CA1121331A - Method for making rock bits - Google Patents
Method for making rock bitsInfo
- Publication number
- CA1121331A CA1121331A CA000358204A CA358204A CA1121331A CA 1121331 A CA1121331 A CA 1121331A CA 000358204 A CA000358204 A CA 000358204A CA 358204 A CA358204 A CA 358204A CA 1121331 A CA1121331 A CA 1121331A
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- bit
- bit body
- rock
- steel
- weld
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
Abstract of the Disclosure Segments of a rock bit are secured together by electron-beam welding. The segments are slightly spaced apart prior to welding by a thin shim of alloying metal such as titanium which improves ductility of the weld and is a strong carbide-former during welding. The shim is positioned between adjacent segments in the region of the crown or dome of the bit. The resulting welded interface is a fine-grain stress-relieved structure with good ductility and resistance to cracking.
Description
~.Z~L3~
~IETHOD FOR MAXING ~OCK BITS
_ Field of the Invehtion The present invention is concerned with a method of forming a rock bit body having a plurality of separately formed segments that are to be welded together, and with a rock bit including a plurality of separately formed segments welded together.
_ross-reference ~o rela-~ed appiication The present application has been divided from our application Serial No. 30~,873, filed July 21, 1978.
Back~round of the Invention Rotary rock bits are used to penetrate earth formations in the drilling of oii an~ gas wells, geothermal steam wells, and related deep bores of accurately controlled diameter and direction. Typical modern rock bits have a main body with a threaded upper or pin end adapted for a~tachment to a drill pipe used i~ conventional rotary drilling. A plura~ity of co~ical~y shaped cutters or "cones" are rotatably mounted on legs extending downwardly fro~ ~he main body~ and the cones have teeth or hard ~nserts which contact and crush the rock formation being penetra~ed. Drilling mud is pumped through ~he drill pip~ and passages i~ the bit body to cool ~he bi~, and ~o flush cuttings from ~h~ hottom of ~he hole to the sur~ace.
The maiA ~ody of a typical modern ~i~ i3 made by welding ~ogether sev~ral ~us~lly .~hree) mating segmen~s. -.
- 1 - ' .
..
1 The lower end of each segment is a depending lPg having a bearing pin at its lower end ~or rotatably supporting a rock-boring cutter cone. Each segment usually includes a pressure-compensated lubrioant reservoir for supplying grease to the cone bearing.
In a typical three-cone bit, each segment has a pair of flat mating faces or faying surfaces oriented 120 degrees apart, and each face mates with a corresponding face on the adjacent segment. The assembly of three seg,ments forms the main body of the bit, and the flat'faces of adjacent segments lie in planes intersecting substantially along the bit axis. The segments are clamped in a holding fixture, checked for "gage" or diametral accuracy, and, t~en welded together along the faying surfaces.
,;~
Rock'bits are subjected to extreme loads during drilling, and the segments must be secured together with a high-strength weld to avoid cracking.
A crack in the body of a rock bi~ can lead to leakage of drilling fluid from the interior o~ the bit to the exterior.
Rock bits are often operated with abrasive drilling mud at ....
pressures o~ over 1500 psi in the interior of the bit body.
Leakage of drilling mud through a weld cracX in the steel bit body can rapidly enlarge th~ crack to produce severe leakage.
Such "wash-out" o~ the weld can ohange the flow direction of drilling fluid and degrade performance of the bit~ Wear of 5 the cones on the rock bit can be a significan~ problem if the ~ ..
mud-stream direction is n~t properly controlled. Pressure loss due to large leakage can result in premature pulling of the ~ -dr 11 string with consequent loss of drilling time.
It has been comm~n practice for many years to use arc ~eld-~ng to melt a filler me~al into the inter~aces between thesegments to weld the segments together. This form of welding li.;~l331~
1 is expe~sive and time consuming, and requires a highly skilled operator if consistent results are to be achieved. A weld of this type does not always result in the strength which is desired in the welded assembly. Deep welds can require many passes to add enough filler metal to complete the weld. This method of welding also involves significant heating of the segments wh, ich may a~fect preyious heat treatment of the welded parts a~d cause unpredictable warping of the completed bit outside of desixed dimensional tolerances. Damage to resilient seals installed before welding can also be a problem arising from excessive heating.
Energy-beam welding is an alternate technique which has been perfected as ~ general welding method in recent years;
~he mating surfaces of the parts to be welded are irradiated wi~h a focused beam of energy which melts the surfaces and forms a welded interface which may extend deeply betwee~ the parts in the direction of beam penetration. ~aser beams and the like can be used as energy sources, but mos~ commercial welding machines o~ this type use a high-energy electron beam which is generated in a vacuum chamber in which the parts to be welded are supported. The heat-affected zone lateral to the direction of the ~eam is shallow (minimizing warping and ¦ distortion of the parts), and substantially ~he entire faying l surfaces of rock~bit seyments can be welded to form a strong 251 main body for the bit. Such welds are characterized by a depth of penetration much larger than the width of the heat-affected %one.
¦ Use of energy-beam welding in the construc~ion of rock-¦ bit bodies is d~salose~ in U.S. Patents 3,907,191 30 ~
~ ~ . 3 ~ 3 31 1 and 3,987,859 which di~cuss electron-beam welding methods in greater detail; These patents teach a procedure in which the bit segments are clamped together with mating faces in abutting ~ontact without intervening spacers or shims. The segments are then electron-beam welded along the contacting surfaces of the mating faces.
We have found that a significant improvement in weld integrity an~ quality arises from placing a thin shim of an alloying metal such as titanium between the mating ~ace~ of the segments prior to welding with energy-beam techniques.
Preferably, the shim ls positioned' at the central part of the ~it-body dome or crown where the segments converge together, and shim thickness is limited to about 0~010 inch to avoid an excessive gap between the parts whioh could interfere with ~ormation of a properly welded interface between the segments.
Use of stee} shims between the ~egments of a'rock-bit body has been known for many year~ as a dimensional control for assuring that bits assembled by gas or arc welding would 20 have a correct gage diameter. Such shims were used when measurement showed that ~he gage diameter was out of tolerance~ These shims, however, were isola~ed from the welded interfac,e and'did not aff~ct the metallurgical properties of the weld.
25 ¦ A slurry of titanium powdex i~ acetone ha~ also been tried at one edge o the interface to be electron-beam welded. Such a slurry was appliad to ~he surface of the body adjacent the Y-~haped intersection of the mating faces to be welded a$ter the ~egments were assembled. The powder 30 was placed o~ ~he dome sur~ace and appeared to be sca~ered l~.Z1331 1 during electron-beam welding. It is believed that no more than a surface portion of the weld bead could be ~ffected by the powder. No changes in weld properties were noted.
So far as~is known, shims o~ titanium or other alloying metal have not previously been positioned between the s~rfaces o ~teel rock-bit segments to be welded. Filler metal foil of aluminum alloy ha~ been described for inhibiting cracking during welding of aiuminum, and filler metal wire for electron-~eam welding steel is also known for inhibiting cracking. See, for example, pages 530, 535, 536, 555 and 556 of Welding and Brazing~` Metals ~and~oo~, Vol. 6, 8th Edition, American Society for Metals (1971).
Another advantage o~ the use o~ shims is that the resulting opening of a slight gap between the segment faying surfaces in the region of the dome acts as a stress-relieving mechanism ~or the weld which minimize~ re~idual stresse~
and the ri~k o~ cracking~ The me~al of the shim acts as a filler in ~ritical xegions to avoid depressions at the weld surface~
The shim metal alloys with the metal of ~he segments in the weld, thereby improving the weld ductility and crack resistance. When titanium or the like is used as the shim metal, it acts a~ a scavenger and stabilizer which deoxidi~es the weld and st~bilize~ any exce~s ~arbon as titanium carbide 25 to avoid embri~tlement and cracking. The resultiny weld is a fine-grain ~tructure of improved ductility and impact ~trength, and exce~ive hardening of the weld during cooling is avoided.
3~3~
In accordance with this invention there is provided a method for ~orminy a rock bit body haviny a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-boring cutter cones, and a dome portion form-ing a web transverse to the axis of the body between the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of forming a plurality of steel rock~bit body segments, each segment having a pair of faying surfaces~ each o~ such faying surfaces being prepared for welding to a faying surface on an adjacent segment; ~nd forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least one of such weld beads along the shank portion of the body having substantially the same com-position as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a different alloy content than the steel of the segments for enhancing crack resistance of such weld beads.
