Introduction to medium frequency power supply and medium frequency induction melting furnace

1. Medium frequency power supply is a power supply device that converts industrial frequency 50HZ AC power into medium frequency (150HZ or above to 20KHZ). It converts three-phase industrial frequency AC power into DC power after rectification, and then converts DC power into adjustable medium frequency current to supply medium frequency alternating current flowing through capacitors and induction coils, generating high-density magnetic lines in the induction coil, and cutting the metal materials contained in the induction coil, generating large eddy currents in the metal materials.
2. Medium frequency induction furnace often refers to an induction furnace powered by a power supply with a current frequency in the range of 150-8000Hz. The most commonly used frequency is 150-2500Hz. As the capacity of the furnace increases, the current frequency used decreases. The capacity of the medium frequency induction furnace ranges from 50KG to 20T, and the current frequency is 2500-150Hz accordingly.
3. The medium frequency induction furnace uses a medium frequency power supply to establish a medium frequency magnetic field, so that the ferromagnetic material generates induced eddy currents and heats up, achieving the purpose of heating the material. The medium frequency heating furnace uses a 200-2500Hz medium frequency power supply for induction heating, melting, and heat preservation. The medium frequency electric furnace is mainly used for melting carbon steel, alloy steel, cast iron; special steel, and can also be used for melting copper, aluminum and other non-ferrous metals and their alloys and heat preservation of liquid metal. It has strong adaptability to furnace charges and is suitable for intermittent operation; the equipment is small in size, light in weight, high in efficiency, low in power consumption, fast melting and heating, easy to control furnace temperature, and high in production efficiency. The medium frequency induction furnace is a special smelting equipment suitable for smelting high-quality steel and alloys. It has the advantages of fast melting speed, high production efficiency, strong adaptability, flexible use, good electromagnetic stirring effect, convenient startup and operation, and molten steel covered by slag (reducing atmospheric pollution to molten steel).
4. Equipment advantages
Due to the fast heating speed of this heating method, there is very little oxidation. The oxidation and burning loss of medium frequency heating forgings is only 0.5%, the oxidation and burning loss of gas furnace heating is 2%, and the coal-fired furnace reaches 3%. The medium frequency heating process saves materials. The medium frequency furnace has a fast heating speed, high production efficiency, less oxidation and decarbonization, extended mold life, superior working environment, improved workers' working environment and company image, no pollution, low energy consumption, fast melting speed, good power saving effect, and less burning; the medium frequency furnace has a self-stirring function, uniform melting temperature and metal composition, good medium frequency furnace electric heating working environment, good medium frequency furnace starting performance, empty furnace and full furnace can reach 100% start.
5. Use conditions: altitude does not exceed 3000m; ambient temperature is within the range of 3-40℃; (anti-freeze measures are required in areas below 0℃); the monthly average value of the maximum relative humidity in the use area is not more than 90%; there is no conductive dust, explosive gas and corrosive gas that can seriously damage metal and insulation around.
6. High speed, energy saving, stable and reliable KGPS series, IGBT series high and low voltage high power series melting furnace features
● High melting efficiency, good power saving effect, compact structure, strong overload capacity.
● Low temperature around the furnace, less smoke and dust, good working environment.
● Simple operation process, reliable melting operation.
● Uniform metal composition.
● Fast melting temperature rise, easy to control furnace temperature, high production efficiency.
● High furnace utilization rate, convenient replacement of varieties.
● Long arc yoke shields leakage and reduces external magnetic resistance, shields leakage at both ends of the coil, and the inner side of the arc-shaped yoke cross-section is seamlessly attached to the outer wall, which increases the effective magnetic permeability area and provides better support for the coil. The unique forward and reverse coils greatly improve the efficiency of the system.
7. The medium frequency induction furnace uses a single layer of copper tube to roll into an induction coil, and there is a crucible knotted with refractory materials in the water-cooled induction coil to hold the molten metal. An induction furnace usually consists of four parts: power supply, furnace body (mainly induction coil and crucible made of refractory material in the induction coil), capacitor bank (used to improve power factor), control and operating system.
1). Composition and maintenance of induction furnace body
● Induction coil of induction furnace: The induction coil is the heart of the induction furnace. It converts electromagnetic energy into heat energy to melt the metal charge in the crucible. It is wound into a multi-turn coil in a spiral shape by a rectangular copper tube. The surface is sprayed with high-strength insulating paint and wrapped with insulating tape. Refractory glue is also applied between the turns of the medium-frequency furnace. Water cooling rings are installed above and below the induction coil.
● Magnetic yoke of induction furnace: The yoke is made of high-quality silicon steel sheets and distributed around the periphery of the induction coil. It plays the role of supporting the skeleton and also plays the role of restraining the external leakage magnetic flux of the induction coil to prevent the metal components from heating up. 

