Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-04-24
2002-12-31
Jenkins, Daniel J. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C419S005000, C419S006000, C419S018000, 72
Reexamination Certificate
active
06500226
ABSTRACT:
FIELD OF THE INVENTION
The present disclosure is directed to the manufacture of inserts, and more particularly directed to the fabrication of wear resistant cobalt alloy inserts using various sintering techniques including microwave radiation. Inserts are typically installed in drill bits for drilling an oil well.
BACKGROUND OF THE INVENTION
An oil well is drilled with a typical tricone drill bit and assembly with threads to the bottom of a string of drill pipe. It has a hollow threaded member with an axial flow passage within the assembly to direct drilling fluid, usually known as drilling mud, out through a number of openings to wash cuttings away from the cones which form the cutting. Rotation of the drill string and attached drill bit is from the surface of the earth. Teeth on the drill bit are rotated against the face and wall of the well borehole thereby cutting the earth formations as the drill bit rotates, thereby advancing the borehole. The drill bit has three cones mounted for contact against the face of the borehole. Each cone rotates its teeth with the rotation of the drill string, thereby cutting the borehole. Drill bit wear predominately occurs at the teeth. As the teeth wear, the penetration rate declines and the drill bit has to be replaced.
Cones and their teeth have a specified wear rate. Better performance has been obtained by enhancing the wear characteristics of the cone teeth, or “inserts”. Inserts are positioned within each cone hole. The inserts are harder than the metal cone. Most inserts are formed of various carbides, extremely hard materials. Primary contact and wear of the insert occurs at the exposed outer end of the insert. Greater protection yet has been provided from industrial grade diamonds. The optimum wear protection is obtained by the attachment of a cap or crown of industrial grade diamond which covers the exposed insert end. This type of crown is often known as a polycrystalline diamond compact (PDC). The carbide insert body is not pure WC, but is preferably granules of WC which are interspersed with an alloy which binds the WC particles. The preferred alloy is a cobalt based alloy. Likewise, the PDC crown is not a layer of pure diamond, but is an agglomeration of diamond particles held together with a binding metal matrix. Again, this binding material is typically a cobalt based alloy. The PDC cap or crown is normally attached to the WC insert body by ultra high pressure and heat. The sintering material may also contain a substantial amount of cobalt. Specific materials are notable. The insert body is usually WC which is harder than other common metal carbides. While other metal carbides will work in some degree, WC is the common and preferred material. In like fashion, the binding alloy is usually about 15% or so of cobalt in the alloy matrix holding the WC particles together. A common alloy with WC is sold as the model 374 by Roger's Tool Works and includes an alloy having as low as 6% up to about 15% cobalt with other metals of less significance. The cobalt is the most significant part of the alloy as will be discussed below.
In prior art, elements of the insert are typically manufactured separately and subsequently assembled. The manufacture of the components is usually by sintering under very high temperature and very high pressure. This requires equipment which is physically large, and which is also very expensive to manufacture, maintain and operate. In addition, the high temperature can induce adverse chemical and physical changes in insert components, which will be discussed in subsequent sections of this disclosure.
As discussed in U.S. Pat. No. 5,011,515, composite polycrystalline diamond compacts, PDC, have been used for industrial applications including rock drilling and metal machining for many years. As an example, the composite compact consisting of PDC and sintered substrate are affixed as insert elements in a rock drill bit structure. One of the factors limiting the success of PDC is the strength of the bond between the polycrystalline diamond layer and a sintered metal carbide substrate. It is taught that both the PDC and the supporting sintered metal support substrate must be exposed to high pressure and high temperature, for a relatively long period of time, in order to achieve the desired hardness of the PDC surface and the desired strength in the bond between the PDC and the support substrate.
U.S. Pat. No. 3,745,623 (reissue U.S. Pat. No. 32,380) teaches the attachment of diamond to tungsten carbide (WC) support material with an abrupt transition there between. This, however, results in a cutting tool with a relatively low impact resistance. Due to the differences in the thermal expansion of diamond in the PDC layer and the binder metal alloy used to cement the metal carbide substrate, there exists a shear stress in excess of 200,000 psi between these two layers. The force exerted by this stress must be overcome by the extremely thin layer of cobalt which is the common or preferred binding medium that holds the PDC layer to the metal carbide substrate. Because of the very high stress between the two layers which have a flat and relatively narrow transition zone, it is relatively easy for the compact to delaminate in this area upon impact. Additionally, it has been known that delamination can also occur on heating or other disturbances in addition to impact. In fact, parts have delaminated without any known provocation, most probably as a result of a defect within the interface or body of the PDC which initiates a crack and results in catastrophic failure. See also U.S. Pat. No. 4,811,801.
One solution to the PDC-substrate binding problem is proposed in the teaching of U.S. Pat. No. 4,604,106. This patent utilizes one or more transitional layers incorporating powdered mixtures with various percentages of diamond, tungsten carbide, and cobalt to distribute the stress caused by the difference in thermal expansion over a larger area. A problem with this solution is that “sweep-through” of the metallic catalyst sintering agent is impeded by the free cobalt and the cobalt cemented carbide in the mixture. In addition, as in previous referenced methods and apparatus, high temperatures and high pressures are required for a relatively long time period in order to obtain the assembly disclosed in U.S. Pat. No, 4,604,106. Pressures and temperatures are such that, using mixtures specified, the adjacent diamond crystals are bonded together.
U.S. Pat. No. 4,784,023 teaches the grooving of polycrystalline diamond substrates but it does not teach the use of patterned substrates designed to uniformly reduce the stress between the polycrystalline diamond layer and the substrate support layer. In fact, this patent specifically mentions the use of undercut (or dovetail) portions of substrate ridges, which solution actually contributes to increased localized stress. Instead of reducing the stress between the polycrystalline diamond layer and the metallic substrate, this actually makes the situation much worse. This is because the larger volume of metal at the top of the ridge will expand and contract during temperature cycles to a greater extent than the polycrystalline diamond, causing the composite to fracture at the interface. As a result, construction of a polycrystalline diamond cutter following the teachings provided by U.S. Pat. No. 4,784,023 is not suitable for cutting applications where repeated high impact forces are encountered, such as in percussive drilling, nor in applications where extreme thermal shock is a consideration.
By design, all of the cutting surfaces consisting of “conventional” alloys which are disclosed in the above references are “hard” in that they are abrasion and erosion resistant. This is particularly true for PDC material which is also quite brittle and subject to fracturing upon impact. Because of the brittleness and overall hardness, it is not practical and economical to machine surfaces of tools, bearings and the like made of PDC in the manufacturing process for these devices. Alternately, th
Dennis Tool Company
Hubbard Marc A.
Jenkins Daniel J.
Munsch Hardt Kopf & Harr P.C.
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