Vacuum technology

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With the rapid development of modern industrial technology, people have higher and higher requirements for the use of mechanical parts. The more severe use environment puts forward higher requirements for the high temperature resistance, wear resistance, fatigue resistance and other properties of metal materials.

For some specific metal or alloy materials, whether in the early stage of research and development test or in the later stage of mass production, research or obtaining high-performance metal alloy materials need the support of metal smelting equipment, surface heat treatment equipment, etc. in many special heating or smelting methods, induction heating technology is used for smelting metal materials or materials in a certain process Sintering and heat treatment play an important role.

Induction heating technology usually refers to a kind of technology which can make the material with better magnetic induction obtain induction current through the principle of electromagnetic induction under the condition of vacuum to achieve the purpose of heating.

The current passes through the electromagnetic coil around the metal material at a certain frequency, and the changing current produces the induced magnetic field, and makes the metal internal generate the induced current, and generate a lot of heat, which is used to heat the material. When the heat is relatively low, it can be used in vacuum induction heat treatment and other processes. When the heat is high, the heat generated is enough to melt the metal, which is used to prepare metal or alloy materials.

At present, vacuum technology is the most efficient, fast, energy-saving and environmental friendly induction heating technology for metal materials. This technology is mainly used in vacuum furnace and other equipment, and has a wide range of applications.

The solid metal raw materials are put into the crucible wound by the coil. When the current flows through the induction coil, the induction electromotive force will be generated, and eddy current will be generated inside the metal charge. When the current heat is greater than the heat dissipation rate of the metal charge, the heat will accumulate more and more, and when the temperature reaches a certain degree, the metal will melt from the solid to the liquid, so as to achieve the purpose of smelting metal.

Because the whole process takes place in the vacuum environment, it is conducive to the removal of gas impurities in the metal, and the metal alloy material is more pure.
Meanwhile, in the smelting process, through the control of vacuum environment and induction heating, the smelting temperature can be adjusted and the alloy metal can be supplemented in time to achieve the purpose of refining.

In the melting process, because of the characteristics of Vacuum technology, the liquid metal materials in the crucible can be automatically stirred due to the interaction of electromagnetic force, making the composition more uniform, which is also a major advantage of Vacuum technology.

Compared with traditional smelting, vacuum induction smelting has many advantages, such as energy saving, environmental protection, good working environment and low labor intensity. Using  Vacuum technology, the final casting alloy material has less impurities, the added alloy proportion is more appropriate, and more in line with the requirements of the process for various properties of the material.

At present, vacuum technology has been widely used, from thousands of grams of induction furnace used for experimental research to dozens of tons of large-scale induction furnace used for actual production. Because of its advantages such as simple operation process, rapid melting and temperature rise, easy control of smelting process, uniform composition of smelting gold and so on, it has great application prospects, and has been rapidly developed in recent years.

Vacuum sintering
Vacuum sintering refers to the sintering of metal alloy or metal compound powder into metal products and metal billets under vacuum environment (10-10-3pa). In vacuum sintering, there is no reaction between metal and gas, and there is no effect of adsorbed gas. Not only the densification effect is good, but also it can play the role of purification and reduction, reduce the sintering temperature, and the sintering ratio at room temperature can be reduced by 100 ℃ ~ 150 ℃, save energy consumption, improve the life of sintering furnace and obtain high-quality products.
For some materials, it is necessary to realize the combination of particles by means of atom migration through heating, while induction sintering technology plays a role in heating them in this process.

Advantages of vacuum induction sintering
Under vacuum condition, it helps to reduce harmful substances (water vapor, oxygen, nitrogen and other impurities) in the atmosphere and avoid a series of reactions such as decarburization, nitriding, carburizing, reduction, oxidation, etc.

In the process, the amount of gas in the pores is reduced, the chemical reaction of gas molecules is reduced, and the oxide film on the surface of the material is removed before the liquid phase occurs, so that when the materials are melted and combined with each other, the material can be combined more tightly, and the wear resistance and strength are improved.
In addition, vacuum induction sintering can also reduce the cost of products.

Due to the relatively low gas content in vacuum environment, the convection and conduction of heat can be ignored. The heat is mainly transmitted to the material surface by means of radiation. It is also very important to select the appropriate heating components according to the specific sintering temperature and physical and chemical characteristics of the material. Compared with vacuum resistance heating, induction sintering adopts medium frequency power supply to avoid the high temperature insulation problem of vacuum furnace using resistance internal heating.
At present, induction sintering technology is mainly used in the field of iron and steel, metallurgy. In addition, in the special ceramic materials, induction sintering enhances the bond of solid particles, which helps the grain grow, compress the void, and then increase the density to form dense polycrystalline sinter. Induction sintering technology is also widely used in the research of new materials.

Vacuum heat treatment
At present, induction heat treatment technology is widely used, mainly focusing on induction quenching technology. Put the workpiece into the inductor (coil). When a certain frequency of alternating current is introduced into the inductor, an alternating magnetic field will be generated around. The electromagnetic induction of alternating magnetic field makes the work piece produce closed eddy current. Due to the skin effect, that is, the distribution of induced current on the cross-section of the workpiece is very uneven, the current density on the surface of the workpiece is very high, and gradually decreases inward.

The electric energy of the high density current on the surface of the workpiece changes into heat energy, which makes the temperature of the surface increase. That is to say, the higher the frequency of the surface heating current is, the greater the current density difference between the surface and the interior of the workpiece is, and the thinner the heating layer is. The surface quenching can be realized by cooling the heating layer rapidly after the temperature exceeds the critical point of the steel.

It can be seen from the principle of induction heating that the penetration depth of current can be appropriately changed by adjusting the frequency of current passing through the induction coil, and the adjustable depth is also a big advantage of induction heat treatment. However, induction hardening technology is not suitable for complex mechanical parts due to its poor adaptability. Although the quenched workpiece surface has large compressive internal stress and high fatigue fracture resistance, it is only suitable for the production line of simple workpiece.

At present, induction hardening technology is mainly used in the surface hardening of crankshaft, camshaft and other parts in the automobile industry. Although these parts are simple in structure, their working environment is bad, and they have certain requirements for wear resistance, bending resistance and fatigue resistance. It is also the most reasonable method to improve its wear resistance and fatigue resistance by induction quenching.