Cast lead-free copper graphite particle composites for cylindrical bearing and plumbing applications

Copper graphite alloys are known to possess good bearing properties. Centrifugally cast copper-graphite alloys provide a very attractive option for lead free copper alloy bearings and cylindrical plumbing fixtures. Cast copper graphite alloys also provide a much lower cost substitute for powder metallurgy produced sintered bronzes. In addition, graphite is a low cost substitute for lead in copper alloys imparting machinability, low friction and high resistance to sliding wear. Gravity and centrifugal castings of copper alloys containing graphite particles were synthesized, and the hardness, machinability and tribology test were done to evaluate their suitability for certain applications like plumbing fixtures and bearings. In the case of centrifugal casting the microstructure and chemical analysis show that the lighter graphite particles are concentrated near the inner diameter where they will be required for solid lubrication and machinability of inner surfaces. Hardness measurements show that the average hardness of graphite-rich zone is significantly lower than the average hardness of the graphite-free regions. The tribology and machinability tests show that the presence of graphite particles improves the machinability and tribological properties of cast copper alloys.