JP2024088548A - Molten steel level control method - Google Patents

Abstract

A molten steel surface level control method is provided that can automatically detect and continue monitoring abnormalities in a level gauge caused by splash adhesion.
[Solution] The molten steel surface level control method is a molten steel surface level control method for controlling the molten steel surface level to be a target value based on a measured molten steel surface level, and includes the steps of measuring the molten steel surface level using a first level gauge, which is one of two or more level gauges installed (S1), determining whether the first level gauge is abnormal based on the state of the molten steel surface level measured by the first level gauge (S2), and if it is determined that the first level gauge is abnormal, switching to a second level gauge, which is one of the multiple level gauges other than the first level gauge, and measuring the molten steel surface level (S3).
[Selected figure] Figure 4

Description

This disclosure relates to a method for controlling the level of a molten steel surface. This disclosure particularly relates to a method for controlling the level of a molten steel surface in a mold in the steel industry.

In continuous casting of steel, controlling the molten steel level in the mold at a constant level is an important technology for ensuring safety, stable production, and improving quality. Eddy current level gauges are generally used to measure the molten steel level in the mold.

When casting steel continuously, molten steel can scatter inside the mold, known as splash. Due to the measurement principle of the eddy current level gauge, when molten steel adheres to the outer tube of the level gauge, it indicates a certain level. This makes it impossible to monitor and keep the molten steel level inside the mold constant.

As a conventional solution to this problem, for example, Patent Document 1 discloses a method of installing a surveillance camera and ignoring the level indication when splash is detected. Also, for example, Patent Document 2 discloses a method of installing a prevention plate in the mold to prevent splash from adhering to the level gauge.

JP 2004-351469 A Japanese Utility Model Application Publication No. 01-135327

However, although Patent Document 1 proposes a method to reduce the impact when a splash occurs, it does not disclose a method to reduce the impact when molten steel continues to adhere to the level gauge.

Furthermore, the method of Patent Document 2 cannot completely prevent splashes if the prevention plate deteriorates.

The purpose of this disclosure, made in consideration of these circumstances, is to provide a molten steel surface level control method that can automatically detect and continue monitoring abnormalities in a level gauge caused by splash adhesion.

(1) A method for controlling a molten steel surface level according to an embodiment of the present disclosure,
A molten steel level control method for controlling a molten steel level to be a target value based on a measured molten steel level, comprising:
measuring the molten steel surface level with a first level gauge which is one of two or more level gauges installed;
determining whether the first level gauge is abnormal based on a state of the molten steel surface level measured by the first level gauge;
When it is determined that the first level gauge is abnormal, switching to a second level gauge, which is one of the plurality of level gauges other than the first level gauge, to measure the molten steel surface level.

(2) As an embodiment of the present disclosure, in (1),
When the molten steel surface level measured by the first level gauge does not change for a certain period of time, it is determined that the first level gauge is abnormal.

(3) As an embodiment of the present disclosure, in (1) or (2),
The method further includes, when the molten steel surface level is measured by the second level gauge switched from the first level gauge, adjusting a set level so that the molten steel surface level gradually approaches the target value.

(4) As an embodiment of the present disclosure, in any one of (1) to (3),
Each of the plurality of level gauges is an eddy current sensor.

This disclosure provides a molten steel surface level control method that can automatically detect and continue monitoring abnormalities in a level gauge caused by splash adhesion.

FIG. 1 is a schematic diagram showing the configuration of a system including a molten steel level control device that executes a molten steel level control method according to an embodiment of the present disclosure. FIG. 2A is a diagram illustrating a change in the measured value of the molten steel surface level. FIG. 2B is a diagram illustrating an example of a change in the set value of the molten steel surface level. FIG. 2C is a diagram illustrating an example of a change in the nozzle opening degree. FIG. 3 is a diagram showing changes in the molten steel surface level measured by a plurality of level gauges in the embodiment. FIG. 4 is a flowchart showing the process of a molten steel surface level control method according to an embodiment of the present disclosure.

Hereinafter, a method for controlling the level of a molten steel according to one embodiment of the present disclosure will be described with reference to the drawings. Here, the level of the molten steel refers to the level of the surface of the molten steel poured into the mold.

