誘導加熱の金屬への應用(I)

Abstract

An inducton heating circuit is fundamentally a transformer wherein the inductor carrying the alternating currents is a primary and the substence to be heated is made the secondary. And the total power (P) absorbed in the work which is a cylynder in this case is: where H0 represents the magnetic intensity of the solenoid. The conductivity of the cylinder is σ mhos per centimeter cube; a represents the radius of the cylinder; μr permeability; & f, applied frequency.And as the power absorbed in the cylinder to the power lost is proportional to F, it is understood that the importance of using high frequency to an effective coupling and a critical frequency for the effective coupling is: There are three sources of high frequency current which find a commercial acceptance for induction heating.a) A rotating equipment (motor-generator) of frequency from 1000 to 10, 000 is used at capacities up to 10, 000 kilowatts.b) Oscillators of spark-gap type, provide frequecey in the order of 100, 000 to 400, 000 cycles. In Japan this type is conveniently used known as a Torikai's apparatus.c) Frequencies of several hundred thousand cycles are developed by vacuum-tube oscillators with the capacities up to 150 kilowatt input. In Japan there is a tendency to use this type instead of spark-gap oscillator types.Noteworthy applications of the induction heating are as follows.a) Surface hardening. This heating is used for suface hardening for its advantages in technical & economical merit. But to enjoy this merit, design of the work coil (a secondary circuit to heat the substance) is very important and therefore the patents of the coils are too numourous to be mentioned. The majority of machine assembly depend to a large extent on induction hardening, especially large gears of tracks (transmission gear of 10t track & D-8 tractor) are subjected to complete machining, including shaving, in the soft-annealed state. Then they are induction-hardened without distortion, very improved wearing qualities being obtained.b) Heating for Forging and Forming. Many advantages inherent in the use of induction heating for forging operations are responsible for the wide acceptance and use of this way of heating. Induction units which heat slabs for upsetting machines are provided with automatic fixtures, where the passage of the parts thorough the inductor is controlled by a plunger mechanism. A magazine feed runs from the timer or mechanically is tied with the operating lever of the press. The entire operation requires only one operator. But in Japan, this process is still in its infancy, c) Brazing and Soldering. Also many advantages are obtained in brazing and soldering by using an induction heating too. This process is utilized extensively in the automotive, and farm machinery, soldering of cans, high speed tools or carbide tips fixed to mild steel tools etc., and will be developed to infinitely.d) Annealing and Normalizing.e) Welding. f) Cutting. g) Sintering. h) Melting.