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Electron Beam Welding:
MODISON offers high erosion resistant Copper Tungsten material produced by Powder Metallurgy wherein, sintered skeleton of Tungsten is impregnated with Copper. The erosion pattern of this material is far superior to materials produced by other production techniques. This material maintains quite regular shape under extreme arcing conditions and has only uniform roughening effect without cracks and burn-off droplets.
The Tungsten skeleton is protected by impregnated Copper, as it provides evaporative cooling effect in extreme arcing conditions, thereby protecting and limiting the temperature rise of the skeleton and preventing disintegration. The grain size of Tungsten powder has considerable influence on arc erosion behaviour of Copper Tungsten Contact Materials. Grain size of Tungsten is optimized to meet customer’s product needs in order to have low uniform erosion rates and burn-out patterns. All contact materials are produced by impregnation liquid phase sintering (wet sintering of pre-sintered skeleton). Although laboratory tests indicate that minimum erosion occurs when the Tungsten grain size is between 2 and 8 µm, materials made of other grain sizes have also given superior performance in practice. The tungsten content in the composite does influence contact performance. Materials with particularly high Tungsten content consisting of fine powders, quickly develop cracks on the surface when subjected to repeated thermal and mechanical shocks. This can lead to parts of Tungsten skeleton’s disintegration and impairing the function of the Circuit Breaker.
On the other hand, materials which have a slightly higher Copper content (25~30%Cu) show a regular erosion pattern with only a slight roughening of the surfaces.
The final chemical composition can only be maintained within certain limits due to impregnation method of sintering.
Accordingly instead of fixed data, it is only possible to give production dependent ranges for the mechanical and electrical characteristics although, this does not affect the most important functional characteristics – its erosion behaviour to any significant degree.
|Material||Composition||Density Gm/cc||Electrical Conductivity m/mm²||Hardness HV10|
|COPTUNS 50||Wcu 50:50||11.8-12.2||37.93||110-140|
|COPTUNS 60||Wcu 60:40||12.8-13.2||31.48||140-170|
|COPTUNS 65||Wcu 65:35||13.4-13.8||32.76||150-190|
|COPTUNS 70||Wcu 70:30||13.9-14.3||31.03||160-200|
|COPTUNS 75||Wcu 75:25||14.6-15.0||29.31||180-220|
|COPTUNS 80||Wcu 80:20||15.2-15.6||27.58||210-250|
|COPTUNS 80S||Wcu 80:20||15.2-15.6||24||210-250|
|COPTUNS 80H||Wcu 80:20H||15.2-15.7||27.38||200 min|
|COPTUNS 85H||Wcu 85:15H||15.7-16.4||27.38||205 min|
|COPTUNS 75H||Wcu 75:25H||14.7-15.5||29.31||180 min|
S - Special grade with Ni 1.00%
H - High sintered
Generally, Modison offers Arcing Contacts where the Copper Tungsten Tip is joined with the carrier by Electron Beam Welding. This process of welding offers the most reliable joint and minimum heat affected zone (softening of the base part) and thereby maintaining joint properties very close to parent metal properties. The small localized heat affected zone is further improved by reshaping and cold working. EB welding is also especially suitable for joining dissimilar carrier materials such as steel to Cu/Cu/Cr.
Tulip contact & fixed contacts for high voltage Gas circuit breakers up to 800KV