Fine Silver
| Fine silver contacts work well in the light to medium ampere range and are ideal for contact applications requiring a light closing force where low contact resistance is to be maintained. As long as current and voltage are not excessive, silver is recommended for sensitive contacts under light and medium pressure, and will operate satisfactorily for long periods of time. Silver will carry high current loads without excessive heating when circuits are closed because of silver's high electrical conductivity. The arc energy of the circuit is dissipated without excessive temperature increase or detrimental effect on the silver contact due to the high thermal conductivity of silver.
Silver is available in varying degrees of fineness. Fineness refers to the parts silver per thousand. Fine silver, which is the most commonly used material, is minimum 999.0 pure. Also available are AA fine silver minimum 999.5 and high fine minimum 999.9 pure. The latter two are seldom required in contact applications. Silver is a ductile metal and is readily formed into contact rivets, weld buttons or in strip form used in contact stampings. Some disadvantages of fine silver are...a relatively low melting point (1761 F), low hardness, and, under certain conditions, it will pit and transfer. Disadvantages may be overcome by combining silver with such metal as cadmium, copper, nickel, palladium, zinc, gold, platinum, iron, etc. Addition of one or more of these alloying elements will, in some instances, raise the melting point, increase resistance to erosion due to arcing, increase hardness, increase corrosion resistance to undesirable chemical films and resistance to sticking or welding and reduce material loss and transfer. Properties of Fine Silver; DMC-10
Note: Hardness values are for comparative purposes only and should not be used in design specifications. |