U.S. patent application number 12/939714 was filed with the patent office on 2011-02-24 for methods for enhancing a surface of a downhole tool and downhole tools having an enhanced surface.
This patent application is currently assigned to SMITH INTERNATIONAL, INC.. Invention is credited to Sike Xia, Zhou Yong.
Application Number | 20110042145 12/939714 |
Document ID | / |
Family ID | 43604403 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110042145 |
Kind Code |
A1 |
Xia; Sike ; et al. |
February 24, 2011 |
METHODS FOR ENHANCING A SURFACE OF A DOWNHOLE TOOL AND DOWNHOLE
TOOLS HAVING AN ENHANCED SURFACE
Abstract
A downhole tool having a layer of wear resistant material
applied thereon utilizing a thermal spray process and methods of
manufacturing such downhole tools.
Inventors: |
Xia; Sike; (Pearland,
TX) ; Yong; Zhou; (Spring, TX) |
Correspondence
Address: |
SMITH INTERNATIONAL INC.;Patent Services
1310 Rankin Rd.
HOUSTON
TX
77073
US
|
Assignee: |
SMITH INTERNATIONAL, INC.
Houston
TX
|
Family ID: |
43604403 |
Appl. No.: |
12/939714 |
Filed: |
November 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12773164 |
May 4, 2010 |
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12939714 |
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61175148 |
May 4, 2009 |
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Current U.S.
Class: |
175/374 ;
76/108.1 |
Current CPC
Class: |
C23C 4/18 20130101; C23C
30/005 20130101; E21B 10/52 20130101; C23C 4/02 20130101 |
Class at
Publication: |
175/374 ;
76/108.1 |
International
Class: |
E21B 10/50 20060101
E21B010/50; B21K 5/04 20060101 B21K005/04 |
Claims
1. A method for manufacturing a downhole tool comprising: providing
a tool body having a surface; applying a first intermediate layer
to at least a portion of the surface of the tool body; applying a
layer of a first wear resistant material utilizing a thermal spray
process over at least a portion of the first intermediate layer;
and sintering the layer of wear resistant material, wherein the
first intermediate layer is formed of a material having a melting
temperature that is less than the melting temperature of the first
wear resistant material.
2. The method of claim 1, wherein the first intermediate layer
comprises a second wear resistant material.
3. The method of claim 2, wherein the second wear resistant
material is applied using a non-thermal spray process.
4. The method of claim 1, wherein the first intermediate layer
comprises a first buffer material.
5. The method of claim 1, wherein the buffer material comprises a
metal component selected from the group consisting of a metal, a
metal alloy, a metal boride, a metal phosphate, and combinations
thereof.
6. The method of claim 1, wherein the first intermediate layer
comprises a first hardfacing composition.
7. The method of claim 1, wherein the thermal spray process is
selected from the group consisting of a high velocity oxygen fuel
process, a detonation gun process, and a super detonation gun
process.
8. The method of claim 7, wherein the thermal spray process is a
high velocity oxygen fuel spray process.
9. The method of claim 1, wherein the first wear resistant material
comprises hard particles and a binder, and wherein the hard
particles are selected from the group consisting of carbides,
borides, nitrides, and carbonitrides of W, Ti, Mo, Nb, V, Hf, Ta,
and Cr, and wherein the binder is selected from the group
consisting of cobalt, nickel, iron, mixtures, and alloys
thereof.
10. The method of claim 9, wherein the hard particles further
comprise one or more of boronitrides; diamond; and refractory
metals.
11. The method of claim 9, wherein the hard particles comprise
mono-tungsten carbide and the binder comprises cobalt.
12. The method of claim 1, wherein the layer of the first wear
resistant material has a hardness of at least 80 Ra.
13. The method of claim 1, wherein the melting temperature of the
material of the first intermediate layer differs from the melting
temperature of the first wear resistant material by at least
50.degree. C.
14. The method of claim 1, wherein the melting temperature of the
material of the first intermediate layer differs from the melting
temperature of the first wear resistant material by at least
100.degree. C.
15. The method of claim 1, wherein the material of the first
intermediate layer comprises a metal alloy selected from the group
consisting of an iron-based alloy, an aluminum-based alloy, a
nickel-based alloy, a cobalt-based alloy, a copper-based alloy, and
combinations thereof.
16. The method of claim 1, wherein the material of the first
intermediate layer comprises a nickel-based metal alloy.
17. The method of claim 16, wherein the material of the first
intermediate layer further comprises hard particles.
18. The method of claim 1, wherein the surface of the tool body
onto which the first intermediate layer is applied has a non-planar
surface.
19. The method of claim 1, wherein the downhole tool is a roller
cone drill bit comprising a cone which comprises a plurality of
parent cutting elements spaced about the exterior surface of the
body and the first intermediate layer and wear resistant layer are
applied to at least a portion of at least one of the parent
elements.
20. The method of claim 19, wherein a first plurality of parent
elements are arranged in a circumferential gage row and a second
plurality of parent elements are arranged in one or more
circumferential inner rows, and wherein the first plurality of
parent elements in the gage row and the second plurality of parent
elements in the inner rows comprise an intermediate layer and a
layer of a wear resistant material sintered to at least a portion
of the parent elements, and wherein the layer of wear resistant
material in the gage row differs with respect to one or more
properties from the layer of wear resistant material in the inner
rows.
21. The method of claim 20, wherein the one or more properties are
selected from hardness, thickness, hard particle content, hard
particle average grain size, toughness, composition, binder
content, density, porosity, elastic modulus, microstructure,
abrasion resistance, and erosion resistance.
22. The method of claim 1, wherein the method further comprises
applying a second intermediate layer comprising a third wear
resistant material to at least a portion of the first intermediate
layer, and wherein the second intermediate layer is positioned
between the first intermediate layer and the wear resistant layer
of the first wear resistant material, and wherein the second
intermediate layer differs with respect to one or more properties
from the first intermediate layer and the wear resistant layer of
the first wear resistant material.
23. The method of claim 22, wherein the third wear resistant
material of the second intermediate layer provides a gradient in
one or more properties between the first wear resistant material
and the material of the first intermediate layer.
24. The method of claim 22, wherein the third wear resistant
material of the second intermediate layer provides an interruption
in one or more properties between the first wear resistant material
and the material of the first intermediate layer.
25. The method of claim 22, wherein the method further comprises
applying a third intermediate layer positioned between the second
intermediate layer and the wear resistant layer of the first wear
resistant material, and wherein the third intermediate layer is
formed of a material having a melting temperature that is less than
the melting temperature of the first wear resistant material and
less than the melting temperature of the third wear resistant
material.
26. The method of claim 4, wherein the method further comprises
applying a second intermediate layer comprising a third wear
resistant material to at least a portion of the first intermediate
layer and applying a third intermediate layer comprising a second
buffer material to at least a portion of the second intermediate
layer, and wherein the second intermediate layer is positioned
between the first intermediate layer and the third intermediate
layer which is positioned interior of the wear resistant layer of
the first wear resistant material.
27. The method of claim 26, wherein the first wear resistant
material and the third wear resistant material are the same
composition; and wherein the first buffer material and the second
buffer material are the same composition.
28. The method of claim 1, wherein the tool body further comprises
a second intermediate layer positioned between the first
intermediate layer and the wear resistant layer of the first wear
resistant material, and wherein the second intermediate layer
comprises a hardfacing composition having a metal content that is
less than the metal content of the first intermediate layer and
greater than the metal content of the wear resistant layer of the
first wear resistant material.
29. The method of claim 1, wherein the sintering process utilizes
temperatures of at most 1200.degree. C.
30. The method of claim 1, wherein the sintering process utilizes
pressures in the range of from 700 kPa to 11 MPa.
31. The method of claim 1, wherein the material of the first
intermediate layer has a melting temperature that is less than the
tool body.
32. A downhole tool comprising: a tool body having at least two
layers applied on at least a portion of the surface of the tool
body, wherein the at least two layers comprise a wear resistant
layer and a first intermediate layer positioned between the surface
of the tool body and the wear resistant layer, wherein the wear
resistant layer comprises a first wear resistant material which is
applied utilizing a thermal spray process and sintered; and the
first intermediate layer is formed of a material having a melting
temperature that is less than the melting temperature of the first
wear resistant material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of and claims
priority to U.S. patent application Ser. No. 12/773,164, filed May
4, 2010 which claims priority to U.S. Provisional Application No.
61/175,148, filed May 4, 2009, which applications are hereby
incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The invention relates generally to the field of downhole
tools used to bore holes through earthen formations. More
particularly, the invention relates to methods and structures for
improving the performance and/or cost effectiveness of downhole
tools, in particular drill bits.
BACKGROUND OF THE INVENTION
[0003] Drill bits used to bore wellbores or boreholes through
earthen formations include roller cone drill bits. Typical roller
cone bits include a bit body made from steel or similar material.
The bit body includes one or more, typically three, legs which are
welded together to form the bit body. The bit body is typically
adapted to be coupled to a drilling tool assembly ("drill string")
which rotates the bit body during drilling. The legs include a
journal onto which a roller cone is rotatably mounted. The roller
cone typically includes a plurality of cutting elements disposed at
selected positions about the surface of the cone. The cutting
elements are typically of two types: inserts formed of a very hard
material, such as sintered tungsten carbide, that are press fit
into undersized apertures formed in the cone surface; or generally
triangular teeth that are milled, cast, or otherwise integrally
formed from the material of the roller cone. Bits having tungsten
carbide inserts (formed by sintering a tungsten carbide and a
binder) are typically referred to as "TCI" bits, while those having
teeth formed from the cone material are known as "milled tooth
bits." In each case, the cutting elements on the rotating roller
cones functionally breakup the formation to form a borehole by a
combination of gouging and scraping or chipping and crushing. This
action wears the surface of the cutting elements.
[0004] In many types of roller cone drill bits, the roller cone is
sealed with respect to the journal to exclude fluids and debris
from the wellbore from entering the journal. The seal element is
often an elastomer ring or similar device. A lubricant reservoir is
also typically included to provide a lubricant to the bearing
surface. The lubricant is typically some form of petroleum-based
grease or the like.
[0005] Typical roller cone drill bits also include therein fluid
discharge nozzles. The discharge nozzles provide a path for
discharge of drilling fluid from the interior of the drilling tool
assembly to cool, lubricate and clean the roller cones, and to lift
formation cuttings out of the wellbore as the wellbore is being
drilled. Often, such drilling fluid is circulated through the
wellbore at high rates to enable adequate lifting of drill cuttings
which can wear the surfaces of the drill bit.
[0006] For TCI-type roller cone bits, there is generally a
trade-off between the insert length that can be attached within the
roller cone aperture and the size of the journal and seal assembly
that can fit within the interior of the roller cone. The greater
the depth the insert is placed within the roller cone the greater
the extension height above the surface the insert can have, thus,
increasing the rate of penetration (ROP) of the bit. However, such
an increase usually requires sacrificing the space available within
the interior of the roller cone for the journal and seal assembly
which can limit bit life.
[0007] The cost of drilling a wellbore is proportional to the
length of time it takes to drill to the desired depth and location.
The time required to drill the well, in turn, is greatly affected
by the number of times the worn drill bit must be changed in order
to reach the targeted formation. This is the case because each time
the bit is changed, the entire string of drill pipe, which may be
miles long, must be retrieved from the wellbore, section by
section. Once the drill string has been retrieved and the new bit
installed, the bit must be lowered to the bottom of the wellbore on
the drill string, which again must be constructed section by
section. This process, known as a "trip" of the drill string,
requires considerable time, effort and expense.
[0008] Accordingly, it is always desirable to employ downhole tools
such as drill bits which will drill faster and longer and which are
more cost effective and usable over a wider range of formation
hardnesses.
SUMMARY OF THE INVENTION
[0009] In one aspect, one or more embodiments of the present
disclosure relate to a method for manufacturing a downhole tool
comprising providing a tool body having a surface; applying a first
intermediate layer of a material to at least a portion of the
surface of the tool body; applying a layer of a first wear
resistant material utilizing a thermal spray process over at least
a portion of the first intermediate layer; and sintering the layer
of first wear resistant material, wherein the material of the first
intermediate layer is formed of a material having a melting
temperature that is less than the melting temperature of the first
wear resistant material. In one or more embodiments, the downhole
tool may be a drill bit, in particular a roller cone drill bit
having a plurality of cutting elements spaced about an exterior
surface of a cone rotatably attached thereto and having the first
intermediate layer and wear resistant layer applied on at least one
of the cutting elements. In another aspect, one or more embodiments
of the present disclosure relate to a downhole tool having at least
two layers applied on at least a portion of the surface of the tool
body. The at least two layers comprise a wear resistant layer and a
first intermediate layer positioned between the surface of the tool
body and the wear resistant layer; wherein the wear resistant layer
comprises a first wear resistant material which is applied
utilizing a thermal spray process and subsequently sintered. The
first intermediate layer is formed of a material having a melting
temperature that is less than the melting temperature of the first
wear resistant material. In one or more embodiments, the downhole
tool may be a drill bit, in particular a roller cone drill bit
having a plurality of cutting elements spaced about an exterior
surface of a cone rotatably attached thereto and having the at
least two layers applied on at least one of the cutting
elements.
