U.S. patent application number 12/629201 was filed with the patent office on 2010-04-01 for ball hole welding using the friction stir welding (fsw) process.
This patent application is currently assigned to SMITH INTERNATIONAL, INC.. Invention is credited to Madapusi K. Keshavan, Scott M. Packer, Cary A. Roth, Russell J. Steel.
Application Number | 20100078224 12/629201 |
Document ID | / |
Family ID | 42056177 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100078224 |
Kind Code |
A1 |
Steel; Russell J. ; et
al. |
April 1, 2010 |
BALL HOLE WELDING USING THE FRICTION STIR WELDING (FSW) PROCESS
Abstract
A roller cone drill bit includes a bit body, at least one leg
extending downward from the bit body, a journal on each leg, and a
roller cone mounted on each journal. A ball race is configured
between each journal and roller cone, and a plurality of retention
balls is disposed within each ball race. A ball hole extends from
the back face of each leg to the ball race, and a ball hole plug
fits within the ball hole. The ball hole plug is secured to the leg
by a friction stir weld.
Inventors: |
Steel; Russell J.; (Salem,
UT) ; Packer; Scott M.; (Alpine, UT) ; Roth;
Cary A.; (Spring, TX) ; Keshavan; Madapusi K.;
(The Woodlands, TX) |
Correspondence
Address: |
OSHA, LIANG LLP / SMITH
TWO HOUSTON CENTER, 909 FANNIN STREET, SUITE 3500
HOUSTON
TX
77010
US
|
Assignee: |
SMITH INTERNATIONAL, INC.
Houston
TX
|
Family ID: |
42056177 |
Appl. No.: |
12/629201 |
Filed: |
December 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11136609 |
May 23, 2005 |
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12629201 |
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11090317 |
Mar 24, 2005 |
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11136609 |
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11090909 |
Mar 24, 2005 |
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11090317 |
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60573707 |
May 21, 2004 |
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60637223 |
Dec 17, 2004 |
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60652808 |
Feb 14, 2005 |
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Current U.S.
Class: |
175/369 ;
228/112.1 |
Current CPC
Class: |
E21B 10/22 20130101;
E21B 17/16 20130101; E21B 10/26 20130101; B23K 20/128 20130101;
B23K 20/129 20130101; E21B 17/1078 20130101; B23K 20/122 20130101;
C23C 8/60 20130101; B23K 20/1225 20130101; E21B 10/00 20130101;
B23K 20/002 20130101; E21B 31/107 20130101 |
Class at
Publication: |
175/369 ;
228/112.1 |
International
Class: |
E21B 10/22 20060101
E21B010/22; B23K 20/12 20060101 B23K020/12; E21B 10/06 20060101
E21B010/06 |
Claims
1. A roller cone drill bit, comprising: a bit body; at least one
leg extending downward from the bit body, wherein each leg
comprises a leg back face and a journal and each journal has a
journal race surface; a roller cone mounted on each journal,
wherein each roller cone has a roller cone race surface; a ball
race configured between the journal race surface and the roller
cone race surface; a plurality of retention balls disposed within
the ball race; a ball hole extending from the leg back face to the
journal race surface; and a ball hole plug, wherein the ball hole
plug is secured to the leg by a friction stir weld.
2. The roller cone drill bit of claim 1, wherein the ball hole plug
is welded directly to the leg back face without a filler
material.
3. The roller cone drill bit of claim 1, wherein the ball hole plug
material is the same as the leg material.
4. The roller cone drill bit of claim 1, wherein the ball hole plug
comprises a material selected from at least one of austenitic
stainless steel, high alloy carbon steel, and nickel and cobalt
based alloys.
5. The roller cone drill bit of claim 3, wherein the high alloy
materials are nickel based materials.
6. The roller cone drill bit of claim 1, wherein the ball hole plug
comprises the same material as the leg.
7. The roller cone drill bit of claim 1, wherein the ball hole plug
comprises a different material from the leg.
