The effects of graphite particle size and processing on the performance of silver-graphite contacts

The effects of two variables, graphite particle size and sintered density, on the contact performance of silver-4 wt.% graphite materials were evaluated. Materials made with larger graphite particles eroded more slowly, but formed stronger welds relative to materials made using finer graphite particles. The slower erosion is due to the larger intergraphite particle spacing within the material, which allows the establishment of a more cohesive silver matrix. Due to the better silver interconnection, larger silver masses form on the contact surface, which cause the formation of strong welds. Higher sintered density reduced the erosion rate of the materials tested with the greater effect being on the material with the finer graphite particles. The formation of carbon layers on the eroded contact surfaces was noted. A process by which carbon could be deposited from vapor species in the arc is described. >