[0010] In yet another aspect, one or more embodiments of the
present disclosure relate to a drill bit comprising a bit body
having at least one leg extending therefrom; and a roller cone
cutter rotatably mounted on the leg. At least a portion of the
surface of the bit comprises a layer of a wear resistant material
applied utilizing a thermal spray process.
[0011] Other aspects and advantages of the present disclosure will
be apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of an embodiment of an
earth-boring bit made in accordance with the principles described
herein;
[0013] FIG. 2 is a partial cross-sectional view taken through one
leg and one rolling cone cutter of a drill bit as shown in FIG.
1;
[0014] FIG. 3 is a perspective view of one roller cone cutter of
the bit of FIG. 1;
[0015] FIG. 4 is a perspective view of an embodiment of an
earth-boring bit made in accordance with the principles described
herein;
[0016] FIG. 5 is a partial cross-sectional view taken through one
leg and one rolling cone cutter of a drill bit as shown in FIG.
4;
[0017] FIG. 6 is a an enlarged cross sectional view of a milled
tooth cutting element of a roller cone cutter shown in FIGS. 4 and
5 according to an embodiment of the present disclosure;
[0018] FIG. 7 is a scanning electron microscope (SEM) image of a
milled tooth cutting element of a roller cone cutter according to
an embodiment of the present disclosure;
[0019] FIG. 8 is a an enlarged cross sectional view of a milled
tooth cutting element of a roller cone cutter shown in FIGS. 4 and
5 according to another embodiment of the present disclosure;
[0020] FIG. 9 is a an enlarged cross sectional view of a milled
tooth cutting element of a roller cone cutter shown in FIGS. 4 and
5 according to another embodiment of the present disclosure;
and
[0021] FIG. 10 is a partial cross-sectional view taken through one
leg and one rolling cone cutter of a drill bit similar to FIG.
1.
[0022] FIG. 11 is a partial cross-sectional view of a tool body
according to an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0023] In one aspect, embodiments disclosed herein relate to
improved downhole tools. For example, one or more embodiments
disclosed herein relate to downhole tools and methods of
manufacturing such downhole tools. As described herein, downhole
tools may include roller cones, and drill bits incorporating such
roller cones. Downhole tools of the present disclosure having a
layer of wear resistant material applied thereon by a thermal spray
process can exhibit an improvement in one or more properties such
as rate of penetration (ROP), tool life and/or cost
effectiveness.
[0024] The following disclosure is directed to various embodiments
of the invention. The embodiments disclosed have broad application,
and the discussion of any embodiment is meant only to be exemplary
of that embodiment, and not intended to intimate that the scope of
the disclosure, including the claims, is limited to that embodiment
or to the features of that embodiment.
[0025] Certain terms are used throughout the following description
and claims to refer to particular features or components. As one
skilled in the art will appreciate, different persons may refer to
the same feature or component by different names. This document
does not intend to distinguish between components or features that
differ in name only. The drawing figures are not necessarily to
scale. Certain features and components herein may be shown
exaggerated in scale or in somewhat schematic form and some details
of conventional elements may not be shown in the interest of
clarity and conciseness.
[0026] In the following description and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus, should be interpreted to mean "including, but not limited to
. . . ."
[0027] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
[0028] Concentrations, quantities, amounts, and other numerical
data may be presented herein in a range format. It is to be
understood that such range format is used merely for convenience
and brevity and should be interpreted flexibly to include not only
the numerical values explicitly recited as the limits of the range,
but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. For example, a numerical range
of 1 to 4.5 should be interpreted to include not only the
explicitly recited limits of 1 to 4.5, but also include individual
numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4,
etc. The same principle applies to ranges reciting only one
numerical value, such as "at most 4.5", which should be interpreted
to include all of the above-recited values and ranges. Further,
such an interpretation should apply regardless of the breadth of
the range or the characteristic being described.
[0029] As used herein, the mesh sizes refer to standard U.S. ASTM
mesh sizes. The mesh size indicates a wire mesh screen with that
number of holes per linear inch, for example a "16 mesh" indicates
a wire mesh screen with sixteen holes per linear inch, where the
holes are defined by the crisscrossing strands of wire in the mesh.
The hole size is determined by the number of meshes per inch and
the wire size. When using ranges to describe sizes of particles,
the lower mesh size denotes (which may also have a "-" sign in
front of the mesh size) the size of particles that are capable of
passing through an ASTM standard testing sieve of the smaller mesh
size and the greater mesh size denotes (which also may have a "+"
sign in front of the mesh size) the size of particles that are
incapable of passing through an ASTM standard testing sieve of the
larger mesh size. For example, particles having sizes in the range
of from 16 to 35 mesh (-16/+35 mesh) means that particles are
included in this range which are capable of passing through an ASTM
No. 16 U.S.A. standard testing sieve, but incapable of passing
through an ASTM No. 35 U.S.A. standard testing sieve.
[0030] As used herein, unless specified otherwise, the term
"cutting portion" refers to the portion of a parent cutting element
(e.g., milled teeth or generally conical-shaped bodies) including
any layers applied thereto or inserts that extends beyond the
surface of the roller cone cutter. As used herein, unless specified
otherwise, the term "base portion" refers to the portion of a
parent cutting element or insert that extends beneath the surface
of the roller cone cutter and is separate from the cone body.
[0031] As used herein, unless specified otherwise, the term
"leading" refers to the edge, surface, flank, side, half, or
particular region of the cutting portion which leads relative to
the direction of cone rotation about the cone axis.
[0032] As used herein, unless specified otherwise, the term
"trailing" refers to the edge, surface, flank, side, half, or
particular region of the cutting portion which trails or follows
the leading side relative to the direction of cone rotation about
the cone axis. Generally, the trailing side may be disposed
opposite or 180.degree. from the leading side.
[0033] As used herein, unless specified otherwise, the term
"extension height" refers to the axial distance that a cutting
portion extends beyond the surface of the roller cone.
[0034] Referring first to FIGS. 1 and 2, an earth-boring roller
cone bit 10 according to an embodiment of the present disclosure is
shown. Bit 10 includes a central axis 11 and a bit body 12 having a
threaded section 13 on its upper end for securing the bit to the
drill string (not shown). Bit 10 has a predetermined gage diameter
as defined by three roller cone cutters 14, 15, 16 (two of which
are shown in FIG. 1) rotatably mounted on bearing journals (shafts
or pins) that depend from the bit body 12. Bit body 12 is composed
of three sections or legs 19 (two of which are shown in FIG. 1)
that are welded together to form bit body 12. Bit 10 further
includes a plurality of nozzles 18 that are provided for directing
drilling fluid toward the bottom of the borehole and around roller
cone cutters 14-16, and lubricant reservoirs 17 that supply
lubricant to the bearings of each of the cutters. Bit legs 19
include a shirttail portion 19a that serves to protect cone
bearings and seals from damage caused by cuttings and debris
entering between the leg 19 and its respective roller cone.
[0035] Referring now to FIG. 2, in conjunction with FIG. 1, each
roller cone cutter 14-16 is rotatably mounted on a pin or journal
20, with an axis of rotation 22 oriented generally downwardly and
inwardly toward the center of the bit. Drilling fluid is pumped
from the surface through fluid passage 24 where it is circulated
through an internal passageway (not shown) to nozzles 18 (FIG. 1).
Each roller cone 14-16 is typically secured on pin or journal 20 by
locking balls 26. In the embodiment shown, radial and axial thrust
are absorbed by roller bearings 28, 30, thrust washer 31 and thrust
plug 32; however, the present disclosure is not limited to use in a
roller bearing bit but may equally be applied in a friction bearing
bit, where roller cones 14-16 would be mounted on journals 20
without roller bearings 28, 30. In both roller bearing and friction
bearing bits, lubricant may be supplied from reservoir 17 to the
bearings by an apparatus that is omitted from the figures for the
sake of clarity. The lubricant is sealed and drilling fluid
excluded by an annular seal 34. The borehole created by bit 10
includes sidewall 5, corner portion 6 and bottom 7, best shown in
FIG. 2.
[0036] Referring still to FIGS. 1 and 2, each roller cone cutter
14-16 includes a back face 40 and nose portion 42. Further, each
roller cone 14-16 includes a generally frustoconical surface 44
that is adapted to retain inserts 60 that scrape or ream the
sidewalls of the borehole as roller cones 14-16 rotate about the
borehole bottom. Frustoconical surface 44 will be referred to
herein as the "heel" surface of roller cones 14-16, it being
understood however, that the same surface may sometimes be referred
to by others skilled in the art as the "gage" surface of a roller
cone cutter.
[0037] Extending between the heel surface 44 and nose 42 is a
generally conical cone body surface 46 having a plurality of parent
cutting elements which are generally conical in shape 70, 80, 81,
82. The parent elements 70, 80, 81, 82 have a layer of wear
resistant material 201 applied by a thermal spray process and
subsequently subjected to conditions sufficient to sinter the wear
resistant material (i.e., sintered) to form wear resistant cutting
elements that gouge or crush the borehole corner 6 and bottom 7 as
the roller cones 14-16 rotate about the borehole. Conical surface
46 typically includes a plurality of generally frustoconical
segments 48 generally referred to as "lands" which are employed to
support the cutting elements 80-82 as described in more detail
below. Grooves 49 are formed in cone surface 46 between adjacent
lands 48. Frustoconical heel surface 44 and conical surface 46
converge in a circumferential edge or shoulder 50. Although
referred to herein as an "edge" or "shoulder," it should be
understood that shoulder 50 may be contoured, such as a radius, to
various degrees such that shoulder 50 will define a contoured zone
of convergence between frustoconical heel surface 44 and the
conical surface 46.
[0038] In the embodiment shown in FIGS. 1 and 2, each roller cone
cutter 14-16 includes a plurality of wear resistant cutting
elements 70, 80, 81, 82, as described above, and a plurality of
heel row inserts 60. Exemplary roller cone 14, illustrated in FIG.
2, includes a plurality of heel row inserts 60 that are secured in
a circumferential heel row 60a in the frustoconical heel surface
44. Roller cone 14 further includes a circumferential gage row 70a
of gage wear resistant cutting elements 70 comprising a layer of
wear resistant material 201 applied by a thermal spray process and
sintered to parent cutting elements which are integrally formed
with the cone body 41 and located along or near the circumferential
shoulder 50. Roller cone 14 further includes a plurality of inner
row wear resistant cutting elements 80-82 which also comprise a
layer of wear resistant material 201 applied by a thermal spray
process and sintered to parent cutting elements which are
integrally formed with the cone body 41 and arranged in
spaced-apart inner rows 80a, 81a, 82a, respectively. Bit 10 may
include one or more additional inner rows containing wear resistant
cutting elements in addition to inner rows 80a, 81a, 82a. Heel
inserts 60 generally function to scrape or ream the borehole
sidewall 5 to maintain the borehole at full gage, to prevent
erosion and abrasion of heel surface 44, and to protect the
shirttail portion 19a of bit leg 19. Cutting elements 80-82 of
inner rows 80a-82a are employed primarily to gouge or crush and
remove formation material from the borehole bottom 7. Inner rows
80a-82a of roller cone 14 are arranged and spaced on roller cone 14
so as not to interfere with the inner rows on each of the other
roller cone cutters 15, 16. Gage cutter elements 70 cut the corner
of the borehole and, as such, perform sidewall cutting and
bottomhole cutting.
[0039] Inserts 60 each include a base portion and a cutting
portion. The base portion of each insert is disposed within a
mating socket drilled or otherwise formed in the cone steel of
roller cone cutters 14-16. Each insert 60 may be secured within the
mating socket by any suitable means including without limitation an
interference fit, brazing, or combinations thereof. The cutting
portion of the insert 60 extends from the base portion of the
insert and includes a cutting surface for scraping or reaming
formation material. The cutting portion of the heel row insert 60
is depicted as a dome-shaped surface, however, a person of ordinary
skill would appreciate that other configurations may also be used.
In particular, the heel row may contain wear resistant cutting
elements similar to those utilized in the gage and inner rows but
having a lower extension height. The present embodiment will be
understood with reference to one such roller cone 14, roller cones
15, 16 being similarly, although not necessarily identically,
configured. Such a roller cone cutter as shown in FIG. 2 is merely
one example of various arrangements that may be made according to
the present disclosure. For example, although not depicted in FIG.
