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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.
Silver NickelAg/Ni Silver Nickel Typical Properties CMW® D505F (95.0% Silver / 5% Nickel), CMW® D510F (90.0% Silver / 10% Nickel) and CMW® D50F (85.0% Silver / 15.0% Nickel) These silver nickel compositions are produced from metal powder and the lower nickel compositions, CMW® D505F and CMW® D510F, have good ductility, can be fabricated into wire and headed into rivets, discs, or solid buttons. CMW® D505F is a higher wear resistant material and CMW® D510F is used in both AC and DC applications. CMW® D50F can also be fabricated into wire, however it has a more narrow range of headability. This material also has good resistance to mechanical wear under high contact force and maintains a stable surface resistance.
Silver GraphiteAg/C Silver Graphite Typical Properties The lower graphite containing materials such as CMW® D582F, D581F, D583F and D158F are able to be made into wire and cold formed into contact rivets over a limited size range.
GoldAu Gold Based Materials Typical Properties Elkonium® 76 (90% Au / 10% Cu) and Pure Gold (99.9% Au min) Elkonium® 76 is CMW's gold-copper alloy that is completely tarnish resistant at ordinary atmospheric temperatures. Compared to the other CMW® gold Elkonium® alloys, it has improved resistance to welding, and particularly cold welding. When used as a positive contact operating against an Elkonium 32® alloy negative contact in low voltage DC applications, the combination resists transfer and sticking at currents up to 4 amperes. Availability:
Pure Gold has complete resistance to atmospheric tarnish and oxidation. It does not contribute to polymer formations like platinum and palladium alloys. Wrought gold metal is very soft and prone to welding and has very few contact applications. Electroplated coatings of gold on silver and other base metals are used in dry circuit application and to provide long shelf life reliability. Gold is alloyed with other metals to improve hardness, contact performance, and reduce cost.
PlatinumPt Platinum Materials Typical Properties Elkonium® 30 (99.9% Pt min.) Elkonium® 30 material by CMW is commercially pure platinum (99.90% minimum purity) Freedom from tarnish and low hardness makes it a very reliable contact in low force, low current AC and DC applications. It is recommended for sensitive instruments and relays, particularly where contacts are open for long periods of time. Availability:
PalladiumElkonium® 40 (99.9% Pd min.) Elkonium® 40 is CMW's trademark for commercially pure palladium (9.90 minimum purity). Its good corrosion resistance and low hardness makes it a desirable contact for low current applications where forces are relatively low and reliability of making circuit is important. It is used in aircraft relays at currents under 1 ampere, in telephone relays and in instruments. It is often chosen for applications where contacts area open for long periods of time. Availability:
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