CA1254552A

CA1254552A - Bearing system for a roller cone rock bit

Info

Publication number: CA1254552A
Application number: CA000498333A
Authority: CA
Inventors: David R. Hall
Original assignee: Megadiamond Industries Inc
Current assignee: Megadiamond Industries Inc
Priority date: 1984-12-21
Filing date: 1985-12-20
Publication date: 1989-05-23
Also published as: MX162428A; IT1182101B; FR2583100A1; IT8548952A0; GB2168737A; FR2583100B1; GB8531433D0; DE3545438A1; GB2168737B

Abstract

ABSTRACT OF THE DISCLOSURE

A roller cone rock bit is disclosed with an improved bearing system. The improvement comprises a journal bearing which is substantially frusto-conically shaped and a roller cone bearing which is reverse shaped to mate with the journal bearing. The invention also includes a means for maintaining the journal and roller cone bearing in compression against each other.
In the preferred embodiment, the journal and roller cone bearings comprise polycrystalline diamond and the compression is maintained by a threaded bolt which is tightened to the point of putting the bolt in tension.
In one preferred embodiment, the bolt is threaded into the cone and rotates in the center of the journal. In another preferred embodiment, the bolt is threaded into the leg or the journal and the cone rotates about it.
In both of these embodiments, thrust bearings are located between the head of the bolt and the leg or cone surface contacted. The bolt's threads can either be locked in place, or allowed to self-tighten as the cone rotates during drilling.

Description

i4~

IMPROVED BEARING SYSTEM FOR A ROLLER CONE ROCK BIT
BACKGROUND OE THE INVENTION
Field of the Invention The present invention relates generally to the field of earth boring bits and, more particularly, to roller cone rock bits.

Descrietion of the Prior Art Roller cone rock bits generally comprise a main bit body which can be attached to a rotary drill string. The bit body usually includes two or three legs which extend downward. Each leg has a journal extending at a downward and inward angle. A roller cone, with cutters, "teeth", or ridges positioned on its outer surface, is rotatively mount-ed on each jour-lS nal. During drilling, the rotation of the drill stringproduces rotation of each roller cone about its journal thereby causing the cutter elements to engage and dis-integrate the rock.
Because of their aggressive cutting action and resultant faster penetration rates, roller cone rock bits have been widely used for oil, gas, and geo-thermal drilling operations. However, certain problems exist which limit the useful life and effectiveness of roller cone rock bits- The useful life of a rock bit ~5~;~

is an especially critical consideration when viewed in light of the great expense in time and money required to remove and replace the entire drilling s-tring be-cause of bit failure.
The bearings used between the journals and the cones are the source of significant problems. These bearings operate in an extremely hostile environment due to high and uneven loads, elevated temperatures and pressures, and the presence of abrasive grit both in the hole cuttings and the drilling 1uid. This is par-ticularly true when drilling deep holes. In addition, some rock bits such as those used in geothermal explora-tion are subject to corrosive chemical environments.
Another factor which can lead to early bearing failure 15 is the inability of the bearings to withstand changes in the moment of forces directed against the roller cone. As the inserts on the gage row gradually wear down, the sides of the hole become less defined. As a result, the forces from the side of the hole increase.
These increased side forces tend to push the cone off its original axis of rotation, thereby "pinching" the bearings in their races and contributing to early bear-ing failure.
Unfortunately, these extreme conditions often cause failure of the roller cone bearings before any part of the bit, even before the cone's cutters. In addition, as the bearings wear, they can allow for more "wobble" of the cones. As a result, a roller cone bit with worn bearings does not track as well in the hole and has a reduced penetration rate. Also, these limits on the bearing's capacity in turn limit both the load which can be applied to the bit as well as the angular velocity at which the bit can be rotated, thereby estab-lishing constraints on achievable penetration rates and feasible cutter designs.

the earlier roller c ng structure was rel ti Patent Nos. 1 649 858 cone rOck bit with a f Ype bUshing located b t h bearingS had a ut so did the other c r~ as harder and lon mented tungsten Carbid the ther compOnent as these new bits wer per hOles through hard made to improve the b igher 1Oads for lOnge iournal and r 1 ~ the tYPical bearingS b t ler cone Consist of c b friction bearingS Th ball or rOller beari ion, absorb radially di ain the rOller cone o th ringS are used bOth fo "
tiDg Sureaces are di oe the journal aDd ab aS well as eor radi 1 b aCes are di5posed par 11 nd absorb radially di and Cool ants are freqU
life of bearings One d te the bearings In bit Cessary to seal the b g eaSe and keep out th d MSt of these bits ir and pressure comp as Well as the high t r in drilling de~p hol ~4~

