JPH0417611A - Method for operating ladle refining furnace - Google Patents

Abstract

PURPOSE:To improve the refining efficiency by charging of a large electric power to electrodes by providing means for detecting the currents to be supplied to the electrodes and the arc voltages of the electrodes and determining a set value at the time of heating and refining a molten steel by using arcs. CONSTITUTION:The arc currents are supplied from a power source device 5 via a current control means 6 to the electrodes 2 to generate the arcs 13 between the front ends 2a of the electrodes and the front surface 11a of the molten steel 11, by which the molten steel 11 is heated and refined. The arc currents flowing in the electrodes 2 at this time are detected by a current detector 7 and the current control means 6 is controlled by a current controller 8 according to the detected values, by which the preset value is obtd. The arc voltages of the electrodes 2 are detected and a lifting mechanism 3 is controlled according to the detected value by an electrode lifting controller 10, by which the electrodes 2 are lifted and the arc voltages are controlled to the preset value. The damage of the side walls la of the ladle 1 by the arc radiation is prevented in this way and the refining efficiency by the charging of the large electric power is improved.

Description

[Detailed description of the invention] C Industrial application field] This invention relates to a method of operating a ladle refining furnace.

[Conventional technology]

When refining molten steel in a ladle refining furnace, the operation is performed by keeping the ratio of the arc current flowing through the electrodes to the arc voltage of the electrodes constant.

[Problem to be solved by the invention]

In this conventional method of operating a ladle smelting furnace, when the arc current is increased in order to increase the power input to the electrodes and improve the efficiency of smelting, the arc voltage is increased accordingly, and the above-mentioned The ratio is held constant. The arc voltage is increased by raising the electrode to increase the length of the arc between the tip of the electrode and the upper surface of the molten steel. However, when the electrode is raised in this way, the tip of the electrode may come out above the upper surface of the slag, resulting in a situation where arc generation occurs outside the slag. When the arc goes outside the slag, the distance between the electrode and the side wall of the ladle is small because the refining is done inside the ladle, so the refractory on the inner surface of the side wall of the ladle absorbs the radiant heat of the arc. A problem arises in that the material is damaged (melted) by being damaged. For this reason, in order to prevent such problems from occurring, there is usually a problem in that the operation must be carried out with the power input to the electrodes being suppressed.

The present invention was made to solve the problems (technical problems) of the prior art described above, and it increases the current supplied to the electrode while keeping the tip of the electrode in the slag. It is an object of the present invention to provide a method of operating a ladle refining furnace that can improve refining efficiency by applying high power to the electrodes while preventing damage to the side walls.

[Means to solve problems]

In order to achieve the above object, the present invention takes the measures as described in the claims above, and its effects are as follows.

[Effect]

When a current is supplied to the electrode, an arc is generated between the tip of the electrode and the upper surface of the molten steel, and the molten steel is heated and refined by the arc. In the above case, the power applied to the electrodes is increased by increasing the current supplied to the electrodes. In this case, the current increase is performed while the tip of the electrode remains located within the slug. Therefore, the arc is always inside the slag, and the slag blocks the radiant heat of the arc from reaching the side walls of the ladle.

〔Example〕

The drawings showing the embodiments of the present application will be described below.

In the ladle refining furnace shown in FIG. 1, reference numeral 1 denotes a ladle, which has a structure in which the inner surface of an outer jacket made of, for example, a steel plate is lined with a refractory material.

Reference numeral 2 denotes electrodes arranged in the upper part of the space inside the ladle 1, and there are a plurality of electrodes, for example, three graphite electrodes for Sanwa AC, in a triangular position when viewed from above, as is well known, and each can be moved up and down. It is located in 3 shows a well-known electrode lifting mechanism for lifting and lowering the electrode 2. As shown in FIG. 4 is a circuit for supplying power to the electrode 2, which is called a main circuit. Reference numeral 5 denotes a power supply device provided in the supply circuit 4, which is, for example, a furnace transformer.

Reference numeral 6 denotes a current adjusting means provided in the supply circuit 4 for adjusting the current supplied to the electrode 2. For example, a structure in which a thyristor is provided in each three-phase circuit is used. Reference numeral 7 denotes a current detector attached to the circuit between the electrodes 2 and the adjustment means 6, and is for detecting the arc current flowing through each electrode 2, and for example, a current transformer is used. Reference numeral 8 denotes a current control device, which compares the detected value of the actual arc current obtained by receiving the signal from the current detector 7 with a set value preset in the device 8, and uses the result of the comparison. Accordingly, the firing angle of the thyristor in the current g1 node means 6 is controlled so that the detected value approaches the set value. Further, the device 8 is configured such that the arc current value during operation of the ladle refining furnace can be preset as the above set value by manual operation or automatic control. 9 indicates an arc voltage detection end. This detection end is for detecting the arc voltage of the electrode 2, and generally the r! between the sii means G and the electrode 2 is used. ! It is constructed by connecting a conducting wire for detection to the J path or electrode 2. Reference numeral 10 denotes an electrode elevation control device that compares the actual arc voltage detected at the detection end 9 with a set value preset in the device 10, and adjusts the actual arc voltage according to the comparison result. The elevating mechanism 3 is configured to control the elevating mechanism 3 so that the value approaches the set value. Further, the device 10 is configured such that the arc voltage value during operation of the ladle n refining furnace can be preset as the above set value by manual operation or automatic control.

