DODUCO Kontaktwerkstoffe sind optimal auf die jeweiligen Anforderungen der Anwendung abgestimmt und werden in unserer hauseigenen Forschungs- und Entwicklungsabteilung stetig getestet und optimiert.
Silver (Fine or Pure Silver)
Properties:
- Highest electrical and thermal conductivity
- Low contact resistance
- Limited arc erosion resistance
- Low weld resistance at high make currents
- Tendency towards material transfer in DC circuits
- Affinity to sulfide formation
- Resistance against oxidation
- Very good formability
- Easy to attach by welding and brazing
AgNi 0.15 (Fine Grain Silver)
Properties in comparison with Fine-Silver:
- Slightly higher arc erosion resistance
- Slightly higher mechanical strength
- Low contact resistance
Silver-Copper (AgCu3…28)
Properties in comparison with Fine-Silver:
- Higher arc erosion resistance
- Less tendency towards material transfer
- Höhere mechanische Festigkeit
- Gute Verformbarkeit
- Gute Löt- und Schweißbarkeit
AgCuNi (ARGODUR 27)
Properties:
- Properties similar to AgCu3
- Somewhat higher arc erosion resistance compared to Fine-silver
- Finely dispersed micro structure
- Good switching properties at elevated temperatures
AgMgNi (ARGODUR 32)
Properties:
- High electrical conductivity
- Hard and brittle after precipitation hardening (up to 700°C)
Silver-Palladium (AgPd 30…50)
Properties:
- Resistant against sulfur containing environment
- Highest arc erosion resistance for AgPd30
Silver-Nickel (Ag/Ni)
Ag/Ni 10…20
Properties:
- Made by powder metallurgy, sintered and extruded
- High arc erosion resistance for currents up to 100 A
- Resistant to welding for make currents up to 100 A
- Good arc mobility properties
- Good arc extinguishing properties
- Non-conducting arcing
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Non-conducting arcing condensates on the insulating material walls
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Low contact resistance
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High electrical and thermal conductivity
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Increased mechanical strength
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Good formability
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Easy to attach by welding and brazing
Ag/Ni 30…40
Properties:
- Contact properties similar to Ag/Ni 10…20
- Higher arc erosion resistance
- Higher contact resistance
- Slightly less formability
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 other metal oxides and applying special manufacturing processes 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.
Silver-Zinc Oxide (Ag/ZnO)
Silver-zinc oxide contact materials with 6 – 10 wt-% oxide content, including small other metal oxide additives, are manufactured exclusively by powder metallurgy. For applications in AC relays, wiring devices and appliances an additive of Ag₂WO₄ applied in the form of coated powders 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 offer for some applications an economic alternative to the Ag/SnO₂ containing contact products.
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 (Ag/C) or parallel (Ag/C D or DF) 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 bottom layer is necessary for attachment. This can be achieved by de-carbonizing a thin layer through heat treatment or by compound extrusion of Ag/C billets with fine silver. 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. For Ag/C components with the graphite particles oriented parallel to the contact surface the weld resistance is especially high. 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 with horizontal graphite orientation an improvement of the erosion resistance can be achieved if part of the graphite powder is substituted with suitable fibers (Ag/C DF). The weld resistance of these materials depends on the proportion of the different 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 40-60 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 because of the formation of a CO containing cover gas during arcing, which in turn limits the access of oxygen und resulting oxide formation on the contact surface. For even higher restrictions 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 (CUWODUR)
Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application. To increase the wettability of the tungsten skeleton by copper a small amount of nickel < 1 wt% is added to the starting powder mix. 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/C 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. During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA the tungsten skeleton requires special high mechanical strength. For such applications a high temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H).
For high voltage load switches the most advantageous contact system consists of a contact tulip and a contact rod. Both contact assemblies are made usually from the mechanically strong and high conductive CuCrZr material and W/Cu as the arcing tips. The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding. Other attachment methods include brazing and cast-on of copper followed by cold forming steps to increase hardness and strength.
The main application areas for CUWODUR 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.
Oliver Lutz
Sales contact materials
Tel.: + 49 (0) 7231 602-566
Mail: kontaktwerkstoffe@doduco.net
