Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
Initially, Foulcourt and Heaviside proposed theories about eddy currents and induction heating, which subsequently developed into a steady stream of theoretical research (1, 2, 8–23). However, this work has not yet been applied to improvements in induction heating coils and power supplies, and is only now becoming increasingly understood and applied. these theories of induction heating, which can produce unique heating effects on workpieces of various shapes, such as solid and hollow cylinders and flat plates. Examples of heating workpieces of various shapes and metal materials are given, illustrating the depth of penetration of the induction heating current. The relationships between frequency, resistivity, and permeability are discussed. The effects of current penetration depth, magnetic field, and workpiece size on induced power are also discussed in this chapter.
Induction heating is based primarily on three fundamental principles: electromagnetic induction, the "skin effect," and heat conduction.
Transformer Principle
Although the basic concepts of induction heating can be represented using principles similar to those of the well-known transformer, a simulated single-turn short-circuited secondary coil is more suitable for induction heating. The above concepts are illustrated using an induction heater and a load. It must be emphasized that this is only a very brief description. The diagram shows a simple transformer. When magnetic flux leakage is zero, the load current should equal the supply current multiplied by the turns ratio. The losses in the primary and secondary coils are directly related to the winding losses. If the secondary coil is considered a single turn, the short-circuit current in the secondary coil will be very large, resulting in considerable power consumption.
This effect is shown in the diagram. Furthermore, the "losses" in the primary and secondary coils will equal the power supply. Therefore, the coupling between the primary and secondary coils must be idealized to achieve a simple turns ratio. Using the above perspective, Consider the circuit for the cylindrical heating load shown in the figure as a transformer with a multi-turn primary coil and a single-turn short-circuited secondary coil, separated by a small air gap. It's important to note that when the current frequency is high, the "skin effect" occurs, a topic discussed in detail in later chapters. The induced current density gradually decreases from the surface to the center of the heated workpiece, and the rate of decrease increases with increasing frequency. This rate of decrease also depends on the resistivity and relative permeability of the heated material.
