JP2769325B2 - Electrode position control method for DC arc furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the position of a movable electrode (also referred to as an arc electrode) of a DC arc furnace, and more particularly to a method for controlling the position of an electrode in a DC arc furnace. The present invention relates to a method for controlling the electrode position of a DC arc furnace, which is capable of stably and satisfactorily performing the above.

(Prior Art) In general, for example, in a DC arc furnace for iron making, a material to be melted such as scrap as a raw material for melting (hereinafter referred to as scrap) while generating an arc from a movable electrode.
Is melted to obtain molten steel at the furnace bottom, but the shape of the scrap changes moment by moment when the scrap is melted,
Alternatively, since a dent is formed in the molten steel and the arc voltage changes with the dent, it is necessary to control the movable electrode complicatedly in order to reliably obtain a desired arc voltage, that is, to surely connect the arc.

For this reason, conventionally, as shown in FIG. 2, after the scrap 2 is filled inside the DC arc furnace 1 and the furnace lid 3 is closed on the upper part of the furnace, a movable electrode such as a carbon electrode is placed from the upper part of the furnace lid 3. 4, a desired arc current is always passed between the movable electrode 4 and the furnace bottom electrode 8 via the furnace transformer 5, the thyristor converter 6, and the smoothing reactor 7, and a predetermined voltage is applied. An arc is generated from the tip of the movable electrode 4 while the position of the movable electrode 4 is controlled so as to melt the scrap 2 sequentially. That is, when the arc is generated, the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 is detected by the voltage detector 9, and the voltage between the detected voltage Vr and the set voltage Vd predetermined by the voltage setter 10 is detected. The deviation is obtained by a subtractor 11, and a proportional integral operation is performed by an adjustment unit 12 so that the voltage deviation becomes zero, and an operation output (control signal) obtained by this operation is supplied to an electrode lifting / lowering motor 13. The electrode lifting / lowering motor 13 rotates forward or backward based on the operation output, and the winch 14 winds or rewinds the other end of the wire 15 having one end as a fixed end. The mast 16 is controlled to move up and down. At this time, the holder arm 17 fixed horizontally above the mast 16 moves up and down together, so that the movable electrode 4 is moved up and down via the holder arm 17 and a predetermined distance is set between the movable electrode 4 and the furnace bottom electrode 8. Is applied, and a desired arc is generated from the tip of the movable electrode 4.

Therefore, in this type of electrode lifting / lowering control method, when the set voltage is smaller than the detected voltage (Vd−Vr <0), the movable electrode 4 is lowered, and the set voltage is larger than the detected voltage (Vd−Vr−0).
When the relationship of Vr> 0) is established, control is performed so that the movable electrode 4 is moved up and down. In the control of the arc current, the arc current is extracted from the DC output side of the thyristor converter 6 or the output side of the hearth electrode 8, and the detected current Ir
The gate control angle α is determined by the automatic current regulator so that the current deviation between the current and the set current Id becomes zero, and the gate of the thyristor converter 6 is controlled according to the gate control angle α.

(Problems to be Solved by the Invention) In the electrode position control method as described above, basically, the voltage between the movable electrode 4 and the furnace bottom electrode 8, that is, the arc voltage is proportional to the arc length. The arc voltage and the electrode position are also in a proportional relationship, and the control of the arc voltage is performed by controlling the movable electrode 4 to move up and down. That is, when the movable electrode is raised, the arc voltage is proportionally increased, and when the movable electrode is lowered, the arc voltage is reduced proportionally. However, when an arc was generated between the movable electrode 4 and the molten steel, the relationship between the actual arc voltage and the position of the movable electrode was measured, and the relationship was as shown in FIG. Are not necessarily linearly proportional. As a cause of this, a dent of the molten steel surface due to the arc jet can be considered. Therefore, the control becomes unstable between the points A and B in FIG. 3 (for example, the arc voltage does not increase even if the movable electrode is raised, or the arc voltage is reduced even if the movable electrode is lowered). There is a problem in that good control cannot be performed, for example, an overshoot phenomenon due to the integration operation occurs, the input power becomes unstable, and an arc break occurs. Therefore, since the arc length cannot be accurately grasped only by the position of the movable electrode, it is necessary to control the arc by properly grasping the relationship between the arc voltage and the position of the movable electrode.

The present invention has been made to solve the above-described problems, and its object is to control the electrode position extremely well and prevent the occurrence of arc breakage without causing control instability or overshoot. It is an object of the present invention to provide a method of controlling an electrode position of a DC arc furnace capable of performing the above.

