A METHOD OF MAKING DIAMOND PARTICLES AND METAL BOND ABRASIVE BODY PRODUCED THEREWITH

Abstract: An MD diamond particle which is characterised by having striated surfaces. These particles key better in a metal matrix and so also provided is a metal bonded abrasive body containing these particles. The particles are made by the known method of making MD diamond particles, save that a particular alloy is used as solvent.

Description: DESCRIPTIO "DlLiOND PARTICLES" THIS invention relates to diamond particles and to a method of raking such particles. Diamond particles of the MD (Metal Bond) type and of the SD (Saw Diamond) type are used extensively in industry. Both particle are strong, blocky crystals of cubo-octahedral habit and having well-defined cubic and octahedra smooth faces. Such particles of synthetic origin have only a small metal inclusion content and are yellow in colour. The larger particles, i.e. of size greater than 250 microns are of the SD type and the smaller particles, i.e. the particles of size less than 250 microns, are of the MD type. MD diamond particles are used in metal bond grinding wheels and other such metal bond abrasive tools, while SD particles are used in saw segments and impregnated drill bits. Metal bond grining wheels, saw segments and other metal bond abrasive bodies have as a common characteristic the fact that the bonding matrix is a metal or alloy. Metal bond grinding wheels consist of a hub to which is bonded a peripheral grinding or working portion. The peripheral grinding portion comprises a mass of diamond or like abrasive particles held in a metal or alloy matrix. The concentration cf abrasive in the grinding portion is typically in the range 20 to 35 percent by volume. Saw segments also comprise a mass of diamond or like abrasive particles held in a metal or alloy matrix, the concentration of abrasive typically being in the range 3 to 10 percent by volume. Examples of matrices for metal bond abrasive bodies are bronze, cobalt, nickel and iron and alloys containing any one of these metals. Hereinafter the term "MD diamond particle" will be used to cover both MD and SD particles. The present invention provides, according to one aspect, a novel MD diamond particle having striated (or grooved) surfaces. It has been found that such particles are superior to conventional DID particles because they key better to a metal matrix because of the striated surfaces. The invention also relates to the use of these particles in a metal bond abrasive body. The invention, according to this aspect, provides a metal bond abrasive body comprising a mass of MD diamond particles having striated surfaces held in a metal matrix. The metal matrix may be a pure metal or an alloy. The concentration of diamond particles in the body will depend o the nature of the body as described above. The diamond content may be made up solely of the striated MD particles or the diamond content may be a mixture of striated MD particles and standard smooth surfaced MD particles. The metal bond abrasive body will typically be the working portion of a metal bond abrasive wheel or a saw segment or an impregnated drill bit. The invention will further be described with reference to the accompanying drawings in which : Figure 1 is a iron/cobalt/nickel phase diagram; Figure 2 is a carbon temperature/pressure phase diagram; Figure 3 is a photograph of a striated MD diamond particle of the invention; Figure 4 is a photograph of a standard smooth surfaced MD abrasive particle; and Figure 5 illustrates graphically certain comparative data. The striated MD diamond particles of the invention are made in the conventional manner, save that a particular metal solvent is used. The particular metal solvent is an alloy of iron with nickel and/or cobalt. The useful alloys are those iron-rich alloys falling within the area A B C of Figure 1 and those falling anywhere in the phase diagram which contain a suitable amount of a good carbide-forming element such as tantalum,manganese, chromium, silicon, tungsten, molybdenum, vanadium and titanium or mixturcsof two or more of these elements. The amount of the carbide-former present will depend on its tendency to form carbides and the amount of iron present in the alloy. The amount of carbide former will however, typically be in the range 10 to 0,1%, preferably 5 to 0,1, ó,by weight of the alloy. The striated MD diamond particles are made by subjecting a carbonaceous material such as graphite in the presence of the alloy to elevated conditions of temperature and pressure suitable for MD diamond formation. This method forms another aspect of the invention. As is known in the art, growth of MD diamond particles takes place in a region close to the Berman-Simon line in the carbon phase diagram illustrated in the attached Figure 2. Typically the graphite and alloy in powder form are placed in the reaction capsule of a conventional high temperature/pressure apparatus and then the mixture in the reaction capsule subjected to the elevated conditions of temperature and pressure. These elevated conditions are typically a temperature of 15000C and a pressure of 55 kilobars. For smaller particles of less than 250 microns these elevated conditions are maintained for a period of 1 to 20 minutes while for larger particles greater than 250 microns these elevated conditions are maintained for a period in excess of 20 minutes. Examples of suitable alloys in the practice of the invention are as follows (all percentages being by weight): Percent Percent Percent 1. 70 Fe 30 Co 2. 80 Fe 20 Ni 3. 50 Fe 49 Co 1 Va 4. 49 Fe 49 Co 2 Si 5. 49,75 Fe 49 Co 0,25 Ti 6. 45,5 Fe 45,5 Co 9 Cr The photograph of the attached Figure 3 illustrates a typical striated MD particle of the invention while the photograph of Figure 4 illustrates a typical smooth-surfaced MD particle of the prior art. An example of the invention will now be described. Graphite powder and powdered iron/cobalt alloy, containing 70 percent by weight iron and 30 percent by weight cobalt, were placed in a suitable reaction capsule which was then placed in the reaction zone of a conventional high temperature/ pressure apparatus. The temperature and pressure of the contents of the capsule were raised until a temperature of 15000C and a pressure of 55 kilobars was reached. These elevated conditions were maintained for a period of 40 minutes. The temperature was allowed to drop to ambient and the pressure was released. Recovered from the capsule, using conventional recovery techniques, was a mass of MD diamond particles having striated surfaces. The particles had a size in the range 350 to 420 microns. The striated MD particles were incorporated in a plurality of saw segments. The concentration of diamond in the saw segments was 7,5 percent by volume and the metal matrix was cobalt. The segments were then brazed to a set of saw blades in the conventional manner. Similar segments were made using standard smooth surfaced MD diamond particles of the same strength, shape, size and metal inclusion of the striated particles. These segments were also brazed to a set of saw blades. The two sets of saw blades were tested in the cutting of Paarl and Norite Granites under the following conditions: Paarl Norite Blade Speed 1900 r.p.m; (35m/s) l900 r.p.m. (35m,s) Depth of Cut 10 mm 15 mm Speed of Cut 2m/min 2m/min Cutting Rate 200 Cm2/min 300 Cm2/min Water Flow Rate 80 1/mien 80 1/mien No. of Cuts/Slot 6 4 No. of Slots/test 8 8 Amount of Granite O.96m2 O.96m2 removed/test The results of these cutting tests are shown graphically in Figure 5. Figure 5 compares two characteristics called "rough" and "deep hole". The characteristic "rough" is a measure of the amount of particles which exhibited rough surfaces after the test. The roughness resulted from the particle being firmly held in the matrix and wearing during cutting. The characteristic "deep hole" is a measure of the amount of holes produced in the saw segments resulting from pull-out of diamond particles. The hicker the "rough" value and the lower the "deep hole" value the firmer the particle was held in the matrix. It can clearly be seen from Figure 5 that the striated particles were neld more firmly in the metal matrix than were the standard smooth-surfaced particles.

