Commutation with metal fiber brushes

For many years it has been widely held that metal fiber brushes cannot be used on commutators because the chopping action of commutator bars would cause fiber breakage and catastrophic wear, and current surges across adjoining bars would cause severe arcing and thus fast erosion. Recent experiments with copper fiber brushes in a protective argon atmosphere, using simulated commutation as well as running them as working brushes in an electromotor, contradict both of these assumptions. No fiber breakage was observed, arcing was only moderately stronger than with carbon brushes, and the total dimensionless wear rate in the motor was only about twice that on a polished copper rotor under otherwise comparable conditions