JPS622609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating an arc furnace and an arc furnace, and particularly proposes a new method that can advantageously reduce damage to the hearth and shorten the melting time.

In an arc furnace for steelmaking, an arc is generated between the scrap and an electrode in order to melt the scrap inside the furnace. Not all of the arc heat generated is consumed to melt the scrap, but is also absorbed into the refractory lining the furnace, heating it and damaging it. Particularly in the early stages of melting (boring stage to puddle formation stage), the lower end of the electrode is close to the hearth, so the more arc heat is applied, the more likely the hearth is to be damaged, and the hearth becomes perforated. In order to avoid such hearth damage, it is possible to reduce the arc power at the initial stage of melting, but this has the problem of prolonging the time required for melting and reducing productivity.

Conventionally, in this regard, the input power was changed manually based on the operator's intuition while assuming the electrode tip, or the input power was changed when a level meter detected the lowest point position of the electrode lifting mast that grips the electrode. This was dealt with by methods such as stepwise reduction. In the former case, the power is reduced when the electrode is close to the hearth, and increases as the electrode moves away from the hearth, but the distance between the electrode and the hearth is adjusted by eye or intuition. Because of this, they were often placed too close to the hearth, damaging it and requiring repairs after tapping. In addition, this method had the disadvantage that efficient dissolution was not possible. On the other hand, in the latter case, there was a drawback that the power supply was not continuously controlled in accordance with the electrode position, and therefore the hearth could not be protected. In particular, in this method, the lowest point of the electrode is determined, and the arc power is only lowered when the electrode reaches that position, so high arc power is usually supplied until the lowest point is approached. The problem is that repeated operations over a long period of time cause a floor digging phenomenon, which also causes the position of the lowest point to fluctuate, making efficient power supply difficult.

Moreover, as is common to all of the above-mentioned conventional methods, the positional changes of multiple electrodes are not individually grasped, so in an actual arc furnace, the lower end of each electrode and the hearth Considering that the distances between the electrodes are different, there was also the problem that even if all the electrodes were controlled in a comprehensive manner, it would not be possible to achieve truly appropriate control.

The present invention solves the drawbacks of the conventional methods described above, and provides an operating technology for an arc furnace that can minimize damage to the hearth, apply as much power as possible, and shorten the melting time, and is necessary for its operation. This paper proposes an arc furnace with an electrode lifting device, a power control device, etc. attached to the furnace body. The details of the configuration will be explained below.

Figure 1 of the drawings is a diagram showing the behavior of the tip of the electrode 2 and the scrap inside the furnace at the initial stage of melting in the steelmaking arc furnace 1, and the melting progresses from a to b to c in the figure.
Proceed in this order. That is, after ignition, the electrode 2 reaches the hearth during a boring period operation a in which it descends toward the hearth while boring the scrap,
As a result of the operation during the tundish formation period in which the molten steel produced during the boring period is sequentially stored in the hearth, the state shown in b is reached. In this state b, the arc directly contacts the refractories of the hearth, so if the arc power is increased at this point, the hearth will be severely damaged and a floor digging phenomenon will occur. However, in state c shown in the figure, when the melting stage operation begins, the amount of molten steel stored increases, so even if the arc power is increased, the hearth is blocked by molten steel and will not be damaged.

From this point of view, the present inventors studied the relationship between the distance between the electrode and the hearth and the arc power, and obtained the knowledge shown in FIG. 2. The arc power decreases as the electrode approaches the hearth 5, but once the distance between the electrode and the hearth reaches the lowest point of the electrode and the amount of molten steel increases, the electrode 2... If the arc furnace is operated in such a way that the arc power is constantly controlled to a level commensurate with the movement of each electrode 2, in which the arc power is gradually increased as the It was found that the desired effects of protecting the hearth and shortening the melting time could be obtained.

In particular, in the operation of the arc furnace according to the present invention, before each scrap charge, each electrode 2 is brought into contact with the hearth, and the lowest point position of the electrode 2 is determined depending on the hearth height. By correcting this, the lowest point position is always determined accurately, and the arc power is controlled using this as a reference. In this way, accurate arc power can always be supplied even if the floor is dug due to repeated operations.

Next, the arc furnace used when carrying out the arc furnace operation of the present invention, and in particular the power control device attached to this furnace, will be explained. Figure 3 shows its configuration. Reference numeral 1 in the drawing is the furnace body of an arc furnace for steelmaking, into which scrap is charged and electrode 2 is inserted.
The scrap 4 is melted by generating an arc between the scrap 4 and the scrap 4. This electrode 2 is held by an electrode lifting mast 3, and the electrode lifting mast 3 has a structure in which the electrode lifting mast 3 is moved up and down in the vertical direction by feeding and feeding a wire 4 wound around a wire drum 5. A pressure detector 8 is installed in the middle of the wire 4 to detect tension and loosening of the wire 4. The wire drum 5 is connected to a motor 6 and a motor rotation detector 7.

