Вплив окислів металів на ерозійну стійкість контактів електричних апаратів

А. М. Мрачковський, С. О. Бурлака

Анотація


THE INFLUENCE OF METAL OXIDES ON EROSIVE STABILITY OF CONTACTS OF ELECTRIC DEVICES

  1. A.   Mrachkovskyi ,S. Burlaka

Silver and its alloys are widely used as a material for contacts of electric apparatuses up to 1000V. Due to the scarcity and expensive silver, there is a need to increase the strength of the electrostatic resistance of the silver-based contacts.The known sintered electro-contact materials on the basis of silver of the type AgKdln and KMK A-10 have insufficient electroerosive stability and high toxicity.

Electrical erosion and mechanical wear of the contacts can be controlled by the structure of materials. Principles of structure formation for bursting contacts assume the presence in electrically conductive and thermal conductive matrix of additives with excellent physical and mechanical properties. Such additives can perform various functions, strengthen the matrix, extinguish the arc, and change the work of the electron output, which affects the mobility of the arc base. When moving the arc from one separate inclusion to another, there is a dissipation of the energy of the arc, reducing the amount of energy that is absorbed by contact - the parts. Such a structure prevents the formation of a molten crater and reduces the ejection of the material under the action of an electric arc.

The main criterion of additives is high thermodynamic stability, which is characterized by the absence of chemical interaction with matrix metal and a small tendency to coalescence, when a soluble-sedimentary process of a material occurs at high temperatures. These requirements correspond to oxides of metals.

The results of researches on the electrodeposite stability of a new contact material on the basis of silver with additives of metal oxides increase the durability of the investigated material in 1,5 times compared with the serial type of KMK-A10.

Research of a new composite material on the basis of silver with additives of tin oxides, tungsten, indium was obtained by powder metallurgy. The production technology of the composite material includes the following operations: mixing silver powder with powders of other additives: tin oxides, indium and zirconium metal; restoration of a mixture of silver with additives in a medium of hydrogen at a temperature of 650 ° C, a holding time of 2 hours; The resulting powders of silver alloys - tin, silver - tin - indium and zirconium powder were subjected to internal oxidation at 750 ° C for 2 hours; A powder of tungsten trioxide (WO3) was added to the resulting powders and contact blanks were pressed.

The results of the tests showed that when introduced into the silver matrix of the listed ingredients with the extraction of toxic cadmium oxide, the electrosphere stability of the contact details is increased by 1.5 times (Figure) and provides a high degree of environmental cleanliness of the material. This is achieved by a positive influence on the contact properties of metal oxides, which are introduced into the silver matrix. Metals oxides have the following properties: in a wide range of concentrations are fused with silver, have high pressure and easy sublimation, so as not to form oxide accumulation on the contact surface, in a wide range of alloys have the ability to internal oxidation, do not contribute to re-ignition of the electric arc.

Due to the relatively high hardness of tin oxide (SnO2), which is (Hv = 60 ksg / mm2) in comparison with silver (Ag) - (Hv = 25kg / mm2), the hardness of the silver matrix increases due to the location of small particles of SnO2 in the middle of Ag .

Driving of indium oxide (In2O3) contributes to the leakage of the internal oxidation of the contact material, accelerates the diffusion of tin into silver, resulting in evenly distributed tin particles throughout the material, thereby increasing the strength and hardness of the material as a whole.

The introduction of zirconium (Zr) into the contact material dispersedly changes the silver matrix, since the hardness (Hv = 150 kgf / mm2) is six times the silver hardness (Hv = 25 kgf / mm2). Also zirconium absorbs oxygen from molten silver, the solubility of which is about 20 volumes of the melt. At lower temperatures, oxygen released from the melt is rapidly absorbed by zirconia, which reduces the spatter of liquid silver and the time of burning the electric arc.

Additives of tungsten oxide (WO3) are well moistened and coated with solid particles of SnO2 oxides, which remain in an overheating state in the mass of silver melting under the action of an electric arc. This allowed SnO2 particles to remain in the molten mass of silver, to increase its viscosity, which positively affects the wear resistance. This material is characterized by a high degree of environmental safety, a sufficient level of contact properties, relatively low cost and is recommended for the replacement of serial contacts such as KMK A-10.


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Посилання


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