Fracture resistant domed insert

Abstract

A cutting element for earth-boring drill bits comprising a generally domed cutting surface comprising a superabrasive material, formed by a high-pressure high-temperature sintering method known in the art, integrally bonded to a cylindrical substrate having a truncated conical interfacial surface, consisting of a top surface and a circumferential shoulder joined by tapered sidewalls, and the base of the substrate being adapted for insertion into an earth-boring tool. The top surface of the substrate may form a circle, a square, or a polygon, and the sidewalls may be smooth or form one or more polygons.

Description

RELATED APPLICATIONS

[0001] None.

BACKGROUND OF THE INVENTION

[0002] This invention relates to cutting inserts for use in drilling subterranean formations such as oil, gas, and geothermal wells. More particularly, this invention relates to a cutting insert that is comprised of a tough, hard metal substrate featuring a truncated conical interfacial surface. The cutting insert has one or more layers of a superabrasive material are bonded under high-pressure and high-temperature to the interfacial surface in such a manner so as to form a generally domed cutting table. Inserts of the present invention demonstrate fracture toughness capable of withstanding the dynamic loads associated with drilling a variety of subterranean formations.

[0003] Cutting elements coated with superabrasive materials such as polycrystalline diamond or cubic boron nitride are used widely in the drilling industry for drilling deep oil, gas, and geothermal wells. Superabrasive cutting elements have been used on most styles of drill bits that are used for subterranean drilling. The roller cone bit is an example of a drill bit that has benefited from the presence of at least some superabrasive cutting elements primarily located in the gage and heel rows of the bit. A roller cone bit usually has two or three cones that are rotationally affixed to the bit body by means of sealed bearings. As the bit body is rotated under the load of the drill string, the individual cones rotate independently of each other. The cutting elements arrayed about the cone bodies inflict a compressive stress on the formation being drilled causing it to fail. The crushed rock is flushed away from the bit and carried to the surface by the circulating drilling fluid, or mud, and new rock is exposed to the cutting elements of the bit.

[0004] Because superabrasive materials have high compressive strengths, they are an ideal material for use in deep well drilling. However, such materials are susceptible to stress fractures that result in spalling, fracturing, and delamination of the superabrasive cutting table. Stress on the cutting table of the insert comes from both within the insert and from the formation being drilled. Stresses on the drill bit due to subterranean conditions are largely controlled by the driller, but because of the differences in rates of thermal expansion, elastic moduli, and bulk compressibilities between the superabrasive and the substrate to which it is bonded, enormous internal residual stresses are present along the interfacial surfaces of the cutting element. These stresses may lead to failure of the superabrasive coating despite the skill of the operator.

[0005] Studies have shown that by modifying the shape of the surface to which the superabrasive is bonded residual stresses may be reduced and fracture toughness thereby increased. This patent discloses a domed cutting insert having a modified interfacial surface that yields a superabrasive coating having sufficient fracture toughness to withstand the compressive stresses of subterranean drilling.

SUMMARY OF THE INVENTION

[0006] The cutting element substrate of the present invention is comprised of tough cemented metal carbides and has a cylindrical base adapted for insertion into an earth-boring tool such as a roller cone bits. The substrate of the cutting element of the present invention has a truncated conical interfacial surface opposite its base end. The truncated conical interfacial surface is integrally bonded to a superabrasive material such as polycrystalline diamond or cubic boron nitride at high pressure and high temperature. The actual shape of the truncated conical surface may be round, oval, or a predetermined polygonal shape. The tapered sides of the truncated conical surface may also comprise flats having a predetermined polygonal shape such as trapezoid or rectangle. Additionally, the tapered sides of the conical surface may comprise flutes. The truncated conical surface may even have surface protrusions or posts to further reinforce the superabrasive material to which it is bonded. Another variation includes a peripheral lip on the edge of the truncated conical surface, which also increases bonding strength. A circumferential shoulder is formed as the truncated conical surface begins tapering from the base of the cylindrical substrate. The use of a truncated conical interfacial surface underlying the superabrasive generally domed cutting table permits the use of a tough metal carbide substrate and decreases point pressure during drilling. Instead of high-pressure strains localized over a small area during drilling, the compressive and shear type stresses induced from drilling is spread out over the flat truncated conical surface thereby reducing overall strain on the cutting insert.

