Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-10-25
2001-03-06
Lillis, Eileen D. (Department: 3673)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S426000, C175S430000, C451S540000, C451S541000, C051S293000
Reexamination Certificate
active
06196341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to superabrasive cutting elements used in drill bits to perform earth boring, and specifically relates to superabrasive cutting elements which are structured to reduce residual tensile stresses proximate the cutting edge perimeter of the cutting element.
2. Description of Related Art
Superabrasive cutting elements are manufactured for placement in drill bits which are used for drilling or boring earth formations. The majority of superabrasive cutting elements comprise a portion of superabrasive material which is positioned to contact the earth formation for cutting, and a substrate member to support the superabrasive portion and provide structure for attachment of the cutting element to the drill bit. The superabrasive portion is typically a “table” comprised of a polycrystalline diamond compact (PDC) or other suitable material, such as cubic boron nitride, and the substrate is often formed from a material, such as cemented tungsten carbide, or other suitable material compatible with the superabrasive portion.
The configuration of cutting elements varies widely and the patent literature is replete with examples of various cutting element designs. The variety in configurations of cutting elements is principally directed by a desire or need to form a structurally stronger, tougher and more wear-resistance and fracture-resistant element. It is well-known, for example, that superabrasive cutting elements can fail or may have limited service life due to stress fractures, which manifest themselves in fracture, spalling and micro-chipping of the superabrasive table. Drilling in hard rock or shale formations, or formations with hard rock stringers, is especially damaging. It is known that the tendency toward such stress fractures or failures is caused by the fact that the materials comprising the superabrasive portion, or diamond table, and the substrate have different coefficients of thermal expansion, elastic moduli and bulk compressibilities. After formation of cutting elements by the known high temperature and high pressure techniques, the table and substrate materials subsequently shrink at different rates during cooling, resulting in internal residual stresses in the superabrasive table, notably in the vicinity of the interface between the table and substrate. Consequently, the diamond table material tends to be in residually stressed compression while the substrate material tends to be in residually stressed tension prior to being subjected to cutting loads experienced during drilling operations. Fracturing of the cutting element may result at the cutting edge, whether on the table, at the perimeter of the cutting edge or near the interface between the diamond table and the substrate. Further, such residual stresses in the cutting element may provoke delamination of the table from the substrate or delamination in the table itself under the extreme temperatures and pressures of drilling.
Various solutions have been suggested in the art for modifying the internal residual stresses in cutting elements to avoid or limit the described failures. Hence, the configuration of the cutting element may be designed to address the residual stress problem. Cooperative table and substrate configurations which purport to address the issue of cutting element failure are disclosed, for example, in U.S. Pat. No. 5,007,207 to Phaal; U.S. Pat. No. 5,120,327 to Dennis; U.S. Pat. No. 5,355,969 to Hardy, et al.; U.S. Pat. No. 5,494,477 to Flood, et al.; U.S. Pat. No. 5,566,779 to Dennis; U.S. Pat. No. 5,605,199 to Newton; EP 0322214 issued to De Beers Industrial Diamond; EP 0214795 issued to De Beers Industrial Diamond and EP 0687797 issued to Camco Drilling Group.
The cutting element configurations disclosed in the prior art have demonstrated varying degrees of success in modifying the stress states in the cutting element. It would be advantageous, however, to provide a cutting element configuration which further improves upon the reduction of residual tensile stresses in the superabrasive layer of the cutting element, particularly on the cutting face and in the area near the perimeter of the cutting edge.
SUMMARY OF THE INVENTION
In accordance with the present invention, the substrate of a superabrasive cutting element is specifically structured with a reduced dimension circumferential portion adjacent the table/substrate interface about which is located an annular ring or skirt of superabrasive material to substantially reduce tensile stresses in the superabrasive portion of the cutting element near the perimeter of the cutting edge and on the cutting face. The substrate of the superabrasive cutting element may also be structured to provide interior annular grooves filled with superabrasive material, thereby further modifying the tensile stresses in the superabrasive table. Because the coefficient of thermal expansion (COTE) of the substrate material is typically higher than the coefficient of thermal expansion of the superabrasive material and, in combination, the different COTE values are responsible for a significant portion of the residual tensile stresses in conventional cutting elements, the reduced dimension circumferential portion of the substrate adjacent the interface beneficially modifies the residual tensile stresses which occur in the superabrasive portion. The proposed mechanism for the reduction of tensile stress in the present invention is twofold: 1) the reduced volume of substrate which has less ability to pull the diamond or superabrasive table, and 2) the relative locations of the outside superabrasive ring and inner carbide material. Additionally, the portion of superabrasive material positioned about the perimeter of the cutting element enhances the modification of residual stresses in the superabrasive portion near the perimeter of the cutting edge. The configuration of the cutting element of the present invention facilitates reduced residual tensile stresses in the superabrasive member near the perimeter of the cutting element and on its cutting face, thereby increasing the ability of the cutting element to withstand higher loading conditions compared to other known configurations.
In a first embodiment of the invention, the substrate is formed with a reduced dimension circumferential portion which provides a substantially cylindrical profile in the substrate about which an annular portion of superabrasive material is formed. The annular portion of superabrasive material is part of the superabrasive table of the cutting element and extends downwardly from an upper superabrasive layer which contacts the top surface of the substrate. The upper superabrasive layer and annular portion are preferably formed from the same type and grade of superabrasive material, but may comprise different types and grades of material. Finite element analyses show that the distance to which the annular portion is selected to extend downwardly from the upper superabrasive layer of the superabrasive portion or, in other words, the height of the reduced dimension circumferential portion, determines the amount to which the residual stresses near the perimeter of the superabrasive portion are reduced. Generally, reduction of residual tensile stresses is greatest in the particular instance of a configuration of this embodiment, given the thickness of the superabrasive table and superabrasive ring, when the annular portion extends below the upper superabrasive layer a distance of between about 0.030 inches (about 0.08 cm) and about 0.060 inches (about 0.15). The distance to which the annular portion extends below the upper superabrasive layer will generally increase as the height or depth of the cutting element increases in order to optimize reductions in tensile stress at the perimeter.
In additional embodiments of the cutting element described heretofore, one or more annular grooves may be formed in the top surface of the substrate within the bounds of, and in proximity to, the outer edge of the reduced dimension circum
Baker Hughes Incorporated
Britt Trask
Lee Jong-Suk
Lillis Eileen D.
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