- Also in accordance with this invention there is provided a three-cone rock bit comprising:
~ a-steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string, three depending legs at the other end o~ the bit body;
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.),. , 33~
a rock-borin~ cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion ~orming a web transverse to the a~is of the rock bit between the hollow shank portion and the exterior of the rock bit;
a plurality of weld beads along the shank portion of the bit body in each of three locations spaced 120 apart around the shank portion, at least o~e of such weld beads having a composition substantially the same as the composition of the steel of the bit body; and a weld bead in each of three secotrs in the dome portion of the bit body, the three weld beads meeting in a Y-shaped intersection on the axis of the rock bit and extending generally radially therefrom, each of said weld beads being a continuation of a weld bead on the shank portion and having a different alloy content than the s~eel of the bit body fox enhancing crack resistance thereof~
Further in accordance with this invention there is provided a rock bit comprising: .
a steel rock bit body having a holluw, generally cylindrical shank portion at one end;
means on the shank portion or connection of thP
rock bit to a drill strings a pl~rality of depending legs at the other end of the bit body, a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body betw~en the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit, and D
~ ~ Z~331 JL~.
at least one weld bead along at least a portion of the bit body, a portion of such a~leld bead having a composi-tion substantially the same as the compositlon of the steel of the bit body, and another portion of such weld bead having a different alloy content than the steeI of the bit body for enhancing a metallurgical property thereof.
Further in accordance with the invention there is provided a method for forming a rock bit body having a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-bor.ing cutter cones, and a dome portion forming a web transverse to the axis of the body be-tween the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of:
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least some of such weld beads along the shank portion of t~.ebody having substantially the same composi-tion as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a sufficiently different alloy content than the steel of the segments for improving ductility of such weld beads relative to weld beads along the shank portion.
~.2~33~
Description of th _Drawings FIG. 1 is an elevation~ partly in section, of a complete rock bit;
FIG. 2 is a pictorial view of an individual segment of the rock bit body;
FIG. 3 is a perspective view of a shim for an assembly of sements;
FIG. 4 is a semi-schematic end view of the crown or A.l l~.Z1331 1 dome of the bit, showing the segments aligned together and with shims positioned between the faying surfaces ln preparation for beam welding;
FIG. S is ~n elevation of one faying surface of the third 5 weld in a three-cone rock bit with an L~shaped shim in place;
. FIG~ 6 is a side view of a two-cone rock b.it; and J FIG. 7 is an end view, partly in section, of the rock bit of FIG. 6.
10 Description of the Preferred Embodiment A typical rock bit 10 of a type suitable for construction according to this invention is shown in FIG. 1. The bit illus-trated is a three-cone journal-bearing bit, but it is to be understood that other styles of bits of this general type are lS suitable ~or assem~ly by the techniques described herein. For example, bits with antifriction bearings, or with different numbers of cones, are within the scope of the present invention, and the particular style shown in ~IG. 1 is simply by way of example~
Bit 10 includes three cone-shaped cutters ll mounted on journal-bearing pins 12 integrally formed at the lower end portions of legs 13 d~pending from three bit segments 14 which comprise the main body of the bit. Each cutter can have milled teeth (not shown), or can carry a`plurality of sintered tungsten
~IETHOD FOR MAXING ~OCK BITS
_ Field of the Invehtion The present invention is concerned with a method of forming a rock bit body having a plurality of separately formed segments that are to be welded together, and with a rock bit including a plurality of separately formed segments welded together.
_ross-reference ~o rela-~ed appiication The present application has been divided from our application Serial No. 30~,873, filed July 21, 1978.
Back~round of the Invention Rotary rock bits are used to penetrate earth formations in the drilling of oii an~ gas wells, geothermal steam wells, and related deep bores of accurately controlled diameter and direction. Typical modern rock bits have a main body with a threaded upper or pin end adapted for a~tachment to a drill pipe used i~ conventional rotary drilling. A plura~ity of co~ical~y shaped cutters or "cones" are rotatably mounted on legs extending downwardly fro~ ~he main body~ and the cones have teeth or hard ~nserts which contact and crush the rock formation being penetra~ed. Drilling mud is pumped through ~he drill pip~ and passages i~ the bit body to cool ~he bi~, and ~o flush cuttings from ~h~ hottom of ~he hole to the sur~ace.
The maiA ~ody of a typical modern ~i~ i3 made by welding ~ogether sev~ral ~us~lly .~hree) mating segmen~s. -.
- 1 - ' .
..
1 The lower end of each segment is a depending lPg having a bearing pin at its lower end ~or rotatably supporting a rock-boring cutter cone. Each segment usually includes a pressure-compensated lubrioant reservoir for supplying grease to the cone bearing.
In a typical three-cone bit, each segment has a pair of flat mating faces or faying surfaces oriented 120 degrees apart, and each face mates with a corresponding face on the adjacent segment. The assembly of three seg,ments forms the main body of the bit, and the flat'faces of adjacent segments lie in planes intersecting substantially along the bit axis. The segments are clamped in a holding fixture, checked for "gage" or diametral accuracy, and, t~en welded together along the faying surfaces.
,;~
Rock'bits are subjected to extreme loads during drilling, and the segments must be secured together with a high-strength weld to avoid cracking.
A crack in the body of a rock bi~ can lead to leakage of drilling fluid from the interior o~ the bit to the exterior.
Rock bits are often operated with abrasive drilling mud at ....
pressures o~ over 1500 psi in the interior of the bit body.
Leakage of drilling mud through a weld cracX in the steel bit body can rapidly enlarge th~ crack to produce severe leakage.
Such "wash-out" o~ the weld can ohange the flow direction of drilling fluid and degrade performance of the bit~ Wear of 5 the cones on the rock bit can be a significan~ problem if the ~ ..
mud-stream direction is n~t properly controlled. Pressure loss due to large leakage can result in premature pulling of the ~ -dr 11 string with consequent loss of drilling time.
It has been comm~n practice for many years to use arc ~eld-~ng to melt a filler me~al into the inter~aces between thesegments to weld the segments together. This form of welding li.;~l331~
1 is expe~sive and time consuming, and requires a highly skilled operator if consistent results are to be achieved. A weld of this type does not always result in the strength which is desired in the welded assembly. Deep welds can require many passes to add enough filler metal to complete the weld. This method of welding also involves significant heating of the segments wh, ich may a~fect preyious heat treatment of the welded parts a~d cause unpredictable warping of the completed bit outside of desixed dimensional tolerances. Damage to resilient seals installed before welding can also be a problem arising from excessive heating.
Energy-beam welding is an alternate technique which has been perfected as ~ general welding method in recent years;
~he mating surfaces of the parts to be welded are irradiated wi~h a focused beam of energy which melts the surfaces and forms a welded interface which may extend deeply betwee~ the parts in the direction of beam penetration. ~aser beams and the like can be used as energy sources, but mos~ commercial welding machines o~ this type use a high-energy electron beam which is generated in a vacuum chamber in which the parts to be welded are supported. The heat-affected zone lateral to the direction of the ~eam is shallow (minimizing warping and ¦ distortion of the parts), and substantially ~he entire faying l surfaces of rock~bit seyments can be welded to form a strong 251 main body for the bit. Such welds are characterized by a depth of penetration much larger than the width of the heat-affected %one.
¦ Use of energy-beam welding in the construc~ion of rock-¦ bit bodies is d~salose~ in U.S. Patents 3,907,191 30 ~
~ ~ . 3 ~ 3 31 1 and 3,987,859 which di~cuss electron-beam welding methods in greater detail; These patents teach a procedure in which the bit segments are clamped together with mating faces in abutting ~ontact without intervening spacers or shims. The segments are then electron-beam welded along the contacting surfaces of the mating faces.
We have found that a significant improvement in weld integrity an~ quality arises from placing a thin shim of an alloying metal such as titanium between the mating ~ace~ of the segments prior to welding with energy-beam techniques.
Preferably, the shim ls positioned' at the central part of the ~it-body dome or crown where the segments converge together, and shim thickness is limited to about 0~010 inch to avoid an excessive gap between the parts whioh could interfere with ~ormation of a properly welded interface between the segments.
Use of stee} shims between the ~egments of a'rock-bit body has been known for many year~ as a dimensional control for assuring that bits assembled by gas or arc welding would 20 have a correct gage diameter. Such shims were used when measurement showed that ~he gage diameter was out of tolerance~ These shims, however, were isola~ed from the welded interfac,e and'did not aff~ct the metallurgical properties of the weld.