8. The roller cone drill bit of claim 7, wherein the ball hole plug
comprises material with a higher yield strength and higher
toughness than the leg.
9. The roller cone drill bit of claim 1, wherein the ball hole plug
is heat treated.
10. The roller cone drill bit of claim 1, further comprising a
keyhole in the friction stir weld.
11. The roller cone drill bit of claim 1, wherein no keyhole
remains in the friction stir weld.
12. The roller cone drill bit of claim 1, wherein the ball hole
plug comprises: a plug head, wherein the plug head comprises a top
surface and a side surface; a plug body; and a ball retainer
end.
13. The roller cone drill bit of claim 12, wherein the top surface
of the plug head is flush with the leg back face.
14. The roller cone drill bit of claim 12, wherein the friction
stir weld extends down the entire side surface of the plug
head.
15. The roller cone drill bit of claim 12, wherein the friction
stir weld extends down to a depth of the side surface.
16. The roller cone drill bit of claim 12, wherein the plug head is
non-cylindrical.
17. The roller cone drill bit of claim 16, wherein the ball hole is
non-cylindrical at the opening to the leg back face.
18. A roller cone drill bit, comprising: a bit body; at least one
leg extending downward from the bit body, wherein each leg
comprises a leg back face and a journal and each journal has a
journal race surface; a roller cone mounted on each journal,
wherein each roller cone has a roller cone race surface; a ball
race configured between the journal race surface and the roller
cone race surface; a plurality of retention balls disposed within
the ball race; a ball hole extending from the leg back face to the
journal race surface, wherein the ball hole is non-cylindrical near
the leg back face; and a ball hole plug, wherein the ball hole plug
is secured to the leg by a friction stir weld, the ball hole plug,
comprising: a plug head, wherein the plug head is non-cylindrical;
a plug body; and a ball retainer end.
19. The roller cone drill bit of claim 19, wherein the ball
retainer end has a mating curve with the same radius of curvature
as the race.
20. A method for retaining a roller cone on a bit leg, comprising:
mounting a roller cone on a journal extending downward from the bit
leg; inserting a plurality of retention balls into a ball hole
extending through a leg back face to the journal; inserting a ball
hole plug into the ball hole; and friction stir welding the ball
hole plug to a back face of the bit leg.
21. The method of claim 21, further comprising providing an
additive material and friction stir mixing the additive material
into the bit leg.
22. The method of claim 21, further comprising covering the ball
hole plug with a plate prior to friction stir welding, wherein the
friction stir welding welds the ball hole plug, the plate, and the
bit leg together.
23. The method of claim 23, wherein the ball hole plug is friction
stir welded to the bit leg prior to friction stir welding the
plate.
24. The method of claim 21, wherein the ball hole plug comprises a
non-cylindrical head and the ball hole is non-cylindrical near the
back face of the bit leg.
25. The method of claim 21, further comprising welding a plurality
of bit legs together.
26. A method for retaining a roller cone on a bit leg, comprising:
inserting a plurality of retention balls into a ball hole;
inserting a ball hole plug into the ball hole; friction stir
welding the ball hole plug to a back face of the bit leg using a
friction stirring tool; and removing the friction stirring
tool.
27. The method of claim 27, further comprising removing the
friction stirring tool at an initial removal location.
28. The method of claim 27, further comprising removing the
friction stirring tool by a gradual removal process, wherein the
gradual removal process comprises: beginning the removal of the
friction stirring tool at an initial removal location; gradually
removing the friction stirring tool as the friction stirring tool
is moved a distance away from the initial removal location; and
completely removing the friction stirring tool at a distance from
the initial removal location.
29. The method of claim 27, wherein removing the friction stirring
tool comprises pulling the friction stirring tool onto a
sacrificial material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit pursuant to 35 U.S.C.
.sctn.120 as a continuation-in-part application of U.S. patent
application Ser. No. 11/136,609, filed on May 23, 2005, which
claims priority to all of the subject matter included in
provisional applications with Ser. No. 60/573,707, filed May 21,
2004, Ser. No. 60/637,223, filed Dec. 17, 2004 and Ser. No.