3~397,928; 3 476 195 f the se f ea tureS add iCation usually re d or Pinned~ on th hiCh the legs are weld ion~ because of th h ure on the sealS and l 1 Speed at which th Perated is ften li i harder, more we~ alSO increased by r resistant materi 1 P y carburizing ha d Y for the bearing su f CmPlexity and co t lS tion U S p ~ U-S- Patent No 4 054 nt No 4, lso, 301 tea h g Polycrystalline diam d nose thrust bearin tent No. 4,260 203 t 20 Plycrystalli hrUSt bearing surfa amnd Although the aring Surfaces may b ther materials the d nt for certain prope ti 25 the in diamond In particul Vation that Plycry t ns in compression aUse the '203 design h et Perpendicular to Polycrystal 1 ine di a That is, as the thr t , the radial bea i the Patent does not di cone on the iurnal th hod With ball bearingS hi POint in the bearing U.S. Patent No. 4,145,094 shows a somewhat aring System for roll se ball bearings to r t i hat design, the cone is eCtron beam Welding an member onto the journal after it has been inserted into the cone~ thereby "plugging" the cone onto the journal.
SVM~ ~ OF THE INvENTIoN
fore the seneral object n to Provide an improved b rock bit which wi 11 perf ~ at higher rotati higher applied loads.
, the present invention i proved bearing system for roller cones on roller cone partiCularly, the inventi bit with a frusto-coni on the journal which m t aring surface on the r 11 ncludes a means for pre l pression between these t faces.
In the preferred embodiment, the compression an elongate pin which i one~ extends through th has a feature at the oth g urface contacting a thr t face on the leg of the bit. In simplest form, this pin i s threadably attached bolt rotates within the journal, and there is a pair of type bearings between th an Utside Surface of th 5~2 . ~

preferred embodiment th ongate pin which is att h r leg, extends through th the Other end with a th with a thrust bearing f on the outside of the cone.
In the preferred embodiment, the journal, hrUSt bearings Compri S
he Preferred embOdiment g a stream of the drilli es This results in b f ing and lubricating of the bearings.

ESCRIPTIoN OF THE DRAWIN
ent inventiOn will be m the following detailed d mbdimentS, read in accompanying drawings, wherein:
is a perspective view and cross section of a typical prior art roller cone rock bit;
Figure 2 is a sectional view illustrating a first preferred embodiment roller cone bit of the pre-sent invention with a frusto-conical bearing inter~ace between the journal and the roller cone;
s a perspective view of f conically shaped journal bearing suitable for use in he embodiment of Figure 2 Figure 4 is a schematic diagram showing a of a pair of frusto-coni p ation and resolution of f thereon.
Figure 5 is a sectional view of a second pre-ment wherein the retaini taChed to the leg of th bi ~$48~

AILED DEscRIp~IoN
the drawings~ Figur a tYPical prior artis Comprised of a m i 13 adaPted to be thr d g (not shown). Extendi legS 14, each of whi h h ren A cone 16 which h Y mUnted onto each iou 10 1 he iournal 15 by a s t ce cut intO the iourn l n fabrication~ the ball b e through passage 19 Th led by plug 20 and th 15 b to the ball bearing 18 t Communicates with p Wi th lubri cant reser 24 is lcated with th g er PreSsures and temp s- An elastomerlc se 1 2 and the journal and s he drilling debris out aring 27 serves to ab b ia11Y to the one whi aring 28 serve the sa frCes direct a SeCtinal vie iment of the present i ro 11 er cone rock bi t bit body 31 which has an end 32 which is adapted to be y attached to a drill st i extends down from the main bit body. The preferred inCludes two Other le would be equally spaced around the bit body. Bits have ith one, two~ three O

;2 he Scope of thiS inve ti e leg 34 and extends t A roller cone 36 is r t 1 35 Cutters 37 ar engagins the bOttom f PreSent invention is th rUcture~ the rOller Y al 1 owing for deeper p k al terna ti ve embOdime t 10 eintegral tee~h or ann 1 Gage i nsert s 38 a ne to engage ma the important iameter of the hOle lS tom the Side of the h 1 Y arrow C increase and th ff its original axi on the jOurnal 35 is P bearing 41. It is n t e frusto-conically sh the curved side surf P or bttom. This be 3 and fUrther d preferred embodiment 25 tnts are discussed in St a Portion of th nal bearing surface ond As used herein th mond and its abbrevi ti mPrising diamond cry t l high preSsure and t of randomly oriented y directly bonded to adj PrPerties of Plycr t (pcC8~) are quite simil ~2~4SS:~ .

PCD, much of the discussion of PCD will also apply to ns that will be discus d preferred material A m ti conical bearing 42 is mounted within the roller cone 36- In the preferred embodiment, the mating surface of this roller cone bearing 42 also comprises polycrystal-diamond is thread2b1y attached t i ne 36. The bolt 43 wi11 36. In one preferred b a locking pin 61 may be inserted through the passage 62 n place, thereby preventi ve to the cone which w een the thru t b The bolt may also be p e cone 36 using Other m th welding, application of locking compounds, peening, etc.
In yet another embodiment, the inventor dis-Urprising reSult that wh bearing 41 and roller cone bearing 42 are comprised of PDC, it is possible to allow the bolt to remain un-by be self-tightening with the bearings bind- In particular, instead of causing 5 tl~e bearings to bind, the self-tightening of the bolt fiCial function of maint i f compression against e h wear- ACcordingly it in the preferred embodiments to permit t30 tightening of the bolt- It is deemed within the ordi-art to select a pitch fwhich would avoid placing too much stress on the bolt and maximize the benefits of this self-tightening action 3 eXtends through a hol 5 nd has a head 47 which i ~2$~

