Note: Descriptions are shown in the official language in which they were submitted.
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DRILLING BIT HAVING A CUTTING ELEMENT. CO-SINTERED WITH A CONE STRUCTURE
PRIORITY CLAIM
This application claims the benefit of the filing date of United States Patent
Application Serial No. 11/710,091, filed February 23, 2007, for "EARTH-BORING
TOOLS AND CUTTER ASSEMBLIES HAVING A CUTTING ELEMENT
CO-SINTERED WITH A CONE STRUCTURE, METHODS OF USING THE
SAME."
TECHNICAL FIELD
The present invention generally relates to earth-boring tools having one or
more
rotatable cones. More particularly, embodiments of the present invention
relate to
methods of forming cutter assemblies having a cone comprising a particle-
matrix
composite material for use in such earth-boring tools, to cutter assemblies
formed by such
methods, and to earth-boring tools that include such cutter assemblies.
BACKGROUND
Earth-boring tools, including rotary drill bits, are commonly used for
drilling bore
holes or wells in earth'formations. One type of rotary drill bit is the roller
cone bit (often
referred to as a "rock" bit), which typically includes a plurality of conical
cutt.ing elements
(often referred to as "cones" or "cutters") secured to legs dependent from the
bit body.
For example, the bit body of a roller cone bit may have three depending legs
each having
a bearing pin. A rotatable cone may be mounted on each of the bearing pins.
The bit
body also may include a threaded upper end for connecting the drill bit to a
drill string.
In some roller cone bits, the rotatable cones may include inserts or compacts
that
are formed from a particle-matrix composite material and secured within mating
holes
formed in an exterior surface of the cone body. The inserts protrude from the
exterior
surface of the cone body, such that the inserts engage and disintegrate an
earth formation
as the rotatable cone rolls across the surface of the earth formation in a
well bore during a
drilling operation. Such inserts may be formed by compacting a powder mixture
in a die.
The powder mixture may include a plurality of hard particles (e.g., tungsten
carbide) and
a plurality of particles comprising a matrix material (e.g., a metal or metal
alloy material).
The compacted powder mixture then may be sintered to form an insert. In some
roller
cone bits, the body of the rotatable cones (or at least the outer shells of
the rotatable
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cones) may be formed of steel. The particle-matrix composite material from
which the
inserts are formed may be relatively more resistant to abrasive wear than the
body (or at
least the outer shell) of the rotatable cones. During drilling operations, it
is possible that a
body of a rotatable cone may wear to the extent that one or more inserts may
fall out from
the hole in which it was secured due to excessive wear of the region of the
cone body
surrounding the hole.
In additional roller cone bits, the rotatable cones may include teeth that are
milled
or machined directly into an exterior surface of the cone body. After
machining the teeth,
hardfacing material may be applied to the teeth, gage, and other formation-
engaging
surfaces of the cone body in an effort to reduce wear of such formation-
engaging surfaces.
The hardfacing material typically includes a particle-matrix composite
material. For
example, the hardfacing material may include tungsten carbide granules or
pellets
embedded within a metal or metal alloy.
Various techniques known in the art may be used to apply a particle-matrix
composite hardfacing material to a surface of a work piece, such as an earth-
boring tool.
For example, a hollow cylindrical tube may be formed from a matrix material,
and the
tube may be filled with hard particles (e.g., tungsten carbide). At least one
end of the tube
may be sealed and positioned near the surface of the work piece. The sealed
end of the
tube then may be melted using an arc or a torch. As the tube melts, the
tungsten carbide
particles within the hollow, cylindrical tube mix with the molten matrix
material as it is
deposited onto the work piece. In additional methods, a substantially solid
rod
comprising the particle-matrix composite hardfacing material may,be used in
place of a
hollow tube comprising matrix material that is filled with hard particles.
Additional arc welding techniques also may be used to apply a hard-facing
material to the exterior surface of the work piece. For example, a plasma-
transferred arc
may be established between an electrode and a region on the exterior surface
of the work
piece on which it is desired to apply a hard-facing material. A powder mixture
including
both hard particles and particles comprising matrix material then may be
directed through
or proximate the plasma transferred arc onto the region of the exterior
surface of the work
piece. The heat generated by the arc melts at least the particles of matrix
material to form
a weld pool on the surface of the work piece, which subsequently solidifies to
form the
particle-matrix composite hardfacing material.
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Hardfacing applications may be relatively labor intensive, and hardfacing
thickness and uniformity of coverage may be difficult to control in a
repeatable manner.
Furthermore, application of hardfacing material to the teeth of a rotatable
cone may
reduce the sharpness of the cutting edges of the teeth. Some grinding of the
hardfacing to
desired shapes may be performed. U.S. Patent No. 6,766,870, discloses a method
of
shaping hardfaced teeth through a secondary machining operation. However,
sharpening
the hardfaced teeth by grinding adds another step and substantial labor and
machining
cost in a process for manufacturing a roller cone bit.
DISCLOSURE OF THE INVENTION
In some embodiments, the present invention includes methods of forming cutter
assemblies for use on earth-boring tools. The methods include sintering a less
than fully
sintered cone structure to a desired final density to fuse at least one
cutting element, also
termed inserts herein, to the cone structure. The less than fully sintered
cone structure
may comprise hard particles and a matrix material.
