The intermediate frequency induction furnace is induction furnace with operating frequency in the range of 150 to 10000Hz. It has the advantages of fast melting speed, high production efficiency, strong adaptability, flexible use, good electromagnetic stirring effect, and easy start-up and operation.
IF Induction Furnace
IF Induction furnaces with frequencies in the range of 150 to 10000 Hz are called medium frequency induction furnaces. The medium frequency induction furnace is a special smelting equipment suitable for smelting high-quality steel and alloys. It has fast melting speed, high production efficiency, strong adaptability, flexible use, good electromagnetic stirring effect, easy start-up operation, and the molten steel is covered by slag (reduces atmospheric pollution). contamination of molten steel and other advantages. The complete set of equipment of the medium frequency induction furnace includes: power supply and electrical control part, furnace body part, transmission device and water cooling system. The medium frequency induction furnace is especially suitable for large, medium and small furnaces with a capacity of 10kg and tens of tons. It is suitable for smelting steel, cast iron, non-ferrous metals such as copper and aluminum and their alloys and maintaining the heat of liquid metal. It has strong adaptability to the furnace charge and is suitable for For intermittent operation, the furnace structure and usage conditions are similar to the power frequency centerless induction furnace. Since the 1970s, with the increasing power and reliability of high-efficiency, static and metal-saving thyristor intermediate frequency power supplies, intermediate frequency furnaces have developed rapidly at home and abroad. They have obvious advantages not only in small and medium-sized capacity but even in large-scale applications. In terms of capacity, it is also replacing the power frequency centerless induction furnace.
Composition of IF Induction Furnace
The medium frequency induction furnace uses a single layer of copper tubes rolled into an induction coil, and there is a refractory knotted crucible in the water-cooled induction coil to contain the molten metal. Induction furnaces usually consist of four parts: power supply, furnace body (mainly the induction coil and the crucible made of refractory materials in the induction coil), capacitor bank (used to improve the power factor), control and operating system.
- Induction furnace body (1) Induction coil of the induction furnace: The induction coil is the heart of the induction furnace. The induction coil converts electromagnetic energy into thermal energy to melt the metal charge in the crucible. It is made of a rectangular copper tube and is wound into a multi-turn coil with a spiral shape. Spray high-strength insulating paint and wrap it with insulating tape. Refractory clay is also applied between the turns of the intermediate frequency furnace. There are water-cooling rings above and below the induction coil. (2) Magnetic yoke of the induction furnace: The yoke is made of high-quality silicon steel sheets and is distributed around the periphery of the induction coil to support the skeleton. It also restrains the leakage magnetic flux outside the induction coil to prevent metal components from heating. (3) Water-cooled cables of induction furnaces: Frequent furnace tilting can easily cause the flexible wires of the water-cooled cables to break, and loose connecting bolts at the terminals may cause current imbalance. Generally, the life of the water-cooled cables is determined to be three years based on the number of furnace tilts. They need to be replaced after three years. If the bolts become discolored, they need to be updated and tightened in time. (4) Furnace lining of induction furnace: Induction furnace has high temperature during production, and the furnace temperature changes greatly. It is also subject to slag erosion and electromagnetic stirring. High-temperature molten iron directly washes away the crucible lining. The furnace lining is easily damaged, and the cost of building the furnace is high, which prolongs the induction period. The service life of the furnace lining and reducing the frequency of furnace construction are very important to reduce costs. (5) Crucible leakage alarm device for induction furnace: In order to ensure safe production, prevent the occurrence and expansion of furnace leakage accidents, help judge the usage of the furnace lining, and extend the age of the furnace, it is necessary to set up a crucible leakage alarm system. Generally, a DC-type alarm device is used, which is installed with a stainless steel wire bottom electrode (first electrode) in contact with the molten iron and a stainless steel plate (mesh) side electrode (second electrode) between the furnace lining induction coil.
- Induction furnace hydraulic system It consists of hydraulic device, control panel, tilting furnace hydraulic cylinder, furnace cover hydraulic cylinder, etc. The seals of the hydraulic system should be checked regularly for leaks. If found, the sealing ring should be replaced, and lubricating oil should be added to each rotating part regularly (the rotating self-lubricating spherical bearing of the tilting furnace needs to be filled with old grease when filling it. until the oil spills out), otherwise it will easily cause damage.
