Electrical Contacts

Powder Metal Contacts

CMW powder Metallurgy processes provide a cost effective method of producing electrical contacts with dimensional characteristics such as solder traps, radii and projections and in many different shapes and compositions. Some of these compositions begin with Silver powder, yet others start with a pressed Tungsten or Molybdenum base material. Different powder mixes provide useful, but vastly different properties. Our CMW® D54 and D55 Silver Cadmium Oxide materials provide superior ant-sticking properties, while our Elkonite® G17 and G18 materials exhibit good arc resistance as do our Tungsten based Elkonite® 1W3 and 5W3 materials. Many CMW materials used for high voltage applications requiring arc tolerant materials are produced using powder metallurgy. Please refer to our “High Voltage / Arc Tolerant Contacts” section for more detailed information on additional materials.

Silver Cadmium Oxide

Ag/CdO Silver Cadmium Oxide Typical Properties

CMW® D54 and CMW® D55 Silver-Cadmium Oxide Contacts

CMW silver cadmium oxide materials are part of a family of silver-semi-refractory materials and have relatively high electrical conductivity combined with other desirable features such as low stable contact resistance and excellent resistance to sticking and welding. Silver-semi-refractory materials are not always true alloys, but rather mixtures of silver and other elements. These materials are usually fabricated as mixtures of constituent powders by conventional powder metallurgy techniques for both mechanical and chemical reasons. Chemically, powder metallurgy techniques are used because many of the constituent materials used in the production of silver-semi-refractory materials do not have compatible melting temperatures or are not soluble in each other. However, in the case of silver-cadmium oxides, it is possible to form true alloys of the elements and then convert one or more of the elements into an oxide by internal oxidation techniques. More information concerning these types of silver cadmium oxide materials (Type F and Type X materials) can be found in our “Silver Contacts” section.

CMW® D54 (90% Silver / 10% Cadmium Oxide) and CMW® D55 (85% Silver / 15% Cadmium Oxide) are produced as individual contacts by traditional powder metallurgy techniques (mix - press - sinter - repress to density). Normally, the powder metallurgy type materials are used in disc or rectangular shapes. The powder metallurgy process provides an economical method of producing radii, projections for welding or locating, indentations for solder traps and round or irregularly shaped contacts without material loss.

While the cadmium oxide content can be readily varied, the two standard materials (10% CdO and 15% CdO) satisfy most contact requirements. The contacts can be supplied with a "backing" layer of fine silver which is recommended for attachment by brazing. If omitted, the cadmium oxide can cause a brazing alloy to develop brittle phases and ultimately a detachment of the braze. Besides standard discs and rectangles, irregular shapes typical of powder metallurgy parts can be produced economically.

The addition of cadmium oxide to silver greatly improves the anti-welding characteristic. Of Ag/CdO materials, the powder metallurgy type has the least tendency to welding or sticking of all. It is the material of choice for arcing contacts of medium-low to medium-high current rating where "non-sticking" primary concern and erosion rates higher than wrought type Ag/CdO can be tolerated. It is not used in "high reliability - low current" applications (where CMW Elkonium® materials are best), nor in "high current circuit breaking" (where Elkonite® materials are superior). Generally this makes it a choice for "high-end" household and "low-end" industrial relay and contactor applications.

The cost of Ag/CdO materials are directly tied to the cost of silver and the silver content of the material. As would be expected, the conductivity (and therefore resistance to temperature rise) is better with higher silver content.

Silver Graphite

CMW® D58 (95.0% Silver / 5.0% Graphite)
CMW® D1058 (90.0% Silver / 10.0% Graphite)

The materials with the higher percentages of graphite, such as CMW® D58 and D1058, are used as make and break contacts usually operating in conjunction with silver nickel or other silver base alloys. CMW® D58 is used in industrial circuit breakers usually operating against CMW® D56.

CMW® D58 and D1058 are usually furnished as a round or rectangular disc or as a special pressed shape. When brazing these materials, it is necessary to have a silver rich layer on the surface, which is to be brazed or tinned with, braze alloy.

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Silver Nickel

CMW® D50 (85.0% Silver / 15.0% Nickel)

CMW® D50 can be used for circuit breaker and switching applications in conjunction with other contact materials. CMW® D50 has good wear resistance and can be made into a variety of shapes and radii using CMW powder metallurgy processes.

CMW Elkonite® materials such as our Elkonite® Silver-Molybdenum, Silver-Tungsten, Silver-Tungsten Carbide, Copper-Tungsten and Copper-Tungsten Carbide materials are produced using powder metallurgical processes and these are excellent for higher voltage applications requiring arc tolerant materials. Please click on our High Voltage / Arc Tolerant section to find detailed information on these CMW materials.