hole 54. This head 47 is adapted to receive a tool for tightening such as a hex or allen wrench. Adjacent to the head 47 of the bolt 43 is a thrust bearing or washer 46 which mates with a second thrust bearinq 45 which is in turn adjacent to the leg 34. Each of these thrust bearings 46 and 45 may either be bonded in their posi-tion ~i.e. to the head 47 or leg 34 respectively) or may be non-attached. As can be seen, a recess 56 in the leg 34 is adapted to receive the thrust bearinys 45 and 46 along with the head 47. It may also be desir-able to secure a cover over this recess 56 or fill it with a filler material such as epoxy for protection during drilling. In the preferred embodiment, the mat-ing bearing surfaces of the thrust bearings 45 and 46 comprise polycrystalline diamond. Also, in the pre-ferred embodiment, the thrust bearings have a substan-tially planar interface. In alternative embodiments it may be desirable to shape the head 47 and bearings 45 and 46 to provide a frusto-conical interface between the thrust bearings.
It will be observed that a space 57 is left between the distal end surface S9 of the journal bear-ing 41 and the internal surface 58 of the roller cone 36. Also, the proximate end surface 60 of the roller cone 36 does not contact the journal 35 or the leg 34.
These two features are important because they allow the roller cone bearing 42 to be freely compressed against the journal bearing 41. In other words, in the pre-ferred embodiment, the frusto-conical journal bearing is the only surface on the journal or leg which pre-vents the roller cone from moving axially in the direc-tion indicated by arrow B.
The inventor has discovered that, in using this arrangement, the frusto-conical bearings and the bolt with its thrust washers cooperate to produce at i5~

ant benefitS~ First ti put the frusto-conic 1 b In particular the b 1 Put it in tension and th nes in a Stat PreSsion is highly be fi r cone b~aring is the inventorls ob y strong in compreSsi n- Therefore~ if on st for it to be pre 1 d order to minimize th t xperience. In othe ng is less likely t 15 t may be deleterious t th PeCially true for thi dUring drilling the PC
ads from multiple dir is confisuration impr 20 Thi aintain itS original e of the fact that th niCal bearing5 and th gUlar cross-section t k the pposite Sides f aring interface and th gS make up three Side When force is appli d Y direction, there is a es to WhiCh the forc rmal component. ~or e reased forces from th ( n the direction ir,di thrust bearing interf one bearing doeS not ff of the journ 1 b 5~i2 r embodiment, the distal 5 doe5 contact the su f nS are carefully faces 58 and 59 to cont cient compression betw e bearings. In this b inClude PCD Over at 1 nd 59. Allowing the t ct WOuld provide prot ti bearing against excessive axial loads encountered dur-e same result can also b 1 Surface 60 of the c the leg 34 of the bit- Providing this ~backstop~ to j rnal and roller cone b loads may be desirable i ogenous formations or it tring- These embodime t ing the exact amount of bolt could be tigh~en d surfaces contact and then backed off.
nOted that the preferr d thi5 baCkstop~ to pr t cone bearing against a i 1 prised to discover that th ~5 system with this particular goemetry does operate well 1 loads. As discussed i with Figure 4, it was th large axial loads would cause the frusto-conical bear-not provided with a se bearing to absorb these axial loads. To the contrary, the inventor has found that the high axial loads areal to the bearings cper ti ther embodiment, instead bolt to retain the cone 36 on the journal 35, a post is d to the cone in the sa s~

instead integral with the cone. This post has threads on the end which extend into the recess 56 of the leg 34. A nut is then threaded onto that post with two thrust washers between it and the leg. In yet another embodiment, a hole passes through both the journal and the cone and a bolt with threads on both ends is in-serted therethrough. A nut is threaded onto each end and thrust bearings are placed between each nut and the leg or an outer distal surface of the cone. In this embodiment it may be desirable to allow both nuts to self-tighten. This could result in better adjustment of the tension on the bolt through varying stages of wear on the elements of the bit.
Another important advantage of the preferred embodiment of the present invention is that it offers a bit which can be fabricated with greater ease. First, the fabrication of typical prior art roller cone rock bits involves a complex "pinning" step where the ball bearings are inserted through a hole into a race in order to retain the cone on the journal. In contrast, the roller cones of the preferred embodiment can be attached by simply inserting the retaining bolt through the leg and threading it into the cone.
Second, in typical prior art fabrication~
~5 because of the complexity of the pinning operation and spatial limitations, each leg is usually forged sepa-rately. After a cone is pinned on each leg, the legs are welded onto a main bit body. (See U.S. Patent No.
4,266,622 for a discussion of the problems inherent in this process.) In contrast, because the cones of the present invention are attached in a simpler process, it may be possible to form the legs as an integral part of the bit body and yet be able to attach the cones.
Also, if spatial limitations prevent attaching the cones over the jcurnals when the legs are already in place, the preferred embodiment can be modified slightly. In particular, the journals can be made separate from the legs. In this way, the journals can be inserted into the cones, the cones and journals slid into their posi-tion, and then tne retaining bolt inserted through theleg into the cones. The journals can be indexed with the leg to insure correct positioning and retention on the leg.
A further advantage gained by this simplifi-cation of the fabrication process is that it Will makereconditioning of worn out bits possible. At present, the standard practice in the drilling industry is to discard the entire bit when any part of it fails since the cones or bearings cannot be replaced with the weld-ed legs approach. With the present invention, it ispossible to replace the cones without destroying and refabricating the whole bit. Therefore, it will be economical to use each of the parts of the bit to its fullest extent. Indeed, preliminary tests show that it will be the bearings that have the longest life expec-tancy. Thus, the bearings can be removed when the bit body and cutters are worn out and put into a new bit.
An advantage which also stems from this sim-plification of the bit fabrications is that it will now be possible to service roller cone bits in the field.
That is, because the cones may be removed and attached in a relatively simple operation and with standard tools, it will be possible to change cones at the drill-ing site. In addition to replacing worn out cones, it 30 will also be possible for a driller to maintain an in-ventory of cones with different types of cutters and thereby be better able to tune the cutting characteris-tics of the bit in response to the formation in which he is drilling. Under present technology, the driller is required to maintain a costly inventory OI entire bits to accomplish the 5ame result.

