SU1266875A1 - Method for controlling electrical parameters of electric arc steel melting furnace - Google Patents

Abstract

The invention relates to ferrous metallurgy, in particular to steelmaking in electric arc furnaces. The purpose of the invention is to increase the productivity of the arc furnace and reduce the specific consumption of electrodes and is achieved by short-term vertical displacements of the electrodes with a steady increase in the range of electromechanical oscillations of the research institute of the electrode of the arc furnace operating in the set maximum load limit time intervals. The damping of oscillations during the period of the melting of wells is made with a reduction of the length of the arc by, and during the period of the liquid bath - (L by decreasing the length of the arc by 15-20%. 1 Il.

Description

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The invention relates to ferrous metallurgy, in particular, to steelmaking in electric arc furnaces. The purpose of the invention is to increase the output of the arc furnace, reduce the consumption of electrodes. Changing the arc length by means of vertical displacements of the electrodes allows one to quench the near-resonant electromechanical oscillations of the electrodes. The reason for the emergence of electromechanical self-oscillations, according to modern concepts of the electric arc melting process, is the interaction of a number of factors (magnetic arc blowing, electrodynamic forces, geometry of the crater electrode system, etc.). Their impact on the electrodes and the charge can excite beats and resonance phenomena, since the intrinsic frequency characteristics of the electrode and the electrical component. over the course of the heat change. Although a combination of factors that excite the near-resonance mode arises by chance, the presence of KpynHO j lumpy charge at low power consumption (under conditions of its restriction) contributes to the preservation of this combination for a long time (up to several minutes), especially the current geometry of this topic crater electrode , and the sustainable maintenance of near-electrical electromechanical regime. This increases the risk of electrode breakage, both as a result of fatigue effects, and as a result of a massive mass collapse of the charge — instead of its gradual deposition in the absence of electromechanical effects. In addition, near-resonance modes (as well as electrode breakdowns) are accompanied by reverse effects on the power supply network, worsening its mode of operation. Therefore, when controlling the electric mode of an arc furnace, especially when limiting the maximum electric power consumed, it is very important to detect the emergence of near-resonant electromechanical modes (for example, by recording and analyzing the components of the vibration of electrodes) and to take timely control actions to suppress them. Near-resonance electromechanical electrodes oscillations of the electrodes are most easily eliminated by changing the arc length by 15–20% by short-term vertical displacement of the electrodes. For smaller movements. It is possible to save the mode of near-resonance oscillations of the electrodes and there is a risk of their breakdowns. The direction of movement of the electrodes (up or down) to eliminate oscillations is determined by the stage of the melting period. So in the period of pro-. melting wells typically operate on short arcs with maximum power. An additional reduction in the arc length is even briefly dangerous due to the possible overload of the supply transformer and the supply power grid. Therefore, during the period of manhole melting, it is necessary to dampen the oscillations by increasing the arc length, but not more than 20% due to the possible arc collapse. If near-resonant electrode oscillations occurred during arc burning in a melted well in the liquid bath stage, when they usually work on long arcs, it is necessary to damp the electrode oscillations by reducing the arc length by 15–20%. At this stage, the power plant has power reserves and therefore a short-term increase in power is not dangerous. Thus, short-term vertical movement of the electrodes violates a combination of factors, an oscillating mode arises and is maintained by the bigger, due to changes in the geometry of the crater-electrode system, and can be used as one of the means of saving the electrodes, reducing downtime of the arc furnace breakdowns, suppression of negative effects of reverse effects of electromechanical processes accompanying electric arc melting on the operation mode of the power supply network. The drawing shows a graph of the time distribution from the start of melting to electrode breakage. The indicated electromechanical phenomena and their consequences confirm with actual data for a 100-ton arc furnace with a transformer of 60 MVA rated power. 137 phase electrode breakdowns were recorded in heap array No. 1, in array No. 2-43. The distribution of the moments of breakdowns of the electrodes of the phases in both arrays implies that two areas of thickening are observed, covering over 90% of all failures. The first time indication corresponds to the electrode beating to a depth of the order of its diameter, when the mass collapse of the charge is low. The main and, moreover, direct principle of the breakdown of this group are electrodynamic forces. The second condensation corresponds to the period of deposition of the charge, and, together with electrodynamic forces, the collapse can also be the cause of breakdowns of this group. However, in this case, the electrodynamic forces have an indirect effect, increasing the intensity of the collapse and thus the risk of electrode breakage, if they are not likely, a gradual collapse, or deposition of the charge, which does not always lead to electrode breakage. In the overwhelming majority of cases, the geometry of the electrode breakage has a characteristic appearance and is consistent with the direction of polarization of electromechanical oscillations. These facts confirm that the most important direct or indirect cause of electrode breakage is electrodynamic forces.

To experimentally study the vibration behavior of the electrodes, a series of measurements were carried out, respectively, GOST 15094-69 and 9899-79 s. - using a VBA-2 / MCHEP vibration measuring sensor, a Spectrum type converter converter, a KSU-2M secondary device. The sensor installs from above the furnace arch on the electrode holder, since measurements of this kind directly in the crater are not possible. A series of diagrams was obtained (the movement speed of the diagram tape was 180 mm / h), with electrode breakage and without breakage. In all cases, before the breakdown of the electrode, oscillations of the output signal with a frequency of 2–5 Hz were recorded, which steadily increased 2–2.5 times, occurring within 3–6 min, and lasted up to the breakdown. The duration and nature of the emerging mode is quite sufficient for its recognition and realization of control actions in the case of automatic and manual control of melting. The actual range of vibrations of the lower part of the electrode exceeds that measured at the electrode holder by at least an order of magnitude, and its state approaches the plastic one, and the observed duration of the amplified electrodynamic effects is sufficient for the appearance and development of fatigue effects in the electrode material leading to its destruction.

An experimental illustration of the simplest effect on the suppression of electrodynamic forces is the change in the geometric characteristics of the crater-electrode system by the vertical movement of the electrode. Steadily increasing the oscillation sweep registered the sweat several times, for example, by 20 and 97 minutes. In the first of these cases, the span is reduced after a brief rise of the electrode (the arc length is increased by 20%), in the second - by a short fall of the electrode (arc length decreases by 20%) ( ,

Thus, the proposed method allows to achieve the goals set for improving the performance of the arc furnace and reducing the specific consumption of electrodes by 20% by preventing their breakdowns, as well as reducing the negative reverse effect of electromechanical processes in the arc furnace on the operation mode of the power supply mains.

Claims (1)

Invention Formula The method of controlling the electric mode of an electric arc furnace, including reducing the active power of the furnace in the presence of electromechanical oscillations of the electrode at specified intervals by changing the current and / or voltage, in order to reduce the consumption of the electrodes and increase the performance of the furnace during the excitation of stably increased electromechanical oscillations of the electrode, briefly change the length of the arc by vertical movement of the electrode, while the length of the arc increases by 15-20% in the process of passing the wells and reduced by 15-20% in the well passed. Ml-up t breaks