CA1157463A

CA1157463A - Floating seal for earth boring bit

Info

Publication number: CA1157463A
Application number: CA000390789A
Authority: CA
Inventors: Anton F. Zahradnik
Original assignee: Hughes Tool Co
Current assignee: Hughes Tool Co
Priority date: 1981-05-11
Filing date: 1981-11-24
Publication date: 1983-11-22
Also published as: ZA823026B; JPS57193691A; GB2098284B; GB2098284A; SE8202908L

Abstract

ABSTRACT OF THE DISCLOSURE

An earth boring bit has a bearing seal that floats to accommodate angular and axial movement of the cutter with respect to the shaft. The seal is located in an annular groove formed in the shaft. A supporting ring is located in the groove. The supporting ring has an in-ner diameter larger than the inner diameter of the groove to provide a clearance for allowing the supporting ring to float. An elastomeric ring is located on the outer circumference of the supporting ring. The supporting ring presses the elastomeric ring into sealing contact with the cutter. The elastomeric ring is also pressed on its sides to provide sealing.

Description

~5'7~3 B~CKGROUND OF TIIE INVF,~lTION
___ This invention relates in general to earth boring bits, and in particular to a bearincJ seal for earth boring bits.
This inven-tion concerns particularLy the type o~
earth borincJ bit tha-t employs -three rotatable cutters mounted on de~encling bear~nc~ shaE-ts. ~ach conical cut-ter rotatcs on its bcarin~ shaEt as the drill bit is rotated. The cutter las teeth of tun~sten carbicle in-serts on its exterior for disintegrating th~ ear~h. The bearings are usually either a journal type, or they may employ roller hearings. ~rhe bearings are supplied with lubricant and sealed by an elastomeric seal located in a groove formed in the bearing shaft at its base.
Because o~ tolerances, particular]y with the roll-er bearing type bearin~s, the cutter will have radial, axial and an~ular movements relative to the bearin~
shaft. The seal, which usually is in sliding contact with the c~ltter, wi11 experience var~ing degrees of pres-sure because of this movernent, tending to cause leakacle.
There have been several proposals in the past to provide a floatincJ seal that is able to move ra(lially to accommo-date the cutter rnovement.

. ~ :

1157~63 SUMMI~RY OY T~IE INVENTION

This invention provides an improved Eloating seal for the bearings of an earth boring bit. In the preferred em-bodiment, a groove for the seal is ~ormed in the shaft near its intersection with the head section. ~ suppor-~ing ring is located in this annular groove. PreEerably, the supporting riny is a split ring tha~ can be expanded for installation, however, has a minimum diameter. rrhe mini-mum diameter is greater than the inner diameter of the groove, providing an annular clearance on the inside of the supporting ring to allow it to float.
~ n elastomeric ring is located on the outer circum-ference of the supporting ring, and preferably is an O
ring. The supporting ring urges the elastomeric rin~ into sealing and sliding contact with the cutter. Means are provided to prevent the O-ring from moving along the axis of the shaft and for providing sealing against the sides of the O-ring. In the preferred embodiment, ~his consists o~ a backup ring, which squeezes the O-ring agains-t 1,he sides of the groove and also protects the O-ring from cut-tlngs.
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,, ~ ~ , -, 1 1 5'74B3 RIEF DESCRIPTION F_THE DR~WINGS

Fig. 1 is a par-tial vertical sectional vie~w of an earth boring bit constructed in accordance with this in-vention.
Fig. 2 is an enlarge~ vertical sect.ional view of part o the bearing seal of the earth boring bit of Fig. 1.
Fig. 3 is a sectional view of t}le earth boring bit of Fig. 1, taken along the line III-III of FicJ. 1.