Although, preliminary tests show that the bearing of the present invention performs well at high-er loads and rotational speeds without any lubrication, it is considered desirable in the preferred embodiment to cool and lubricate the journal and roller cone bear-ings 41 and 42 as well as the thrust washers 46 and 45.
This is accomplished in the preferred embodiment by providing a passage 52 which communicates at one end with a central cavity 51 in the bit body 31 which in turn communicates with a source of drilling fluid in the drill string. A grate or screen 53 is located in the central cavity 51 to prevent large particles from entering the passage 52. The other end of the passage 52 cornmunicates with the hole 54 in the journal. In - 15 this way, a stream of the drilling fluid can pass over the journal and roller cone bearings and the thrust washers 45 and 46. It was a surprising result that a drilling fluid such as typical drilling mud could work well as both a lubricant and coolant for the bearing of the preferred embodiment. Drilling mud typically con-tains high quantities of abrasive silicate particles.
Many bits are designed to keep the mud away from the bearings. With the present invention, when the bearing is comprised of polycrystalline diamond, these silicate particles are actually ground by the polycrystalline diamond surfaces and result in fine particles which function as a lubricant on the diamond bearing sur- -faces. Accordingly, the preferred embodiment does not require seals to keep the drilling mud away from the bearings, but rather uses the drilling mud as a lubri-cant and coolant.
~ igure 3 is a perspective view of the frusto-conically shaped journal bearing 41 of the preferred embodiment. This bearing is shaped to mate with a re-verse shaped roller cone bearing (rlot shown). In the most preferred embodiment, the journal bearing com-prises a base member 71 which holds polycrystalline diamond inserts 72 in holes 73. Each insert 72 con-sists of a layer of polycrystalline diamond 74 bonded directly to a cemented tungsten carbide back 75. These - carbide-backed inserts 72 are formed by sintering a mass of diamond crystals adjacent to the pre-cemented carbide piece using ultra high pressure and tempera-tures.
10The height, radius, and slope of the base member 71 are dictated by the various design parameters such as the size and shape of the cone. In particular, the dimensions of the frusto-conical bearings must be selected with the following considerations in mind.
The bearing must fit within the cone and allow a suffi-cient wall thickness for the roller cone. The dimen-sions of the bearing must also allow for a sufficient thickness of the journal which also has the hole 54 passing through it. Because of the tremendous amount of wear on the gage row of the bit, it is important that the frusto-conical bearings do not extend to the exterior of the bit. That is, the part of the bearing closest to the gage row should be contained within the hole of the cone. In addition, the slope of the bear-ing also affects the retention of the cone on the jour-nal as it is subjected to the multi-directional forces from the side and bottom of the hole. With a large angle between the bearing surface and the axis of rota-tion the forces from the side and bottom of the hole will have more of a shear component at the interface of the journal and roller cone bearing than those same forces would have with a smaller angle. For the pre-ferred embodiment, the angle is 20 between the bearing surface and the axis of rotation.

General mechanical principles tend to lead those skilled in the art to conclude that the frusto-conical geometry would be inappropriate for friction bearings which experience high forces directed axially.
A frusto-conical friction bearing with high axial loads would act much like a wedge, in which the force normal to the face of the wedge would exceed the applied down-ward force. Figure 4, which is a~schematic cross sec-tion of a pair of frusto-conical friction bearings, illustrates this point. As the roller cone bearing 82 is pushed onto the journal bearing''81 with the axial force represented by arrow Fa, the.~rce to resist that motion is represented by arrow Fr. ~owever, because the two bearing surfaces are not attaehed,- the onl-y counteractive force must be normal to the two surfaces and is represented by arrow Fn. Because the normal force Fn is at an angle to the force Fr, it must be of a greater magnitude than the force~Fr. As a result, the normal force Fn (the force which determines the frictional force between the two b~arings) is magnified.
In trigonometric terms, ~é applied force F
and the normal force Fn of the frust'o,-conical journal bearing 81 against the frusto-conical roller cone bear-ing 82 are related by the following equations:
l) Fn = Fa sin 0, à~d~[F = F i 0

