Application of the hottest electromagnetic stirrer

2022-08-24
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Application of electromagnetic stirrer in aluminum industry as a mature technical means, electromagnetic stirring technology has been successfully applied to the field of non-ferrous metal production in China since the national "Seventh Five Year Plan", and has achieved good economic and social benefits. Practice has proved that electromagnetic stirrer is a necessary equipment for aluminum and aluminum alloy production

1. Development history and current situation of electromagnetic stirring technology

at present, electromagnetic stirring technology has been very mature, and it has been widely used in the field of ferrous metallurgy all over the world

during the "Seventh Five Year Plan" period, China Nonferrous Metals Industry Corporation listed the development of electromagnetic stirring device for aluminum melting furnace as the key scientific and technological research topic of the "Seventh Five Year Plan". Successfully developed the "furnace bottom plate type" electromagnetic stirring device, filled the domestic gap, reached the international level in the late 1980s, passed the ministerial appraisal, won the second prize of scientific and technological progress of Nonferrous Metals Industry Corporation, and was also listed as a key new technology promotion project during the national "Eighth Five year plan" and "Ninth Five Year Plan"

2. Working principle and characteristics of electromagnetic stirrer

electromagnetic stirrer is generally composed of low-frequency power supply device, inductor and cooling system. The low-frequency power supply device converts the power frequency electricity of 50Hz heat sealing strength experiment into a two-phase orthogonal low-frequency power supply. The frequency is determined according to the size of the furnace and the structure of the inductor, which is generally selected between 0.5 ~ 5Hz. The inductor is located at the bottom of the furnace (see Figure 1), which is composed of iron core and coil. The cooling system is used to cool the coil and core, so that the coil and core will not be damaged by overheating

Figure 1 Schematic diagram of sensor installation

the working principle of the electromagnetic stirrer is similar to that of the linear motor. The sensor is equivalent to the stator of the motor, the aluminum melt is equivalent to the rotor of the motor, and the thickness of the furnace bottom determines the air gap of the motor. Therefore, it is equivalent to a linear motor with a large air gap. When a low-frequency current is introduced into the inductor coil, a traveling wave magnetic field will be generated. This magnetic field passes through the furnace bottom and acts on the aluminum melt, generating induced potential and current in the aluminum melt. This induced current acts with the magnetic field to generate electromagnetic force, so as to promote the directional flow of aluminum melt and play the role of stirring

it can be seen that electromagnetic stirring relies on electromagnetic force to stir the metal liquid non-contact, and will not pollute the melt like stirring with an iron rake. The stirring force can be adjusted by changing the size of the current, and the stirring direction can be changed by changing the phase of the two-phase current. Therefore, the stirring is convenient and sufficient to make the melt temperature and alloy composition uniform, which is very important in the process of aluminum melting and casting. The electromagnetic stirring device is generally equipped with strong stirring, weak stirring, positive stirring, reverse stirring, automatic stirring and other mixing methods, which can meet the different needs of the production process. The electromagnetic stirring device is an irreplaceable equipment in the aluminum melting and casting industry

3. Effect of using electromagnetic stirring device

the electromagnetic stirring device used in aluminum melting furnaces in China has a history of more than ten years, and the electromagnetic stirring technology is mature. The following effects can be obtained by using electromagnetic stirrer in the smelting process:

(1) because electromagnetic stirring is non-contact stirring, there is no pollution to the melt during stirring, which is of great significance for smelting high-purity aluminum and aluminum alloys

(2) electromagnetic stirring is sufficient, and the alloy composition of the melt is uniform, so the quality of the alloy can be greatly improved. Electromagnetic stirring does not have the quality difference caused by manual stirring due to the different skills, physical strength and even labor attitude of operators, and the quality control is easy. Figure 2 shows the change curve of alloy composition (mg) measured in the test, and the sampling points are shown in Figure 3. After magnesium ingot is added to the molten aluminum, electromagnetic stirring is carried out, and the alloy composition is uniform after 5 minutes

Figure 2 alloy composition change curve figure 3 alloy composition sampling point distribution

(3) electromagnetic stirring can make the melt temperature tend to be consistent, so that the temperature difference between the upper and lower parts of the melt is less than 10 ℃. It can even be controlled at 5 ℃, and the melt temperature can be reduced by 50 ℃ in the smelting process to save energy. The temperature change curve of the upper and lower parts of the melt is shown in Figure 4. It can be seen that the temperature of the melt is basically uniform after stirring for 2 minutes

Figure 4 temperature change curve of the upper and lower parts of the melt after stirring

(4) because the electromagnetic stirrer can fully stir the melt, the melt temperature is uniform, the alloy composition can be well diffused, and the mass and heat transfer of the melt are promoted, so the melting time can be shortened. The actual measurement of 10t250kw resistance reverberatory furnace shows that the melting time of ZL102 alloy with qualified composition in one heat can be shortened by 20%, and the production capacity of the equipment has been improved

(5) electromagnetic stirring does not damage the oxide film on the melt surface, which can reduce the oxidation of metal, which not only reduces the burning loss, but also reduces the amount of oxide slag. Electromagnetic stirring can make the oxide slag flow to the furnace door, which is convenient for slag removal, reduce the slag removal time, reduce the phenomenon of oxide slag hanging on the furnace wall, reduce the number of furnace cleaning, and greatly extend the service life of the furnace

(6) electromagnetic stirring can reduce the labor intensity of workers

wood plastic composites give full play to their advantages. Foreign data and domestic practice show that using electromagnetic stirring device in the smelting process of aluminum can reduce the inhomogeneity of melt alloy composition to less than 3 ‰, reduce energy consumption by 10% - 15%, shorten smelting time by about 20%, reduce burning loss by 0.5%, reduce the amount of oxide slag by 20% - 50%, and reduce the number of furnace cleaning by 50%

although the price of the electromagnetic stirrer is high, the inductor of the electromagnetic stirrer must be installed at the bottom of the furnace, and the enterprise needs to have a certain amount of capital to invest in replacing parts for free. But compared with the benefits obtained, it is still worth it. Domestic practice shows that after the electromagnetic stirrer is put into use, the investment can generally be recovered within one to two years, even without considering the benefits of quality improvement. The use of electromagnetic stirring technology is economically desirable

at present, the aluminum market in China is highly competitive and weak, and some enterprises have encountered difficulties in production and operation. However, this is also an opportunity. Enterprises can take advantage of the opportunity with fewer production tasks to carry out technological transformation, improve product quality and reduce the cost of 980.7, so that enterprises can get out of the trough and rebuild brilliance

Tangshan meinit electric company

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