Silver Coated Tungsten Carbide Powder for Electric Contact Material

The electric contact is the key element of the switchgear. It bears the function of conducting current, its performance directly affects the reliability and service life of the switching apparatus. Therefore, the switch electrical contact should have good electrical conductivity, high resistance to welding and corrosion resistance and so on.

The electric contacts of silver tungsten carbide and silver tungsten are usually used in circuit breakers. The silver tungsten carbide contacts have better oxidation resistance, resistance to welding and relatively stable contact resistance than the silver tungsten contacts. The promotion of silver tungsten carbide and silver tungsten carbide graphite static and dynamic contact has become the main contact point used in the current circuit breaker.

The silver carbide contact is made of silver nitrate crystal and tungsten carbide powder as raw material. The silver carbide electric contact is prepared by chemical coating and liquid phase penetration process. The silver coated tungsten carbide composite powder is prepared by liquid phase deposition. The principle is to replace the silver separation by metal activity and silver strong copper. To form a composite powder particle, the outer layer is silver and the inner layer is a tungsten carbide particle structure. The composite powder can solve the uneven mixing of the powder caused by the traditional mechanical mixing and realize the powder structure connected with the silver matrix. The process includes the following steps:

(1) Silver carbide coating powder was prepared by chemical coating method: preparation of silver nitrate solution, tungsten carbide powder and copper powder mixed aqueous solution, slowly adding silver nitrate solution to the uniform stirring of tungsten carbide powder and copper powder mixed aqueous solution, the chemical replacement reaction occurred, the replacement silver quickly deposited on the surface of tungsten carbide particles, forming a silver package carbonization. Tungsten carbide powder slurry was cleaned, filtered and dried to obtain silver tungsten carbide coated powder.

(2) Coating powder granulating, coating powder with additives, mixing, reducing, and adding lubricant, drying in a hydrogen drying furnace with protective atmosphere at 200~300°C, forming the skeleton of tungsten carbide by cold press molding by powder automatic press.

(3) The prepared pure silver sheet was placed above the skeleton of tungsten carbide. The column was placed on the graphite plate and sent into a hydrogen sintering furnace with protective atmosphere for 1200~1300°C infiltration.

(4) The melt permeable material is repressed and polished, the pressure is 12-14T/cm², the pressure is maintained for 2~3s, then the final silver carbide contact product is obtained by surface polishing.

The silver 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, resistance to arc erosion and wear resistance.

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