' ~ :l5'~163 SCRl:l"L`:lON ~ 1'EI~ ;O E~ML~ODlML~
_ _____ __ __ .
Fig. 1 illustrates an earth borincJ bit ll particular~
ly constructecl for drilling blast ho],es for minincJ. I'arth borinc~ bit 11 has three heacl sections 13 (only one sho~n), which are subsecluently welded together. Each heacl sec-tion 13 has a depe~ndi~J bearillcJ pin or shaEt lS. ~n annular groove 17 is formecl in shat 15 at its intersection with head section 13. Groove 17 is rcctangular in transverLie cross-section, as shown in Fic~. 1, Witil a depth about the same as its width. Groove 17 is formed normal to -the axis of shaft 15.
Referrinc~ to Fig~ 2, groove 17 has a cylinclrical base or inner diameter 19, and inner and outer sidewalls 21 and 22 tha-t are parallel with each other and normal to base 19.
A supporting ring 23 is placed inside groove 17 during as-sembly. Supporting ring 23 is preferably metal, ancl is cut into at a single point 25, as shown in Fig. 3, for installa-tion. Although supporting ring 23 is stif, the separation at point 25 enables ring 23 to be expanded for inser-tion over shaft 15. Once over groove 17, the resiliency oE rinc,~
23 will cause the ends of support ring 23 at point 25 to close toyether as shown in Fig. 3. ~fter installation, the ends of ring 23 could be tack welded back together, if de-sired. Once installedl ring 23 will be incontac-tlble, de-fin:ing a rninimum diameter oE rincJ 23. ~ing 23 is cylinelrical ~nd has a width that is slightly less than the wiclth of <~roove 17 to allow it to rnove radially in groove 17. The inner dia-meter of ring 23, when at its minimum ~iameter position shown in Fig. 3, is c~rcater -than the diametcr of base 1~ by about 1/16 inch. This results in an empty annular space or clear-ancc between ring 23 and base 19 Eor allowinc~ ring 23 to float or move radially ~/ith respect to shaft ].5. The outer diarlleter of ring 23 is less than the outer cliameter o groove 17 de~ining an annular cavity i.n groove 17 on the outer cir-cumference oE rincJ 23~
A backup ring 27, preferably of an elastomeric rnater-ial, is located in groove 17, with its inner circumEerence in ~ 157~3 contact wi.th thc~ outer ci.rculnerence oE rinc~ ~3~ tiaclcup rincJ 27 is rectanc~ular in cross-section and haS a cross-sectional width thcl~ is about one third the width of c3roove 17. l~he cross-sectional heic3ht of backup ring 27 is selected so that its outer circu:mFerence cxtends above groove l7.
Sidewall 21, supportincJ rinc~ 23 ancl backup rinc3 27 clefine an annular space Eor .receiving an elastomeric rincJ, preferably a conventional O-rincJ 29. O-rinc~ 29 is circular i.n transvers~ cross-sec-tion, as shown in Fi(~. 2.
The transverse cross-sectional diameter of O-rinc3 29 is slightly greater than the cross-sectional width oE ~he annular space provided be-twcerl backup ring 27 and sicle-wall 21, to provide sealincJ and prevent axial movement of O-rinc3 29. The outer diameter of O-riny 29 is select ed so that it will extencl above the top of ~roove 17 a selected amount~ The inner diameter of O-ring 29 is the same as the outer diameter o supportin~ ring 23. In the preferred embodiment, O-ring 29 is softer than bac~-up ring 27, ~referah1y ahout 90 durometer Eor backup rin~J27 and 70--~0 durometer for O-ring 29.
ReerrincJ aga.in to Fig. l, a cutter 31 of clenerall.y conical confic~uration i.s rnoun~ed ro~ata~ly on shaft 15.
Cutter 31. has a ~:lura:li.ty oE cutt.incJ ~lements, 5uch as sintered tunc3sten c,arbide inserts 33 on its exterior.
Cutter 33 has a central, axial cavi.ty 35 that receives shaft 15. An annular backface 37 surrounds ~he entrance to cavity 35. nackface 37 is located in a plane ~hat is normal to -the ~IY~i'i of bcaring pi.n 15.
In the cmbodiment shown i.n Fig. 1, a nose bu~ton 39 i~ moun~ecl in ~he l~ase oE cavit~ 35 for frictioncll con~
tact ~ith a matincJ inlay 40 mounted to the end o~ the shaft 15. Nose button 3g and in]ay ~1 a.re o~ harder metal than shaft 15 and cutter 31. A slot 41 formed in inlay 40 leads from the center to the side o~ inlay ~0.

