Electric Induction Furnace

General Description

The electric induction furnace whose frequency ranges from 150 Hz to 10000 Hz is called a medium frequency induction furnace. A medium frequency furnace is special smelting equipment suitable for smelting high-quality steel and alloy. It has the advantages of fast melting speed, high production efficiency, strong adaptability, flexible use, good electromagnetic stirring effect, convenient start-up and operation, molten steel covered by slag (reducing air pollution to molten steel), etc. The complete equipment of electric induction furnace includes power supply and electrical control part, furnace body part, transmission device and water cooling system.

The electric induction furnace is especially suitable for large, medium and small furnaces with a 10kg capacity of tens of tons. It is used for melting steel, cast iron, copper, aluminum and other non-ferrous metals and their alloys, and for heat preservation of liquid metals. It has strong adaptability to furnace charge and is suitable for intermittent operation. The furnace structure and service condition are similar to those of a power frequency coreless induction furnace. Since the 1970s, with the increasing power and reliability of high efficiency, static and metal saving thyristor medium frequency power supply, electric induction furnace has been developed rapidly at home and abroad. It has obvious advantages in small and medium capacity and is replacing power frequency coreless induction furnace in large capacity.

Form

The electric induction furnace is made of a single-layer coil of copper tube, and there is a crucible with the refractory knot in the water-cooled induction coil to hold the melted metal. Induction furnace usually consists of four parts: power supply, furnace body (mainly induction coil and crucible made of refractory material in induction coil), capacitor bank (used to improve power factor), control and operation system.

1. Electric Induction Furnace Body

(1) Induction coil of induction furnace: the induction coil is the heart of the electric induction furnace, through which the electromagnetic energy is transformed into heat energy to melt the metal burden in the crucible. The multi-turn coil is made of a rectangular copper tube in a spiral shape. The surface is sprayed with a high-strength insulating paint and wrapped with insulating tape. Fire-resistant mortar is also applied between the turns of the electric induction furnace, and a water-cooled ring is set above and below the induction coil.

(2) Yoke of electric induction furnace: the yoke is made of a high-quality silicon steel sheet, which is distributed on the periphery of the induction coil to support the framework and restrain the magnetic flux leakage outside the induction coil, to prevent the heating of metal components.

(3) Water cooling cable of electric induction furnace: due to frequent furnace tilting, the flexible wire of the water cooling cable is easy to break, and the connecting bolt at the terminal is loose, which may cause current imbalance. Generally, the service life of the water cooling cable is determined as three years according to the number of furnace tilting, and it needs to be replaced after three years. If the bolt changes color, it needs to be updated and tightened in time.

(4) Furnace lining of induction furnace: in production, the temperature of the induction furnace is high, the furnace temperature changes greatly, the electric induction furnace also bears slag erosion and electromagnetic stirring, the high-temperature molten iron directly washes the crucible furnace lining, the furnace lining is easy to be damaged, and the cost of furnace construction is high. It is very important to prolong the service life of furnace lining and reduce the frequency of furnace construction for reducing the cost.

(5) Crucible leakage alarm device of electric induction furnace: to ensure safe production, prevent the occurrence and expansion of leakage accident, help to judge the service condition of furnace lining and prolong furnace life, it is necessary to set up crucible leakage alarm system. Generally, a DC alarm device is adopted, and stainless steel wire bottom electrode (first electrode) contacting with molten iron and stainless steel plate (net) side electrode (second electrode) between induction coils of furnace lining are installed respectively.

2. Hydraulic system of electric induction furnace

It is composed of a hydraulic device, control platform, tilting furnace hydraulic cylinder, furnace cover hydraulic cylinder, etc. It is necessary to regularly check whether there is leakage at each sealing part of the hydraulic system. If it is found, the sealing ring should be replaced, and each rotating part should be lubricated with lubricating oil regularly (for the rotary self-lubricating spherical bearing of tilting furnace, it is necessary to add the old oil to overflow when adding lubricating grease), otherwise, it is easy to cause damage.