In additional embodiments, the present invention includes cutter assemblies
for
use on an earth-boring tool having one or more cutting elements co-sintered
and integral
with a cone structure. The cone structure and the cutting elements each may
comprise a
particle-matrix composite material. The material composition of cone structure
may
differ from the material composition of at least one of the cutting elements.
In yet further embodiments, the present invention includes earth-boring tools
having at least one such cutter assembly rotatably mounted on a bearing pin.
DESCRIPTION OF THE DRAWINGS
Wlvle the specification concludes with claims particularly pointing out and
distinctly claiming that which is regarded as the present invention, the
advantages of this
invention may be more readily ascertained from the following description of
the invention
when read in conjunction with the accompanying drawings in which:
FIG. I is a side elevational view of an earth-boring drill bit according to an
embodiment of the present invention;
FIG. 2 is a partial sectional view of one embodiment of a rotatable cutter
assembly, including a cone, of the present invention and that may be used with
the
earth-boring drill bit shown in FIG. 1;
FIG. 3 is a schematic view illustrating one method that may be used to form a
cone of a rotatable cutter assembly according to an embodiment of the present
invention;
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FIG. 4 is a schematic view illustrating another method that may be used to
fonn a
cone of a rotatable cutter assembly according to another embodiment of the
present
invention;
FIG. 5A-5C illustrate one embodiment of a method that may be used to form a
rotatable cutter assembly of the present invention, such as the rotatable
cutter assembly
shown in FIG. 2;
FIGS. 6A-6C illustrate another embodiment of a method that may be used to form
a rotatable cutter assernbly that embodies teachings of the present invention,
such as the
rotatable cutter assembly shown in FIG. 2;
FIG. 7 is a side elevational view of another embodiment of an earth-boring
drill
bit of the present invention;
FIG. 8 is a partial sectional view illustrating another embodiment of a
rotatable
cutter assembly, including a cone, of the present invention and that may be
used with an
earth-boring drill bit, such as the earth-boring drill bit shown in FIG. 7;
FIG. 9 is a partial cross-sectional view of one embodiment of a tooth
structure that
may be used to provide a rotatable cutter assembly of the present invention,
such as the
cutter assembly shown in FIG. 8; and
FIG. 10 is a partial cross-sectional view of another embodiment of a tooth
structure that may be used to provide a rotatable cutter assembly of the
present invention,
such as the cutter assembly shown in FIG. 8.
MODE(S) FOR CARRYING OUT THE INVENTION
The illustrations presented herein are not meant to be actual views of any
particular material, apparatus, system, or method, but are merely idealized
representations
which are employed to describe the present invention. Additionally, elements
common
between figures may retain the same numerical designation.
The term "green" as used herein means unsintered.
The term "green structure" as used herein means an unsintered structure
comprising a plurality of discrete particles held together by a binder
material.
The term "brown" as used herein means partially sintered.
The term "brown structure" as used herein means a partially sintered structure
comprising a plurality of particles, at least some of which have partially
grown together to
provide at least partial bonding between adjacent particles. Brown structures
may be
formed by partially sintering a green structure.
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The term "sintering" as used herein means densification of a particulate
component involving removal of at least a portion of the pores between the
starting
particles (accompanied by shrinkage) combined with coalescence and bonding
between
adjacent particles.
As used herein, the tenn "[metal]-based alloy" (where [metal] is any metal)
means
commercially pure [metal] in addition to metal alloys wherein the weight
percentage of
[metal] in the alloy is greater than the weight percentage of any other
component of the
alloy.
As used herein, the term "material composition" means the chemical composition
and microstructure of a material. In other words, materials having the same
chemical
composition but a different microstructure are considered to have different
material
compositions.
As used herein, the term "tungsten carbide" means any material composition
that
contains chemical compounds of tungsten and carbon, such as, for example, WC,
W2C,
and combinations of WC and W2C. Tungsten carbide includes, for example, cast
tungsten carbide, sintered tungsten carbide, and macrocrystalline tungsten
carbide.
The depth of well bores being drilled continues to increase as the number of
shallow depth hydrocarbon-bearing earth formations continues to decrease.
These
increasing well bore depths are pressing conventional drill bits to their
limits in terms of
performance and durability. Several drill bits are often required to drill a
single well bore,
and changing a drill bit on a drill string can be expensive.
New particle-matrix composite materials are currently being investigated in an
effort to improve the performance and durability of earth-boring rotary drill
bits. By way
of example and not limitation, bit bodies for fixed-cutter type earth-boring
rotary drill bits
that include such particle-matrix composite materials, and methods for forming
such bit
bodies, are disclosed in pending United States Patent Application Serial No.
11/271,153,
filed November 10, 2005 and pending United States Patent Application Serial
No.
11/272,439, also filed November 10, 2005. In addition, earth-boring rotary
drill bits
having rotatable cutter assemblies that comprise a cone formed from such
particle-matrix
composite materials, as well as methods for forming such cones, are disclosed
in pending
United States Patent Application Serial No. 11/487,890, filed July 17, 2006.
