Bearings are usually lubricated with mineral oil-based lubricants, preventing wear on the bearing from metal on metal contact. In Germany, approximately one million tons of lubricant are used every year. The manufacture, application and disposal of oil is a burden on the environment.
Introducing water-based lubricants would greatly benefit environmental protection. But until now, the fact that metal parts corrode when they come into contact with water has been a major obstacle. A working group at the Fraunhofer IWM, MicroTribology Centrum μTC, in Freiburg has succeeded in using additives to change water in such a way that it could be used as a lubricant at some point in the future. This meant a double success for Dr. Tobias Amann and his colleagues at the Fraunhofer IWM: first, the lubrication achieved is much better, since water is not as viscous as oil. Second, corrosion is prevented.
The researchers developed the details of their process using a slide bearing, a bearing which resembles a ring that surrounds a rotating steel shaft. The ring is made of several layers structured from the outside to the inside as follows: a sleeve surrounding the bearing, a layer of aluminum and a layer of sintered metal that surrounds the shaft itself. The trick is that the inner sintered layer is traversed by a small channel which lets water flow between the rotating shaft and the outer aluminum layer. This direct connection is decisive in the electrochemical process, based on the fact that an electric voltage arises between a base metal such as aluminum and a more precious metal such as iron, even without having to apply any kind of external electric field.