Tungsten Carbide Silver Contacts Prepared By High-energy Ball Milling

Electrical contacts are the core components of electrical switches, which play the roles of switching on, carrying and sectional current. Their performance largely determines the performance and reliability of electrical switches. Because of the high melting point of tungsten carbide and its strong resistance to electric corrosion, silver carbide has excellent conductivity and thermal conductivity, silver tungsten carbide materials also have good performance.

Because of its corrosion resistance and thermal conductivity, silver tungsten carbide contact materials are widely used in circuit breakers, contactors and other electrical switches.

At present, the manufacturing technology of tungsten carbide silver contact materials is sintering and infiltration. Recently, compared with the traditional mechanical mixing process, the nano-sized WC-Ag contact material prepared by high-energy ball milling method has higher sintering density, hardness and conductivity.

The tungsten carbide powder with average particle size of 1.06 micron, silver powder with particle size of - 300 mesh and nickel powder with particle size of - 200 mesh were selected. According to the total weight of 2 kg and the weight ratio of silver to tungsten carbide: nickel = 50:49:1, the tungsten carbide powder and nickel powder were weighed and loaded into the ball mill. The ball mill was installed on the planet by adding 150 ml alcohol and 10 kg_6mm carbide ball. The ball mill is continuously milled 48h at 250r/min speed.

The powder was dried at 120 ℃ for 2 hours. The dried powder and silver powder were loaded into the ball mill with 0.04 kg stearic acid and 20 kg 6 cemented carbide ball. The ball mill was sealed and vacuum pumped. The ball mill was installed on the planetary ball mill and continuously milled for 12 hours at 250 r/min rotational speed. The mixture powder was pressed into compact in the carbide mould at the pressure of 3T/cm². The compact was sintered in a hydrogen furnace. The sintering parameters were as follows: sintering temperature 1100 ℃, heating rate 10 ℃/min, holding time 2h.

The sintered blank was repressed at the pressure of 10T/cm 2, and the repressed blank was re-fired in a vacuum furnace. The parameters of the re-fired blank were as follows: the re-fired temperature was 900 ℃, the heating rate was 12 ℃/min, and the holding time was 1.5h.

Compared with the existing infiltration process, the improved process can prepare the contact materials with wider quality of silver and tungsten carbide, and the resulting contact materials have finer grains, more uniform metallographic structure, higher density and hardness, higher arc damage resistance and lower resistivity; mixed with the chemical reaction method to produce silver tungsten carbide. Compared with the method of combining powder with infiltration, the whole manufacturing process does not produce any waste water and other wastes, and the process is simpler.

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