An earth-boring drill bit 10 according to an embodiment of the present
invention
is shown in FIG. 1. The earth-boring drill bit 10 includes a bit body 12 and a
plurality of
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rotatable cutter assemblies 14. The bit body 12 may include a plurality of
integrally
formed bit legs 16, and threads 18 may be formed on the upper end of the bit
body 12 for
connection to a drill string. The bit body 12 may have nozzles 20 for
discharging drilling
fluid into a borehole, which may be returned along with cuttings up to the
surface during a
drilling operation. Each of the rotatable cutter assemblies 14 include a cone
22
comprising a particle-matrix composite material and a plurality of cutting
elements, such
as the cutting inserts 24 shown. Each cone 22 may include a conical gage
surface 26.
Additionally, each cone 22 may have a unique configuration of cutting inserts
24 or
cutting elements, such that the cones 22 may rotate in close proximity to one
another
without mechanical interference.
FIG. 2 is a cross-sectional view illustrating one of the rotatable cutter
assemblies 14 of the earth-boring drill bit 10 shown in FIG. 1. As shown, each
bit leg 16
may include a bearing pin 28. The cone 22 may be supported by the bearing pin
28, and
the cone 22 may be rotatable about the bearing pin 28. Each cone 22 may have a
central
cavity 30 that may be cylindrical and may form a joumal bearing surface
adjacent the
bearing pin 28. The cavity 30 may have a flat thrust shoulder 32 for absorbing
thrust
imposed by the drill string on the cone 22. As illustrated in this example,
the cone 22 may
be retained on the bearing pin 28 by a plurality of locking balls 341ocated in
mating
grooves formed in the surfaces of the cone cavity 30 and the bearing pin 28.
Additionally,
a seal assembly 36 may seal the bearing spaces between the cone cavity 30 and
the
bearing pin 28. The seal assembly 36 may be a metal face seal assembly, as
shown, or
may be a different type of seal assembly, such as an elastomer seal assembly.
Lubricant may be supplied to the bearing spaces between the cavity 30 and the
bearing pin 28 by lubricant passages 38. The lubricant passages 38 may lead to
a
reservoir that includes a pressure compensator 40 (FIG. 1).
As previously mentioned, the cone 22 may comprise a sintered particle-matrix
composite material that comprises a plurality of hard particles dispersed
through a matrix
material. In some embodiments, the cone 22 may be predominantly comprised of
the
particle matrix composite material. The hard particles may comprise diamond or
ceramic
materials such as carbides, nitrides, oxides, and borides (including boron
carbide (B4C)).
More specifically, the hard particles may comprise carbides and borides made
from
elements such as W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al and Si. By way of
example and
not limitation, materials that may be used to form hard particles include
tungsten carbide
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(WC, W2C), titanium carbide (TiC), tantalum carbide (TaC), titanium diboride
(TiB2),
chromium carbides, titanium nitride (TiN), vanadium carbide (VC), aluminum
oxide
(A1203), aluminum nitride (AIN), boron nitride (BN), and silicon carbide
(SiC).
Furthennore, combinations of different hard particles may be used to tailor
the physical
properties and characteristics of the particle-matrix composite material. The
hard
particles may be formed using techniques known to those of ordinary skill in
the art.
Most suitable materials for hard particles are commercially available and the
formation of
the remainder is within the ability of one of ordinary skill in the art.
The matrix material may include, for example, cobalt-based, iron-based,
nickel-based, iron and nickel-based, cobalt and nickel-based, iron and cobalt-
based,
aluminum-based, copper-based, magnesium-based, and titanium-based alloys. The
matrix material may also be selected from commercially pure elements such as
cobalt,
aluminum, copper, magnesium, titanium, iron, and nickel. By way of example and
not
limitation, the matrix material may include carbon steel, alloy steel,
stainless steel, tool
steel, nickel or cobalt superalloy material, and low thermal expansion iron or
nickel based
alloys such as INVAR . As used herein, the term "superalloy" refers to an
iron, nickel,
and cobalt based-alloys having at least 12% chromium by weight. Additional
exemplary
alloys that may be used as matrix material include austenitic steels, nickel
based
superalloys such as INCONEL 625M or Rene 95, and INVAR type alloys having a
coefficient of thermal expansion that more closely matches that of the hard
particles used
in the particular material. More closely matching the coefficient of thermal
expansion of
matrix material with that of the hard particles offers advantages such as
reducing
problems associated with residual stresses and thermal fatigue. Another
exemplary
matrix material is a Hadfield austenitic manganese steel (Fe with
approximately 12% Mn
by weight and 1.1 % C by weight).
