Abrading ultra-hard stones

Abstract: An ultrahard stone, such as a diamond gem stone, is cut or kerfed by moving the cutting edge of a diamond compact relative to and in contact with the stone. The diamond compact may be in the form of a disc with with a cutting edge thickness of 0.5 to 1 mm. Preferably, the diamond compact is thermally stable at 1200°C in an inert or non-oxidising atmosphere.

Description: This invention relates to the abrading of diamond stones. Diamond gem stones may be cut into a variety of shapes and sizes depending on the applications to which they are to be put. For example, thin slivers of diamond may be cut from a gem stone diamond for use as surgical blades. The cutting tool which is generally used is a phosphor-bronze disc having fine diamond particles embedded in a peripheral cutting edge. A limitation of this tool is that cutting can only be effected along certain soft planes of the diamond. Kerfing is a process whereby a shallow groove is cut into a diamond stone. Kerfing is usually carried out using a phosphor-bronze disc as described above. GB-A-2 078 572 discloses a method of kerfing a gem stone, comprising feeding a moving saw blade with respect to the stone until the saw blade comes into contact with the surface of the stone; ceasing the feed and holding the stone stationary with respect to the saw blade for a substantial period of time, so that a very small groove is cut in the surface of the stone; and slowing feeding the saw blade with respect to the stone to cut a kerf at the position of said groove. EP-A-0 208 414 discloses a composite diamond abrasive compact comprising a thermally stable diamond compact comprising bonded diamond forming a coherent, skeletal mass and a second phase, which compact is bonded directly to a cemented carbide substrate. SUMMARY OF THE INVENTION The present invention provides the use of a diamond compact in the cutting or kerfing of a diamond stone. The invention is as set forth in Claim 1. DESCRIPTION OF EMBODIMENTS Diamond compacts are well known in the art and comprise a mass of diamond particles bonded into a polycrystalline hard conglomerate. The diamond content of compacts is 70 percent by volume or higher. Compacts are made under conditions of elevated temperature and pressure similar to those used to synthesise diamond. Diamond compacts may contain a second phase which consists of or contains a diamond catalyst. Such diamond compacts are on the market and are described, for example, in US Patent Specifications Nos 3,745,623 and 4,063,909. Diamond compacts of this type are usually prone to degradation at temperatures above 750 to 800°C. Diamond compacts are also known which are thermally stable at temperatures of 1200°C in an inert or non-oxidising atmosphere. These compacts will either have no second phase or a second phase which does not adversely affect the diamond at higher temperatures. An example of a thermally stable diamond compact which contains a second phase is one wherein the second phase consists essentially of silicon in the form of the metal and/or carbide. Thermally stable diamond compacts are described in US Patent Specifications Nos 4,224,380 and 4,534,773 and British Patent Specification No 2,158,086. Thermally stable diamond compacts are preferred in the practice of the invention. The polycrystalline nature of a diamond compact allows it to be used to cut or kerf a diamond stone in any direction which gives it an advantage over the known phosphor-bronze disc. Further, cooler cutting can be achieved with less risk of damage to the stone and the cutting process is not affected by imperfections in the stone. The invention lies in the use of a diamond compact in the cutting or kerfing of a diamond stone. The steps used in the cutting and kerfing of the diamond stone will be the same as those conventionally used. Generally, the diamond compact will be provided in the form of a disc with a fine cutting edge. Typically this cutting edge will have a thickness of no more than 0,5 to 1 mm. The compact will be rotated, e.g. at a rotational speed of 80 to 300 rpm, and the rotating compact edge brought into contact with the diamond stone and progressively moved therein. Slivers or slices can be cut off the stone or a shallow groove can be cut therein.

Claims: Use of a diamond compact, in the form of a disc having a cutting edge on the periphery thereof and rotatable about the longitudinal axis of said disc, in cutting or kerfing a diamond stone. Use according to Claim 1 wherein the diamond compact is thermally stable at a temperature of 1200°C in an inert or non-oxidising atmosphere. Use according to Claim 1 or Claim 2 wherein the cutting edge has a thickness of 0.5 to 1 mm.

Inventors: BURNS ROBERT CHARLES, LEVITT CHARLIE MAURICE, TOLKOWSKY GABRIEL SHRAGA, BURNS, ROBERT CHARLES, LEVITT, CHARLIE MAURICE, TOLKOWSKY, GABRIEL SHRAGA
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1989
Main classification: B28D5
IPC codes: B28D5