60/652,808, filed Feb. 14, 2005, and non-provisional applications
with Ser. No. 11/090,909, filed Mar. 24, 2005 and Ser. No.
11/090,317, filed Mar. 24, 2005. The above referenced applications
are hereby incorporated by reference in their entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments disclosed herein relate generally to roller cone
drill bits used in wellbore operations. In particular, embodiments
disclosed herein relate generally to ball hole plugs and methods of
welding ball hole plugs to roller cone drill bits using friction
stir welding.
[0004] 2. Background Art
[0005] Historically, there have been two main types of drill bits
used drilling earth formations, drag bits and roller cone bits. The
term "drag bits" refers to those rotary drill bits with no moving
elements. Drag bits include those having cutters attached to the
bit body, which predominantly cut the formation by a shearing
action. Roller cone bits include one or more roller cones rotatably
mounted to the bit body. These roller cones have a plurality of
cutting elements attached thereto that crush, gouge, and scrape
rock at the bottom of a hole being drilled.
[0006] Roller cone drill bits typically include a main body with a
threaded pin formed on the upper end of the main body for
connecting to a drill string, and one or more legs extending from
the lower end of the main body. Referring to FIG. 1, a conventional
roller cone drill bit, generally designated as 10, consists of bit
body 11 forming an upper pin end 12 and a cutter end of roller
cones 13 that are supported by legs 14 extending from body 11. Each
leg 14 includes a journal 15 extending downwardly and radially
inward towards a center line of the bit body 11, with cones 13
mounted thereon. Each of the legs 14 terminate in a shirttail
portion 16. The threaded pin end 12 is adapted for assembly onto a
drill string (not shown) for drilling oil wells or the like.
[0007] Conventional roller cone bits are typically constructed from
at least three segments. The segments are often forged pieces
having an upper body portion and a lower leg portion. The lower leg
portion is machined to form the shirttail section and the journal
section. Additionally, lubricant reservoir holes, jet nozzle holes,
and ball races are machined into the forgings. Roller cones are
rotatably mounted to a bearing system on the formed journals, and
the leg segments are positioned together longitudinally with
journals and cones directed radially inward to each other. The
segments may then be welded together using conventional techniques
to form the bit body. Upon being welded together, the internal
geometry of each leg section forms a center fluid plenum. The
center fluid plenum directs drilling fluid from the drill string,
out nozzles to cool and clean the bit and wellbore, etc.
[0008] Roller cone bits may use a roller bearing system, a journal
bearing system, or a combination of the two to allow rotation of
the roller cones about the journal. Each type of bearing system is
ordinarily comprised of a number of separate components, including
primary bearings, secondary bearings, a seal system, features that
resist thrust loading, and a lubrication system. Also typical to
both bearing systems are cone retention balls, which are used to
prevent roller cones from separating from their journals.
[0009] Generally, roller bearing systems use rollers to separate
the roller cones from the journal. A cone retention ball bearing is
usually provided to carry axial load, and the rollers typically
carry radial loads. Journal bearing systems, on the other hand, use
a film of lubricant to separate the roller cones from the journal.
The inner surfaces of roller cones are specially designed so the
film of the lubricant prevents contact between the roller cone and
journal. Roller bearings are common in roller cone drill bits,
especially in roller cone drill bits with diameters larger than
twelve inches, because they can reliably support large loads and
generally perform well in the drilling environment. Bits having
small diameters commonly use journal bearing systems because there
is less space to install suitably sized rollers in a small
cone.
[0010] Referring to FIG. 2, a typical ball bearing system is shown
within a roller cone drill bit leg. Roller bearings 201 are placed
around the journal 202 prior to sliding the journal 202 into the
roller cone body 203. Alternate bearing systems may be used to
separate the roller cone body 203 from the journal 202, such as
floating bearings or a journal bearing system. The journal 202 has
a journal race surface 204, and the roller cone body 203 has a
roller cone race surface 205, which meets to form a ball race 206.