25 ¦ A slurry of titanium powdex i~ acetone ha~ also been tried at one edge o the interface to be electron-beam welded. Such a slurry was appliad to ~he surface of the body adjacent the Y-~haped intersection of the mating faces to be welded a$ter the ~egments were assembled. The powder 30 was placed o~ ~he dome sur~ace and appeared to be sca~ered l~.Z1331 1 during electron-beam welding. It is believed that no more than a surface portion of the weld bead could be ~ffected by the powder. No changes in weld properties were noted.
So far as~is known, shims o~ titanium or other alloying metal have not previously been positioned between the s~rfaces o ~teel rock-bit segments to be welded. Filler metal foil of aluminum alloy ha~ been described for inhibiting cracking during welding of aiuminum, and filler metal wire for electron-~eam welding steel is also known for inhibiting cracking. See, for example, pages 530, 535, 536, 555 and 556 of Welding and Brazing~` Metals ~and~oo~, Vol. 6, 8th Edition, American Society for Metals (1971).
Another advantage o~ the use o~ shims is that the resulting opening of a slight gap between the segment faying surfaces in the region of the dome acts as a stress-relieving mechanism ~or the weld which minimize~ re~idual stresse~
and the ri~k o~ cracking~ The me~al of the shim acts as a filler in ~ritical xegions to avoid depressions at the weld surface~
The shim metal alloys with the metal of ~he segments in the weld, thereby improving the weld ductility and crack resistance. When titanium or the like is used as the shim metal, it acts a~ a scavenger and stabilizer which deoxidi~es the weld and st~bilize~ any exce~s ~arbon as titanium carbide 25 to avoid embri~tlement and cracking. The resultiny weld is a fine-grain ~tructure of improved ductility and impact ~trength, and exce~ive hardening of the weld during cooling is avoided.
3~3~
In accordance with this invention there is provided a method for ~orminy a rock bit body haviny a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-boring cutter cones, and a dome portion form-ing a web transverse to the axis of the body between the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of forming a plurality of steel rock~bit body segments, each segment having a pair of faying surfaces~ each o~ such faying surfaces being prepared for welding to a faying surface on an adjacent segment; ~nd forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least one of such weld beads along the shank portion of the body having substantially the same com-position as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a different alloy content than the steel of the segments for enhancing crack resistance of such weld beads.
- Also in accordance with this invention there is provided a three-cone rock bit comprising:
~ a-steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string, three depending legs at the other end o~ the bit body;
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.),. , 33~
a rock-borin~ cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion ~orming a web transverse to the a~is of the rock bit between the hollow shank portion and the exterior of the rock bit;
a plurality of weld beads along the shank portion of the bit body in each of three locations spaced 120 apart around the shank portion, at least o~e of such weld beads having a composition substantially the same as the composition of the steel of the bit body; and a weld bead in each of three secotrs in the dome portion of the bit body, the three weld beads meeting in a Y-shaped intersection on the axis of the rock bit and extending generally radially therefrom, each of said weld beads being a continuation of a weld bead on the shank portion and having a different alloy content than the s~eel of the bit body fox enhancing crack resistance thereof~
Further in accordance with this invention there is provided a rock bit comprising: .
a steel rock bit body having a holluw, generally cylindrical shank portion at one end;
means on the shank portion or connection of thP
rock bit to a drill strings a pl~rality of depending legs at the other end of the bit body, a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body betw~en the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit, and D
~ ~ Z~331 JL~.
at least one weld bead along at least a portion of the bit body, a portion of such a~leld bead having a composi-tion substantially the same as the compositlon of the steel of the bit body, and another portion of such weld bead having a different alloy content than the steeI of the bit body for enhancing a metallurgical property thereof.
Further in accordance with the invention there is provided a method for forming a rock bit body having a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-bor.ing cutter cones, and a dome portion forming a web transverse to the axis of the body be-tween the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of:
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least some of such weld beads along the shank portion of t~.ebody having substantially the same composi-tion as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a sufficiently different alloy content than the steel of the segments for improving ductility of such weld beads relative to weld beads along the shank portion.
~.2~33~
Description of th _Drawings FIG. 1 is an elevation~ partly in section, of a complete rock bit;
FIG. 2 is a pictorial view of an individual segment of the rock bit body;
FIG. 3 is a perspective view of a shim for an assembly of sements;
FIG. 4 is a semi-schematic end view of the crown or A.l l~.Z1331 1 dome of the bit, showing the segments aligned together and with shims positioned between the faying surfaces ln preparation for beam welding;
FIG. S is ~n elevation of one faying surface of the third 5 weld in a three-cone rock bit with an L~shaped shim in place;
. FIG~ 6 is a side view of a two-cone rock b.it; and J FIG. 7 is an end view, partly in section, of the rock bit of FIG. 6.
10 Description of the Preferred Embodiment A typical rock bit 10 of a type suitable for construction according to this invention is shown in FIG. 1. The bit illus-trated is a three-cone journal-bearing bit, but it is to be understood that other styles of bits of this general type are lS suitable ~or assem~ly by the techniques described herein. For example, bits with antifriction bearings, or with different numbers of cones, are within the scope of the present invention, and the particular style shown in ~IG. 1 is simply by way of example~
Bit 10 includes three cone-shaped cutters ll mounted on journal-bearing pins 12 integrally formed at the lower end portions of legs 13 d~pending from three bit segments 14 which comprise the main body of the bit. Each cutter can have milled teeth (not shown), or can carry a`plurality of sintered tungsten
2 carhide ins rts 15 suitable for drilling hard formations. The cutter cones are re~ained on journal pin5 1~ by conventional -locking balls 16 which are fed into a ball-bearing race through a ball passage ~not shown) after the cutters are mounted as is well known in the art.-.
1~.Z3 331 1 A pin end 17 at the upper end of the bit body remote from cutters 11 is threaded for attachme~t to a drill collar (not shown) at the lower end of a drill string made up of pieces of drill pipe. The drill collar seats on a shoulder 20 on the extexior of the bit body. The pin or shank end of the rock bitis generally cylindrical although the threaded portion is often conical, and is sometimes~r~erred to as the tool joint. Each ¦ cutter and associated segment may also be provided with a con-ventional lubrication system which is omitted from the drawings for clarity. The lubrication system supplies grease to the bearing surfaces, and grease seals 18 are t~pically provided between the cutters and segment legs to prevent loss of lubricant.
A central interior portion 19 at the upper end of the bit is hollow and communicates with passages (not shown in FIG. 1) in the ~it legs leading to openings or jet orifices adjacent the cutter cones. Drilling mud is pumped from the surace through the drill pipe to flow through these openings adjacent the cutters, and to carry rock par~icles back to the surface through the annulus around the bit and drill-pipe string.
In the center portion of the bit body between the shank end ¦ and the cone-supporting lower ends of the legs is a web 26 of steel sepArating the interior of the hollow shank end from a bit-body dome or crown undersur~ace which extends o~er the cones.
The fea~ures described thus far are conventional and well known ¦ in the art, and, ~or brevity, will not ~e discussed in greater detail.
Referring to F~G. 2, each segment 14 has a pair of angularly oriented fla~ faces or faying sur~aces 22 which extend longitudinally along a sha~ portion 23 of ~he segment.
. , , 112~331 1 The mating or faying surfaces 22 are normally oriented at an angle of 120 to each other so the three segments commonly used to form a complete bit ~ody will fit together tightly when assemble~ for final welding. The three segments used in a 5 typical three-cone bit are substantially identical and the planes of the faying surfaces intersect generally along the bit axis.
An inner surface 25 o~ the segment shank portion is con-cave to form a 120 segment of central interior poxtion 19 of ~he bit body~ The concave crown or dome surface on the under-side of web 26 extends downwardly and outwardly rom the lower end of mating surfaces 22 to a tapered and curved lower end of the segment leg called a shirttail 27. The steeply incli~ed portion of the crown'or dome surface leading to the cone-suppsrting lower ~nd por~ion of the leg is conventionallycalled a throat surface 21. A flat leg backface 30 (FIG. 2~ is positioned at the base of pin 12;
, A boss 28 having an opening 29 therethrough is formed at one side of the crown surface to receive a tungst~n-carbide nozzle' (not sh'own~ for passage of drilling mud pumped through central interior portion l9 (FIG. l) of the bit body during use of the bit. Bearingpin 12 extends inwardly and downwardly from leg backface 30, and inc~udes conventional features such as a spindle or nose bearing 31 and an annular ball-race groove 32 ~o receive retaining balls 16.
Before ass'embling the bit ~ody, a cutter cone is mounted on the bearing pin 12 of eac~ segment leg. Ball passages and lubricant ports, if any, are plugged to prevent in~rusion of unwanted materials. Such'subassemblies of segment and cone are conventional, and three such subassemblies are used to form a complete three-cone bit body.
. ,~''..,' ' ' ''' ' " .