- Water cooling system for induction furnace Ensure the quality of the cooling water and check regularly for scale. If there is scale, clean it immediately to ensure the cooling effect. The cooling water quality requirements of general power frequency furnaces: pH value is 6 to 9, hardness <10 mg equivalent/L, total solid content does not exceed 250 mg/L, cooling water temperature rise <25°C; water quality of cooling water used for intermediate frequency power supply : pH value is 7~8, hardness <1.5mg equivalent/L, suspended solids: 50mg/L, resistivity>4000Ω·cm. The circulating water in the circulating pool should be tested regularly. When the hardness of the circulating water exceeds 2 mg equivalent/L, the circulating water in the system should be drained and replaced. The cooling water tower should be drained regularly to replace it with new soft water to prevent pipes and nozzles from being clogged, affecting the cooling effect and the service life of the furnace lining.
- Electrical control system of induction furnace The dust on the surface of the main circuit and induction coil should be cleaned regularly. Conductive metal dust in the foundry, iron beans splashed during tapping, etc. fall on the surface of the main copper bar or induction coil, which will reduce its insulation ability and cause discharge and ignition, which is very easy to happen. Cause damage to electrical components. Compressed air without water can be used for blowing. The main circuit copper bar connection screws also need to be checked and tightened regularly, otherwise due to the increase in contact resistance, greater heat will be generated at the connection, causing the insulating material to carbonize and cause leakage.
Advantage of IF Induction Furnace
Compared with the power frequency centerless induction furnace, the medium frequency induction furnace has the following advantages. (1) Under the same capacity, the input power of the intermediate frequency furnace is high, which can be 2 to 3 times that of the power frequency furnace, thus greatly improving the melting rate of the furnace and reducing power consumption. (2) There is no need for residual melt and large frit, and melting can be started at any time, reducing power consumption. (3) All or part of the melt can be poured every time it is discharged from the furnace, so the operation flexibility is greater. (4) The power can be adjusted easily and can adapt to different power requirements for melting, heat preservation and oven drying. (5) During operation, the operating frequency changes with the resonant frequency of the load circuit and automatically maintains a high power factor in the load circuit. It does not need to be adjusted by increasing or decreasing the load capacitance like a power frequency furnace. (6) The three-phase balance of the power frequency input end does not require an LC three-phase balancing device like the power frequency furnace. (7) Under the same output, the capacity of the intermediate frequency furnace is small, thus greatly reducing the floor area, reducing infrastructure investment and improving space utilization.
IF Induction Furnace Maintenance
The maintenance work of the medium frequency induction furnace is very important. It can detect various hidden dangers in time, avoid major accidents, extend the service life, ensure safe production, improve the quality of castings, and reduce costs. Regularly record the relevant electrical parameters, cooling water temperature and shell temperatures of key parts of the furnace body (furnace bottom, furnace side, induction coil shell, copper bar, etc.), so that the use of the electric furnace can be monitored at any time. Start the diesel generator regularly to ensure reliable operation.
- Carry out regular maintenance, lubrication and tightening of the electric furnace according to the prescribed time (for example: use anhydrous compressed air to systematically remove dust from the induction coil, copper row, electric control cabinet, etc.; lubricate each lubricating part; tighten the bolts).
- Observe the water pressure gauge, water temperature gauge and check the aging degree of the water delivery hose every day; regularly check the flow rate of each cooling water branch to ensure that the pipeline is not blocked and the pipe joints are not leaking, especially the cooling water joints in the solid power supply cabinet. Water leakage is absolutely not allowed. If water leakage is found, tighten the pipe joint clamp or replace the clamp; regularly check the water stored in the water tower spray pool, expansion water tank, power supply cabinet, and water tank, and replenish water in time; Check the condition of the backup pump and use the backup pump every 3 to 5 days to ensure that the backup pump is absolutely reliable.
- Check whether the capacitor is leaking oil. If there is oil leakage from the capacitor terminal, use a wrench to tighten the nut at the bottom of the terminal.
- Mid-term maintenance. Use ethanol to grind the porcelain insulators, brackets, rectifier part diodes, brackets, capacitor porcelain insulators, IGBT (silicon controlled) main contact parts, inverter and intermediate frequency AC copper bars, etc. on the AC incoming line side; replace the aging output in the electrical cabinet. Water pipes, clear the faucet bottleneck, IGBT (thyristor) water cooling block, replace the AC copper bus insulation board, individual capacitors, etc.