U.S. patent application number 10/917231 was filed with the patent office on 2005-04-14 for apparatus and method for selective laser-applied cladding.
Invention is credited to Griffo, Anthony, Viswanadham, Ramamurthy.
Application Number | 20050077090 10/917231 |
Document ID | / |
Family ID | 34425832 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050077090 |
Kind Code |
A1 |
Viswanadham, Ramamurthy ; et
al. |
April 14, 2005 |
Apparatus and method for selective laser-applied cladding
Abstract
A method for applying a wear-resistant material to a rock bit is
disclosed that includes depositing a coating on a selected area of
the rock bit, applying a heated wear-resistant material using a
laser assisted cladding apparatus to a selected portion of the rock
bit, wherein the coating is selected to have material properties to
prevent significant bonding between the heated wear-resistant
material and the coated area of the rock bit.
Inventors: |
Viswanadham, Ramamurthy;
(Spring, TX) ; Griffo, Anthony; (The Woodlands,
TX) |
Correspondence
Address: |
OSHA & MAY L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Family ID: |
34425832 |
Appl. No.: |
10/917231 |
Filed: |
August 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60494876 |
Aug 13, 2003 |
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Current U.S.
Class: |
175/374 ;
175/435 |
Current CPC
Class: |
C23C 24/085 20130101;
E21B 10/50 20130101 |
Class at
Publication: |
175/374 ;
175/435 |
International
Class: |
E21B 010/00 |
Claims
What is claimed is:
1. A method for applying a wear-resistant material to a rock bit,
comprising: depositing a coating on a selected area of the rock
bit; and applying a heated wear-resistant material to the rock bit,
wherein the coating is selected to have material properties to
prevent significant bonding between the heated wear-resistant
material and the coated area of the rock bit.
2. The method of claim 1, wherein the selected areas of the rock
bit comprises inserts.
3. The method of claim 1, wherein the coating comprises at least
one selected from the group consisting of a carbide, a boride, and
a nitride of a metal selected from group IVA, VA, VIA transition
metal.
4. The method of claim 1, further comprising removing the heated
wear-resistant material from the selected area of the rock bit.
5. The method of claim 1, wherein applying comprises using a laser
assisted cladding apparatus.
6. An insert having a coating on a portion thereof for use in a
rock bit, comprising: a substrate; and a coating deposited on at
least one portion of said substrate in an amount sufficient to
reduce bonding of a wear-resistant material to said substrate.
7. The insert of claim 7, wherein the coating comprises at least
one selected from the group consisting of a carbide, a boride, and
a nitride of a metal selected from group IVA, VA, VIA transition
metal.
8. A method of fabricating a drill bit, comprising: forming a body
of the drill bit; forming a plurality of holes in portions of the
body to receive coated inserts; inserting at least one coated
insert into at least one of said plurality of holes; cladding at
least one selected area of said body with a wear-resistant
material.
9. The method of claim 8, wherein the laser-assisted cladding
apparatus comprises a feed line and a laser.
10. The method of claim 9, wherein the feed line comprises the
wear-resistant material.
11. The method of claim 10, further comprising disposing the feed
line in parallel with the laser.
12. The method of claim 8, further comprising cooling the drill
bit.
13. The method of claim 8, further comprising removing the
wear-resistant material from the plurality of coated inserts.
14. The method of claim 8, wherein the cladding comprises using a
laser-assisted cladding apparatus.
15. The method of claim 14, wherein the wear resistant material is
deposited in a single step.
16. A system for performing a cladding process, comprising: a
processor; a memory operatively coupled to a laser-assisted
cladding apparatus, wherein the apparatus comprises a feed line,
wherein the feed line comprises a wear-resistant material, and a
laser.
17. The system of claim 16, wherein the memory stores a program
readable by the processor.
18. The system of claim 17, wherein the program contains a
geometric information of a rock drill bit.
19. A rock bit made using the method of claim 1.
20. A rock bit comprising an insert in accordance with claim 6.
21. A method for selectively applying cladding to a rock bit,
comprising: depositing, in a one step process, wear resistant
material on a selected region of a cone, without contacting inserts
on that cone.