2) Ff = Fn = Fa ~sin 0~
where ~ is the angle between the outer surface of the bearing and the a~is of rotation-of the roller cone, is the coefficient of friction of the bearing material, and Ff is the frictional force resisting the rotation of the roller cone bearing 82 on t~e journal bearing 81. With respect to the forces normal to the surface of the bearing, the applied force Fa is magnified by a factor of l/sin a . As ~ approaches 0 (i.e. as the bearing becomes steeper) l/sin ~ goes to infinity, and 12~

the normal force Fn becomes infinitely large. The practical result is that the normal forces in a frusto-conical friction bearing experiencing high axial loads would become so large as to exceed the frictional force Ff and cause the bearing to seize. A surprising result of the present invention is that, even with a high load of precompression, no such seizing occurs when a material such as polycrystalline diamond is used for the bearing material.
Referring again to Figure 3, the position, size and number of inserts in each bearing is selected so as to insure that the polycrystalline diamond sur-faces support the loads between the roller cone and the journal. As shown, each insert 72 protrudes slightly from the outer surface of the base member 71. In the depicted embodiment, there are three annular rows of inserts on each bearing. On the journal bearing, there are ten inserts in the row closest to the leg, eight inserts in the middle row, and eight inserts in the distal row. On the roller cone bearing, there are nine inserts in each of the three rows. This particular arrangement was selected so as to provide a proper amount of overlapping of the polycrystalline diamond surfaces at any given point of rotation of the cone.
In another preferred embodiment, there are two annular rows of inserts in each bearing, and the angular spac-ing between inserts is chosen such that there are dif-ferent numbers of inserts in corresponding rows of the cone and journal bearings so as to provide for smooth operation. One bearing may contain closely-spaced in-serts while the inserts in the other bearing may be fairly wide spaced. Naturally, the gap between the inserts on one of the bearings must be smaller than the diameter of the inserts on the other bearing. Alterna-tive embodiments include designs wherein there areeither fewer or more inserts as well as more rows.

Polycrystalline diamond (PCD) is most prefer-red as the bearing surface material. Although PCD is extremely wear-resistant, it is relatively brittle, i.e. it has relatively low tensile strength. As a re-S sult, PCD would not be expected to perform well in theroller cone bit bearing application where such high and uneven impact loads are experienced. However, the in-ventors discovered that this problem could be solved by maintaining the PCD bearings in a state of compression.
That is, the inventor realized that the extremely hlgh compressive strength of PCD could be used to offset its low tensile strength. When the bearings are maintained in a state of compression, the tensile forces are greatly reduced. Therefore, the pre-compressed PCD can survive the high impact loads exerted on the journal and roller cone bearings.
Another reason that one would not naturally think to use polycrystalline diamond as a bearing is that most uses of PCD to date have been for cutting, grinding or abrading operations. That is, it would be though that PCD is too rough or abrasive to be success-ful as a bearing. However, it has been found that when two PCD surface are well polished and fit together well, that the coefficient of friction is actually quite low. The inventor has measured value as low as O.OOS over wide ranges of loads and speeds ranging up to 40,000 lbs. axial pre-compression and 1,000 r.p.m.
In fact, most likely due to its high compressive strength, the coefficient of friction remains low over an impressive range of applied loads- This low coeffi-cient of friction at high applied loads is very impor-tant in relation to the frusto conical geometry which is discussed with respect to Figure 4.
Another advantage which was discovered in using PCD for the bearings of the preferred embodiment is PCD's high thermal conductivity. In particular, it is important for the bearings to be able to dissipate the heat which builds up during use.
Still another advantage of the preferred em-bodiment using PCD is its relative inertness. That is, in most bearings which are subjected to high loads at high temperatures, there is a problem of welding of the c~ntacting surfaces. To avoid this problem, many such bearin~s are made from dissimilar metals, a solution which can introduce new problems related to dissimilar coefficients of thermal expansion etc. In contrast, when PCD is used in the present invention, the fact that diamond is relatively unreactive, obviates these problems.
Alternative embodiments may employ materials other than polycrystalline diamond for the bearing sur-face of the frusto-conical roller cone and journal bearings. Polycrystalline cubic boron nitride exhibits many of the same properties as PCD and additionally possesses much better thermal stability and as such may be substituted in the bearing of the present invention.
In addition, particular ceramic or cermet materials may be found to possess the requisite properties to be of use in the bearing system.
Both the bacX 75 and the polycrystalline diamond layer 74 are pre-shaped to conform to the cur-vature and slope of the outer surface of the journal bearing. The PCD layer 74 is shaped during the ultra-high pressure/temperature pressing cycle by being sintered adjacent to the carbide back 75 which has pre-viously been correctly shaped. Likewise, the inserts in the roller cone bearing (not shown) are pre-shaped to conform to the curvature and slope of the inside surface of the roller cone bearing. The pre-shaping o~
the diamond layer to as near the required shape as possible, as opposed to starting with flat or other nonconforming shapes, has been found to be important for three reasons. First, polycrystalline diamond is extremely wear resistant. Accordingly, it would re-quire large amounts of time and effort to grind or cutthe polycrystalline diamond to fit the final shape.
Second, because the polycrystalline diamond is a relatively brittle material, it is important that before the polycrystalline inserts are allowed to wear against each other, they present smooth surfaces. In other words, if the polycrystalline diamond pieces ex-perience point to point contact, they would be likely to chip or crack. As a result, it is important to have the polycrystalline diamond pieces conforming to the curvature and slope of the bearing interface before use.
Third, the inventor has discovered that the final finishing of the polycrystalline diamond surfaces can be accomplished by simply running the two bearings against each other at high speeds and at high loads.
This simplification of the finishing process would not ba possible if the polycrystalline diamond surfaces were not already close to their final shapes.
In addition to the preferred method of using PCD inserts set into frusto-conical base members, there exist alternative methods of forming PCD bearing surfaces with the frusto-conical shape of the present invention. Theoretically, it would be desirable to produce a bearing for the present invention with a single piece of PCD, with or without a carbide backing, which could be used for the journal or roller cone bearing. However, using present high pressure technology, it is not possible to produce pieces of PCD
of a sufficient size.
A feasible alternative is to produce several PCD segments or "tiles" which could be fit together to ~ ~9;;~

