Patent Application
20090065260
1. Field of Invention
The present disclosure relates generally to earth-boring bits and particularly to improved head sections for such bits.
2. Description of Prior Art
The earliest rolling cutter earth-boring bits had teeth machined integrally from steel, conically shaped, earth disintegrating cutters. These bits, commonly known as “steel-tooth” or “mill-tooth” bits, are typically used for penetrating relatively soft geological formations of the earth. The strength and fracture-toughness of steel teeth permits the effective use of relatively long teeth, which enables the aggressive gouging and scraping action that is advantageous for rapid penetration of soft formations with low compressive strengths.
However, it is rare that geological formations consist entirely of soft material with low compressive strength. Often, there are streaks of hard, abrasive materials that a steel-tooth bit should penetrate economically without damage to the bit. Although steel teeth possess good strength, abrasion resistance is inadequate to permit continued rapid penetration of hard or abrasive streaks.
Consequently, it has been common in the art since at least the early 1930s to provide a layer of wear resistant metallurgical material called “hardfacing” over those portions of the teeth exposed to the severest wear. In addition to the teeth, other portions of the bit body are hardfaced, those include the gage surfaces of the rolling cutters and the shirttails of the bit legs. For the purposes of discussion herein, the term hardfacing refers to the material provided to the bit body. Hardfacing composition refers to the materials which make up the hardfacing. The hardfacing composition typically consists of extremely hard particles, such as sintered, cast or macrocrystalline tungsten carbide dispersed in a steel, cobalt or nickel alloy binder or matrix. The composition is typically packaged in a tube and applied by heating with a torch to weld hardfacing to the subject surface. Thus a surface having been hardfaced has a dispersion of hard particles in the matrix disposed thereon.
After hardfacing, the cone is preferably heat treated, which typically includes carburizing and quenching from a high temperature to harden the cone. The particles are much harder than the matrix but more brittle. After hardening, the matrix has a hardness value preferably in the range from 53 to 68 Rockwell C (RC). The mixture of hard particles with a softer but tougher steel matrix is a synergistic combination that produces a good hardfacing.
There have been a variety of different hardfacing materials and patterns, including special tooth configurations, to improve wear resistance or provide self sharpening. Generally, the hardfacing applied to the teeth of new bits is in a pre-application ratio range of 50 to 80 percent carbide particles, typically about 70 percent, in a metal matrix of iron, nickel, cobalt or their alloys. Typically the carbide particles are carbides of Groups IVB, VB, and VIB. The thickness of the hardfacing deposit on new bits is usually about 1/16 to ⅛ inch over the flanks, end portions and top of the crest of the tooth. Portions of the hardfacing may be somewhat thicker. The thicker portions are generally where the flanks intersect the crest. These thicker portions may be up to double that of other areas.
Commonly, a mixture of sintered, macrocrystalline, or cast tungsten carbides is captured within a mild steel tube. The steel tube containing the carbide mixture is then used as a welding rod to deposit hardfacing onto the desired surface, usually with a deoxidizer, or flux.
The present disclosure includes an earth boring bit comprising, a bit body, a cantilevered bearing shaft depending from the bit body, a cutter mounted for rotation on the bearing shaft, a plurality of cutting elements disposed on the cutter, and hardfacing affixed to the bit, wherein the hardfacing comprises a mixture of carbide materials, a matrix of iron, nickel, cobalt and alloys thereof, and an amount of fullerene. The fullerenes considered for use with the present invention include spheres made of carbon atoms (buckyballs), elliptical bodies made with carbon atoms, and tubes made of carbon atoms (carbon nanotubes). The fullerene materials can be doped or undoped. Moreover, the fullerene material may comprise compounds referred to as C60, C70, C80, to name but a few. The carbide materials considered include crushed cast tungsten carbide, crushed sintered tungsten carbide, spherical sintered tungsten carbide, spherical cast carbide, macrocrystalline tungsten carbide, and combinations thereof. The mixture may further comprise a carbon steel niobium alloy, boron, silicon, and mixtures thereof. Also included is a drilling system employing the earth boring bit.
The amount of fullerene material included with the mixture may range from up to about 0.05 percent by weight of mixture to about 15 percent by weight of the mixture. Other weight percents include up to about 0.1 percent by weight of the mixture, up to about 0.5 percent by weight of the mixture, up to about 1.0 percent by weight of the mixture, up to about 5 percent by weight of the mixture, and up to about 10 percent by weight of the mixture.
The scope of the disclosure herein also includes a method of hardfacing an earth boring bit comprising forming a hardfacing composition comprising a mixture of carbide materials, a matrix of iron, nickel, cobalt and alloys thereof, and an amount of carbon fullerene material and applying the hardfacing composition to a portion of the bit.
The method may further comprise forming a tube rod by filling a tube with the mixture. Rods may also be formed by sintering the material in a graphite form. Optionally, the rod may be formed by first extruding then sintering. The carbide materials include sintered tungsten carbide, crushed cast tungsten carbide, spherical cast carbide, macrocrystalline tungsten carbide, and combinations thereof. The amount of fullerene material has similar ranges and amounts as noted above.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
Referring to
Cones 21, 23, generally three (one of which is obscured from view in
One embodiment of a hardfacing composition in accordance with the present disclosure comprises a mixture of carbide materials combined with a metal matrix along with an amount of fullerene material. The fullerenes considered for use with the present invention include spheres made of carbon atoms (buckyballs), elliptical bodies made with carbon atoms, tubes made of carbon atoms (carbon nanotubes—including single and multi-walled tubes), Endohedral fullerenes, and combinations thereof. Fullerenes may be described as a collection of carbon atoms formed into a three dimensional cage like fused-ring polycyclic system. Moreover, the fullerene material may comprise compounds commonly referred to as C20, C40, C60, C70, C80, C84, C86, C90, C100, and C540 to name but a few. The fullerene materials can be doped or undoped. The doping materials may include, but are not limited to, scandium, yttrium lanthanides, barium, strontium, alkali metals such as potassium, and tetravalent metals such as, zirconium and hafnium.
The matrix material may comprise iron, nickel, cobalt and alloys thereof. The carbide materials considered for use with the present mixture include crushed cast tungsten carbide, crushed sintered tungsten carbide, spherical sintered tungsten carbide, spherical cast carbide, macrocrystalline tungsten carbide, and combinations thereof.
The amount of fullerene material may range from around 0.05% by weight of the mixture to in excess of about 15% by weight of the mixture. Specific amounts of fullerene making up the mixture include 0.075% by weight, 0.1% by weight, 0.5% by weight, 1.0% by weight, 5% by weight, 10% by weight, and 15% by weight. Additionally, any of the above referenced percentage values may make up either the minimum or the maximum of fullerene material in the mixture. Moreover, weight percent ranges of an amount of fullerene in the mixture are available using all possible combinations of the above referenced percentage values.
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It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.
