Equipment used in the processes of heat processing, heat treatment, heat assembly, welding and smelting of metal materials in all walks of life
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High frequency power supply, also known as electronic tube frequency converter, isHigh frequency induction furnaceKey equipment.High frequency power supply and induction heating technology are the devices with the highest heating efficiency, fastest speed, low energy consumption and environmental protection for metal materials.It has been widely used in heat processing, heat treatment, heat assembly, welding, smelting and other processes of metal materials in all walks of life.It can not only heat the workpiece as a whole, but also heat the workpiece locally;It can realize the deep heat transmission of the workpiece, and can also only heat its surface and surface intensively;It can not only directly heat metal materials, but alsoNon metallic materialsPerform indirect heating.wait.Therefore, induction heating technology will be applied more and more widely in all walks of life.
Local heating of workpiece by induced currentSurface heat treatmenttechnology.This heat treatment process is commonly used for surface quenching, local annealing or tempering, and sometimes overall quenching and tempering.In the early 1930s, the United States and the Soviet Union began to apply induction heating method to surface quenching of parts.With the development of industry, the induction heating heat treatment technology has been continuously improved and its application scope has also been expanded.
Fundamentals
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Put the workpiece into the inductor (coil). When a certain frequency of alternating current is connected to the inductor, an alternating magnetic field will be generated around it.The electromagnetic induction of the alternating magnetic field causes a closed induced current eddy current in the workpiece.The induced current is unevenly distributed on the section of the workpiece. The current density on the surface of the workpiece is very high and gradually decreases inward. This phenomenon is called skin effect.The electric energy of the high-density current on the surface of the workpiece is converted into heat energy, which increases the temperature of the surface, that is, to realize surface heating.The higher the current frequency is, the greater the current density difference between the surface and the interior of the workpiece is, and the thinner the heating layer is.The surface quenching can be realized by cooling rapidly after the heating layer temperature exceeds the critical point temperature of steel.
classification
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According to the frequency of alternating current, induction heating heat treatment can be divided into five categories: ultra-high frequency, high frequency, ultra audio frequency, intermediate frequency and power frequency. ①The current frequency used for UHF induction heating heat treatment is up to 27 MHz, and the heating layer is extremely thin, only about 0.15 mm, which can be used for thin layer surface quenching of complex shaped workpieces such as circular saws. ②The current frequency used for high frequency induction heating heat treatment is usually 200~300 kHz, and the heating layer depth is 0.5~2mm. It can be used for surface quenching of gears, cylinder liners, cams, shafts and other parts. ③The current frequency used for ultrasonic induction heating heat treatment is generally 20~30 kHzSmall module gearWhen heated, the heating layer is roughly distributed along the tooth profile, and the service performance is good after fire cleaning. ④The current frequency used for medium frequency induction heating heat treatment is generally 2.5~10 kHz, and the depth of heating layer is 2~8 mm. It is mainly used for surface quenching of large module gears, shafts with larger diameter, cold rolls and other workpieces. ⑤The current frequency used for power frequency induction heating heat treatment is 50-60 Hz, and the heating layer depth is 10-15 mm, which can be used for surface quenching of large workpieces.
Features and Applications
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induction heatingIts main advantages are: ① no overall heating, small deformation of the workpiece, and small power consumption. ②No pollution. ③The heating speed is fast, and the surface of the workpiece is oxidized and decarburized slightly. ④The surface hardening layer can be adjusted as required, which is easy to control. ⑤Heating equipment can be installed onMachining production lineIn addition, it is easy to realize mechanization and automation, facilitate management, reduce transportation, save manpower, and improve production efficiency. ⑥The martensite structure of the hardened layer is fine, and the hardness, strength and toughness are high. ⑦After surface quenching, the surface of the workpiece has a large compressive internal stress, and the workpiece has a high resistance to fatigue fracture.
Induction heating heat treatment also has some disadvantages.Compared with flame quenching, induction heating equipment is more complex and has poor adaptability. It is difficult to ensure the quality of some workpieces with complex shapes.
Induction heating is widely used for surface quenching of gears, shafts, crankshafts, cams, rolls and other workpieces to improve their wear resistance and fatigue fracture resistance.The rear half axle of automobile adoptsInduction surface hardeningThe number of fatigue cycles under design load is about 10 times higher than that under quenching and tempering treatment.The workpiece material for induction heating surface quenching is generally medium carbon steel.In order to meet the special needs of some workpieces, a specialLow hardenability steel。Workpieces made of high carbon steel and cast iron can also be surface quenched by induction heating.Common water orPolymerAqueous solution.
equipment
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Induction heating heat treatment equipment is mainly composed of power supply equipmentQuenching machineAnd sensors.The main function of power supply equipment is to output alternating current with appropriate frequency.High frequency current power supply equipment has electronic tubesHigh frequency generatorAnd silicon controlled inverter.The intermediate frequency current power supply equipment is a generator set.General power supply equipment can only output current of one frequency. Some equipment can change the current frequency, or directly use 50 Hz power frequency current for induction heating.
The selection of power supply equipment is related to the heating layer depth required by the workpiece.For workpiece with deep heating layer, power equipment with lower current frequency shall be used;For workpieces with shallow heating layer, power equipment with high current frequency shall be used.Another condition for selecting a power supply is the power of the device.As the heating surface area increases, the required power supply power increases accordingly.When the heating surface area is too large or the power supply is insufficient, the method of continuous heating can be used to make the workpiece and the inductor move relatively. The front side is heated and the back side is cooled.However, it is better to heat the whole heating surface once.In this way, the hardened surface layer can be tempered by using the residual heat in the center of the workpiece, which simplifies the process and saves electric energy.
Induction hardening machineIts main function is to position the workpiece and carry out necessary movement.In addition, a device for providing quenching medium shall be attached.Quenching machineIt can be divided into standard machine tools andSpecial machine toolThe former is applicable to general workpieces, while the latter is applicable to complex workpieces produced in large quantities.
When conducting induction heating heat treatment, in order to ensure the heat treatment quality and improve the heat efficiency, the inductor with proper structure must be designed and manufactured according to the shape and requirements of the workpiece.Common sensors include outer surface heating sensor, inner hole heating sensor, plane heating sensor, universal heating sensor, special heating sensor, single heating sensor, composite heating sensor, smelting furnace, etc.
