The mixed powder sintering method involves uniform mixing of the Cu powder and the Cr powder in a certain range of particle size, followed by compaction, sintering, and the like to prepare a Cu-Cr alloy contact material uniformly distributed in the Cr particles. However, the products produced by this process have a higher voidage (10%-30%) and must be processed for densification. Process flow and typical microstructure of mixed powder sintering preparation technology.
The molten C. solution is infiltrated into the interstitial spaces of the Cr particle framework through high-pressure impregnation to obtain even distribution of Cr particles. C: Cr alloy contact materials China's earliest introduction of the German Siemens company's technology, infiltration method for the preparation of CuCr alloy Later, the White Line developed a single crystal furnace to infiltrate the Cr powder after sintering into an ingot.
Its relative density is 98%-99%, but due to the shrinkage effect of Cu liquid cooling, core-free or local copper-free defects and abnormal enrichment of Cr are often generated. The process of pressure infiltration process and the typical product microstructure. Cr powder induces mixing of C. powder. Two Irc skeleton pre-firing pressure impregnation method is to pre-fabricate Cr powder particles with a certain particle size range into the skeleton structure. The main quality problems that currently exist in these two methods are: (1) The gas content in the material is too high. The powder metallurgy technology produces C:, a Cr alloy contact material process, due to the strong suction of C, and C: powder, and the multiple processes and complexity of the powder metallurgy process, it is difficult to obtain low gas content. material.
(2) The particle size control of the Cr phase in the material is difficult. In the Cu-C: alloy contact material, as the Cr particle size decreases and is evenly distributed, the breaking performance of the Cu-C: alloy contact is improved, but at present The production of Cu-C: alloy, due to Cr in the high-temperature sintering process is prone to aggregation and growth, and its final size is mostly 70 to 15. Spell m, can not meet the vacuum circuit breaker to high voltage, large capacity, miniaturization of the development Claim.
(3) The product is difficult to achieve the defects of densification of the solidification of the powder metallurgy process, ie, the difference in the density of the material, the Cu and C:} phases in the alloy are not sufficiently tightly bonded, holes and other sintering defects are generated inside the material, and the vacuum switch actually operates. It will greatly reduce the switching performance and pressure strength of the switch, affecting the reliability of the switch.
(4) Recovery of production anaerobic material Cr is a diffusion type melt in the Cu liquid, and alloying is difficult. Using conventional techniques, Cu and Cr in Cu-Cr alloy cannot be separated and recovered. Therefore, a large amount of Cu-Cr alloy scrap contacts and scraps can only be accumulated or sold as scraps, which can reduce material utilization and increase the cost of production.
In view of the above problems, in recent years, both domestic and foreign academics and industry are committed to the development of new Cu-Cr alloy contact materials and their preparation techniques. At present, there are two main ways: First, adding high in the Cu-Cr alloy Melting point metals and trace elements can increase the voltage resistance of alloys with low Cr content.
Japan's Mitsubishi Corporation has developed a material that incorporates 0.3% Bi, Te, and Sb in a Cu-Cr alloy, which reduces the cut-off value of the contact material and improves the resistance to welding. A kind of Cu-Cr-Fe contact material developed by the Beijing Iron and Steel Research Institute has a Fe content of about 5%. On the one hand, it can improve the liquid-phase sintering process. On the other hand, solid solution strengthening and dispersion strengthening produced by Fe element can Improve the withstand voltage strength, ensure that the breaking performance is not affected, improve the resistance to welding, and reduce the cut-off value, such as the average cut-off value of CuCrFe7 is 2% lower than CuCr50, and reduce part of the cost.
Another way to solve the current problems of Cu-Cr alloys is to improve process parameters or to seek new manufacturing processes. In order to overcome the disadvantages of traditional powder metallurgy technology, so far, many new Cu-C alloy contact materials have been developed, including vacuum arc melting and laser surface remelting.
In the arc melting method, a Cu-Cr electrode vacuum-sintered by isostatic pressing is used as a fusible electrode in an arc melting apparatus. In a vacuum or in an inert gas, the Cu-Cr electrode rapidly melts in the water under the high temperature of the DC arc. The copper mold solidifies to form an ingot. Siemens uses an arc consumable electrode smelting method [8] to obtain a Cu-Cr contact material with an average particle size of one-tenth of the infiltration method.
The surface of the contact is formed with thin particles, dense structure, and even distribution of thin layers to improve the performance of the material. Electroslag smelting method Chuanchuan is a new process developed for arc smelting which is easy to produce chromium dendrites. Slag is used as a heating element. When the Cu-Cr alloy liquid passes through the slag pool, the oxides are trapped and the oxidation in the raw material is removed. Inclusions, to avoid producing Cr dendrites.
Due to the more uniform distribution of Cr particles in the alloy powder and the smaller size, the average size of Cr particles in the final product can reach z-20. The performance comparison of Cu-Cr contact materials prepared by various methods. In recent years, mature injection molding near-final technology has gradually been applied to the research and development of Cu-Cr contact materials. The product is performed in a vacuum or inert atmosphere with a short process flow, so that the gas content in the as-deposited material can be controlled.
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