In one embodiment of the present invention, the sintered particle-matrix
composite material may include a plurality of -400 ASTM (American Society for
Testing
and Materials) mesh tungsten carbide particles. For example, the tungsten
carbide
particles may be substantially composed of WC. As used herein, the phrase "-
400 ASTM
mesh particles" means particles that pass through an ASTM No. 400 mesh screen
as
defined in ASTM specification El 1-04 entitled Standard Specification for Wire
Cloth and
Sieves for Testing Purposes. Such tungsten carbide particles may have a
diameter of less
than about 38 microns. The matrix material may include a metal alloy
comprising about
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50% cobalt by weight and about 50% nickel by weight. The tungsten carbide
particles
may comprise between about 60% and about 95% by weight of the composite
material,
and the matrix material may comprise between about 5% and about 40% by weight
of the
composite material. More particularly, the tungsten carbide particles may
comprise
between about 70% and about 80% by weight of the composite material, and the
matrix
material may comprise between about 20% and about 30% by weight of the
composite
material.
In another embodiment of the present invention, the sintered particle-matrix
composite material may include a plurality of -635 ASTM mesh tungsten carbide
particles. As used herein, the phrase "-635 ASTM mesh particles" means
particles that
pass through an ASTM No. 635 mesh screen as defined in ASTM specification E11-
04
entitled Standard Specification for Wire Cloth and Sieves for Testing
Purposes. Such
tungsten carbide particles may have a diameter of less than about 20 microns.
The matrix
material may include a cobalt-based metal alloy comprising substantially
commercially
pure cobalt. For example, the matrix material may include greater than about
98% cobalt
by weight. The tungsten carbide particles may comprise between about 60% and
about
95% by weight of the composite material, and the matrix material may comprise
between
about 5% and about 40% by weight of the composite material. After forming, the
cone 22
may exhibit a hardness in a range extending from about 75 to about 92 on the
Rockwell A
hardness scale.
FIGS. 3, 4, and 5A-5C illustrate embodiments of a method that may be used to
form the cone 22 and the cutter assembly 14 shown in FIG. 2. In general, this
method
includes providing a powder mixture, pressing the powder mixture to form a
billet,
forming a green or brown cone structure from the billet, and sintering the
green or brown
cone structure to a desired final density.
FIG. 3 illustrates a method of pressing a powder mixture 42 to form a green
billet
that may be used to form the cone 22. As illustrated in FIG. 3, the powder
mixture 42
may be pressed with substantially isostatic pressure within a mold or
container 44. The
powder mixture 42 may include a plurality of the previouslydescribed hard
particles and
a plurality of particles comprising a matrix material, as also previously
described herein.
Optionally, the powder mixture 42 may further include one or more additives
such as, for
example, binders (e.g., organic materials such as, for example, waxes) for
providing
structural strength to the pressed powder component, plasticizers for making
the binder
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more pliable, and lubricants or compaction aids for reducing inter-particle
friction and
otherwise providing lubrication during pressing.
The container 44 may include a fluid-tight deformable member 46. For example,
the deformable member 46 may be a substantially cylindrical bag comprising a
deformable and impermeable polymeric material, which may be an elastomer such
as
rubber, neoprene, silicone, or polyurethane. The container 44 may further
include a
sealing plate 48, which may be substantially rigid. The deformable member 46
may be
filled with a powder mixture 42 and optionally vibrated to provide a uniform
distribution
of the powder mixture 42 within the deformable member 46. The sealing plate 48
may be
attached or bonded to the deformable member 46, which may provide a fluid-
tight seal
therebetween.
The container 44, with the powder mixture 42 therein, may be placed within a
pressure chamber 50. A removable cover 52 may be used to provide access to the
interior
of the pressure chamber 50. A gas (such as, for example, air or nitrogen) or a
fluid (such
as, for example, water or oil), which may be substantially incompressible, is
pumped into
the pressure chamber 50 through a port 54 at high pressures using a pump (not
shown).
The high pressure of the fluid may cause the member 46 to deform, and the
fluid pressure
may be transmitted substantially uniformly to the powder mixture 42. The
pressure
within the pressure chamber 50 during isostatic pressing may be greater than
about 35
megapascals (about 5,000 pounds per square inch). More particularly, the
pressure within
the pressure chamber 50 during isostatic pressing may be greater than about
138
megapascals (20,000 pounds per square inch).
In additional methods, a vacuum may be provided within the flexible container
44
and a pressure greater than about 0.1 megapascals (about 15 pounds per square
inch) may
be applied to the deformable member 46 of the container 44 (by, for example,
the
atmosphere) and may compact the powder mixture 42. Isostatic pressing of the
powder
mixture 42 may form a green billet, which may be removed from the pressure
chamber 50
and the container 44 after pressing for machining. In some embodiments, the
resulting
billet may have a generally cylindrical configuration.
FIG. 4 illustrates an additional method of pressing a powder mixture 56 to
form a
green billet that may be used to form the cone 22 shown in FIG. 2. The method
illustrated
in FIG. 4 comprises forming a billet using a rigid die 58 having a cavity for
receiving the
powder mixture 56. The powder mixture 56 may be the same as the powder mixture
42
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used in the method illustrated in FIG. 3. The cavity of the die 58 may be
generally
conically-shaped, and may form an overall conical billet. Alternatively, the
cavity may be
cylindrical, and may form a cylindrical billet. A piston or ram 60 may
sealingly engage
the walls of the die 58. A force may act on the piston 60 and may press the
powder
mixture 56 into a green billet with a coherent shape suitable for machining.
The green billet, whether formed by the method illustrated in FIG. 3 or FIG.