● Water-cooled cable of induction furnace: Frequent furnace tilting may cause the flexible wire of water-cooled cable to break and the connecting bolts at the terminal to loosen, which may cause current imbalance. Generally, the life of water-cooled cable is three years according to the number of furnace tilting. It needs to be replaced after three years. If the bolts change color, they need to be updated and tightened in time.
● Lining of induction furnace: Induction furnace has high temperature and large furnace temperature changes during production. It also bears slag erosion and electromagnetic stirring. High-temperature molten iron directly washes the crucible lining, which is very easy to damage. The cost of building a furnace is high. Extending the service life of the induction furnace lining and reducing the frequency of building a furnace are very important for reducing costs.
● Crucible leakage alarm device of induction furnace: In order to ensure safe production, prevent the occurrence and expansion of leakage accidents, help judge the use of the lining, and extend the life of the furnace, it is necessary to set up a crucible leakage alarm system. Generally, a DC alarm device is used, and a stainless steel wire bottom electrode (first electrode) in contact with the molten iron and a stainless steel plate (net) side electrode (second electrode) between the lining induction coil are installed respectively.
2). The hydraulic system of the induction furnace
It consists of a hydraulic device, an operating console, a hydraulic cylinder for tilting furnaces, a hydraulic cylinder for furnace covers, etc. The hydraulic system seals should be checked regularly for leakage. If found, the seals should be replaced, and the rotating parts should be lubricated regularly with lubricating oil (the self-lubricating spherical bearings of the tilting furnace should be filled with grease until the old oil overflows), otherwise it is very easy to cause damage.
3). Water cooling system of the induction furnace
Ensure the quality of the cooling water and regularly check for scale. If there is scale, it should be cleaned immediately to ensure the cooling effect. The water quality requirements of the cooling water of the general power frequency furnace are: pH value 6-9, hardness <10mg equivalent/L, total solid content not exceeding 250mg/L, cooling water temperature rise <25℃; the water quality of the cooling water used for the medium frequency power supply: pH value 7-8, hardness <1.5mg equivalent/L, suspended solids: 50mg/L, resistivity >4000Ω·cm. The circulating water in the circulating water 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 regularly drained and replaced with new soft water to prevent the pipes and nozzles from being blocked, which will affect the cooling effect and the service life of the furnace lining.
4). The electronic control system of the induction furnace
Compared with the industrial frequency coreless induction furnace, the medium frequency induction furnace has the following advantages.
● Under the same capacity, the input power of the medium frequency furnace is high, which can be 2 to 3 times that of the industrial frequency furnace, thereby greatly improving the melting rate of the furnace and reducing power consumption.
● No residual melt and large melting blocks are required, and melting can be started at any time, reducing power consumption.
● All or part of the melt can be dumped each time the furnace is taken out, so the operation flexibility is greater.
● The power adjustment is convenient, which can adapt to the different power requirements during melting, heat preservation and furnace baking.
● 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, without the need to adjust by increasing or decreasing the load capacitance like the industrial frequency furnace.
● The three-phase balance of the industrial frequency input end does not require the installation of an LC three-phase balancing device like the industrial frequency furnace.
● Under the same output, the capacity of the medium frequency furnace is small, so the floor space is greatly reduced, infrastructure investment is reduced, and space utilization is improved.
5). Features of KGPS series and IGBT series heating furnaces
● Fast heating speed, high production efficiency, less oxidation and decarbonization, saving materials and forging die costs
● Since the principle of medium frequency induction heating is electromagnetic induction, its heat is generated in the workpiece itself. Ordinary workers can carry out continuous forging tasks ten minutes after going to work with a medium frequency electric furnace, and there is no need for professional workers to carry out furnace burning and furnace sealing work in advance. There is no need to worry about the waste of billets heated by coal furnaces due to power outages or equipment failures. Since this heating method heats up quickly, there is very little oxidation. Compared with coal-fired furnaces, each ton of forgings can save at least 20-50 kg of steel raw materials, and its material utilization rate can reach 95%. Since this heating method heats evenly and the temperature difference between the core and the surface is very small, the life of the forging die is greatly increased in forging, and the surface roughness of the forging is also less than 50um.
● Superior working environment, improving the working environment of workers and the image of the company, no pollution, low energy consumption
● Compared with coal furnaces, workers in induction heating furnaces will no longer be baked and smoked by coal furnaces under the scorching sun, and can meet the various indicators of the environmental protection department. At the same time, it establishes the company's external image and the future development trend of the forging industry. Induction heating is the most energy-saving heating method in electric heating furnaces. The power consumption of a ton of forgings heated from room temperature to 1100℃ is less than 360 degrees.
● Uniform heating, extremely small temperature difference between the core and the surface, and high temperature control accuracy.
● Induction heating generates heat in the workpiece itself, so the heating is uniform and the temperature difference between the core and the surface is extremely small. The application of temperature control system can achieve precise control of temperature and improve product quality and qualified rate.
● The medium frequency induction furnace heating device has the advantages of small size, light weight, high efficiency, excellent heat processing quality and favorable environment. It is rapidly replacing coal-fired furnaces, gas furnaces, oil furnaces and ordinary resistance furnaces. It is a new generation of metal heating equipment.
● The medium frequency furnace is the main equipment of the casting, forging and heat treatment workshop. Its working stability, reliability and safety are the guarantee for the normal and stable operation of the casting, forging and heat treatment production line of the flow operation.