[0007] Superabrasive material used as a cutting surface is well known in prior art. The superabrasive material used in this invention consists of natural diamond, polycrystalline diamond, cubic boron nitrides, or any combinations thereof The generally domed shape of the superabrasive material that forms the cutting table of the insert behaves much like a continuous truss bridge with self-supporting arches and an interconnected rigid framework. The self-supporting truss like strength of the polycrystalline dome increases the overall fracture strength of the polycrystalline cutting surface. Working in concert with the generally domed cutting table, which may comprise polygonal surfaces, the truncated conical shape of the tough substrate reduces spalling, cracking, fracture, and delamination of the cutting surface during compressive drilling through a variety of subterranean formation, including those having periodic discontinuities such as hard rock stringers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a perspective view of a substrate depicting a truncated conical interfacial surface with a supporting circumferential shoulder.

[0009] FIG. 2 is an aerial view of the substrate in FIG. 1.

[0010] FIG. 3 is cross sectional side view of one half of the substrate as taken through line 1-1 of FIG. 2.

[0011] FIG. 4 is an external side view of a cutting insert of the present invention depicting a generally domed cutting table.

[0012] FIG. 5 is a cross sectional side view of one half of the cutting element in FIG. 4 as taken through line 1-1 of FIG. 2 and including the integrally bonded superabrasive cutting surface.

[0013] FIG. 6 is a perspective view of a substrate depicting a truncated conical interfacial surface with a supporting circumferential shoulder and tapered rectangular flats.

[0014] FIG. 7 is an aerial view of the substrate in FIG. 6.

[0015] FIG. 8 is a cross sectional side view of one half of the substrate including the integrally bonded superabrasive cutting surface as taken through line 2-2 of FIG. 7.

[0016] FIG. 9 is an aerial view of a substrate depicting a truncated conical interfacial surface with a square top surface, trapezoidal side flats, and a supporting circumferential shoulder.

[0017] FIG. 10 is an aerial view of a substrate depicting a truncated conical interfacial surface with an octagonal top surface, generally rectangular side flats, and a supporting circumferential shoulder.

[0018] FIG. 11 is frontal cross-section view of a cutting insert of the present invention depicting polygonal surfaces of the cutting table.

[0019] FIG. 12 is a side cross-section view of the cutting insert of FIG. 11 depicting polygonal surfaces of the cutting table.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Cutting elements associated with the present invention used in earth-boring tools typically consist of two main parts: a substrate made of fracture tough material and a cutting surface, or cutting table, composed of a superabrasive material such as polycrystalline diamond or cubic boron nitride. The present invention relates to the shape of the cutting element substrate and the shape of the cutting surface, and how those shapes combine to permit the use of a tough carbide substrate and to reduce point stress concentrations during compressive use. A detailed description and associated drawings are described below.

[0021] A substrate 12 composed of a fracture tough material is illustrated in FIG. 1, as an embodiment of the present invention. The substrate 12 may consist of any number of fracture tough materials such as tungsten carbide, nickel, cobalt, nickel or cobalt carbides, or any number of cemented carbide materials. The substrate 12 includes a generally cylindrical base 11 for insertion into an earth-boring tool, such as a drill bit. A truncated conical interfacial surface 14 is formed at the opposite end of the substrate for supporting a superabrasive cutting table. Truncated conical interfacial surface 14 includes tapered sides 24 and a truncated top surface 26. The present invention includes variations in the shape of the truncated top surface 26 and the tapered sides 24 which will be illustrated in later drawings. A supporting circumferential shoulder 22 is formed between the outer perimeter of the substrate 12 and the inner base perimeter of the tapered sides 24 of truncated conical interfacial surface 14. This circumferential shoulder 22 connects the truncated conical interfacial surface 14 with the cylindrical base 11. The circumferential shoulder 22 may join the tapered side 24 at an obtuse angle, or it may be formed substantially perpendicular to the tapered sides 24 and generally parallel to the truncated top surface 26. However, the shoulder formed does not need to be strictly perpendicular as will be noted in later drawings of the invention. The circumferential shoulder aids compaction of the superabrasive matrix during pre-sintering assembly and lends support to the superabrasive cutting surface during formation of the cutting element during the high pressure, high temperature process. The supporting circumferential shoulder 22 gives a sort of base layer upon which the superabrasive matrix can obtain its footing and buttress upward formation of the cutting surface. The truncated top surface 26 and tapered sides 24 are substantially flat and smooth. The perimeter of truncated top surface 26 may be defined by predetermined polygonal shapes, as illustrated in the drawings of this disclosure.

