Induction Heating

In this chapter, some details of the theoretical basis of induction heating will be discussed; the electromagnetic theory of metal heating will be discussed, while in the next chapter, the principles of heat conduction will be discussed in the application of induction heating. Relatively speaking, there is little new material in this area, because both problems have been widely discussed in the literature, but it can be considered that this theory has been brought together and in standard SI units for the first time.

Induction Heating

Therefore, the following guidelines have been followed in writing these chapters:

1. Derive the theory from first principles and gain a deep understanding of the relevant mechanisms;

2. Provide the experienced engineer with equations that are exactly consistent with the work and explain the application of these equations. This chapter will give an overview of the electromagnetic effects, induced flux, current and power distribution when the workpiece is subjected to an external magnetic field. First, a thick plate is used to study the principles by simple mathematical solutions;

these studies can be expressed in simple sinusoidal functions and exponential functions, which are more common than hyperbolic functions or Bessel functions. In fact, a deep understanding of the simple mathematics of semi-infinite plates is sufficient to solve many problems, and all other solutions are just more sophisticated calculations. Another way to save energy is to use the residual heat in the continuous casting process.

Here the bar is sent directly from the casting site to the reducer, the surface is quenched and the heat is lost by radiation, resulting in a temperature gradient from the surface to the center. If induction heating is used at this stage without cooling, the required heating power can be much less. For example, the power required to heat from ambient temperature to the billet rolling temperature (15 minutes) is 100 MW, which can be reduced to 35 MW with 1 minute of reheating.

In some cases, the size of the bar to be heated through requires a transverse heating system. For smaller bars, the conveying mechanism is simple, but larger bars can be handled by a step-by-step method. The efficiency of the smaller bars can greatly save energy compared to the sequential method. At 60 Hz, a 2 mm bar requires 30% less power, and at 1 kHz, a 38 mm bar requires 40% less power. At 3 kHz, a 25 mm bar requires 45% less power.

The only way to get an accurate cost comparison is to perform an accurate analysis based on the specific
requirements of the equipment being designed. The prices in the examples in this chapter are based on 1976 and 1977 prices and may vary greatly. In particular, fuel costs vary