JPH113778A - Judging method of melting progress in arc furnace - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for judging the progress of melting, particularly in a period in which the transition from the latter stage to the refining stage is easy, and is not affected by generated splash or combustion gas in the furnace. SOLUTION: A vibration sensor 11 is attached to a furnace shell outer wall surface of an arc furnace 10 to detect furnace body vibration generated from an arc 5 and transmitted to a furnace shell 1, and when the vibration level falls below a set level, from a later stage of melting. It is determined that it is time to shift to the refining period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the progress of melting of a cold iron source in an arc furnace for manufacturing molten steel by melting a cold iron source such as iron scrap and direct reduced iron.

[0002]

2. Description of the Related Art In recent years, an increasing number of processes for melting steel scrap generated by an arc furnace have been increasing due to resource and environmental problems. This arc furnace consumes a lot of electric power to melt the scrap,
It is desired to switch to setting of voltage and current suitable for the situation, and to improve power use efficiency. A particularly important time is the transition from the long arc to the short arc to the late melting period and the subsequent refining period,
It is important to accurately determine the timing of the transition from the late melting period to the refining period. For this purpose, it is necessary to accurately grasp the progress of melting of the material in the furnace. Conventionally, in order to grasp the progress of the melting, a method of visually observing the inside of the furnace when the input electric energy reaches a predetermined amount has been adopted.However, during arcing, observation is difficult due to dust generation and flame. ,
In addition, there is another problem that the degree of melting differs depending on the scrap material and the like, so that it is necessary to check the number of times.

In addition to this visual inspection, (a) a method of calculating the impedance from changes in the arc voltage and current or their elements and determining the change based on the change (b) the position of the electrode or the change per unit time (C) Method to judge based on the change of outlet temperature of cooling water for cooling the furnace body (d) Detecting radiated light from molten steel in the furnace by placing an optical sensor on the furnace lid Method (Tokuhei 6-5)
No. 0674) has been put to practical use.

[0004]

However, these conventional methods have the following problems. According to the methods (a) and (b), when the arc is generated in the material before melting, a change is seen, but when the melting progresses and the arc is generated in the molten steel, a signal is output. No change is seen. For this reason, it is not possible to evaluate the state of the late melting stage, which shifts from the most important melting period to the refining period. In the method of (c), when the molten steel splash generated by the arc or the acid lance accumulates on the inner wall of the furnace and a metal layer is formed, the heat insulating effect appears and cannot be detected correctly. This metal layer is not constant, and therefore cannot be evaluated under the same conditions, so that application is difficult. In addition, the oxygen from the acid lance hits the inner wall, and the effect of the flow of combustion gases in the furnace can further introduce errors. The method (d) has a problem that there is an effect of dust generated in the furnace or a flame of combustion, and there is a problem that maintenance is troublesome because a splash easily blocks a light emitting hole.

The present invention improves the conventional method of judging the progress of melting in an arc furnace, is easy to maintain, is free from the influence of splashes and combustion gas in the furnace, and particularly shifts from the latter stage to the refining stage. It is an object of the present invention to provide a method for judging the progress of dissolution during a period of time.

[0006]

According to the present invention, there is provided a method for judging the progress of melting in an arc furnace according to the present invention, wherein a vibration sensor is attached to an outer surface of a side wall of the arc furnace, and the vibration sensor detects furnace body vibration generated during melting of the material. The degree of dissolution is determined based on the change in the vibration level.

[0007] The vibration generated by the strong thundering sound generated by the arc as the heating source is transmitted to the material such as the remaining scrap existing on the front surface of the furnace wall and further transmitted to the furnace shell. Then, the vibration level decreases as the dissolution proceeds and the remaining material decreases. Therefore, in the present invention, a vibration sensor is attached to the outer wall surface or pillar of the furnace shell of the arc furnace, preferably on the outer wall surface near the upper surface level of the molten steel, and the vibration sensor detects the furnace body vibration transmitted to the furnace shell. And
The amount of residual material is evaluated based on the detected vibration level, and the degree of progress of melting is evaluated. When the vibration level is reduced, the degree of progress of melting and the time of transition to the refining period are determined. Further, in the present invention, in order to exclude vibration due to the jet sound of oxygen blown into the furnace, a filter is added, and attention is paid to the vibration inherent in the arc, which is the source of the vibration. That is, the output of the vibration sensor is passed through a filter and used as a signal in a specific frequency band including the natural frequency of the arc to determine the degree of melting.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a melting progress judging device used in the method of the present invention. In FIG. 1, 1
Is a furnace shell of an arc furnace 10, 2 is a furnace lid, and 3 is a graphite electrode. When electricity is supplied to the graphite electrode 3, an arc 5 is generated between the scrap 4 or the molten steel 6 in the furnace, and the arc heat generates the scrap 5. 4 is melted to produce molten steel 6 and slag 7. In order to detect the furnace body vibration transmitted to the furnace shell 2 with the strong thunder sound emitted by the arc 5 as this heat source,
A vibration sensor 11 is mounted on the outer wall of the furnace shell near the upper surface level of the molten steel, an output signal of the vibration sensor 11 is amplified by an amplifier 12, and a filter 13 that passes only a specific frequency band is used.
Is input to the vibration measuring device 14 and converted into a vibration level by a converter (not shown). In accordance with the change in the vibration level and the decrease in the vibration level, the fact that the dissolution has advanced is displayed on the chart display 15 and the dissolution progress evaluation device 16
It is determined at which stage the dissolution progress status is. Here, a reference value for judging the transition time from the late melting period to the refining period, which is particularly important, is set. When the vibration level falls below the set level, the evaluation device 16 sends the voltage / current setting device 17 Send a setting change signal. Based on this setting change signal, the electrode elevation control device 18 and the arc current control device 19 are respectively controlled, and the arc voltage is reduced, the current is increased, and switching to the short arc is performed.
The voltage and current settings are changed according to the conditions inside the furnace. In addition, the blowing of the coal powder into the slag and the blowing of oxygen into the molten steel are started by the output of the transition timing to the refining period.

