Manufacture of two-component products

Abstract: A method is provided for making a product which comprises two layers of different materials bonded to each other. The product will typically be a composite abrasive compact. The method includes the steps of providing a mould (10) having an internal base surface (16) profiled to a desired shape, making a first slurry of a particulate material in a liquid medium which is capable of setting at least to a green state, introducing the slurry (20) into the mould (10), causing the medium to set to produce at least a green state mass (20), removing the green state mass (20) from the base (16), that green state mass (20) having a surface complementary to the profiled internal base surface (16) of the mould (10), depositing, on the profiled complementary surface of the green state mass, a layer of a second slurry containing a different particulate material in a liquid medium which is capable of setting at least to a second green state, and causing the medium of that second slurry to set to produce at least a second green state mass (26) which is bonded to the first green state mass (20).

Description: This invention relates to the manufacture of abrasive products. Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. The abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline hard conglomerate. The abrasive particle content of abrasive compacts is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable. Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate. Such supported abrasive compacts are known in the art as composite abrasive compacts. The composite abrasive compact may be used as such in the working surface of an abrasive tool. Examples of composite abrasive compacts can be found described in United States Patent Specifications Nos. 3,745,623, 3,767,371, 3,743,489 and 4,063,909. Composite abrasive compacts are generally produced by placing the components, in powdered form, necessary to form an abrasive compact on a cemented carbide substrate. This unbonded assembly is placed in a reaction capsule which is then placed in the reaction zone of a conventional high pressure/high temperature apparatus. The contents of the reaction capsule are subjected to conditions of elevated temperature and pressure at which the abrasive particles are crystallographically stable. Other effective cubic boron nitride abrasive bodies which do not contain as high an abrasive particle content as abrasive compacts are also known and used in the art. Such abrasive bodies generally comprise a sintered body containing 40 to 60 volume percent of cubic boron nitride particles uniformly dispersed in a continuous ceramic bonding matrix. These abrasive bodies are also made under temperature and pressure conditions at which the cubic boron nitride is crystallographically stable. United States Patent Specification No. 4,469,802 describes such a body. European Patent Publication No. 0278703 published 17 August 1988 describes and claims a method of making an abrasive body which comprises a layer of bonded ultra-hard abrasive particles bonded to a substrate, including the steps of providing the substrate, depositing a layer of the components necessary to form the layer of bonded ultra-hard abrasive particles, in particulate form, in an organic binder on a surface of the substrate, and subjecting the substrate and layer to conditions of elevated temperature and pressure at which the ultra-hard abrasive particle is crystallographically stable. The layer of particulate components may be deposited on the surface of the substrate by suspending the particulate components in a liquid containing the organic binder dispersed or dissolved therein, depositing the liquid suspension on the surface and removing the liquid from the suspension. The layer of bonded ultra-hard abrasive particles will typically be a diamond or cubic boron nitride abrasive compact. EP-A-O 246 438 discloses a method of forming an article comprising the steps of (a) forming a mixture comprising (1) powders selected from the group of metal powders, ceramic powders, and mixtures thereof, (2) a gel-forming material having a gel strength, measured at a temperature between 0°C and about 22°C on a gel consisting essentially of about 4 wt.% of the gel-forming material and water, of at least about 100 g/cm², and (3) a gel-forming material solvent, and (b) moulding the mixture at a temperature sufficient to produce a self-supporting article comprising the powders and a gel comprising the gel-forming material. The preferred gel-forming material is an agaroid, and the preferred moulding method is injection moulding. According to the present invention, there is provided a method as claimed in Claim 1. The two layers may have different characteristics such as abrasiveness, density, thermal conductivity or the like. The invention has particular application to the manufacture of composite abrasive compacts. In this case, the particulate material of the one slurry will be capable of producing cemented carbide while the particulate material of the other slurry will be capable of producing an abrasive compact. The two-component green state product will be subjected to conditions of elevated temperature and pressure suitable to produce an abrasive compact. Figures 1 to 3 illustrate a mould in various stages during the method of the invention. The liquid medium is preferably water containing a suitable binder dissolved or dispersed therein, the binder being capable of forming a gel on application of heat. Such binders should decompose or volatilise at a temperature of about 350°C or lower. Examples of such binders are organic binders such as cellulose ethers or esters. An example of a particularly suitable binder is methyl cellulose. Methyl cellulose forms a gel at a temperature of between 50 and 100°C. When the two-component abrasive product produced is a composite abrasive compact, the water and binder must be removed prior to the application of the elevated temperature and pressure conditions. This removal may be achieved by heating. Preferably the heating takes place in two stages. In the first stage, the water is removed by heating the green state mass or masses to a temperature above 100°C. Thereafter, the binder may be volatilised or decomposed by heating the green state mass or masses to the appropriate temperature to cause this to happen. For the manufacture of composite abrasive compacts, the conditions of elevated temperature and pressure which are used are typically a pressure in the range 25 to 70 kilobars and a temperature in the range 1400 to 1600°C. Typically, these elevated conditions are maintained for a period of 10 to 30 minutes. The abrasive particles of the abrasive compact may be self-bonded or there may be present a second phase. It is preferred that the abrasive compact has a second phase. When the abrasive particles are diamond, the second phase will typically be, or contain, a catalyst or solvent for diamond manufacture such as cobalt. When the abrasive particle is cubic boron nitride, the second phase will typically contain or consist of aluminium, an aluminium alloy or ceramic compound. The particle size of the components in the slurries will vary according to the nature of the product being produced. Where the product is a composite abrasive compact, the particles will generally be fine, for example less than 150 microns. The invention provides an effective way of producing a two-component product which has an interface between the two components profiled in the suitable configuration. For example, the interface may be corrugated, scalloped, grooved or have any other similar shape. An embodiment of the invention will now be described with reference to the accompanying drawing. Referring to Figure 1, there is shown a mould consisting of two parts - a sleeve 10 and a removable base 12. The sleeve 10 is of right circular cylindrical shape. The base 12 has an upwardly projecting portion 14 which is received with a snug fit in the sleeve 10. The top surface 16 of the projecting portion 14 has a number of upwardly projecting ridges 18. A first slurry is made consisting of a mass of carbide and cobalt powders suspended in water which contains methyl cellulose dissolved therein. This slurry 20 is poured into the mould to fill the sleeve 10, as illustrated by Figure 2. The slurry 20 is heated to a temperature of between 50°C and 100°C to cause the methyl cellulose to gel producing a green state mass. The base 12 is removed from the sleeve and the sleeve inverted, as illustrated by Figure 3. The green state mass 20 has a plurality of grooves 22 formed in the upper surface 24, those grooves 22 having the same shape as the ridges 18. A second slurry is made. The second slurry consists of a mass of diamond particles suspended in water containing methyl cellulose dissolved therein. The slurry is poured on to the surface 24 so that it fills the grooves 22 and the remainder of the sleeve 10 (see Figure 3). The slurry is heated to a temperature of between 50°C and 100°C to cause the methyl cellulose to gel producing a second green state mass 26 which is bonded to the first green state mass 20. The two-component green state product is removed from the sleeve and placed in an appropriate capsule or canister for insertion in the reaction zone of a high temperature/high pressure apparatus. The canister and its contents are heated, for example, in an oven, to a temperature above 100°C to drive off the water from the green state masses 20, 26. Thereafter the canister and contents are heated to a temperature of approximately 350°C to cause the methyl cellulose to decompose. The loaded canister is placed in the reaction zone of a high temperature/high pressure apparatus and subjected to a temperature of 1500°C and a pressure of 55 kilobars and these conditions are maintained for a period of 10 minutes. Recovered from the reaction zone is a composite abrasive compact comprising a diamond compact layer 26 bonded to a cemented carbide substrate 20. This composite compact is of the groove-cutter type. In an alternative method, the green state cemented carbide producing slurry 20 is sintered under suitable conditions to produce cemented carbide from the first green state mass prior to introduction of the diamond-containing slurry into the sleeve. The remainder of the steps are as described above.

