Materials Research In Sliding Electric Contacts

For more than one hundred years, painters style electrical brushes and various modifications thereof in the form of assemblies of metal wires, were universally used for sliding electrical contacts. They were replaced by monolithic graphite brushes only at the turn of the century. Monolithic graphite brushes shed Carbon particles as a result of scouring abrasion, and are transferred throughout a generator or motor by the same cooling air used to keep the current-carrying brushes cool. These particles can bridge microcircuits and/or gaps between the commutator bars, and result in the failure of electronic equipment and/or shorting across the commutator bars causing arcing in the motors/generators. Additionally, brush waste tends to embed within insulating varnishes, causing low insulation resistance and resulting in component overheating. In severe cases complete loss of power or class C fire can occur. Cleaning brush waste has been made more difficult under new environmental regulations that ban the use of chlorinated and fluorinated solvents. This limits cleaning to non-ionic soap and water, and requires a 7-10 day drying period prior to placing the component back into service. The restrictive architecture of generators and motors prevents complete removal and neutralization of cleaning solutions, necessitating more frequent cleaning. The major goals of Phase I are to establish the feasibility of (1) demonstrating performance, well above that attained by monolithic brushes, in non-laboratory settings, (2) widening material choices beyond the previously studied copper, alpha - brass, silver and gold, (3) devising strategies for relatively simple replacement of monolithic brushes by fiber brushes in existing systems, and (4) reducing the cost of state-of-the-art metal fiber brushes.