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Sintered Corundum (Sol Gel), CERALOX
The newest member of the abrasives family is sintered corundum. The starting material is aluminium monohydrate (boehmite), which is processed to a colloidal Al2O3 dispersion (semi-solid gel), calcined (dried) and then comminuted in a crushing mill. Several sintering processes then usually follow, which impart to the grain its final strength and its hardness, which is slightly above that of white aluminium oxide. |
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Sintered corundum grinding wheels are just as suitable for standard applications as for creep feed and high-performance grinding of the most diverse materials. There are hardly any restrictions in this respect, apart from those materials for which diamond is to be used as the abrasive. Even very hard tool steels and all HSS grades can be ground astonishingly well with it. However, it cannot achieve the performance of CBN. Nevertheless, economical substitution of CBN is possible in cases where only individual components or small numbers of workpieces are to be worked.
Sintered corundum has a property foreign to other types of grain: It does not become blunt! The reason for this is the extremely small crystallite size of 0.0002 mm to about 0.0005 mm, depending on the production process. This means on average 20 to 50 times smaller crystallites compared with pure corundum. During use, grain particles (crystallites) of varying size chip off, depending on the external pressure on the grinding wheel, and immediately expose sharp-cutting points again behind them. Even if removal rates are low no blunting can be detected, which sometimes can also be a problem in respect of the surface quality which can be achieved. If the dressing infeed ad is reduced by a factor of 5 – 10 compared with that for conventional grinding wheels, sintered corundum operates in the optimum manner and even low surface roughnesses become controllable. The tool life of a sintered corundum grinding wheel can be 10 to 20 times higher than that of other conventional wheels (pure corundum, silicon carbide). However, the price is only about 1.5 to 3 times higher. It depends on the grain mixture chosen, since sintered corundum wheels in practice are usually made of grain combinations (secondary grains and/or special grinding effects), apart from small mounted grinding points. |
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