Fraunhofer IWM scientists have developed a new Eco-friendly approach for lubricating machine bearings in factories.
Machine bearings are usually lubricated with mineral oil-based lubricants; these lubricants help prevent wear on the bearing from metal on metal contact.
They are nevertheless one of the major contributors of air and water pollution in the world.
Introducing water-based lubricants could greatly benefit the environment – provided we find a solution to prevent corrosion that usually occurs when metal parts come into contact with water.
Now scientists from Fraunhofer IWM have found a way to remedy this by using additives to change water in such a way that it could be used as a lubricant.
The benefits according to Dr. Tobias Amann and his colleagues are two-fold: first, the lubrication achieved is much better since water is not as viscous as oil; and second, it helps prevent corrosion.
The IWM team 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 electro-chemical process; an electric voltage arises between a base metal even without having to apply any kind of external electric field.
The electric voltage arising between the aluminum in the slide bearing, and the iron in the shaft, are essential for creating the water lubricant.
“We mix what are called ionic liquids into the water,” explains Dr. Tobias Amann. “The ionic liquids are fluid salts which contain anions and cations.”
These ions are rearranged in the electric field and then collect on the interior side of the sintered metal ring in such a way that their ends are pointing upward, toward the rotating shaft. This forms a kind of galvanically generated protective layer on which the shaft can glide.
The ion-water mixture is better for the environment than oil, and it also helps to make slide bearings even more efficient.
The new process also ensures that corrosion is avoided. Normally the oxygen in the water reacts with steels containing iron, ultimately resulting in rust. The electric field prevents this from happening.