22. The method of claim 21, wherein the one step process comprises
using a laser assisted cladding apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit under 35 U.S.C. .sctn. 119
to U.S. Provisional Application Ser. No. 60/494,876, filed on Aug.
13, 2003. This provisional application is hereby incorporated by
reference in its entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to methods and apparatus for
depositing a material on a substrate. More specifically, the
invention relates to methods and apparatus for depositing a wear
resistant layer on a substrate.
[0004] 2. Background Art
[0005] Drilling in the earth is commonly accomplished by using a
drill bit having a plurality of rock bit roller cones ("cutter
cones") that are set at angles relative to the drill string axis.
The bit essentially crushes the formations through which it drills.
The roller cones rotate on their axes and are, in turn, rotated
about the main axis of the drill string. In drilling boreholes for
oil and gas wells, blast holes, and raise holes, rock bit roller
cones constantly operate in a highly abrasive environment. This
abrasive condition exists during drilling operations even with the
use of a medium for cooling, circulating, and flushing the
borehole. Such a cooling medium may be either drilling mud, air, or
another liquid or gas.
[0006] When drilling a hard formation, a bit with tungsten carbide
inserts projecting from the body of a rolling cone generally is
utilized due to the inserts' relative hardness. However, the
carbide inserts are mounted in a relatively soft metal (e.g. steel)
that forms the body of the rolling cone. This relatively soft body
may be abraded or eroded away when subjected to the high abrasive
drilling environment. This abrasion or erosion occurs primarily due
to the presence of relatively fine cuttings and chips from the
formation that are in the borehole.
[0007] Additional causes include the direct blasting effect of the
drilling fluid used in the drilling process, and the rolling or
sliding contact of the cone body with the formation. When the
material supporting the inserts is substantially eroded or abraded
away, the drilling forces either may break the inserts or may force
them out of the rolling cone body. As a result, the bit is no
longer effective in cutting the formation. Moreover, the inserts
that break off from the rolling cone may further damage other
inserts, the rolling cones, or other parts of the bit, eventually
leading to a catastrophic failure.
[0008] Erosion of the rolling cone body usually is most pronounced
on the inner and outer edges of the lands of the cone surface. This
area is immediately adjacent to the insert and the groove between
two rows of inserts. The heaviest wear on the rolling cone surface
lands is usually on the inner edges of the outer rows and on the
outer edges of the inner rows. When drilling relatively soft but
abrasive formations, the bit is able to penetrate at an extremely
high rate. This can result in individual cutting inserts
penetrating entirely into the abrasive formation, causing the
formation to come into contact with the cone shell body.
[0009] When such abrasive contact occurs, the relatively soft cone
shell material will wear away at the edges of the surface lands
until the interior portion of the insert becomes exposed. The
retention ability of the cone body is reduced, thereby ultimately
resulting in the potential loss of the inserts and reduction of bit
life. Because the penetration rate is related to the condition of
the bit, the drill bit life and efficiency are of paramount
importance in the drilling of boreholes. Accordingly, various
methods of hardfacing rock bit cones for erosion or abrasion
protection have been attempted.
[0010] For example, thermal spraying has been used to coat the
entire exposed surfaces, including the inserts, of a rolling cone
with a hardfacing material. Another method involves placing small,
flat-top compacts of hard material in the vulnerable cutter shell
areas to prevent cone erosion. Since erosion of groove surface can
be the main cause of insert loss, methods have been developed to
apply hardfacing material to both the lands and the grooves of a
roller cone.
[0011] It should be noted that inserts are typically retained in a
roller cone by the interfacial tension generated when the insert is
press-fitted into a drilled hole in the rolling cone body.
Accordingly, any method used to alleviate the erosion of the
rolling cone must take into consideration that the interfacial
tension holding the insert must be retained.
[0012] FIG. 1 illustrates a typical prior art rock bit for drilling
boreholes. The rock bit 10 has a steel body 20 with threads 14
formed at an upper end and three legs 22 at a lower end. Each of
the three rolling cones 16 are rotatably mounted on a leg 22 at the
lower end of the body 20. A plurality of cemented tungsten carbide
inserts 18 are press-fitted or interference fitted into insert
sockets formed in the cones 16.
