In recent years, Electroheat Technologies LLC of the United States and Eldec Schwerk Induction GmbH of Germany have proposed the use of dual-frequency simultaneous induction heating quenching to make the contour quenching of gears realistic. It is the first time that this induction heating method can accelerate the austenitization. To achieve "self-quenching", which has the advantage of laser quenching. Such devices are also available for sale in Japan.
The SDF technology supplies both the intermediate frequency MF and the high frequency HF energy on one induction coil. The amplitudes of the two frequencies can be controlled independently, that is, the output share ratio of MF and HF can be adjusted at the same time, preferably at the root and the top of the tooth. The surface of the bit is hardened to meet the technical requirements of the workpiece. In order to achieve the true contour hardening of the gear without affecting the organization and performance of the core, the heating time should be less than 0.5 s, while the power ratio to the root and flank is approximately 2:1. It has been reported that for Ф70mm automotive gears, the power requirements are about 400kW MF and 200 kW HF, and the heating time is 0.5s, so that the maximum output can reach 3600/h. Obviously, the shorter the heating time is, the more favorable it is to reduce the deformation when a certain surface hardening depth is reached. Another advantage of applying SDF technology is that it can increase the surface residual compressive stress of the treated component, which is advantageous for improving the fatigue strength.
(2) Liquid medium induction carburizing LINCARB is a simple, inexpensive and pollution-free process. The treated workpiece and the heating inductor are immersed in the active medium containing carbon liquid, and the surface of the workpiece is heated by the induced high-frequency current to rapidly heat the surface of the workpiece to a temperature below the melting point of the material, and the liquid active medium is directly decomposed on the surface of the workpiece. A large number of atomic high-activity carbons are absorbed by the surface of the workpiece and diffused to a certain depth of the workpiece to complete the carburizing process. It is also suitable for Ti alloys and some superalloys other than steel. Under certain processing conditions, the surface layer of the steel can have a high wear-resistant Lasite layer with a carbon content of 2% to 6.67%. Therefore, this is a high-efficiency method that can complete the whole process of chemical heat treatment in seconds and minutes, and the surface layer structure and properties are improved compared with conventional chemical heat treatment.
2.3.3 Vacuum heat treatment: vacuum heat treatment technology has no oxidation, no decarburization, degreasing and degassing, good surface quality, small deformation, good comprehensive performance, long service life, pollution-free and pollution-free, automation Many outstanding advantages, such as high and energy conservation, have developed rapidly in China in the past 20 years. However, it also has the disadvantage that some alloying elements such as Mn and Cr in the workpiece will evaporate in a vacuum, so it is protected by inert gas or nitrogen in the production. In addition, its equipment investment is large, it should be able to recover in a short period of time after the production task is full.
Since the 1990s, many new technologies have emerged, such as high pressure gas quenching and ultra high pressure gas quenching, vacuum cleaning technology, high temperature and ultra high pressure vacuum heat treatment technology, vacuum high pressure gas quenching furnace with double convection circulation system, gas vacuum furnace, fluid state. Vacuum furnace, hot wall vacuum carburizing furnace, continuous vacuum furnace, etc. According to development, future metal processing will rely more on vacuum technology. It is estimated that at the end of the 20th century, vacuum heat treatment furnaces in industrialized countries accounted for 23% of heat treatment equipment.
Some people have quantitatively compared the thermal conductivity of various liquid quenching media under different pressures. It can be seen from the comparison that as the gas pressure increases, the thermal conductivity increases. The heat transfer capacity of commonly used cooling gas is very different. The cooling capacity of H2 in N2, H2, He and Ar is the strongest, followed by He, N2 and Ar. The N2 is the cheapest, so the application is the most widely used. . For gas quenching furnaces of 2 MPa or more, He is mostly used, but since He is expensive, it should be considered for recycling.
The double-chamber high-pressure gas quenching is superior to the single-chamber furnace in cooling effect. After the austenitizing heating, the workpiece is moved to the cold chamber furnace for gas quenching, which can reduce the quality of the material to be cooled by 50%. It can be reduced to increase the gas flow rate, that is, increase the cooling rate.
There are many manufacturers of vacuum furnaces in the world, and the United States, Japan, Britain, France and other products are put into use in China. The two-chamber high-pressure gas-quenching vacuum furnace developed by Schmetz in Germany has been designed to separately separate the heating chamber and the cooling chamber, which improves the thermal efficiency, saves energy and reduces pollution, and has the following characteristics: (1) Double blowers for cooling and heating (fan) structure; (2) 2R ventilation flaps with automatic control; (3) hot brake structure with sealed heat insulation; (4) automatic transfer of workpiece transfer mechanism, movement in furnace heating chamber and cooling chamber. The company's dual-chamber high-pressure gas quenching vacuum furnace is well designed to solve the high-pressure gas flow cycle cooling in high-pressure gas quenching heat treatment, heating chamber heat flow circulation soaking and heating and cooling chamber vacuum sealing and heat insulation, product performance and function. Excellent, can be said to be one of the examples of vacuum heat treatment furnaces optimized for modern design.
The hot wall vacuum carburizing furnace is a vacuum carburizing furnace specially designed and developed according to actual production requirements, which solves many problems of the traditional cold wall vacuum carburizing furnace. Its characteristics are as follows: (1) hot-wall structure, the vacuum chamber shell does not use water-cooled structure, the vacuum inside the insulation layer reduces the heat loss caused by water cooling, so that the furnace temperature distribution and uniformity are improved, and the energy consumption of the heating element is reduced by about 60. (2) closed radiant tube heating element, the heating element is not in direct contact with the hydrocarbon decomposition gas in the furnace; (3) the ceramic fiber insulation material is made into a heat insulation layer, which can be oxidized (air) into the furnace and blown away in the furnace Carbon black on the wall surface; (4) Automatic carbon black system, after the furnace temperature reaches 850 ° C, the air is blown into the furnace to burn off the carbon black, and the work of periodically cleaning the furnace chamber is successfully eliminated. It is not only used for vacuum carburizing, but also for various types of carburizing processes, such as endothermic atmosphere carburizing, methanol carburizing and nitrogen-based atmosphere carburizing.
The development, development and promotion of gas vacuum furnace equipment and technology are in line with energy-saving technical policies and industrial needs. The electric heating vacuum furnace has the following characteristics: (1) high thermal efficiency, high production efficiency; (2) lower operating cost; (3) reduced maintenance, Ipson International of Germany introduced the design structure of several gas vacuum furnaces and A new model developed in recent years.
The intelligent control of high-pressure gas quenching vacuum furnace is very important. It is required to change the heating mode of the workpiece, change the cooling mode and cooling speed, so that the workpiece can obtain excellent performance and reduce deformation, thereby improving production efficiency and quality level and reducing dispersion. At the same time, it can save energy, save gas source, and gradually realize flexibility. In recent years, the process parameters control fusion CAD technology, database and expert system of high-pressure gas quenching vacuum furnace have become increasingly mature.
Vacuum heat treatment In order to maintain the brightness of the workpiece and excellent surface quality, to meet the technical requirements of high-precision parts or the needs of subsequent processing, the workpiece should be cleaned, degreased and dried before and after processing. Several improved vacuum degreasing cleaning technologies have appeared in recent years. . Japan's Fujitsu Company uses solvent oil cleaning agent to degrease the workpiece, and then distills off and recycles the effluent. This method is cheaper and suitable for small and medium-sized enterprises, and its development is promising. Domestic related products have appeared in vacuum cleaning.
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