~ ~5'~'163 l~ plu~a]i~y oE rvllel bear:ings 43, each c~lindric~l :in shape, are mo-lnted be-tween a reduced d:iarneter p~L-tion of shaft 15 and cavity 35. A second and lar~er diame-ter set of roller bearings 45 are moun~ed between cavi-ty 35 and shaft 15 immediately inward from groove 17. Cutter 31 is re-tained on sha-Et 15 by a snap ring 47 located be-tween -the roller ~earings 43 and 45. Snap ring 47 fits within mating grooves of cutter 31 and shaf-t 15, as taught in U.S. Patent No. 4,236,764, issued -to 1~dward M. Galle on December 2, 1980, all oE which material is incorporated by reference. Cutter 31 has a smooth, cv-lindrical seat 49 formed in cavi-ty 35 between roller bearings 45 and backface 37.
As shown in Fig. 2, O-ring 29 is sclueezed between lS seat 4~ and the incontractible supporting ring 23.
O~ring 29 will also be under some axial pressure or s~ueeze between backup ring 27 and groove 21. sac]cup ring 27 wiLl be in contact with seat 49, but not under any significant radlal compression. rrhe particular a- .
mount of radial and axial squeezc is selcctecl so as to provide adequate radial sealing between O-rincJ 29 and cutter seat ~9, and axial sealiny between O-ring 29, groove 17 and backup ring 27. The squeeze, which is the percent of deformation with respect to transverse cross sectional dimension in the relaxecl condition, should be as low as possible to avoid excessive friction and heat.
A pressure differen-tial of about 50-60 psi ~pounds per square inch) across O-ring 29 between cavity 35 and the bit exterior, and a temperature of about 200F (~hr.en-heit) rnaxitnum ~lre cxpected. rrhe squeeze calculations must consider that under this maximum ternperature O-rinfJ
29 ~till volumetrically e~.pand about six percent Alsv, preferably the squeez~ is less than with prior art, O-ring seals used in drill hits, such as tau~ht in U.S.
35 l'atent No. 3,397,928, which is currently about 17 percent.
The desired range of squeeze is calculated in a con-ventional manner, taking into consideration manufac~urincJ

