A particle ejection mechanism for brushwear

A hypothetical mechanism to explain wear associated with thermal mounding in carbon graphite electrical brushes is introduced. Contact between a brush thermal mound and a sliding/conducting rotor initiates a thermal cycle in which extreme temperatures inside the mound alter material property values and intensify stresses. Temperatures and stresses evolve until mound failure occurs, probably near the edge of the contact zone between the thermal mound and the rotor. The mound detaches from the brushface, and with the mechanical support provided by the mound removed, the entire brush body tilts until contact is reestablished with some other elevated portion of the brushface. A thermal mound is born, and the thermal cycle begins. Using the particle ejection mechanism as a basis, wear rates, hot spot speeds, and thermal mound lifetimes are calculated, related, and compared to experimentally obtained values. Agreement between theory and experiment is shown to be excellent. Finally, an attempt is made to demonstrate how this mechanism may account for moving hot spots, widely varying wear rates, environmental effects, and vastly different performance characteristics in electrical brushes.<
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