CA1171072A - Rock bit - Google Patents

Abstract

IMPROVED ROCK BIT
Abstract of the Invention A rotary cutting member of a rock bit is journaled on an axle portion of the bit body and provides a cavity between the axle portion and cutting member in which there are disposed a plurality of bearing elements for rotatably supporting the loads of the cutting member on the axle portion. A pressurized fluid passageway extends through the bit body to the cavity for transmitting bearing conditioning fluid to the bearings. At least one annular array of bearing elements is encased and supported in a ring of semi rigid porous, permeable plastic material having bearing lubricant in the pores and forming the bearing cage. The cage and encased bearing elements fill the radial distance of the cavity to initially substantially block delivery of bearing conditioning fluid through the cavity. Under bit operating conditions the plastic material is generally expelled from the cavity thereby opening the cavity to the pressurized bearing conditioning fluid from said fluid passageway,

Description

~ ~7 ~72 This invention relates generally to impro~ed rock bits. More particularly, but not by way of lirnitation, this invention relates to an improved rock bit that has a cutter member journaled to an axle with the load carrying bearing elements therebetween initially encapsulated in an expellable permeable porous plastic material that, during its presence, seals and lubricates the bearing elements and upon expulsion during use permits further bearing lubrication or conditioning from a source of pressur.ized fluid.

This application relates to applicant's own U.S.
Patent No. ,4,280,571, January 24, 1980. -Rock bits operate in extremely harsh en~ironments while dri.lling a borehole in search of oil or gas, and when drillin~.the ~oreh~le in wh~ch blasting charges are set for min,ing opera~ions. A borehole may contain a pressurized drilling mud which,is del~yered down the drill string and throu~h.the bit ,~or circulatin~ th.e cuttin~s out of the borehole as well as cooling the bit and, to some extent, ,proYiding lubricati~g fluid to the bit or proyiding a pres- i sure to a sealed lubricant reservoir within th.e bit. Alter- ~
natively, pressurized air, although there is usually some .
water present, may be ~irculated through internal passages ,in the.bi.t to the load b.earing elements between the journal axle and the rotatafile cutter to cool or lu~ricate or other-wise condition, the bearing elements ! and also 1' mab/~