2, it is understood that the wear resistant material may be applied
to only a portion of the parent cutting element (e.g., the leading
edge or surface). Additionally, although not depicted in FIG. 2, it
is understood that the wear resistant material may also be applied
to the exterior surface of the cone body.
[0040] An enlarged view of a roller cone 14 is shown in FIG. 3. As
shown, the roller cone cutter 14 includes a gage row 70a having a
plurality of wear resistant cutting elements 70 circumferentially
arranged about the cone, and an inner row 80a adjacent thereto.
Inner row 80a is positioned axially inward of gage row 70a. Cutting
elements 70, in this embodiment, are oriented so as to engage the
corner portion of the borehole while wear resistant cutting
elements 80 are oriented so as to engage the bottom of the
borehole. Roller cone 14 additionally has inner rows 81a and 82a
circumferentially arranged about the cone. Inner row 81a is
positioned axially inward of inner row 80a and inner row 82a is
positioned axially inward of inner row 81a (i.e., closer to the
nose of the roller cone).
[0041] The gage row, one or more inner rows, and/or heel row may
comprise wear resistant cutting elements comprising a layer of wear
resistant material applied by a thermal spray process and sintered
to a parent cutting element. In some embodiments, one or more of
the inner rows may comprise wear resistant cutting elements
comprising a layer of wear resistant material applied by a thermal
spray process and sintered to a parent cutting element while the
gage row and optionally the heel row comprise inserts, such as
TCIs, that are secured into the cone body. In some embodiments, the
gage row may comprise wear resistant cutting elements comprising a
layer of wear resistant material applied by a thermal spray process
and sintered to a parent cutting element while the inner rows and
optionally the heel row comprise inserts, such as TCIs, that are
secured into the cone body. Such inserts may be formed by
subjecting a metal carbide and a binder to conditions sufficient to
sinter the materials (sintered inserts). The metal carbide may be
selected from carbides of W, Ti, Mo, Nb, V, Hf, Ta and Cr. The
binder may be selected from Group VIII elements of the Periodic
Table (CAS version in the CRC Handbook of Chemistry and Physics),
in particular cobalt, nickel, iron, mixtures and alloys thereof.
Preferably, the inserts comprise a metal carbide of tungsten
carbide and a binder of cobalt. The inserts may be formed of a
sintered mixture of metal carbide and binder (e.g., a semi-round
top heel insert or TCI) and optionally may also include a layer of
ultra hard material such as polycrystalline diamond (e.g., a
pre-flat heel cutter or a diamond enhanced insert).
[0042] Such a roller cone drill bit as shown in FIG. 1 is merely
one example of various arrangements that may be used in a drill bit
which is made according to the present disclosure. For example, the
roller cone drill bit illustrated in FIG. 1 has three roller cones.
However, one, two and four roller cone drill bits are also known in
the art. Therefore, the number of such roller cones on a drill bit
is not intended to be a limitation on the scope of the present
disclosure.
[0043] The body of the roller cone cutter may be formed from any
suitable material for forming a roller cone cutter. The type of
material may be chosen based on the end use application such as
oilfield, mining, water-wells, etc. Suitable materials may include
steel alloys, composite materials, and other metal-based alloys
(e.g., nickel-based alloys and cobalt-based alloys). Suitable steel
alloys may include low alloy steels, high alloy steels and carbon
steels. Low alloy steels, as used herein, contain at most 8% by
weight (% w), based on the total weight of the steel, of alloying
elements. Such alloying elements may include one or more of
manganese, silicon, aluminum, nickel, chromium, cobalt, molybdenum,
vanadium, tungsten, titanium, niobium, zirconium, nitrogen, sulfur,
copper, boron, lead, tellurium, and selenium. High alloy steels, as
used herein, contain greater than 8% w of alloying elements and
include stainless steels and tool steels. Carbon steel, as used
herein, is a steel whose properties are determined primarily by the
amount of carbon present. Apart from iron and carbon, manganese up
to 1.5% w may be present as well as residual amounts of alloying
elements such as nickel, chromium, molybdenum, etc. It is when one
or more alloying elements are added in sufficient amount that it is
classed as an alloy steel. Composite materials, as used herein, may
be formed using an infiltration process (as distinguished from a
sintering process which uses greater temperatures and/or pressures)
and may comprise a metal carbide, nitride, and/or carbonitride and
a metal infiltrant. The metal infiltrant may be any metal or metal
alloy suitable for infiltrating and forming a composite material.
Such metal infiltrants may include Group VIII elements of the
Periodic Table, in particular nickel, cobalt, iron, mixtures and
alloys thereof. Such metal infiltrants may also include Group IB
elements of the Periodic Table (as used herein the CAS version in
the CRC Handbook of Chemistry and Physics), in particular copper
and alloys thereof. The roller cones may be formed by any of a
variety of methods. The methods may include forging, machining,
casting, molding, injection-molding, weld-forming, laser-forming,
and combinations thereof.
[0044] The roller cone cutter includes a plurality of parent
cutting elements (or structures). The parent cutting elements may
be milled teeth or generally conical-shaped bodies or projections
(different from milled teeth). As used herein, the term "milled
teeth" or "milled tooth" is meant to include parent cutting
elements that are generally triangular in a cross-section taken in
a radial plane of the cone. The milled teeth or generally
conical-shaped bodies or projections are arranged such that there
is a leading edge or surface which leads the element relative to
the direction of motion of the cone and a trailing edge or surface.
The generally conical-shaped bodies may have a continuously
contoured cutting portion. For example, the generally
conical-shaped bodies may have a continuously contoured leading
side having a radius of curvature greater than 0.050 inches (1.27
mm). The generally conical-shaped bodies may have angular portions.
The generally conical-shaped bodies may have a shape selected from
ballistic, conical, dome-shaped, hemispherical, semi-round,
symmetrical, asymmetrical, chisel-shaped, inclined chisel-shaped,
symmetrically chamfered, asymmetrically chamfered, and combinations
thereof. The parent cutting elements may be formed of any suitable
materials. Suitable materials include those described above for the
roller cone body (e.g., non-sintered cutting elements/inserts) and
are not meant to include inserts formed by sintering a metal
carbide and a binder. The type of material may be chosen based on
the end use application such as oilfield, mining, water-wells,
etc.
[0045] The parent cutting elements may be integrally formed with
the body of the roller cone. In other words, the cone body and the
parent cutting elements may be a single piece or unitary structure.
Alternatively, the parent elements may be formed separately from
the cone body and may include a base portion and a cutting portion.
The base portion of the parent elements may be secured within
mating sockets (or apertures) by interference press fit, welding,
brazing or the like. The parent cutting elements may be formed of
the same material as the body of the roller cone cutter or may be
formed of a different material to provide one or more different
properties between the parent cutting element and the cone body.
The one or more properties may include hardness and toughness. For
example, the parent cutting elements may be formed of a different
material (e.g., different steel or composite material) from the
cone body which has a greater hardness as compared to the material
of the cone body.
[0046] After the roller cone cutter is formed, a wear resistant
material is applied by a thermal spray process to at least a
portion (e.g., the leading surface or flank) of at least one of the
parent cutting elements on the surface of the cone. Suitably, the
wear resistant material may be applied to the entire surface of the
parent element. Optionally, the wear resistant material may also be
applied to the surface of the cone body. There are a variety of
thermal spray processes which are known in the art and all the
various processes involve high velocity ballistic application of
particles onto a target surface, typically by feeding a powder into
a gaseous effluent of a combustion chamber into which fuel in the
form of hydrogen or hydrocarbons and oxygen are fed. The powder is
heated to very high temperatures and then emitted from the
combustion chamber at very high velocities onto the target surface
where it impacts, spreading itself onto the surface. Suitably, the
thermal spray process may be selected from a detonation gun process
(D-gun), a super detonation gun process (Super D-gun), a high
velocity oxygen fuel (HVOF) process, a high velocity air fuel
(HVAF) process, a plasma spray process and a flame spray process.
Preferably, the thermal spray process may be selected from
detonation gun, super detonation gun and high velocity oxygen fuel
processes. Such detonation gun processes are described in U.S. Pat.
No. 4,826,734 and U.S. Pat. No. 5,075,129, which processes are
incorporated herein by reference in their entirety. Such super
detonation gun processes are described in U.S. Pat. No. 5,535,838,
which processes are incorporated herein by reference in their
entirety. Such high velocity oxygen fuel processes are described in
further detail below. More preferably, the thermal spray process
may include a high velocity oxygen fuel process which may utilize a
gaseous or liquid fuel, in particular a liquid fuel. Equipment for
use in a HVOF process is commercially available from Praxair
Surface Technologies, Inc. and Sulzer Metco, Inc. Examples of
gas-fueled HVOF equipment are the air- or water-cooled DIAMOND
JET.RTM. series by Sulzer Metco, Inc. and examples of liquid-fueled
HVOF equipment are the JP.TM. series by Praxair Surface
Technologies, Inc. and the WOKAJET.TM. series by Sulzer Metco,
Inc.
[0047] In a HVOF spray process, a spray axis of an apparatus for
the thermal spray process may be preferably aligned perpendicular
to a surface of the roller cone cutter. The nozzle of the apparatus
then emits detonation waves of hot gases at very high velocities,
for example 700 to 3300 ft/sec (200 to 1000 meters/sec), the
detonation waves entraining a powder of the wear resistant
material. The fuel may be hydrogen or a hydrocarbon and may be
provided in a gaseous or liquid form. A fluid substance such as
liquid carbon dioxide may be used to cool the surface of the roller
cone during the thermal spray process, to prevent the surface of
the roller cone from being heated above 400.degree. F.
(approximately 200.degree. C.). The thermal spray process may be
repeated a number of times until a desired thickness is
reached.
[0048] In one or more embodiments, additional wear resistant
material layers may be applied to the substrate (e.g., parent
cutting element) which may or may not be applied using a thermal
spray process. For example, one or more of the additional wear
resistant layers may be applied using the techniques described
herein for the buffer layer.
[0049] After applying the wear resistant material by a thermal
spray process, the roller cone cutter may be subjected to a
sintering process. The sintering process can provide for improved
bonding (and thus improved performance) since a substantial amount
of metallurgical bonding occurs between the particles of the wear
resistant material and between particles of the wear resistant
material and the surface onto which the material is applied (e.g.,
the parent cutting elements). Without sintering, mechanical bonding
is the primary bonding mechanism. The sintered wear resistant
material may have a hardness of at least 80 Rockwell "A" hardness
(Ra), in particular at least 85 Ra. The thickness of the sintered
layer of wear resistant material may have a thickness of at least
0.125 mm (0.005 inches), as described herein, for example in the
range of from 0.125 to 25 mm (0.005 to 1 inch), from 0.25 to 13 mm
(0.01 to 0.5 inches), from 0.35 to 10 mm (0.015 to 0.4 inches), or
from 0.5 to 5 mm (0.02 to 0.2 inches). The thickness of the wear
resistant layer may be chosen based on the particular drilling
application.
[0050] The sintering process uses temperature and pressure
conditions sufficient to consolidate and bond the wear resistant
material to the parent cutting elements. Sintering processes may
include vacuum sintering, inert gas sintering, microwave sintering,
induction furnace sintering, or hot isostatic pressing (HIP). The
temperature of the sintering process may range from 800.degree. C.
to 1600.degree. C. or from 900.degree. C. to 1400.degree. C., for
example 950.degree. C., 1000.degree. C., 1050.degree. C.
1075.degree. C., 1100.degree. C., 1125.degree. C., 1150.degree. C.,
1175.degree. C., 1200.degree. C., 1225.degree. C., 1250.degree. C.,
or 1300.degree. C. The sintering process may be conducted using any
suitable pressure depending on the sintering process utilized. For
example, the pressures may range from 100 mPa (millipascals) to 11
MPa (megapascals), such as 101 kPa (kilopascals), 500 kPa, 700 kPa,
1000 kPa, 1400 kPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa,
5 MPa, 5.5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, or 10 MPa. In one or
more embodiments, the pressure may range from 700 kPa to 11 MPa or
from 1400 kPa to 5.5 MPa, for example 750 kPa, 1000 kPa, 1450 kPa,
2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, or 5 MPa. The
duration of the sintering process at the specified pressures and
temperatures may be at least 30 seconds or at least 1 minute. The
duration of the sintering process at the specified pressures and
temperatures may be at most 100 hours or at most 75 hours. The
duration of the sintering process at the specified pressures and
temperatures may be in the range of from 30 seconds (0.0083 hours)
to 50 hours (180000 seconds) or from 1 minute (0.0167 hours) to 24
hours (1440 minutes), for example 5 minutes (0.083 hours), 15
minutes (0.25 hours), 30 minutes (0.5 hours), 45 minutes (0.75
hours), 1 hour (60 minutes), 1.25 hours (75 minutes), 1.5 hours (90
minutes), 1.75 hours (105 minutes), 2 hours (120 minutes), 4 hours
(240 minutes), 8 hours (480 minutes), 12 hours (720 minutes), 16
hours (960 minutes), or 20 hours (1200 minutes). The sintering
process may be conducted in one or more steps or stages. When using
multiple steps/stages, different parameters may be used between
different steps/stages (e.g., different pressures, temperatures, or
duration). One skilled in the art would also appreciate that the
pressure, temperature and duration of the sintering process may
vary depending on the sintering process employed.