A ball hole 207 extends from the back face 208 of the drill bit leg
209 to the journal race surface 204. A plurality of cone retention
balls 210 are then inserted through the ball hole 207 into the ball
race 206, to hold the roller cone 203 on the journal 202. Once the
balls 210 are in place, a ball hole plug 211 is inserted into the
ball hole 207 and welded into place, to prevent the roller cone 203
from slipping off the journal 202.
[0011] To prevent damage to the cone retention balls 210 and edges
of the ball hole 207, cutter designs known in the art have the ball
hole 207 placed at 180 degrees from the load bearing zone of the
journal 202. This placement is selected to prevent forcing the
balls 210 against the rough edges of the ball hole 207 as they pass
over the hole 207. If the ball hole 207 were positioned in the load
bearing zone, the balls 210 would forcibly impact the edges of the
ball hole 207, probably resulting in metal chips and debris being
removed from the journal 202 so as to contaminate the lubricant and
eventually destroy the bearings and seals.
[0012] Contained within the bit body is a grease reservoir system
(not shown). A lubricant passage 212 is provided from the reservoir
to race surfaces 204, 205 formed between the journal 202 and roller
cone body 203, to lubricate race surfaces 204, 205 by a lubricant
or grease composition. Lubricant or grease also fills the portion
of the ball hole 207. Lubricant or grease is retained in the
bearing structure by a resilient seal 213 between the roller cone
203 and journal 207.
[0013] For many applications, roller cone drill bits are limited by
the bearing capacity or bearing life of the bit. A contributing
cause of bearing failure in roller cone systems is failure of the
weld joint between the ball hole plug and the back face of the leg.
In addition to providing a secure weld, protection of the weld
joint from wear, erosion and corrosion is necessary to prevent
failure of the plug and/or leg in the plug region, and ultimately,
failure of the bit.
[0014] Current methods of welding the ball hole plug to the back
surface of the bit leg are difficult to implement and may cause
flaws in the weld joint. For example, GMAW welding can cause
porosity, inclusions, cracks and an area of un-fused material at
the weld root, any of which can lead to premature failure by
initiating fatigue stresses. Further, in gas or plasma arc welding,
heat of the arc weld and molten weld deposit can potentially affect
the seal integrity of the weld joint. Additionally, dissimilar
chemistry in a deposit weld metal and the leg steel may cause
galvanic corrosion in caustic or acidic drilling conditions.
[0015] Another cause of bearing failure in roller cone drill bit
systems is spalling, which may occur, for example, when the ball
hole plug is not exactly in line with the journal race surface and
continuously passing retention balls flake off material from the
plug. When the surface spalls, debris contaminates the lubricant
which causes rapid wear and damage to the rest of the operable
bearing and seal components which eventually results in bearing
failure. Accordingly, there exists a continuing need for
developments in securing a ball hole plug to a bit leg that may at
least provide for increased bearing life.
SUMMARY OF INVENTION
[0016] In one aspect, embodiments disclosed herein relate to a
roller cone drill bit including a bit body, at least one leg
extending downward from the bit body. Each leg includes a leg back
face and a journal and each journal has a journal race surface, a
roller cone mounted on each journal, wherein each roller cone
includes a roller cone race surface, a ball race configured between
the journal race surface and the roller cone race surface, a
plurality of retention balls disposed within the ball race, a ball
hole extending from the leg back face to the journal race surface,
and a ball hole plug. The ball hole plug is secured to the leg by a
friction stir weld.
[0017] In another aspect, embodiments disclosed herein relate to a
roller cone drill bit including a bit body and at least one leg
extending downward from the bit body. Each leg includes a leg back
face and a journal and each journal has a journal race surface. A
roller cone is mounted on each journal, wherein each roller cone
has a roller cone race surface. A ball race is configured between
the journal race surface and the roller cone race surface, and a
plurality of retention balls is disposed within the ball race. A
ball hole extends from the leg back face to the journal race
surface, wherein the ball hole is non-cylindrical near the leg back
face. A ball hole plug is secured to the leg by a friction stir
weld. The ball hole plug includes a plug head, wherein the plug
head is non-cylindrical, a plug body, and a ball retainer end.