[0013] When in use, the rock bit is threaded onto the lower end of
a drill string (not shown) and lowered into a well or borehole. The
drill string is rotated by a rig rotary table with the carbide
inserts in the cones engaging the bottom and side of the borehole
25 as shown in FIG. 2. As the bit rotates, the cones 16 rotate on
the bearing journals 19 and essentially roll around the bottom of
the borehole 25. The weight on the bit is applied to the rock
formation by the inserts 18 and the rock is crushed and chipped by
the inserts. A drilling fluid is pumped through the drill string to
the bit and is ejected through nozzles 26 (shown in FIG. 1). The
drilling fluid then travels up the annulus formed between the
exterior of the drill pipe and the borehole 25 wall, carrying with
it most of the cuttings and chips. In addition, the drilling fluid
serves to cool and clean the cutting end of the bit as it works in
the borehole 25.
[0014] FIG. 2 shows the lower portion of the leg 22 which supports
a journal bearing 19. A plurality of cone retention balls ("locking
balls") 21 and roller bearings 12a and 12b surround the journal 19.
An O-ring 28, located within an O-ring groove 23, seals the bearing
assembly.
[0015] The cone includes multiple rows of inserts, and has a heel
portion 17 located between the gage row inserts 15 and the O-ring
groove 23. A plurality of protruding heel row inserts 30 are about
equally spaced around the heel 17. The heel row inserts 30 and the
gage row inserts 15 act together to cut the gage diameter of the
borehole 25. The inner row inserts 18 generally are arranged in
concentric rows and they serve to crush and chip the earthen
formation.
[0016] As used herein, the term "erosion" will refer to both
erosion and other abrasive wear. Much of the erosion of the cone
body typically occurs between the gage row inserts 15 and heel row
inserts 30. Furthermore, erosion also may occur at the lands 27
between the gage row inserts 15 and inner row inserts 18.
Generally, a "land" refers to a surface on a rolling cone where
insert holes are drilled on the cone. It is also possible that
erosion may occur in the grooves 24 between successive inner row
inserts 18. These areas on a rolling cone surface are collectively
referred to as "areas susceptible to erosion." Erosion in these
areas may result in damage to the cone and/or loss of the inserts.
In highly erosive environments, the whole cone body may be
subjected to severe erosion and corrosion.
[0017] As noted above, a number of methods have been proposed for
applying a hardfacing layer to the surfaces of the cones. In
particular, laser cladding is a material deposition technique where
the energy of a laser is used to deposit a well-bonded hardfacing
layer onto a substrate. For wear resistant applications, this layer
tends to be formed of composite materials containing one or more
hard phases dispersed in a relatively softer matrix. Many such
hardfacing materials are known in the art, for example, U.S. Pat.
No. 6,196,338, assigned to the assignee of the present
invention.
[0018] Typical prior art techniques involving laser cladding
involve depositing a cladding material using a first, non-laser
technique, and then laser fusing the cladding material to the
substrate. U.S. Pat. No. 4,781,770 discloses one typical prior art
technique. That patent discloses, with reference to FIG. 3, that a
plurality of insert retention holes 146 are drilled in the exterior
shell 128. Typically, the insert holes are drilled to be
approximately 0.003 inch smaller in diameter than the hard cutter
inserts 142, which are to be press fitted into the holes 146.
[0019] A force of approximately several thousand pounds may be
required to press the cutter inserts 142 into place in the insert
holes 146. In the '770 patent, the finished cone 120 is sprayed
with cladding material 154 in the form of powder through a nozzle
160 (referencing FIG. 4). The powder may be a mixture of carbides
in a matrix, which may be blended with an organic mixture, such as
cellulose acetate, to facilitate adhesion to the cone surface 128
during spraying. Alternatively, a high velocity plasma spray may be
used to spray the powder 154, as shown in FIG. 3. The powder spray
unit is not shown. The powder is then densified and fused with a
laser source 150 (see FIG. 3). Further, the '770 patent discloses
that the entire exterior shell 128 of the intermediate steel body
144 is treated with the laser beam 152 in a raster pattern by using
a mechanical scanner.