tolerances. In one embodiment the radial squeeze is in the range from 9.6 to 10.2 percent, and -the axial squee~e is ~3 to 6 percent bcfore assembly. After assembly, the a~ial squeeze will incre.lse since the raclial in~erfeLence will deform O-ring 2~, prcssing its sides outwarcl.
rrhe embodiment o~ Ficl. 1 has a c~lindrical reservoir S1 sealed from ~he exterior by a cap r~3 retained in place by a retaining r:incJ 55. ~ piston 57 is slidahly and re--ciprocally carried inside reservoir Sl. Piston S7 is sealed in reservoir 51 by an O-rinc3 59~ Piston 57 has a cavity ox socket 61 on its upper side that mates witll a socket 63 formed in cap 53. A coil spring 65 fits with-in sockets 61 and 63 and urges piston 57 downward. Spring 65 is shown comE~ressed in ~iCJ. 1 and has the capacity to push piston 57 cdownward into contact with the base of res-ervoir 51.
A lubricant passage ~7 extends downward throucJh head section 13 from the ~ase of reservoir 51. Another lubri-cant passage 69 is iocated paralle1 with the axis o shaft 15 and extends from the bo-t~om oE passaye 67 to the end of shaft lS ancl thr.ough the inlay ~0. ~n entrance port 71 ex-tends from the exterior of head section 13 to passa~e 67 for introducing lubricant into the reservoir 51. Entrance port 71 i5 sealed by a removable plucJ 73.
To assemble bit 11, supportinc3 rincJ 23 will be slipp-ed over sha~t 15 and inserted into yroove 17. Backup riny ~7 will be placed in groove 17 agains~ outer sidewall 22.
Then, O-rinq 29 will be clrawn over sha~t 15 and inserted into cJroove 17 between backup ring 27 and inner sidewall 21. Roller hea~inys 43 and ~5 will be placed in cavi~y 35 of cutter 31, and snap ring 47 will be placed in its ~Jroove ~ithin cutter cavit~ 35. Then -the cutter is pushecl over shaft 15 until snap rin~ 47 snaps into its matiny groove in shaft lS. C`utter backface 37 wil.l be 'located sli(Jhtly out-ward from yroove 17. The seat 4g in cutter cavity 35 will press and deform O-ring 29.
The three head sections 13 with assembled cu~ters 31 are then welded to~ether. Threads (not shown) are then 1 ;l5'7~183 _9_ mach:i.ned on the top of the bi-t for securing to dri:ll p:ipe.
Piston 57 .is placed in reservoi.r 51. Coil sprincJ 65 is placed on top of piston 57 ancl cap 53 is securecl in place.
Io fill with lu~-icaIl~ normal:Ly a vacu~lm will be drawn on the system through por-t 71. After th~ passages and spaces have been evacuatecl lubricant is in-troduced through port 71 filling reservoir 51 passacJes 67 69 and the spaces in cutter c:av.ity 35 }.ctwe~n roller bearinc3s ~3 roller bearings 45 and shaEt 15. Sorne lubrican~ will be removed h~fore runni.ncJ-to allow for volumetric expansion of th~
lubricant with temperature increase.
In operation ~he bi-t shown in the fiyures will be secured tv a section of drill pipe and used to drill ~last holes for mining purposes. ~ir will be puMped down the drill string and throucJh the bit ou-t nozzles (not shown) for coolin~ an~l removing cu~tings. The static pressure surrouncling bi-t 11 at the bottom of the hole will be a-t-mospIIeric. The bi.~ wil.l. be ro-ta-~ed with each cutter 31 rotating on each shaEt 15. Similar bits having similar seal arranc~ements rnay b~ used in oil gas water ancl other mi.neral exploration drilling and the drillinc3 fluid may be a liquid instead of air.
The outer circurnference of O-ring 29 will be in slid-ing contact with cutter seat 49. ~he pressure on the sides 25 of 0-rinc3 29 between sidewall 21 and backup riny 27 will normally prevent supporting riny 23 O-ring 29 and backup ring 27 from rotating with respect to shaft 15 although some rotation may occur. If 50, the inner side of O-rincJ
29 would be in sliding contact with groove inner wall 21 30 and backup rinc3 27 in sliding contact with outer wall 22.
Backup ring 27 w.i:Ll prcvent cuttin~Js frorn enterillcJ and con-tacting G-rinc3 29. ~s cutter 31 rota-tes supportinc3 ring 23 is ~rec to Inove radia].ly ~ .h respcct to the a:~is of shaft 15 t~ accommodate radial and angular movement of cut-ter 31 with respect to shaft 15. Ihis movement of support-.iny ring 23 allows O-riny 29 co stay in substantially the same amount of compression against seat 49 thus provid-iny an effective seal ac]ai.nst the entrance of external 1 ~ 5'7'~S3 -!0-materials ancl sea:linc3 the lu~ric.lnt.
Backup ring 21 cooperates with groove 17 ~o serve as means for pressincJ agains-t the sides of O--ring 29 ~or seal~
i.ng and to prevent movemen-t o O-ri.ng 29 along the a~:is o-f shaft 15. The backup riny 27 also helps prevent cuttings damaye -to O-ring ?.9. ~iston 57 will maintain cl posi-tive pressure on ~he lu~ri.cant in the ~eclr.Lng arear;. .~s lubri-cant is depletecl because oE :rictional. heat, pi.ston 57 wil].
move downwarcl in reservoi:r 51 to mai.nE:ain a supply of lubri--cant to the b~aring areas.
The i.nvention has significant advantacJes. The sealmeans floats with respect to the shaft to accommodate 0bbl.ing of the cu-tte.r on the shaft and maintain an ef-ective seal. The seal is simple in construction.and easy to install.
While the invention has been shown in only one oE
its forrns, it should be apparent to those ski].led in the art that it is not so limited but is susceptible -to var-ious changes and modi.fications without departinq from the spirit of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an earth boring bit of the type having a cutter rotatably mounted with bearings on a shaft, an improved seal means located in an annular groove provided between the cutter and shaft for sealing the bearings, comprising:
a supporting ring located in the annular groove, defining an annular space between the supporting ring and a cylindrical surface formed on the shaft and another annular space between the supporting ring and a cylindrical surface formed on the cutter;
an elastomeric ring located in one of the annular spaces and supported by the supporting ring in sealing and sliding contact with one of the cylindrical surfaces, the other annular space being empty, the supporting ring separating the elastomeric ring from any contact with the other cylindrical surface;
the groove having side walls spaced apart a distance that is fixed regardless of any outward movement of the cutter on the shaft, so that side squeeze on the elastomeric ring remains constant despite outward cutter movement on the shaft.