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through jetting ports in the bit to remove the cuttings from the borehole. Also, the bits are subjected to thousands of pounds of force exerted thereon to force the cutting structure to disintegrate very hard formations as the drill bit is rotated in the borehole.
It is highly desirable, of course, to make the drill bit last as long as possible and to cut as much borehole as possible, without having to remove the bi-t from the drilling string and place a new one thereon. In order to achieve this longer life, cutting structures have been improved, the materials forming the drill bit have been improved, and all types of improvements have been attempted and made to the load bearing structure itself. ~nong these, there has been proposed and used a sealed reservoir of lubricant in the bit arm which is connected to the bearing cavity between the cutter member and the journal axle through passageways in the axle and having a pressure responsive member forming some por~ion thereof. Thus, due to the pressure of the environment, the lubricant is continuously urged into the bearing cavity to replenish that which escapes therefrom. In such circumstances, the cavity containing the bearings must be sealed from the ex-ternal environment and leakage of the seals can seriously affect the lubricating system. Also, it ls difficult to provide a sufficiently large reservoir to supply enough lubrication to last for the desired period of time.
As previously stated, some of the bits used in drilling blast holes for mining, have been.provided with pressurized air passages in the axle that circulate air, which is pumped down the drill string and into the bit, into the load bearing structure and outwardly therefrom to cool the bearings and prevent cuttings from getting into the bearing cavity. In such environment it is particularly important that air flow therethrough be continuously maintained as such pressurized air prevents ingress into the bearing cavity of the detritus and also provides a flowing coolant to prevent the bearing elements from overheating.
The only lubrication provided is that which has been initially packed around the bearing elements which is primarily a tacky axle grease that maintains the bearing ele-ments in proper disposition during assembly of the bit as such lubricant is blown out of the cavity relatively soon after the pressurized air is circulated therethrough.
The object of this invention then is to provide a rotary rock bit having an improved bearing lubrication and seal in the bearing cavity that will extend the operating life of the bit.
. Accoridng to one aspect of the present invention there is provided an improved rotary drill bit including a bit body, an axle on the body, a cutter rotatably journaled on the axle and defining with the axle an outer and inner bearing race respectively, and an annular array of load bearing elements positioned between the axle and cutter at the bearing races. The bit includes means for supporting the beari~n.g element$ in the annular array.including a semi-solid porous plastic ~el composed of lubricatin~ oil and plastic polymer ~ith binder ~ibers generally dispersed throughout to provi~de a flexible, lu~ricating bearin~ cage, The bearing assembly is dis~osed against one of the bearing races prior to the çutter beln~ as,~,e~bled on the a~le~
According to another.aspect of the invention, the rotary rock bit assem,bly includes.a bit body arranged to be connected in a dri:ll s,tring and has an axle portion on the ~ody with. a cutter means journaled Oll the axle port~on and an annula,r ~:ea,~in~:caVity ~etween the axle portion and the cutting ~ea,xing mem,ber~ ~earing m,eans is dis~osed in the cav,ity for su~pox~ing the load o~ the cuttin~ me~ber~ and the body and a,xl,e po.rtion define pressurized fluid passage means terminating at the beairin~ caYity for transmitting bearin~ conditionin~
~lui:d to th.e bearin~ m,eans. A lubricant containin~ plasti:c material is interposed in the cayity and is between and in con-t,act with. the ~earing means and at least partially ~ills the bearin~ caYity to lubxicate the bearing means and substantially block the caYity f~om, the transmission of pressurized fluid therethrou,~h~ The ~aterial has binder fibers dispersed therein, .,.. ,~, .
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and the material is flexible and under bit operating conditions is gradually expelled from the cavity by the force of pressur-i~ed fluid to substantially permit bearing conditioning fluid flow through the cavity.
Brief Description of the Drawing _ .
The ~oregoin~ and additional objects and advantages of the invention will become more apparent as the following detailed description is read in conjunction with the accompany-i~ng drawing, wherein like reference characters denote like parts in all ~iews, and wherein.
Figure 1 is a pictorial view of a tricone rotary rock.hit;
Fîgure 2 is an enla~ged partial cross-section taken throu~h.one arm of the,bit in Figure 1 illustrating one aspect of the i`nvention;
Figure 3 is an iso~etric yiew Gf an annular array of bearing elements of the rock bit encapsulated in a ring of permeable plastic m"ateri~l exteriorly of the bearing cavi-ty;
and~
~igure 4 is a y,iew similar to Figure 2 showing the .bit asse~bled with:the roIler bearings encapsulated in the plastic material.
Detail'ed Descrip'tion'o'f 'the Prefer~'ed'Embodiment Referring to ~he drawing and Figure 1 in particular, shown there~in~, and ~enerally des~nated by the refe~ence cha,racter 10~, is a bi't cons~tructed in accordance with the in venti~Pn. T~e particular fiit ;llustrated is a tricone rotary xock bit used ~o~ drilling blast holes. The ~it includes a body 12 haying three arms 14 depending therefrom (only two can ~e seen in F~ure lI, and a pin portion 16 that is threaded at 18 for connecting the bit 10 into a drilling string (not shown), A rolling cuttmg ~ber 20 is located,o.n each of the arms 14 and is rotata~le relative t~ereto as will be described. Each.of the cutting n~mhers 20 is illustrated as including a plurali-ty of hard inserts 22, which.
~ay bel~e of tungsten carbide, distributed about the c,utting m~bers 20 to accomplish.the disint,e~ration of a formation.in a particular manner. me bit bcdy also includes a nozzle 24 that is located bet.ween each.of the arms 14 and is arran ed to direct air or wat dcwnwardly relatively between the :

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--s--cutter members 20 to clean the cutter memher 20 and to flush cuttings from the bore as it is drilled.
Referring to Figure 2, it can be seen therein that each cutting member 20 has a hollow interior definingn a mouth portion 29 and is mounted adjacent the arm on an axle portion 26 of each arm 14. The annular space betwe~n the exterior of the axle portion 26 and the hollow interior of the cutting member 20 defines a bearing cavity 27 that is configured to receive a plurality of annular arrays of bearings, roller bearings 28, and ball bearings 30, a pilot bushing 32, and a thrust button 34. The pilot bushing 32 encircles part of the axle portion 26 that is known as the pilot pin.
The axle porti~n 26 has a hole 36 drilled therethrough into the cavity 27 in which the ball bearings 30 are disposed. The passageway 36 is sized to receive the ball bearings 30 and is provided to permit the ball bearings 30 to be inserted in the appropriate bearing cavity after the rolling cutting member 20 has been placed on -the axle portion 26. After the ball bearings 30 have been inserted, a plug 38 is welded in the hole 36 to prevent the ball bearings 30 Erom coming out oE the bearing cavity 27, thereby r~taining the cutter on the axle.
As illustrated in Figure 2, the plug 38 includes a reduced diameter center portion 40 for reasons that will be explained. After the plug 38 is in place, the outer end of the opening 36 is plugged with weld as illustrated at 42.
Each bit arm 14 has a pressurized fluid passageway 44 formed therein that extenas from the interior of the bit body 12 to the hole 36 adjacent the reduced diameter portion 40 of the plug 38. In this e~bodiment the passageway 44, the hole 36, Eluid passages or ports 46, 48 and 50, each of which extends from the openings 36 to a respective bearing area of the axle portion 26, completes the usual air cooling system of the bit for delivering pressurized conditioning air to the bearings.
In the improved bit of the instant invention the opening 36 around the reduced diameter portion 40 of the plug 38, the ports 46 and 48 are filled with a permeable 7 ~

