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→Copper–Tungsten (CUWODUR) Materials
=== Copper–Tungsten (CUWODUR) Materials===
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 [[#figures4|(Figs. 5 – 8)]] (Figs. 2.138 – 2.141) <xr id="fig: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.
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 wellas electrodes for spark gaps and over voltage arresters <xr id="tab:tab2.41Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials"/> (Table 2.41).
<figure id="fig:Physical Properties of Copper Tungsten CUWODUR Contact Materials">
<figtable id="tab:tab2.41Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials">
'''Table 2.41: Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials'''
<table class="twocolortable">