~ ~ . l r ~
. ' /~- ~
~ 3 3 1 To assemble the bit, the several segment subassemblies are positioned together in a conventional clamping jig (not shown) with each faying surface 22 in face-to-face alignment with a corresponding faying surface on the adjacent segment. Typical clamping ~igs and assembly`fixtures suitable for use with electron-beam welding are shown in the aforementioned U.S.
Patënts No. 3,907,191 and No. 3,987,859~
. .
FIG. 4 shows schematically the undersurface of the bit body crown or dome with the three bit segments positioned together prior to welding. Legs 13 are shown in cross section.
Beore the segments are clamped together, a shim 35 of the type shown in FIG. 3 is inserted between two of the three pairs of mating faaes in the position sho~ in phantom line in FIG. 2.
Each shim is configured to fit against the lower, roughly rectangular part of the mating face of the bit segment in web 26 of the bit.
The dimensions of shim 35 will differ according to the size of the bit being manufactured, but the shim typically has a width of about 3/8 inch to 1 inch, and a length of 3 inches or more, to correspond to the dimensions of the welded portion of the segment faying surface adja~ent the dome of the bit.
Preferably, each shim is bent along one longitudinal edge to form a small perpendicularly extending lip 36. The lip limits the *epth of inser~ion of the shim between the mating faces prior to final cl~mpLng of the vi~ ~egm;2nts, and provides filler metal during welding.
.
~. , 1~.2L331 1 As mentioned hereinafter, two shims 35 are placed in the two welding interfaces which are the first and second to be electron-beam welded. A different shim 37 is used in the third welding interface. FIG~. S shows one fayir.g surface 22 of the third welding interface with a shim 37 in place. The balance of the structure of the segment is omitted. Third shim 37 has an "L" shape with one arm extending along the faying surface in the dome p~rtion of the bit. This part of L-shaped shim 37 ¦ corxesponds to straight shims 35 in the first two welding 0¦ interaces. T~e other ar~ of L-sha~3d shim 37 extends along the faying surface toward shank portion 23 of the segment.
This arm of the L-shaped shLm extends to the region of shouldsr 20. If desired, two straight shims laid in place like an L
can be used in the third welding interface instead of the L-shaped shim illustrated in FIG~ 5.
Thin sheet-metal stock is used to make the shims 35 and 37, and shim thickness is preferably limited to about 0.010 inch to avoid an excessi~e gap in the welding interface between the segments which could interfere with electron-beam welding ~0 of the faying surfaces. Sheet materials in the rar.ge of about 0.003 to 0.007 inch thickness have been found to be preferable for making the shims.
After the segments ha~e been properly positioned and clamped with the ~hims 35 and 37 in place in the three interf~es 25 ~o be welded, the elec:tron-beam welding ~rocess can be commenced,.
One of the three interfaces with a ~traight shim 35 is indexed to the beam positionO ~he electron beam is then used to make~
. ',' ,' .
,~
J~ ` .
~.Z~3~31 1 a ligh~ tack weld between the legs commencing in center 41 (FIG. 2) of the dome and proceeding outwardly to an outer corner 42 of mated faying surfaces 22 and then along shank portion 23. ~he direc~ion of..traverse of the electron beam is then reversed and power increased to produce a weld of the desired depth, which in most areas is the full width of faying surfaces 22.
Tha electron beam is also rapidly oscillated to assure melting of steel from both less as well as melting of the shim. Thus, the full depth weld cycle commences at an end 43 of the ~hank portion and proceeds along the interface to center 41 of the dome. In the crown or dome region, the . electron beam intersects the bit surface at an angle of about . 25 from the surface and extends in a direction towards the bit 15 axis. Since ~he angle of the electron gun is usually fixed, the electron beam intersects the surface o~ the bit body in the shank portion at a much higher angle. In one embodiment . such a weld bead has a d pth of about an inch in some areas, a width ~lateral to the direction of beam penetration) of about l/8 inch, and a hea~ affected zone about 1/32 inch wide on each side of the weld bead.
When the first weld is completed, the bit is indexed 120 around its axis to bring the nex~ interface into the electron beam position, and the cycle is repeated until all ~hree welds have been made. Straigh~ shims 35 are used in the first two welds and an L-shaped shim 3~ is preferably used in the third weld.
.
. ...
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.
~.2~. 33~
1 After-the three welds are made, there are three weld beads which intersect in a Y-shaped intersection in the center of the dome portion of the bit body on the bit axis. The weld heads are 1~0 apart, and extend radially outwardly from the center of the dome portion and along the shank or pin portion of the bit body. Such a weld bead in the dome portion has a different alloy content than the steel of the segments, and preferably has gxeater ductility than the segment steel.
When the welds are completed, pin end 17 ~FIG. 1) is machined and threaded to~provide a tool-joint connection on the shank portion of the bit body for connec~ion to a drill string. Other finishing operations such as installation of mud jets, lubrication of bearings, and installation of pressure compensators are normally completed after welding.
The shims i~ the dome portion of the bit body serve several purposes in construc~ion of the bito ~he metal of the shim provides an alloying metal for the steel in the dome portion of the bit segments or enhancing ductility and crack resistance. Dilution by the metal of the shim can reduce carbon content of the metal in the weld bead. The shim pro-vides space for stress relief of the weld, particularly in the dome portion~ The metal of the shim can also combine wi~h carbon or other materials which could adversely affect w~ld proper~ies. Melting o the ex~ra metal in ~he shim and in lip 36 of the shim can minimize depressions in the weld metal surface.
A particularly suitable material fox the shim is titanium.
When ti~anium alloys with the steel of the bit sesments several ; !
, ''''' ~ 1331 1 improvements in metallurgical properties of the weld bead can result. Ferrite in the weld bead can be stre~gthened b~ solid solution of titanium. The titanium tends to promote a fine grain structure and deoxidizes the weld bead. Adverse harden-ing of the weld bead during rapid cooling after passage of the electron beam is inhibited. Impact strength, fatigue resis-tance, and du~tility of the weld bead are enhanced. ~ardness 1 of the weld bead can be lower than in the absence of titanium.
¦ Thus, for example hardness di~ferences from Rockwell C-27 to Rockwell B-95 can occur. It is particularly significant to provide a higher alloy content in the weld beads in the dome portion where three weld beads intersect in a Y at the axis of the bit. Such a Y-shaped intersection o~ weld beads is subject to high stress levels, and enhanced metallurgical properties are important~
Another benefit of titanium in the weld bead adjacent the crown arises from its ability to stabilize carbon by formation o~ titanium carbide. Parts of the bit segments are carburized before assembl~, but the region to be welded is protected fxom carburizing by con~entional "stop-off" ma~erials which inhibit diffusion of carbon into the steel segment. Such stop-of~ materials are applied ko the surface as a slurry or electroplate, and pinhole imperfections may occur, leading to carburized spots in regions to be welded. Such high-carbon ~5 regions in a weld bead can be deleteriously brittle~
Accidental carbon leakag2 can be rectified by presence of titanium or other strong carbide forming material in the welding shims. The ti~anium car~ide i5 present as 3 separa~e .
~ .
~1 .
l~.Z1 3 ~1 1 phase in small particles, a~ does not significantly diminish ductility~ Other carbide-forming metals having a stronger affinity ~or carbon than does iron can be included in the shim.
Other alloying metals can also be used in the shims.
Suitable materials can include titanium alloys, zirconium, columbium, molybdenum, nickel, alloys of such metals, nickel-chromium stainless steels such as type 310, and iron alloys ¦ including titanium, zirconium, columbium, molybdenum and/or ¦ ni~kel. Iron can be used for diluting alloy content and decreasing hardenability. Cobalt can provide dilution although it is not a ferrite strengthener. Some other metals can be present in limited quantities which contribute to the desired properties o~ the weld bead and can make desirable additions.
Thus, for exampler the titanium alloy Ti-6Al-4V can be employed, the aluminum serving to deoxidize and grain re~ine the weld bead and vanadium contributing strength.
Typical materials for forming the segments of a rock bit include AISI type 8720 steel or AISI type 4815 steel. Other materials which al}oy with such steel for-enhancing ductility and/or toughness and increasing fatigue resis~ance of the weld ¦ bead will be apparent to thos~ skill~d in metallurgical arts.
¦ The shims provided in the dome portion of the rock ~it ¦ provides some ~ivergence be~een the faying suraces of the ¦ segments. It is believed ~hat the presence of the shim helps 25 ¦ minimize residual stresses due ~o weld me~al shrinkage. ~hen the third weld is made in a typical three-cone rocX bit, the other ~wo welds axe rigid and shrinkage can leave large residual tensile s~resses giving a tendency toward cracking. The shim . ,' 1~.213~1 1 in the third weld is particularly helpful in avoiding such a problem.
