Silver-Carbon Contact Materials
Silver-carbon (graphite) contact materials are used currently in a diverse range of applications. Use of silver-carbon in rheostatic devices is primarily due to the self-lubricating properties of these materials. In addition, the material is used in circuit breaker and switching applications due to its very good anti-welding properties and its relatively stable contact resistance. The carbon content can be varied from .5% to 8% of the contact mass. The resistance to sticking increases as the carbon content increases. The disadvantages of silver-carbon are its relatively high erosion rates, poor arc mobility, its limited ductility and its relatively high cost.
The materials have limited ductility but may be fabricated in strip and wire form when lower concentrations of carbon are specified. From this strip and wire, rivet contacts, discrete contacts, including laminated products and various contact assemblies can be produced. When more than 1% carbon is required, unit compaction processes are employed. Silver-carbon contact materials are typically supplied with a silver rich surface on the face which will be attached to the contact support. Discrete contacts can be supplied with or without a solder alloy on the attachment surface. Resistance welded and brazed assemblies are available as well.