Contact Mater­ials

Silver (Fine or Pure Silver)

Properties:

AgNi 0,15 (Fine Grain Silver)

Properties:

Silver-Copper (AgCu3…28)

Properties:

AgCuNi (ARGODUR 27)

Properties:

AgMgNi (ARGODUR 32)

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Silber-Palladium (AgPd 30…50)

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Silver-Nickel (Ag/Ni)

Ag/Ni 10…20
Properties:
Silver/Nickel Ag/Ni 30…40
Properties:

Silver-Tin Oxide (Ag/SnO₂)

Silver-tin oxide contact materials are characterized by high electrical contact life, low contact resistance, high resistance against welding of the contact parts, good arc moving properties and environmental compatibility. By adding additives Ag/SnO₂ contact materials can be optimized for different applications and utilization categories. Choosing the most suitable material for a given use is best performed during a technical consultation meeting.

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Silver-Zinc Oxide (Ag/ZnO)

Silver-zinc oxide contact materials with 8 – 10 wt-% oxide content, including small other metal oxide additives, are manufactured exclusively by powder metallurgy. For applications in AC relays, wiring devices Ag/ZnO compositions have shown good electrical performance. As for other silver-metal oxide materials the processing includes the production of semi-finished materials followed by manufacturing contact tips and/or contact rivets. Due to their high welding and arc erosion resistance Ag/ZnO contact materials are an economic alternative to Ag/SnO₂.

Silver-Graphite (Ag/C)

Silver-graphite contact materials are predominantly manufactured by extrusion of sintered Ag/C billets. The extrusion results in a high degree of densification of the material and graphite particle alignment along the direction of extrusion. Depending on the type of semi-finished material, either strip or in the form of rods, the graphite particles will be oriented either perpendicular or parallel to the switching surface. Because of the graphite particles dispersed in the silver matrix, Ag/C contact parts cannot be welded or brazed directly to substrates. Therefore a graphite-free lower layer is necessary for attachment. This can be achieved by de-carbonizing a thin layer through heat treatment.Ag/C contact materials exhibit a very high resistance to contact welding, higher than any other contact material, but on the other side have only limited arc erosion resistance. This switching behavior is caused by the reaction of the embedded graphite with the atmosphere at high temperatures due to electric arc. Since the contact surfaces after arcing consist of fine silver the contact resistance remains very low over the electrical life of such contact parts. A disadvantage of Ag/C materials is their low arc erosion resistance. For Ag/C materials an improvement of the erosion resistance can be achieved if part of the graphite powder is substituted with suitable graphite fibers. The weld resistance of these materials depends on the proportion of the graphite powder particles.

Silver-Tungsten (Carbide)-materials (Ag/W, Ag/WC, Ag/WC/C)

Silber-Tungsten (Ag/W)
Silver-tungsten contact materials combine the high electrical conductivity of silver with the high arc erosion resistance of the high-melting tungsten. These materials containing typically 50-80 wt-% tungsten are usually manufactured by powder metallurgy either through liquid phase sintering or by infiltration. Under repeated switching operations at nominal arcing currents poorly conductive surface layers of tungsten oxide or intermetallic oxides (Silver-Tungstate) are often formed on the contact surface of Ag/W. These may result in a significant increase of the contact resistance leading to temperature rise during current flow that can exceed specified limits. Therefore Ag/W is often paired to Ag/C contact parts in many switchgear designs. Ag/W contact materials are mainly used as arcing contacts in higher load circuit breakers and as main contacts in protective switching devices for lower and medium loads.
Silver-Tungsten Carbide Graphite-materials (Ag/WC; Ag/WC/C)

This family of contact materials typically containing 35-65 wt-% tungsten carbide consists of a combination of the hard and wear resistant WC with high conductivity Ag. Compared to Ag/W these Ag/WC materials are characterized by a higher weld resistance. They also exhibit a lower increase in contact resistance under nominal load switching duty. 

For even higher requirements on heat rise small additives of graphite are used which in turn however reduce the arc erosion resistance to a certain degree. Such silver-tungsten carbide+graphite materials with 27 wt-% WC and 3 wt-% graphite or 16 wt-% WC and 2 wt-% graphite are manufactured as discrete tips utilizing the press-sinter-repress (PSR) process.

Copper-tungsten (CU/W)

Copper–tungsten (CUWODUR) materials with typically 60-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application. W/Cu materials exhibit a very high arc erosion resistance. Compared to silver–tungsten materials they are however less suitable to carry permanent current. With a solid tungsten skeleton as it is the case for W/Cu infiltrated materials with 70-85 wt% tungsten the lower melting component copper melts and vaporizes in the intense electrical arc. At the boiling point of copper (2567°C) the still solid tungsten is efficiently “cooled” and remains pretty much unchanged.

 

The main application areas for CU/W materials are as arcing contacts in load and high power switching in medium and high voltage switchgear as well as electrodes for spark gaps and over voltage arresters.

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