US20080202814A1 - Earth-boring tools and cutter assemblies having a cutting element co-sintered with a cone structure, methods of using the same - Google Patents

Abstract

Methods of forming cutter assemblies for use on earth-boring tools include sintering a cone structure to fuse one or more cutting elements thereto. In some embodiments, one or more green, brown, or fully sintered cutting elements may be positioned on a green or brown cone structure prior to sintering the cone structure to a final density. Cutter assemblies may be formed by such methods, and such cutter assemblies may be used in earth-boring tools such as, for example, earth-boring rotary drill bits and hole openers.

Description

FIELD OF THE INVENTION
• 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 OF THE INVENTION
• 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 cutting 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 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 maybe 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.
• 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. Pat. No. 6,766,870, the entire disclosure of which is incorporated herein in its entirety by this reference, 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.
BRIEF SUMMARY 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.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• While 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 conjuction with the accompanying drawings in which:
• FIG. 1 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 inFIG. 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;
• FIG. 4 is a schematic view illustrating another method that may be used to form 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 inFIG. 2;
• FIGS. 6A-6C illustrate another embodiment of a method that may be used to form a rotatable cutter assembly that embodies teachings of the present invention, such as the rotatable cutter assembly shown inFIG. 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 inFIG. 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 inFIG. 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 inFIG. 8.
DETAILED DESCRIPTION OF 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.
• 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 term “[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 U.S. patent application Ser. No. 11/271,153, filed Nov. 10, 2005 and pending U.S. patent application Ser. No. 11/272,439, also filed Nov. 10, 2005, the disclosure of each of which application is incorporated herein in its entirety by this reference. 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 U.S. patent application Ser. No. 11/487,890, filed Jul. 17, 2006, the disclosure of which is incorporated herein in its entirety by this reference.
• An earth-boringdrill bit10 according to an embodiment of the present invention is shown inFIG. 1. The earth-boringdrill bit10 includes abit body12 and a plurality ofrotatable cutter assemblies14. Thebit body12 may include a plurality of integrally formedbit legs16, andthreads18 may be formed on the upper end of thebit body12 for connection to a drill string. Thebit body12 may havenozzles20 for discharging drilling fluid into a borehole, which may be returned along with cuttings up to the surface during a drilling operation. Each of therotatable cutter assemblies14 include acone22 comprising a particle-matrix composite material and a plurality of cutting elements, such as the cutting inserts24 shown. Eachcone22 may include aconical gage surface26. Additionally, eachcone22 may have a unique configuration of cutting inserts24 or cutting elements, such that thecones22 may rotate in close proximity to one another without mechanical interference.
• FIG. 2 is a cross-sectional view illustrating one of therotatable cutter assemblies14 of the earth-boringdrill bit10 shown inFIG. 1. As shown, eachbit leg16 may include abearing pin28. Thecone22 may be supported by the bearingpin28, and thecone22 may be rotatable about the bearingpin28. Eachcone22 may have acentral cavity30 that may be cylindrical and may form a journal bearing surface adjacent thebearing pin28. Thecavity30 may have aflat thrust shoulder32 for absorbing thrust imposed by the drill string on thecone22. As illustrated in this example, thecone22 may be retained on thebearing pin28 by a plurality of lockingballs34 located in mating grooves formed in the surfaces of thecone cavity30 and thebearing pin28. Additionally, aseal assembly36 may seal the bearing spaces between thecone cavity30 and thebearing pin28. Theseal assembly36 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 thecavity30 and thebearing pin28 bylubricant passages38. Thelubricant passages38 may lead to a reservoir that includes a pressure compensator40 (FIG. 1).
