Patent GB-1309389-A (GB)
Title: Automatically detecting and controlling arc furnace operating conditi ons during the charge metling stage
IPC: H05B7/148
Filed: 1970-01-28
Abstract: 1309389 Automatic control of arc furnaces ISHIKAWAJIMA-HARIMA JUKOGYO KK 28 Jan 1970 [20 Feb 1969] 58346/69 Heading G3R [Also in Division H2] In an arc furnace of the type wherein the position of the electrode is automatically controlled to maintain at a predetermined value an impedance signal derived from the arc current and voltage, the five periods A, B, C, D and E forming the charge melting stage and respectively corresponding to ignition, boring down, establishing of a small pool of liquid, shielded arc and flat bath, are automatically determined by the system shown to which are applied a signal a representing the instantaneous electrode position, a signal b representing the lowest position reached by the electrode during the preceding part of the charge melting stage, a signal k ZA representing the arc impedance, a signal P representing the power consumed by the furnace and predetermined signals B1---B7 representative of desired furnace opera- The system operates as follows:- (1) the initial value of signal b is stored in a memory element ME which provides an "ignition period-start" instruction (C) (2) the output signal of the element ME is applied to a comparator CO 1  together with the signal b and, when the difference between these two signals reaches the value of signal B1, a "boring down period-start" instruction (d) is provided. (3) the signal b is periodically stored in a sampling element GR and is also applied to a comparator CO 3  together with the signal B3. Element GR supplies a comparator CO 2  also fed with the signal B2, the comparator CO 2  providing an output signal when the signal from element GR, equal to the difference between the last value of the signal b and the previously stored value, becomes less than the value of signal B2. When the signal b becomes less than the value of signal B3, the comparator CO 3  provides an output signal which, with that from the comparator CO 2 , is applied to a logic circuit AND I  which provides an "establishing period of a small pool of liquid-start" instruction (e) (4) After instruction (e) has been obtained, the power signal P is integrated by a watt-hour meter IPC whose output signal is applied to a comparator CO 7  together with the signal B7, the comparator CO 7  providing a "shielded arc period-start" instruction (f) when the signal from meter IPC equals the value of signal B7. (5) After the instruction (f) has been obtained, the impedance signal k ZA is transmitted to a low pass filter LF whose output is applied to a rectifier RE supplying a comparator CO 5  together with the signal B5. On each occasion when the signal from rectifier RE exceeds the value of signal B5, the comparator CO 5  transmits a pulse to a counter PC which counts the number of pulses per unit time for comparison with the signal B6 in a comparator CO 6 . The latter provides an output signal whenever the output of counter PC is less than the value of signal B6. A comparator CO 4  derives the difference between signals a and b and, when this difference exceeds the value of the signal B4, transmits an output signal to a logic circuit AND  II  which also receives the output signal of the comparator CO 6  and, on the simultaneous appearance of these two signals, provides a "flat bath period-start" instruction (g). Following this instruction the electrode voltage is reduced. The instructions (c)---(g) may indicate or control the power necessary for the relevant period. The signals B1---B7 can be determined on the basis of past experience. The way in which signals a and b are obtained is described, Fig. 1 (not shown), and typical characteristics are discussed relating the variation of signals a and b with time, Figs. 2 and 3 (not shown), and the variation with time of the output of the comparator CO 5  Figs. 5 and 6 (not shown).