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Berlin

CERAMIC bearings can be used safely in industry now that German researchers
have developed a computer model to predict when they are close to cracking up.
The model has been developed by researchers at the Fraunhofer Institute for
Mechanics of Materials in Freiburg.

Bearings made from ceramic materials such as silicon nitride are much admired
because the material is harder and lighter than steel, so the bearings last
longer. Ceramic materials can also be immersed in corrosive liquids, unlike
steel, and they require less lubrication.

Although hybrid bearings made of ceramics and metal are becoming more common,
few companies have been willing to adopt bearings made completely from ceramics.
Industrial engineers “don’t trust them,” says Michael Rombach from the
Fraunhofer Institute. “They feel that the bearings cannot be safe.”

Ceramic materials are more brittle than steel and can fail suddenly and
catastrophically. Engineers have limited experience with such materials and
cannot predict how they will behave.

But Rombach and his colleagues, working together with the company Cerobear,
based in Herzogenrath, near Aachen, have removed some of the guesswork. They
loaded bearings to their breaking point, and compared the laboratory results
with theoretical models. The result is a computer program that predicts the load
that can be carried by a ceramic bearing of any size or shape.

Rombach says all-ceramic bearings could have a bright future in the chemical
or food processing industries. Steel bearings used in industrial pumps, for
instance, need to be sealed off from food for reasons of hygiene, and from
corrosive liquids to protect the bearing. A ceramic bearing can be immersed in
such liquids with the liquids providing the lubrication.

William Coblenz, the Pentagon official responsible for research on ceramic
bearings, says that the US military is beginning to adopt hybrid bearings.

Coblenz says hybrid rollers eliminate the most common problem with metal
bearings—lubrication failure. When this occurs, the metal rollers become
welded to the surrounding metal surface. But at present, all-ceramic bearings
are not widely used. “The only place we’re looking at all-ceramic bearings is in
instruments like gyroscopes,” says Coblenz.