[0020] However, laser cladding the entire cone surface is
problematic in that if cracks develop in the cladding, they will
invariably lead to cracks in the inserts, leading to early bit
failure. What is needed, therefore, are apparatus and methods for
depositing a hardfacing layer on a cone, without damaging either
the surface of the cone, or the inserts affixed thereto.
SUMMARY OF INVENTION
[0021] In one aspect, the present invention relates to a method for
applying a wear-resistant material to a rock bit that includes
depositing a coating on a selected area of the rock bit, and
applying a heated wear-resistant material using a laser assisted
cladding apparatus to a selected portion of the rock bit, wherein
the coating is selected to have material properties to prevent
significant bonding between the heated wear-resistant material and
the coated area of the rock bit.
[0022] In one aspect, the present invention relates to a coated
insert for use in cladding applications that includes a substrate,
and a coating deposited on at least one portion of said substrate
in an amount sufficient to reduce bonding of a wear resistant
material to said substrate, wherein the coating is a carbide, a
boride, or a nitride of a metal selected from group IVA, VA, VIA
transition metal.
[0023] In one aspect, the present invention relates to a method of
fabricating a drill bit that includes forming a body of the drill
bit, forming a plurality of holes in portions of the body to
receive coated inserts, inserting a plurality of coated inserts
into said plurality of holes, and cladding at least one selected
area of said body with a wear resistant material, wherein the
cladding comprises using a laser-assisted cladding apparatus to
deposit the wear resistant material in a single step.
[0024] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 shows a prior art drill bit;
[0026] FIG. 2 shows a cross-section of a single leg and cone of the
prior art drill bit of FIG. 1;
[0027] FIG. 3 illustrates a prior art laser cladding technique;
[0028] FIG. 4 illustrates a prior art laser cladding technique;
[0029] FIG. 5a illustrates a cone in accordance with one embodiment
of the present invention;
[0030] FIG. 5b illustrates one embodiment of a laser assisted
cladding apparatus in accordance with the present invention;
[0031] FIG. 6 illustrates a coated insert in accordance with an
embodiment of the present invention;
[0032] FIG. 7 illustrates an automated system including a computer,
in accordance with an embodiment of the present invention;
[0033] FIGS. 8a and 8b illustrate an apparatus for laser cladding
in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0034] The present invention relates to apparatus and methods for
laser-applied cladding. In particular, embodiments of the present
invention provide methods and apparatus for applying cladding to
selected cone surfaces and/or leg surfaces in rotary mining bits.
As used herein, the term "cladding" refers to the wear resistant
material that may be applied to a substrate, or to the act of
depositing the material. "Cladding process" is an alternative term
given to the process of depositing cladding to form a "cladding
layer" on the surface of the substrate. "Coating" is used to refer
to a protective coating which may be applied to selected surfaces
of the substrate, to prevent significant bonding between the
cladding and the substrate, it is also used to refer to the process
of applying a coating. As used herein, the term insert is not
intended to be limited to an insert for a roller cone bit but is
generally used to refer to any cutting element to be inserted into
a cutting tool, such as a cutter inserted into a fixed cutter bit.
Further, embodiments of the present invention relate to inserts for
use in rock bit applications. As used herein, the term "rock bit"
expressly includes roller cone bits, fixed cutter bits, or any
other type of bit for cutting through earth formations.
[0035] Thus, instead of applying cladding only to the desired
portions of the drill bit, as is typical in the prior art, cladding
may be applied to the entire bit with a special coating on those
sections where it is not desired to have cladding. The coating
prevents the cladding from bonding to the substrate, leaving
cladding on the desired portion only.
[0036] By "selected" the inventors mean the selective placement of
cladding or selectively bonding the cladding to a substrate.
Selective placement means that the cladding is applied to selected
areas, while selective bonding involves pre-coating the substrate
with a material that prevents the cladding from bonding to selected
areas. Thus, some embodiments of the present invention provide
techniques for providing cladding with a significant difference in
bond strength of the cladding in an uncoated region and a coated
region.
[0037] In accordance with embodiments of the invention, a coating
is used that significantly decreases the bond strength of the
cladding to the coated region as compared to an uncoated region.
Afterwards, cladding may be deposited over an entire surface. The
cladding will not significantly bond to the coated regions, and can
easily be removed or allowed to fall off.
