Early contact materials with pure tungsten, molybdenum, pure copper and precious metals silver, vacuum switch almost all use the refractory metals such as W, Mo, as contact materials. Such persons head material with a series of advantages, such as there is proper breaking capacity, good compressive strength and resistance to fusion welding, the appropriate heat transfer coefficient and electrical conductivity, the arc ablation rate is small, contact the service life is long, etc., until now has been widely used in vacuum switch breaking small current. But high melting point of pure metal contact material has many shortcomings, such as breaking current and high level of river closure, limiting the use of vacuum switch. Started developing composite contact after the present study is more low voltage electrical appliances silver based contact materials, double layer or multilayer compound contact materials, vacuum switch, high voltage and other closed switch with contact materials.
Foreign study of electrical contact element and material has a history of seven hundred and eighty years. At present foreign production and research and development of electrical contact materials company mainly AMI DODUCO (Germany), the OMG company (USA), the Metalor company (Switzerland), etc.In our country since 1956 in contact materials research and production, after nearly 50 years of development, the current domestic engaged in electrical contact materials production enterprises for more than 60 (means only members of the wga's electrical alloy), total about 12000 employees, assets of about 1.2 billion yuan. In more than 60 branch members, mostly private enterprises (about 90%), about 10 enterprises with certain scale and technical strength, the product variety, technical personnel and production equipment is complete. In terms of the varieties and properties of contact materials, the current international domestic all can produce the electric contact material variety, in general, also can satisfy the demand of the electric switch
Electrical contact materials in the switch electrical function is to connect and disconnect the electric current in the electric circuit, switch electric contact material research mainly develop and improve the performance from the following several aspects:(1) physical properties: low resistivity and vapor pressure, high thermal conductivity, melting point, boiling point, melting heat and latent heat of sublimation, and good thermal stability, heat capacity is the largest, high electron work function, to ensure that the arc voltage is high and the lowest current.: (2) mechanical properties at room temperature and high temperature and high strength, high hardness, and good plasticity and toughness.(3) the electrical contact performance: requirements arc burning resistance and contact resistance is low and stable, fusion welding and metal transfer tend to be small.(4) performance: chemicals for a wide range of different media with good corrosion resistance, not easy oxidation, carbonization, sulfide in the atmosphere
