What Is Induction Heating?

Electromagnetic induction heating, or induction heating for short, is a method of heating conductor materials such as metallic materials. It is mainly used for metal hot working, heat treatment, welding and melting.

Induction heating is a relatively new process, and its application is mainly due to its unique properties. When a rapidly changing current flows through a metal workpiece, a skin effect occurs, which causes the current to be concentrated on the surface of the workpiece and generates a highly selective heat source on the metal surface. Faraday discovered the merit of the skin effect and the notable phenomenon of electromagnetic induction. He is also the founder of induction heating. Induction heating does not require an external heat source, but uses the heated workpiece itself as a heat source. This method does not require the workpiece to be in contact with the energy source, that is, the induction coil. Other properties include the ability to select different heating depths based on frequency, precise local heating based on the coil coupling design, and high power density, or high power density.

A heat treatment process suitable for induction heating should take full advantage of these characteristics and design a complete equipment according to the following steps.

First, the process requirements must be consistent with the basic characteristics of induction heating. This chapter will describe the electromagnetic effects in the workpiece, the distribution of the combined current, and the absorbed power. According to the knowledge of the heating effect and temperature effect of the induced current, and the temperature distribution at different frequencies, different metals and workpiece shapes, users and designers can decide to discard them according to the requirements of technical conditions. .

Second, the specific form of induction heating must be determined according to whether it meets the requirements of technical conditions. It should also widely grasp the application and development situation, and the main application trends of induction heating.

Third, once the suitability and best use of induction heating are determined, the inductor and power supply system can be designed.

Many problems in induction heating are similar to some basic sensibility knowledge in engineering, and they are generally derived from practical experience. It can also be said that without a proper understanding of the shape of the inductor, the frequency of the power supply, and the thermal performance of the heated metal, it is impossible to design an induction heater or system.

The effect of induction heating is the same as flame quenching under the influence of invisible magnetic fields. For example, the higher frequencies (above 200,000 Hz) generated by high-frequency generators can generally generate intense, rapid, and localized heat sources, which are equivalent to the effects of small and concentrated high-temperature gas flames. Conversely, the heating effect of the intermediate frequency (1000 Hz and 10000 Hz) is relatively dispersed and slow, and the heat penetrates deeper, similar to the larger and open gas flames. ^[2]

Induction heating surface quenching has the advantages of good surface quality, small brittleness, hard to be oxidized and decarburized on the quenched surface, and small deformation, so the induction heating equipment is in metal

Modern induction heating power supply is developing towards high power and high frequency. This is a considerable challenge for modern power electronics. The traditional method is to use devices in series and parallel, but this has the problem of sharing current and voltage between devices. Especially when there are many devices in series and parallel, you need to ensure accurate synchronization signals to avoid circulating current between devices. Damage to power electronics. But in many cases this is difficult to guarantee with precision. Especially when there are many series-parallel devices with large power levels, its excellent characteristics can effectively reduce the circulating current between the inverter bridges in parallel. The parameter design can balance the power distribution of the bridges, reduce the device losses, and thus effectively It solves some problems in the parallel connection of inverter bridges, which is beneficial to the multi-bridge parallel connection of induction heating power supply, and improves the output power and reliability.

Circulation analysis of induction heating parallel module

The biggest advantage of LLC resonant load is that it is conducive to the parallel connection of multiple machines in induction heating. It does not need to add any components between the inverters. Even if the signal delay angle of each bridge is large, it can ensure the system to work normally and suppress each The circulating current between the bridges regulates the output power of each inverter.

Future characteristics of induction heating equipment

With the increase of the degree of automation control of the induction heat treatment production line and the high reliability requirements of the power supply, the development of a complete set of heating process equipment must be strengthened. At the same time, the induction heating system is developing in the direction of intelligent control. The intelligent heating power system with computer intelligent interface, remote control and automatic fault diagnosis, miniaturization, suitable for field work, high efficiency and energy saving control performance is becoming a future development goal.