[0022] FIG. 2 is an aerial view of the substrate in FIG. 1. A circle 36 defines the truncated conical surface perimeter of truncated top surface 26. The tapered sides 24 slope upward and are cropped at a desired height forming truncated top surface 26. The circumferential shoulder 22 is formed from the substrate body 12 and is of sufficient width to support the superabrasive before and during the sintering process of the domed superabrasive cutting surface. The shoulder also gives support to the cutting table during subterranean drilling, increasing the fracture toughness of the cutting table.

[0023] FIG. 3 illustrates a cross sectional side view of the substrate taken along the lines 1-1 in FIG. 2. FIG. 3 includes only one half of the substrate, the other half being a mirror image of the illustrated half. The cylindrical base 11 of substrate 12 is adapted for insertion into an earth-boring tool as shown by the chamfers on the edges. The truncated conical interfacial surface 14 includes truncated top surface 26 and tapered sides 24. The transition from the tapered sides 24 to the truncated top surface 26 may be gradual or abrupt. FIG. 3 depicts a gradual transition from the circumferential shoulder 22 to the tapered sides 24 to the truncated top surface 26 while maintaining a definite slope upward from the base to the plateau of the truncated conical interfacial surface 14. A gradual transition is preferred because of its effect on the stresses along the junction of the shoulder and the tapered walls. The circumferential shoulder 22 in FIG. 3 is substantially perpendicular to the tapered sides 24. This illustration shows a filleted edge between the circumferential shoulder 22 and the tapered sides 24. Still, the edges between the two surfaces could be exactly perpendicular if desired and such a configuration is not outside the scope of the invention. Gentle sloping is however, the preferred variation.

[0024] FIG. 4 illustrates an embodiment of the invention that combines the substrate with the generally domed cutting table. Cutting element 10 comprises a fracture tough substrate 12 and a superabrasive cutting surface. The superabrasive material employed in the cutting surface is well known in the prior art and common in the drilling industry. The superabrasive material is selected from the group consisting of diamond, polycrystalline diamond, or cubic boron nitride. These materials are integrally bonded to the substrate 12 during a high pressure, high temperature sintering process. The terms PCD, polycrystalline diamond, diamond powder matrix, or superabrasive material will be used hereafter to refer to such materials. The superabrasive cutting surface 20 has a generally domed shape 27 formed over the truncated conical interfacial surface 14. The domed shape of the cutting surface combines with the interfacial surface of the substrate to give the insert fracture toughness suitable for drilling a variety of subterranean formations, including those where hard rock stringers are encountered.

[0025] FIG. 5 is a cross sectional side view of FIG. 4 taken through lines 1-1 of FIG. 2. The cutting element 10, as shown in FIG. 5, is one half the cutting element in FIG. 4. Cutting element 10 includes a generally cylindrical substrate 12 composed of fracture tough material with a base 11 adapted for insertion into an earth-boring tool. Opposite the base end 11 of substrate 12 is a truncated conical interfacial surface 14 consisting of a truncated top surface 26 and tapered sides 24. Joining the truncated conical interfacial surface 14 to the substrate 12 is a circumferential shoulder 22 used to support the superabrasive cutting surface 20, especially during its formation. A superabrasive cutting surface 20 is formed on top of the truncated conical interfacial surface 14. The superabrasive cutting surface 20 is integrally bonded to the truncated conical interfacial surface 14 of the substrate through the high-pressure, high-temperature process. The substrate 12 is placed into a generally domed loading container with diamond powders and refractory metals creating a diamond matrix that is placed over the substrate. When subjected to a high pressure, high temperature process, the diamond powders contacting the truncated top surface 26 and tapered sides 24 of the substrate 11 are pressed to form a superabrasive cutting surface 20 that takes on the shape of the loading container. The generally dome like shape 27 of superabrasive material bonded to the substrate yields superior compressive strength. Because of the thickness 25 of the cutting surface 20, the superabrasive dome 27 permits the use of a fracture tough carbide insert and acts like a self-supporting bridge or a continuous truss bridge. The self-supporting truss like strength of the superabrasive dome 27 increases overall fracture strength of the cutting surface 20 and thus increases the lifetime of the cutting element 10.