material that has a lubricant in the pores of the material.
It will also be noted and as illustrated at 52, that the permeable material fills the spaces between the roller bearings 2~ and between the cutter member 22 and the arm 14. Similarly, and as can he seen at 54, the bearing cavity 27 is also filled with the permeable material virtually encapsulating the ball bearings 30. Since the permeable material can be poured or injected into the bit lO, the material infiltrates virtually all of the openings or cavities that are formed between the cutter member 20 the axle portion 26 and the load carrying bearing, and after setting to its gelatinous condition, seals the cavity 27 from external cuttings entering the cavity at the cutter mouth 29 and also plugs the passage 44 against the passage of any conditioning fluid.
In addition to the material into the passages and cavity as above described, it is also contemplated by the invention to sncapsulate the bearing elements, such as roller bearings 28, in the plastic material prior to assembly of the components with sufficient material to fill the correspo~ing portion of the bearing cavity 27 when assembled and with the plastic material, after setting, providing a cage support for the bearing elements.
In this regard, reference is now made to Figures 3 and ~. As therein seen, an annular array of the roller bearings 28 is encapsulated in an annular ring 56 of the porous permeable plastic material externally of the bearing cavity 27, such as by depositing the bearings in an appropriately sized mold and injection molding or casting the permeable material thereinto and permi-tting it to set.
The ring 56 i6 then axially split along one side (as shown) so it can be opened (by bending or flexing the plastic material) to permit it to be slipped over the corresponding axial portion of the axle 26 or alternatively assembled within the mouth portion 29 of the hollow interior of the cutting member 20, prior to the cutting member assembled on the axle portion 26. However, in that the roller bearings 28 are spaced quite closely together (in some instances they are abutting one another) the plastic ring 56 is given ., ~7~0~

additional structural support by the axially opposite ends thereof having short projections 58, 60 so that through these annular portions there is an uninterrupted plastic ring except for the split. Also, as the axial dimension of the plastic ring 56 is substantially the same as the axial dimension of the roller bearings 28 these projections 58, 60 maintain the roller bearings from being axially displaced or lost from the ring 56 during shipping and handling of the rings which provide the cage for such bearings. The axle 26 is undercut as at 62 to accommodate the annular projection 58 and the cone is undercut as at 63 to accommodate annular rib 60.
It will also be noted that in the pre~erred embodiment of Figures 3 and 4 wherein only one annular array of bearing elements is encapsulated, it is the bearing row closest to the mouth 29 of the cone cutter 20 so that the plastic material can act as a seal against the ingress of external cuttings into the bearing cavity 27. Further it is to be understood that the dimensions of the ring 56 and bearings 28 encapsulated therein corresponds substantially to the dimension of the portion of the cavity 27 receiving the encapsulated bearings so that at least this portion of the cavity 27 is substantially full to initially block the flow of conditioning fluid (which may be air or lubricant) through the cavity 27.
In that the conditioning fluid is blocked Erom flow and only one annular array of multiple annularbearing arrays is encapsulated, it is necessary to provide a lubricant to the other bearings (30, 32, 34) in the cavity 27 that has a high quality lubricity capable of operation under the conditions. Thus, the remaining portion of cavity 27 is lubricated with a lubricant such as a high extra-pressure mineral oil blend lubricant previously used in sealed rock bit lubrication systems.
The porous permeable plastic material utilized is clearly described in U. S. Patents 3,541,011 issued November 17, 1970 to William J. Davis et al and 3,547,819 issued December 15, 1970 also to William J. Davis et al. As described therein, the permeable material is a gel formed by ", nixing a lubricating oil with either high molecular weight polyethylene or low molecular weight polyethylene or a combination thereof in certain ratios, and elevating the temperature to specified range. Some of the gels are virtually l:iquid while some are very rigid. For use in the bit 10, it is preEerred that the gel be composed of a mixture o the high molecular weight polymers, and low molecular weight polymers and a sa-tisEactory lubrlcant with a sufficient quantity of the low molecular weight polymers being utilized so that the resulting material will, under the temperature and pressure to which it is exposed during drllling operations, be gradually expelled from the cavity 27. Thus, due to the temperature of ~he bit and pressure on the conditioning fluid within the bit which is transmitted to the plastic material in the cavity, the material will eventually be extruded out of the bearing cavity 27 which will then be lubricated and/or cooled by the flow of the pressurized conditioning fluid such as lubricant or air therethrough.
An annular molded or cast ring of the roller bearings 28 caged in a suitable permeable plastic material is presently co~nerically available from a licensee under the above patents (SKF Industries Inc., King of Prussia, PA
19406). This plastic material is sold under the registered trademakr POLY-OIL of General Polymeric Corporation, Reading, PA. Initially, a composition of such material comprising approximat.ely 73% by weight of a synthetic base lubricant and 26% by weight of polyethylene encasing the annular roller bearing array forming a bearing and cage assembly was supplied the corporate assignee o the present invention ~or assembly in a blast hole bit as described with reerence to Figures 3 and 4. Later, the material composition was changed to comprise approximately 65% by weight of a synthetic gear oil as the lubricant, 29~ by weight o a polyethylene, and 5% by weight of molydisul~ide a~ an added solid lubricant. The bearing life of rotary bits with either of the above material~ encapsulating -the rollers with pressurized air supplied therethrough after the plastic material was extruded was substantially increased 7 ~
g over the life of the bearing in ~imilar bits that were solely conditioned by flowing pressurized air.
However, it is also within the scope of the present invention to increase the effective strength and toughness (ductility) of the plastic material withou-t otherwise affecting the ability of the plastic material to provide the permeable porous lubricating capability . This is accomplished by adding fiberous reinforcing such as fibers of carbon, glass, boron or other compatible binder ibers. Thus, such a composition would include a liquid lubricant comprising between 50% to 65% by weight of the composition, a solid lubricant (i.e. MoS2) comprising 5~ by weight, a polyethylene comprising between 15~ to 30% by weight, and fibers comprising 4% to 20% by weight of the compo~ition.
Such fibers could be included in the composition of the material that is injected into the bit passages or prior to being cast or molded within the final set material to provide a stronger, high precision cage for the bearings. In this environment the fibers shouid be on the order of between 0.10 to 0.40 inches in length and 0.002 to 0.02 inches in diameter.
With the thus composed plastic materials encapsulating a bearing row within a rock bit, it is possible to provide a considerably extended operating life to the bit 10, since the permeable plastic material with its lubricant will ~eal the bit against the intrusion of deleterious material, trap metal debris generated during bearing break-in and operation and at the same time, provide in situ lubrication until the lubrication in the permeable material has been expended and/or the material expelled from the cavity. When this occurs, the bit is then in Yubstantially the same condition that it would have been had the permeable material not been placed in the bit to start with. Thus, an additional operating period for the bit is provided.
It will, of course, be understood that although an air-cooled blast hole bit has been described as the preferred embodiment, the permeable material used in ~ h~