• As previously mentioned, thecone22 may comprise a sintered particle-matrix composite material that comprises a plurality of hard particles dispersed through a matrix material. In some embodiments, thecone22 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 (WC, W₂C), titanium carbide (TiC), tantalum carbide (TaC), titanium diboride (TiB₂), chromium carbides, titanium nitride (TiN), vanadium carbide (VC), aluminum oxide (Al₂O₃), aluminum nitride (AlN), boron nitride (BN), and silicon carbide (SiC). Furthermore, 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 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 38 microns. The matrix material may include a metal alloy comprising about 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, thecone22 may exhibit a hardness in a range extending from about 75 to about 92 on the Rockwell A hardness scale.
• FIGS. 3,4, and5A-5C illustrate embodiments of a method that may be used to form thecone22 and thecutter assembly14 shown inFIG. 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 apowder mixture42 to form a green billet that may be used to form thecone22. As illustrated inFIG. 3, thepowder mixture42 may be pressed with substantially isostatic pressure within a mold orcontainer44. Thepowder mixture42 may include a plurality of the previously described hard particles and a plurality of particles comprising a matrix material, as also previously described herein. Optionally, thepowder mixture42 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 more pliable, and lubricants or compaction aids for reducing inter-particle friction and otherwise providing lubrication during pressing.
• Thecontainer44 may include a fluid-tight deformable member46. For example, thedeformable member46 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. Thecontainer44 may further include a sealingplate48, which may be substantially rigid. Thedeformable member46 may be filled with apowder mixture42 and optionally vibrated to provide a uniform distribution of thepowder mixture42 within thedeformable member46. The sealingplate48 may be attached or bonded to the deformable member46, which may provide a fluid-tight seal therebetween.
• Thecontainer44, with thepowder mixture42 therein, may be placed within apressure chamber50. Aremovable cover52 may be used to provide access to the interior of thepressure chamber50. 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 thepressure chamber50 through aport54 at high pressures using a pump (not shown). The high pressure of the fluid may cause themember46 to deform, and the fluid pressure may be transmitted substantially uniformly to thepowder mixture42. The pressure within thepressure chamber50 during isostatic pressing may be greater than about 35 megapascals (about 5,000 pounds per square inch). More particularly, the pressure within thepressure chamber50 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 theflexible container44 and a pressure greater than about 0.1 megapascals (about 15 pounds per square inch) may be applied to thedeformable member46 of the container44 (by, for example, the atmosphere) and may compact thepowder mixture42. Isostatic pressing of thepowder mixture42 may form a green billet, which may be removed from thepressure chamber50 and thecontainer44 after pressing for machining. In some embodiments, the resulting billet may have a generally cylindrical configuration.
• FIG. 4 illustrates an additional method of pressing apowder mixture56 to form a green billet that may be used to form thecone22 shown inFIG. 2. The method illustrated inFIG. 4 comprises forming a billet using arigid die58 having a cavity for receiving thepowder mixture56. Thepowder mixture56 may be the same as thepowder mixture42 used in the method illustrated inFIG. 3. The cavity of the die58 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 ram60 may sealingly engage the walls of thedie58. A force may act on thepiston60 and may press thepowder mixture56 into a green billet with a coherent shape suitable for machining.
• The green billet, whether formed by the method illustrated inFIG. 3 orFIG. 4, may be machined in the green state to form agreen cone structure22A shown inFIG. 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 thegreen cone structure22A, 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 agreen cone structure22A that may be used to form the cutter assembly14 (FIGS. 1-2). As illustrated inFIG. 5A, in some embodiments, thegreen cone structure22A may have an overall shape corresponding to the desired final shape of thecone22, and may include various features such as acentral cavity30 for providing a journal bearing surface adjacent a bearing pin28 (FIG. 2) andapertures62 for receiving cutting inserts24 therein (FIG. 2).
