Water as Bearing Grease

Rolling and sliding bearings are usually lubricated with various oils that pollute the environment when leaking. Institute of Mechanics of Materials. Fraunhofer IWM has developed an innovative method that allows lubricating slide bearings not with oils, but with water.

According to the Institute of Mechanics of Materials. Fraunhofer, in Germany alone, about 1 million tons of lubricant is used annually. In Russia, this figure reaches 2.5 million tons. The production, use and disposal of lubricating oils is a heavy burden for the environment.

The introduction of water-based lubricants will significantly improve environmental protection. But until now, the main obstacle was the fact that metal parts corrode upon contact with water. To solve this problem, the Fraunhofer IWM working group in Freiburg was able to develop a special bearing design that can be lubricated with water with special additives.

A sliding bearing consists of several layers: an outer sleeve ring, an aluminum layer and an inner ring that contacts the shaft. The know-how lies in the fact that there is a small channel in the inner ring, which passes water between the rotating shaft and the outer aluminum layer. This direct connection is crucial in the electrochemical process that occurs when steel and aluminum are in contact.

Turning water into a lubricant

The Fraunhofer researchers use an electrochemical reaction between aluminum in a plain bearing and steel in a shaft to turn water into a lubricant based on an ionic liquid containing cations and anions.

These ions accumulate on the inner side of the inner metal ring and form a protective layer on which the shaft can slide.

The research team has already demonstrated the viability of the process and is currently looking for partners with whom they plan to further optimize ionic liquids.

More efficient electric motors

The researchers argue that the ion-water mixture is not only environmentally friendly, but also helps to make the bearings more efficient because they are less viscous than oil. In addition, corrosion of steel surfaces is reduced.

The Fraunhofer IWM specialists also developed a new tribometer capable of monitoring metal wear and friction values directly on the plain bearing during operation.

Until now, bearing wear could only be measured by disassembling the bearing before evaluating and measuring surfaces. The new tribometer allows you to measure wear on site, not only facilitating the development of possible water-based lubricants, but also continuously monitor the condition of the bearings.

New application of the familiar principle in cathodic corrosion protection

A water lubricant in slide bearings with galvanic coupling, developed by Fraunhofer IWM, is a new application of the well-known principle: active cathodic corrosion protection. This technology prevents corrosion of metals that come in contact with water. An “sacrificial” anode is introduced into the aqueous medium, which slowly dissolves, emitting ions into the liquid during the process and creating a small flow of electrons to the metal to be protected, acting as a cathode. Then a negatively charged protective layer is formed on the metal surface, preventing tribocorrosion. This is due to the fact that positively charged cations from an ionic liquid or water lubricant accumulate on this negatively charged surface.