[0051] The wear resistant material applied by the thermal spray
process may comprise hard particles and a binder. The hard
particles may be selected from carbides, nitrides, and
carbonitrides of tungsten (W), titanium (Ti), molybdenum (Mo),
niobium (Nb), vanadium (V), hafnium (Hf), tantalum (Ta), and
chromium (Cr). Suitably, the hard particles may be selected from
carbides of W, Ti, Mo, Nb, V, Hf, Ta and Cr. The hard particles may
further comprise boronitrides, diamond, and refractory metals such
as tungsten (W), molybdenum (Mo), niobium (Nb), tantalum (Ta), and
rhenium (Re).
[0052] The binder may comprise a metal component which may be any
suitable metal or metal alloy. The metal may be selected from Group
VIII metals, Group 1B metals, and Group IIIA metals, for example
nickel, iron, cobalt, copper, silver, gold, aluminum, and mixtures
thereof. Metal alloys may be selected from iron-based alloys,
aluminum-based alloys, nickel-based alloys, cobalt-based alloys,
copper-based alloys, and combinations thereof. In one or more
embodiments, the metal alloy may additionally contain one or more
alloying elements selected from chromium, molybdenum, silicon,
phosphorous, aluminum, boron, nickel, iron, cobalt, manganese,
zinc, tin, silver, and carbon. The term "metal-based" is used
herein, unless indicated otherwise, to denote the metal element
present in the greatest weight percent in the alloy.
[0053] In one or more embodiments, the wear resistant material used
to form wear resistant layers of greater hardness may comprise a
metal binder selected from cobalt, nickel, iron, mixtures and
alloys thereof; or a metal alloy binder selected from iron-based
alloys, nickel-based alloys, cobalt-based alloys, and mixtures
thereof. Examples of binder compositions include cobalt; cobalt and
chromium; cobalt and iron; nickel and iron; and a combination of
nickel, molybdenum, chromium, iron, and cobalt.
[0054] In one or more embodiments, the wear resistant material used
to form intermediate wear resistant layers having a lower melting
temperature may comprise a suitable iron-based, cobalt-based or
iron-based with cobalt alloy which may also contain one or more of
the following: chromium, molybdenum, aluminum, boron, silicon, and
nickel; or a suitable copper-based or copper-based with nickel
alloy which may also contain one or more of the following:
manganese, chromium, zinc, tin, silver, silicon, carbon and iron;
or a suitable iron-based alloy with nickel which may also contain
one or more of the following: chromium, molybdenum, silicon and
phosphorous; or a suitable nickel-based alloy which may contain one
or more of the following: boron, silicon, chromium, tungsten,
molybdenum, cobalt, and iron, for example nickel, chromium and
boron (Ni--Cr--B) alloys. As used herein, the term "melting
temperature" of a material is defined to be the solidus temperature
of the metal component in the material. Table 1 below describes
examples of nickel-based alloys suitable for use as a low melting
temperature metal alloy.
TABLE-US-00001 TABLE 1 Metal Alloy Composition (% weight)* Hardness
(HRc) Melting Point (.degree. C.) A.) Carbon (0.5); Chromium 45-50
1025 (13.8); Boron (2.3); Silicon (3.4); Iron (4.8); Nickel
(balance) B.) Carbon (0.55); 58-63 1032 Chromium (16.5); Boron
(3.6); Silicon (4.8); Iron (3.0); Molybdenum (3.5); Copper (2.1);
Nickel (balance) C.) Carbon (2.9); Chromium 58-63 1065 (7.5); Boron
(1.4); Silicon (2.4); Iron (2.5); Cobalt (6.2); Nickel (balance)
*denotes pre-application weight percentages
[0055] Preferably, the hard particles comprise tungsten carbide and
the binder comprises cobalt when the wear resistant material is
used as an outer layer or a harder intermediate wear resistant
layer. The tungsten carbide may comprise mono-tungsten carbide,
although other tungsten carbides such as cemented and cast may be
used.
[0056] In one or more embodiments, the tungsten carbide hard
particles of the wear resistant material may have an average
particle (or grain) size in the range of from 0.5 to 44 microns
(micrometers), for example from 1 to 20 microns, from 1 to 10
microns, or 2 to 6 microns. The binder may be present in an amount
of at least 3% w, based on the total weight of the wear resistant
material pre-application, in particular in the range of from 10 to
50% w, for example 12% w, 15% w, 17% w, 20% w , 25% w, 30% w, 40%
w, or 45% w, on the same basis. The hard particles may be present
in an amount in the range of from 50 to 98% w or 80 to 95% w, based
on the total weight of the wear resistant material pre-application,
for example 55% w, 65% w, 70% w, 75% w, 85% w, or 90% w, on the
same basis. The sintered wear resistant material may have a
porosity less than 0.8% by volume. With such low porosity, the
actual density approaches the theoretical density. The sintered
wear resistant material as applied by the thermal spray process has
improved properties, such as improved bonding, as discussed above.
These improved properties can lead to an improvement in bit
performance, in particular bit durability.
[0057] In an exemplary embodiment, parent cutting elements in
different areas of the roller cone may be provided with wear
resistant material layers having different properties. One or more
properties may differ and may be selected from hardness, thickness,
hard particle content, hard particle average grain size, toughness,
composition, binder content, density, porosity, elastic modulus,
microstructure, abrasion resistance, and erosion resistance. In
particular, the binder content and/or the hard particle average
grain (or particle) size may differ. As used herein, the terms
"different" or "differ" are not meant to include typical variations
in manufacturing. For example, a first plurality of parent cutting
elements may be arranged in a circumferential gage row and a second
plurality of parent cutting elements may be arranged in one or more
circumferential inner rows. The first plurality of parent elements
may be provided with a layer of wear resistant material applied by
a thermal spray process and subsequently sintered. The second
plurality of parent elements may also be provided with a layer of
wear material applied by a thermal spray process and subsequently
sintered. The layer of wear resistant material on the gage row
parent cutting elements may differ with respect to one or more
properties from the layer of wear resistant material on the inner
row parent cutting elements.
[0058] As used herein, a "layer" is meant to include a region
containing wear resistant material with the same properties which
includes typical variations in manufacturing. It is understood that
a thermal spray process may be repeated several times using the
same wear resistant material to obtain the desired thickness of a
particular layer.
[0059] Bits incorporating roller cones prepared according to this
embodiment are believed to provide an improved drill bit, in
particular, a more durable and cost effective bit. A more cost
effective bit may be provided as the wear resistant material is
applied to parent cutting elements using a thermal spray process
and subsequently sintered. This provides for a reduction in
manufacturing costs, for example the usage of tungsten carbide
inserts (TCI) can be decreased, the amount of labor can be reduced
and the manufacturing process can be simplified. In some
embodiments, when using a generally conical-shaped body integrally
formed with the cone body as a parent cutting element, a larger
journal, bearing, and/or seal assembly may be used since a base
portion of an insert does not have to be accommodated within the
cone body. This can extend the bit life due to reduced breakage,
improved bearing life, and/or improved seal life.
[0060] In one or more embodiments, a roller cone drill bit has a
plurality of parent cutting elements having at least two layers, an
outer layer and a first intermediate layer, applied on at least a
portion (e.g., a leading surface or flank) of at least one of the
parent cutting elements. At least one of the at least two layers
being applied utilizing a thermal spray process and comprising a
wear resistant material, as discussed above. Suitably, the layers
may be applied to the entire surface of the parent cutting element.
Optionally, one or more of the layers may also be applied to the
surface of the cone body. Suitably, the parent cutting element may
have three, four, five, six or more layers applied thereto.
Referring to FIGS. 4, 5 and 6, a milled tooth roller cone bit 30
according to an embodiment of the present disclosure is shown. The
milled tooth roller cone drill bit 30 includes a central axis 11
and a steel bit body 212 having a threaded coupling ("pin") 113 at
one end for connection to a conventional drill string (not shown).
At the opposite end of the drill bit body 212 there are three
roller cones 112, 114, 116 for drilling earthen formations to form
an oil well or the like ("wellbore"). Bit 30 has a predetermined
gage diameter as defined by three roller cone cutters 112, 114, 116
(two of which are shown in FIG. 4) rotatably mounted on bearing
journals (shafts or pins) (not shown) that depend from the bit body
212. Bit body 212 is composed of three sections or legs 119 (two of
which are shown in FIG. 4) that are welded together to form the bit
body. Bit 30 further includes a plurality of nozzles 115 that are
provided for directing drilling fluid toward the bottom of the
borehole and around roller cone cutters 112, 114, 116, and
lubricant reservoirs 117 that supply lubricant to the bearings of
each of the cones. Bit legs 119 include a shirttail portion 119a
that serves to protect cone bearings and seals from damage caused
by cuttings and debris entering between the leg 119 and its
respective roller cone.
[0061] Referring now to FIG. 5, in conjunction with FIG. 4, each
roller cone cutter 112, 114, 116 is rotatably mounted on a pin or
journal 120, with an axis of rotation 122 oriented generally
downwardly and inwardly toward the center of the bit. Drilling
fluid is pumped from the surface through fluid passage 124 where it
is circulated through an internal passageway (not shown) to nozzles
115 (FIG. 4). Each roller cone 112, 114, 116 is typically secured
on pin or journal 120 by locking balls 126. In the embodiment
shown, radial and axial thrust are absorbed by roller bearings 128,
130, thrust washer 131 and thrust plug 132; however, the present
disclosure is not limited to use in a roller bearing bit but may be
equally applied in a friction bearing bit, where roller cones 112,
114, 116 would be mounted on journals 120 without roller bearings
128, 130. In both roller bearing and friction bearing bits,
lubricant may be supplied from reservoir 117 to the bearings by an
apparatus that is omitted from the figures for the sake of clarity.
The lubricant is sealed and drilling fluid excluded by an annular
seal 134. The borehole created by bit 30 includes sidewall 5,
corner portion 6 and bottom 7, best shown in FIG. 5.
[0062] Referring still to FIGS. 4 and 5, each roller cone cutter
112, 114, 116 includes a back face 140 portion and a nose portion
142. Further each roller cone 112, 114, 116 includes a generally
frustoconical surface 144 which will be referred to herein as the
"heel" surface of roller cones 112, 114, 116. Although not shown in
FIGS. 4 and 5, the heel surface of roller cones 112, 114, 116 may
contain one or more heel row inserts, as discussed above, secured
within mating sockets (or apertures).
[0063] Extending between the heel surface 144 and nose 142 is a
generally conical surface 146 having a plurality of teeth
integrally formed with the surface of the cone. Frustoconical heel
surface 144 and conical surface 146 converge in a circumferential
edge or shoulder 150. Although referred to herein as an "edge" or
"shoulder," it should be understood that shoulder 150 may be
contoured, such as a radius, to various degrees such that shoulder
150 will define a contoured zone of convergence between
frustoconical heel surface 144 and conical surface 146.
[0064] Referring again to FIG. 4, the roller cones 112, 114, 116
are shaped and mounted so that as they roll, radially-extending
steel teeth 414 integrally formed from the steel of the roller
cones 112, 114, 116 gouge, chip, crush, abrade, and/or erode the
earthen formations (not shown) at the bottom of the wellbore. The
teeth 414G in the circumferential row around the heel of the cone
112 are referred to as the "gage row" teeth 414G in the "gage row"
170a. They engage the corner portion of the hole being drilled near
its perimeter or "gage". The teeth 414i in the circumferential
inner rows between the gage row and the nose of the cone are
referred to as the "inner row" teeth 414i in the inner rows 180a
and 181a. They engage the bottom of the borehole being drilled.
Inner rows 180a and 181a are arranged and spaced on roller cone 112
so as not to interfere with the inner rows on each of the other
roller cone cutters 114, 116. Fluid nozzles 115 direct drilling
fluid ("mud") into the hole to carry away the particles of
formation created by the drilling.
[0065] Such a roller cone drill bit as shown in FIG. 4 is merely
one example of various arrangements that may be used in a drill bit
which is made according to the present disclosure. For example, the
roller cone drill bit illustrated in FIG. 4 has three roller cones.
However, one, two and four roller cone drill bits are also known in
the art. The arrangement of the teeth 414 on the cones 112, 114
shown in FIG. 4 is just one of many possible variations. In fact,
it is typical that the teeth on the three cones on a rock bit
differ from each other so that different portions of the hole are
engaged by each of the three roller cones so that collectively the
entire bottom of the hole is drilled. A broad variety of tooth and
cone geometries are known and do not form a specific part of this
disclosure, nor should the present disclosure be limited in scope
by any such arrangement.
