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→Copper–Tungsten Materials
Copper–tungsten materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application [[#figures4|(Figs. 5 – 8)]] <!--(Figs. 2.138 – 2.141)--> (<xr id="tab:Physical Properties of Copper Tungsten CUWODUR Contact Materials"/><!--(Table 2.39)-->). 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 (<xr id="tab:Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials"/><!--(Table 2.40)-->). 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 usually 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 W/Cu 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 (<xr id="tab:Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials"/><!--(Table 2.41)-->).
<figtable id="tab:Physical Properties of Copper Tungsten CUWODUR Contact Materials">
[[File:Physical Properties of Copper Tungsten CUWODUR Contact Materials.jpg|right|thumb|Physical Properties of Copper Tungsten (CUWODUR) Contact Materials]]
</figtable>
<div class="multiple-images">
<figtable id="tab:Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials">
<caption>'''<!--Table 2.40:-->Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials'''</caption>
<table class="twocolortable">
<tr><th><p class="s12">Material/ DODUCO- Designation</p></th><th><p class="s12">Properties</p></th></tr><tr><td><p class="s12">W/Cu F</p><p class="s12">CUWODUR F</p></td><td><p class="s12">Very high arc erosion resistance,</p><p class="s12">Uniform erosion pattern after high operation frequency, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock</p></td></tr><tr><td><p class="s12">W/Cu G</p><p class="s12">CUWODUR G</p></td><td><p class="s12">Very high arc erosion resistance, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock.</p></td></tr><tr><td><p class="s12">W/Cu H</p><p class="s12">CUWODUR H</p></td><td><p class="s12">Very high arc erosion resistance, very high mechanical strength, Especially high resistance against thermal and mechanical shock.</p></td></tr></table>
</figtable>
<figtable id="tab:Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials">
<caption>'''<!--Table 2.41:-->Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Tungsten–Copper Contact Materials'''</caption>
<table class="twocolortable">
<tr><th><p class="s12">Material</p></th><th><p class="s12">Application Examples</p></th><th><p class="s12">Form of Supply</p></th></tr><tr><td><p class="s12">W/Cu F</p></td><td><p class="s12">Transformer tap changers,</p><p class="s12">Medium voltage circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts</p></td></tr><tr><td><p class="s12">W/Cu G</p></td><td><p class="s12">Overvoltage arresters with spark gap,</p><p class="s12">Medium voltage circuit breakers, Medium voltage power switches, High voltage power switches and circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts; Contact tulips, rods and tubes</p></td></tr><tr><td><p class="s12">W/Cu H</p></td><td><p class="s12">High voltage power switches and circuit</p><p class="s12">breakers for very high short circuit currents</p></td><td><p class="s12">Welded contact parts; Contact tulips,</p><p class="s12">rods</p></td></tr></table>
