EP0878602A2

EP0878602A2 - Cutting elements faced with superhard material

Info

Publication number: EP0878602A2
Application number: EP98303775A
Authority: EP
Inventors: Nigel Dennis Griffin
Original assignee: Camco International UK Ltd
Current assignee: ReedHycalog UK Ltd
Priority date: 1997-05-16
Filing date: 1998-05-14
Publication date: 1998-11-18
Also published as: GB2325481A; GB9709861D0; GB9810215D0; EP0878602A3; GB2325481B; ZA984058B

Abstract

A preform element, such as may be used as a cutting element in a drag-type rotary drill bit, comprises a polycrystalline diamond facing table bonded to a tungsten carbide substrate. The rear face of the facing table is formed with a series of elongate ribs and grooves, and the front face of the substrate is formed with a series of elongate ribs and grooves which interengage the grooves and ribs respectively in the facing table. The ribs and grooves on each surface include ribs which are spaced from adjacent grooves so that the part ofthe surface which extends from the bottom of a groove to the apex ofthe adjacent rib is non-linear and discontinuous. The discontinuity between each rib and groove may be an intervening surface portion which is flat, inclined, curved or otherwise shaped.

Description

The invention relates to elements faced with superhard material, and particularly to preform elements comprising a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate of material which is less hard than the superhard material.

Preform elements ofthis kind are often used as cutting elements on rotary drag-type drill bits, and the present invention will be particularly described in relation to such use. However, the invention is not restricted to cutting elements for this particular use, and may relate to preform elements for other purposes, for example as cutters on roller cone and percussive (hammer) bits. Also, elements faced with superhard material, of the kind referred to, may also be employed in workpiece-shaping tools, high pressure nozzles, wire-drawing dies, bearings and other parts subject to sliding wear, as well as elements subject to percussive loads as may be the case in tappets, cams, cam followers, and similar devices in which a surface of high wear resistance is required.

Preform elements used as cutting elements in rotary drill bits usually have a facing table of polycrystalline diamond, although other superhard materials are available, such as cubic boron nitride. The substrate of less hard material is often formed from cemented tungsten carbide, and the facing table and substrate are bonded together during formation of the element in a high pressure, high temperature forming press. This forming process is well known and will not be described in detail.

Each preform cutting element may be mounted on a carrier in the form of a generally cylindrical stud or post received in a socket in the body of the drill bit. The carrier is often formed from cemented tungsten carbide, the surface of the substrate being brazed to a surface on the carrier, for example by a process known as "LS bonding". Alternatively, the substrate itself may be of sufficient thickness as to provide, in effect, a cylindrical stud which is sufficiently long to be directly received in a socket in the bit body, without being brazed to a carrier. The bit body itself may be machined from metal, usually steel, or may be moulded using a powder metallurgy process.

Such cutting elements are subjected to extremes of pressure and temperature during formation, high temperature during mounting on the bit body, and are also subjected to high temperatures and heavy loads when the drill is in use down a borehole. It is found that as a result of such conditions spalling and delamination of the superhard facing table can occur, that is to say the separation and loss of the diamond or other superhard material over the cutting surface of the table.

This may also occur in preform elements used for other purposes, and particularly where the elements are subjected to repetitive percussive loads, as in tappets and cam mechanisms.

Commonly, in preform elements of the above type the interface between the superhard table and the substrate has usually been flat and planar. However, particularly in cutting elements for drill bits, attempts have been made to improve the bond between the superhard facing table and the substrate by configuring the rear face of the facing table so as to provide a degree of mechanical interlocking between the facing table and substrate.

One such arrangement is shown in U.S. Patent Specification No. 5120327 where the rear surface of the facing table is integrally formed with a plurality of identical spaced apart parallel ribs of constant depth. The facing table also includes a peripheral ring of greater thickness, the extremities of the parallel ribs intersecting the surrounding ring. U.S. Specification No. 4784023 illustrates a similar arrangement but without the peripheral ring.