Warpage of an elongated weld joint can occur unless special precautions are ta~en. Thus, for example, when two -pieces are welded edge-to-edge, weld metal shrinkage during progression along the weld joint can tighten the joint to cause warpage nearer the end of the weld. A slight divergence along the seam to be welded can compensate for this effect.
The shLm in the crown or ~ome where the segment welds end provides divexgence which is believed to relieve stresses in the weld joint and minimize tendencies to crack. Such stress relief is particularly helpful where the three weld beads intersect. --In a three-cone rock bit, the third or last weld to be made has the greatest effect on residual stress. It has baen found that by providing a dome-portion shim which also extends at least part way along the faying surfaces toward the shank of the bit t significant Lmprovements in welding can be achieved.
The use o three t~tanium shims in the welds significantly 2Q decreased the xe~uirement for reworkin~ electron-beam-welded bi~s as compared with elec~xon-beam-welded bits without shims.
Use of an L-shaped shim in the third or final weld to be made caused a ~ur~her significant decrease in the requirements for xeworking.
After a rock bit is welded~ it is inspected and any cracks which could cause leakage from the interior of the bit are reworked by welding to close the crack. Such reworking is ~`
cos~ly and time consuming.
.
9.
~ ~.21331 1 About 200 roc)c bits were madc by clectron-beam welding thr~e s~gmen~s together as described above, but without any shims between the faying surfaces oP adjacent segments. Over three-fourths o~ these bits needed some reworking of the welds.
. Three titanium shims of the type illustrated in FIG. 3 were used in the welds in the dome portion of about 2000 rock bits. The reworking requirement decreased significantly to l about 12% of the bits.
10¦ Thereafter two straight shims as illustrated in FIG. 3 were used in two of the three welds~ An L-shaped shim was used in the third and final weld in lieu of the straight shLm on almost 600 bits. The bits requiring reworking dropped to l les5 than 2%. It is believed that the need for this residual 15¦ reworking is due primarily to other fa~tors, such as fit between the segments, improper indexing, errors in beam power or pvsition, or the like.
¦ The L-shaped shim pro~ides filler metal in the portion l of the third or final weld extending approximately to the 201 shoulder adjacent the pih joint of the bit. The spacing ¦ provided by this shim, and the extra metal and enhancement of metallurgical properties of the weld bead in this region con-¦ tribute to the decrease in reworking.
¦ ~lectron beam welding can cause some loss of material 25 ¦ from the weld bead, particularly whan the baam intersects ¦ the surface of the par~ being we~ded at a low angle, The lip ¦ 36 (FIG. 3) on the shim helps compensate for such possibleloss of me~al by providin~ extra material a~ the surface most I .. .. ...
39 I .
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1 subject to such loss. The lip also helps in positioning the shim before welding. ~f convenient, other enlarged portions such as a bead along one edge o the shim can be used to help in positloning the shim and providing extra metal at the edge of the mating faces of the weld.
The shim should be limited to a~out 0.010 inch thick.
With thicker shims there is a grea~er possibility of the electron beam penetrating too deeply and causing pinhole leaks through the weld bead. Such a pinhole can lead to a washout of the type mentioned a~ove with respect to cracks in the-dome.
The weld bead in electron~beam welding is only about 1/8 inch wide and thicker shLms can provide too much alloying metal for good weld-bead properties.
Generally it is preferred that the shLm have a thickness in the range of from about 0.003 to about 0~007 inch. Such thickness provides adequate alloying metal for enhancing weld-bead properties, and adequate spacing for stress relief without over dilution of the base metal or significant risk o~ pinhole leaks. Preferably, the width of the shim is sub-stantially e~ual ~o the anticipa~ed depth of penetration of the weld bead to assure a higher alloy content throughout the dome weld as compared with the steel o~ the segments.
When the rock bit body is com~leted by welding the thr~e subassemblies together, it has a threaded shank portion at one end for connection to a drill string and three legs dependins from the other endO T~e cutter cones are mounted on the lower ends of the legs. The roc~ bi~ has three weld beads spaced 120 apart extending along the hollow shank por~ion. Excep~ for . . ,:............ ..
I .
l ~ ' ',.~_ 1, ~L/, .
.2~3;~1 1 part of the third or final weld which is made, the shank portions of these weld be~ds have substantially the same co~po-sition as the steel used in forming the bit segments. The weld beads con~inue into the dome portion of the bit body to the Y-shaped intersection in the center. Each weld bead in the dome portion of the rock bit has a higher alloy content than the steel of the bit body due to melting of the shim. ~his weld bead with a different alloy content has enhanced metallur-gical properties for minimizing any tendency toward cracking 0 in the stressed portion of the rock bit body. The weld beads ... . ....
on the shank portion of the rock bit body are not subjected to the same types of stresses as those in the dome portion, and control of metallurgical properties of the weld bead is not as critical.
FIGS. 6 and 7 illustrate in side and end views, respec-tively, a two-cone rock bit 50 having parts of the body electron-beam welded together. This arrangement indicates the versatility of the electron-beam welding technique described herein.
In two-cone bit 50, a unitary steel body 51 is forg d and provided with a pin joint 52 at its shank end. Two cutter cones 53 having tungsten-carbide inserts 54 are mounted on the lower or downhole end of the bit. Each cone 53 is mounted on a leg 56 which is made as a separate part and welded into a mating pocket in bit body 51.
A mud jet orifice 57 is p~ovided on the axis of the bit body. Additional mud jet orifices 5B are provided nearer the gage or periphery of he bit for directing drilling fluid , . ..
1~ 2~331 1 toward the ~ottom of ~he hole being drilled in a region between cutter cones 53. Each of these outboard drilling-mud orifices 58 is in a separate steel insert 59 fitted into a mating pocket in bit body 51.
~nserts 59 and cutter mounting legs 56 are electron-beam welded to bit body 51. Thus r for example, heavy lines 61 in FIG. 7 show the 1QCUS of the weld beads. A titanium shim is advanta~eously placed between the faying surfaces of such a leg or însert and the bit body ~or enhancing the metallurgical propPrties of t~e weld bead, providing filler metal, and for spacing ~he faying surfaces apar~ for minimizing residual stresses. Such a shim is advantageously employed in the last portion of the weld to be made or can be included throughout the weld bead.
In the first embodiment described above, three shims are used in the three interfaces of a typical ~hree-~cone rock bit.
In ~his embodiment, an alternative arrangement is to employ two shims, one as illustrated in E'IG. 5 and a second shIm of twice the length as the shLms 35 illustrated ln FIG. 3. The second shim has a cen~ral 60-degree bend to form a shallow ¦ UV" with 120-degree separation o~ ~he legs of the l'V".
¦ The angled or V-shap~d shim fits into two interfaces, and I . ~ . .
¦ the L-shaped shim fits between the other two mating fac~s of bit legs to fsrm the third weld. The shims are readily formed as separate sheets of metal. ~owever, a pla~ed, fl~me sprayed or sputtered layer ca~ be applied to one or both of the faying surfaces to perform as described herein. Wire or a screen can be used in some circumstances~ Tapered shims can be useful in . ' '
1~.Z3 331 1 A pin end 17 at the upper end of the bit body remote from cutters 11 is threaded for attachme~t to a drill collar (not shown) at the lower end of a drill string made up of pieces of drill pipe. The drill collar seats on a shoulder 20 on the extexior of the bit body. The pin or shank end of the rock bitis generally cylindrical although the threaded portion is often conical, and is sometimes~r~erred to as the tool joint. Each ¦ cutter and associated segment may also be provided with a con-ventional lubrication system which is omitted from the drawings for clarity. The lubrication system supplies grease to the bearing surfaces, and grease seals 18 are t~pically provided between the cutters and segment legs to prevent loss of lubricant.
A central interior portion 19 at the upper end of the bit is hollow and communicates with passages (not shown in FIG. 1) in the ~it legs leading to openings or jet orifices adjacent the cutter cones. Drilling mud is pumped from the surace through the drill pipe to flow through these openings adjacent the cutters, and to carry rock par~icles back to the surface through the annulus around the bit and drill-pipe string.
In the center portion of the bit body between the shank end ¦ and the cone-supporting lower ends of the legs is a web 26 of steel sepArating the interior of the hollow shank end from a bit-body dome or crown undersur~ace which extends o~er the cones.
The fea~ures described thus far are conventional and well known ¦ in the art, and, ~or brevity, will not ~e discussed in greater detail.
