resistance and increasing current density in a monolithic brush maximum current density is 600 amp per square inch while with fiber brushes current densities of 20 000 amp per square inch can be realized the individual brush fibers are able to adapt to the unevenness of the ring surface because of their elasticity and flexibility the fibers in actual contact with the ring are biased by other fibers which comprise the brush these properties also greatly reduce brush bounce caused when the brush hits a high spot on the ring surface at high ring speed the fact that brush bounce is greatly reduced and the fact that the need for lubrication is minimized because of the very low forces between contact members permit the fiber brush contact system to be operated in conjunction with very high ring speeds tests to date have shown that the adventitious lubricants in the environment i e hydrocarbons and other airbourn gaseous contaminants will provide adequate lubrication such that fiber brush contact assemblies can be operated for periods of time in excess of 50 hours at speeds of 30 000 rpm slip ring assemblies used in instrumentation systems to monitor a parameter such as temperature on the rotating portion of turbine engine may be required to operate at speeds of 10 000 to 60 000 rpm in these systems auxiliary equipment is required to cool a freon tf u00ae and oil mixture which is circulated throughout the slip ring assembly.