U.S. Patent Specification No. 5011515 shows an arrangement where the substrate and facing table of a preform element have interengaging complementary surface irregularities which are so shaped that the concentration of substrate material continuously and gradually decreases from the substrate into the facing table, through the region of surface irregularities.

The present invention sets out to provide further novel designs of preform element having a non-planar interface between the facing table and the substrate, and where the configuration of the interface achieves a redistribution and reduction of the interface stress between the facing table and the substrate.

According to the invention there is provided a preform element including a facing table of superhard material having a front face, and a rear face bonded to a front face of a substrate of a material which is less hard than the superhard material, the front face of the substrate being formed with surface irregularities which interengage with complementary surface irregularities on the rear face of the facing able, the concentration of the substrate material generally decreasing through the region of said surface irregularities, from the substrate into the facing table, there being a discontinuity in the rate of decrease of substrate material in at least one location through said region.

The rate of decrease of concentration of substrate material may increase or decrease at the location of said discontinuity. Alternatively, the concentration of substrate material may change to a lower value, or temporarily to a higher value, at the location of said discontinuity.

The invention also provides a preform element including a facing table of superhard material having a front face, and a rear face bonded to the front face of a substrate which is less hard than the superhard material, the rear face of the facing table comprising a surface formed with a plurality of elongate ribs and grooves, and the front face of the substrate comprising a surface which is bonded to the surface of the facing table and is formed with a plurality of elongate ribs which are bonded within said grooves in the facing table, and a plurality of elongate grooves within which are bonded said ribs on the facing table, said ribs and grooves on each surface including ribs which are spaced from adjacent grooves so that a portion of the surface on which the ribs and grooves are formed extends from a side edge of a rib to a side edge of an adjacent groove.

Such arrangement has the effect of forming a "step" between an adjacent rib and groove. In prior art arrangements each rib is usually immediately adjacent a groove, in a generally sinusoidal or castellated formation, so that the side wall of the groove forms a continuation of the side wall of the rib with no step between them. However, the present invention does not exclude arrangements where some of the ribs and grooves at the interface have this prior art configuration.

Preferably the ribs and grooves on each surface are substantially parallel, and are substantially equally spaced apart. However, the invention includes arrangements where the ribs and grooves are non-parallel and/or are unequally spaced.

Preferably also the ribs and grooves are spaced alternately apart on each surface, although arrangements are possible which include two or more ribs and/or two or more grooves adjacent one another.

Each rib or groove may be of substantially constant width and/or depth along its length. All of the ribs or grooves on a surface may be of similar cross-sectional size and/or shape. Alternatively, the ribs and grooves in each surface may be of different cross-sectional size and/or shape. For example, the grooves in the surface of the substrate may be smaller in cross-section than the ribs on that surface.

Each groove and/or rib may be tapered in cross-sectional shape as it extends away from the surface on which it is formed. It may be arcuate, e.g. part-circular, in cross-section. In this case the ribs and grooves may be of substantially the same depth but of different radii of curvature.

In prior art arrangements the formations providing the non-planar interface between the facing table and substrate may typically have a depth of the order of 0.8 mm, and preform elements according to the present invention may provide grooves and ribs of this or any other appropriate depth. However, the interface design according to the present invention may be effective at depths which are shallow compared with the prior art. For example, the depth of each rib or groove, measured from the surface on which it is formed, may be in the range of 0.01 mm to 0.15 mm. In one preferred embodiment of the invention the depth of each rib and groove is about 0.1 mm.

Similarly, the spacing apart of the ribs or grooves may also be small. Thus the spacing between the central longitudinal axis of each rib or groove and an adjacent rib or groove may be in the range of 0.1 mm to 1 mm, and in a preferred embodiment is about 0.5 mm.

