2021年9月6日星期一

Toughening Properties of Silver and Nickel Contacts Evaluation by Tungsten and Tungsten Oxide

In life, silver-nickel contact materials are widely used in relays, circuit breakers for low current ratings because of their good ductility and low contact resistance.

When current levels exceed 20 A, conventional AgNi contact materials exhibit weaker resistance to soldering and erosion, limiting their range of application. However, by adding a small amount of additives, the electrical properties can be improved, thus expanding its application area. Some scholars have studied that adding tungsten or tungsten oxide can improve the performance of AgNi contact materials. 

silver nickel contact image

The W or WO3, which accounts for 1.5% of the total, was made into silver-nickel contacts (containing 85% of silver content) by powder mixing, isostatic pressing, sintering, extrusion, subsequent wire drawing and riveting. Each contact material was repeated 5 times using the same resistive load in the test. The current and mechanical structure ensured that all tests had comparable arcing energy with supply voltages and load currents of 220 V and 25 A, respectively. After the 5000 operation, the contact is removed from the equipment and cleaned by ultrasonic in alcohol. After drying, the weight is weighed and the weight loss is calculated. 

The comparison of test results shows that the two different additive silver and nickel contact materials with tungsten powder or tungsten oxide have no obvious difference in the microstructure of the material, but there are big differences in the electrical properties such as material transfer and arc erosion. In the simulation of electrical performance test, the tendency of the addition of WO3 is that the mass loss and the microstructure of arc-affected zone are worse than that of tungsten powder. 

The addition of 1.5% W in AgNi contact materials can reduce the maximum welding power and reduce the arc erosion compared with 1.5% WO3. Therefore, tungsten powder may be better applied at low current level AC contactors.

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