Wear rate reductions in carbon brushes conducting current and sliding against wavy copper surfaces

Wear tests are presented in which a carbon brush, loaded by a constant force spring, conducts current and slides against smooth and wavy copper rotors. The wavy rotors possessed surface waves of tens to hundreds of microns. With brush current varying from zero to 40 amperes, carbon brushes slid over the smooth and wavy rotors and wear rates (μgm/sec) were plotted versus rotor speed. Wear rates on the wavy rotor were generally less than wear rates on the smooth rotor at certain rotor speeds. Evidence suggests that wear rates were most reduced at those rotor speeds where surface waves on the wavy rotor passing beneath the brush caused the brush-stiffness-rotor system to resonate. Studies of contact voltage drop suggest that under these resonant conditions, the brush and rotor stayed connected. Also, no evidence of arcing or micro-arcing was found on the copper track. This study shows appreciable reductions (up to 50%) in wear rate possible on brush rotor systems by prescribing tiny surface waves on the rotor and running the rotor at speeds such that the surface waves induce micro-vibrations and resonance.