JPH038290A - Electrode control method for arc furnace - Google Patents

Abstract

PURPOSE:To improve fusion efficiency by directly position-controlling an electrode, repeating the holding and lowering of the electrode so as to avoid frequent lifting/lowering motion, and melting an insertion material at the preset arc length. CONSTITUTION:An insertion material S is inserted into a furnace body 6, an electrode 3 is lowered to start an arc, then it is held at the fixed height position for the preset period, and part of the insertion material S is melted. The electrode 3 is lowered by the height corresponding to the fusion quantity of the insertion material S during the hold time, and the holding and lowering of the electrode 3 are repeated thereafter to melt the insertion material S. A power detector 20 detects that the near flat bath stage is attained via the fed power quantity and lowers the lower end of the electrode 3 to the position apart from the solution level by the preset distance. The detector 20 again detects that the flat bath stage is attained and lowers the electrode 3 to the vicinity of the solution level to refine a solution. The electrode 3 is properly lowered in sequence in response to the fusion quantity, the insertion material S is melted at the preset arc length, thus no hunting occurs, and fusion efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control method for controlling the elevation and descent of a movable electrode in an arc furnace for melting charging materials such as raw material scrap for steelmaking.

[Conventional technology]

In general, in arc furnaces, where the charge material is melted using the arc heat of the electrodes, the melting efficiency can be increased if the arc heat is absorbed into the charge material with less loss. Melting efficiency can be improved by melting with a long arc length in the middle stage and melting with a short arc length in the final stage of melting, when scrap changes to molten steel and the furnace wall is often exposed. However, conventional electrode control has been based on current control or impedance control that maintains the current or impedance constant during arc discharge, so the position of the electrode is not directly controlled, and the electrode moves as the charge material melts in the furnace. In addition to constantly repeating the lifting and lowering, the material may disintegrate or come into contact with the material, or "scrap" may occur.
Due to the difference in resistance between when electricity is applied between the molten steel and the furnace bottom electrode and when the current is applied between the molten steel and the furnace bottom electrode, a hunting phenomenon of the 74 poles occurs, which frequently causes a significant deterioration of melting efficiency. Ta.

[Problem to be solved by the invention] This invention solves the above-mentioned conventional problems, and N! f
An object of the present invention is to provide an electrode control method in an arc furnace that can suppress the sensitive movement of No. 1 and improve melting efficiency.

[Means to solve the problem]

However, in the electrode control method of the present invention, the 1st electrode is driven up and down.
In an arc furnace in which the charge material is melted by the arc heat of the i-electrode, the charge material is charged into the furnace body, the electrode is lowered toward the charge material, and after ignition, the electrode is held at a certain height. The electrode is held in position for a predetermined period of time to melt a portion of the charge material, and then the electrode is lowered by a height corresponding to the amount of charge material dissolved during the holding time, and the above-mentioned holding and lowering of the electrode is then repeated. Then, the charged material is melted in the initial stage of melting to 1 melting V1 stage, and when the near flat bath stage is detected by the input power, the lower end of the electrode is lowered to a position a predetermined amount ff1llll from the bloodletting point. A method for controlling an electrode in an arc furnace, characterized in that the electrode is further lowered to a position approaching the phlebotomy point to refine the molten metal. be.

[Effect]

In the electrode control method of the present invention, the Ti electrode is repeatedly held at a constant position and lowered by a height corresponding to the amount of charge material melted during the holding time, and the Ti electrode is loaded from the initial melting stage to the main melting stage. Since the incoming material is melted, the position of the electrode is directly controlled without using current or impedance as in conventional methods, and the electrode is lowered to the appropriate position in sequence according to the amount of melting, creating the desired arc without excessive hunting or vertical movement. Dissolution can be carried out using a phlegm. Also, in the near-flat bath period and flat bath period, melting and refining can be carried out at the desired arc length without hunting and with little heat loss to the furnace wall.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

In Figure 1, 1 is a furnace transformer connected to the furnace power supply, 2
is a thyristor rectifier connected to the secondary side of this transformer, and the electrode (movable electric bridge) 3 and the furnace bottom 1fffi are connected to the output side of the thyristor rectifier.
4 are connected. 5 is a glue handle for protecting the rectifier,
6 is a furnace body, 7 is a furnace lid, 8 is an electrode support provided with an electrode holder 9 that holds the electrode 3, and 10 is an electric winch type drive machine that drives the electrode support up and down, and is used for winding wire. The winding rf411 is connected to the electric motor 8112. 13 is a pulse generator connected to the rotating shaft of this electric motor 12, and the height H from the reference position 14 to the lower end of the electrode holder 9 is
It emits a pulse proportional to , as a holder position signal. In addition, 15 is a beam 'Fi' on the upper side of the furnace body 6.
This is a laser beam type electrode lower end detector placed toward the pole 3, and is provided at a height h from the reference position 14. When pulling up the electrode 3 during scrap loading, etc. When the electrode passes in front of the electrode lower end detector 15, a detection signal is emitted, and the length under the neck of the electrode 3 is determined by subtracting the height h from the holder position H (measured by the pulse generator 13) at that time. On the other hand, 20 is a power detector that detects the amount of electric power input to the furnace (accumulated electric energy), 21 is an arc current detector, and 22 is used to issue electrode lifting commands and commands according to the control procedure described later. 23 is a phase control device that outputs a firing angle signal (phase control signal) according to the current command to the thyristor rectifier 2. 24 is a lift control @
The device drives an electric motor in response to the electrode lifting/lowering command to lift/lower the electrode 3 by a predetermined amount.

