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

The effects of graphite particle size and sintered density on the contact performance of silver-5 wt.% graphite materials were evaluated. Materials made from 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 causes the formation of strong welds. Higher sintered density reduced the erosion rate of the materials tested, with the greater effect being for 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.<>