According to a further aspect of the present invention, therefore, there is provided a preform element including a facing table of superhard material having a front face, and a rear face bonded to the front face of a substrate which is less hard than the superhard material, the rear face of the facing table comprising a surface formed with a plurality of elongate ribs and grooves, and the front face of the substrate comprising a surface which is bonded to the surface of the facing table and is formed with a plurality of elongate ribs which are bonded within said grooves in the facing table, and a plurality of elongate grooves within which are bonded said ribs on the facing table, the depth of each rib or groove being in the range of 0.01 mm to 0.15 mm. Preferably the depth of each rib or groove is about 0.1 mm.

In any of the above arrangements said surfaces on which the ribs and grooves are formed may be substantially flat, apart from said ribs and grooves, or may be convexly or concavely curved.

The facing table may be formed with a thickened peripheral rim which projects into the substrate.

In any of the above arrangements also there may be provided between the facing table and substrate a transition layer of a material having at least one property, such as hardness, which is intermediate the corresponding property of the facing table and substrate. In this case the inter-engaging ribs and grooves may be formed between the facing table and transition layer, in which case the transition layer is regarded as forming part of the substrate for the purposes of the present invention, or between the transition layer and substrate, in which case the transition layer is regarded as forming a part of the facing table for the purposes of the present invention. In some cases ribs and grooves according to the invention may be provided both between the facing table and transition layer and between the transition layer and substrate.

The facing table may be formed from polycrystalline diamond and the substrate may be formed from cemented tungsten carbide.

The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the accompanying drawings in which:

Figure 1 is a side elevation of a typical drag-type drill bit in which preform cutting elements according to the present invention may be used,

Figure 2 is an end elevation of the drill bit shown in Figure 1,

Figure 3 is a diagrammatic cross-section of one form of preform cutting element in accordance with the present invention,

Figure 4 is a diagrammatic perspective view of the substrate of the element shown in Figure 3,

Figure 5 is a diagrammatic section, on an enlarged scale, showing the shape of the interface between the layers of the cutting element in greater detail,

Figure 6 is another diagrammatic section of the interface shown in Figure 5, together with an associated diagrammatic graph showing the reduction in the percentage of substrate material when passing across the interface from the substrate into the facing table, and

Figures 7-13 are similar views to Figure 6 showing alternative shapes of interface with associated graphs.

Figures 1 and 2 show a typical full bore drag-bit of a kind to which cutting elements ofthe present invention are applicable. The bit body 10 is machined from steel and has a shank formed with an externally threaded tapered pin 11 at one end for connection to the drill string. The operative end face 12 of the bit body is formed with a number of blades 13 radiating from the central area of the bit, and the blades carry cutter assemblies 14 spaced apart along the length thereof The bit has a gauge section including kickers 16 which contact the walls of the borehole to stabilise the bit in the borehole. A central passage (not shown) in the bit and shank delivers drilling fluid through nozzles 17 in the end face 12 in known manner, so as to clean and cool the cutter assemblies.

Each cutter assembly 14 is generally cylindrical and comprises a preform cutting element in the form of a circular tablet comprising a facing table of superhard material, usually polycrystalline diamond, bonded to a substrate which is normally of cemented tungsten carbide. The rear surface of the substrate may be bonded, for example by LS bonding, to a co-axial cylindrical stud which is secured in a socket in the bit body, or the substrate itself may be of sufficient axial length to be secured within the socket.

Figures 3 and 4 show one form of preform cutting element in accordance with the present invention. The cutting element is in the form of a circular tablet and comprises a polycrystalline diamond front facing table 20 bonded to a cemented tungsten carbide substrate 21. In accordance with the present invention the interface 22 between the facing table and substrate is configured to provide interengaging ribs and grooves.

As may best be seen in Figure 4, the ribs and grooves are parallel and extend across the whole of the substrate and facing table, ribs and grooves being spaced alternately apart across the substrate and facing table.

Figure 5 shows diagrammatically, on an enlarged scale, the cross-sectional shapes ofthe ribs and grooves, the facing table 20 and substrate 21 being shown slightly separated for clarity.

