Commutation with metal fiber brushes

Two principal explanations are given for why metal fiber brushes could be unsuitable for commutation, thereby severely restricting their possible range of technological application. These are (1) high wear rates due to fiber breakage caused by mechanical chopping action of commutator bar edges, and (2) fast erosion at the trailing edges due to arcing, which also affects monolithic brushes, but to a lesser degree. Recent experiments with 50- mu m-diameter bare and silver-plated copper fiber brushes in a protective argon atmosphere, using simulated commutation and running them as working brushes in an electromotor, suggest that these problems may be overcome by the use of much thinner fibers than the >or=100- mu m-diameters that have been used in the past. No fiber breakage was observed, arcing was only moderately stronger than with carbon brushes, and the total dimension-less wear rate in the motor was only about twice that on a polished copper rotor under otherwise comparable conditions.<>