Patent GB-1259341-A (GB)
IPC: B24D7/00
Filed: 1969-01-07
Abstract: 1,259,341. Abrasive tools. DENTSPLY INTERNATIONAL Inc. 7 Jan., 1969 [9 Jan., 1968], No. 999/69. Heading B3D. [Also in Division C7] Abrasive particles are secured to a metallic support e.g. to form a diamond coated grinding wheel, by coating the particles and support with a high tensile metal using vapour deposition. The vaporized metal is capable of reacting chemically with the surface of the particles and metallurgically with the surface of the support. A potential is created in an atmosphere of the vapour between the vapour source and the support. The abrasive tool may be a grinding wheel, drill, burr (e.g. a dental burr), hone, saw, rotary dressing wheel etc. A support base 32 of metal, e.g. steel, is shaped and finished to provide a prepared surface. Diamond particles in a desired size range are adhered to the surface e.g. (1) by rolling the particles under pressure into the surface, (2) by adhesive, or (3) by electrically charging the base, which orientates the particles. Matrix metal 40 of high tensile strength is then vapour deposited to effect bonding; the metal in vapour state reacts with the outer surface of the diamond particles to form a thin metal carbide layer 42 with which further metal unites and also reacts with the surface of the support base to form a layer of alloy. The matrix metal is preferably a hard metal (e.g. chromium, cobalt, molybdenum, titanium, tungsten etc.). The metal vapour may be obtained from molten metal or from metal electrodes across which an arc is struck, or may be obtained from gaseous metal carbonyls or vaporized solutions of metal carbonyls in readily vaporized solvents (e.g. chromium carbonyl, cobalt carbonyl, molybdenum carbonyl, nickel carbonyl, titanium carbonyl, tungsten carbonyl), nitrosyl carbonyls (e.g. cobalt nitrosyl carbonyl), metal hydrides (e.g. titanium hydride), organometallic compounds (e.g. diphenyl[biscyclopentadienyl]titanium, biscyclopentadienyl chromium) and metal halides (e.g. beta cobalt[II]iodide, molybdenum tetraiodide). The support base is preferably preheated to a temperature slightly below that of complete decomposition of the chemical compound from which the metal is derived, the heating being performed in a vacuum or inert atmosphere. The matrix coating may be thin so that a lattice structure results. This improves chip clearance, thus reducing loading of the tool, and also aids conduction of heat from the cutting edges of the diamond particles to the support base from which it is dissipated by conduction or by the use of liquid cutting compound. The voids between the particles may be impregnated with a solid or semi-solid lubricating material. In a tool for coarse grinding, the diamond particles 38 are coated with hard matrix metal 40 to a limited extent, and are then coated with relatively soft matrix metal 46, e.g. aluminium, zinc, copper, lead, affording a limited amount of resilience or elasticity for withstanding shock. Apparatus for making a tool comprises a vacuum chamber 50 in which is a crucible 53 containing matrix metal 54 and surrounded by means such as an induction coil 55 to melt the metal and cause an ionic vapour 56 to be emitted. A negatively charged plate 58 attracts the ions away from the molten metal. An electric field is applied between an electrode 60 and the support base 32 to produce a beam of ions; which passes through an electrostatic focusing electrode 66, between a pair of vertical deflector plates 78 and between a pair of horizontal deflector plates 80, finally impinging on diamond particles 74 adhered to the support base 32 which is rotated about an axis 72.