ABRASIVE BODY

Abstract: An abrasive body comprises an abrasive layer (10) bonded to a substrate (12) along an interface (14) and an abrasive projection (20) extending from the interface (14) into the substrate (12) and extending from a point on the periphery of the abrasive layer (10) to another point on the periphery of the abrasive layer (10). The projection (20) has two stepped regions (22, 24), the one stepped region (24) being further from the interface than the other stepped region (22).

Description: ABRASIVE BODY BACKGROUND OF THE INVENTION This invention relates to an abrasive body and more particularly to an abrasive body which can be used as a tool insert. Composite abrasive compacts are products used extensively as inserts for abrasive tools such as drill bits. Such composite abrasive compacts comprise an abrasive compact layer bonded to a cemented carbide support. The abrasive compact will typically be a diamond abrasive compact, also known as polycrystalline diamond or PCD, or a cubic boron nitride compact, also known as polycrystalline CBN or PCBN. Composite abrasive compacts are manufactured under elevated temperature and pressure conditions, e.g. diamond or cubic boron nitride synthesis conditions. As it is known that PCD composite compacts contain considerable residual stresses as a result of the high temperature/high pressure conditions used in their manufacture. Further, methods of mounting such compacts into drill bits, for example press fitting or brazing, can modify the stress distributions in the compacts. Additional stresses are imposed on the compacts during their use in applications such as drilling. Stresses may be introduced into the interface between the abrasive compact layer and the cemented carbide support. These stresses may be reduced or modified by providing a recess which extends into the cemented carbide support from the compact/carbide interface and which is filled with the abrasive compact. In the prior art, the recess has taken various shapes such as a plurality of concentric rings, a V- shaped recess, a cross-shaped recess, and a recess which incorporates a number of steps. A purpose in most of such designs is to reinforce and support the cutting edge by providing overall rigidity for the composite compacts. United States Patent 5,685,769 discloses a tool component comprising an abrasive compact layer bonded to a cemented carbide substrate along an interface. The abrasive compact layer has a working surface on the side opposite to the interface which is flat and presents a cutting edge or point on its periphery. A recess is provided, that recess extending into the substrate from the interface. The recess has a shape, in plan, of at least two strips which intersect. Examples of suitable shapes are V-shape and X-shape. Compact material fills the recess and is bonded to the substrate. The base of the recess may be flat or have one or more discontinuities. United States Patent No. 5,472,376 describes a tool component comprising an abrasive compact layer bonded to a cemented carbide substrate along an interface. A recess extends from the interface into the substrate and is filled with abrasive compact. The recess has a stepped configuration and is located entirely within the carbide substrate. SUMMARY OF THE INVENTION According to the present invention, an abrasive body, for use, for example, as a tool insert, comprises an abrasive layer bonded to a substrate along an interface and an abrasive projection extending from the interface into the substrate and extending from a point on the periphery of the abrasive layer to another point on the periphery of the abrasive layer, the projection having at least two stepped regions, the one stepped region being further from the interface than the other. Each stepped region will generally have a surface parallel to the interface and a surface transverse thereto. In one form of the invention, the projection comprises a strip which extends from one peripheral edge of the abrasive layer to an opposite peripheral edge thereof. The stepped regions in the strip may extend from the same one peripheral edge of the abrasive layer to the opposite peripheral edge thereof. Preferably, the stepped regions are essentially parallel to each other. The projection may have outer shallow stepped regions sandwiching therebetween an inner stepped region. In this projection, the inner stepped region may have a surface parallel to the interface, and the outer stepped regions may also have surfaces parallel to the interface. The parallel surface of the inner region may be joined to the parallel surfaces of the outer regions by connecting surfaces and the parallel surfaces of the outer regions may be joined to the interface by connecting surfaces. The connecting surfaces are preferably at an angle other than 90° to the surfaces which they join. The connecting surfaces may be straight or curved. Preferably, the connecting surfaces between the inner stepped region and the outer stepped regions are straight and parallel to each other, and the connecting surfaces between the parallel surfaces of the outer stepped regions and the interface are concavely curved relative to the inner stepped region. In another form of the invention, the projection has an essentially triangular shape having one or more outer shallow stepped regions and an inner deeper stepped region. Preferably, an outer shallow stepped region is provided on each of the three sides of the triangular shaped projection. In this form of the invention, each stepped region may have a surface parallel to the interface and a connecting surface joining the parallel surface to another surface. Such connecting surfaces preferably define an angle other than 90° to the surfaces which they join. The connecting surfaces between the parallel surfaces of the outer regions and the inner region may be concavely curved relative to the inner region. The connecting surfaces between the parallel surfaces of the outer regions and the interface may be straight. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a first embodiment of the invention, Figure 2 is a section along the line 2-2 of Figure 1 , Figure 3 is a view of Figure 1 in the direction of arrow A, Figure 4 is a plan view of a second embodiment of the invention, Figure 5 is a section along the line 5-5 of Figure 4, and Figure 6 is a sectional side view of a further embodiment of the invention. DESCRIPTION OF EMBODIMENTS The abrasive body may have various shapes, but is preferably is right- circular cylindrical. The periphery of the abrasive layer will generally provide a cutting edge for the body. This cutting edge may be covered by a layer of cemented carbide and reached only once the cemented carbide has worn away, in use. The substrate will typically be a cemented carbide substrate. The cemented carbide of the substrate may be any known in the art such as cemented titanium carbide, cemented tungsten carbide, cemented tantalum carbide, cemented molybdenum carbide, or mixtures thereof. As is known, such cemented carbides will typically have a binder content of 3 to 30% by mass. The metal binder will typically be cobalt, iron or nickel or an alloy containing one or more of these metals. The abrasive layer will generally be an abrasive compact layer or a layer of diamond produced by chemical vapour deposition (CVD). When the abrasive layer is an abrasive compact layer, it will preferably be a diamond compact layer or a cubic boron nitride compact layer. A first embodiment of the invention will now be described with reference to Figures 1 to 3. Referring to these figures, there is shown an abrasive body comprising an abrasive compact layer 10 bonded to a substrate 12, generally a cemented carbide substrate, along an interface 14. The top surface 16 of the layer 10 provides an abrasive surface for the body and the peripheral edge 18 provides a cutting edge. Extending into the substrate 12 from the abrasive compact layer 10 is an abrasive compact projection 20. The projection 20 consists of two outer stepped regions 22 and a central stepped region 24, deeper than the outer stepped regions 22. The outer stepped regions 22 each have a surface 26 which is parallel to the interface 14 and a surface 28 which connects the surface 26 to the interface 14. Surfaces 28 define an angle other than 90° to surfaces 26 and interface 14. Further, connecting surfaces 28 are concavely curved relative the central stepped region 24. The central stepped region 24 is deeper in the substrate 12 than the outer stepped regions 22. The region 24 has a surface 30 which is parallel to the interface 14 and surfaces 32 which connect the surface 30 to the surfaces 26. Surfaces 32 define an angle other than 90° to the surface 30 and the surfaces 26. The surfaces 32 are straight and parallel to each other. The shapes of the connecting surfaces 28, 32 may be different to those illustrated. A second embodiment of the invention will now be described with reference to Figures 4 and 5. Referring to these figures, an abrasive body comprises a layer of abrasive compact 40 bonded to a substrate 42, particularly a cemented carbide substrate, along an interface 44. The surface 46 of the abrasive compact layer 40 provides an abrasive surface for the body, while the peripheral edge 48 provides a cutting edge. An abrasive compact projection 50 extends from the interface 44 into the substrate 42. This projection is essentially triangular in shape, as can be seen from Figure 4. The sides 52 of the triangle are straight while the apices 54 are truncated and coincident with a side edge of the abrasive body. The triangular shaped projection 50 has outer, shallow stepped regions 56 and an inner, deeper stepped region 58. The outer, stepped regions 56 each have a surface 60 parallel to the interface 44 and a surface 62 which connects the surface 60 to the interface 44. The surfaces 62 are at an angle other than 90° to the surfaces 60 and interface 44. Further, the surfaces define the outer edges of the projection and are straight. The inner, deep stepped region 58 has a surface 64 parallel to the interface 44 and surfaces 66 which connect the surface 64 to the surfaces 60 of the outer, shallow stepped regions 56. The surfaces 66 define an angle other than 90° to the surface 64 and the surfaces 60. The connecting surfaces 66 are concavely curved relative to the surface 64. The connecting surfaces 62 and 66 may have shapes different to those illustrated. The abrasive bodies described above may be made by methods known in the art. Generally, this will involve providing a cylindrical shaped cemented carbide body having a recess, to receive components necessary to make an abrasive compact, formed in one end thereof. An example of such a body, to produce an abrasive body of Figures 1 to 3, is shown in Figure 6. Referring to this figure, a cemented carbide body 70 is of right-circular cylindrical shape having flat ends 72 and 74. A recess 76 is provided in the end 72. This recess is filled with the components necessary to make an abrasive compact. The thus produced unbonded assembly is placed in the reaction zone of a conventional high temperature/high pressure apparatus to form an abrasive compact of the components which bonds to the body 70. The abrasive body, illustrated by Figures 1 to 3, is produced by simply removing the sides of the body 70, as illustrated by the dotted lines. However, the bonded body which is recovered from the reaction zone after compact formation, and without removal of the carbide sides, may be used as a tool insert itself, and forms another aspect of the invention. In this form of the insert, its edge 78 which will provide the cutting edge. This edge is likely to wear away fairly rapidly until the abrasive compact edge 80 is reached. Thereafter, it is this edge 80 which provides the cutting edge for the component. It has been found that PCD and PCBN, particularly PCD, abrasive bodies having interfaces with projections of the type described above and illustrated in the drawings, provide excellent reinforcement and support for the cutting edge of the PCD or PCBN layers by providing overall rigidity for the bodies. Further, in use the cutting edges in the regions 34 of the Figures 1 to 3 embodiment and the regions 54 of the Figures 5-6 embodiment will generally be employed. The extra abrasive available in these regions increases the effective abrasive action of the body.