[0066] The example teeth on the roller cones shown in FIGS. 4 and 5
are generally triangular in a cross-section taken in a radial plane
of the cone. Referring to FIG. 6, such a tooth 414 has a leading
flank 216 and a trailing flank 217 meeting in an elongated crest
218. The flanks and crest of the tooth 414 are covered with two
layers 502 and 501. Alternatively, only a portion (e.g., the
leading flank and/or crest) of each such tooth 414 may be covered
with both layers. Layer 502 is the outermost layer and layer 501 is
a first intermediate layer positioned between the surface of the
tooth and the outer layer 502. It has been found that it can be
particularly advantageous to provide at least two layers to a
parent cutting element at least one of which is applied utilizing a
thermal spray process and comprises a wear resistant material. Such
roller cones can provide for a more durable drill bit.
[0067] The material used for forming the body of the roller cone
cutter has been described above. At least one layer applied to the
parent cutting element is applied using a thermal spray process.
Examples of thermal spray processes include those described
hereinbefore. The thermally sprayed layer comprises a wear
resistant material. The wear resistant material comprises hard
particles and a binder, as discussed above. The at least two layers
may or may not be subsequently sintered after application on the
roller cone. In one or more embodiments, the layer of wear
resistant material may be sintered and have a hardness of at least
80 Rockwell "A" hardness (Ra), in particular at least 85 Ra. The
sintered layer of wear resistant material may have a porosity which
is less than 0.8% by volume. With such low porosity, the actual
density approaches the theoretical density. Layers of wear
resistant material may have a thickness of at least 0.125 mm (0.005
inches), in particular in the range of from 0.125 to 7.6 mm (0.005
to 0.3 inches), from 0.2 to 5 mm (0.008 to 0.2 inches), from 0.25
to 2.5 mm (0.01 to 0.1 inches), or from 0.4 to 1.25 mm (0.015 to
0.05 inches). The desirable thickness depends on the end-use
application as well as the number of layers applied to the parent
cutting element.
[0068] In one or more embodiments, the total thickness of the one
or more layers applied (including all wear resistant layers,
hardfacing layers and buffer layers combined) may be at least 0.125
mm (0.005 inches), at least 0.35 mm (about 0.015 inches), at least
0.75 mm (about 0.03 inches), at least 1.25 mm (about 0.05 inches),
at least 2.5 mm (about 0.1 inches), at least 5 mm (about 0.2
inches), or at least 7.5 mm (about 0.3 inches). The total thickness
of all the layers applied may be at most 40 mm (about 1.5 inches),
at most 30 mm (about 1.25 inches) or at most 25 mm (about 1 inch).
For example the total thickness of all the layers applied may be
0.5 mm (about 0.02 inches), 1 mm (about 0.04 inches), 1.5 mm (about
0.06 inches), 2 mm (about 0.08 inches), 5.5 mm (about 0.22 inches),
10 mm (about 0.4 inches), 12 mm (about 0.5 inches), 15 mm (about
0.6 inches), or 20 mm (about 0.8 inches). The desirable total
thickness may depend on the particular end-use application.
[0069] In an exemplary embodiment, the outer layer may comprise a
first wear resistant material applied by a thermal spray process
and the first intermediate layer may also be applied to the parent
cutting element using a thermal spray process. The first
intermediate layer may comprise a second wear resistant material.
The second wear resistant material comprises hard particles and a
binder, as discussed above. The second wear resistant material
differs with respect to one or more properties from the wear
resistant material in the outer layer. The one or more properties
may be selected from hardness, hard particle content, hard particle
average grain size, toughness, composition, binder content, melting
temperature, density, porosity, elastic modulus, microstructure,
abrasion resistance, and erosion resistance. In particular, the
binder content, melting temperature, and/or the hard particle
average grain (or particle) size may differ. The difference in
properties may provide a gradient in one or more properties between
the surface of the substrate and the outer layer. Alternatively,
the difference in one or more properties may provide for an
interruption in properties between the surface of the substrate and
the outer layer. In one or more embodiments, three or more wear
resistant layers applied by a thermal spray process may be
used.
[0070] In an exemplary embodiment, as depicted in FIG. 7, the outer
layer 502 may comprise a wear resistant material applied by a
thermal spray process and the first intermediate layer 501h may
comprise a hardfacing composition applied to the milled tooth
(i.e., parent cutting element) using welding processes known in the
art. Such welding processes may be selected from oxyacetylene
welding, plasma transferred arc, atomic hydrogen welding, tungsten
inert gas welding, and gas tungsten arc welding. Layers of
hardfacing composition may have a thickness of at least 0.5 mm
(0.02 inches), in particular in the range of from 1 to 5 mm (0.04
to 0.2 inches). Alternatively, the first intermediate layer may
comprise a wear resistant material applied by a thermal spray
process and the outer layer may comprise a hardfacing composition
applied to the parent cutting element using a welding process. In
one or more embodiments, three or more layers may be used.
[0071] As shown in FIG. 7, a milled tooth 414 includes a first
intermediate layer 501h and an outer layer 502 applied to parent
cutting element 514. The first intermediate layer 501h comprises a
hardfacing composition and the outer layer 502 comprises a wear
resistant material. The thickness of the hardfacing layer (i.e.,
the first intermediate layer 501h) is greater than the thickness of
the wear resistant layer (i.e., the outer layer 502). The
hardfacing layer comprises a carbide phase containing a primary
carbide of spherical cemented tungsten carbide-cobalt (sometimes
referred to as sintered tungsten carbide-cobalt), a secondary
carbide of crushed cast tungsten carbide, and a mono-tungsten
carbide; and an iron-based matrix. The outer layer 502 comprises
hard particles of mono-tungsten carbide and a binder of cobalt. The
outer layer of wear resistant material exhibits excellent bonding
to the first intermediate layer of hardfacing, creates a smoother
(i.e., less rough) exterior surface as compared to the hardfacing
layer, and provides a beneficial compressive stress to the surface.
Use of such a roller cone is believed to lead to an improvement in
the performance of the drill bit by increasing ROP and/or extending
the bit life due to the improvement in wear resistance and
toughness of the surface.
[0072] The hardfacing composition may comprise a matrix and a
carbide phase which comprises one or more metal carbides. The
hardfacing composition contains metal carbides having a greater
average particle size than the hard particles in the wear resistant
material. As used herein, the term "carbide phase", is meant to
include the materials which typically may be placed within a
welding tube or which may be placed upon a welding wire, i.e., the
filler. As used herein, the term "matrix" is meant to include the
matrix material which includes materials other than those in the
carbide phase. The matrix may be any metal or metal alloy, for
example a metal or metal alloy as described above for the binder of
the wear resistant material. In one or more embodiments, the matrix
may be selected from iron, nickel, cobalt, mixtures and alloys
thereof. In an example embodiment, the matrix may be an iron-based
alloy. Such iron-based alloys may include, but are not limited to,
soft steels. As used herein, the term "soft steel" is meant to
include steel materials which have a low carbon content, for
example steel having a carbon content of less than 0.15% by weight,
based on the total weight of the steel (i.e., mild steel). Examples
of mild steel include, but are not limited to, AISI (American Iron
and Steel Institute) 1010 (0.1% w carbon), AISI 1008 (0.08% w
carbon), and AISI 1006 (0.06% w carbon) grades of steel.
[0073] The carbide phase ("filler") may be present in any suitable
amount, for example in the range of from 50% to 75% by weight,
based on the total weight of the hardfacing composition
pre-application, in particular from 55% w to 70% w, on the same
basis. Thus, the matrix may be present in an amount of from 25% to
50% by weight, based on the total weight of the hardfacing
composition pre-application, in particular from 30% w to 45% w, on
the same basis. All percentages given herein are pre-application
percentages unless specified to the contrary.
[0074] The carbide phase may comprise a deoxidizer. A suitable
deoxidizer may include a silicomanganese composition which may be
obtained from Chemalloy in Bryn Mawr, Pa. A suitable
silicomanganese composition may contain 65% w to 68% w manganese,
15% w to 18% w silicon, a maximum of 2% w carbon, a maximum of
0.05% w sulfur, a maximum of 0.35% w phosphorus, and a balance
comprising iron. Suitably, the deoxidizer may be present in a
quantity of at most 5% w, based on the total weight of the carbide
phase pre-application, for example about 3% w to about 4% w, on the
same basis, may be used.
[0075] The carbide phase may also comprise a temporary resin
binder. A small amount of thermoset resin may be desirable for
partially holding the particles in the carbide phase together so
that they do not shift during application, e.g., welding. Suitably,
the resin binder may be present in a quantity of at most 1% w,
based on the total weight of the carbide phase pre-application, for
example about 0.5% w, on the same basis is adequate. The term,
"deoxidizer", as used herein, refers generally to deoxidizer with
or without the resin. Suitably, the deoxidizer/resin binder will
form no more than about 5% w, preferably about 4% w, based on the
total weight of the carbide phase.
[0076] The carbide phase includes a primary carbide and optionally
a secondary carbide. Various hardfacing compositions are disclosed
in U.S. Pat. No. 4,836,307, U.S. Pat. No. 5,791,422, U.S. Pat. No.
5,921,330, U.S. Pat. No. 6,659,206, and U.S. Pat. No. 6,782,958.
These references are herein incorporated by reference in their
entirety.
[0077] Suitably, the one or more metal carbides are mechanically
bonded to a surface by a metal ("matrix"). Once applied, the
carbide particles are in effect suspended in a matrix of metal
forming a layer on the surface. The carbide particles give the
hardfacing material hardness and wear resistance, while the matrix
metal provides fracture toughness to the hardfacing.
[0078] Many factors affect the properties of a hardfacing
composition in a particular application. These factors include the
chemical composition and physical structure (size and shape) of the
carbides, the chemical composition and microstructure of the matrix
metal or alloy, and the relative proportions of the carbide
materials to one another and the matrix metal or alloy.
[0079] The primary metal carbide may comprise any suitable metal
carbide. The metal carbide may include, but is not limited to,
tungsten carbide, chromium carbide, molybdenum carbide, niobium
carbide, tantalum carbide, titanium carbide, vanadium carbide, and
mixtures thereof, in particular tungsten carbide. The metal carbide
may be in the form of crushed particles or spherical particles
(i.e., pellets). The term "spherical", as used herein and
throughout the present disclosure, means any particle having a
generally spherical shape and may not be true spheres, but lack the
corners, sharp edges, and angular projections commonly found in
crushed and other non-spherical particles. The term, "crushed", as
used herein in the present disclosure, means any particle having
corners, sharp edges and angular projections commonly found in
non-spherical particles.
[0080] The metal carbide may comprise a cemented carbide comprising
a metal carbide and a metal binder. The carbide may include, but is
not limited to, tungsten carbide, chromium carbide, molybdenum
carbide, niobium carbide, tantalum carbide, titanium carbide,
vanadium carbide, and mixtures thereof, in particular tungsten
carbide. The metal binder may include Group VIII elements of the
Periodic Table, in particular cobalt, nickel, iron, mixtures
thereof, and alloys thereof. Preferably, the metal binder comprises
cobalt. The cemented carbide may be in the form of crushed
particles or spherical particles (i.e., pellets).
[0081] Suitably, the primary carbide may be a tungsten carbide.
Many different types of tungsten carbides are known based on their
different chemical compositions and physical structure. Three types
of tungsten carbide suitably used in hardfacing drill bits are cast
tungsten carbide, mono-tungsten carbide, and cemented tungsten
carbide. These carbides may be in the form of crushed particles or
spherical particles (i.e., pellets). The primary carbide may be
selected from cast tungsten carbide, mono-tungsten carbide and
cemented tungsten carbide.
[0082] Tungsten generally forms two carbides, mono-tungsten carbide
(VVC) and ditungsten carbide (W.sub.2C). Cast carbide is a eutectic
mixture of the WC and W.sub.2C compounds, as such the carbon
content in cast carbide is sub-stoichiometric, (i.e., it has less
carbon than the mono-tungsten carbide). Cast carbide is typically
made by resistance heating tungsten in contact with carbon in a
graphite crucible having a hole through which the resultant
eutectic mixture drips. The liquid is quenched in a bath of oil and
is subsequently comminuted to the desired particle size and
shape.
[0083] At least a portion of any cast tungsten carbide particles
may be present in the form of particles having a core (or inner
region) of cast tungsten carbide and a shell (or outer region) of
mono-tungsten carbide. Such cast tungsten carbide particles are
described in U.S. Patent Publication No. 2007/0079905, which is
incorporated by reference in its entirety (see page 1, paragraph 13
through page 3, paragraph 33). Such cast tungsten carbide particles
may have a bound carbon content in the range of from 4% w to 6% w,
based on the total weight of the particle, in particular from 4.5%
w to 5.5% w, more in particular 4.3% w, to 4.8% w, on the same
basis. The free carbon content of such cast tungsten carbide
particles may be at most 0.1% w, on the same basis. Such cast
tungsten carbide particles may be made using a process wherein cast
tungsten carbide powder is heated in the presence of a carbon
source to a temperature of 1300 to 2000.degree. C., preferably 1400
to 1700.degree. C.
