Degradation process of a sliding system with Au-plated slip-ring and AgPd brush for power supply

Sliding contact is still an important mechanism to transmit current or electric power from a stationary equipment to a moving device. A power supply slip-ring used in a chip mounter is presently 20 millions rotations in life, but expected to have longer life time. In this paper a slip-ring with Au plated on Ni base-plated layer is investigated in reliability against AgPd brush. Test conditions are 400rpm in rotation speed and 0-5A in operation current. Contact resistance and surface morphology are observed with operation time. Consequently, the lifetime is dependent on load current, with or without lubricant and sample, while the surface deterioration process is almost same. Namely firstly the Au plated layer is worn out, secondly the Ni base-plated layer and finally the wear reaches the bulk metal. At that time the contact resistance sharply increases and the life is over. At the final stage of the lifetime the contact surface is covered with black film which is estimated to be an oxide of a constituent element of the bulk metal by EPMA analysis.