Next, Figures 2 to 6 show the electrode control method of the electrode 3 in the DC arc furnace having the above configuration and having a capacity of 20 TON (inner diameter of the furnace body 6 = 3080 m, see Figure 7 for vertical dimensions of the furnace body 6). Flow chart and electrode I11 in the figure
This will be explained with reference to FIG. 7, which shows the current situation.

First, Figure 2 shows the overall electrode control, and shows the furnace body 6 after tapping.
When the furnace M7 and the electrode 3 are raised and rotated laterally before charging the scrap material into the furnace, in step 25, the electrode lower end detector 15 and the pulse generator 13 detect the position of the electrode 3. Measure the lower neck quality 1,
The zero point position of the position measurement of the electrode 3 corresponds to the upper end surface 6a of the Ti extreme upper and lower end furnace body 6. Finally, this position. The distance from the moving electrode 3 to the lower end of the electrode 3 can be measured using the output signal of the pulse generator 13 as the electrode position.
The electrode position measuring circuit in the electrode control device 22 is reset. Then, in step 26, scrap (g human resources) S
is charged into the furnace body 6 until it reaches the upper end surface 6a of the furnace body,
After the furnace cover is deposited, the electrode 3 is lowered to energize and fire, and the electrodes are controlled during the initial melting stage, main melting stage, and near flat bath stage, respectively, in steps 30, 40, and 60, detailed steps of which will be described later, to melt the scrap. and step 70
In step 2, determine whether or not double loading is to be carried out based on the total scheduled scrap loading of the charge, and if double loading is to be carried out, proceed to step 2.
Return to step 5 and perform continuous loading and melting, and when the continuous loading is gone, step 80 will change the electrode control during the flat bath period to J.
3, after the refining is completed, the steel is tapped for J3 to complete the melting of the charge, and the next charge will be melted in the same manner.

Next, to explain in detail the electrode system (2) in each dissolution stage, first, the details of step 30 are as shown in Fig. 3, and when the electrode 3 is lowered and fired as described above, the firing is performed in step 31. The arc position (approximately coincident with the zero point position ffL in this embodiment) is set as the operation reference position, and the electrode 3 is held (stopped) at this position.

In this state, the tap voltage is set to 300V to protect the furnace lid.
, Suff'=z'/7S is melted at a set current of 15=30 kA. (See Figure 8(a)) Changes in the current during melting are monitored in step 32, and if the current decreases significantly and falls below 30% of the set voltage I, remove the scrap. Assuming that there is a collapse, etc., the decrease continuation time t is set to a predetermined set time t in step 33.

(for example, 2 seconds) or not, and if it continues for a long time, control the electrodes in step 34! I] The device 22 issues a lowering command to lower the electrode 3 by 10ag, and lowers the electrode 3. In addition, the 7-current is set to N current I, which is 1
If it is 10% or more, the electrode -
Assuming that the distance between scraps has become too small, step 35
Then, the phase control device 23 sets the firing angle of the thyristor rectifier 2 to 11 to maintain the arc current at the set current 8. As the melting progresses, a part of the scrap S becomes molten steel M as shown in FIG. 8(b), and the arc length increases. is the set power consumption P
+ 3 = 500 kwh or more, the initial dissolution stage is considered to have ended and the process proceeds to the next main dissolution stage. In addition, the above P
The power consumption of 1 s-500 kWh is the scrap II (scrap opening in a short cylindrical space with a diameter of 3080 mm and a height of 200 mm) for a depth of approximately 200 mm of the scrap S filled in the furnace body 6. This is the power input port required for melting.

Next, in the main dissolution period shown in Figure 4, first step 4
1, the electrode 3 is lowered from the operation reference position by a height of 200 m corresponding to the amount of scrap melted and held at the lowered position, and the set (tap) voltage is 460 V% and the set current is 1.
．． -30kAr, melting the scrap S. (Refer to FIG. 8(C)) Correct control is performed in steps 42 to 45 similar to steps 32 to 35 above to deal with fluctuations in the arc current during melting, and in step 46, the input power port P is changed to the set power consumption Pa. , = 500 kwh, the total amount of input power Pa after the start of the main melting period is the set power consumption I P for scrap melting in the main melting period.
23-1000 kwh (step 47
), the lower end position of the electrode is at the upper end surface 6a of the furnace body, i.e., at the position t? J
L. (step 48), and the lower end of the electrode is not further below the position 1400 m+ from the upper end surface 6a of the furnace body (step 49). After confirming each of the above, in step 50, the electrode 3 is lowered by a height of 200 am corresponding to the amount of scrap to be melted according to the power consumption Pas, held at that position, and then returned to step 42 to repeat the melting process. If it is detected in step 48 that the lower end of the electrode has reached below 1600 ae+, the electrode 3 is raised to the 1600 m position (step 51), and in step 49 the lower end of the electrode has reached below 1400 am. If this is detected, the amount of descent of the electrode 3 is set to 200 li or less and the above 16
00 position (step 52), and continue melting. In step 47, when the total of input power slip P at each electrode position becomes equal to or greater than the set power consumption P2s, the main melting period has ended. , transition to ii control for the next near-flat bus period.