[0038] It should be noted that, while the description provided
below references "insert bits," it is expressly within the scope of
the present invention that the methods and apparatus described
herein may be used more generally to deposit cladding on a
substrate. In general, techniques and apparatus disclosed by the
present invention may be used wherever the selected application of
a wear resistant compound to a substrate is desired.
[0039] One of the primary considerations when applying cladding to
a drill bit or a roller cone is to avoid damaging the inserts. As
noted above, prior art laser cladding techniques first apply the
cladding material using some other technique and later fuse the
cladding material onto the roller cone using laser beams. With this
approach, a significant amount of energy is imparted to the bit.
This often leads to cracks in the cladding. If cracks develop, the
inserts may also crack, leading to premature failure of the bits.
In order to avoid inadvertently cracking the inserts, prior art
techniques generally do not apply cladding to the areas immediately
adjacent to the insert. However, this approach is problematic
because relatively large areas of the cone surface are left
unprotected.
[0040] Embodiments of the present invention, however, allow
cladding to be deposited over the entire surface of the cone in a
one step process. The cladding does not bond to the coated regions
of the cone (which, in one embodiment, comprises the inserts), but
rather only substantially bonds to the uncoated regions.
[0041] FIG. 5a illustrates an embodiment of the invention in
accordance with one aspect of the invention. In FIG. 5a, cone (200)
includes multiple rows of inserts (206), and has a heel portion
(208) located between gage row inserts (212) and an O-ring groove
(23). A plurality of protruding heel row inserts (214) are spaced
around the heel portion (208). As shown in FIG. 5a, a
laser-assisted cladding apparatus (220) is shown depositing wear
resistant layer (210) on a surface of cone (200). In particular,
the laser-assisted cladding apparatus (220) is shown depositing the
wear resistant layer (210) between two rows of teeth (206).
[0042] The laser-assisted cladding apparatus (220) is now discussed
in more detail with reference to FIG. 5b. In general, the
laser-assisted cladding apparatus (220) comprises a cladding feed
line and a laser (230). In one embodiment, the cladding feed line
comprises a wear resistant powder (such as tungsten carbide) feed
line (240). Also, in a particular embodiment, a portion of the
powder feed line (240) and the laser (230) are arranged so as to be
"in line." That is, the powder feed line (240) and laser (230) are
disposed parallel to one another so that the laser energy heats the
powder (and in some cases, melts a portion of the powder) as it is
transmitted through the powder feed line into the laser path.
[0043] Although one embodiment uses a single laser source for
pre-heating the wear resistant material and for laser cladding, one
of ordinary skill in the art would appreciate that separate laser
sources may be used for pre-heating and cladding.
[0044] Some of the laser beam energy also heats the substrate
(namely a surface of the cone and/or leg). The heated or partially
melted wear resistant powder is directed (referred to as the
"entrained powder") towards the surface of the slightly heated
substrate. As a result, the heated or partially melted wear
resistant powder is deposited on the surface of the cone. The
present inventors have discovered that a novel coating may be
applied to selected surfaces of a cone to prevent bonding of the
cladding (wear resistant powder). In a particular embodiment, the
coating is applied to at least one insert to reduce damage to the
insert during the cladding process and to prevent bonding of
cladding to the insert.
[0045] A typical wear resistant powder comprises a tungsten
carbide-cobalt powder. In one embodiment, the wear resistant powder
may comprise a cobalt content of about 7 to 20 weight percent, a
carbon content of about 0.5 to about 6 weight percent, and a
tungsten content from about 74 to 92.5 weight percent. However,
depending on the particular application, the relative weight
percents of the various chemical components may be varied. In
addition, it should be understood that any wear resistant material
capable of being applied by a laser cladding process is within the
scope of the present invention.
[0046] As shown in FIG. 6, a coating 604 in accordance with
embodiments of the present invention, may be applied over the top
and side surfaces of the insert 602, over the entire insert 602, or
over selected portions of the insert. Those having ordinary skill
in the art will recognize that a number of coatings may be
suitable, so long as they provide an improved resistance to bonding
between the cladding and the substrate.