Claims: CLAIMS: - 1. An MD diamond particle characterised by having striated surfaces. 2. A method of making a MD diamond particle having striated surfaces comprising subjecting a carbonaceous material in the presence of a metal alloy to elevated conditions of temperature and pressure suitable for MD diamond formation, characterised in that the alloy is selected from an iron-rich alloy falling in the area A B C of the attached Figure 1 and an alloy of the attached phase diagram of Figure 1 containing a suitable amount of a good carbide-forming element. 3. A method of claim 2 wherein the good carbide-forming element is selected from the group of tantalum, manganese, chromium, silicon, tungsten, molybdenum, vanadium and titanium and a mixture of two or more of these elements. 4. A method of claim 3 wherein the carbide-forming element is present in the alloy in an amount of 10 to 0,1% by weight. 5. A method of claim 3 wherein the carbide-forming element is present in the alloy in an amount of 5 to 0,1% by weight. 6. A method of claim 2 wherein the alloy is selected from the following alloys, all percentages being by weight: Percent Percent Percent 1. 70 Fe 30 Co 2. 80 Fe 20 Ni 3. 50 Fe 49 Co 1 Va 4. 49 Fe 49 Co 2 Si 5. 49,75 Fe 49 Co 0,25 Ti 6. 45,5 Fe 45,5 Co 9 Cr A method of any one of claims 2 to 4 wherein the carbonaceous material is graphite. 8. h metal bond abrasive body comprising a mass of diamond particles having striated surfaces held in a metal matrix. 9. A metal bond abrasive body of claim 8 which is a saw segment or impregnated drill bit. 10. A metal bond abrasive body of claim 8 which is the working portion of a metal bond grinding wheels.

Inventors: DAVIES, GEOFFREY JOHN
Applicants: DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1980
Main classification: C09K3
IPC codes: B01J3, C01B31, C04B35, B24D3, C09K3