Referring to Figure 5: the facing table 20 has a flat rear surface, indicated by the dotted line 23, on which are formed alternately spaced parallel grooves 24 and projecting ribs 25. The grooves and ribs are generally part-circular in cross-section and are of constant cross-sectional shape, so as to be of constant width and depth along their lengths. The grooves and ribs are of the same depth, but the grooves are wider than the ribs, being of greater radius of curvature.

Each groove 24 is spaced laterally from the adjacent rib 25 so that a portion 26 of the surface 23 on which the ribs and grooves are formed extends from a side edge of each rib 25 to the side edge of the adjacent groove 24, so as to form a step 27 between each rib and groove.

The front surface 28 of the substrate 21 is similarly configured in a complementary formation with projecting ribs 29 and grooves 30, the grooves being of the same depth as the ribs but of smaller width. Adjacent ribs and grooves are separated by a portion 31 of the surface 28 so as to form a step 32 between each rib and groove. The ribs 29 on the substrate are received and bonded within the grooves 24 on the facing table, and the ribs 25 on the facing table are received and bonded within the grooves 30 on the substrate, so that the

surface portions

26 and 31 between the ribs and grooves engage and are also bonded together.

As is well known, preform elements of this general type are manufactured by first forming a solid substrate 21 with a configured front surface, as shown in Figure 4. The ribs and grooves may be formed on the substrate by any suitable process, for example by moulding or machining, laser cutting or the like.

The pre-formed substrate is then placed in a mould and a layer of diamond particles is applied to the front face of the substrate so that the particles fill the spaces between the ribs and grooves on the substrate and also provide a facing layer of the required thickness above the substrate. The substrate and facing layer are then subjected to extremely high pressure and temperature in a press, during which process the diamond particles bond together and also become bonded to the substrate.

A transition layer may be provided between the superhard material of the facing table 20 and the less hard material of the substrate 21. In the case where the ribs and grooves are formed at the interface between the rear surface of the superhard material and the transition layer, the transition layer is regarded, for the purposes of the present invention, as forming part of the substrate. Conversely, the ribs and grooves may be formed at the interface between the transition layer and the substrate 21, in which case the transition layer is regarded as forming part of the facing table. In either case, the interface between the facing table or substrate and the transition layer which is not formed with ribs and grooves in accordance with the present invention may be planar, or may be otherwise configured to provide some other form of non-planar interface. Alternatively, both interfaces may be formed with ribs and grooves arranged in accordance with the present invention.

Figure 3 also indicates diagrammatically a case where a transition layer 21a is provided which forms part of the substrate. The transition layer 21a may have a hardness or other characteristics intermediate the corresponding characteristics of the facing table 20 and substrate 21.

As previously mentioned, the dimensions of the ribs and grooves according to the present invention may be significantly smaller than the dimensions of the formations in prior art non-planar interfaces. Thus, the depth of each rib and groove, indicated at "h" in Figure 5, may be about 0.1 mm and the spacing between the central longitudinal axes of adjacent ribs and grooves, indicated at "l" in Figure 5, may be .5 mm. Although "h" and "I" may be of any dimensions, "h" is preferably in the range of 0.01 mm to 0.15 mm and "l" is preferably in the range of 0.1 mm to 1 mm.