[0018] In another aspect, embodiments disclosed herein relate to a
method for retaining a roller cone on a bit leg, including mounting
a roller cone on a journal extending downward from the bit leg,
inserting a plurality of retention balls into a ball hole extending
through a leg back face to the journal, inserting a ball hole plug
into the ball hole, and friction stir welding the ball hole plug to
a back face of the bit leg.
[0019] In yet another aspect, embodiments disclosed herein relate
to a method for retaining a roller cone on a bit leg, including
inserting a plurality of retention balls into a ball hole,
inserting a ball hole plug into the ball hole, friction stir
welding the ball hole plug to a back face of the bit leg using a
friction stirring tool, and removing the friction stirring
tool.
[0020] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a conventional roller cone drill bit.
[0022] FIG. 2 is a conventional ball bearing system of a roller
cone drill bit.
[0023] FIGS. 3A and 3B show a ball hole plug friction stir welded
to a bit leg.
DETAILED DESCRIPTION
[0024] Generally, embodiments disclosed herein relate to securing a
ball hole plug to a roller cone drill bit leg. In particular,
embodiments disclosed herein relate to securing the ball hole plug
using friction stirring. Embodiments of the present disclosure
related to securing the ball hole plug may also relate to
improvements in assembly of the ball hole plug into the ball hole
by fitting a shaped plug into a corresponding shaped ball hole
prior to friction stirring.
[0025] Friction stirring is a process by which frictional heat
plasticizes, mixes, and forges metal, metal alloys, and other
materials. Friction stirring uses a combination of rotational and
directional motion applied to the surface of an object to be
treated. A rotating member is conventionally applied to the surface
that is to be friction stirred and is moved in a particular
direction until a plasticized state of the material is achieved.
The rotating member is moved along the surface to treat the
material by changing the material microstructure. Friction stirring
includes friction stir processing, friction stir mixing, and
friction stir welding (FSW). Friction stir processing is a
treatment process, which generally involves engaging two or more
previously adjoined materials (i.e., previous weld) to strengthen
or improve the weld characteristics. Alternatively, friction stir
processing may refer to treating a single material of a workpiece.
FSW involves engaging two or more adjoining materials to form a
weld.
[0026] In one embodiment of the present disclosure, as shown in
FIGS. 3A and 3B, a ball hole plug 311 is friction stir welded to
the leg back face 309. A tool used for friction stirring is
characterized by a generally cylindrical tool 300 having a shoulder
301 and a pin 302 extending downward from the shoulder. The pin 302
is rotated as force is exerted to urge the pin 302 and a workpiece
330 together. The workpiece 330, in FIG. 3A, includes the ball hole
plug 311, the back face of the leg 309, and an interface 360
between the ball hole plug 311 and the leg 309. Frictional heating
caused by the interaction between the rotating pin 302 and the
workpiece 330 causes the workpiece material to soften without
reaching the melting point of the material, which results in
plasticization of the workpiece material. Once sufficient heat is
generated, the pin 302 is plunged into the workpiece 330 through
the interface 360. The tool 300 is then moved along the workpiece
330, plasticizing the workpiece material as it flows around the pin
302. The friction stirring tool 300 is moved along the interface
360 in such a manner that the pin 302 presses into the interface
360 at an orientation that is co-planar with the interface 360
between the two materials. The result is a solid state bond 370
between the ball hole plug 311 and the leg 309. Friction stir
welding does not require a solder or filler material to form a
bond, but the use of an additional material is not necessarily
outside the scope of the present invention. Additional material may
be used, for example, to add corrosion inhibitors, wear resistant
material, and other material enhancing properties.
[0027] The resulting solid state bond of a friction stir weld is an
inter-metallic atomic bond formed by mechanical deformation. A
solid-state bond differs from bonds formed by conventional welding
techniques (i.e., welds resulting in a fusion bond or solder or
braze bond) in that conventional welding techniques include melting
the welding material and then cooling the material to form a bond.