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lubricating the bearings can be utiliæed in virtually any type of rock bit, and thus, this invention should not be limited to the specific embodiment described.
Having described but a single embodiment of the invention, it will of course be understood that many changes and modifications can be made thereto, without departing from the spirit of the invention.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS

1. An improved rotary drill bit comprising, a bit body, an axle on said body, a cutter rotatably journaled on said axle and defining with said axle an outer and inner bearing race respectively, and, an annular array of load bearing elements positioned between said axle and cutter at said bearing races, wherein the improvement comprises:
means for supporting said bearing elements in said annular array comprising a semi-solid porous plastic gel composed of lubricating oil and plastic polymer with binder fibers generally dispersed throughout to provide a flexible, lubricating bearing cage; and wherein, said bearing assembly is disposed against one of said bearing races prior to said cutter being assembled on said axle.

2. A drill bit according to claim 1 wherein said plastic gel forming said cage further includes a solid lubri-cant randomly dispersed throughout.

3. A drill bit according to claim 2 wherein said polymer, oil, fibers and solid lubricant are present in the approximate range of weight ratios of:
50.% to 6.5% oil, 15% to .30.% polymer, 4%. to 20.% fibers and 5% solid lubricant.

4. An improved rotary rock bit assembly comprising a bit body arranged to be connected in a drill string, an axle portion, on said body, a cutter member journaled on said axle portion, an annular bearing cavity between said axle portion and said cutting member, bearing means disposed in said cavity for supporting the load of the cutting member, said body and axle portion defining pressurized fluid passage means terminating at said bearing cavity for transmitting bearing conditioning fluid to said bearing means, wherein said improvement comprises:

a lubricant containing plastic material interposed in said cavity and between and in contact with said bearing means and at least partially filling said bearing cavity to lubricate said bearing means and substantially blocking said cavity from the transmission of pressurized fluid there-through;
said material having binder fibers dispersed therein, wherein said material is flexible and under bit operating conditions is gradually expelled from said cavity by the force of pressurized fluid to subsequently permit bearing conditioning fluid flow through said cavity.

5. Bearing structure according to claim 4 wherein said lubricant containing plastic material defines a cage for said bearing means with said cage and bearing means dis-posed on said axle portion or within said cutter prior to said cutter member being assembled thereto.