Referring to F~G. 2, each segment 14 has a pair of angularly oriented fla~ faces or faying sur~aces 22 which extend longitudinally along a sha~ portion 23 of ~he segment.
. , , 112~331 1 The mating or faying surfaces 22 are normally oriented at an angle of 120 to each other so the three segments commonly used to form a complete bit ~ody will fit together tightly when assemble~ for final welding. The three segments used in a 5 typical three-cone bit are substantially identical and the planes of the faying surfaces intersect generally along the bit axis.
An inner surface 25 o~ the segment shank portion is con-cave to form a 120 segment of central interior poxtion 19 of ~he bit body~ The concave crown or dome surface on the under-side of web 26 extends downwardly and outwardly rom the lower end of mating surfaces 22 to a tapered and curved lower end of the segment leg called a shirttail 27. The steeply incli~ed portion of the crown'or dome surface leading to the cone-suppsrting lower ~nd por~ion of the leg is conventionallycalled a throat surface 21. A flat leg backface 30 (FIG. 2~ is positioned at the base of pin 12;
, A boss 28 having an opening 29 therethrough is formed at one side of the crown surface to receive a tungst~n-carbide nozzle' (not sh'own~ for passage of drilling mud pumped through central interior portion l9 (FIG. l) of the bit body during use of the bit. Bearingpin 12 extends inwardly and downwardly from leg backface 30, and inc~udes conventional features such as a spindle or nose bearing 31 and an annular ball-race groove 32 ~o receive retaining balls 16.
Before ass'embling the bit ~ody, a cutter cone is mounted on the bearing pin 12 of eac~ segment leg. Ball passages and lubricant ports, if any, are plugged to prevent in~rusion of unwanted materials. Such'subassemblies of segment and cone are conventional, and three such subassemblies are used to form a complete three-cone bit body.
. ,~''..,' ' ' ''' ' " .
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. ' /~- ~
~ 3 3 1 To assemble the bit, the several segment subassemblies are positioned together in a conventional clamping jig (not shown) with each faying surface 22 in face-to-face alignment with a corresponding faying surface on the adjacent segment. Typical clamping ~igs and assembly`fixtures suitable for use with electron-beam welding are shown in the aforementioned U.S.
Patënts No. 3,907,191 and No. 3,987,859~
. .
FIG. 4 shows schematically the undersurface of the bit body crown or dome with the three bit segments positioned together prior to welding. Legs 13 are shown in cross section.
Beore the segments are clamped together, a shim 35 of the type shown in FIG. 3 is inserted between two of the three pairs of mating faaes in the position sho~ in phantom line in FIG. 2.
Each shim is configured to fit against the lower, roughly rectangular part of the mating face of the bit segment in web 26 of the bit.
The dimensions of shim 35 will differ according to the size of the bit being manufactured, but the shim typically has a width of about 3/8 inch to 1 inch, and a length of 3 inches or more, to correspond to the dimensions of the welded portion of the segment faying surface adja~ent the dome of the bit.
Preferably, each shim is bent along one longitudinal edge to form a small perpendicularly extending lip 36. The lip limits the *epth of inser~ion of the shim between the mating faces prior to final cl~mpLng of the vi~ ~egm;2nts, and provides filler metal during welding.
.
~. , 1~.2L331 1 As mentioned hereinafter, two shims 35 are placed in the two welding interfaces which are the first and second to be electron-beam welded. A different shim 37 is used in the third welding interface. FIG~. S shows one fayir.g surface 22 of the third welding interface with a shim 37 in place. The balance of the structure of the segment is omitted. Third shim 37 has an "L" shape with one arm extending along the faying surface in the dome p~rtion of the bit. This part of L-shaped shim 37 ¦ corxesponds to straight shims 35 in the first two welding 0¦ interaces. T~e other ar~ of L-sha~3d shim 37 extends along the faying surface toward shank portion 23 of the segment.
This arm of the L-shaped shLm extends to the region of shouldsr 20. If desired, two straight shims laid in place like an L
can be used in the third welding interface instead of the L-shaped shim illustrated in FIG~ 5.
Thin sheet-metal stock is used to make the shims 35 and 37, and shim thickness is preferably limited to about 0.010 inch to avoid an excessi~e gap in the welding interface between the segments which could interfere with electron-beam welding ~0 of the faying surfaces. Sheet materials in the rar.ge of about 0.003 to 0.007 inch thickness have been found to be preferable for making the shims.
After the segments ha~e been properly positioned and clamped with the ~hims 35 and 37 in place in the three interf~es 25 ~o be welded, the elec:tron-beam welding ~rocess can be commenced,.
One of the three interfaces with a ~traight shim 35 is indexed to the beam positionO ~he electron beam is then used to make~
. ',' ,' .
,~
J~ ` .
~.Z~3~31 1 a ligh~ tack weld between the legs commencing in center 41 (FIG. 2) of the dome and proceeding outwardly to an outer corner 42 of mated faying surfaces 22 and then along shank portion 23. ~he direc~ion of..traverse of the electron beam is then reversed and power increased to produce a weld of the desired depth, which in most areas is the full width of faying surfaces 22.
Tha electron beam is also rapidly oscillated to assure melting of steel from both less as well as melting of the shim. Thus, the full depth weld cycle commences at an end 43 of the ~hank portion and proceeds along the interface to center 41 of the dome. In the crown or dome region, the . electron beam intersects the bit surface at an angle of about . 25 from the surface and extends in a direction towards the bit 15 axis. Since ~he angle of the electron gun is usually fixed, the electron beam intersects the surface o~ the bit body in the shank portion at a much higher angle. In one embodiment . such a weld bead has a d pth of about an inch in some areas, a width ~lateral to the direction of beam penetration) of about l/8 inch, and a hea~ affected zone about 1/32 inch wide on each side of the weld bead.
When the first weld is completed, the bit is indexed 120 around its axis to bring the nex~ interface into the electron beam position, and the cycle is repeated until all ~hree welds have been made. Straigh~ shims 35 are used in the first two welds and an L-shaped shim 3~ is preferably used in the third weld.
.
. ...
,' ! ~ ~ ~
.
~.2~. 33~
1 After-the three welds are made, there are three weld beads which intersect in a Y-shaped intersection in the center of the dome portion of the bit body on the bit axis. The weld heads are 1~0 apart, and extend radially outwardly from the center of the dome portion and along the shank or pin portion of the bit body. Such a weld bead in the dome portion has a different alloy content than the steel of the segments, and preferably has gxeater ductility than the segment steel.
When the welds are completed, pin end 17 ~FIG. 1) is machined and threaded to~provide a tool-joint connection on the shank portion of the bit body for connec~ion to a drill string. Other finishing operations such as installation of mud jets, lubrication of bearings, and installation of pressure compensators are normally completed after welding.
The shims i~ the dome portion of the bit body serve several purposes in construc~ion of the bito ~he metal of the shim provides an alloying metal for the steel in the dome portion of the bit segments or enhancing ductility and crack resistance. Dilution by the metal of the shim can reduce carbon content of the metal in the weld bead. The shim pro-vides space for stress relief of the weld, particularly in the dome portion~ The metal of the shim can also combine wi~h carbon or other materials which could adversely affect w~ld proper~ies. Melting o the ex~ra metal in ~he shim and in lip 36 of the shim can minimize depressions in the weld metal surface.
A particularly suitable material fox the shim is titanium.
When ti~anium alloys with the steel of the bit sesments several ; !
, ''''' ~ 1331 1 improvements in metallurgical properties of the weld bead can result. Ferrite in the weld bead can be stre~gthened b~ solid solution of titanium. The titanium tends to promote a fine grain structure and deoxidizes the weld bead. Adverse harden-ing of the weld bead during rapid cooling after passage of the electron beam is inhibited. Impact strength, fatigue resis-tance, and du~tility of the weld bead are enhanced. ~ardness 1 of the weld bead can be lower than in the absence of titanium.
¦ Thus, for example hardness di~ferences from Rockwell C-27 to Rockwell B-95 can occur. It is particularly significant to provide a higher alloy content in the weld beads in the dome portion where three weld beads intersect in a Y at the axis of the bit. Such a Y-shaped intersection o~ weld beads is subject to high stress levels, and enhanced metallurgical properties are important~
Another benefit of titanium in the weld bead adjacent the crown arises from its ability to stabilize carbon by formation o~ titanium carbide. Parts of the bit segments are carburized before assembl~, but the region to be welded is protected fxom carburizing by con~entional "stop-off" ma~erials which inhibit diffusion of carbon into the steel segment. Such stop-of~ materials are applied ko the surface as a slurry or electroplate, and pinhole imperfections may occur, leading to carburized spots in regions to be welded. Such high-carbon ~5 regions in a weld bead can be deleteriously brittle~
Accidental carbon leakag2 can be rectified by presence of titanium or other strong carbide forming material in the welding shims. The ti~anium car~ide i5 present as 3 separa~e .