4,
may be machined in the green state to form a green cone structure 22A shown in
FIG. 5A.
In additional methods, however, the green billet may be partially sintered to
form a
brown billet, and the brown billet then may be machined to form a brown cone
structure
(not shown). The brown billet may be less than fully dense to facilitate
machining
thereof. Green or brown structures, such as the green cone structure 22A, a
brown cone
structure, or a green or brown billet, may be machined in substantially the
same manner as
for steel cones known in the art. However, because shrinkage may occur during
subsequent sintering processes, the dimensions of the green or brown
structures may be
over-sized to accommodate for shrinkage.
FIG. 5A illustrates a green cone structure 22A that may be used to form the
cutter
assembly 14 (FIGS. 1-2). As illustrated in FIG. 5A, in some embodiments, the
green cone
structure 22A may have an overall shape corresponding to the desired final
shape of the
cone 22, and may include various features such as a central cavity 30 for
providing a
joumal bearing surface adjacent a bearing pin 28 (FIG. 2) and apertures 62 for
receiving
cutting inserts 24 therein (FIG. 2).
Optionally, displacement members 64 may be inserted into the apertures 62 for
preserving a desired size, shape and orientation of each of the apertures 62
during a
subsequent sintering process. The displacement members 64 may comprise dowels
that
are dimensioned to the desired final dimensions of the aperture 62 in the cone
22 to be
formed for each insert 24. The displacement members 64 may be formed of a
material,
such as a ceramic, that will remain solid and stable at the sintering
temperature.
Additionally, the displacement members 64 may be formed of a porous and/or
hollow
material to facilitate their removal from the resulting fully sintered cone 22
after the
sintering process. The apertures 62 may be larger in diameter than the
displacement
members 64 before sintering, and may shrink during sintering to the diameters
of the
displacement members 64.
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In some embodiments, the green cone structure 22A shown in FIG. 5A may be
heated and sintered in a furnace to a desired final density to form a fully
sintered cone 22
shown in FIG. 5B. The fully sintered cone 22 is shown in FIG. 5B after the
displacement
members 64 (FIG. 5A) have been removed from the fully sintered cone 22.
In some embodiments, the finrnace may comprise a vacuum furnace for providing
a vacuum therein during the sintering process. In additional embodiments, the
furnace
may comprise a pressure chamber for pressurizing the cone therein as it is
sintered.
Furthermore, the furnace may be configured to provide a controlled atmosphere.
For
example, the fumace may be configured to provide an atmosphere that is
substantially
free of oxygen in which the cone may be sintered.
As a non-limiting example, it may be desirable to provide a cone 22 comprising
a
sintered tungsten carbide material. To form such a cone, a green cone
structure 22A may
be formed that includes a plurality of particles comprising tungsten carbide
and a plurality
of particles comprising a cobalt-based matrix material, the particles being
bound together
by an organic binder material. In such methods, the green cone structure 22A
may be
sintered at a temperature of between about five hundred degrees Celsius (500
C) and
about fifteen hundred degrees Celsius (1500 C). The sintering temperature may
differ
between particular particle-matrix composite material compositions.
During the sintering process, the green cone structure 22A may undergo
shrinkage
and densification as it is sintered to a final density to form the cone 22.
After sintering,
the cone 22 may have the desired exterior configuration, which may include the
apertures
62, and the central cavity 30. Limited or no furt.her machining may be
necessary for these
surfaces. The cavity 30, or other surfaces, may be machined after sintering.
For example,
the bore surfaces of the cavity 30 may be ground and polished to achieve a
desired surface
finish.
As shown in FIG. 5C, after the cone 22 has been formed and the optional
displacement members 64 removed, cutting inserts 24 may be secured within the
apertures 62. The cutting inserts 24 may have a size and shape selected to
provide a tight
and secure press-fit between the cutting inserts 24 and the apertures 62. In
additional
embodiments, the cutting inserts 24 may be bonded within the apertures 62
using an
adhesive. In yet other embodiments, the cutting inserts 24 may be secured
within the
apertures 62 using a soldering or brazing technique.
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The central cavity 30 may be finish machined and the cone 22 may be mounted to
the bearing pin 28 in a conventional manner (FIG. 2). The cutting inserts 24
may be
formed separately from the cone 22 in a manner similar to that in which the
cone 22 is
formed. Although the cutting inserts 24 may also be formed of a sintered
particle-matrix
composite material, the composition of the particle-matrix composite material
of the
cutting inserts 24 may differ from the composition of the particle-matrix
composite
material of the cone 22.
In additional methods, rather.than fonning a green or brown billet comprising
a
sintered particle-matrix composite material and machining the green or brown
billet to
form a green or brown cone structure, a green billet may be sintered to a
desired final
density to provide a fully sintered billet. Such a fully sintered billet then
may be
machined to form the fully sintered cone 22 shown in FIG. 5B using traditional
machining
methods or ultrasonic machining methods. As such a fully sintered billet may
be
relatively difficult to machine, use of ultrasonic machining methods may
facilitate the
machining process. For example, ultrasonic machining methods may include
applying a
high frequency vibratory motion to the machining tool, which may enhance
removal of
material from the fully sintered billet.