(Means and Actions for Solving the Problems) In order to achieve the above object, according to the present invention, a movable electrode for melting an object to be melted in a DC arc furnace is lowered to detect the energization with the furnace bottom electrode. The set electrode position is set as a reference point A,
As long as the position of the movable electrode is between the reference point A and the point B above the reference point A by a specified value determined in accordance with the applied power, the position of the movable electrode is set to the set position. The electrode position is controlled by the position control system, and while the position of the movable electrode is above the point B, the electrode position is controlled by the voltage control system so that the voltage of the movable electrode becomes the set voltage. Thus, the electrode position is controlled by position control in a region where the relationship between the arc voltage and the movable electrode position is not linearly proportional, and the electrode position is controlled by voltage control in a region where the relationship between the two is linearly proportional. , And control instability and overshoot phenomenon can be eliminated.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an overall configuration example of an electrode position control system of a DC arc furnace to which the method of the present invention is applied.
The same parts as those in the drawings are denoted by the same reference numerals, and the description thereof will be omitted.
Here, only different parts will be described.

As shown in FIG. 1, the system includes a voltage control system including a voltage detector 9, a voltage setter 10, a subtractor 11, and an adjustment unit 12, and a position detector 18, a position setter 19, a subtractor 20, It comprises a position control system consisting of a section 21 and a switching control system consisting of a current setter 22, a function generator 23, and a switch 24.

Here, the voltage detector 9 detects the voltage Vr between the movable electrode 4 and the furnace bottom electrode 8, and the voltage setter 10 sets the set voltage Vd in advance. Also, the subtractor 11
The voltage deviation (Vd−Vt) between the voltage Vr detected by the voltage detector 9 and the set voltage Vd set by the voltage setting device 10 is calculated. Further, the adjustment unit 12 receives the voltage deviation from the subtractor 11, performs a proportional-integral operation so that the voltage deviation becomes zero, and outputs an operation output (control signal) by voltage control.

On the other hand, the position detector 18 detects the position Pr of the movable electrode 4, and the position setting device 19 sets the set position Pd in advance. Further, the subtractor 20 calculates a position deviation (Pd−Pr) between the position Pr detected by the position detector 18 and the set position Pd set by the position setter 19. further,
The adjustment unit 21 receives the position deviation from the subtractor 20 as an input, performs a proportional-integral operation so that the position deviation becomes zero, and outputs an operation output (control signal) by position control.

On the other hand, the current setter 22 presets a current Id corresponding to a set current in an arc current constant current control system (not shown). Further, the function generator 23 calculates the position Pr detected by the position detector 18 and the set current set by the current setter 22.
The switching unit 24 outputs a switching command based on Id. Further, the switching unit 24 responds to the switching command from the function generator 23 to output an operation output (control signal) by voltage control and an operation output (control signal) by position control. And is given to the electrode lifting / lowering motor 13. That is, as shown in FIG. 3, the function generator 23 lowers the movable electrode 4 to conduct electricity between the furnace bottom electrode 8, in other words, the electrode position at which the contact between the movable electrode 4 and the molten steel surface is detected. When the reference point A is set, the position of the movable electrode 4 is between the reference point A and a point B that is above the reference point A by a specified value determined according to the applied power based on the set current Id. During this period, a switching command is output to give the operation output by the position control to the motor 13 for raising and lowering the electrode, while the operation output by the voltage control is output while the position of the movable electrode is above the point B.

Next, a method of controlling the electrode position of the DC arc furnace in the present embodiment will be described.

Now, by firing the thyristor converter 6,
A DC voltage is applied between the movable electrode 4 and the furnace bottom electrode 8 of the DC arc furnace 1, the movable electrode 4 comes into contact with molten steel and an arc is generated from the tip of the movable electrode 4, and the DC arc furnace 1 Operation commences. On the other hand, a voltage Vr between the movable electrode 4 and the furnace bottom electrode 8 is detected by a voltage detector 9, and a voltage deviation (Vd−Vr) of the detected voltage Vr from a set voltage Vd is obtained by a subtractor 11. Next, the adjustment unit 12 performs a proportional-integral operation so that the voltage deviation becomes zero, and an operation output by the voltage control is output to the switch 24. Also, the position of the movable electrode 4
Pr is detected by the position detector 18 and the detected position Pr is
At 20, a position deviation (Pd-Pr) from the set position Pd is obtained.
Next, the adjusting section 21 performs a proportional-integral operation so that the position deviation becomes zero, and the operation output by the position control is changed by the switch.
Output to 24.

