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Diamond
Diamond is pure carbon and the hardest of all known materials. Due to its hardness, diamond has become increasingly important for machining in state-of-the-art technology. Today synthetic diamond grit is the material preferably used in abrasive engineering practice. The starting substance is carbon in the form of graphite. The synthesis occurs after extreme pressures and temperatures are applied. Due to its fine crystalline structure and the resulting properties, e.g. maximum abrasion resistance and edge-holding quality, diamond is superior to all other abrading media. Diamond belongs to the “super hard” group of cutting materials.
Diamond is restricted by its thermal load capacity if subjected to temperatures exceeding 700°C, e.g. when grinding steel materials
Applications
Materials that can readily be machined with diamond tools include: welded and thermal sprayed alloys, electrocarbons, precious and semiprecious stones, ferrite, fireproof materials, glass-fiber and carbon-fiber reinforced plastics, glass, graphite, semiconductor materials, hard metal, ceramics, natural and artificial stones, oxide ceramics, porcelain and quartz. In exceptional cases cast steel and gray cast iron can also be machined with diamond tools.
CBN (cubic boron nitride)
CBN is a 100% synthetic product which is the second hardest abrading medium after diamond. Due to its chemical-physical properties, CBN is primarily used to process hard-to-machine steels with a high alloy content and/or hardness. The CBN abrasive grain is manufactured using virtually the same synthesis technique as for synthetic diamond abrasive grain. The starting substance for CBN is hexagonal boron nitride. Like diamond, CBN belongs to the “super hard” group of cutting materials.
Application
CBN can withstand temperatures of up to 1300°C and has a slight tendency to react chemically to metals. Due to its fine crystalline structure and the resulting properties, e.g. a high abrasion resistance and edge-holding quality, it offers advantages in comparison to conventional abrading media, especially for grinding hard-to-machine and hardened steels >55HRC, e.g. HSS or chrome alloyed steels. Lowering the temperature during grinding prevents changes in the structure of the material edge zone, and therefore grinding cracks and soft skin formation. High accuracy regarding dimension, shape and concentricity as well as long tool life can thus be achieved using CBN grinding tools.
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