GB724480A - Improvements in or relating to induction heating - Google Patents

Abstract

724,480. Induction heating. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. May 6, 1953 [June 26, 1952], No. 12572/53. Class 39 (3), An induction heating system comprises an oscillator having a tank circuit embodying an inductor through which a magnetic material to be heated passes, power amplifier means having its input circuit coupled to draw power from said oscillator, and a second inductor through which the magnetic material passes, in the output circuit of the power amplifier. Travelling steel strip 1 passes through an inductor 2 in the tank circuit of an oscillator 5, and also through inductors 3, 4 energized from power amplifiers 6, 7 respectively. The amplifier input circuits are coupled to draw power from the oscillator, and are fed with D.C. bias voltage from sources 11 and 12 which are regulated in voltage by a regulator 16 operatively connected to a temperature responsive device 14. The arrangement is such that when the strip reaches a predetermined temperature the device 14 acts through the regulator 16 to set the bias voltages of the amplifiers at such values that the strip is maintained at that temperature. Power supplies 8 and 9 feed the oscillator and amplifiers. More particularly, the oscillator is supplied. from conductors 23, 25, Fig. 2, and has triodes 21, 22 and a tank circuit comprising the heating inductor 2, capacitors 26-28 and an adjustable inductor 29. Its power output is adjusted by rheostats 35, 36, or by varying the cathode heating current. The latter is fed through a saturable core reactor 37 having a winding 38 the current in which may be varied. A further control of the oscillator output is provided by a second saturating winding 41 shunted by a variable resistor 39. The power amplifier 6 includes triodes 51, 52, 55, 56, and a tank circuit comprising heating inductor 3, adjustable inductors 57, 58, and capacitors 59, 59A. The amplifier 7 includes triodes 61-68 and tank circuit comprising heating inductor 4; adjustable inductors 75-78 and capacitors 81-84. Leads 42, 43 are connected as shown from the oscillator circuit to the grids of the amplifier triodes, and causes the circulation in the amplifier tank circuits of amplified current at the oscillator frequency.. A D.C. bias voltage is applied to the grids of triodes 51, 52, 55,.56, by the D.C. generator H. which is also connected to the variable resistor 39 and the winding 41. The generator 11 has two field windings, one connected to a D.C. source and the other to the regulator 16. When the strip temperature rises above the desired value the generator voltage is increased to reduce the amplifier tank currents. A fall in the strip temperature has the opposite effect. Similarly, the D.C. source 12 has -one pole connected to the grids of the triodes of the amplifier 7, and the bias voltage thereof is automatically controlled in the same way. Specification 575,424, [Group XXXV], is referred to.