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¨C10mm,¡± says Dr-Ing Hartmut Göhler, project manager at the Fraunhofer Institute for Manufacturing and Advanced Materials (IFAM) in Dresden. ¡°The hollow spheres are 40¨C70% 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
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