FIGS. 6A-6C illustrate an additional embodiment of a method that may be used
to
form a cutter assembly (such as the cutter assembly 14 shown in FIG. 3) of the
present
invention. As discussed in further detail below, the method generally includes
providing
a less than fully sintered green or brown cone comprising a plurality of
apertures, inserting
inserts into the apertures in the green or brown cone, and sintering the
resulting structure
to a desired final density to secure the inserts to the cone. In this manner,
the inserts may
be co-sintered and integral with the cone. In some embodiments, the inserts
may
comprise less than fully sintered green or brown inserts, and the green or
brown inserts
may be sintered to a desired final density simultaneously with the cone. In
other
embodiments, the inserts may be fully sintered when they are inserted into the
corresponding apertures of the green or brown cone.
Furthermore, the inserts may have a composition gradient that varies from a
region or regions proximate the interface between the inserts and the cone and
a region or
regions proximate the formation engaging surface or surfaces of the inserts.
For example,
the regions of the inserts proximate the interface between the inserts and the
cone may
have a material composition configured to facilitate or enhance bonding
between the
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inserts and the cone, while the regions proximate the formation engaging
surface or
surfaces of the inserts may have a material composition configured to enhance
one or
more material properties or characteristics such as, for example, hardness,
toughness,
durability, and wear resistance. As one non-limiting example, the regions of
the inserts
proximate the interface between the inserts and the cone may have a first
matrix material
substantially similar to the matrix material of the cone, while the regions
proximate the
formation engaging surface or surfaces of the inserts may have a second matrix
material
selected to enhance one or more of the hardness, toughness, durability, and
wear
resistance of the inserts. In such embodiments, the concentrations of the
first matrix
material and the second matrix material in the inserts may vary either
continuously or in a
stepwise manner between the regions proximate the interface and the regions
proximate
the formation engaging surface.
Referring to FIG. 6A, a green cone structure 22A may be formed or otherwise
provided as previously described in relation to FIG. 5A. A plurality of green
cutting
inserts 24A may be provided. Each of the green cutting inserts 24A may
comprise a
plurality of hard particles and a plurality of particles comprising a matrix
material, and the
particles may be held together by an organic binder material. As previously
discussed, the
composition of the green cutting inserts 24A may differ from the composition
of the green
cone structure 22A. Furthermore, the green cutting inserts 24A may have a
composition
gradient that varies from a region or regions proximate the interface between
the inserts
and the cone and a region or regions proximate the formation engaging surface
or surfaces
of the inserts, as previously mentioned.
In some methods, additional green elements or components other than the green
cutting inserts 24A also may be secured to the green cone structure 22A prior
to sintering.
By way of example and not limitation, one or more green bearing structures 68A
that are
to define bearing surfaces of the cone may secured within the central cavity
30 of the
green cone structure 22A. Similar to the green cutting inserts 24A, each of
the green
bearing structures 68A may comprise a plurality of hard particles and a
plurality of
particles comprising a matrix material, and the composition of the green
bearing
structures 68A may differ from the composition of the green cone structure
22A.
As illustrated in FIG. 6B, the green cutting inserts 24A may be provided
within
the apertures 62 of the green cone structure 22A, and the green bearing
structures 68A
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may be secured at a selected location within the central cavity 30 of the
green cone
structure 22A.
By way of example and not limitation, the green cutting inserts 24A and the
apertures 62 within the green cone structure 22A may be sized and shaped so as
to
provide an average clearance therebetween of between about 0.025 millimeters
(0.001 in.)
and about 0.635 millimeters (0.025 in.). Such clearances also may be provided
between
the green bearing structures 68 and the green cone structure 22A.
After assembling the various green components to form a structure similar to
that
shown in FIG. 6B, the structure may be sintered to a desired final density to
form the fully
sintered structure shown in FIG. 6C. During the sintering process the cone 22,
including
the apertures 62 or other features, the cutting inserts 24 or other cutting
elements, and the
bearing structures 68 may undergo shrinkage and densification. Furthennore,
the cutting
inserts 24 and the bearing structures 68 may become fused and secured to the
cone 22. In
other words, after the sintering process, cutting inserts 24 and bearing
structures 68 may
be co-sintered and integral with the cone 22 to provide a substantially
unitary cutter
assembly 14'.
After the cutter assembly 14' has been sintered to a desired final density,
various
features of the cutter assembly 14' may be machined and polished, as necessary
or desired.
For example, bearing surfaces 70 on the bearing structures 68 may be polished.
Polishing the bearing surfaces 70 of the bearing structures 68 may provide a
relatively
smoother surface finish and may reduce friction at the interface between the
bearing
structures 68 and the bearing pin 28 (FIG. 2). Furthermore, the sealing edge
72 of the
bearing structures 68 also may be machined and/or polished to provide a shape
and
surface finish suitable for sealing against a metal or elastomer seal, or for
sealing against a
sealing surface located on the bit body 12 (FIG. 2).