Claims: CLAIMS 1. An abrasive body comprises an abrasive layer bonded to a substrate along an interface and an abrasive projection extending from the interface into the substrate and extending from a point on the periphery of the abrasive layer to another point on the periphery of the abrasive layer, the projection having at least two stepped regions, the one stepped region being further from the interface than the other. 2. An abrasive body according to claim 1 wherein each stepped region has a surface parallel to the interface and a surface transverse thereto. 3. An abrasive body according to claim 1 or claim 2 wherein the projection comprises a strip which extends from one peripheral edge of the abrasive layer to an opposite peripheral edge thereof. 4. An abrasive body according to claim 3 wherein the stepped regions in the strip extend from the same one peripheral edge of the abrasive layer to the same opposite peripheral edge thereof. 5. An abrasive body according to claim 3 or claim 4 wherein the stepped regions are essentially parallel to each other. 6. An abrasive body according to any one of claims 3 to 5 wherein the projection has outer shallow stepped regions sandwiching therebetween a deeper inner stepped region. 7. An abrasive body according to claim 6 wherein the inner stepped region has a surface parallel to the interface and the outer stepped regions have surfaces parallel to the interface. 8. An abrasive body according to claim 7 wherein the parallel surface of the inner region is joined to the parallel surfaces of the outer regions by connecting surfaces and the parallel surfaces of the outer regions are joined to the interface by connecting surfaces. 9. An abrasive body according to claim 8 wherein the connecting surfaces are at an angle other than 90° to the surfaces which they join. 10. An abrasive body according to claim 8 or claim 9 wherein the connecting surfaces are straight or curved. 11. An abrasive body according to claim 8 or claim 9 wherein the connecting surfaces between the inner stepped region and the outer stepped regions are straight and parallel to each other and the connecting surfaces between the parallel surfaces of the outer stepped regions and the interface are concavely curved relative to the inner stepped region. 12. An abrasive body according to claim 1 or claim 2 wherein the projection has an essentially triangular shape having one or more outer shallow stepped regions and an inner deeper stepped region. 13. An abrasive body according to claim 12 wherein an outer shallow stepped region is provided on each of the three sides of the triangular shaped projection. 14. An abrasive body according to claim 12 or claim 13 wherein each stepped region has a surface parallel to the interface and a connecting surface joining the parallel surface with another surface. 15. An abrasive body according to claim 14 wherein each connecting surface defines an angle other than 90° to the surfaces which it joins. 16. An abrasive body according to claim 14 or claim 15 wherein the connecting surfaces between the parallel surfaces of the outer regions and the parallel surface of the inner region are concavely curved relative to the inner region. 17. An abrasive body according to any one of claims 14 to 16 wherein the connecting surfaces between the parallel surfaces of the outer regions and the interface are straight. 18. An abrasive body according to any one of the preceding claims wherein the abrasive layer has an upper surface defining a cutting edge. 19. An abrasive body according to any one of the preceding claims wherein the abrasive layer is selected from an abrasive compact layer and a layer of diamond produced by chemical vapour deposition. 20. An abrasive body according to any one of the preceding claims wherein the substrate is a cemented carbide substrate. 21. An abrasive body substantially as herein described with reference to any one of Figures 1 to 6 of the accompanying drawings.

Inventors: BEX PHILLIP ALEXANDER, TANK KLAUS, BEX, PHILLIP, ALEXANDER, TANK, KLAUS
Applicants: BEX PHILLIP ALEXANDER, DE BEERS IND DIAMOND, TANK KLAUS, BEX, PHILLIP, ALEXANDER, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED, TANK, KLAUS
Application year: 1999
Main classification: E21B10
IPC codes: E21B10