• Optionally,displacement members64 may be inserted into theapertures62 for preserving a desired size, shape and orientation of each of theapertures62 during a subsequent sintering process. Thedisplacement members64 may comprise dowels that are dimensioned to the desired final dimensions of theaperture62 in thecone22 to be formed for eachinsert24. Thedisplacement members64 may be formed of a material, such as a ceramic, that will remain solid and stable at the sintering temperature. Additionally, thedisplacement members64 may be formed of a porous and/or hollow material to facilitate their removal from the resulting fully sinteredcone22 after the sintering process. Theapertures62 may be larger in diameter than thedisplacement members64 before sintering, and may shrink during sintering to the diameters of thedisplacement members64.
• In some embodiments, thegreen cone structure22A shown inFIG. 5A may be heated and sintered in a furnace to a desired final density to form a fully sinteredcone22 shown inFIG. 5B. The fully sinteredcone22 is shown inFIG. 5B after the displacement members64 (FIG. 5A) have been removed from the fully sinteredcone22.
• In some embodiments, the furnace 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 furnace 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 acone22 comprising a sintered tungsten carbide material. To form such a cone, agreen cone structure22A 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, thegreen cone structure22A 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, thegreen cone structure22A may undergo shrinkage and densification as it is sintered to a final density to form thecone22. After sintering, thecone22 may have the desired exterior configuration, which may include the apertures.62, and thecentral cavity30. Limited or no further machining may be necessary for these surfaces. Thecavity30, or other surfaces, may be machined after sintering. For example, the bore surfaces of thecavity30 may be ground and polished to achieve a desired surface finish.
• As shown inFIG. 5C, after thecone22 has been formed and theoptional displacement members64 removed, cutting inserts24 may be secured within theapertures62. The cutting inserts24 may have a size and shape selected to provide a tight and secure press-fit between the cutting inserts24 and theapertures62. In additional embodiments, the cutting inserts24 may be bonded within theapertures62 using an adhesive. In yet other embodiments, the cutting inserts24 may be secured within theapertures62 using a soldering or brazing technique.
• Thecentral cavity30 may be finish machined and thecone22 may be mounted to thebearing pin28 in a conventional manner (FIG. 2). The cutting inserts24 may be formed separately from thecone22 in a manner similar to that in which thecone22 is formed. Although the cutting inserts24 may also be formed of a sintered particle-matrix composite material, the composition of the particle-matrix composite material of the cutting inserts24 may differ from the composition of the particle-matrix composite material of thecone22.
• In additional methods, rather than forming 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 sinteredcone22 shown inFIG. 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 filly sintered billet.
• FIGS. 6A-6C illustrate an additional embodiment of a method that may be used to form a cutter assembly (such as thecutter assembly14 shown inFIG. 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 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 toFIG. 6A, agreen cone structure22A may be formed or otherwise provided as previously described in relation toFIG. 5A. A plurality of green cutting inserts24A may be provided. Each of the green cutting inserts24A 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 inserts24A may differ from the composition of thegreen cone structure22A. Furthermore, the green cutting inserts24A 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 inserts24A also may be secured to thegreen cone structure22A prior to sintering. By way of example and not limitation, one or moregreen bearing structures68A that are to define bearing surfaces of the cone may secured within thecentral cavity30 of thegreen cone structure22A. Similar to the green cutting inserts24A, each of thegreen bearing structures68A may comprise a plurality of hard particles and a plurality of particles comprising a matrix material, and the composition of thegreen bearing structures68A may differ from the composition of thegreen cone structure22A.
• As illustrated inFIG. 6B, the green cutting inserts24A may be provided within theapertures62 of thegreen cone structure22A, and thegreen bearing structures68A may be secured at a selected location within thecentral cavity30 of thegreen cone structure22A.
• By way of example and not limitation, the green cutting inserts24A and theapertures62 within thegreen cone structure22A may be sized and shaped so as to provide an average clearance therebetween of between about one-thousandth of an inch (0.001 in.) and about twenty-five thousandths of an inch (0.025 in.). Such clearances also may be provided between thegreen bearing structures68 and thegreen cone structure22A.
