German researchers have managed to produce hollow metallic spheres a few millimetres in diameter which could be used to produce lightweight bearings which would be especially attractive for transport applications.

“For the first time we’ve been able to produce hollow metal spheres in the required diameter of just 2–10mm,” says Dr-Ing Hartmut Göhler, project manager at the Fraunhofer Institute for Manufacturing and Advanced Materials (IFAM) in Dresden. “The hollow spheres are 40–70% lighter than solid ones.”

The process starts with polystyrene balls which are lifted and held by an air current over a fluidised bed while a mixture of metal powder and a binder is sprayed onto them. When the metal layer is thick enough, it is heated to evaporate the organic components, the polystyrene and the binder. A fragile ball of metal remains.

This is sintered at just below melting temperature, and the metal powder granules bind together to form a hard shell which is stable enough to be ground. The wall thickness can be set to between a few tenths of a millimetre and one millimetre.

Göhler sees the technique having applications wherever a low mass inertia is required. “Hollow spheres will create applications which have not been possible up to now,” he predicts. The researchers have already produced steel spheres, and plan to work with other metals such as titanium and various alloys in future.