[0026] FIG. 6 illustrates alternative embodiment of the present invention. The substrate 12 includes a cylindrical base 11 and truncated conical interfacial surface 14. Unlike the cutting element in FIG. 1, the tapered sides 24 of the truncated conical interfacial surface 14 of FIG. 6 are rectangular flats 34. The use of flat surfaces on the tapered sides of the substrate increases the volume of superabrasive material used in the cutting element. The higher volume of superabrasive material in the cutting table increases the life of the cutting surface while the generally domed configuration of the cutting table in combination with the truncated conical interfacial surface provides a cutting element having sufficient fracture toughness to withstand the dynamic loads associated with oil and gas well drilling. A circle 36 defines the top surface perimeter of the truncated top surface 26. A shoulder 22 is formed substantially perpendicular to the tapered sides 24 of truncated conical interfacial surface 14. This drawing shows how the shoulder need not be strictly perpendicular to the tapered sidewalls of the truncated conical interfacial surface but is generally parallel to the truncated top surface 26. The shoulder 18 lends support to the superabrasive cutting surface during formation of the cutting element through a high pressure, high temperature process. The shoulder 22 gives a sort of base layer upon which the diamond powder matrix can obtain its feet. This type of shape behaves much like a continuous truss bridge with self-supporting arches and an interconnected rigid framework. The self-supporting truss-like strength of the polycrystalline dome increases the overall fracture strength of the polycrystalline cutting surface. The generally domed cutting table, in concert with the truncated conical interfacial surface of the substrate of the present invention, enables the cutting element to withstand spalling, cracking, fracture, and delamination of the cutting surface during compressive drilling.

[0027] FIG. 7 illustrates a top view of substrate 12 in FIG. 6 with truncated top 26 in circular shape 36. Forming the tapered sides 24 leading up to the truncated top 26 are rectangular flats 34. A supporting circumferential shoulder 22 forms the outer top perimeter of the substrate 12.

[0028] FIG. 8 depicts a cross sectional side view of FIG. 7 as taken through lines 2-2 of FIG. 7. A cutting element 10 as shown in FIG. 8 is one half of the element in FIG. 7. Cutting element 10 includes a generally cylindrical substrate 12 with base end 11 adapted for insertion into an earth-boring tool. Opposite the base end 11 is a truncated conical interfacial surface 14, which includes truncated top surface 26 and tapered sides 24. Connecting the truncated conical interfacial surface with the substrate is a circumferential shoulder 22. In this particular embodiment of the invention, it is noted how the formation of the truncated top surface, tapered sides, and circumferential shoulder differ from the previous embodiment. This embodiment employs a series of oblique angles to define the junction between the truncated top surface to the tapered sides and the tapered sides to the circumferential shoulder. Thus the transitions from the truncated top to the tapered sides and from the tapered sides to the circumferential shoulder are not substantially perpendicular. These oblique transitions serve to relieve points of stress concentration that might otherwise be present. Additionally, the corners forming the intersection of the oblique angles are not filleted but abrupt and clearly defined as opposed to the substrate in FIG. 3. The truncated conical interfacial surface 14 is specifically fashioned to bond with the cutting surface 20 during a high pressure, high temperature sintering process. The cutting surface 20 is formed to have a generally dome like shape 27 with a substantial thickness 25 on top of the truncated conical interfacial surface 14. This type of shape behaves much like a continuous truss bridge with self-supporting arches and an interconnected rigid framework. The self-supporting truss like strength of the polycrystalline dome increases the overall fracture strength of the polycrystalline cutting surface.

[0029] FIGS. 9 and 10 illustrate other variations in the shape of the truncated conical interfacial surface of the substrate. However, the cross sectional side view as depicted in FIG. 8 is not different for both substrates depicted in FIGS. 9 and 10 as well as the general shape the base portion of the substrate. In fact, FIG. 8 depicts a cross sectional side view taken along lines 3-3 and 4-4 of FIGS. 9 and 10 respectively. Accordingly, only aerial views of the various truncated conical interfacial surfaces of FIGS. 9 and 10 are illustrated. FIG. 9 depicts a truncated conical interfacial surface that is roughly the shape of a truncated pyramid. The truncated pyramid includes a truncated top surface 26 with a square perimeter 46 and tapered sides 24 forming trapezoids 44. The tapered sides formed are not strictly limited to definitional trapezoids as the base side of the trapezoids shown forms an arc whereas conventional trapezoids have two sides parallel to each other. Either variety however can be formed depending on manufacturer interests. Interconnecting the trapezoidal sides 44 and the outer perimeter of the substrate 12 is the circumferential shoulder 22. As noted earlier, the flat surfaces along the tapered walls of the interfacial surface serve to increase the volume of superabrasive material present in the cutting element. The higher volume of material not only serves to increase fracture toughness of the cutting element, it also adds to the overall life of the cutting table.