3. Water Cooling System of Electric Induction Furnace

Ensure the quality of cooling water and check whether there is a scale regularly. If there is scale, clean it immediately to ensure the cooling effect. The cooling water quality requirements of a general power frequency furnace are as follows: pH value is 6-9, hardness is less than 10mg equivalent / L, total solid content is less than 250mg / L, and temperature rise of cooling water is less than 25 ℃; The water quality of cooling water used for medium frequency power supply: pH 7-8, hardness < 1.5mg equivalent / L, suspended solids: 50mg / L, resistivity > 4000 Ω· cm。 The circulating water in the circulating pool should be tested regularly. When the hardness of the circulating water exceeds 2mg equivalent / L, the circulating water in the system should be emptied and replaced. The cooling water tower should be discharged regularly in exchange for new soft water to prevent the blockage of pipes and nozzles, which will affect the cooling effect and the service life of the furnace lining.

4. Electric control system of electric induction furnace

The dust on the surface of the main circuit and induction coil should be cleaned regularly. Conductive metal dust and iron beans splashed during tapping in the foundry workshop will fall on the surface of the main copper bar or induction coil, which will reduce its insulation capacity, cause discharge and ignition, and easily cause damage to electrical components. Compressed air without water can be used for blowing. The connection screw of the main circuit copper bar also needs to be checked and tightened regularly, otherwise, due to the increase of contact resistance, it will generate large heat at the connection, carbonize its insulating material and cause electric leakage.  

Advantages

Compared with frequency coreless induction furnace, electric induction furnace has the following advantages.

(1) Under the same capacity, the input power of a medium frequency furnace is high, which can be 2-3 times that of a power frequency furnace, thus greatly improving the melting rate of the furnace and reducing power consumption.

(2) Electric induction furnaces can start melting at any time and reduce power consumption.

(3) All or part of the molten liquid can be poured out each time, so the operation is flexible.

(4) The power saving is convenient, which can adapt to the different requirements of power in melting, heat preservation and oven drying.

(5) The operating frequency changes with the resonant frequency of the load circuit, and automatically makes the load circuit maintain a higher power factor. It is not necessary to adjust the load capacitance as the power frequency furnace does.

(6) It is not necessary to set LC three-phase balance device like power frequency furnace for power frequency input three-phase balance.

(7) Under the same output, the capacity of the electric induction furnace is small, so the floor area is greatly reduced, the infrastructure investment is reduced, and the space utilization rate is improved.  

Maintenance

The maintenance of an electric induction furnace is very important. It can find all kinds of hidden dangers in time, avoid major accidents, extend service life, ensure safe production, improve casting quality and reduce cost. The electric parameters, cooling water temperature and shell temperature of key parts of the furnace (furnace bottom, furnace side, induction coil shell, copper bar, etc.) are recorded regularly to monitor the operation of the furnace at any time. Start the diesel generator of the electric induction furnace regularly to ensure reliable operation.

1) Regularly maintain, lubricate and fasten the electric induction furnace according to the specified time (e.g. use anhydrous compressed air to remove dust from an induction coil, copper bar, electric control cabinet, etc.); The lubricating parts are lubricated; Tighten the bolts).

2) Observe the water pressure gauge, water temperature gauge of the electric induction furnace and check the aging degree of the water delivery hose every day; Regularly check the flow of each cooling water branch to ensure that the pipeline is not blocked and the pipe joint is not leaking, especially the cooling water joint in the solid power cabinet. If any leakage is found, tighten the pipe joint clamp or replace the clamp; Regularly check the amount of water in the spray pool and expansion tank of the water tower, power cabinet and water tank, and replenish the water in time; Check the condition of the standby pump frequently, and use the standby pump every 3-5 days to ensure the absolute reliability of the standby pump.

3) Check the capacitor of the electric induction furnace for oil leakage. If there is oil leakage at the capacitor terminal, the nut at the bottom of the terminal can be tightened with a wrench.

4) Medium-term maintenance of the electric induction furnace. The ceramic insulator, bracket, diode, bracket and capacitor of rectifying part, IGBT main contact part, inverter and medium frequency AC copper bar of AC incoming line side are ground with ethanol; Replace some aging water pipes of electrical cabinet, dredge the bottleneck of water nozzle, IGBT water cooling block, and replace AC copper bar insulation board and individual capacitors.

If you are interested in the electric induction furnace, please mail at marketing2@hanrm.com for your solution.

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