[0084] Mono-tungsten carbide is essentially stoichiometric tungsten
carbide. One type of mono-tungsten carbide is macro-crystalline
tungsten carbide. Macro-crystalline tungsten carbide may be formed
using a high temperature thermite process during which ore
concentrate is converted directly to mono-tungsten carbide.
[0085] Another type of mono-tungsten carbide is carburized tungsten
carbide which is typically multicrystalline in form, i.e., composed
of tungsten carbide agglomerates. Carburized tungsten carbide may
be formed using a carburization process where solid-state diffusion
of carbon into tungsten metal occurs to produce mono-tungsten
carbide. Typical mono-tungsten carbide contains a minimum of 99.8%
by weight of tungsten carbide with a total carbon content in the
range of from about 6.08% to about 6.18% by weight, preferably
about 6.13% by weight, based on the weight of tungsten carbide.
[0086] Cemented tungsten carbide comprises small particles of
tungsten carbide (e.g., 1 to 15 microns), in particular
mono-tungsten carbide, bonded together with a metal binder such as
Group VIII elements of the Periodic Table, in particular cobalt,
nickel, iron, mixtures and alloys thereof, preferably cobalt.
Cemented tungsten carbide may be produced by mixing an organic wax,
mono-tungsten carbide and metal binder; pressing the mixture to
form a green compact; sintering the green compact at temperatures
near the melting point of the metal binder; and comminuting the
resulting sintered compact to form particles of the desired
particle size and shape.
[0087] At least a portion of any cemented carbide may be in the
form of super dense cemented carbide. The term "super dense
cemented carbide", as used herein, includes the class of sintered
particles as disclosed in U.S. Patent Publication No. 2003/0000339,
the disclosure of which is incorporated herein by reference (page
2, paragraph 19 through page 3, paragraph 47). Such super dense
cemented carbide particles are typically of substantially
spheroidal shape (i.e., pellets) and have a predominantly closed
porosity or are free of pores. The process for producing such
particles starts from a powder material with a partially porous
internal structure, which is introduced into a furnace and sintered
at a temperature at which the material of the metal binder adopts a
pasty state while applying pressure to reduce the pore content of
the starting material to obtain a final density.
[0088] The secondary carbide differs in composition from the
primary carbide and may be any suitable metal carbide, as described
above. Suitably, the secondary carbide may also be a tungsten
carbide. Such secondary carbide may be selected from cast tungsten
carbide, mono-tungsten carbide and cemented tungsten carbide. The
secondary carbide may be present in a lesser quantity than the
primary carbide, measured based on weight.
[0089] In an exemplary embodiment, the hardfacing composition may
comprise a primary carbide of cemented carbide, preferably cemented
tungsten carbide containing a cobalt metal binder, and a secondary
carbide of cast tungsten carbide. Preferably, the cemented carbide
may be spherical in form. Preferably, the cast carbide may be
present in a quantity of at least 10% w, in particular at least 15%
w, more in particular at least 22% w, based on the total weight of
the carbide phase pre-application. Preferably, the cast carbide
comprises particles having sizes in the range of from 30 to 80 mesh
(-30/+80 mesh), in particular 40 to 80 mesh (-40/+80 mesh), more in
particular 40 to 60 mesh (-40/+60 mesh) pre-application.
Preferably, the cast tungsten carbide may be present in crushed
form. Preferably, the primary carbide may include a first quantity
of cemented carbide having particle sizes in the range of from 16
to 25 mesh (-16/+25 mesh), in particular from 16 to 20 mesh
(-16/+20 mesh), and/or a second quantity of cemented carbide
comprising particles having sizes in the range of from 25 to 40
mesh (-25/+40 mesh), in particular from 30 to 40 mesh (-30/+40
mesh). The hardfacing composition may also comprise mono-tungsten
carbide comprising particles having sizes capable of passing
through 300 mesh or greater mesh sizes, in particular from 300 to
500 mesh (-300/+500 mesh). In this embodiment, the first quantity
of cemented carbide may be present in an amount of at least 10% by
weight, based on the total weight of the carbide phase
pre-application, in particular in the range of from 20 to 70% by
weight, based on the total weight of the carbide phase, more in
particular from 20 to 50% w, on the same basis. In this embodiment,
the second quantity of cemented carbide may be present in an amount
of at least 10% by weight, based on the total weight of the carbide
phase, in particular in the range of from 15 to 45% by weight,
based on the total weight of the carbide phase pre-application,
more in particular from 15 to 35% w, on the same basis. The
mono-tungsten carbide may be present in an amount in the range of
from 5 to 15% by weight, based on the total weight of the carbide
phase, in particular from 8% w to 12% w, on the same basis.
[0090] In an exemplary embodiment, the hardfacing composition may
comprise a primary carbide of cemented tungsten carbide containing
a cobalt metal binder having sizes in the range of from 25 to 60
mesh (-25/+60 mesh), in particular 30 to 40 mesh (-30/+40 mesh)
pre-application. The secondary carbide of cast tungsten carbide
preferably has particles having sizes in the range of from 80 to
325 mesh (-80/+325 mesh), in particular from 100 to 200 mesh
(-100/+200 mesh) pre-application. Preferably, the cast tungsten
carbide may be present in crushed form. The hardfacing composition
may also comprise mono-tungsten carbide comprising particles having
sizes capable of passing through 300 mesh or greater mesh sizes, in
particular from 300 to 500 mesh (-300/+500 mesh). In this
embodiment, the quantity of cemented carbide may be present in an
amount of at least 25% by weight, based on the total weight of the
carbide phase pre-application, in particular in the range of from
35 to 80% by weight, based on the total weight of the carbide
phase, in particular from 45 to 75% w, on the same basis. The cast
tungsten carbide may be present in an amount in the range of from
10 to 45% by weight, based on the total weight of the carbide
phase, in particular from 15% w to 25% w, on the same basis. The
mono-tungsten carbide may be present in an amount in the range of
from 5 to 15% by weight, based on the total weight of the carbide
phase, in particular from 8% w to 12% w, on the same basis.
[0091] In an exemplary embodiment, the hardfacing composition may
comprise a carbide phase comprising mono-tungsten carbide in a
quantity of at least 80% w, based on the total weight of the
carbide phase, in particular at least 90% w, same basis.
Alternatively, the hardfacing composition may comprise a carbide
phase comprising cast tungsten carbide having a core of cast
tungsten carbide and a shell of mono-tungsten carbide, as described
above, in a quantity of at least 80% w, based on the total weight
of the carbide phase, in particular at least 90% w, same basis. The
carbide particles may be spherical or crushed in form. The carbide
particles may have sizes in the range of from 80 to 200 mesh
(-80/+200 mesh) pre-application. In this embodiment, the carbide
phase may be present in an amount of from 60% w to 75% w or 67.5% w
to 72.5% w, for example 70% w, based on the total weight of the
hardfacing composition pre-application. The matrix may be present
in an amount of from 25% w to 40% w or 27.5% w to 32.5% w, for
example 25% w to 30% w.
[0092] In one or more embodiments, an intermediate layer may be
used which may be applied by a thermal spray process, as described
above, or may be applied by a non-thermal spray process. The
intermediate layer may comprise a material having a hardness that
is less than the wear resistant material and any hardfacing
composition that may be used (i.e., an intermediate hardness). In
one or more embodiments, the intermediate layer may comprise a
buffer material having a hardness of less than 65 HRc (Rockwell
Hardness). As used herein, such an intermediate layer may be termed
a "buffer layer." One or more of such intermediate buffer layers
may be used, for example at least two or at least three or at least
four buffer layers may be used. In one or more embodiments, at
least two buffer layers may be placed adjacent one another to form
a gradient within the buffer layers with respect to one or more
properties. The one or more properties may be selected from one or
more of the following: coefficient of thermal expansion; hardness;
toughness; melting temperature; and composition. One or more of the
buffer layers may be positioned adjacent the surface of the
substrate (e.g., the surface of the tool body such as a parent
cutting element), between two wear resistant material layers,
between two hardfacing layers, and/or between a hardfacing layer
and a wear resistant material layer. The intermediate buffer layer
may be one of the at least two layers applied to a substrate (e.g.,
a parent cutting element) (i.e., the first intermediate layer).
[0093] A buffer layer may comprise a metal component. The metal
component may be selected from a metal, a metal alloy, a metal
boride, a metal phosphate, and combinations thereof. The metal or
metal alloy may be any suitable metal or metal alloy. Examples of
metals and metal alloys for use in a buffer material may include
those metals and metal alloys described above for the wear
resistant material. Examples of metal boride materials may include
nickel boride or iron boride. Examples of metal phosphate materials
may include nickel phosphate or iron phosphate.
[0094] In one or more embodiments, the buffer material may
additionally comprise a minor amount of hard particles as described
herein (e.g., carbides of W, Ti, Mo, Nb, V, Hf, Ta and Cr), for
example a chromium carbide and/or a tungsten carbide such as
monotungsten carbide. Such hard particles may be present in an
amount of less than 50 percent by weight (% w), based on the total
weight of the buffer material pre-application, for example at most
45% w, at most 40% w, at most 30% w or at most 25% w, on the same
basis.
[0095] A buffer layer may be applied by any suitable technique, for
example a thermal spray process, a welding process, or a coating
process such as painting, slurry dipping, taping, plating, etc. A
buffer layer may or may not be sintered, and if sintered, the
buffer layer may be sintered in a separate sintering process from
the other layers applied to the substrate. The thickness of a
buffer layer may be at most 2.5 mm (0.1 inches), for example in the
range of from 0.025 to 2.5 mm (0.001 inches to 0.1 inches) or from
0.25 to 1.3 mm (0.01 to 0.05 inches).
[0096] In one or more embodiments, the buffer material in the
buffer layer may be selected such that the buffer material has a
lower melting temperature than the substrate to which it is applied
and/or any wear resistant material or hardfacing layers applied
thereon. For example, the melting temperature of the buffer
material may be less than 1300.degree. C., or less than
1200.degree. C., or at most 1100.degree. C., or at most
1050.degree. C.
[0097] The one or more intermediate layers may comprise a wear
resistant layer, a hardfacing layer, or a buffer material, as
described herein. In one or more embodiments, the intermediate
layer(s) and outer layer may be coterminous with each other, in
other words substantially overlap. The intermediate layer(s) and
outer layer may differ with respect to one or more properties. The
one or more properties may be selected from hardness, hard particle
content, hard particle average grain size, toughness, composition,
metal content, melting temperature, density, porosity, elastic
modulus, microstructure, abrasion resistance, and erosion
resistance. For example, the melting temperature and hardness may
differ between layers. The difference in properties may provide a
gradient in one or more properties between the surface of the
substrate and the outer layer. For example, the melting temperature
and hardness may decrease moving inwardly of the outer layer toward
the substrate. Alternatively, the difference in one or more
properties may provide for an interruption in properties between
the surface of the substrate and the outer layer.
[0098] Using at least one intermediate layer, whether a wear
resistant layer, hardfacing layer or buffer layer, which has a
lower melting temperature than the substrate and outer layer can
allow for the metal or metal alloy to diffuse across the boundary
between the substrate and adjacent intermediate layer which can
fill out any gaps, voids or porosity in the bounding area allowing
for improved bonding properties. A lower sintering temperature
(e.g., a temperature suitable for substantially melting or
partially melting the material of the intermediate layer) may be
used and solubility can be increased which also can enhance
metallurgical bonding during any subsequent sintering process that
may be applied. Such intermediate layers can be used for improved
bonding of an adjacent layer, for reducing failure from cracking of
the applied layers (improved wetting of adjacent surfaces and/or
improved transition in thermal expansion properties).
[0099] The one or more lower melting temperature intermediate
layers may have a melting temperature of less than 1300.degree. C.,
or less than 1200.degree. C., or at most 1100.degree. C., or at
most 1050.degree. C. In one or more embodiments, the one or more
lower melting temperature intermediate layers may have a melting
temperature that may be at least 50.degree. C. less than that of an
outermost wear resistant material layer applied using a thermal
spray process, for example at least 75.degree. C. less, at least
100.degree. C. less, at least 150.degree. C. less, or at least
200.degree. C. less than that of an outer most wear resistant
material layer applied using a thermal spray process.