The high rates of heating and cooling during conventional welding
may result in non-uniformity throughout the microstructure of the
welded material, which may create different strain rates and
increased stress within the welded material. A solid state bond, on
the other hand, does not require the workpiece material to melt.
Thus, more uniformity of the microstructure, and better mechanical
properties of the welded material may be achieved. For example, a
solid state bond may have substantially no metallurgical
discontinuities, including minimal or no porosity.
[0028] Referring back to FIGS. 3A and 3B, the ball hole plug 311
comprises a plug head 312, a plug body 313, and a ball retainer end
314. The plug head 312 comprises a top surface 316 and a side
surface 317. The plug head top surface 316 is flush with the back
face surface of the leg 309, and the plug head side surface 317
fits against the ball hole wall 307, at the opening portion 308 of
the ball hole, to create the interface 360 between the ball hole
plug 311 and the leg 309. However, the plug head 312 may initially
protrude from the back face surface of the leg 309 in order to have
a flush surface with the leg back face after friction stirring. The
ball retainer end 314 has a concave surface 315 with a radius of
curvature that mates with a corresponding radius of curvature of
the cone retention balls 310.
[0029] Generally, ball hole plug heads 312 are cylindrical in
shape. However, it is within the scope of the present disclosure
that the plug head 312 may be cylindrical or non-cylindrical in
shape. When the plug head 312 is cylindrical in shape, it may be
difficult to orient the ball hole plug 311 in such a manner that
the plug retainer end 314 configures exactly to the cone retention
balls 310. However, in accordance with various embodiments of the
present disclosure, the ball hole 307 is formed in a shape
corresponding with a non-cylindrical plug head 312. The
corresponding shapes are oriented in a position that secures the
retainer end 314 in configuration with the cone retention balls 310
when the plug head 312 is inserted into the ball hole 307.
[0030] Any non-cylindrical shaped plug head and corresponding ball
hole is within the scope of the present disclosure, including, for
example, an oval-shaped plug head, a plug head with at least one
flat side, a triangular-shaped plug head, a rectangular plug head,
etc. Additionally, the plug head may be non-symmetrical in shape,
such that the plug head has a notch, a protrusion, or other
variation from the general shape of the plug head.
[0031] As shown in FIG. 3A, the pin 302 may be plunged to a depth
in the workpiece 330 such that part of the interface 360 is
friction stir welded. Alternatively, as shown in FIG. 3B, the pin
302 may have sufficient depth so as to friction stir weld the
entire height of the ball hole plug head 312. Friction stir welding
the workpiece such that the entire plug head 312 is completely
consumed may yield a reduced subsurface notch affect at the weld
root. A reduced subsurface notch affect may be desirable because
the notch affect can promote failure by allowing fatigue crack
initiation sites. However, depending on the geometry of the plug
head, the entire head may not be consumed. For example, rather than
friction stirring the entire plug head 312, only the joint
interface 360 around the plug head may be friction stirred.
Furthermore, it is within the scope of the present disclosure that
the diameter of the pin 302 may be smaller, larger, or equal to the
diameter of the plug head 312. Likewise, the shoulder 301 may be
smaller, larger, or equal to the diameter of the plug head 312.
[0032] Large forces may be exerted between the pin and the
workpiece in order to apply sufficient pressure to the workpiece to
cause plasticization of the material. For example, for friction
stir welding an aluminum alloy workpiece of 1/4-inch thickness,
forces of up to 4000 pounds or more may have to be exerted between
the pin and the workpiece. Where the workpieces have sufficient
structural strength and rigidity, some of the force may be absorbed
by the workpieces themselves.
[0033] Furthermore, FIGS. 3A and 3B show a friction stirring tool
300 positioned at an orientation that is co-planar with the
interface 360 between the ball hole plug head 312 and the leg 309.