• After assembling the various green components to form a structure similar to that shown inFIG. 6B, the structure may be sintered to a desired final density to form the fully sintered structure shown inFIG. 6C. During the sintering process thecone22, including theapertures62 or other features, the cutting inserts24 or other cutting elements, and the bearingstructures68 may undergo shrinkage and densification. Furthermore, the cutting inserts24 and the bearingstructures68 may become fused and secured to thecone22. In other words, after the sintering process, cuttinginserts24 and bearingstructures68 may be co-sintered and integral with thecone22 to provide a substantiallyunitary cutter assembly14′.
• After thecutter assembly14′ has been sintered to a desired final density, various features of thecutter assembly14′ may be machined and polished, as necessary or desired. For example, bearing surfaces on the bearingstructures68 may be polished. Polishing the bearing surfaces of the bearingstructures68 may provide a relatively smoother surface finish and may reduce friction at the interface between the bearingstructures68 and the bearing pin28 (FIG. 2). Furthermore, the sealingedge72 of the bearingstructures68 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 body12 (FIG. 2).
• The green cutting inserts24A and thegreen bearing structures68A may be formed from particle-matrix composite materials in much the same way as thegreen cone structure22A. The material composition of each of the green cutting inserts24A,green bearing structures68A, andgreen cone structure22A 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 inserts24A may be selected so as to form cutting inserts24 comprising 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 thecone22.
• The cutting inserts24 may be formed from a variety of particle-matrix composite material compositions. The particular composition of anyparticular insert24 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 bit10 (FIG. 1). Additionally, cutting inserts24 having different material compositions may be used on asingle cone22.
• By way of example and not limitation, in some embodiments of the present invention, the cutting inserts24 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 thecone22. As another non-limiting example, the concentration of the hard particles in the particle-matrix composite material of the cutting inserts24 may be greater than a concentration of hard particles in a particle-matrix composite material of thecone22.
• Although thecutter assembly14′ shown inFIG. 6C is illustrated as comprising thecone22, the cutting inserts24, and the bearingstructures68, it is contemplated that in additional embodiments, thecutter assembly14′ may not be formed with separategreen bearing structures68A, as described herein. Furthermore, as described above, thecutter assembly14′ may be formed by combining agreen cone structure22A, green cutting inserts24A, andgreen bearing structures68A 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 form a unitary, integral cutter assembly structure.
• While thecutter assembly14′ previously described herein has acone22 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-boringdrill bit74 according to an embodiment of the present invention which comprises a plurality ofcutter assemblies80 each having acone88 that includes cuttingteeth104.
• As shown inFIG. 7, the earth-boringdrill bit74 has abody76 that may havethreads78 formed on its upper end for connection to a drill string. Thebit body76 may have three integrally formedbit legs82, each supporting a bearing pin84 (Not shown). In some embodiments, thebit body76 and the bearing pins84 may be formed of a steel alloy in a conventional manner. Additionally, thebit body76 may havenozzles86 for discharging drilling fluid into the borehole, which may be returned along with cuttings up to the surface during a drilling operation.
• As shown inFIG. 7, eachcone88 may have a plurality of rows of cuttingteeth104. Theteeth104 may vary in number, have a variety of shapes, and the number of rows may vary. Aconical gage surface106 may surround theback face102 of eachcone88 and define the outer diameter of thebit74. As discussed in further detail below, one portion of eachtooth104 may be integrally formed with the body of eachcone88, and another portion of eachtooth104 may be formed using a separate green or brown structure that is fused to thecone88 during a sintering process.