The arc furnace used to carry out the above method of operating an arc furnace includes a furnace body 1, an electrode 2, an electrode lifting device, and a power control device for controlling the power supplied to the electrode. It is something.
The power control device includes a power supply controller 9 that mainly supplies arc power according to the electrode position during the melting process by setting the amount of power required for melting determined by the raw material (scrap) and the operation mode, and a power supply controller 9 that supplies arc power mainly according to the electrode position. An electrode position counter 11 outputs a level signal and an electrode position signal corrected to zero by bringing the lower end of the electrode into contact with the hearth surface, and detects sequential changes in the relative position of the hearth and the lower end of the electrode before the electrode reaches its lowest point. A descending power setter 12 receives the electrode position output signal shown and outputs an arc current gradual reduction command for each electrode to the power supply controller, and compares the electrode position signal with a preset electrode lowest point position. A comparator 13 detects when the electrode reaches its lowest point, a power counter 14 counts the amount of power started in response to the comparator output signal until it reaches a predetermined molten steel storage amount, and a power counter 14 detects when the electrode reaches its lowest point. After reaching the predetermined amount, the rising power setting device 15 detects that the molten steel storage amount has reached a predetermined amount and outputs a signal to the power supply controller 9 to gradually increase the arc current flowing through each electrode. .

The operation of this device will be explained below. First, while scrap is not being charged into the steelmaking arc furnace 1, the electrode 2 is lowered into the furnace and brought into contact with the hearth. At this time, the relative distance between the electrode and the hearth becomes zero, and an electrode/hearth contact signal 52 is generated by the pressure detector 8 that detects loosening of the electrode wire 4, and an electrode position movement signal 51 is output from the motor rotation detector 7.
is input into the electrode position counter 11, and the electrode relative position signal 53 is zero-corrected for each operation by the counter's zero set and count.
is obtained. The output of the corrected electrode relative position signal 53 thus obtained is input to the descending power setting device 12, and the descending power setting device 12 adjusts the arc according to the progress of melting so that the input/output characteristics become as shown in FIG. A power reduction setting signal 54 is output to the power supply controller 9 in the direction of lowering the power. The electrode relative position signal 53 also enters the comparator 13 and is compared with a certain predetermined electrode relative position reference signal 55.
Detects when the tip of the device reaches the hearth.

The output signal of the comparator 13 is an arc power integration start signal 56, and an arc power signal 57.
At the same time, the electric energy counter 14 enters, and the electric energy after the electrode 2 reaches the hearth is integrated. Since this integrated amount is proportional to the amount of molten steel, a molten steel amount signal 58 is obtained as an output. As the melting progresses further, the electrode relative position signal increases, the arc power is increased, and the rising power setting device 15 puts the arc power on the curve shown in FIG. is giving to

As is clear from the above explanation, according to the present invention, damage to the hearth is reduced, reducing the cost of repairing the furnace after steel is tapped, and in terms of melting time, waste and variation due to operators as in the past are reduced. It was shortened.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the situation inside the arc furnace at the initial stage of melting, FIG. 2 is a power supply characteristic diagram of the present invention, and FIG. 3 is a block diagram of the power control device. DESCRIPTION OF SYMBOLS 1... Steelmaking arc furnace, 2... Electrode, 3... Electrode lifting mast, 4... Wire, 5... Wire drum, 6
...Motor, 7...Motor rotation detector, 8...Pressure detector, 9...Power supply controller, 11...Electrode position counter, 12...Downward power setter, 13...Comparator, 1
4... Electric energy counter, 15... Increased power setting device,
51... Electrode position movement signal, 52... Electrode/hearth contact signal, 53... Electrode relative position signal, 54... Power lowering setting signal, 55... Electrode relative position reference signal, 56...
Integration start signal, 57...Arc power signal, 58
... Molten steel amount signal, 59... Rising power setting signal.

Claims (1)

[Claims] 1. When operating an arc furnace by controlling the power supply, the lower end of each electrode is pressed against the hearth and the lower end of each electrode is pressed against the hearth prior to arc ignition and scrap charge. The lower point position is corrected, and the arc power is gradually decreased according to the lowering of the electrode until each electrode lowered during the boring operation reaches the corrected electrode lowest point position, and after reaching the lowest point position, the electrode A constant low arc power is applied until the cumulative power required for a predetermined amount of molten metal to accumulate in the hearth, which is sufficient to protect the hearth, and then, as the electrode rises, arc power is applied according to the width of the rise. A method of operating an arc furnace characterized by gradually increasing the amount of melting to reach the final stage of melting. 2. In an arc furnace in which the furnace body is equipped with an electrode, an electrode lifting device, and a power control device for controlling the power supplied to the electrode, the necessary power is supplied in accordance with the transition of the electrode position. an electrode position counter that outputs a position-corrected electrode position signal; and an electrode position counter that receives the electrode position output signal that indicates sequential changes in the relative position of the lower end of the hearth electrode before the electrode reaches the lowest point. A descending power setting device outputs an arc current gradual reduction command for each electrode to the power supply controller, and the electrode position signal is compared with a preset electrode lowest point position to detect arrival of the electrode lowest point position. a comparator, a power counter that counts the amount of power that starts in response to the comparator output signal until it reaches a predetermined molten steel storage amount, and a molten steel storage amount that reaches a predetermined amount after the electrode reaches the lowest point. 1. An electric arc furnace comprising: a power control device configured with a rising power setting device that detects the occurrence of a change in temperature and outputs a signal to the power supply control to gradually increase the arc current flowing through each electrode.