Development of induction heating technology and equipment
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The rapid development of power electronic devices and technologies in the 20th century has greatly promoted the development of induction heating technology.
In 1957, the United States developed a thyristor as a milestone in power electronics, marking the beginning of modern power electronics technology and the revolution in induction heating technology. In 1966, Switzerland and West Germany first used thyristors to develop induction heating devices, and the induction heating technology began to develop rapidly.
After the 1980s, power electronic devices developed rapidly again, and devices such as GTO, MOSFET, IGBT, MCT, and SIT appeared one after another. Inductive heating devices have also gradually abandoned thyristors and are beginning to adopt these new devices. IGBTs and MOSFETs are more commonly used today, IGBTs are used in higher power applications, and MOSFETs are used in higher frequency applications. According to reports, foreign countries can use IGBT to achieve induction power of more than 1000kW, the frequency exceeds 50kHz. MOSFETs are more suitable for high-frequency applications, usually used in small and medium power applications of several kilowatts, the frequency can reach more than 500kHz, even a few megahertz. However, there are also high-power induction heating devices using MOSFETs, such as the 2000kW/400kHz device developed by the United States.
The real application of induction heat treatment technology in China began in 1956 and was introduced from the former Soviet Union, mainly in the automotive industry. With the manufacture of power supplies in the 20th century, induction hardening process equipment has also been developed. At present, the domestic induction hardening process equipment manufacturing industry is also expanding, and there are many varieties of products. The equipment that originally needed to be imported is gradually replaced by national products. While saving foreign exchange for the country, it has developed domestic related enterprises. At present, the service target of the induction heating manufacturing industry is mainly the automobile manufacturing industry. In the future, the modern metallurgical industry will have a greater demand for induction heating.
First, induction heating characteristics
Induction heating technology is fast, clean, energy-saving, easy to automate and online production, high production efficiency, is an internal heat source, is a non-contact heating method, can provide high power density, has a highly flexible choice on the heating surface and depth Sex, can work in various carrier gases (air, protective gas, vacuum), low loss, no physical pollution, in line with environmental protection and sustainable development policy, is one of the green environmental heating process. It has become the mainstream of heat treatment technology with controlled atmosphere heat treatment and vacuum heat treatment.
Its main applications are:
(1) Metallurgical non-ferrous metal smelting, heat treatment of metal materials, heat penetration of profiles produced by forging, extrusion, rolling, etc., welds produced by welded pipes.
(2) Mechanically manufacturing quenching of various mechanical parts, and heating of heat treatment such as tempering, annealing and normalizing after quenching; and heat transfer before pressure processing.
(3) Seals for light industrial cans and other packaging, such as the sealed packaging of the famous Tetra Pak.
(4) Heating of electronic tube vacuum degassing.
(5) Special applications such as plasma, surfacing, etc.
Taking FAW as an example, in the production of medium-sized cars, light-duty cars and cars, nearly 200 kinds of parts need induction heating and quenching treatment. From the shape and size of induction-heated and quenched parts, it can be called a variety of patterns and sizes. Have. With the continuous development of induction hardening technology, induction hardened parts have risen to about 50% of all heat treated parts. According to relevant data, in China's automotive industry, the application of induction heat treatment is entering the ranks of the world's advanced level.
Second, the new process of induction heating
The induction heating process is the main embodiment of the level of induction heating technology, and is the basis of technological development. The advanced induction heating process technology can effectively exert the characteristics of induction heating to achieve efficient and energy-saving local heat treatment.
(1) Longitudinal induction heating quenching half shaft longitudinal induction heating quenching has been used in the automotive and tractor industries. The semi-axial longitudinal heating is a quenching. In Germany and the United States, there is a semi-axis quenching special machine tool, which is heated, calibrated and quenched on one machine to improve productivity. The equipment with the same output of one quenching and continuous quenching has a footprint of 40m2 and 115m2.
(2) Crankshaft neck fillet quenching After the crankshaft neck fillet is quenched, the fatigue strength is doubled compared with the normalized fire. The Cummins and NH engine crankshafts produced in China have adopted this process.