• FIG. 8 is an enlarged partial cross-sectional view illustrating a portion of one of thecutter assemblies80 mounted on abearing pin84, and shows each of theteeth104 rotated about thecone88 into the plane of the figure so as to illustrate the so-called “cutting profile” defined by the cutting surfaces of all theteeth104 on thecone88. As shown inFIG. 8, each bearingpin84 of thedrill bit74 may support one of thecutter assemblies80. Eachcone88 of thecutter assemblies80 may have acentral cavity90 that provides a journal bearing surface adjacent thebearing pin84. Thecone88 may have aflat thrust shoulder92 and may have alock groove94 formed within thecentral cavity90. In such a configuration, asnap ring96 may be located in thelock groove94 and a mating groove may be formed on thebearing pin84 for locking thecone88 in position on thebearing pin84. Thecone88 also may have aseal groove98 for receiving aseal100. Theseal groove98 may be located adjacent aback face102 of thecone88. By way of example and not limitation, theseal100 may be an elastomeric ring. In some embodiments, theback face102 of thecone88 may comprise a substantially flat annular surface surrounding the entrance to thecentral cavity90.
• Lubricant may be supplied to the spaces between thecentral cavity90 of thecone88 and thebearing pin84 bylubricant passages108. Thelubricant passages108 may lead to a reservoir that includes a pressure compensator110 (FIG. 7).
• Thecone88 may comprise a particle-matrix composite material as previously described in relation to thecone22 shown inFIG. 2. Similarly, thecone88 may be formed using methods substantially similar to those previously described in relation to thecone22 with reference toFIGS. 3 and 4. In general, thecone88 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 thecutter assembly80 shown inFIGS. 7 and 8. As shown therein, in some methods that embody teachings of the present invention, agreen cone structure88A may be provided by machining a greet billet. Thegreen cone structure88A may include a plurality oftooth base structures105A. Aprotruding feature116 may be provided on each of the tooth base structures I05A, and agreen cap structure112 may be provided on each of the protruding features116. Thegreen cap structures112 may be formed from the same materials and in substantially the same manners previously described in relation to the green cutting inserts24A (FIGS. 6A-6B). In some embodiments, thegreen cap structures112 may be secured to the protruding features116 using an adhesive. Thetooth base structures105A together with thegreen cap structures112 thereon define a plurality ofgreen teeth structures104A.
• After assemblinggreen caps structures112 on thetooth base structures105A to form thegreen teeth structures104A, the resulting structure may be sintered to a desired final density to form the fully sinteredcutter assembly80 as shown inFIGS. 7 and 8.
• The material composition of thegreen cap structures112 and thegreen cone structure88A 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 thegreen cap structures112 may be selected so as to form, upon sintering thegreen cap structures112, 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 cone88 (FIGS. 7 and 8).
• FIG. 10 illustrates another embodiment of a method of the present invention and that may be used to form thecutter assembly80 shown inFIGS. 7 and 8. The method is substantially similar to that previously described in relation toFIG. 9. Agreen cone structure88B may be provided that is substantially similar to thegreen cone structure88A shown inFIG. 9. Thegreen cone structure88B, however, may include a plurality of tooth base structures105B, each of which has anaperture118 therein. In this configuration, agreen plug structure114 may be provided within each of theapertures118. Thegreen plug structures114 may be formed from the same materials and in substantially the same manners previously described in relation to the green cutting inserts24A (FIGS. 6A-6B) and the green cap structures112 (FIG. 9). In some embodiments, thegreen plug structures114 may be secured within theapertures118 using an adhesive. The tooth base structures105B together with thegreen plug structures114 may define a plurality ofgreen teeth structures104B.
• After assemblinggreen plug structures114 on the tooth base structures105B to form thegreen teeth structures104B, the resulting structure may be sintered to a desired final density to form the fully sinteredcutter assembly80 as shown inFIGS. 7 and 8.
• As described above, thecutter assembly80 shown inFIGS. 7 and 8 may be formed by combining agreen cone structure88A,88B withgreen cap structures112 and/orgreen plug structures114 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, thegreen cone structure88A shown inFIG. 9 may be partially sintered to form a brown cone structure (not shown), and thegreen cap structures112 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 teeth104 (FIG. 7). As another non-limiting example, thegreen plug structures114 shown inFIG. 10 may be partially sintered to form brown plug structures (not shown), and the brown plug structures may be assembled with thegreen cone structure88B. The resulting structure then may be sintered to a final density to fuse the plug structures to the cone structure and form the teeth104 (FIG. 7).
• 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.