Therefore, according to the present invention, it is possible to accurately grasp the transition time to the low voltage and large current short arc, which is particularly important in the latter part of the melting period, and to dispose the vibration sensor outside the furnace shell. As a result, no troubles such as splashes and flames occur and there is no maintenance problem. In addition, since there is almost no metal ingot at the upper surface level of molten steel, there is no such influence, and vibration according to the amount of the remaining cold iron source can be detected with good reproducibility. Setting and blowing of oxygen and coal powder become possible, and the dissolving efficiency is improved.

[0010]

Embodiments of the present invention will be specifically described below. Embodiment 1 FIG. Arc furnace (furnace diameter: 7200 mm, height: 60
(00 mm) was melted with a 30-inch graphite electrode at a maximum power of 750 V and a power capacity of 120 kA. Further, 6000 Nm ³ / hr of acid was fed from a water-cooled oxygen lance through a working port provided on the furnace side wall. When the molten metal was accumulated in the furnace, coal powder was blown into the slag at 80 kg / min to perform refining. Outside the furnace shell, a vibration sensor was attached near the upper surface of the molten steel at the time when the melting was completed to detect the vibration of the furnace shell. FIG. 2 shows a chart obtained by measuring the vibration level through a receiver and a converter. As can be seen from this chart, the vibration level decreases as scrap in front of the furnace wall decreases in the late stage of melting. Then, when the voltage dropped to 80 dB, the set voltage was lowered to 600 V and the current was increased to 130 kA. When the temperature further decreased to 70 dB, the coal powder was blown into the slag and oxygen was blown into the molten steel.
At this time, the voltage was set to 550V. In addition, as a result of a test conducted with a small amount of scrap as small as 120 tons,
Again, the timing at which the vibration level drops to 80 dB or less was slightly more than 20% earlier than when 150 t was charged. As a result, it was found that the furnace shell vibration level corresponded very well to the progress of melting.

As described above, by grasping the melting progress status based on the vibration level, the switching to the short arc and the transition timing to the refining period can be appropriately performed, so that the constant electric power amount up to that time can be reached. Then, compared with the operation by switching pattern control, 10-20 kW
An improvement in the unit power consumption of h / t was observed. Furthermore, there was no trouble due to dust, flame, or splash, and it was found that there was no problem in maintenance.

Embodiment 2 FIG. In the melting furnace described above, the vibration sensor was set to have high sensitivity even in a high frequency range of 2 kHz or more, and as a result of observation with changing the detection frequency band, 50
It was found that the signal near 0 Hz best captured the progress of dissolution. In addition to the fact that signals in the high frequency range of 1 kHz or higher are unlikely to appear, the effect of the jet sound of the oxygen lance appears. At a low frequency, vibrations caused by the movement of the electrode lifting / lowering system and equipment attached to the furnace are superimposed. Therefore,
In a furnace with a small arc power, it is effective to provide a band-pass filter in front of the receiver near a frequency unique to the arc in order to eliminate these vibrations. The frequency specific to the arc is in the range of about 100 Hz to 500 Hz. In an AC arc furnace, it is preferable to select the frequency centered on twice or six times the commercial frequency.

[0013]

As described above, according to the present invention,
A vibration sensor is installed on the outer surface of the side wall of the arc furnace to detect furnace body vibration generated from the melting arc and transmitted to the furnace shell, so maintenance is easy and the effect of generated splash and combustion gas in the furnace is reduced. The vibration level of the furnace body vibration detected by the vibration sensor accurately indicates the state of scrap remaining in the furnace from the late melting stage to the refining period, which is particularly important. The transition timing to the refining period can be properly performed. As a result, wasteful electric power in the latter stage of melting can be suppressed, the electric power consumption can be reduced, and damage to the furnace wall refractory can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus for determining the progress of dissolution used in the method of the present invention.

FIG. 2 is a diagram showing a measurement result of a vibration level in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace shell 2 Furnace lid 3 Graphite electrode 4 Scrap 5 Arc 6 Molten steel 7 Slag 10 Arc furnace 11 Vibration sensor 12 Amplifier 13 Filter 14 Vibration measuring instrument 15 Chart display 16 Dissolution progress evaluation device 17 Voltage / current setting device 18 Electrode raising / lowering Control device 19 Arc current control device

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Ken Yao 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (3)

[Claims] 1. A vibration sensor is attached to an outer surface of a side wall of an arc furnace, and the vibration sensor detects a furnace body vibration generated during melting of a material, and determines a progress of melting based on a change in the vibration level. For determining the progress of melting in a rotating arc furnace. 2. The determination of the progress of melting in an arc furnace according to claim 1, wherein when the vibration level of the vibration of the furnace body becomes equal to or less than a predetermined value, it is determined that it is time to shift from a later stage of melting to a refining period. Method. 3. The method according to claim 1, wherein an output of said vibration sensor is passed through a filter to be used as a signal in a specific frequency band including a natural frequency of the arc for judging the degree of melting. For determining the progress of melting in an arc furnace.