~ .
~1 .
l~.Z1 3 ~1 1 phase in small particles, a~ does not significantly diminish ductility~ Other carbide-forming metals having a stronger affinity ~or carbon than does iron can be included in the shim.
Other alloying metals can also be used in the shims.
Suitable materials can include titanium alloys, zirconium, columbium, molybdenum, nickel, alloys of such metals, nickel-chromium stainless steels such as type 310, and iron alloys ¦ including titanium, zirconium, columbium, molybdenum and/or ¦ ni~kel. Iron can be used for diluting alloy content and decreasing hardenability. Cobalt can provide dilution although it is not a ferrite strengthener. Some other metals can be present in limited quantities which contribute to the desired properties o~ the weld bead and can make desirable additions.
Thus, for exampler the titanium alloy Ti-6Al-4V can be employed, the aluminum serving to deoxidize and grain re~ine the weld bead and vanadium contributing strength.
Typical materials for forming the segments of a rock bit include AISI type 8720 steel or AISI type 4815 steel. Other materials which al}oy with such steel for-enhancing ductility and/or toughness and increasing fatigue resis~ance of the weld ¦ bead will be apparent to thos~ skill~d in metallurgical arts.
¦ The shims provided in the dome portion of the rock ~it ¦ provides some ~ivergence be~een the faying suraces of the ¦ segments. It is believed ~hat the presence of the shim helps 25 ¦ minimize residual stresses due ~o weld me~al shrinkage. ~hen the third weld is made in a typical three-cone rocX bit, the other ~wo welds axe rigid and shrinkage can leave large residual tensile s~resses giving a tendency toward cracking. The shim . ,' 1~.213~1 1 in the third weld is particularly helpful in avoiding such a problem.
Warpage of an elongated weld joint can occur unless special precautions are ta~en. Thus, for example, when two -pieces are welded edge-to-edge, weld metal shrinkage during progression along the weld joint can tighten the joint to cause warpage nearer the end of the weld. A slight divergence along the seam to be welded can compensate for this effect.
The shLm in the crown or ~ome where the segment welds end provides divexgence which is believed to relieve stresses in the weld joint and minimize tendencies to crack. Such stress relief is particularly helpful where the three weld beads intersect. --In a three-cone rock bit, the third or last weld to be made has the greatest effect on residual stress. It has baen found that by providing a dome-portion shim which also extends at least part way along the faying surfaces toward the shank of the bit t significant Lmprovements in welding can be achieved.
The use o three t~tanium shims in the welds significantly 2Q decreased the xe~uirement for reworkin~ electron-beam-welded bi~s as compared with elec~xon-beam-welded bits without shims.
Use of an L-shaped shim in the third or final weld to be made caused a ~ur~her significant decrease in the requirements for xeworking.
After a rock bit is welded~ it is inspected and any cracks which could cause leakage from the interior of the bit are reworked by welding to close the crack. Such reworking is ~`
cos~ly and time consuming.
.
9.
~ ~.21331 1 About 200 roc)c bits were madc by clectron-beam welding thr~e s~gmen~s together as described above, but without any shims between the faying surfaces oP adjacent segments. Over three-fourths o~ these bits needed some reworking of the welds.
. Three titanium shims of the type illustrated in FIG. 3 were used in the welds in the dome portion of about 2000 rock bits. The reworking requirement decreased significantly to l about 12% of the bits.
10¦ Thereafter two straight shims as illustrated in FIG. 3 were used in two of the three welds~ An L-shaped shim was used in the third and final weld in lieu of the straight shLm on almost 600 bits. The bits requiring reworking dropped to l les5 than 2%. It is believed that the need for this residual 15¦ reworking is due primarily to other fa~tors, such as fit between the segments, improper indexing, errors in beam power or pvsition, or the like.
¦ The L-shaped shim pro~ides filler metal in the portion l of the third or final weld extending approximately to the 201 shoulder adjacent the pih joint of the bit. The spacing ¦ provided by this shim, and the extra metal and enhancement of metallurgical properties of the weld bead in this region con-¦ tribute to the decrease in reworking.
¦ ~lectron beam welding can cause some loss of material 25 ¦ from the weld bead, particularly whan the baam intersects ¦ the surface of the par~ being we~ded at a low angle, The lip ¦ 36 (FIG. 3) on the shim helps compensate for such possibleloss of me~al by providin~ extra material a~ the surface most I .. .. ...
39 I .
I -I . ,, ,,,,~
I ' ,~.
~L~.2~3~
1 subject to such loss. The lip also helps in positioning the shim before welding. ~f convenient, other enlarged portions such as a bead along one edge o the shim can be used to help in positloning the shim and providing extra metal at the edge of the mating faces of the weld.
The shim should be limited to a~out 0.010 inch thick.
With thicker shims there is a grea~er possibility of the electron beam penetrating too deeply and causing pinhole leaks through the weld bead. Such a pinhole can lead to a washout of the type mentioned a~ove with respect to cracks in the-dome.
The weld bead in electron~beam welding is only about 1/8 inch wide and thicker shLms can provide too much alloying metal for good weld-bead properties.
Generally it is preferred that the shLm have a thickness in the range of from about 0.003 to about 0~007 inch. Such thickness provides adequate alloying metal for enhancing weld-bead properties, and adequate spacing for stress relief without over dilution of the base metal or significant risk o~ pinhole leaks. Preferably, the width of the shim is sub-stantially e~ual ~o the anticipa~ed depth of penetration of the weld bead to assure a higher alloy content throughout the dome weld as compared with the steel o~ the segments.
When the rock bit body is com~leted by welding the thr~e subassemblies together, it has a threaded shank portion at one end for connection to a drill string and three legs dependins from the other endO T~e cutter cones are mounted on the lower ends of the legs. The roc~ bi~ has three weld beads spaced 120 apart extending along the hollow shank por~ion. Excep~ for . . ,:............ ..
I .
l ~ ' ',.~_ 1, ~L/, .
.2~3;~1 1 part of the third or final weld which is made, the shank portions of these weld be~ds have substantially the same co~po-sition as the steel used in forming the bit segments. The weld beads con~inue into the dome portion of the bit body to the Y-shaped intersection in the center. Each weld bead in the dome portion of the rock bit has a higher alloy content than the steel of the bit body due to melting of the shim. ~his weld bead with a different alloy content has enhanced metallur-gical properties for minimizing any tendency toward cracking 0 in the stressed portion of the rock bit body. The weld beads ... . ....
on the shank portion of the rock bit body are not subjected to the same types of stresses as those in the dome portion, and control of metallurgical properties of the weld bead is not as critical.
FIGS. 6 and 7 illustrate in side and end views, respec-tively, a two-cone rock bit 50 having parts of the body electron-beam welded together. This arrangement indicates the versatility of the electron-beam welding technique described herein.
In two-cone bit 50, a unitary steel body 51 is forg d and provided with a pin joint 52 at its shank end. Two cutter cones 53 having tungsten-carbide inserts 54 are mounted on the lower or downhole end of the bit. Each cone 53 is mounted on a leg 56 which is made as a separate part and welded into a mating pocket in bit body 51.
A mud jet orifice 57 is p~ovided on the axis of the bit body. Additional mud jet orifices 5B are provided nearer the gage or periphery of he bit for directing drilling fluid , . ..
1~ 2~331 1 toward the ~ottom of ~he hole being drilled in a region between cutter cones 53. Each of these outboard drilling-mud orifices 58 is in a separate steel insert 59 fitted into a mating pocket in bit body 51.
~nserts 59 and cutter mounting legs 56 are electron-beam welded to bit body 51. Thus r for example, heavy lines 61 in FIG. 7 show the 1QCUS of the weld beads. A titanium shim is advanta~eously placed between the faying surfaces of such a leg or însert and the bit body ~or enhancing the metallurgical propPrties of t~e weld bead, providing filler metal, and for spacing ~he faying surfaces apar~ for minimizing residual stresses. Such a shim is advantageously employed in the last portion of the weld to be made or can be included throughout the weld bead.
In the first embodiment described above, three shims are used in the three interfaces of a typical ~hree-~cone rock bit.
In ~his embodiment, an alternative arrangement is to employ two shims, one as illustrated in E'IG. 5 and a second shIm of twice the length as the shLms 35 illustrated ln FIG. 3. The second shim has a cen~ral 60-degree bend to form a shallow ¦ UV" with 120-degree separation o~ ~he legs of the l'V".