[0030] FIG. 10 illustrates another variation in the shape of the truncated top 26 of the truncated conical interfacial surface of the substrate 12. Truncated top 26 is an octagonal shape 56 formed by tapered sides 24 in the shape of rectangular flats 54. Again, interconnecting the trapezoidal sides 54 and the outer perimeter of the substrate 12 is the circumferential shoulder 22. Interconnecting the trapezoidal sides 44 and the outer perimeter of the substrate 12 is the circumferential shoulder 22. Various shapes in the truncated conical interfacial surface yield different surface areas, which affect the bonding strength between the substrate and the superabrasive cutting surface.

[0031] FIG. 11 illustrates a face-on cross-sectional view of yet another version of the present invention wherein the cutting insert 10 comprises a tough carbide base portion 12 and a cutting table 27 comprising a superabrasive material 20 that is bonded to the substrate in a high pressure high temperature sintering process. FIG. 12 is a side view of the insert of FIG. 11. The substrate 12 presents a cylindrical shape while the interfacial surfaces, consisting of the shoulder 22, the tapered sides 24, and top surface 26, form a polygonal interfacial surface, such as an oval, to which the superabrasive is bonded. The broad face of the cutting table serves to increase the area of penetration of the cutting insert and the increased surface area of the cutting table reduces point stress concentration. The increased depth of the superabrasive permits the use of a tough carbide substrate while imparting truss-like strength to the cutting table. These elements combine to produce a cutting insert suitable for penetrating fracture resistant subterranean formations.

[0032] FIG. 13 illustrates a cross sectional view of another version of a cutting insert 10 of the present invention wherein the cutting table 27 is a truncated cone mounted onto a cylindrical substrate 12. As in the former versions of the present invention, the top of the substrate 20 may present a plane circle or a polygon. The relatively sharp truncated conical cutting table 27 may be particularly useful in soft formations where an aggressive cutting insert is acceptable.

[0033] Other possible variations of the invention not shown in the drawings, but known in the art, are presented here. One variation may be to provide tapered sides having reinforcing nodules extending into the cutting surface. The purpose of such posts is to further reinforce and strengthen the cutting surface, to promote adhesion of the cutting table to the substrate, and to prevent substantial cracking, spalling, and delamination during compressive drilling.

[0034] Another variation to the truncated conical interfacial surface is tapered sides having flutes. The flutes increase the surface area of the truncated conical interfacial surface and enhance adhesion strength of the cutting surface to the substrate.

[0035] One advantage of the present invention is its unidirectional behavior meaning that the cutting insert can rotate in any direction and still perform productively. Some cutting inserts in the prior art are directionally based and must be correctly implanted in the rotating drill head to function properly. If a mistake is made in the setting of such cutting elements in the rotating drill head, boring efficiency is reduced and cutting element failure imminent. With the present invention, no such problems exist. The insert can be placed into the rotating drill bit with ease and without undue concern for its orientation.

Claims

1. A cutting element for earth-boring drill bits, comprising:

a generally domed cutting surface comprising a superabrasive material, formed by a high-pressure high-temperature sintering method known in the art, integrally bonded to a cylindrical substrate having a generally truncated conical interfacial surface, consisting of a top surface and a circumferential shoulder joined by tapered side walls, and the base of the substrate being adapted for insertion into an earth-boring tool.

2. The cutting element of claim 1, wherein the surfaces of the generally domed cutting table comprise polygonal shaped surfaces.

3. The cutting element of claim 1, wherein the generally domed cutting table has sufficient thickness to withstand compressive drilling of subterranean formations.

4. The cutting element of claim 1, wherein the substrate is composed of a fracture tough material selected from the group consisting of cemented metal carbide.

5. The cutting element of claim 1, wherein the truncated interfacial surface comprises a top surface forming a circle, a square, a polygon, or a combination thereof.

6. The cutting element of claim 1, wherein the tapered walls of the interfacial are surface smooth.

7. The cutting element of claim 1, wherein the tapered walls of the interfacial surface form one or more polygons.

8. The cutting element of claim 1, wherein the tapered walls of the interfacial surface form a truncated pyramid.

9. The cutting element of claim 1, wherein the tapered sidewalls join the circumferential shoulder at an oblique angle.

10. The cutting element of claim 1, wherein the tapered sidewalls join the shoulder and top along a filleted surface.