Next, the switching of the operation output in the switch 24 is performed as follows. That is, when the detection position Pr of the movable electrode 4 detected by the position detector 18 is between the reference point A and the point B above the reference point A in FIG. A switching command to output an operation output by the position control from the adjustment unit 21 is output to the device 24. As a result, while the position Pr of the movable electrode 4 is between the reference point A and the point B, an operation output by the position control from the adjuster 21 is given to the electrode lifting motor 13. When the electrode lifting / lowering motor 13 rotates forward or backward in response to the operation output, the movable electrode 4 is controlled to be raised or lowered.

When the detection position Pr of the movable electrode 4 detected by the position detector 18 is above the point B in FIG. 3, the function generator 23 sends a voltage control signal from the adjustment unit 12 to the switch 24. A switching command to output an operation output by the above is output. Thereby, while the position Pr of the movable electrode 4 is above the point B, the operation output by the voltage control from the adjusting unit 12 is given to the electrode lifting / lowering motor 13. When the electrode lifting / lowering motor 13 rotates forward or backward in response to the operation output, the movable electrode 4 is controlled to be raised or lowered.

As described above, in this embodiment, the movable electrode 4 for melting the scrap 2 or heating the molten steel in the DC arc furnace 1 is used.
Is lowered, and the electrode position at which the energization (contact with the molten steel surface) with the furnace bottom electrode 8 is detected is set as a reference point A, and the movable electrode 4
Is between the reference point A and the point B above the reference point A by a specified value determined in accordance with the applied power, the position Pr of the movable electrode 4 is the set position Pd. As described above, the electrode position is controlled by the operation output by the position control from the position control system, and while the position Pr of the movable electrode 4 is above the point B, the voltage Vr of the movable electrode 4 becomes the set voltage Vd. As described above, the electrode position is controlled by the operation output by the voltage control from the voltage control system.

Therefore, since the control can be performed by properly grasping the relationship between the arc voltage Vr and the position Pr of the movable electrode 4, the control becomes unstable between points A and B, Since the shoot phenomenon does not occur, the input power can be stabilized by performing extremely good control, and the occurrence of arc break can be prevented.

The electrode lifting device is not limited to the electric type, but may be a hydraulic type.

Further, in the above embodiment, when the adjusters 12 and 21 include the integration operation, the output from the function generator 23 may be transmitted so as to cut off the integration operation while the respective adjustment systems are not selected.

(Effects of the Invention) As described above, according to the present invention, a movable electrode for melting a substance to be melted in a DC arc furnace is lowered, and an electrode position at which conduction with the furnace bottom electrode is detected is determined as a reference point. A, and while the position of the movable electrode is between the reference point A and the point B above the reference point A by a specified value determined in accordance with the applied power, the position of the movable electrode is equal to the set position. The position of the movable electrode is controlled by the voltage control system so that the voltage of the movable electrode becomes the set voltage while the position of the movable electrode is above the point B. Since the control is performed, it is possible to provide an electrode position control method for a DC arc furnace capable of controlling the electrode position extremely effectively and preventing occurrence of arc breakage without causing control instability or overshoot phenomenon. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of an electrode position control system of a DC arc furnace to which the present invention is applied, FIG. 2 is a configuration diagram showing a conventional electrode position control system of a DC arc furnace, and FIG. FIG. 4 is a characteristic diagram for explaining a relationship between an arc voltage and an electrode position. DESCRIPTION OF SYMBOLS 1 ... DC arc furnace, 2 ... Scrap, 4 ... Movable electrode, 5 ... Transformer for furnace, 6 ... Thyristor converter, 7 ...
... smoothing reactor, 8 ... furnace bottom electrode, 9 ... voltage detector, 10 ... voltage setting device, 11 ... subtractor, 12 ... adjustment unit,
18 Position detector, 19 Position setting device, 20 Subtractor,
21 …… adjustment unit, 22 …… current setter, 23 …… function generator,
24 ... Switch.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Shoichi Takahashi, 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Toshimichi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Inside the Company (72) Inventor Kinzo Okazaki 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Fuji Electric Co., Ltd. 5590 (JP, B1) (58) Field surveyed (Int. Cl. ⁶ , DB name) F27B 3/08, 3/28 F27D 11/08 H05B 7/148

Claims (1)

(57) [Claims] A movable electrode for melting a substance to be melted in a DC arc furnace is lowered, and an electrode position at which conduction with a furnace bottom electrode is detected is set as a reference point A, and the position of the movable electrode is set at the reference point. A
And a point B above the reference point A by a specified value determined according to the input power, the position of the movable electrode is set to the set position by the position control system so that the position of the movable electrode becomes the set position. Control is performed, and while the position of the movable electrode is above the point B, the electrode position is controlled by a voltage control system so that the voltage of the movable electrode becomes a set voltage. An electrode position control method for a DC arc furnace.