However, in accordance with another embodiment of the present
disclosure, the friction stirring tool may be moved along an
interface in such a manner that the pin is oriented perpendicular
to the interface plane. For example, a layer of wear resistant
material may be applied to the outer surface of a drill bit,
thereby creating an interface perpendicular to the pin. Depending
on the component being friction stirred and its configuration, one
skilled in the art would appreciate that either orientation of the
tool may be used.
[0034] The ball hole plug and the bit leg may be formed from the
same material, or alternatively, they may be formed from dissimilar
material. Further, the ball hole plug may be formed from material
with a higher yield strength and toughness than the leg material.
The ball hole plug and leg may be formed from material selected
from, for example, at least one of the following: austenitic steel,
carbon steels, low alloy carburizing steel, high alloy carbon
steel, and high alloy materials. High alloy materials include, for
example, iron-, cobalt-, or nickel-based materials, which may be
used for higher strength or improved corrosion resistance.
Additionally, the ball hole plug material may be subjected to
different processing conditions than the leg material. For example,
the ball hole plug material may be annealed or heat treated to have
the same hardness as the leg material.
[0035] Furthermore, additional material may be added to the
friction stirring process, so as to control mechanical properties
of the resulting workpiece material, including one or more of the
following unique properties: improved corrosion resistance, higher
toughness or equivalent toughness, higher hardness, fatigue
resistance, crack resistance, minimal or no significant heat
affected zone, and higher yield strength and wear resistance than
the base material used in a drill bit. In one embodiment of the
present disclosure, an additive material is friction stirred into
the roller cone drill bit leg, including over the ball hole plug
weld to increase wear resistance. For example, an additive material
may be applied by conventional methods to hardface the outer
surface of a drill bit. The hardfacing may then be treated using
the friction stirring methods disclosed herein, depending on the
desired material properties for the particular application, such as
hardness, toughness, casing-friendly wear resistance, etc.
[0036] Additive material may include, for example, metal matrix
composites, ferrous alloys such as steel and stainless steel,
non-ferrous materials such as aluminum, aluminum alloys, and
titanium, super alloys such as nickel, iron-nickel, and
cobalt-based alloys generally suitable for use at temperatures
above 1,000 degrees Fahrenheit, and air hardened steels. These
materials may be described as "high melting temperature compounds,"
or compounds having a melting temperature greater than steel.
Additional elements in the types of materials that may be friction
stirred include, but are not limited to, diamond, tungsten carbide,
chromium, molybdenum, manganese, silicon, carbon, boron, tungsten,
aluminum, titanium, niobium, tantalum, vanadium, nickel, cobalt,
zirconium, phosphorus, and rhenium.
[0037] Additive materials may be applied to the back face of a
drill bit leg, including over the ball hole plug weld by any means
known in the art, as described in U.S. patent application Ser. No.
______ (Attorney Docket Number 05516/446001), which is filed
concurrently herewith and is incorporated by reference in its
entirety. For example, additive material may be applied as hard
particles, as a tape, or as a plate to the leg base material prior
to friction stirring. Methods of application include: thermal
spraying, plasma spraying, using adhesives to bind the friction
stirring material to the base material, entrenching a packed powder
into the surface of the base material, sandwiching a first friction
stirring material between the base material and a second friction
stirring material, etc.
[0038] Alternatively, the additive material may have been welded to
a base material using a variety of conventional techniques, such as
GMAW (gas metal arc welding), GTAW (gas tungsten arc welding), PTA
(plasma transferred arc), FCAW (flux cored arc welding), etc. Due
to the phase transformations (to liquid state, then cooled to a
solid state) that occur during such conventional techniques, the
microstructure can possess undesirable characteristics, such as
precipitation of unwanted phases or structures, grain growth, and
residual stresses. Thus, one or more thermal treatments may have
been performed on the welded material (including pre- and/or
post-heat treatments) to relieve some of those residual stresses
and minimize cracking. In accordance with embodiments of the
present disclosure, the additive material may subsequently be
friction stir processed to achieve an improved fine-grained
microstructure (with improved material properties).
