copper
Cu is the most widely used conductive material and contact material. Aluminum is also the most widely used conductive material, but its conductivity, heat conduction, melting point, boiling point and hardness are not as good as copper. The conductivity and thermal conductivity of copper are second only to silver (Ag). Copper is the main contact material before the composite material is not developed. The weakness of copper as a contact material is easy to oxidize in the air. At less than 200 c, the CuO surface film can be generated from 10 to 1000nm, and an additional layer of CuO surface film is attached at more than 200 degrees C, and its resistivity can reach 106 Omega. When the temperature reaches 120 C, the contact resistance can be increased by 3 times because of the influence of the surface oxide film. The abnormal wear and tear will be observed in the oil, and its solubility and arc resistance are not as good as tungsten (W), molybdenum (Mo) and other metals. However, copper is the most widely used contact material, and many multiple composite materials (alloy or powder metallurgy) are based on copper, from the comprehensive index of electrical conductivity, arc resistance and price.
silver
The conductivity and thermal conductivity of silver are the most metal, but the production is limited and the price is high, so the usage is limited. Silver surface film (oxide film or sulfurized film) is an ideal fixed contact material because it is easy to crush or not wear. It is often used as a coating for copper and aluminum. However, because of its small hardness, melting point and low boiling point, small current contacts such as relays can only be used, and strong current contacts are made of silver alloy or composite materials.
Tungsten and molybdenum
The biggest feature of tungsten and molybdenum is melting and gasification, high temperature, hard quality, so wear resistance and resistance to fusion welding, but poor conductivity, thermal conductivity, breaking capacity is not strong. The tungsten in the air can produce a 5nm thick surface film, and it is easy to produce tungsten powder under the action of arc. So it is often used to make a composite contact material with high conductive metal for large current.
Gold, platinum, palladium, etc.
This kind of metal is not easy to oxidize, but it is expensive, and it is used for weak electrical contacts or plug-in parts with high precision and sensitivity. Titanium (Ti), zirconium (Zr) and indium (In) are often used as additives to meet some special requirements of contacts.
chromium
Chromium is the rising star of the contact material. Chromium is in the same column with aluminum and tungsten in the periodic table. In some respects, it has similar properties. It is the metal with the highest melting point and boiling point in each cycle. The corrosion resistance of chromium is strong and the affinity for oxygen is great. During the interruption process of the vacuum switch, the evaporation film of chromium has an inspiratory effect, which ensures that the interrupter has a constant vacuum and prolongs its service life. Copper and chromium alloy materials (CuCr) are widely used in vacuum switches, and CuCr materials are also used in SF6 circuit breakers.
Two element multivariate material
The material is divided into two kinds: alloy and composite. The composite is different from that of conventional smelting (Cu-Zn), lead tin (Pb-Sn), stainless steel (Fe-Cr) and other conventional smelting (smelting) alloys. It is a mechanical mixture. It is made by a certain process of sintering of the non intersoluble high conductive material and high melting point material after a certain process. Because its manufacturing method is similar to ceramics, it is also called as a kind of ceramic. Metal ceramic material or powder metallurgy material. Each component of this mixture can be combined in any proportion, which is impossible for smelting metallurgy. Because this material can maintain the physical properties of different materials, it can complement each other and improve the comprehensive performance of contacts. Some composite materials are remelting (such as copper and chromium (CuCr)) in vacuum after mixing in a certain proportion and process. After the arc remelting, the metallographic structure of the composite is greatly improved, and the properties of the material are closer to the "alloy". We are here to call it CuCr alloy. The contact of the actual high-power switch can not be separated from the alloy material. Because the properties of the high pressure arc and the vacuum arc are very different, the material of the vacuum switch contact is different from the contact material in the air, oil and SF6. Therefore, we will give a brief explanation according to the requirements of the two different environments.
Contact material in 1. high pressure arc
Copper tungsten (Cu-W) and silver tungsten (Ag-W) have excellent arc resistance, and their tungsten content is always 50%~80%, which is suitable for high and medium voltage switches. The arc resistant end is made of copper - tungsten material. In medium pressure air blowing circuit breakers, Ag-W or silver, tungsten and graphite (Ag-W-C) are more used, and silver and molybdenum (Ag-Mo) is more widely used in low voltage automatic switch and plastic case circuit breaker than Ag-W and Ag-W-C.
The high conductivity (low melting point) material of molten metal is kept in the skeleton of high melting point metal when the contact is produced by the breaking circuit, which greatly limits the spatter of molten metal. While the contact is closed, the high conductivity material exerts its low resistance. The above capillary action is more resistant to wear in vacuum arc environment.
The largest characteristics of silver graphite (Ag-C) and copper - graphite (Cu-C) are high resistance to welding and good sliding, and are also widely used in arc contacts, nozzle or sliding contact.
Silver - cadmium oxide (Ag-CdO), silver - palladium (Ag-Pd), silver - platinum (Ag-Pt), silver - cadmium (Ag-Cd), silver - nickel (Ag-Ni) and so on are the more contact materials used in low voltage switchgear. Cd can generate CdO at high arc temperature, while CdO can decompose into Cd vapor and oxygen, and has a significant air blow effect. Because Cd is a toxic substance, it is replacing Ag-CdO with silver nickel oxide (Ag-NiO) and silver one or two tin oxide 13 and oxidation of two indium (Ag-SnO2-In2O3). The alloy of Ag and Ni can increase the hardness and improve the transfer of the liquid bridge during the welding and breaking process. (the metal is drawn between the movable and static contacts during the breaking process, and the fracture is often biased. "