Silver-coated Tungsten Carbide Powder for Electrical Contact Materials

Electrical contacts are the key components of switchgear, which bear the function of conducting current. Their performance directly affects the reliability and service life of switchgear. Therefore, switchgear requires electrical contacts to have good conductivity and thermal conductivity, low contact resistance and temperature rise, high resistance to fusion welding and electrical erosion.

Silver tungsten carbide contacts are made from silver nitrate crystals and tungsten carbide powders by chemical coating and liquid infiltration process. Silver-coated tungsten carbide composite powders are prepared by liquid deposition method. The principle is that silver ions are replaced and deposited on the surface of tungsten carbide particles by copper with stronger metal activity than silver. The composite powder can solve the problem of non-uniform powder mixing caused by traditional mechanical mixing and realize the powder structure connected by silver matrix. The process of this method includes the following steps:

(1)Silver-tungsten carbide coated powder prepared by chemical coating method: silver nitrate solution, tungsten carbide powder and copper powder mixed aqueous solution were prepared. Silver nitrate solution was slowly added into the mixed aqueous solution of tungsten carbide powder and copper powder under uniform stirring, and chemical displacement reaction took place. The replaced silver was rapidly deposited on the surface of tungsten carbide particles to form silver-coated carbon. Tungsten carbide particle powder slurry was cleaned, filtered and dried to obtain silver tungsten carbide coated powder.

(2)Coated powder pelletizing, doping additives, mixing, reducing, adding lubricants, and drying pelletizing at 200-300 ℃ in a hydrogen drying furnace with protective atmosphere, and cold pressing by powder automatic press to produce Ag-WC skeleton;

(3)Sintering and infiltration of the skeleton. The prepared pure silver sheets are placed above the silver tungsten carbide skeleton and arranged on the graphite plate in arrays. They are fed into a hydrogen sintering furnace with protective atmosphere and infiltrated at 1200-1300 ℃ at high temperature.

(4)Repressing and polishing of infiltrated products, cold pressing the infiltrated products on the hydraulic press, the pressure is 12-14T/cm², keeping the pressure for 2-3 seconds, and then polishing the surface to obtain the final silver tungsten carbide contact products.

The silver tungsten carbide contact material prepared by this method has the advantages of high density, high hardness, low and stable contact resistance, uniform metallographic structure, good resistance to high temperature oxidation, arc erosion and wear resistance.

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