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→Copper–Tungsten (CUWODUR) Materials
=== Copper–Tungsten (CUWODUR) Materials===
Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten areproduced by the infiltration process with the tungsten particle size selectedaccording to the end application ''(Figs. 2.138 – 2.141) (Table 2.39)''. To increasethe 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 ''(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 with70-85 wt% tungsten the lower melting component copper melts and vaporizesin the intense electrical arc. At the boiling point of copper (2567°C) the still solidtungsten is efficiently “cooled” and remains pretty much unchanged.
During very high thermal stress on the W/Cu contacts, for example during shortcircuit currents > 40 kA the tungsten skeleton requires special high mechanicalstrength. For such applications a high temperature sintering of tungsten fromselected particle size powder is applied before the usual infiltration with copper(example: CUWODUR H).
For high voltage load switches the most advantageous contact system consistsof a contact tulip and a contact rod. Both contact assemblies are made usuallyfrom the mechanically strong and high conductive CuCrZr material and W/Cu asthe arcing tips. The thermally and mechanically highly stressed attachmentbetween the two components is often achieved by utilizing electron beamwelding or capacitor discharge percussion welding. Other attachment methodsinclude brazing and cast-on of copper followed by cold forming steps toincrease hardness and strength.
The main application areas for CUWODUR materials are as arcing contacts inload and high power switching in medium and high voltage switchgear as well
as electrodes for spark gaps and over voltage arresters ''(Table 2.41)''.
'''Table 2.39: 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]]
[[File:Micro structure of2.jpg|right|thumb|Micro structure of W/Cu 70/30 G, W/Cu 70/30 H, W/Cu 70/30 F, W/Cu 80/20 H]]
'''Table 2.40: ''' Contact and Switching Properties of Copper–Tungsten
(CUWODUR) Contact Materials
[[File:Contact and Switching Properties of Copper Tungsten.jpg|right|thumb|Contact and Switching Properties of Copper-Tungsten (CUWODUR) Contact Materials]]
'''Table 2.41: ''' Application Examples and Forms of Supply for Tungsten–
Copper (CUWODUR) Contact Materials
[[File:Application Examples and Forms of Supply for Tungsten.jpg|right|thumb|Application Examples and Forms of Supply for Tungsten-Copper (CUWODUR) Contact Materials]]