(3) Low-hardenability steel gear quenching As early as the 1970s, China had carried out 55DT, 60DT, 70DT steel research and achieved preliminary results. Later, due to the unstable hardenability of steel, etc., low-tempered steel was not used continuously. produce. In 1992, the founder of Russian low-tempered steel, Dr. K.3ЩЕПЕЛЯКОВСКЦЦ came to China to give lectures and went to a steel mill to investigate the conditions for smelting low-hardened steel. He believed that the plant was fully equipped to produce low-tempered steel. YB2009-1981 "Low-hardenability titanium-containing high-quality carbon structural steel" in the control of alloying elements is different from Russia, (Russia) 1054-74, 58 (55ПП) steel element content for Mn, Cr, Ni, Cu four The sum of the elements requires <0.5% (mass fraction), while the YB2009-8155Ti steel specifies <0.5% (mass fraction) for the sum of the three elements of Cr, Ni and Cu, which may be the key.
Russia's low-tempered steel and controlled hardenability steel have been widely used in automobiles, tractor rear axle gears, excavator gears, transmission cross shafts, rolling bearings for train cars, automotive leaf springs and railway spiral springs, etc., which have achieved great economic benefits. .
(4) Induction resistance quenching It is well known that the tooth portion of the steering rack is quenched by induction resistance method, and more than three imported machine tools have been produced in China. A British machine tool used this process for gear production and found that the gears were essentially non-deformed after quenching and could then enter the assembly process.
(5) The new equipment for crankshaft journal fixed heating and quenching is called FrankproTM, and the two-and-a-half fixed heating sensor replaces the 8-word semi-annular rotating heating belt. This set of equipment can quench and temper the curved neck. Compared with the old process, it has the advantages of energy saving, small floor space, small deformation of the workpiece and long life of the inductor.
Third, induction heating power supply and technology
In the power supply, the thyristor intermediate frequency replaces the machine generator. In the early 1990s, the domestic thyristor power plant was springing up and blossoming everywhere. After the competition of the survival of the fittest, the production plant has now stabilized. At present, the thyristor power supply is developing to the IGBT transistor power supply, and the high frequency of the electron tube will be developed into the MOSFET transistor power supply. The portable transistor super audio and high frequency power supply market is highly competitive, and its future quality will be high and the technical level will be high. Who can stand firm.
Domestic intermediate frequency power supplies currently use a parallel resonant inverter structure. Therefore, while researching and developing a larger capacity parallel inverter intermediate frequency power supply, the development of a series inverter intermediate frequency power supply with simple structure and easy to start frequently is a problem to be solved in the field of domestic intermediate frequency induction heating devices, especially in melting and casting applications. In the middle, the series inverter power supply is easy to realize the constant power output under all working conditions (helping to reduce the power consumption per ton) and the multi-load power distribution control of one machine, which is more worthy of popularization and application.
In the super-audio (10 ~ 100kHz) range, due to the limitations of the switching characteristics of the thyristor itself, it has brought great technical difficulties to the development of the power supply of this frequency band. Although in the 1980s, Zhejiang University developed a 50kW/50kHz super-audio power supply using a thyristor frequency multiplier circuit, a 30kHz thyristor super-audio power supply was developed using a time division circuit, but the load was nonlinear due to the double resonant circuit coupling of the frequency multiplier circuit. The variable heating load parameter and the resonant loop parameter matching debugging are quite complicated, and the time division circuit control and the main loop structure are complicated, and the utilization of the inverter tube is low, so it is not well popularized and applied.
In the early 1970s and early 1980s, modern semiconductor micro-integrated processing technology and power semiconductor technology were combined to develop a large number of fully-controlled power electronic semiconductor devices (GTR, MOSFET, SIT, SITH, MCT, etc.) for all-solid-state super audio. The development of high frequency power supply has laid a solid foundation.
In the high frequency (above 100 kHz) frequency band, foreign countries are currently in the transition phase from the traditional tube power supply to the transistorized all solid state power supply. Some companies in Japan adopted SIT, and the power level reached 1000 kW, 200 kHz, 400 kW, and 400 kHz in the late 1980s.