[0039] In one embodiment of the present disclosure, a plate may be
friction stir welded to the back surface of a drill bit leg and
cover the ball hole. The plate may comprise nickel or stainless
steel alloys, high strength steel alloys, or any air hardenable
steel, including D2 and A2 steel, or alloy steels such as 4815,
9313, and 8720 steels. In such an embodiment, the ball hole plug
may be welded (by conventional means or by friction stir welding)
to the leg prior to friction stir welding the plate to the leg, or
alternatively, the ball hole plug and the plate may be friction
stir welded to the leg during a single friction stirring process.
However, while the leg may be friction stirred prior to or after
assembly of the drill bit, the ball hole plug must be welded before
the drill bit, in particular the multiple leg forgings, is
assembled. Thus, if a plate is to be friction stir welded after
assembly of the drill bit, the ball hole plug must have been welded
to the leg prior to welding the plate to the leg.
[0040] Friction stir welding typically leaves lower asperity
heights and results in a smoother finish than conventional welding
techniques. However, a friction stirred surface may have a
depressed surface height, i.e., a keyhole, at the location where
the friction stirring tool was removed from the workpiece.
Depending on the application of the workpiece being friction
stirred, a keyhole may be left in the workpiece, the keyhole may be
filled, or the keyhole may be diminished by certain tool removal
processes. In one embodiment of the present disclosure, a keyhole
is left in the ball hole plug material upon removal of the friction
stirring tool. In another embodiment of the present disclosure, a
gradual removal process is used to minimize the occurrence of a
keyhole at the point of exit. The gradual removal process includes:
beginning the removal of the friction stirring tool at an initial
location in the workpiece; gradually pulling the friction stirring
tool out of the workpiece as the tool is moved a distance away from
the initial removal location; and finally, completely removing the
friction stirring tool at a distance from the initial position. The
removal process may also be aided by use of a secondary,
sacrificial material onto which the friction stirring tool may be
pulled, to minimize the effect of the tool removal on the leg.
[0041] Using the friction stir treatment methods of the present
disclosure, the solid-state processing principles associated with
friction stirring, may likely reduce the microstructure defects
present in the original weld or deposit, reducing the incidence of
cracking. By reducing the incidence of cracking, the need for
additional heat processing treatments, such as pre- and/or
post-heat treatments may be eliminated. Moreover, the processing
technique may be less hazardous, which may also allow for friction
stirring at any given location, including at the rig site, allowing
for better rebuild service. Another byproduct of the friction
stirring techniques of the present disclosure may be a reduction in
the surface roughness, i.e., reduced asperity heights, as compared
to a conventional weld. Lower asperity heights result in a smoother
finish, which reduces an apparent need for surface finishing or
grinding.
[0042] In addition to the above mentioned benefits of friction
stirring over conventional welding techniques, a greater hardness
of the friction stirring material may be achieved without losing
toughness. Specifically, friction stirring results in materials
having a refined grain microstructure. Refined grain
microstructures provide the friction stirred material with both
increased toughness and increased strength, as well as increased
corrosion resistance, and other favorable material characteristics.
Conventional welding, on the other hand, generally results in
materials having an inverse relationship between strength and
toughness (toughness decreases as strength is increased).
[0043] Increased hardness depends on the material composition and
type of material being friction stirred. The bit leg material is
generally made of low alloy carburizing steels, such as 4815, 8720,
4718, and 9313. However, other materials, such as 4130, 4145, and
other alloy steels, may be used as bit leg material. Friction
stirring 4815 steel that has been heat treated to have a hardness
of 36-40 HRc may yield a hardness increase of 5-10 HRc. However,
friction stirring 4140 steel or 4130 steel, for example, may result
in an increased hardness of 20 HRc or more. Such improved hardness
may result from the change in the material microstructure (i.e.,
through grain refinement/recrystallization to produce fine
precipitates such as carbides). Further, friction stir welding a
ball hole plug to a bit leg may result in the weld strength being
higher than the strength of the parent material (the original
material being friction stir welded).
[0044] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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