Application of electromagnetic stirring technology in aluminum melting industry

Application of electromagnetic stirring technology in aluminum melting industry

Application of electromagnetic stirring technology in aluminum melting industry

Aluminum alloy is one of the most widely used nonferrous metal structural materials in the world’s industry.

It is mainly used in the aerospace industry, aviation industry, shipbuilding industry, machinery manufacturing industry, automobile industry, chemical industry and civil industry.

In the production process of aluminum alloy, most of the contact stirring method is used, which has low production efficiency, serious energy waste, and will also cause secondary pollution of the melt.

The principles and advantages of electromagnetic stirring process technology, using its safety and economic advantages, improve the efficiency and product quality of aluminum alloy production.

Electromagnetic stirring is based on the principle of electromagnetic induction.

A low-frequency current is passed through the inductor to generate an alternating traveling wave magnetic field.

The molten liquid generates an induced potential and current under the action of the magnetic field.

The induced current interacts with the magnetic field to generate an electromagnetic force, which drives the molten liquid to move regularly, thereby achieving the purpose of stirring.

By changing the direction and intensity of the traveling wave magnetic field, the stirring direction and stirring intensity of the molten liquid can be effectively adjusted.

1. Function of Electromagnetic stirrer equipment

⭐Composition homogenization: make the alloy composition of the melt uniform, reduce the relative deviation of chemical composition, meet the alloy’s requirements for composition uniformity, and effectively adjust the composition in primary aluminum production and scrap aluminum recycling.

⭐Ensure the quality of the melt: the stirring process does not destroy the oxide layer, which can reduce the absorption of hydrogen and oxygen by the melt, ensure the quality of the melt, and reduce burning loss.

⭐Temperature homogenization: make the temperature of the upper and lower parts of the melt uniform, reduce the smelting temperature, increase the melting degree of the alloy components at the bottom of the melt, and reduce energy consumption.

⭐Improve production efficiency: During the remelting process of aluminum ingots, the melting time can be shortened and labor efficiency can be improved.

In the production process of aluminum alloys, contact stirring technology has been used in the past, that is, workers must open the furnace door during the production process and use iron rakes to directly stir the aluminum alloy melt manually, which causes a large heat loss.

⭐Reduce pollution: It does not pollute the molten aluminum, which is of great significance for smelting high-purity aluminum and alloys with strict control of iron elements.

⭐ Reduce labor intensity: The labor intensity of workers is also high when the iron rake is operated manually for stirring.

Due to the limitation of the size of the furnace door, the stirring range is small, the stirring uniformity is poor, the production efficiency is low, energy is wasted, and it is easy to cause secondary pollution of the aluminum alloy melt.

Electromagnetic stirring does not require manual stirring, which can reduce the labor intensity of workers and improve working conditions.

2. Installation method of electromagnetic stirrer

Electromagnetic stirrers have different installation forms in different application occasions.

There are two main installation forms of electromagnetic stirrers for aluminum melting furnaces: “bottom-mounted” and “side-mounted”.

At present, the application in China is mainly furnace bottom installation, because the sensor is placed at the bottom of the furnace, and the magnetic field acts on the aluminum liquid through the refractory layer of the furnace bottom.

According to the principle of magnetohydrodynamics, the molten liquid near the bottom of the furnace is affected by a larger magnetic field force, and the upper part of the molten liquid is affected by a smaller magnetic field force.

The closer the molten liquid is to the bottom of the furnace, the greater the flow rate, and the larger the effective area.

The strong surge of a large amount of middle and lower molten liquid drives the entire furnace molten liquid to flow regularly according to the law of magnetic field force, and its stirring effect is good and the comprehensive economic benefits are high.

Side-mounted electromagnetic stirring is mainly an installation form for some special applications or old furnace reconstruction (cannot be installed at the bottom of the furnace).

3. Working principle of electromagnetic stirrer

*The process technology of electromagnetic stirrer, its working principle is to use a special variable frequency power supply to change three-phase alternating current into ultra-low frequency two-phase or three-phase orthogonal alternating current, and then use the working principle of linear asynchronous induction motor to generate a traveling wave magnetic field with variable electromagnetic direction and electromagnetic size, also called a translational magnetic field.

Under the action of the traveling wave magnetic field, this magnetic field can pass through the bottom of the furnace to act on the molten aluminum, and promote the molten aluminum to move in a regular directional parallel manner in the aluminum furnace, thereby completing the contactless stirring of the aluminum solution in the furnace.

*A set of induction coils that are fed with alternating current will generate an appropriate voltage phase difference at their terminals.

Due to the alternating effect of the electromagnetic field, the metals in the electromagnetic stirrer system, including liquid metal, will induce an oscillating magnetic field and current density field, thereby forming a Lorentz force field.

Due to the phase relationship between them, what is generated is not just an oscillating motion, but a force field that causes the aluminum liquid to produce a rotational motion.

*It can be seen that electromagnetic stirring mainly relies on electromagnetic force to stir aluminum liquid non-contactly, and it will not easily contaminate the melt like manual stirring with an iron rake.

The stirring intensity can be adjusted by changing the magnitude of the current, and the automatic stirring direction can be changed by simply changing the phase of the two-phase current.

Therefore, the stirring is convenient and sufficient, so that the temperature of the melt and the aluminum alloy composition are produced uniformly.

*The electromagnetic stirring process generally consists of a low-frequency power supply device, a frequency conversion controller, an isolation transformer, an electrical control cabinet, a furnace bottom sensor and a cooling system.

The frequency conversion controller is the core of the electromagnetic stirring process technology;

The sensor should be placed at the bottom of the aluminum melting furnace and is composed of an iron core and a coil;

The cooling system is mainly used to cool the iron core and coil of the sensor so that the iron core and coil will not be damaged due to overheating of the furnace.

4. Electromagnetic stirrer parts

4.1 Power part

Variable frequency power supply: converts industrial frequency AC power into low-frequency power supply to provide the required low-frequency current for the inductor, and adjusts the size and direction of the stirring force by changing its voltage, frequency and phase.

4.2 Core components

Inductor: usually composed of an iron core and a winding, the winding is usually made of a copper tube.

When a low-frequency current passes through, an alternating traveling wave magnetic field is generated, causing the melt to generate an induced potential and current, and then move under the action of electromagnetic force.

There are two installation methods: bottom-mounted and side-mounted.

4.3 Cooling parts

Cooling device: Most of them are pure water cooling devices, which include single-circulation water-air type and double-circulation water-water type, used to cool components such as variable frequency power supply and sensor to prevent overheating damage.

4.4 Movable and load-bearing parts

Functional trolley: It can realize the movement and positioning of the equipment, facilitate the stirring operation of the smelting furnace at different positions, and can also carry other parts.

4.5 Control and monitoring part

Control system: realizes various parameter settings, operation control and automatic operation of electromagnetic stirring equipment, such as adjusting stirring intensity, frequency, time, etc.

Monitoring system: contains various sensors for real-time monitoring of the operating status of the equipment, such as temperature sensors to monitor component temperature, current sensors to monitor current size, and liquid level sensors to monitor melt level, etc., to ensure stable and efficient operation of the equipment.

4.6 Accessories

Include various connecting lines, pipes, valves, etc., which are used to connect various components to ensure the integrity and normal operation of the equipment.