In Europe and the United States, due to the high-state loss of SIT (SIT operating in the unsaturated zone) and other defects, its high-frequency power devices are dominated by MOSFETs. With the modularization and large capacity of MOSFET power devices, the capacity of MOSFET high-frequency induction heating power supplies has been rapidly developed. Spain uses MOSFET current-type induction heating power supply to achieve 600kW, 400kHz. In 1989, the current-type MOSFET induction heating power supply developed by Germany reached 480kW and 50-200kHz. The current-type MOSFET induction heating power supply produced by Belgian InductoEiphiac Company can reach 1000kW, 15~600kHz. Zhejiang University developed a 20kW, 300kHz MOSFET high-frequency power supply in the 1990s, which has been successfully applied to the surface heat treatment of small tools and thermal stress assessment of aircraft turbine blades.
At present, the induction heating power supply mainly uses thyristors in the intermediate frequency band, and the IGBT is mainly used in the super audio frequency band. In the high frequency frequency band, due to the high conduction loss and the like of the SIT, the MOSFET power supply is mainly developed internationally. Although the induction heating power supply uses a resonant inverter, it is beneficial for the power device to achieve soft switching. However, the induction heating power supply usually has a large power, and has many special requirements for power devices, passive components, cables, wiring, grounding, and shielding. Therefore, there are still many application basic technologies that need to be further explored to achieve high-frequency induction heating power supply, especially the advent of new high-frequency high-power devices (such as MCT, IGBT and SIT power devices), which will further promote the high-frequency induction heating power supply. development of.
Considering the large capacity of the induction heating power supply from the perspective of the circuit, the large-capacity technology can be divided into two categories: one is the series and parallel connection of the devices; the other is the series or parallel connection of multiple bridges or multiple power supplies. In the series and parallel mode of the device, the voltage equalization problem of the series device and the current sharing problem of the parallel device must be carefully dealt with. Due to the discreteness of the device manufacturing process and parameters, the number of series and parallel connections of the device is limited, and the number of series and parallel connections is limited. The more the device, the worse the reliability of the device. The series and parallel technology of multiple power supplies is an effective means to further re-capacitize on the basis of device string and parallel technology. With reliable power string and parallel technology, it can be easily passed through series and parallel in the case of proper capacity of single machine. The operation mode is to obtain a large-capacity device, and each single device is only one unit (or one module) of the device.
Induction heating power inverters mainly have parallel inverters and series inverters. The output of the series inverter can be equivalent to a low-impedance voltage source. When the two voltage sources are connected in parallel, the amplitude, phase and frequency of each other. Different or fluctuating will lead to a large circulation, so that the current of the inverter device is seriously uneven. Therefore, the parallel inverter has difficulty in parallel expansion; and for the parallel inverter, the DC large reactor at the input of the inverter It can act as a current buffer between each parallel inverter, so that the AG/DG or DG/DG link at the input has enough time to correct the deviation of DC current, achieve multi-machine parallel expansion, transistorized super audio, high frequency current Parallel inverter structures are often used, and parallel inverters are easy to be modularized and large-capacity is one of the main reasons.
The load of the induction heating power supply is various, and the power inverter and the load are an organic whole. The matching transformer is used to connect the power supply and the load sensor. The matching transformer for the high frequency and super audio power supply is from the magnetic material to the winding. The structure is being further optimized and improved. At the same time, three passive components can be replaced by three passive components from the circuit topology to eliminate the transformer and achieve efficient and low-cost matching.
Induction heating power supplies, thyristors, transistors and tube tubes can be produced in China. Thyristor power supplies have been in production for many years. At present, IGBT power supplies are more used by users because of their advantages. MOSFET power supply high efficiency, low voltage, but the price is high, is gradually replacing the tube high frequency power supply. Portable small-scale high-frequency power supplies are widely used in China because of their low price and convenience, and even enter foreign markets.
UHF power supply (27.12MHz), which used to rely on imports, has been produced by at least two companies in China, which has solved the need for special processes such as blades and saw blades.
With the improvement of the automation control level of the induction heat treatment production line and the high reliability requirements of the power supply, it is necessary to strengthen the development of the heating process complete device. At the same time, the induction heating system is developing in the direction of intelligent control. The induction heating power system with control functions such as computer intelligent interface, remote control and automatic fault diagnosis is becoming the development goal of the next generation.