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Metal heat treatment: induction heating heat treatment

A surface heat treatment process using induction current to locally heat the workpiece. This heat treatment process is often used for surface hardening, for local annealing or tempering, and sometimes for overall hardening and tempering. In the early 1930s, the United States and the Soviet Union began to apply induction heating to surface hardening of parts. With the development of industry, the technology of induction heating has been improved and its application scope has been expanding.


Vacuum heat treatment furnace

Metal heat treatment: induction heating heat treatment

The basic principle of metal heat treatment is to put the workpiece into the inductor (coil) (Fig. 1 Induction heating principle)? When the inductor is fed with alternating current of a certain frequency, alternating magnetic field is generated around it. The induction effect of eddy current is induced by the electromagnetic induction of metal heat treatment alternating magnetic field. The distribution of induced current on the workpiece section is very uneven? The surface current density of the workpiece is very high? The current density decreases inward gradually (Fig. 2 along the workpiece section)? This phenomenon is called skin effect. The electrical energy of the high density current on the surface of the workpiece is changed to heat energy, so that the surface temperature is N? The higher the current frequency is, the larger the current density difference between the surface and the inner part of the workpiece is, the thinner the heating layer is. When the temperature of the heating layer exceeds the critical temperature of the steel, it can be cooled rapidly, so that the surface hardening can be realized.
 Classification according to the frequency of alternating current?
 Induction heating heat treatment can be divided into 5 categories: UHF, HF, UHF, if and power frequency.
 (1) UHF induction heating with a current frequency as high as 27 MHz? The heating layer is extremely thin? Only about 0.15 mm? It can be used for surface hardening of complex workpieces such as circular saws.
 (2) Frequency of current used in high frequency induction heat treatment is usually 200-300 kHz? The depth of heating layer is 0.5-2 mm? It can be used for surface hardening of gear, cylinder liner, cam, shaft and other parts.
 (3) Ultrasound frequency induction heating is usually 20-30 KHz? Ultrasound frequency induction current is used to heat small modulus gears? The heating layer is distributed along the tooth profile? The performance is better.
 (4) The current frequency used in the intermediate frequency induction heating heat treatment is generally 2.5-10 kHz? The depth of heating layer is 2-8 mm? It is usually used for surface quenching of large modulus gears, large diameter shafts and cold rollers.
 _The frequency of current used in induction heating is 50-60 Hz? The depth of heating layer is 10-15 mm? It can be used for surface hardening of large workpieces.
 What are the main advantages of induction heating?
 (1) it is not necessary to heat the whole workpiece with small deformation and low power consumption.
 No pollution.
 3. The heating speed is fast. The surface of the workpiece is oxidized and decarbonization is lighter.
 (4) the surface hardened layer can be adjusted according to need, easy to control.
 _Heating equipment can be installed on the line of machining students? Easy to realize mechanization and automation? Easy to manage? And can reduce transportation? Save manpower? Improve students? Efficiency.
 The hardened layer has fine microstructure, hardness, strength and toughness.
 After surface quenching, the surface of the workpiece has a higher compressive internal stress, and the workpiece has higher fatigue resistance.
 Induction heating heat treatment also has some disadvantages. Compared with flame quenching, induction heating equipment is more complex and less adaptable. It is difficult to guarantee the quality of some workpieces with complex shapes.
 Induction heating is widely used for surface hardening of workpieces such as gears, shafts, crankshafts, cams and rolls to improve their wear resistance and fatigue breaking resistance. The fatigue cycle times of the rear axle of the automobile under the design load are about 10 times higher than that under the quenching and tempering treatment. Induction hardening surface hardening material is usually medium carbon steel. In order to meet the special needs of some workpieces, low hardenability steel has been developed for induction heating surface quenching. High carbon steel and cast iron? Workpieces can also be made? Enzyme apricot? Especially the lack of grains, grains, grains, grains and bones.
 Equipment for induction heating and heat treatment is mainly composed of power supply equipment, quenching machine tools and inductors.
 The main function of power supply equipment is to output alternating current with suitable frequency. The high frequency current power supply equipment has two kinds: the electron tube high frequency generator and the silicon controlled frequency converter. The intermediate frequency current power supply equipment is the generator set. General power supply equipment can only output a frequency of current? Some equipment can change the current frequency? Can also be directly used 50 Hz power frequency current induction heating.

The selection of power supply equipment is related to the depth of heating layer required by the workpiece. Workpiece with deep heating layer? Power supply equipment with low current frequency? Workpiece with shallow heating layer? Power supply equipment with high current frequency should be used. Another condition for selecting power equipment is device power. The heating surface area increases, and the power supply needed increases correspondingly. When the heating surface area is too large or the power supply is insufficient, the workpiece and the sensor are moved relative to each other, the front is heated and the rear is cooled. But it is better to heat the entire heating surface. In this way, the hardened surface can be tempered by heat from the center of the workpiece, thus simplifying the process and saving electricity.
 The main function of induction hardening machine is to locate the workpiece and carry out necessary movement. In addition, a device for quenching medium should also be attached. Quenching machine tools can be classified as standard? Running? Port? Bo? The former applies to ordinary workpieces? The latter applies to a large number of complex workpieces.
In induction heat treatment, in order to ensure the quality of heat treatment and improve the thermal efficiency, sensors with appropriate structure must be designed and manufactured according to the shape and requirements of the workpiece. Commonly used inductors are external surface heating inductor? Inner hole heating inductor? Plane heating inductor and so on (Figure 3 commonly used high frequency inductor). For variable cross-section shaft parts, the o can be heated by transverse magnetic field. According to the heating method, inductors can be divided into inductors for heating at the same time and inductors for continuous heating. In order to improve the efficiency of production, a small inductor can also design inductors that can simultaneously heat multiple parts. In order to improve the thermal efficiency of the orifice and the plane heating inductor and obtain the ideal heating profile, a magnetic conductor can be installed on the inductor to make the current distribution reasonable.

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