The choice of diamond is an expensive constructional solution, but essential for increased wear resistance of the dressing tool. In addition to the classical SD-grits, there are also MCD and CVD logs, PCD dressing pieces, etc. The application of HP/HT diamonds synthesized at 1600вЊ and 7 GPa has been highly successful over the 25 years or more for dressing tools. In most situations, natural or synthetic diamonds form the basic component for the active cutting surface of a dressing tool. Lower-quality stones may have been processed by either crushing and/or ball-milling, or even reclaimed from old form rolls or drill bits where they have previously been subjected to high temperatures or severe conditions. The highest quality stones are as-mined virgin material. Here, the quality of the end product depends on the reliability of the diamond source and of the ability of the toolmaker to sort diamonds according to requirements. Although significant quantities of processed material are still used in grinding wheel applications, it is the larger stones used in single-point and form-roll dressing tools that are of most significance. With this type of economic pressure it is not surprising that the diamonds used by industry are those rejected by the gem trade because of either color, shape, size, crystal defects such as twins or naats, or inclusion levels, or are the processed fragments, for example, from cleaving gems. Very small gem-quality stones, once considered too small for jewelry and used in profiling dressing discs, are now being cut and lapped by countries such as India. The demand for diamonds for jewelry is such that premium stones used in the 1950s for single-point tools are more likely now to be used in engagement rings. If anything, the real cost of natural diamond has actually increased especially for higher quality stones. Due to this, synthetic diamonds are retained well in resinoid bonds and perform better than natural diamonds by 30% up to 100%.Дespite the dramatic growth in synthetic diamond, demand for natural diamond has not declined. These are more friable and have coarser faces as compared to natural diamond. Conversely, there is a good interaction between resin bond and metal-cladding, increasing the effective surface of the grit.Д®arly synthetic diamonds were obtained by converting graphite at 1500вЊвЂ“3000вЊ (2800вЏвЂ“5500вЏ) and 5.2 to 10.35 MPa (0.75 to 1.5 Г— 10 6 psi), in the presence of catalysts such as iron, chromium, nickel, titanium, radium, and cobalt. The surface tension of diamond grits worsens the contact characteristics between resin and diamond, making difficult the extraction of worn diamond grits from the bond. Metal-clad polycrystalline grits provide the possibility of high stock removal rates. Weak crystals used in resinoid grinding wheels are free-cutting. These are very prone to fragmentation and partial break-up with dark spots within the grits that correspond to metallic inclusions. Due to the crowding in the melt, the normal growth pattern is inhibited, so grits having undefined geometric shapes are obtained that look like an agglomerate of smaller crystals. Polycrystalline grits that are highly friable are produced by greatly accelerating the nucleation rate within the press so the diamond nuclei precipitate from the melt in a large number. The almost perfect crystals are obtained through a slow growth, low-density nucleation process, with limited metallic inclusion and little or low interaction between various grits that are growing within the melt. The easily recognizable cubic or cubo-octahedral shape reflects the characteristic crystallographic structure of diamond.

Monocrystalline grits are utilized for particularly demanding applications. Synthetic diamond may be monocrystalline or polycrystalline. Ichiro Inasaki, in Tribology of Abrasive Machining Processes, 2004 11.3.2 Synthetic Diamond

Diamond dimensions 260