The green cutting inserts 24A and the green bearing structures 68A may be
fo.rmed from particle-matrix composite materials in much the same way as the
green cone
structure 22A. The material composition of each of the green cutting inserts
24A, green
bearing structures 68A, and green cone structure 22A may be separately and
individually
selected to exhibit physical and/or chemical properties tailored to the
operating conditions
to be experienced by each of the respective components. By way of example and
not
limitation, the composition of the green cutting inserts 24A may be selected
so as to form
cutting inserts 24 comprising a particle-matrix composite material that
exhibits a different
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hardness, wear resistance, and/or toughness different from that exhibited by
the
particle-matrix composite material of the cone 22.
The cutting inserts 24 may be formed from a variety of particle-matrix
composite
material compositions. The particular composition of any particular insert 24
may be
selected to exhibit one or more physical and/or chemical properties tailored
for a
particular earth formation to be drilled using the drill bit 10 (FIG. 1).
Additionally,
cutting inserts 24 having different material compositions may be used on a
single cone 22.
By way of example and not limitation, in some embodiments of the present
invention, the cutting inserts 24 may comprise a particle-matrix composite
material that
includes a plurality of hard particles that are harder than a plurality of
hard particles of the
particle-matrix composite material of the cone 22. As another non-limiting
example, the
concentration of the hard particles in the particle-matrix composite material
of the cutting
inserts 24 may be greater than a concentration of hard particles in a particle-
matrix
composite material of the cone 22.
Although the cutter assembly 14' shown in FIG. 6C is illustrated as comprising
the
cone 22, the cutting inserts 24, and the bearing structures 68, it is
contemplated that in
additional embodiments, the cutter assembly 14' may not be formed with
separate green
bearing structures 68A, as described herein. Furthermore, as described above,
the cutter
assembly 14' may be formed by combining a green cone structure 22A, green
cutting
inserts 24A, and green bearing structures 68A to form a green cutter assembly
structure,
and subsequently sintering the green cutter assembly to a desired final
density. The
present invention is not so limited, however, and methods according to further
embodiments of the present invention may include assembling green structures,
brown
structures, fully sintered structures, or any combination thereof, and then
sintering or
reheating sintered components to the sintering temperature and causing the
various
components to fuse together to fonn a unitary, integral cutter assembly
structure.
While the cutter assembly 14' previously described herein has a cone 22 that
includes insert-type cutting structures, cutter assemblies having cones that
include
tooth-type cutting structures also may embody teachings of the present
invention, and
embodiments of methods of the present invention may be used to form cutter
assemblies
having cones that include such tooth-type cutting structures. For example,
FIG. 7
illustrates another earth-boring drill bit 74 according to an embodiment of
the present
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invention which comprises a plurality of cutter assemblies 80 each having a
cone 88 that
includes cutting teeth 104.
As shown in FIG. 7, the earth-boring drill bit 74 has a body 76 that may have
threads 78 formed on its upper end for connection to a drill string. The bit
body 76 may
have three integrally formed bit legs 82, each supporting a bearing pin 84
(Not shown). In
some embodiments, the bit body 76 and the bearing pins 84 may be formed of a
steel
alloy in a conventional manner. Additionally, the bit body 76 may have nozzles
86 for
discharging drilling fluid into the borehole, which may be returned along with
cuttings up
to the surface during a drilling operation.
As shown in FIG. 7, each cone 88 may have a plurality of rows of cutting
teeth 104. The teeth 104 may vary in number, have a variety of shapes, and the
number of
rows may vary. A conical gage surface 106 may surround the back face 102 of
each cone
88 and define the outer diameter of the bit 74. As discussed in further detail
below, one
portion of each tooth 104 may be integrally formed with the body of each cone
88, and
another portion of each tooth 104 may be formed using a separate green or
brown
structure that is fused to the cone 88 during a sintering process.
FIG. 8 is an enlarged partial cross-sectional view illustrating a portion of
one of
the cutter assemblies 80 mounted on a bearing pin 84, and shows each of the
teeth 104
rotated about the cone 88 into the plane of the figure so as to illustrate the
so-called
"cutting profile" defined by the cutting surfaces of all the teeth 104 on the
cone 88. As
shown in FIG. 8, each bearing pin 84 of the drill bit 74 may support one of
the cutter
assemblies 80. Each cone 88 of the cutter assemblies 80 may have a central
cavity 90 that
provides a journal bearing surface adjacent the bearing pin 84. The cone 88
may have a
flat thrust shoulder 92 and may have a lock groove 94 formed within the
central cavity 90.
In such a configuration, a snap ring 96 may be located in the lock groove 94
and a mating
groove may be formed on the bearing pin 84 for locking the cone 88 in position
on the
bearing pin 84. The cone 88 also may have a seal groove 98 for receiving a
seal 100. The
seal groove 98 may be located adjacent a back face 102 of the cone 88. By way
of
example and not limitation, the seal 100 may be an elastomeric ring. In some
embodiments, the back face 102 of the cone 88 may comprise a substantially
flat annular
surface surrounding the entrance to the central cavity 90.
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Lubricant may be supplied to the spaces between the central cavity 90 of the
cone 88 and the bearing pin 84 by lubricant passages 108. The lubricant
passages 108
may lead to a reservoir that includes a pressure compensator 110 (FIG. 7).