[0047] In some embodiments, the coating is a boride, nitride, or
carbide of a group IVA, VA, or VI transition metal (Ti, Zr, Hf, V,
Nb, Ta, Cr, Mo, W), or mixtures thereof. In a particular
embodiment, the coating is TiN. The coating 604 has been discovered
to prevent the bonding of an applied wear resistant layer to the
insert 602.
[0048] By using the coating 604, it has been discovered that
cladding inadvertently applied to the insert may simply be brushed
off. Thus, cladding can be applied to the entire surface of the
cone, without attempting to avoid the inserts. Accordingly, a
significant time reduction in applying a cladding layer to the cone
surface may be realized. This is due to the fact that by using
coated inserts, wear resistant material may be deposited without
regard to whether the material is being deposited over an insert or
over the cone. As previously noted, without such a coating, laser
cladding of cone surfaces often causes the inserts to prematurely
fail.
[0049] It should be noted that while reference is made to a cone
surface and inserts disposed in the cone, the coatings of the
present invention have a broader application. In particular, it is
expressly within the scope of the present invention that coatings
in accordance with the present invention may be used generally to
prevent the deposition of cladding to selected portions of a
substrate.
[0050] Some embodiments of the invention relate to systems for
performing the cladding process described above. A system in
accordance with the invention typically includes a processor and a
memory operatively coupled to the laser-cladding apparatus. In some
embodiments, a system may be implemented on a general-purpose
computer having a processor, a memory, and may optionally include
other hardware. For example, as shown in FIG. 7, a typical computer
(750) includes a processor (752), a random access memory (754), and
a storage device (e.g., permanent memory or hard disk) (756). The
computer (750) may also include input means, such as a keyboard
(758) and a mouse (760), and output means, such as a monitor (762).
Note that the general purpose computer is only for illustration and
embodiments of the invention may take other forms.
[0051] In a system in accordance with the invention, the memory
stores a program readable by the processor. The program may
comprise a computer-aided design (CAD) rendering of a drill bit on
which a cladding layer is to be deposited. The CAD rendering may
include geometric information such as the location of the teeth,
journal angle, and other such information as required. This
information may then be transmitted to the laser-assisted cladding
apparatus (shown as 220 in FIG. 5a), so that the wear resistant
layer may be deposited in the areas surrounding the inserts (206,
212, and/or 214) shown in FIG. 5a, without contacting the inserts.
In this fashion, the process can be automated, wherein a user can
select a stored drill bit configuration, and allow the
laser-assisted cladding apparatus (220) to deposit the cladding
layer without further operator intervention.
[0052] FIGS. 8a and 8b illustrate an apparatus for applying
cladding as described above. In FIG. 8a, a cone (800) is shown
mounted on a fixture (802). A portion of the fixture (802) may be
rotated or translated to expose various surfaces of the cone to a
laser (806). The laser (806) may similarly be rotated or translated
to apply wear resistant material, which arrives to the laser head
through powder inlet (810). Additionally, a moveable air flow
outlet (804) may be provided to cool the cone (800) during the
cladding process.
[0053] Further, FIG. 8a shows coated inserts (812), which have been
previously inserted into the cone, prior to cladding. FIG. 8b shows
the apparatus of FIG. 8a during the actual cladding process. As can
be seen in FIG. 8b, the air flow outlet (804) may be moved to
provide a cooling stream of air over the cone (800) surface. This
apparatus allows a relatively large amount of wear resistant
material to be deposited in a short amount of time.
[0054] As noted above, this apparatus and the techniques associated
with the apparatus provide two different types of selectivity.
These are referred to herein as positional selectivity and bonding
selectivity. By positional selectivity, the present inventors mean
that cladding may be deposited (in a one step process) in a
selected region on a cone, for example, without contacting inserts
(or plugs) on that cone.
[0055] By bonding selectivity, the present inventors mean that the
inserts (or selected portions of a substrate) may be treated with a
coating that creates a difference in the bonding strength between
the inserts and the cone with respect to the cladding.
[0056] Advantageously, therefore, one or more embodiments of the
present invention are capable of producing highly erosion-resistant
hardfacing coatings on rock bit cone surfaces to prevent cone shell
erosion during operation. In addition, one or more embodiments of
the present invention provide a cost effective way to reduce insert
cracking often associated with the cladding process.
[0057] 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.
* * * * *