed between the cone 228 and the journal bearing 218, as is most clearly shown in FIGURE 6. Referring now specifically to FIGURES 2 and 6, it can be seen that cylindrical plug face 40 in FIGURE 2 and the rectangular plug face 240 in FIGURE 6 is in constant contact with the cone back faces 30 and 230 thus assuring there are no gaps between the burn plug faces 40 and 240 thereby substantially preventing debris from entering the bearings of the bit. Moreover, the shale burn plugs 38 and 238 may be slideably retained within a hardfacing sleeve (not shown) pressed into the leg back face apertures 36 and 236 to prevent cocking of the burn plug through wear of the plugs 38 and 238 during operation of the bits in a borehole without departing from the scope of this invention. The sleeve also serves to protect the apertures 36 and 236 from wear. It will of course be realized that various other modifications can be made in the design and operation of the present invention. For example, one may utilize other shapes such as oval, elliptical, etc., for the burn plug without departing from the invention. One may also provide a cylindrical shale burn plug with a flat end face that is urged in contact with an annular end face of a rotary cone by an elastomer or spring.

Claims: A sealed bearing rotary cone drill bit (10) comprising: a body (12) having a first pin end (11) and a second cutting end (26), a downwardly extending leg (14), a journal bearing (18, 218) formed integrally with the leg (14) and projecting inwardly therefrom, and an annular shoulder formed at the juncture of the journal bearing (18, 218) and the leg (14); a cutter cone (28, 228) rotatably mounted on the journal bearing (18, 218), the cone (28, 228) having an annular end face (30, 230) adjacent the shoulder, the shoulder and the end face (30, 230) being normal to a rotary axis of the cone (28, 228) and having clearance space therebetween; and the leg (14) having at least one aperture (36, 236) laterally spaced from the leg outer surface, a debris deflecting plug (38, 238) retained within the aperture (36, 236) and forming a debris deflecting ridge (41, 241) extending in a non-radial direction with respect to a radius from an axis of the journal bearing (18, 218), the debris deflecting plug (38, 238) being so positioned in the aperture (36, 236) to orient the debris deflecting ridge (41, 241) such that debris is directed away from the clearance space between the leg (14) and the cone (28, 228), characterized by means (44, 244) for resiliently biasing a face (40, 240) of the deflecting plug (38, 238) toward the annular face (30, 230) of the cone (28, 228). The drill bit as set forth in claim 1 wherein the means (44, 244) for urging the debris deflecting plug (38, 238) against the annular face (30, 230) of the cone (28, 228) is an elastomeric material. The drill bit as set forth in claim 1 wherein the means (44, 244) for urging the debris deflecting plug (38, 238) against the anular face (30, 230) of the cone (28, 228) is a spring. The drill bit as set forth in any of the preceding claims wherein the aperture (36) formed in the leg (14) is a cylindrical bore, the cylindrical bore being normal to and intersecting the shoulder, the debris deflecting plug (38) being a cylindrically shaped pin adapted to be inserted within the cylindrical bore in the leg (14), the exposed face of the pin adjacent to the cone (28) having said ridge (41). The drill bit as set forth in any of the preceding claims wherein means (42, 43, 236) are provided for preventing the debris deflecting plug (38, 238) from rotating within the bore (36, 236) formed in the leg (14). The drill bit as set forth in any of the preceding claims comprising means (42, 43) for preventing rotation of the cylindrical debris deflecting plug (38) comprising a detent (42) extending from the debris deflecting plug (38), the detent (42) being adapted to be retained within a complementary groove (43) formed in the annular shoulder adjacent a wall of the aperture (36), the detent (42) preventing the debris deflecting plug (38) from rotating as it engages the surface of the cone (28). The drill bit as set forth in any of the preceding claims wherein the aperture (236) is rectangular in shape, the aperture (236) being oriented at an oblique angle with respect to a radius from the axis of the journal bearing (218), the debris deflecting plug (238) being rectangularly shaped and retained by the rectangularly shaped aperture (236), the debris deflecting plug (238) being angled by the aperture (236) such that debris is directed away from the clearance space between the leg (14) and the cone (228). The drill bit as set forth in claim 7 further comprising an elastomeric means (244) contained within the aperture (236) between a bottom of the aperture (236) and a base (237) of the rectangularly shaped debris deflecting plug (238), the elastomeric means (244) serving to urge the debris deflecting plug (238) against the annular face (230) of the cone (228). The drill bit as set forth in any of the preceding claims comprising a plurality of debris defleting plugs (38, 238) in apertures (36, 236) in the leg (14) adjacent to a face (30, 230) of the cone (228).

Inventors: CAWTHORNE CHRIS E, ERBENECK GARY, OLIVER MICHAEL S, CAWTHORNE, CHRIS E., ERBENECK, GARY, OLIVER, MICHAEL S.
Applicants: SMITH INTERNATIONAL, SMITH INTERNATIONAL, INC.
Application year: 1991
Main classification: E21B10
IPC codes: E21B10