The effects of apparent contact area on thermal and electrical properties of Ag-MoS2-C/sub graphite/ brushes in contact with coin-silver slip rings

Brushes for slip ring assemblies are often run-in to increase their apparent area of contact to the ring. An investigation was undertaken to determine the effect of this run-in and the resultant higher apparent contact area on the thermal characteristics of the brush during current loading. An experiment was conducted at reduced pressure by placing thermocouples at various brush locations as well as under the ring to determine the temperature rise of one brush during electrical loading. Voltage probes were also used to determine voltage drop across the contacts. The response of the brush/ring system to various current levels and apparent contact areas was found. A finite difference model was also constructed of the brush and the brush/ring interface to study the effect of electrical loading on the thermal and potential fields in the brush. It was determined that the effect of apparent area of contact on the thermal properties of the slip ring system studied here are inconsequential to the function of the system. It was also concluded that the real area of contact of the system is independent of apparent area of contact.