ROTARY DRILL BIT

Abstract: A rotary drill bit comprising at least one rotatably carried roller cutter (12) is provided with a seal (18), which separates the bearing spaces of a forward bearing (14) and a rear roller bearing (16). For purposes of ensuring efficient cleaning of the bearing space of the rear bearing (16) flushing fluid is supplied to the forward portion of the race thereof. For purposes of further decreasing the risk that impurities enter into the bearing system through a gap (20) between the roller cutter (12) and the bit body (10) a seal (29) having check valve function may be mounted in the gap (20).

Description: ROTARY DRILL 31 This invention relates to a rotary drill bit of the type com¬ prising at least one roller cutter, which is rσtatably car¬ ried over a bearing system. The bearing system comprises at least a forward and a rear bearing. Passage means is provi¬ ded in the bit body for supplying fluid, such as compressed air, to the bearing system for flushing and when needed cool¬ ing thereof. In rotary drill bits having conical roller cutters, which are rotatable on the bit body, a satisfactory lubrication and cooling of the bearings are .of utmost importance. There¬ fore, the bearing space is usually ' sealed at the annular, gap between the roller cutter and the bit body, and -filled with suitable lubricant. In operation, however, there is a risic in such designs that impurities penetrate past the seal and enter into the bearing system, thereby causing mechanical damages on the ' bearings. The object of the present invention is to provide a rotary drill bit in which there is ensured a satisfactory lubrica¬ tion and cooling of the forward bearing at the top of the roller cutter, i.e. the end of the roller cutter opposed to the bit body, -since the working temperature is higher at " this end than at the opposite end. The object of the inven¬ tion is also to provide a rotary drill bit in ' which impuri¬ ties are prevented from entering into the bearing system, while ensuring sufficient cooling and lubrication of the rear bearing at the end of the roller cutter facing the bit body. These and other objects of the invention are attained by giving the invention the characterizing features stated in the- appending claims. The invention is described in detail in the following des¬ cription with reference to the accompanying drawings in which one embodiment is shown by way of example . It is to be _b - r stood that this embodiment is only illustrative of the in¬ vention and that various modifications thereof may be made within the scope of the claims. In the drawings, Pig. 1 shows in section a roller cutter and a bearing pin associated therewith in a rotary drill bit according to the invention. Pig. 2 is a section taken on the line II-II in Pig. 1. Pig. 3 shows a top view of the bearing pin in Pig. 2. Pig. 4 shows on an enlarged scale the encircled portion in Pig. 1. Pig. 1 shows a drill bit for rotary drilling in rock and earth formations. The rotary drill bit comprises in conventional manner three separate legs, which form part of the bit body. A rotary drill bit of this type is disclosed in U.S. Patent No. .19 .79 . Por the sake of clarity only one leg 10 is shown in Pig. 1'. The lowermost portion of the leg 10 is formed as a bearing pin 11 upon which a roller cutter 12 is rot tably carried. The roller cutter 12 is provided with cutting means 1 , in the illustrated embodiment hard metal inserts which are press-fitted in corresponding holes in the roller cutter, so as to break and crush rock and earth formations when the bit is rotated and moved downwards the hole being drilled. The bearing system for the rotatable supporting of the rol¬ ler cutter 12 comprises a forward roller bearing 1 at the top of the roller cutter, i.e. the end of the roller cu * cter opposite to the leg 10, a conical axial roller bearing 15 and a rear roller bearing iβ. The rollers in the roller bea¬ ring 16 are inserted through a loading bore in the leg 10 when the roller cutter 12 is mounted on z e bearing pin 11, whereupon a plug 17 is inserted into the bore and secured therein by welding. . A seal 18 is provided between the bearing 15 and the bearing lβ for sealing the bearing space of the bearings 14, 15. This bearing space is filled with lubricant, for instance through a passage, not shown, in the bearing pin 11, or by means of a lubricating system, not shown, which in conven¬ tional manner comprises a pressure compensator for equalizing the pressures in the lubricant and the fluid in the drill hole. Suitable lubricant is chosen with regard to the high working temperature which arises at the top of the roller cutter. A passage 19 is provided in the leg 10 for supplying fluid, such .as ' compressed air, to the bearing space of the rear rol¬ ler bearing lβ. Normally, this fluid is intended on the one hand to cool the bearing lβ and on the other to clean the bearing space thereof and prevent impurities from entering into the bearing space through the annular gap 20 between the roller cutter 12 and the leg 10. In certain cases, how¬ ever, the fluid might be warmer than the bearing 16, which - means that the primary function of the fluid is to clean the bearing space. The fluid from the passage 19 is conducted through longitu¬ dinal grooves 21, 22 in the underneath side of the plug 17 to recesses 3, 24, 25, 2β in the race of the roller bearing Iβ, The plug 17 forms a portion of the race. The recesses 23, 25 are provided in the plug 17 and turn into the reces¬ ses 24, 26 which are provided in the bearing pin 11. Due to the recesses 24, 2 β the fluid is distributed over a large circumferential extent, thereby ensuring that the fluid may pass between the rollers in the bearing iβ toward the gap 20. The circumferential extension of the recesses 23-26 is preferably larger than three times the diameter of the roi- i *oγ lers in the bearing lβ. The bearing pin 11 is provided with a flange 27, which locks the rollers in the bearing lβ against axial movement. ?or purposes of further facilitating the fluid flow from the re¬ cesses 23, 25 in the plug 17 the flange 27 is provided with a bevelled portion 28, which communicates with the recesses 23, 24, 25, 26. When needed lubricant is delivered in a manner known per se to the fluid flowing through the passage 19 for purposes of ensuring required lubrication of the roller bearing Iβ. Due to the fluid flow out through the gap 20 the risk is* de¬ creased that impurities will enter into the bearing system. For purposes of further decreasing this risk, there is accor¬ ding to the invention provided an annular sealing means 29 having check valve function in the gap 20. The sealing means 29 comprises a rigid body 30 and a resilient lip 31 attached thereto a d extending radially outwards. Due to the lip 31 the fluid may flow out through the gap 20 under low flow resistance while large resistance is maintained against pe¬ netration of impurities into the bearing system. The body 30 of the sealing means is stif ered by means of a metallic plate and attached to the roller cutter 12, for instance glued thereto.

