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Electrical ContactsContact RivetsCold forming (or “heading”) electrical contacts from CMW precious metals such as silver, gold, platinum and copper, as well as silver-cadmium oxide materials and other alloys, is an extremely economical manufacturing method. Attaching contact rivets by staking is also very cost effective. CMW contact rivets can be made with radii faces, large shanks, small shanks, weld projections or flat discs. Composite rivets can also be made with lower cost shank material and high performance precious metal faces. Many CMW materials are well suited for cold forming and are highlighted in this section. Coin SilverCMW® Coin Silver (90% Ag / 10% Cu) and Elkonium®1 (75% Ag / 24.5% Cu / 0.5% Ni) Typical Properties CMW Coin Silver and Elkonium® 1 are copper bearing silver alloys providing low transfer tendencies for high current switching applications. These materials are also highly resistant to mechanical wear and deformation due to their higher hardness than fine silver. These materials are well suited for cold forming into rivets and discs.
Fine SilverAg Fine Silver Typical Properties Fine silver has high thermal and electrical conductivity, providing high heat dissipation and low contact resistance. Fine silver is very ductile and available in a large variety of wire sizes making it ideal for the cold forming manufacturing process.
Silver Cadmium OxideAg/CdO Silver Cadmium Oxide Typical Properties The high conductivity, good wear resistance and wide availability of silver-cadmium oxide wire sizes, combined with their tolerance to arc erosion and anti-sticking (or welding) properties are why silver-cadmium oxide materials are commonly used for cold formed contact rivets and discs. Rivets or small discs are easily headed from silver-cadmium alloy then oxidized (creating “Post Oxidized, Type “X” material) to provide the least tendency for early erosion and enhancing the anti-sticking properties. CMW Pre Oxidized Type “F” silver-cadmium oxide materials up to 13.3% cadmium oxide are “headable” (or suitable for cold forming) and have a homogeneous structure providing uniform contact performance throughout the life of the contact device. However, because of the high strength and hardness of Type “F” materials, the heading ratio of the head diameter to the shank diameter is less than that of Type “X” post oxidized material.
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