The ribs and grooves of the interface described in relation to Figures 3-5 constitute the aforementioned surface irregularities in the front face of the substrate which interengage with complementary surface irregularities in the rear face of the facing table. It will be appreciated that the effect ofthese irregularities is that the concentration of the substrate material over the whole area of the interface decreases in passing from the substrate to the facing table, across the interface. According to the present invention, the steps 32 and flat surface portions 31 between adjacent ribs and grooves cause a discontinuity in the rate of decrease of concentration of substrate material. This discontinuity is illustrated diagrammatically in the graph 33 in Figure 6. Thus, the vertical portion 34 of the graph indicates the region where the percentage of substrate material across the element is 100%. The next portion 35 of the graph shows the decrease of the percentage of substrate material as a result of the projection of the ribs 25 of superhard material into the substrate. At the level of the flat surface portions 31 there is a discontinuity in the rate of decrease of concentration of substrate material as indicated by the horizontal portion 36 of the graph 33, indicating an instant fall in the percentage of substrate material. The projections 29 of substrate material upwardly into the facing table then represent a further gradual decrease in the percentage of substrate material to zero, as indicated by the portion 37 ofthe graph 33.

Figures 7-13 are similar views to Figure 6 of alternative interface configurations, together with their associated graphs showing the decrease in percentage of substrate material when passing across the interface from the substrate into the facing table. In each case the shape ofthe interface is such that there are one or more discontinuities in the gradual rate of decrease of concentration of substrate material across the interface.

Thus, in the arrangement of Figure 7 the steps 38 between the ribs and grooves are not co-planar so that, in passing across the steps 38 the discontinuity is in the form of an increase in the rate of decrease of concentration, as indicated at 39 in the associated graph, rather than the sudden fall to a lower value indicated at 36 in the Figure 6 arrangement.

In the arrangement of Figure 8 the step 40 between adjacent ribs and grooves is generally S-shaped giving a curved discontinuity in the graph, as indicated at 41.

In the arrangement of Figure 9 the step between adjacent curves and grooves is generally Z-shaped, as indicated at 42, providing a discontinuity, as indicated at 43, in the otherwise smooth curve of the decrease in percentage of substrate material.

In Figure 10 the region between adjacent ribs and grooves is of irregular zig-zag shape, as indicated at 44 in Figure 10. This results in a corresponding zig-zag discontinuity 45 in the associated graph of decrease of concentration of substrate material. The discontinuity includes regions where the percentage of substrate material actually temporarily increases over a short distance of the passage across the substrate.

The interface in Figure 11 has ribs and grooves which are generally flat sided rather than curved, with the result that there are a number of sudden falls in the concentration of substrate material as shown by the discontinuities in the associated graph.

In the arrangement of Figure 12 the ribs and grooves are so shaped in cross-section that in one region of the interface, as indicated at 46, the general decrease in the concentration of substrate material includes a region where the concentration temporarily gradually increases.

Figure 13 shows an arrangement where the shapes of the interengaging ribs and grooves are such that one of the discontinuities in the decrease of concentration of substrate material is a temporary sudden increase in the concentration, as indicated at 47 in the graph of Figure 13.

It should be pointed out that the interfaces of Figures 7-13 are shown diagrammatically and are not necessarily to scale, and also the associated graphs of percentage of substrate material in different regions across the interface are also diagrammatic and while they show the general variation in concentration of substrate material across the interface, they are not intended to represent the actual concentrations exactly at each location.