Claims (38)

1. A method of forming a cutter assembly for use on an earth-boring tool, the method comprising:

providing a less than fully sintered cone structure comprising hard particles and a matrix material;

positioning at least one cutting element on the less than fully sintered cone structure; and

sintering the cone structure to a final density to fuse the at least one cutting element to the cone structure.

2. The method ofclaim 1, wherein providing a less than fully sintered cone structure comprises providing a green cone structure.

3. The method ofclaim 2, wherein providing a green cone structure comprises:

mixing the hard particles with particles comprising the matrix material to form a powder mixture; and

pressing the powder mixture to form the green cone structure.

4. The method ofclaim 3, further comprising:

selecting the hard particles from the group consisting of diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si; and

selecting the matrix material from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

5. The method ofclaim 2, further comprising machining at least one aperture in the green cone structure, and wherein positioning at least one cutting element on the less than fully sintered cone structure comprises inserting the at least one cutting element into the at least one aperture of the green cone structure.

6. The method ofclaim 5, further comprising providing an average clearance of between about 0.001 inch and about 0.025 inch between exterior surfaces of the at least one cutting element and the surfaces of the green cone structure within the at least one aperture.

7. The method ofclaim 2, further comprising machining at least one protrusion on the green cone structure, and wherein positioning at least one cutting element on the less than fully sintered cone structure comprises placing the at least one cutting element onto the at least one protrusion of the green cone structure.

8. The method ofclaim 2, wherein positioning at least one cutting element on the less than fully sintered cone structure comprises positioning at least one green cutting element on the green cone structure, and wherein sintering the cone structure comprises sintering the green cone structure with the green cutting element thereon to a final density.

9. The method ofclaim 2, wherein positioning at least one cutting element on the less than fully sintered cone structure comprises positioning at least one brown cutting element on the green cone structure, and wherein sintering the cone structure comprises sintering the green cone structure with the brown cutting element thereon to a final density.

10. The method ofclaim 1, wherein providing a less than fully sintered cone structure comprises providing a brown cone structure.

11. The method ofclaim 10, wherein providing a brown cone structure comprises:

mixing the hard particles with particles comprising the matrix material to form a powder mixture;

pressing the powder mixture to form a green cone structure; and

partially sintering the green cone structure to form the brown cone structure.

12. The method ofclaim 11, further comprising:

selecting the hard particles from the group consisting of diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si; and

selecting the matrix material from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

13. The method ofclaim 10, further comprising machining at least one aperture in the brown cone structure, and wherein positioning at least one cutting element on the less than fully sintered cone structure comprises inserting the at least one cutting element into the at least one aperture of the brown cone structure.

14. The method ofclaim 10, further comprising machining at least one protrusion on the brown cone structure, and wherein positioning at least one cutting element on the less than fully sintered cone structure comprises placing the at least one cutting element onto the at least one protrusion of the brown cone structure.

15. The method ofclaim 10, wherein positioning at least one cutting element on the less than fully sintered cone structure comprises positioning at least one green cutting element on the brown cone structure, and wherein sintering the cone structure comprises sintering the brown cone structure with the green cutting element thereon to a final density.

16. The method ofclaim 10, wherein positioning at least one cutting element on the less than fully sintered cone structure comprises positioning at least one brown cutting element on the brown cone structure, and wherein sintering the cone structure comprises sintering the brown cone structure with the brown cutting element thereon to a final density.

17. The method ofclaim 1, wherein positioning at least one cutting element on the less than fully sintered cone structure comprises positioning at least one cutting element comprising hard particles and a matrix material on the less than fully sintered cone structure.

