Abrasive body

Abstract: An abrasive body, particularly a tool insert, comprises an abrasive layer (10) bonded to a substrate (12) along an interface (14). The abrasive layer (10) extends into the substrate layer (12) to a depth below the interface at the periphery (24) of the body and defines a continuous border (26) around the periphery of the body. The abrasive body is further provided with one or more projections (28,30) which extend from the interface (14) into one of the layers. If the projection (28,30) extends into the abrasive layer (10), it is of the same material as the substrate (12) and integral therewith. If the projection (28,30) extends into the substrate layer (12), it is the same abrasive as the abrasive layer (10) and integral therewith.

Description: BACKGROUND OF THE INVENTION This invention relates to an abrasive body as per the preamble of claim 1. Such an abrasive body is disclosed, as an example by WO 9 215 427. Composite abrasive compacts are products used extensively as inserts for abrasive tools such as drills. 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. 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. The purpose in all such designs is to reinforce and support the cutting edge by providing overall rigidity for the composite compacts. SUMMARY OF THE INVENTION According to the present invention, there is provided an abrasive body as per claim 1. The abrasive body will preferably be circular in plan. The substrate layer will typically be a cemented carbide substrate layer. The cemented carbide for 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 metal binder content of 3 to 30 percent 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. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional side view of a first embodiment of the invention, and Figure 2 is a section along the line 10-10 of Figure 1. An embodiment of the invention is illustrated by Figures 1 and 2. The abrasive body of this embodiment also has application, in particular, as an insert for a drill. The abrasive body comprises a layer 130 of abrasive compact bonded to a cemented carbide substrate 132 along an interface 134. The compact layer has an upper working surface 136 which has cutting edge 138. The edge is illustrated as being a sharp edge. This edge can also be bevelled. The cutting edge 138 extends around the entire periphery of the surface 136. The substrate layer 132 has a flat base surface 140, the edge 142 of which may be sharp, as illustrated, or bevelled. The abrasive compact layer 130 extends below the interface 134 at the periphery 144 of the body defining a ring 146 of abrasive compact. The ring 146 has a sloping side surface 148 between the interface 134 and the base surface 150 of the ring 146. The ring 146 extends around the entire periphery 144 of the abrasive body. Extending into the substrate 132 are two crescent-shaped concentric projections identified as 152a, 152b and 154a, 154b, respectively. The smaller of the projections 152b, 154b are located inside the larger projections 152a, 154a. A further projection 160 extends from one edge 162 to the opposite edge 164 of the abrasive body. This projection is bar-shaped and is defmed by a sloping side surface 166 and a base surface 168. It will be noted that the projection 160 extends into the substrate 132 to a depth greater than that of the crescent-shaped projections 152, 154 and the ring 146. In the embodiment described above, it has been found that the provision of a compact ring around the periphery of the body, and which is integral with the compact layer, improves the integrity of the cutting edge. Further, the compact ring in combination with the profile of the interface, particularly the projections, substantially balances and modifies residual stresses allowing the abrasive body to withstand greater imposed loads and cutting forces. The compact layer is held effectively in compression without any undue tensile stresses in the substrate. The projections described and illustrated in Figures 1 and 2 may be provided with one or more steps so that the depth that they penetrate either the compact layer or the carbide layer from the interface will vary over the length of the projection. The abrasive bodies of the invention may be made by methods known in the art. More particularly, a cemented carbide substrate will have one surface profiled to the desired shape. The components necessary to produce an abrasive compact will then be placed on the profiled surface to form an unbonded assembly and the unbonded assembly subjected to elevated conditions of temperature and pressure suitable to form an abrasive compact layer from the components.

Claims: An abrasive body comprises an abrasive layer (130) bonded to a substrate layer (132) along an interface (134), the abrasive layer (130) extending into the substrate (132) to a depth below the interface (134) at the periphery (144) of the body and defining a continuous border (146) around the periphery (144) of the body, and projections (152, 154, 160) extending from the interface (134) into one of the layers: (i) if the projections (152, 154, 160) extend into the abrasive layer (130), they are of the same material as the substrate (132) and integral therewith; and (ii) if the projections (152, 154, 160) extend into the substrate layer (132), they are the same abrasive as the abrasive layer (130) and integral therewith, and characterized in that the projections include a centrally located elongate projection (160) extending from one edge (162) of the body to an opposite edge (164) of the body and a set (152,154) of crescent-shaped projections which are defined by a convex and a concave edge on each side of the elongate projection (160). An abrasive body according to claim 1 wherein the projections in the sets (152,154) are concentric. An abrasive body according to claim 1 or claim 2 wherein the elongate projection (160) is defined by sides (166) which are parallel. An abrasive body according to any one of claims 1 to 3 wherein the sides (166) of the elongate projection (160) slope from the interface (134) to a base surface (168) of the projection (160). An abrasive body according to any one of claims 1 to 4 wherein the elongate projection (160) extends from the interface (134) into the substrate (132). An abrasive body according to any one of claims 1 to 5 wherein the elongate projection (160) extends from the interface (134) into the substrate (132) to a depth greater than that of the continuous border (146). An abrasive body according to any one of claims 1 to 6 wherein the crescent-shaped projections (152,154) extend from the interface (134) into the substrate (132). An abrasive body according to claim 7 wherein the elongate projection (100) extends from the interface (134) into the substrate (132) to a depth greater than that of both the continuous border (146) and the crescent-shaped projections (152,154). An abrasive body according to any one of the preceding claims which is circular in plan. An abrasive body according to any one of the preceding claims wherein the substrate (132) is a carbide selected from cemented titanium carbide, cemented tungsten carbide, cemented tantalum carbide, cemented molybdenum carbide and mixtures thereof. An abrasive body according to any one of the preceding claims wherein the abrasive layer (130) is an abrasive compact or a layer of CVD diamond. An abrasive body according to any one of the preceding claims which is a tool insert.

Inventors: ADIA MOOSA MAHOMED, VAN JAARSVELDT HENDRIK JACOBUS, ADIA, MOOSA MAHOMED, VAN JAARSVELDT, HENDRIK JACOBUS
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMONDS (PROPRIETARY) LIMITED
Application year: 1999
Main classification: B23B27
IPC codes: B23B51, B24D99