TECHNICAL INFORMATION NORTON WINTER PRECISION TECHNOLOGY TOOL GRINDING / 155 DIAMOND CBN Concentration Carat / cm³ Volume % Concentration Carat / cm³ Volume % C50 2.2 12.5 V120 2.09 12 C75 3.3 18.75 V180 3.13 18 C100 4.4 25 V240 4.18 24 C125 5.5 31.25 V300 5.22 30 DRESSING CLEANING PROFILING SHARPENING Influences macrostructure Influences microstructure Influences microstructure Produces concentricity and grinding wheel profile Generates topography and grain exposure by eroding the bond Removes chips from chip space Need: Shape or re-shape the wheel surface Reset of the: Bond Intended Need: No change in the surface CONCENTRATION According to the Norton Winter system, the concentration value defines the volume fraction of diamond or cBN in the abrasive layer as follows: CONDITIONING Conditioning of a grinding wheel consists of dressing and cleaning: CUBIC BORON NITRIDE (CBN) Boron nitride is found in two structural modifications: Cubic boron nitride (cBN) has the zinc-blende crystal structure equivalent to diamond, and has a hardness just a little below that of diamond. The graphite-like hexagonal modification of boron nitride (hBN) is soft and is used as a lubricant. Compared to diamond, cBN has technological and economic advantages when grinding materials having a chemical affinity to carbon, such as steels and ferrous alloys. Applications for cBN are becoming increasingly economic, and cBN grinding of workpieces with hardness as low as 50 HRC have been demonstrated. DIAMOND Diamond is one of the three carbon modifications (the others are graphite and the fullerenes) and, with a Moh‘s hardness of 10, diamond is the hardest material known. The grinding (Rosiwal) hardness is 140 times higher than that of alumina. Because of its hardness and wear resistance, diamond is used for grinding hard, brittle and shortchipping materials. Examples are tungsten carbide, glass, ceramics, quarz, semiconductor materials, graphite and wear-resistant thermal spray alloys as well as hard-facing alloys, plastics with glass fiber reinforcement, and other difficult to machine materials. Both natural and synthetic diamonds are used in industrial applications. • NATURAL DIAMOND: these diamonds were created in the earth’s mantle under high pressure and temperature (1200 -1400°C). Both single crystals (octahedrons, triangles…) and crushed grit (boart) are used in industrial diamond tools. • SYNTHETIC DIAMOND: synthetic diamond grits are formed in presses in a very high pressure/high temperature (HP/HT) process, at up to 60000 bar and 1500°C, using a variety of solvent/catalyst materials which help to convert graphite into diamond. • MCD: large synthetic diamonds that are produced in a HP/HT process similar to synthetic diamond grit. • PCD: polycrystalline diamond pieces formed by sintering micronized diamond particles together with a binder under HP/HT conditions. • CVD: these diamonds are manufactured by gas phase deposition (methane, hydrogen) at low pressure using a vacuum system. These definitions are not applicable for single layer electroplated tools.
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