[0100] In an example embodiment, one or more intermediate buffer
layers may be positioned adjacent the substrate and one or more
intermediate buffer layers may be positioned between an
intermediate wear resistant material layer and an additional
intermediate or outer wear resistant material layer. In an example
embodiment, the layers applied to the substrate may consist of one
or more buffer layers and one or more wear resistant layers, for
example a first intermediate buffer layer may be applied to the
substrate; a second intermediate wear resistant layer may be
applied over at least a portion of the first intermediate layer; a
third intermediate buffer layer (which may have the same or
different composition as the first intermediate layer) may be
applied over at least a portion of the second intermediate layer;
and an outer wear resistant layer may be applied over at least a
portion of the third intermediate layer (which may have the same or
different composition as the second intermediate layer). For
example, the first intermediate buffer layer may be metal alloy B
from Table 1 above; the second intermediate wear resistant layer
may be 88% w mono-tungsten carbide and 12% w cobalt; third
intermediate buffer layer may also be metal alloy B from Table 1
above; and outer wear resistant layer may be 88% w mono-tungsten
carbide and 12% w cobalt which may be applied using a thermal spray
process and subsequently sintered, for example at 1010.degree. C.
In other embodiments, two or more buffer layers may be applied
between the substrate and intermediate wear resistant layer and
between the intermediate wear resistant layer and the outer wear
resistant layer which two or more buffer layers may provide a
gradient in one or more properties, as discussed herein, between
the adjacent buffer layers or may provide for an interruption in
one or more such properties.
[0101] In another example embodiment, one or more intermediate
buffer layers may be positioned adjacent the substrate and an
intermediate wear resistant layer. The outer layer may be a wear
resistant outer layer. Suitably, a first intermediate buffer layer
may be applied to the substrate; a second intermediate wear
resistant layer may be applied over at least a portion of the first
intermediate layer; and an outer wear resistant layer may be
applied over at least a portion of the second intermediate layer.
For example, the first intermediate buffer layer may be metal alloy
A from Table 1 above; the second intermediate wear resistant layer
may be 83% w mono-tungsten carbide and 17% w cobalt; and outer wear
resistant layer may be 88% w mono-tungsten carbide and 12% w cobalt
which may be applied using a thermal spray process and subsequently
sintered, for example at 1000.degree. C.
[0102] In another example embodiment, one or more intermediate
buffer layers may be positioned adjacent the substrate between the
substrate and an intermediate hardfacing layer and one or more
intermediate buffer layers may be positioned between the
intermediate hardfacing layer and an outer wear resistant material
layer.
[0103] In another example embodiment, a wear resistant intermediate
layer and an outer wear resistant layer may be applied onto at
least a portion of the surface of the substrate. The wear resistant
intermediate layer may be applied to the surface of the substrate
using any suitable technique and has a lower melting temperature
than the outer wear resistant layer applied using a thermal spray
process. For example, first intermediate wear resistant layer may
be 50% w metal alloy C from Table 1 above and 50% w mono-tungsten
carbide, and the outermost wear resistant layer may be 88% w
mono-tungsten carbide and 12% w cobalt which may be applied using a
thermal spray process and subsequently sintered, for example at
1040.degree. C.
[0104] In an example embodiment, the intermediate layer adjacent
the substrate may differ with respect to one or more properties
such as having a lower melting temperature than the wear resistant
layer applied thereon. In an example embodiment, at least three
layers may be applied to a surface of the substrate forming a
gradient in melting temperatures with the lowest melting
temperature material forming the innermost intermediate layer and
the highest melting temperature material forming the outer
layer.
[0105] In one or more embodiments, the interface between the
intermediate layer and the substrate or between intermediate layers
or between intermediate layer and outer layer may be non-planar.
Such non-planar surfaces may include one or more surface features,
for example dimples, projections, ridges, grooves, and the like.
FIG. 11 depicts a portion of a substrate 1193 comprising an
intermediate layer 1191 adjacent the non-planar substrate surface
1190 and an outer wear resistant material layer 1192 adjacent the
intermediate layer forming a substantially planar interface 1194.
Although interface 1194 may be depicted as a planar interface and
interface 1190 a non-planar interface, one skilled in the art based
on the teachings of the present disclosure would appreciate that in
other embodiments interfaces such as 1194 may be non-planar and
interface 1190 may be planar.
[0106] Use of intermediate layers having a lower melting
temperature adjacent the substrate and between wear resistant
material layers having a higher melting temperature can allow for
use of a greater total thickness of layers applied to the substrate
without cracks forming in the wear resistant material.
[0107] In an exemplary embodiment, a second intermediate layer may
be positioned between the first intermediate layer and the outer
layer. The second intermediate layer may comprise a buffer layer,
as described above. Alternatively, the second intermediate layer
may comprise a wear resistant material, as described above. The
wear resistant material comprises hard particles and a binder, as
discussed above. Alternatively, the second intermediate layer may
comprise a hardfacing composition, as discussed above. The material
of the intermediate layers may differ with respect to one or more
properties from the substrate (e.g., parent element) and the outer
layer. One or more properties may be selected from hardness,
thickness, hard particle content, hard particle average grain size,
toughness, composition, melting temperature, binder content,
density, porosity, elastic modulus, microstructure, abrasion
resistance, and erosion resistance. The difference in properties
may provide a gradient there between. Alternatively, the difference
in properties may provide for an interruption in properties.
[0108] In an exemplary embodiment, a third intermediate layer may
be positioned between the second intermediate layer and the outer
layer. The third intermediate layer may comprise a buffer layer, as
described above. Alternatively, the third intermediate layer may
comprise a wear resistant material, as described above. The wear
resistant material comprises hard particles and a binder, as
discussed above. Alternatively, the third intermediate layer may
comprise a hardfacing composition, as discussed above. The material
of the intermediate layers may differ with respect to one or more
properties (as discussed above) from the substrate and the outer
layer. The difference in properties may provide a gradient there
between. Alternatively, the difference in properties may provide
for an interruption in properties. In this embodiment, there may be
one or more additional intermediate layers positioned between the
first intermediate layer and the outer layer. The one or more
additional intermediate layers may comprise a wear resistant
material, a hardfacing composition, or a buffer material, as
described above, and differ with respect to one or more properties
compared to the adjacent layers.
[0109] In an exemplary embodiment, the layers applied to the parent
cutting elements in the gage row may differ with respect to one or
more properties from the layers applied to the parent cutting
elements in the one or more inner rows and/or heel row.
Additionally, the layers applied to the parent cutting elements in
the innermost inner rows (i.e., nearest the nose of the cone) may
differ with respect to one or more properties from the layers
applied to the parent cutting elements in the outermost inner row
(i.e., nearest the gage row). For example, wear resistant material
applied as an outer layer to the parent cutting elements in the
gage row may differ with respect to one or more properties from
wear resistant material applied as an outer layer to the parent
cutting elements in the one or more inner rows.
[0110] In an exemplary embodiment, the inner rows may comprise a
plurality of parent cutting elements with layers applied thereto,
one of which contains a wear resistant material applied by a
thermal spray process which may or may not be subsequently
sintered, while the gage row, and optionally the heel row, comprise
inserts, such as TCIs, that are secured into the cone body.
Alternatively, the gage row may comprise a plurality of parent
cutting elements with layers applied thereto, one of which contains
a wear resistant material applied by a thermal spray process which
may or may not be subsequently sintered, while the inner rows, and
optionally the heel row, comprise inserts, such as TCIs, that are
secured into the cone body. Such inserts are discussed above.
[0111] Referring to FIG. 8, a milled tooth comprising four layers
in accordance with an exemplary embodiment of the present
disclosure is shown. As shown in FIG. 8, a milled tooth 414
includes a first intermediate layer 503, a second intermediate
layer 501, a third intermediate layer 504, and an outer layer 502.
The first intermediate layer 503 is positioned adjacent the surface
of the milled tooth 414. The second intermediate layer 501 is
positioned adjacent the first intermediate layer 503 and the third
intermediate layer 504. The third intermediate layer 504 is
positioned interior of and adjacent the outer layer 502. Although
not drawn to scale, the thickness of the second intermediate layer
501 is greater than any one of the outer layer 502, the first
intermediate layer 503, or the third intermediate layer 504. For
example, the second intermediate layer 501 may comprise a
hardfacing composition and the outer layer 502 and the third
intermediate layer 504 may comprise wear resistant materials
applied using a thermal spray process. The first intermediate layer
503 may comprise a buffer material. The hardfacing layer may
comprise any of the hardfacing compositions described herein, for
example a carbide phase containing a primary carbide of spherical
cemented tungsten carbide-cobalt, a secondary carbide of crushed
cast tungsten carbide, and a mono-tungsten carbide in an iron-based
matrix. The wear resistant material of the outer layer 502 may
comprise hard particles of mono-tungsten carbide and a binder of
cobalt. The wear resistant material of the third intermediate layer
504 may also comprise hard particles of mono-tungsten carbide and a
binder of cobalt; however, the wear resistant material of the third
intermediate layer 504 differs with respect to one or more
properties, as discussed herein such as cobalt content and/or
average particle size of the mono-tungsten carbide, of the outer
layer 502. Alternatively, the third intermediate layer 504 may
comprise a buffer material which may be the same as used in the
first intermediate layer 503 or may differ.
[0112] Referring to FIG. 9, a milled tooth comprising three layers
in accordance with an exemplary embodiment of the present
disclosure is shown. As shown in FIG. 9, a milled tooth 414
includes a first intermediate layer 903, a second intermediate
layer 901, and an outer layer 902. The outer layer 902, the first
intermediate layer 903, and the second intermediate layer 901
comprise wear resistant materials which may be applied using a
thermal spray process. Although not drawn to scale, the thickness
of the first intermediate layer 903 is greater than the thickness
of the second intermediate layer 901 which is greater than the
thickness of the outer layer 902. However, the layers may have the
same thickness or any variety of relative thicknesses. The wear
resistant material of the outer layer 902 and the second
intermediate layer 901 contain hard particles and a binder, for
example mono-tungsten carbide and cobalt. The wear resistant
material of the second intermediate layer 901 differs with respect
to one or more properties, as described herein such as cobalt
content and/or average particle size of the mono-tungsten carbide,
from the outer layer 902. The wear resistant material of the first
intermediate layer 903 differs with respect to one or more
properties, as described herein from the second intermediate layer
901 and the outer layer 902. Use of such a roller cone is believed
to lead to an improvement in the performance of the drill bit by
extending the bit life due to the improvement in wear resistance
and/or toughness of the surface.
[0113] In these embodiments where at least two layers are applied,
the layers may or may not be subsequently sintered. In those
embodiments where the wear resistant layer(s) are sintered, such
sintering may be performed after application of the wear resistant
layer but before a subsequent layer may be applied or the sintering
may be performed after application of all the layers.
[0114] In another embodiment, at least a portion of the bit, for
example the bit leg (e.g., the shirttail section), may comprise a
first intermediate layer of a hardfacing composition, as described
above, and an outer layer of a wear resistant material applied by a
thermal spray process, as described above. One or more additional
intermediate layers may be used, as described above. The first
intermediate layer and the outer layer are positioned on the same
surface of the bit leg (i.e., the layers are placed one upon the
other).
[0115] In another embodiment, at least a portion of the bit, for
example the bit leg (e.g., the shirttail section), may comprise one
or more layers, one layer comprising a wear resistant material
applied by a thermal spray process and subsequently sintered, as
discussed above.
[0116] In another embodiment, the rolling cone cutter may comprise
a plurality of inserts and a plurality of parent cutting elements
with a single layer comprising a wear resistant material applied to
at least a portion thereof by a thermal spray process which may or
may not be subsequently sintered. In one or more embodiments, at
least one of the plurality of parent cutting elements may have at
least two layers applied to at least a portion thereof wherein at
least one of the layers comprises a wear resistant material applied
by a thermal spray process which may or may not be subsequently
sintered. The heel, gage or inner rows may contain parent cutting
elements with a layer of wear resistant material. For example, one
or more inner rows may comprise a plurality of parent cutting
elements with a layer of a wear resistant material applied to at
least a portion thereof by a thermal spray process which may or may
not be subsequently sintered while the gage row, and optionally the
heel row, comprises inserts, such as TCIs, that are secured into
the cone body. Such inserts are discussed above. Alternatively, the
gage row may comprise a plurality of parent cutting elements with a
layer of a wear resistant material while the inner rows, and
optionally the heel row, comprise inserts, such as TCIs, that are
secured into the cone body. In some embodiments, the heel row may
comprise a plurality of inserts; and one or more inner rows, and
optionally the gage row, may comprise a plurality of parent cutting
elements with a layer of a wear resistant material. Placement of
the inserts and parent cutting elements may depend on the
particular application. Suitably, the wear resistant material may
be applied to the entire surface of the parent cutting element.
Optionally, the wear resistant material may also be applied to the
surface of the cone body. The wear resistant material may be a wear
resistant material as described above. Use of such roller cones in
a drill bit with strategically placed inserts and parent cutting
elements may lead to an improvement in bit performance or a
reduction in manufacturing costs.