18. The method ofclaim 17, further comprising:

selecting the hard particles of the at least one cutting element from the group consisting of diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si; and

selecting the matrix material of the at least one cutting element from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

19. The method ofclaim 1, wherein positioning at least one cutting element on the less than fully sintered cone structure further comprises causing the at least one cutting element to have a varying material composition between a first region proximate an interface between the at least one cutting element and the less than fully sintered cone and a second region proximate a formation-engaging surface of the at least one cutting element.

20. The method ofclaim 19, wherein causing the at least one cutting element to have a varying material composition comprises:

causing the first region to have a first material composition selected to enhance bonding between the at least one cutting element and the less than fully sintered cone; and

causing the second region to have a second material composition selected to enhance at least one material property of the at least one cutting element.

21. The method ofclaim 1, further comprising:

positioning at least one bearing structure on the less than fully sintered cone structure; and

fusing the bearing structure to the less than fully sintered cone structure while sintering the cone structure to a final density.

22. The method ofclaim 1, further comprising mounting the cone structure on a bearing pin of an earth-boring tool.

23. An earth-boring tool comprising:

a bearing pin; and

a cutter assembly rotatably mounted on the bearing pin, the cutter assembly comprising:

a cone comprising a particle-matrix composite material having a first material composition; and

at least one cutting element co-sintered and integral with the cone, the at least one cutting element comprising a particle-matrix composite material having a second material composition differing from the first material composition.

24. The earth-boring tool ofclaim 23, wherein the particle-matrix composite material of the cone comprises a plurality of hard particles dispersed throughout a matrix material, the hard particles comprising a material selected from diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si, the matrix material selected from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

25. The earth-boring tool ofclaim 24, wherein the particle-matrix composite material of the co-sintered cutting element comprises a plurality of hard particles dispersed throughout a matrix material, the hard particles comprising a material selected from diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si, the matrix material selected from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

26. The earth-boring tool ofclaim 23, further comprising at least one bearing structure co-sintered and integral with the cone.

27. The earth-boring tool ofclaim 23, wherein the at least one bearing structure comprises a particle-matrix composite material.

28. The earth-boring tool ofclaim 23, wherein the at least one cutting element comprises a cutting insert.

29. The earth-boring tool ofclaim 23, wherein the at least one cutting element comprises at least a portion of a cutting tooth structure.

30. The earth-boring tool ofclaim 23, wherein the at least one cutting element has a varying material composition between a first region proximate an interface between the at least one cutting element and the cone and a second region proximate a formation-engaging surface of the at least one cutting element.

31. A cutter assembly for use on an earth-boring tool, the cutter assembly comprising at least one cutting element co-sintered and integral with a cone structure, the cone structure comprising a particle-matrix composite material having a first material composition, the at least one cutting element comprising a particle-matrix composite material having a second material composition differing from the first material composition.

32. The cutter assembly ofclaim 31, wherein the particle-matrix composite material of the cone structure comprises a plurality of hard particles dispersed throughout a matrix material, the hard particles comprising a material selected from diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W,. Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si, the matrix material selected from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

33. The cutter assembly ofclaim 32, wherein the particle-matrix composite material of the at least one cutting element comprises a plurality of hard particles dispersed throughout a matrix material, the hard particles comprising a material selected from diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si, the matrix material selected from the group consisting of cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys, and titanium-based alloys.

34. The cutter assembly ofclaim 31, further comprising at least one bearing structure co-sintered and integral with the cone structure.

35. The cutter assembly ofclaim 34, wherein the at least one bearing structure comprises a particle-matrix composite material.

36. The cutter assembly ofclaim 31, wherein the at least one cutting element comprises a cutting insert.

37. The cutter assembly ofclaim 31, wherein the at least one cutting element comprises at least a portion of a cutting tooth structure.

38. The cutter assembly ofclaim 31, wherein the second material composition of the at least one cutting element varies between a first region proximate an interface between the at least one cutting element and the cone structure and a second region proximate a formation-engaging surface of the at least one cutting element.

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