Coated gearings and bearings optimised for environmentally acceptable lubricants

Gearings and bearings are machine elements that are subjected to heavy tribological stresses. The pressures are high in the rolling contacts of these machine elements, and this leads to slippage between the surfaces of the contact partners. Correspondingly, the demands on the lubricants are also quite high. Nowadays, additives are used to reduce the friction and wear. However, the biodegradability of additivated lubricants is often not known, although the use of such lubricants can be critical for the environment. The objective of the investigations described in the present paper is to find a way of using lubricants with as few additives as possible but without decreasing the capability, reliability, and life of the machine elements. Thin coatings seem to be a good solution to substitute for the additives. The wear protection of coatings is investigated here with respect to gearings and spindle bearings for machine tools.