Claims: Claiaa 1. Rotary drill bit comprising at least one roller cutter (12) which is rotatably carried on a bearing pin (11) over a bearing system, said bearing system comprising at least a forward bearing (14) and a rear bearing (iβ), and where¬ in at least one passage (19) is provided in the bit body (10) for supplying fluid, such as compressed air, to the bearin -system for flushing and when needed cooling thereof, c h a r a c t e r i z e d in that the passage (19) termi¬ nates into the bearing system at the forward portion of the rear bearing (lβ) between an intermediate sealing means (18) and an annular gap (20) provided between the bit body (10) and the roller cutter (12), said rear bearing being a roller bearing and said sealing means separating the bearing spaces of the forward bearing (14) and the rear bearing (Iβ), and wherein the bearing space of the forward bearing (14) is filled with lubricating means. 2. A rotary drill bit according to claim I, wherein a recess (23-26) is provided in the forward portion of the race of the roller bearing (Iβ), said recess communicating with the passage (19). 3. A rotary drill bit according to claim 2, wherein the circumferential extension of the recess (23-26) is larger than the diameter of a roller in the roller bearing (16), preferably at least three times said diameter. 4. A rotary drill bit according to claim 2 or 3, wherein the bearing pin (11) is provided with a flange (27) in connection with the sealing means (18) for axially securing the rollers in the roller bearing (16), said flange being bevelled in connection with the recess (23-26). 5- A rotary drill bit according to any of the preceding claims, comprising a second annular sealing means (29) mounted in the gap (20), said second sealing means having check valve function so as to allow fluid flow out through the gap under low flow resistance while maintaining large resistance against penetration of impurities into the bearing system. 6. A rotary drill bit according to any of claims 2-4, comprising a plug (17) mounted in a roller loading bore in * the bit body, said plug providing a portion of the race, and said plug having passage means (22) which interconnects the recess (23-26) in the race with the passage (19) in the bit body (10). 7- A rotary drill bit according to claim 6, wherein the passage means (22) in the plug (17) is provided in the side thereof opposite to the race. 8. A rotary drill bit comprising at least one roller cutter (12) which is rotatably carried over a bearing system, said bearing system comprising at least a forward bearing (14) and a rear bearing (16), and wherein at least one passage (19) is provided in the bit body (10) for supplying fluid, such as compressed air, to the bearing system for flushing and when needed cooling thereof, .c h a r a c t e r i z e d in that said passage terminates in the bearing system be¬ tween a first sealing means (18) and an annular gap (20) between the bit body (10) and the roller cutter (12), said first sealing means separating the bearing spaces of the forward and rear bearing (14, 16), and comprising an annular second sealing means (29) mounted in the gap (20), said second sealing means having check valve function so as to allow fluid flow out through the gap (20) under low flow resistance while maintaining large resistance against pene¬ tration of impurities into the bearing system, and wherein the bearing space of the forward bearing (14) is filled with lubricant. 9. A rotary drill bit according to claim 8, wherein the se¬ cond sealing means (29) comprises an elastically yieldable tongue (31) * said tongue being attached to a considerably more rigid body (30) at its inner end and extending radial¬ ly outwards to its free outer end. 10. A rotary drill bit according to claim 9, wherein the body (30) of the second sealing means (29) is attached to the roller cutter (12).

Inventors: KARLSSON LENNART, NORLANDER GOESTA
Applicants: SANDVIK AB, SKF AB
Application year: 1981
Main classification: E21B10
IPC codes: E21B10, F16C19, F16C33, F16J15