[0117] Referring now to FIG. 10, a portion of a earth boring roller
cone bit according to an embodiment of the present disclosure is
shown. Bit 1010 has a predetermined gage diameter as defined by
three roller cone cutters 1014, 1015, 1016 (one of which is shown
in FIG. 10) rotatably mounted on bearing journals (shafts or pins)
that depend from the bit body. The bit body is composed of three
sections or legs 1019 (one of which is shown in FIG. 10) that are
welded together to form the bit body. Bit leg 1019 includes a
shirttail portion 1019a.
[0118] The roller cone cutter 1014 is rotatably mounted on a pin or
journal 1020 oriented generally downwardly and inwardly toward the
center of the bit. The roller cone 1014 is typically secured on pin
or journal 1020 by locking balls 1026. In the embodiment shown,
radial and axial thrust are absorbed by roller bearings 1028, 1030,
thrust washer 1031 and thrust plug 1032; however, the present
disclosure is not limited to use in a roller bearing bit but may
equally be applied in a friction bearing bit, where roller cones
1014-1016 would be mounted on journals 1020 without roller bearings
1028, 1030. In both roller bearing and friction bearing bits,
lubricant may be supplied from a reservoir to the bearings by an
apparatus that is omitted from the figures for the sake of clarity.
The lubricant is sealed and drilling fluid excluded by an annular
seal 1034. The roller cone cutter 1014 includes a back face 1040
and nose portion 1042. Further, the roller cone 1014 includes a
generally frustoconical surface 1044 that is adapted to retain
inserts 1060 that scrape or ream the sidewalls of the borehole as
roller cones 1014-1016 rotate about the borehole bottom.
Frustoconical surface 1044 will be referred to herein as the "heel"
surface of roller cones 1014-1016.
[0119] Extending between the heel surface 1044 and nose 1042 is a
generally conical surface 1046 having a plurality of parent cutting
elements 1080, 1081, 1082 having a layer of wear resistant material
1111 applied by a thermal spray process (without subsequently
sintering) to form wear resistant cutting elements that gouge or
crush the borehole bottom as the roller cones 1014-1016 rotate
about the borehole. Roller cone cutter 1014 includes a plurality of
wear resistant cutting elements 1080, 1081, 1082 having a layer of
wear resistant material applied by a thermal spray process, a
plurality of gage row inserts 1070, and a plurality of heel row
inserts 1060. Exemplary roller cone 1014 includes a plurality of
heel row inserts 1060 that are secured in a circumferential heel
row 1060a in the frustoconical heel surface 1044. Roller cone 1014
further includes a circumferential gage row 1070a of gage row
inserts 1070 and circumferential inner rows 1080a, 1081a, 1082a
comprising a layer of wear resistant material 1111 applied by a
thermal spray process (without subsequently sintering) to parent
cutting elements formed of a different material 1038 from the
material of the cone body 1041, from the material of the gage row
inserts 1039 and from the material of the heel row inserts 1037.
Wear resistant cutting elements 1080-1082 each include a base
portion and a cutting portion. Such heel row and gage row inserts
have been discussed above. The gage row inserts 1070, 1039 and the
heel row inserts 1060, 1037 may be formed from the same or
different materials depending on the particular application. Roller
cone 1014 further includes a plurality of inner row wear resistant
cutting elements 1080-1082 which comprise a layer of wear resistant
material 1111 applied by a thermal spray process (without
subsequent sintering) to parent cutting elements the base portion
of which is disposed within a mating socket drilled or otherwise
formed in the cone body of roller cone cutter 1014 and arranged in
spaced-apart inner rows 1080a, 1081a, 1082a, respectively. Each
wear resistant cutting element 1080-1082 may be secured within the
mating socket by any suitable means including without limitation an
interference fit, brazing, or combinations thereof. Bit 1010 may
include additional rows of inner row wear resistant cutting
elements in addition to rows 1080a, 1081a, 1082a.
[0120] Inserts 1060, 1070 each include a base portion and a cutting
portion. The base portion of each insert is disposed within a
mating socket drilled or otherwise formed in the cone steel of a
roller cone cutter 14-16. Each insert 1060, 1070 may be secured
within the mating socket by any suitable means including without
limitation an interference fit, brazing, or combinations thereof.
The cutting portion of the inserts 1060, 1070 and wear resistant
cutting elements 1080-1082 extends from the base portion of the
insert/element and includes a cutting surface for cutting formation
material. The cutting portion is depicted as a domed surface,
however, a person of ordinary skill would appreciate that other
configurations may also be used. The present embodiment will be
understood with reference to one such roller cone 1014, roller
cones 1015, 1016 (not shown) being similarly, although not
necessarily identically, configured.
[0121] The following illustrates the improved properties of one or
more embodiments of the present disclosure. In the following
examples, hardfacing compositions "Composition A" and "Composition
B" were used. The compositions contained a steel matrix and carbide
phases which are summarized below in Table 1. Wear resistant
material "Composition C" was also used and contained 88% w
mono-tungsten carbide and 12% w cobalt. Composition C was WOKA 3101
powder commercially available from Sulzer Metco, Inc. In the
following examples, the layers of hardfacing compositions had an
approximate thickness of about 0.120 inches (3 mm) and the layers
of wear resistant material had an approximate thickness of about
0.050 inches (1 mm).
TABLE-US-00002 TABLE 1 Carbide Phase Composition Cemented Cemented
Crushed Crushed Tungsten Tungsten Cast Cast Carbide Carbide
Tungsten Tungsten Cobalt Cobalt Quantity Carbide Carbide Pellets***
Pellets*** Carburized Deoxidizer of (-40/+60 (-40/+80 (-16/+20
(-30/+40 Tungsten and resin Carbide mesh) mesh) mesh) mesh) Carbide
(-400 binder Phase Composition [% w]** [% w]** [% w]** [% w]**
mesh)[% w]** [% w]** (% w)* A 27 -- 35 24 10 4 67 B -- 18 40 28 10
4 67 *weight percent of the carbide phase is based on the total
weight of the hardfacing composition (e.g., welding rod)
pre-application: balance is iron-based binder alloy **weight
percent based on the total weight of the carbide phase
pre-application ***the cemented tungsten carbide cobalt was
non-super dense sintered tungsten carbide cobalt
[0122] In comparative example 1, coupon samples were hardfaced with
Composition A using a welding rod comprising the carbide phase, as
described in Table 1, and a mild steel AISI 1008 tube. The
hardfacing composition was applied using an oxyacetylene welding
process. The sample was then subjected to the high stress wear test
according to the ASTM B611 protocols, which measures the wear
resistance and toughness. This test was run again on a fresh coupon
sample of Composition A. The average of the two results is
summarized below in Table 2.
[0123] In comparative example 2, coupon samples were hardfaced with
Composition B using a welding rod comprising the carbide phase, as
described in Table 1, and a mild steel AISI 1008 tube. The
hardfacing composition was applied using an oxyacetylene welding
process. The sample was then subjected to the high stress wear test
according to the ASTM B611 protocols. This test was run again on a
fresh coupon sample of Composition B. The average result for the
two tests is summarized below in Table 2.
[0124] In example 3, coupon samples were hardfaced with Composition
A using a welding rod comprising the carbide phase, as described in
Table 1, and a mild steel AISI 1008 tube. The hardfacing
composition was applied using an oxyacetylene welding process. The
coupon was then subjected to a high velocity oxygen liquid fuel
thermal spray process to provide an outer layer of Composition C.
The sample was then subjected to the high stress wear test
according to the ASTM B611 protocols. This test was run again on a
fresh coupon sample. The average result for the two tests is
summarized below in Table 2.
[0125] In example 4, a coupon sample was subjected to a high
velocity oxygen liquid fuel thermal spray process to provide a
layer of Composition C. The sample was then subjected to the high
stress wear test according to the ASTM B611 protocols. This test
was run again on a fresh coupon sample. The average result for the
two tests is summarized below in Table 2.
TABLE-US-00003 TABLE 2 B-611 Test Results Example Wear Rate
(cc/1000 rev) 1 0.3490 2 0.3909 3 0.3081 4 0.2889
[0126] Examples 3 and 4 showed an improvement in toughness and wear
resistance over comparative examples 1 and 2. In particular, coupon
samples having a layer of wear resistant material applied via a
thermal spray process showed a much better wear
resistance/toughness than coupon samples without such a wear
resistant material applied thereto. This improvement in wear loss
can lead to an improvement in ROP and/or bit durability thus
extending the life of the bit.
[0127] Additionally, in comparative example 5, coupon samples were
hardfaced with Composition B as described in example 2. A coupon
was subjected to a low stress test according to the ASTM G65
protocols, which measures wear resistance. This test measures the
volume loss, and the lower the loss means better wear resistance.
This test was run again on a fresh coupon sample of Composition B.
The average result for the two tests is summarized below in Table
3.
[0128] In example 6, coupon samples were subjected to a high
velocity oxygen liquid fuel thermal spray process with Composition
C to provide a wear resistant material layer. A coupon was
subjected to a low stress test according to the ASTM G65 protocols.
This test was run again on a fresh coupon sample of Composition C.
The average result for the two tests is summarized below in Table
3.
TABLE-US-00004 TABLE 3 G-65 Test Results Example Wear Rate (cc
(.times.10.sup.3)/1000 rev) 5 2.72 6 1.75
[0129] Example 6 showed an improvement in wear resistance over
comparative Example 5. In particular, coupon samples having a layer
of wear resistant material applied via a thermal spray process
showed a much better wear resistance than coupon samples with a
hardfacing composition applied thereto.
[0130] Embodiments of the present disclosure may provide at least
one of the following advantages: improved ROP; improved bit
durability; improved cost-effectiveness; improved hardness;
improved smoothness of the surface of the cutting elements (i.e.,
less surface roughness); ease of control of the coating process;
improved consistency; environmentally friendly manufacturing
process; and improved manufacturing process through automation of
the thermal spray process.
[0131] Embodiments of the present disclosure may provide for a more
cost effective roller cone cutter and bit by reducing the cost of
materials, reducing the cost of labor, reducing the time required
to manufacture, and/or simplifying the manufacturing process
through the elimination of one or more manufacturing steps. The
manufacturing process may also be more environmentally friendly as
the wear resistant material may be applied by an automated process,
thus, reducing operator exposure to the materials during
processing.
[0132] Additionally, while the above embodiments make reference to
discrete layers, no limitation is intended on the scope of the
present disclosure by such a description. In fact, during
application, materials at the interface may blend across the
interface. Therefore, it is specifically within the scope of the
present disclosure that there may be some blending of the multiple
layers at the interface there between.
[0133] While the above embodiments have been described with layers
applied to the surface of parent cutting elements such as generally
conical-shaped bodies and milled teeth, no limitation is intended
on the scope of the present disclosure by such a description.
Additional cone surfaces may also have one or more layers applied
thereto.
[0134] While the above embodiments have been described with each
layer having a substantially uniform thickness, no limitation is
intended on the scope of the present disclosure by such a
description. It is intended to be included in the scope of the
present disclosure that each layer may vary in thickness, for
example the thickness of each layer may be greater on the leading
surface that first engages the formation.
[0135] While the above embodiments have been described with
reference to an oil well borehole, no limitation is intended on the
scope of the present disclosure by such a description. It is
intended to be included in the scope of the present disclosure that
the roller cone cutters and drill bits incorporating such roller
cones may be used in a variety of applications, for example mining,
drilling water-wells, etc.
[0136] While the invention has been shown and described with
respect to a limited number of embodiments, modifications thereof
can be made by one skilled in the art without departing from the
spirit or teaching herein. The embodiments described herein are
exemplary only and are not limiting. For example, the roller cone
drill bits have been described herein as having three roller cones;
however, roller cone drill bits with one, two, or four roller cones
is contemplated within the scope of the present disclosure. For
example, the roller cone drill bits have been described herein as
having cutting elements arranged in circumferential rows; however,
such cutting elements may be arranged in non-circumferential rows
such as spiral, multiple spirals, other patterns of offset cutting
elements or random arrangements, such non-circumferential
arrangements, as described in U.S. Pat. No. 7,370,711, are
incorporated herein by reference in their entirety. For example,
the embodiments disclosed herein may refer to the substrate or
surface of the tool body as being a parent cutting element of a
roller cone; however, any surface of a downhole tool may be coated
in accordance with the present disclosure; for example other
surfaces of a roller cone drill bit (e.g., shirttail and other bit
leg surfaces as well as the roller cone body); fixed cutter drill
bits; percussion/hammer bits; hole openers; reamers; stabilizers;
etc. Many variations and modifications of the system and apparatus
are possible. Accordingly, the scope of protection is not limited
to the embodiments described herein, but is only limited by the
claims which follow, the scope of which shall include equivalents
of the subject matter of the claims.
* * * * *