The cone 88 may comprise a particle-matrix composite material as previously
described in relation to the cone 22 shown in FIG. 2. Similarly, the cone 88
may be
formed using methods substantially similar to those previously described in
relation to the
cone 22 with reference to FIGS. 3 and 4. In general, the cone 88 may be formed
by green
or brown billet, machining the green or brown billet to form a green or brown
cone
structure, and sintering the green or brown cone structure to a desired final
density.
FIG. 9 illustrates one embodiment of a method of the present invention and
that
may be used to form the cutter assembly 80 shown in FIGS. 7 and 8. As shown
therein,
in some methods that embody teachings of the present invention, a green cone
structure
88A may be provided by machining a greet billet. The green cone structure 88A
may
include a plurality of tooth base structures 105A. A protruding feature 116
may be
provided on each of the tooth base structures 105A, and a green cap structure
112 may be
provided on each of the protruding features 116. The green cap structures 112
may be
formed from the same materials and in substantially the same manners
previously
described in relation to the green cutting inserts 24A (FIGS. 6A-6B). In some
embodiments, the green cap structures 112 may be secured to the protruding
features 116
using an adhesive. The tooth base structures 105A together with the green cap
structures
112 thereon define a plurality of green teeth structures 104A.
After assembling. green caps structures 112 on the tooth base structures 105A
to
form the green teeth structures 104A, the resulting structure may be sintered
to a desired
final density to form the fully sintered cutter assembly 80 as shown in FIGS.
7 and 8.
The material composition of the green cap structures 112 and the green cone
structure 88A may be separately and individually selected to exhibit physical
and/or
chemical properties tailored to the operating conditions to be experienced by
each of the
respective components. By way of example and not limitation, the composition
of the
green cap structures 112 may be selected so as to form, upon sintering the
green cap
structures 112, a particle-matrix composite material that exhibits a different
hardness,
wear resistance, and/or toughness different from that exhibited by the
particle-matrix
composite material of the cone 88 (FIGS. 7 and 8).
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FIG. 10 illustrates another embodiment of a method of the present invention
and
that may be used to form the cutter assembly 80 shown in FIGS. 7 and 8. The
method is
substantially similar to that previously described in relation to FIG. 9. A
green cone
structure 88B may be provided that is substantially similar to the green cone
structure 88A
shown in FIG. 9. The green cone structure 88B, however, may include a
plurality of tooth
base structures 105B, each of which has an aperture 118 therein. In this
configuration, a
green plug structure 114 may be provided within each of the apertures 118. The
green
plug structures 114 may be formed from the same materials and in substantially
the same
manners previously described in relation to the green cutting inserts 24A
(FIGS. 6A-6B)
and the green cap structures 112 (FIG. 9). In some embodiments, the green plug
structures 114 may be secured within the apertures 118 using an adhesive. The
tooth base
structures 105B together with the green plug structures 114 may define a
plurality of
green teeth structures 104B.
After assembling green plug structures 114 on the tooth base structures 105B
to
form the green teeth structures 104B, the resulting structure may be sintered
to a desired
final density to form the fully sintered cutter assembly 80 as shown in FIGS.
7 and 8.
As described above, the cutter assembly 80 shown in FIGS. 7 and 8 may be
formed by combining a green cone structure 88A, 88B with green cap structures
112
and/or green plug structures 114 to form a green cutter assembly, and
subsequently
sintering the green cutter assembly to a desired final density. The present
invention is not
so limited, however, and other embodiments of methods of the present invention
may
include assembling green structures, brown structures, fully sintered
structures, or any
combination thereof, and then sintering or reheating sintered components to
the sintering
temperature and causing the various components to fuse together to form a
unitary,
integral cutter assembly structure. By way of example and not limitation, the
green cone
structure 88A shown in FIG. 9 may be partially sintered to form a brown cone
structure
(not shown), and the green cap structures 112 may be assembled with the brown
cone
structure. The resulting structure then may be sintered to a final density to
fuse the cap
structures to the cone structure and form the teeth 104 (FIG. 7). As another
non-limiting
example, the green plug structures 114 shown in FIG. 10 may be partially
sintered to form
brown plug structures (not shown), and the brown plug structures may be
assembled with
the green cone structure 88B. The resulting structure then may be sintered to
a final
density to fuse the plug structures to the cone structure and form the teeth
104 (FIG. 7).
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While teachings of the present invention are described herein in relation to
embodiments of tri-cone rotary drill bits, other types of earth-boring
drilling tools such as,
for example hole openers, rotary drill bits, raise bores, fixed/rotary cutter
hybrid drill bits,
cylindrical cutters, mining cutters, and other such structures known in the
art may embody
the present invention and may be formed by methods that embody the present
invention.
Furthermore, while the present invention has been described herein with
respect to certain
preferred embodiments, those of ordinary skill in the art will recognize and
appreciate that
it is not so limited. Rather, many additions, deletions and modifications to
the described
and illustrated embodiments may be made without departing from the scope of
the
invention as hereinafter claimed. In addition, features from one embodiment
may be
combined with features of another embodiment while still being encompassed
within the
scope of the invention as contemplated by the inventors.