Claims

A preform element including a facing table of superhard material having a front face, and a rear face bonded to a front face of a substrate of a material which is less hard than the superhard material, the front face of the substrate being formed with surface irregularities which interengage with complementary surface irregularities on the rear face of the facing able, the concentration of the substrate material generally decreasing through the region of said surface irregularities, from the substrate into the facing table, characterised in that there is a discontinuity in the rate of decrease of substrate material in at least one location through said region.
A preform element according to Claim 1, wherein the rate of decrease of concentration of substrate material increases at the location of said discontinuity.
A preform element according to Claim 1, wherein the rate of decrease of concentration of substrate material decreases at the location of said discontinuity.
A preform element according to Claim 1, wherein the concentration of substrate material changes to a lower value at the location of said discontinuity.
A preform element according to Claim 1, wherein the concentration of substrate material changes to a higher value at the location of said discontinuity.
A preform element including a facing table of superhard material having a front face, and a rear face bonded to the front face of a substrate which is less hard than the superhard material, the rear face of the facing table comprising a surface formed with a plurality of elongate ribs and grooves, and the front face of the substrate comprising a surface which is bonded to the surface of the facing table and is formed with a plurality of elongate ribs which are bonded within said grooves in the facing table, and a plurality of elongate grooves within which are bonded said ribs on the facing table, characterised in that said ribs and grooves on each surface include ribs which are spaced from adjacent grooves so that a portion of the surface on which the ribs and grooves are formed extends from a side edge of a rib to a side edge of an adjacent groove.
A preform element according to Claim 6, wherein the ribs and grooves on each surface are substantially parallel.
A preform element according to Claim 6 or Claim 7, wherein the ribs and grooves on each surface are substantially equally spaced apart.
A preform element according to any of Claims 6 to 8, wherein the ribs and grooves are spaced alternately apart on each surface.
A preform element according to any of Claims 6 to 9, wherein each rib and groove is of substantially constant width along its length.
A preform element according to any of Claims 6 to 10, wherein each rib and groove is of substantially constant depth along its length.
A preform element according to any of Claims 6 to 11, wherein all of the ribs or grooves on a surface are of similar cross-sectional size.
A preform element according to any of Claims 6 to 12, wherein all of the ribs or grooves on a surface are of similar cross-sectional shape.
A preform element according to any of Claims 6 to 13, wherein each groove and rib is tapered in cross-sectional shape as it extends away from the surface on which it is formed.
A preform element according to Claim 14, wherein each groove and rib is arcuate in cross-section.
A preform element according to any of Claims 6 to 15, wherein the depth of each rib and groove, measured from the surface on which it is formed, is in the range of 0.01 mm to 0.15 mm.
A preform element according to Claim 16, wherein the depth of each rib and groove is about 0.1 mm.
A preform element according to any of Claims 6 to 17, wherein the spacing between the central longitudinal axis of each rib and an adjacent rib is in the range of 0. 1 mm to 1 mm.
A preform element according to Claim 18, wherein the spacing between the central longitudinal axis of each rib and an adjacent rib is about 1.0mm.
A preform element according to any of Claims 6 to 19, wherein said surfaces on which the ribs and grooves are formed are substantially flat, apart from said ribs and grooves.
A preform element according to any of Claims 6 to 19, wherein said surfaces on which the ribs and grooves are formed are convexly curved, apart from said ribs and grooves.
A preform element according to any of Claims 6 to 19, wherein said surfaces on which the ribs and grooves are formed are concavely curved, apart from said ribs and grooves.
A preform element according to any of Claims 6 to 22, wherein the facing table is formed with a thickened peripheral rim which projects into the substrate.
A preform element according to any of Claims 6 to 23, wherein there is provided between the facing table and substrate a transition layer of a material having at least one property which is intermediate the corresponding property of the facing table and substrate.
A preform element according to any of Claims 6 to 24, wherein the facing table is formed from polycrystalline diamond and the substrate is formed from cemented tungsten carbide.
A preform element including a facing table of superhard material having a front face, and a rear face bonded to the front face of a substrate which is less hard than the superhard material, the rear face of the facing table comprising a surface formed with a plurality of elongate ribs and grooves, and the front face of the substrate comprising a surface which is bonded to the surface of the facing table and is formed with a plurality of elongate ribs which are bonded within said grooves in the facing table, and a plurality of elongate grooves within which are bonded said ribs on the facing table, characterised in that the depth of each rib or groove is in the range of 0.01 mm to 0.1 mm.
A preform element according to Claim 26, wherein the depth of each rib or groove is about 0.1 mm.
A preform element including a facing table of superhard material having a front surface, and a rear surface bonded to the front surface of a substrate which is less hard than the superhard material, the rear surface of the facing table and the front surface of the substrate being formed with interengaging arrays of alternating ribs and grooves, characterised in that the part of each said surface which extends from the bottom of a groove to the apex of an adjacent rib is non-linear.