During the near-flat bass period, as shown in Figure 5,
In step 61, the electrode 3 is connected so that the lower end of the electrode is the upper end surface 6 of the furnace body.
Lower and hold until it reaches a position of 1600 am from a, set (tap) voltage 400 V, set Ti current f, -3
5 kAt', the remaining scrap S is melted.

(See Figure 8(d)) Regarding arc current fluctuations during melting, only when the arc current becomes 110% or more of the set current I in steps 62 and 63, the set current is adjusted by the thyristor firing angle IIJIII. maintain it. In step 64, the immersion constant force P3 is set to the power consumption meter P3.
When s = 1000 kwh is reached, it is assumed that all the remaining scraps have been melted, and the process moves to the next step 70 (see FIG. 2) for determining the number of consecutive scraps.

In the flat bath stage, as shown in Fig. 6, the electrode 3 is further lowered in step 71 to hold the lower end of the electrode at a position 1650 ay from the upper end surface 6a, and a short arc length of about 60 ay from the molten steel surface (sill level) is achieved. In order to protect the furnace wall, the set voltage is 260■, and the set current is 1. -40△
Perform refining with. (See FIG. 8(e)) For fluctuations in arc current, correction 1 (1111) is performed in steps 72 to 73 similar to steps 62 to 63 above.
In step 74, when the input power P4 becomes the set power consumption for refining P4s=2000hwh or more,
After finishing the refining, the steel is tapped and the melting process for one layer is completed.

The present invention is not limited to the above embodiments; for example, in the above embodiments, the electrode was held at the arcing position at the initial stage of melting, but a position M slightly above the arcing position may be set as the operating reference position. Also, the operating reference position is the zero point.

It doesn't have to match. Further, the electrode holding position at the initial stage of dissolution or during the near-flat bath period may be lowered in two stages according to the progress of dissolution. Also, the electrode lowering machine at the end of the initial melting period (at the start of the main melting period) and the electrode lowering machine during the main melting period! A value different from the iI value may be adopted, and in this case, the set power consumption ff1P1. and PaS may also be set to different amounts of power depending on the difference in the amount of decrease. In addition, the measurement of the length 1 below the neck of the electrode and the measurement of the lower end position of the electrode are -F
Methods other than those described in the embodiments may be used. It is further preferable that the total length of the electrode is measured together with the measurement of the length j below the neck, and that the addition or replacement of the electrode is also performed in step 25.

Although the above description has been made regarding a DC arc furnace, the present invention can also be applied to an AC arc furnace.

(Effects of the Invention) As explained above, according to the present invention, the position of the electrode is directly controlled, and melting and refining can be performed at a desired arc length without hunting or frequent vertical movement.
It is possible to improve dissolution efficiency.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is an equipment connection diagram of a DC arc furnace, Fig. 2 is a flowchart of the entire process, Figs. 3 to 6 are flowcharts of each melting stage, and Fig. 7 is a flowchart of each melting stage. The diagram showing the electrode υ control situation, FIG. 8, is also an explanatory diagram of the situation inside the furnace. 2... Thyristor rectifier, 3... Electrode, 6... Furnace body, 8... M pole support, 10... VJ machine, 13...
... Pulse energy, 15... Electrode lower end detector,
20...'4 force detector, 21... arc current detector, 22... electrode υ1m device, 23... phase control tll
Device, 24... Lifting control device.

Claims (1)

[Claims] 1. In an arc furnace in which the charge is melted by the arc heat of an electrode that is driven up and down, the charge is charged into the furnace body, the electrode is lowered toward the charge, and after ignition, the charge is melted. The electrode is held at a constant height position for a predetermined period of time to melt a portion of the charge material, and then the electrode is lowered by a height corresponding to the amount of charge material dissolved during the holding time, and the above electrode is By repeating holding and lowering, the charge material is melted from the initial melting stage to the main melting stage, and when it is detected that the near flat bath stage has been reached based on the input power, the lower end of the electrode is moved a predetermined distance from the molten metal surface. An arc furnace characterized by lowering the electrode to a position where it melts, detecting that the flat bath stage has been reached based on the input electric power, and then lowering the electrode further to a position where it approaches the surface of the molten metal to refine the molten metal. Electrode control method.