¦ The angled or V-shap~d shim fits into two interfaces, and I . ~ . .
¦ the L-shaped shim fits between the other two mating fac~s of bit legs to fsrm the third weld. The shims are readily formed as separate sheets of metal. ~owever, a pla~ed, fl~me sprayed or sputtered layer ca~ be applied to one or both of the faying surfaces to perform as described herein. Wire or a screen can be used in some circumstances~ Tapered shims can be useful in . ' '
3~
. , ~ 3~.
long welds. Other suitable shims can be employed in other configurations of rock bits. The process has been described in terms of electron-beam welding, but other energy beam techniqu~s such as a laser having deep weld penetration can also be suitable.
~ ecause of variations of this nature, it will be under-stood that this invention may be practiced o~herwise than as specifically described.
..
.
,;,, ~ ' ' ' ' ,,, __ _~' ~'' ' '~
. , ~ 3~.
long welds. Other suitable shims can be employed in other configurations of rock bits. The process has been described in terms of electron-beam welding, but other energy beam techniqu~s such as a laser having deep weld penetration can also be suitable.
~ ecause of variations of this nature, it will be under-stood that this invention may be practiced o~herwise than as specifically described.
..
.
,;,, ~ ' ' ' ' ,,, __ _~' ~'' ' '~
Claims (19)
1. A method for forming a rock bit body having a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-boring cutter cones, and a dome portion form-ing a web transverse to the axis of the body between the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of:
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least one of such weld beads along the shank portion of the body having substantially the same com-position as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a different alloy content than the steel of the segments for enhancing crack resistance of such weld beads.
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces, at least one of such weld beads along the shank portion of the body having substantially the same com-position as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a different alloy content than the steel of the segments for enhancing crack resistance of such weld beads.
2. A method as recited in claim 1 wherein one of such weld beads has a different alloy content than the steel of the segments along at least part of the shank portion of the body for enhancing crack resistance thereof.
3. A method as recited in claim 1 wherein the segments are electron-beam welded together.
4. A method as recited in any one of claims 1 to 3 wherein such a weld bead in the dome portion of the bit body has a higher content of a metal selected from the group con-sisting of titanium, zirconium, columbium, molybdenum and nickel than the steel of the bit body.
5. A method as recited in any one of claims 1 to 3 where-in such a weld bead in the dome portion of the bit body has a higher titanium content than the steel of the bit body.
6. A method as recited in any one of claims 1 to 3 wherein such a weld bead in the dome portion of the bit body has a higher content of a carbide former than the steel of the bit body, the carbide former being a metal having a stronger affinity for carbon than does iron.
7. A three-cone rock bit comprising:
a steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string;
three depending legs at the other end of the bit body;
a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit;
a plurality of weld beads along the shank portion of the bit body in each of three locations spaced 120° apart around the shank portion, at least one of such weld beads having a composition substantially the same as the composition of the steel of the bit body; and a weld bead in each of three sectors in the dome portion of the bit body, the three weld beads meeting in a Y-shaped intersection on the axis of the rock bit and extending generally radially therefrom, each of said weld beads having a continuation of a weld bead on the shank portion and being a different alloy content than the steel of the bit body for enhancing crack resistance thereof.
a steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string;
three depending legs at the other end of the bit body;
a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit;
a plurality of weld beads along the shank portion of the bit body in each of three locations spaced 120° apart around the shank portion, at least one of such weld beads having a composition substantially the same as the composition of the steel of the bit body; and a weld bead in each of three sectors in the dome portion of the bit body, the three weld beads meeting in a Y-shaped intersection on the axis of the rock bit and extending generally radially therefrom, each of said weld beads having a continuation of a weld bead on the shank portion and being a different alloy content than the steel of the bit body for enhancing crack resistance thereof.
8. A rock bit as recited in claim 7 wherein such a weld bead in the dome portion of the bit body has a higher content of metal selected from the group consisting of titanium, zirconium, columbium, molybdenum and nickel than the steel of the bit body.
9. A rock bit as recited in claim 7 wherein such a weld bead in the dome portion of the bit body has a higher titanium content than the steel of the bit body.
10. A rock bit as recited in any one of claims 7 to 9 wherein the weld beads are characterized by a depth of pene-tration much larger than the total width of the weld bead and heat affected zone.
11. A rock bit as recited in any one of claims 7 to 9 wherein such a weld bead in the dome portion of the bit body has a higher content of a carbide former than the steel of the bit body, the carbide former being a metal having a stronger affinity for carbon than does iron.
12. A rock bit as recited in any one of claims 7 to 9 wherein at least part of one of the weld beads along the shank portion has a different alloy content than the steel of the bit body.
13. A rock bit comprising:
a steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string;
a plurality of depending legs at the other end of the bit body;
a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit; and at least one weld bead along at least a portion of the bit body for securing together segments of the bit body, a portion of such a weld bead having a composition substantially the same as the composition of the steel of the bit body, and another portion of such weld bead having a different alloy content than the steel of the bit body for enhancing crack resistance thereof.
a steel rock bit body having a hollow, generally cylindrical shank portion at one end;
means on the shank portion for connection of the rock bit to a drill string;
a plurality of depending legs at the other end of the bit body;
a rock-boring cutter cone mounted on each leg;
a dome portion of the bit body between the shank portion and legs, the dome portion forming a web transverse to the axis of the rock bit between the hollow shank portion and the exterior of the rock bit; and at least one weld bead along at least a portion of the bit body for securing together segments of the bit body, a portion of such a weld bead having a composition substantially the same as the composition of the steel of the bit body, and another portion of such weld bead having a different alloy content than the steel of the bit body for enhancing crack resistance thereof.
14. A rock bit as recited in claim 13 wherein such weld beads extend across at least a portion of the dome portion of the bit body and such a weld bead in the dome portion of the bit body has a higher content of metal selected from the group consisting of titanium, zirconium, columbium, molybdenum and nickel than the steel of the bit body.
15. A rock bit as recited in claim 13 wherein such weld beads extend across at least a portion of the dome portion of the bit body and such a weld bead in the dome portion of the bit body has a higher titanium content than the steel of the bit body.
16. A rock bit as recited in any one of claims 13 to 15 wherein the weld beads are characterized by a depth of penetration much larger than the total width of the weld bead and heat affected zone.
17. A rock bit as recited in any one of claims 13 to 15 wherein such a weld bead in the dome portion of the bit body has a higher content of a carbide former than the steel of the bit body, the carbide former being a metal having a stronger affinity for carbon than does iron.
18. A rock bit as recited in any one of claims 13 to 15 wherein at least part of one of the weld beads along the shank portion has a different alloy content than the steel of the bit body.
19. A method for forming a rock bit body having a plurality of separately formed segments welded together, the body having a hollow shank portion at one end for connection to a drill string, a plurality of depending legs at the other end for mounting a plurality of rock-boring cutter cones, and a dome portion forming a web transverse to the axis of the body between the hollow shank portion and the exterior of the body adjacent the legs, the method comprising the steps of:
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces at least some of such weld beads along the shank portion of the body having substantially the same composi-tion as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a sufficiently different alloy content than the steel of the segments for improving ductility of such weld beads relative to weld beads along the shank portion.
forming a plurality of steel rock-bit body segments, each segment having a pair of faying surfaces, each of such faying surfaces being prepared for welding to a faying surface on an adjacent segment; and forming weld beads along mating faying surfaces for welding a plurality of such segments together along mating faying surfaces at least some of such weld beads along the shank portion of the body having substantially the same composi-tion as the steel of the segments, and the portion of such weld beads adjacent the dome portion of the body having a sufficiently different alloy content than the steel of the segments for improving ductility of such weld beads relative to weld beads along the shank portion.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000358204A CA1121331A (en) | 1977-07-22 | 1980-08-13 | Method for making rock bits |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US818,144 | 1977-07-22 | ||
| US05/818,144 US4156123A (en) | 1977-07-22 | 1977-07-22 | Method for making rock bits |
| CA307,873A CA1101246A (en) | 1977-07-22 | 1978-07-21 | Method for making rock bits |
| CA000358204A CA1121331A (en) | 1977-07-22 | 1980-08-13 | Method for making rock bits |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121331A true CA1121331A (en) | 1982-04-06 |
Family
ID=27165760
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000358204A Expired CA1121331A (en) | 1977-07-22 | 1980-08-13 | Method for making rock bits |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1121331A (en) |
-
1980
- 1980-08-13 CA CA000358204A patent/CA1121331A/en not_active Expired
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