Claims: A method of making a product comprising two layers of different materials bonded to each other, includes the steps of providing a mould (10) having a removable base (12) and an internal surface (16) profiled to a desired shape on said removable base, making a first slurry of a particulate material in a liquid medium which is capable of setting at least to a green state, introducing the slurry into the mould (10) so that the slurry contacts the profiled surface (16), causing the medium to set to produce at least a green state mass (20), removing the green state mass (20) from the profiled surface (16) by removing said base (12) from said mould (10) and inverting said green state mass (20), that green state mass (20) having a surface complementary to the profiled surface, depositing, on the complementary profiled surface of the green state mass, a layer of a second slurry containing a different particulate material in a liquid medium which is capable of setting at least to a green state, and causing the medium of that second slurry to set to produce at least a second green state mass (26) which is bonded to the first green state mass (20). A method according to Claim 1 wherein the two layers (20, 26) have different abrasiveness, density, thermal conductivity or the like. A method according to Claim 1 or Claim 2 wherein the liquid medium is water containing a suitable binder dissolved or dispersed therein, the binder being capable of forming a gel on application of heat. A method according to Claim 3 wherein the binder is capable of volatilising or decomposing at a temperature of about 350°C or lower. A method according to Claim 3 or Claim 4 wherein the binder is an organic binder selected from cellulose ethers and esters. A method according to Claim 5 wherein the binder is methyl cellulose. A method according to any one of Claims 3 to 6 wherein the slurry or slurries are caused to set to a green state by application of heat thereby causing the binder to form a gel. A method according to any one of the preceding Claims wherein one layer (20) of the product is cemented carbide and the other layer (26) of the product is an abrasive compact and the product is produced from the two-component green state product by first removing the liquid medium from the green state product and thereafter subjecting that product to conditions of elevated temperature and pressure suitable to produce an abrasive compact. A method according to Claim 8 wherein the conditions of elevated temperature and pressure which are used are a pressure in the range 25 to 70 kilobars and a temperature in the range 1400 to 1600°C.

Inventors: BURNAND RICHARD PATRICK, CHAPMAN RAYMOND ALBERT, MARTELL TREVOR JOHN, PARSONS STEPHEN ANTHONY, BURNAND, RICHARD PATRICK, CHAPMAN, RAYMOND ALBERT, MARTELL, TREVOR JOHN, PARSONS, STEPHEN ANTHONY
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1989
Main classification: B23P15
IPC codes: B24D18, B28B1, B24D3, C04B35