2. In an earth boring bit of the type having a cutter rotatably mounted with bearings on a shaft, an improved seal means for sealing the bearings, comprising:
a groove located in the shaft having an inner diameter and side walls;
a supporting ring located in the groove, the supporting ring having a minimum inner diameter larger than the inner diameter of the groove; and an elastomeric ring located in an annular space provided in the groove between the supporting ring and the cutter and pressed radially outward against a seat formed in the cutter by the supporting ring;
the sides of the elastomeric ring being pressed into sealing contact with one of the side walls of the groove, defining a seat for preventing movement of the elastomeric ring along the axis of the shaft;
the side walls of the groove being spaced apart a distance that is fixed regardless of any outward movement of the cutter on the shaft, so that side squeeze on the elastomeric ring remains constant despite outward cutter movement on the shaft;
the elastomeric ring being in sliding contact with one of the seats;
the supporting ring separating the elastomeric ring from any contact with the inner diameter of the groove to allow the supporting ring to move radially with respect to the shaft.

3. In an earth boring bit of the type having a cutter rotatably mounted with bearings on a shaft, an improved seal means located in a groove formed in the shaft for sealing the bearings, comprising:
a split supporting ring located in the groove, the supporting ring being incontractible beyond a minimum inner diameter that is larger than the inner diameter of the groove; and an elastomeric ring located in an annular space provided in the groove between the supporting ring and the cutter and pressed against the cutter by the supporting ring, the elastomeric ring having a cross-sectional width selected so as to provide sealing on the sides of the elastomeric ring when the cutter is assembled;

the sealing on the sides of the elastomeric ring and the supporting ring causing the elastomeric ring to be slidingly engaged by the cutter;
the supporting ring separating the elastomeric ring from any contact with the inner diameter of the groove to allow the supporting ring to move radially with respect to the shaft;
the groove having integral side walls spaced apart a distance that is fixed regardless of any outward movement of the cutter on the shaft, so that side squeeze on the elastomeric ring remains constant despite outward cutter movement on the shaft.

4. In an earth boring bit of the type having a cutter rotatably mounted with bearings on a shaft, an improved seal means for sealing the bearings, comprising:
a groove formed in the shaft with a rectangular cross-section, an inner diameter and integral inner and outer side walls formed perpendicular to the inner diameter;
a split supporting ring located in and extending across substantially the full width of the groove, the supporting ring having an incontractible minimum inner diameter; and an elastomeric ring, circular in cross-section and located in an annular space provided between the supporting ring and the cutter and pressed by the supporting ring radially outward against the cutter;
the elastomeric ring being pressed into sealing contact with one of the side walls of the groove, preventing movement of the elastomeric ring along the axis of the shaft;

the side walls of the groove being spaced apart a distance that is fixed regardless of any outward movement of the cutter on the shaft, so that side squeeze on the elastomeric ring remains constant despite outward cutter movement on the shaft;
the elastomeric ring slidingly engaging a selected one of the cutter and the groove side wall;
the supporting ring separating the elastomeric ring from any contact with the inner diameter of the groove to allow the supporting ring to move radially with respect to the shaft.

5. In an earth boring bit of the type having a cutter rotatably mounted with bearings on the shaft, an improv-ed seal means located in an annular groove formed in the shaft for sealing the bearings, comprising:
a supporting ring located in the groove, the support-ing ring being incontractible when assembled in the groove and having an inner diameter larger than the inner diameter of the groove, defining an annular clearance;
a backup ring located in the groove with an inner cir-cumference in contact with the supporting ring and an outer circumference in contact with the cutter; and an elastomeric ring pressed against the cutter by the supporting ring and also pressed between the backup ring and the groove to provide sealing on the sides of the elas-tomeric ring.

6. In an earth boring bit of the type having a cutter rotatably mounted with bearings on a depending shaft, an improved seal means for sealing the bearings, comprising in combination:
an annular groove formed in the shaft with a rectangu-lar transverse cross-section and inner and outer side walls;
a split supporting ring located in the groove, the sup-porting ring being expansible and having a minimum inner diameter that is larger than the inner diameter of tile groove, the supporting ring having a cross-sectional width slightly less than the cross-sectional width of the groove;
a backup ring of elastomeric material located in the groove in contact with the outer side wall the inner cir-cumference of the backup ring being in contact with the sup-port ring and its outer circumference in contact with the cutter, the backup ring being rectangular in transverse cross-section; and an elastomeric ring of circular cross-section pressed against the cutter by the supporting ring and also pressed between the backup ring and the inner sidewall of the groove, to provide sealing of the sides of the elastomeric ring.