Composition of medium frequency power supply, medium frequency induction melting furnace, diathermy furnace and heat treatment furnace complete set of equipment

● Power supply and electronic control part: KGPS thyristor (thyristor) variable frequency power supply, IGBT variable frequency power supply,
● Furnace body part: medium frequency induction furnace (steel shell, aluminum shell); medium frequency diathermy furnace; medium frequency transformer; inductor,
● Transmission device: hydraulic system of induction furnace, reducer drive device.
● Rectifier transformer for medium frequency power supply, closed-circuit cooling and dewatering system, water cooling system for induction furnace, and alarm device for crucible leakage furnace.

Application

Medium frequency induction furnace is widely used for smelting of ferrous metals, non-ferrous metals, and precious metals (mainly used for smelting steel, alloy steel, special steel, cast iron and other ferrous metal materials and smelting of stainless steel, zinc and other non-ferrous metal materials, and can also be used for smelting and heating of non-ferrous metals such as copper and aluminum, and heat preservation, and can be operated in dual connection with blast furnace); powder metallurgy; forging heating [used for heat penetration, heating supplement, online heating of blue quenching and cutting, local heating, online forging of metal materials (such as precision forging of gears, half-axle connecting rods, bearings, etc.), extrusion, hot rolling, heating before shearing, spray heating, hot assembly, and overall quenching, annealing, tempering of metal materials. ]; parts heat treatment [mainly shafts (straight shafts, variable diameter shafts, camshafts, crankshafts, gear shafts, etc.); gears; sleeves, rings, discs; machine tool screws; guide rails; planes; ball heads; hardware tools and other mechanical (automobile, motorcycle) parts surface heat treatment and overall quenching, annealing, tempering of metal materials], etc.

Our company can undertake projects

Our company undertakes high-speed, energy-saving, stable and reliable KGPS series high, low voltage and high power, IGBT series medium frequency induction heating power supply, medium frequency induction melting furnace, insulation furnace, diathermy furnace, heat treatment furnace complete set of equipment design, manufacturing, installation, commissioning and normal operation technical guidance!