produce contiguous surfaces of PCD for the bearings of the invention. These tiles could be used to cover the entire frusto-conical surfaces, or alternatively could be arranged in annular rows or other configurations which would provide sufficient mating PCD s~lrfaces to support the loads between the roller cone and journal while facilitating rotation of the roller cone about the iournal.
Another alternative method for forming the PCD bearing surfaces of the present invention is to use PCD in a high concentration matrix. In particular, it is possible to fill a mass of PCD chunks or grit with a suitable metal or the like to produce a unitary piece which possesses properties similar to a piece of solid PCD. One advantage is that this high concentration matrix PCD can be produced in much larger pieces than is possible with solid PCD. Accordingly, a single piece PCD bearing surface could be produced.
Yet another alternative for forming the PCD
bearing surface would involve coating base member with PCD. That is, it is possible to coat a iournal bearing base member or a roller cone bearing base member with a layer of PCD through such techniques as flame spraying, electroless plating, etc. In this way, PCD surfaces can be applied to the bearings of the invention.
Although these other alternatives for incor-porating the PCD into the journal and roller cone bear-ings are available, it is noted that the preferred em-bodiment, i.e., pre-shaped PCD inserts held in frusto-conical bases, has exhibited certain surprising andimportant advantages. Naturally, in light of its rela-tively high cost of production, it is economical to use only as much PCD as necessary. It was thought however, that a contiguous PCD surface would be required to pro-vide sufficient smoothness for rotation and load carry-ing capability. Surprisingly, the bearing constructed accordin~ to the preferred embodiment has exhibited ~~ ' remarkable smoothness in rotation and load carrying ~c capability. A further advantage of using discrete P~D
inserts in the bearing is that it allows for improve'a cooling and lubrication of the PCD surfaces. With th'e sligh~ protrusion from the base member, the drillin~' mud can flow around each insert 72. Also, because the PCD inserts do not present a contiguous surface, the~
drilling mud can pass directly over the bearing sur-faces.
Figure 5 shows an embodiment of the inventionwhich is identical to that depicted in Figure 2 except that the retaining bolt 93 in Figure 5 is threaded into the leg 34 as opposed to being threaded into the cone as in Figure 2. The head 98 of the bolt 93 contacts a thrust bearing 96 which mates with a thrust bearing 97 which contacts the bottom surface of a recess 106 in the roller cone 36. Being so attached, the retaining bolt 93 of this embodiment will not rotate with the~
cone 36. However, friction between the mating bearing surfaces on the thrust bearings 95 and 96 and the pit'ch of the threa~s 94 produce a self-tightening effect as with the embodiment depicted in Figure 2. Also, as with the embodiment of Figure 2, it is desirable to maintain the bolt 93 in tension so that the journal bearing 41 and the roller cone bearing 42 are constant-ly pushed against each other resulting in compression of the bearing surfaces.
In a further alternative embodiment not shown, the retaining bolt is made with threads on both ends. A pair of thrust bearings and a nut are fitted' on both ends. These thrust bearings could be planar as shown in Figure 2 and 5, frusto-conical, or other shapes which would produce the best result. The direc-tion and pitch of each set of threads is selected so a's to provide sel~-tightening on both ends. This embodi-ment may be desirable to reduce stress to the retaining bolt.
Although the discussion of the invention has S included only threaded bolts to retain the roller cone on the journal and to maintain compression between the roller cone and journal bearing surfaces, other embodi-ments exist. For example, pins which are welded and/or heat shrunk into place may be used to serve the same two functions. In addition, although the roller cones depicted all use cutting inserts to engage the mate-rial, it should be understood that the bearing system of the present invention is likewise suitable for other types of roller cones such as those which use steel teeth or annular ridges to engage and disintegrate material. Furthermore, although much of the discussion has focused on the use of polycrystalline diamond on the bearing surfaces, it is considered within the scope of the invention to use other materials for the bearing surfaces, such as polycrystalline cubic boron nitride, ceramic or cermet materials, which may perform suitably under these conditions. Certainly, these and other modifications which are within the ordinary skill in the art to make are considered to lie within the scope of the invention as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg;
a journal on each leg having a proximate portion which is adjacent to the leg and a distal portion which extends away from the leg;
a roller cone rotatably mounted on each journal;
a frusto-conically shaped main journal bearing surface on the distal portion of each journal;
a main roller cone bearing surface on each roller cone adapted to mate with the main journal bearing surface;
a cone retention bearing surface for each journal; and retention means for retaining the roller cone on each journal which means is attached to the cone and which has a bearing surface adapated to mate with the cone retention bearing surface on the journal;
wherein the main journal bearing surface, the main roller cone bearing surface, the cone retention bearing surface, and the retention means bearing surface each comprise polycrystalline diamond.

2. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg;
a journal on each leg having a proximate portion which is adjacent to the leg and a distal portion which extends away from the leg;
a roller cone rotatably mounted on each journal;
a frusto-conically shaped main journal bearing surface on the distal portion of each journal;
a main roller cone bearing surface on each roller cone adapted to mate with the main journal bearing surface;
a cone retention bearing surface on the proximate portion of each journal; and retention means for retaining the roller cone on each journal which means is attached to the cone and which has a bearing surface adapated to mate with the cone retention bearing surface on the journal;
wherein the main journal bearing surface, the main roller cone bearing surface, the cone retention bearing surface, and the retention means bearing surface each comprise polycrystalline diamond.

3. The roller cone rock bit of claim 2 wherein the cone retention bearing surface is frusto-conically shaped and arranged such that the diameter of the cone retention bearing surface becomes smaller moving toward the leg.

4. The roller cone rock bit of claim 3 wherein the frusto-conically shaped cone retention bearing surface is arranged so as to be generally perpendicular to the main journal bearing surface.

5. The roller cone rock bit of claim 2 wherein the retention means comprises a ring adapted to thread into the cone after the journal has been inserted therein.

6. The roller cone rock bit of claim 2 wherein each journal is formed integrally with each leg.

7. The roller cone rock bit of claim 6 wherein the retention means comprises at least two segments which together form a ring which is adapted to thread into the cone after the journal has been inserted therein.

8 . The roller cone rock bit of claim 2 wherein each journal is attached to each leg after having a cone mounted thereon.

9. The roller cone rock bit of claim 8 wherein each journal is attached to each leg by a bolt with a post passing through the leg and threading into the journal.

10. The roller cone rock bit of claim 8 wherein each journal has an attaching portion which is threaded into the leg.

11. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg;
a journal mounted on each leg and having a proximate portion which is adjacent to the leg and a distal portion which extends away from the leg;
a roller cone rotatably mounted on each journal;
a frusto-conically shaped main journal bearing surface comprising inserts with polycrystalline diamond bearing surfaces inserted in holes in the distal portion of each journal;
a main roller cone bearing surface on each roller cone adapted to mate with the main journal bearing surface and comprising inserts with polycrystalline diamond bearing surfaces;
a frusto-conically shaped cone retention bearing surface on the proximate portion of each journal which is arranged such that the diameter of the cone retention bearing surface becomes smaller moving toward the leg, the cone retention bearing surface comprising inserts with polycrystalline diamond bearing surfaces;
and a retention ring for retaining the roller cone on each journal which ring is threaded into each cone and which has a bearing surface adapted to mate with the cone retention bearing surface on the journal and which comprises inserts with polycrystalline diamond bearing surfaces.

12. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg, said leg having a journal thereon, said journal having a frusto-conically shaped main journal bearing surface which comprises polycrystalline diamond;
a roller cone rotatively mounted on each journal, said roller cone having a main roller cone bearing surface which mates with the main journal bearing surface and which comprises polycrystalline diamond; and means for maintaining the two bearing surfaces in a state of compression against each other.

13. A roller cone rock bit as in claim 12, wherein said compression means comprises a pin which rotates within the journal, said pin having a first end attached to the roller cone, and a second end including a bearing which mates with a bearing on the leg.

14. A roller cone rock bit as in claim 13, wherein the first end of the pin is threadably attached within the roller cone.

15. A roller cone rock bit as in claim 14 wherein the bearing of the second end of the pin comprises a first thrust washer with a bearing surface, and the bearing on the leg comprises a second thrust washer with a bearing surface, said first and second thrust washer bearing surfaces mating and being maintained in compression against each other.

16. A roller cone rock bit as in claim 12, wherein said retaining means comprises a pin about which the roller cone rotates, and has a first end attached to the journal, and a second end including a bearing which mates with a second bearing surface on the roller cone.

17. A roller cone rock bit as in claim 16, wherein the first end of the pin is threadably attached within the journal.

18. A roller cone rock bit as in claim 17 wherein the bearing of the second end of the pin comprises a first thrust washer with a bearing surface, and the second bearing on the roller cone comprises a second thrust washer with a bearing surface, said first and second thrust washer bearing surfaces mating and being maintained in compression against each other.

19. A roller cone rock bit as in claim 12 further comprising means for passing a stream of drilling fluid over the journal and roller cone bearing surfaces.

20. A roller cone rock bit as in claim 19 wherein the means for passing a stream of drilling fluid over the journal and roller cone bearing surfaces comprises a passage through the bit which communicates at one end with a source of drilling fluid from a drill string and communicates at another end with said journal and roller cone bearings, and an exit passage.

21. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg, each leg having a journal thereon, said journal having a journal bearing with a substantially frusto-conically bearing surface comprising polycrystalline diamond;
a roller cone rotatably mounted on the journal, the roller cone having a roller cone bearing with a surface comprised of polycrystalline diamond which mates with the substantially frusto-conically shaped bearing surface of the journal bearing;
said journal defining a hole which includes the axis of rotation of the roller cone;

a bolt which passes through said hole in the journal and has a first end which is threadably attached to the roller cone, and has a second enlarged end positioned outside of said hole;
a first thrust bearing which is adjacent to said enlarged end and through which said bolt passes said first thrust bearing having a first thrust bearing surface;
a second thrust bearing which is adjacent to said leg and through which said bolt passes, said second thrust bearing having a second thrust bearing surface which mates with said first thrust bearing surface; and said bolt being maintained in tension so as to place said journal bearing and roller cone bearing in compression against each other, and to place said first and second thrust bearing surfaces in compression against each other.

22. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg, each leg having a journal thereon, said journal having a journal bearing with a substantially frusto-conically shaped bearing surface comprising polycrystalline diamond;
a roller cone rotatably mounted on the journal, the roller cone having a roller cone bearing with a bearing surface comprised of polycrystalline diamond which mates with the sub-stantially frusto-conically shaped bearing surface of the journal bearing, said roller cone defining a hole which includes the axis of rotation of the roller cone;
a bolt which passes through said hole in the roller cone and has a first end which is threadably attached to the journal, and has a second enlarged and positioned outside of said hole;
a first thrust bearing which is adjacent to said enlarged end and through which said bolt passes said first thrust bearing having a first thrust bearing surface;
a second thrust bearing which is adjacent to said roller cone and through which said bolt passes, said second thrust bearing having a second thrust bearing surface which mates with said first thrust bearing surface; and said bolt being maintained in tension so as to place said journal bearing and roller cone bearing in compression against each other, and to place said first and second thrust bearing surfaces in compression against each other.

23. A roller cone rock bit comprising:
a main bit body with at least one downwardly extending leg, each leg having a journal thereon, said journal having a journal bearing with a substantially frusto-cOonically shaped bearing surface comprising polycrystalline diamond;
a roller cone rotatably mounted on the journal, the roller cone having a roller cone bearing with a bearing surface comprised of polycrystalline diamond which mates with the substantially frusto-conically shaped bearing surface of the journal bearing, said roller cone defining a hole which includes the axis of rotation of the roller cone;
said journal defining a hole which includes the axis of rotation of the roller cone;
a bolt which passes through said hole in the journal and said hole in the roller cone, said bolt having a first end with a first nut threaded thereon and a second end with a second nut threaded thereon;
a first set of thrust bearings through which the first end of the bolt passes and which are positioned between said first nut and the leg;
a second set of thrust bearings through which the second end of the bolt passes and which are positioned between the second nut and the roller cone; and said first and second nuts being sufficiently tightened to place said bolt in tension, thereby placing said journal bear-ing and roller cone bearing in compression against each other.

24. A roller cone rock bit as in claims 21, 22 or 23 wherein said bolt is self-tightening during drilling.

25. A roller cone rock bit as in claims 21, 22 or 23 further comprising means for passing a stream of drilling fluid over the journal and roller cone bearing surfaces.

26. A roller cone rock bit as in claims 12, 15 or 18 wherein said frusto-conical journal bearing is comprised of a base member with a frusto-conically shaped outer surface, and a plurality of polycrystalline diamond inserts which are held in place by said base member.

27. A roller cone rock bit as in claims 21, 22 or 23 wherein said frusto-conical journal bearing is comprised of a base member with a frusto-conically shaped outer surface, and a plurality of polycrystalline diamond inserts which are held in place by said base member.

28. A roller cone rock bit as in claim 26, wherein said polycrystalline diamond inserts comprise a polycrystalline diamond portion directly bonded to a backing of a cemnened carbide.

29. A roller cone rock bit as in claim 27, wherein said polycrystalline diamond inserts comprise a polycrystalline diamond portion directly bonded to a backing of a cemened carbide.

30. A roller cone rock bit as in claim 26, wherein said polycrystalline diamond inserts are molded to a shape substantially conforming to the slope and curvature of the frusto-conically shaped journal bearing.

31. A roller cone rock bit as in claim 27, wherein said polycrystalline diamond inserts are molded to a shape substantially conforming to the slope and curvature of the frusto-conically shaped journal bearing.

32. The roller cone rock bit of claim 12 wherein the main journal bearing surface comprises a plurality of inserts each having a bearing surface comprised of polycrystalline diamond and wherein each insert is set into holes formed in the journal.

33. The roller cone rock bit of claim 12 wherein the main roller cone bearing surface comprises a plurality of inserts each having a bearing surface comprised of polycrystalline diamond and wherein each insert is set into holes formed in the roller cone.

34. The roller cone rock bit of claim 12 wherein the main roller cone bearing surface comprises a plurality of inserts each having a bearing surface comprised of polycrystalline diamond and wherein each insert is held in place by a frusto-conically shaped shell with holes to receive said inserts.