Next, the operation of the ladle refining furnace will be explained.

Molten steel 11 is placed in the ladle 1 and slag 12 is placed thereon, so that the upper surface 1ta of the mall 11 is covered with the slag 12. In this state, an arc current is supplied from the power supply device 5 to the electrode 2 via the current adjustment means 6, and an arc 13 is generated between the tip 2a of the electrode 2 and the upper surface 11a of the molten steel 11. The molten steel 11 is heated by this arc 13, and as is well known, n
A mirror is done.

The arc current flowing through the electrode 2 during the refining is detected by the current detector 7. The current control device W8 controls the current adjustment means 6 according to the detected value.

As a result, the arc current becomes a preset value.

Further, the arc voltage of the electrode 2 is detected at the detection end 9.

Electrode lifting mechanism W10; lifts 111 according to the detected value
1fill 3 is controlled, and the electrode 2 is raised and lowered. As a result, the arc voltage becomes a preset value.

The arc voltage in the electrode lifting control device 10 is set below the voltage z corresponding to the slag thickness. In this specification, the length of the arc 13 is equal to or less than the thickness of the slag 12 (for example, 100 to 250 mm), and the tip 2a of the electrode 2
The arc voltage in the range in which the state in which the arc voltage is maintained within the slag 12 (the arc voltage is proportional to the arc length between the tip 2a and the upper surface 11a) is called a slag thickness-corresponding voltage. Since the elevation of the electrode 2 is controlled so that the arc voltage is maintained below the voltage corresponding to the slag thickness,
The tip 2a of the electrode 2 is always located within the slug 12. Therefore, even if the arc current to the electrode 2 is increased by the current adjustment means 6, the arc 13 remains in the slag 12, and as a result, the arc 13 is transferred to the portion 1a near the slag line on the inner surface of the side wall of the ladle 1. radiation will not reach the area, and damage to the refractories there (7g ti ) will be prevented.

Next, as described above, arc voltage and arc length are in a proportional relationship. Therefore, in the electrode elevation control device 10, the arc length may be set instead of the arc voltage.

Further, in the ladle refining furnace, a slag thickness measuring means is provided, and the thickness of the slag 12 measured by the means is set in the electrode elevation control device 10, and the upper surface of the molten 1111 is
The electrode elevating mechanism 3 may be controlled so that the dimension between the tip 2a of the electrode 2 and the tip 2a of the electrode 2 does not exceed the set dimension.

Next, FIG. 2 shows an example in which the positional relationship between the current regulating means 6e and the furnace transformer 5e in the main circuit 4e is reversed from that of the previous embodiment. Even in such an example, by controlling the current and controlling the elevation of the electrode in the same manner as in the above case, it is possible to input a large amount of power to the electrode 2e while preventing damage to the side wall of the ladle. can.

It should be noted that parts that are considered to have the same or equivalent structure as those in the previous figure in terms of function are given the same reference numerals as in the previous figure with the letter e, and redundant explanations are omitted.

〔Effect of the invention〕

As described above, in the present invention, an arc 13 is generated by supplying electric power to the electrode 2, and the molten steel 11 in the ladle 1 can be heated and refined by the arc 13, of course. In the above case, the current regulating means 6 can increase the current supplied to the electrode 2, which is useful in improving the efficiency of the refining by inputting a large amount of power.

Moreover, in the present invention, the vertical position of the electrode 2 is independently controlled so that the tip #2a of the electrode 2 is submerged in the slag 12. It has the advantage that the arc current supplied to the electrode 2 can be increased while the electrode 2a remains in the slag 12. This means that even if the distance between the electrode 2 and the side wall inner surface 1a of the ladle is small, since the refining is within the ladle &%1, the side wall inner surface 1a
The slag 12 prevents arc radiation to a, thereby preventing damage thereto.

As described above, the present invention is useful in that it is possible to improve the kneading efficiency by inputting large amounts of power while preventing damage to the side wall 1a of the ladle.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and FIG. 1 shows a control system of a ladle na furnace, and FIG. 2 shows a different example of the positional relationship between the current regulating means and the furnace transformer in a ladle refining furnace. Partial view shown. 1... Ladle, 2... Electrode, 3... Electrode lifting mechanism,
6... Current adjustment means, 11... Molten steel, 12... Slag, 13... Arc. Figure number? a

Claims (1)

[Claims] A plurality of electrodes are placed in the upper part of the space inside the ladle and are moved up and down by a lifting mechanism, while molten steel whose upper surface is covered with slag is left in the ladle, and power is supplied to the electrodes. In a method of operating a ladle refining furnace, in which an arc is generated between the tip of the electrode and the upper surface of the molten steel in the ladle, and the molten steel is heated and refined by the arc, electric power is supplied to the electrode. A current regulating means is provided in the supply circuit, and the current regulating means regulates the current supplied to the electrode, while detecting the arc voltage of the electrode, and adjusting the detected arc voltage to a predetermined slag thickness. A method for operating a ladle refining furnace, characterized in that the lifting mechanism is controlled so that the voltage is below the corresponding voltage, thereby controlling the lifting position of the electrode so that the tip of the electrode is submerged in the slag.