Figure 1 is a schematic diagram showing the configuration of a system including a molten steel level control device. The molten steel level control device includes a plurality of level gauges 5, a judgment unit 7, and a level control unit 9, and executes a molten steel level control method according to one embodiment of the present disclosure. The judgment unit 7 includes a calculation unit 8 that calculates the molten steel level, and a switch for switching the molten steel level output to the level control unit 9. The molten steel level control device controls the molten steel level to a target value based on the measured molten steel level. Details of the level gauges 5, judgment unit 7, calculation unit 8, and level control unit 9 will be described later.

In this embodiment, the molten steel level control device is part of a system for continuously casting steel, and controls the molten steel level in the mold 6 to a target value. In continuous casting of steel, molten steel is supplied from a tundish 1 to the mold 6, and a cast piece in the middle of solidification is withdrawn from the bottom of the mold 6 to produce a continuous cast piece. A sliding nozzle 2 and a submerged nozzle 4 are provided at the bottom of the tundish 1, and an amount of molten steel according to the opening degree of the sliding nozzle 2 is supplied to the mold 6. Here, the molten steel level and the target value are indicated by the height distance from the reference position of the mold 6 (e.g., the bottom of the mold 6). The molten steel level and the target value may be indicated, for example, by the height [mm] from the reference position, or may be indicated by the relative height [%] when the distance from the reference position to the upper limit position is set to 100%.

The level gauge 5, which measures the molten steel surface level in the mold 6, measures the molten steel surface level in a non-contact manner. A known device may be used as the level gauge 5. Various devices have been proposed as the level gauge 5, but in this embodiment, an eddy current sensor is used. The eddy current sensor has excellent response and detection accuracy and is easy to handle. In a system in which the molten steel surface level control method according to this embodiment is performed, two or more level gauges 5, that is, multiple level gauges 5, are installed. Hereinafter, one of the multiple level gauges 5 is assumed to be a first level gauge 5A. Also, one of the multiple level gauges 5 other than the first level gauge 5A is assumed to be a second level gauge 5B. The multiple level gauges 5 may be composed of two, the first level gauge 5A and the second level gauge 5B, or may be composed of three or more including another level gauge 5. In this embodiment, each of the multiple level gauges 5 measures the molten steel surface level.

The molten steel level control device may include, for example, a computer as a hardware configuration. The molten steel level control device may also include at least one or more processors. The processor may be, for example, a central processing unit (CPU) of a computer, but is not limited to this and may be any processor. The molten steel level control device may have the following software configuration. One or more programs used to control the operation of the molten steel level control device are stored in a storage device (for example, a computer memory). When the program stored in the storage device is loaded by the processor, it causes the processor to function as a judgment unit 7, a calculation unit 8, and a level control unit 9.

The calculation unit 8 acquires data measured by each of the multiple level gauges 5 and calculates the molten steel surface level. The calculation unit 8 acquires signals from the level gauges 5, for example, via an amplifier, and may perform amplification processing as necessary. The calculation unit 8 calculates the molten steel surface level so that it can be compared with, for example, a target value. For example, when the target value is set as a relative height [%] from the reference position of the mold 6, the calculation unit 8 may convert the numerical value measured by the level gauges 5 to a molten steel surface level expressed as a relative height [%].

The judgment unit 7 sets a switch so that one of the molten steel surface levels calculated by the calculation unit 8 is output to the level control unit 9. Here, one of the multiple level gauges 5 is assigned for control, and the others are assigned for backup. The judgment unit 7 sets a switch so that the molten steel surface level based on the data measured by the control level gauge 5 is output to the level control unit 9. When the judgment unit 7 judges that the control level gauge 5 is abnormal, it assigns one of the backup level gauges 5 to a new control level gauge 5. In this case, the judgment unit 7 switches the switch so that the molten steel surface level based on the data measured by the new control level gauge 5 is output to the level control unit 9. Here, the order in which the backup level gauge 5 is set as the new control level gauge 5 may be determined according to a predetermined priority order, or may be determined randomly.

Based on the acquired molten steel surface level, the level control unit 9 adjusts the opening of the sliding nozzle 2 so that the molten steel surface level becomes the target value. In this embodiment, the level control unit 9 adjusts the opening of the sliding nozzle 2 via the cylinder 3. For example, when the opening of the sliding nozzle 2 increases, more molten steel is supplied to the mold 6, and the molten steel surface level rises.

Here, in the continuous casting of steel, splash (molten steel scattering) may occur in the mold 6. If molten steel adheres to the level gauge 5 due to splash, the level gauge 5 detects the molten steel that has adhered, making accurate measurement impossible. For example, since the eddy current sensor reacts to magnetic materials, if molten steel, which is a magnetic material, adheres to the outer tube of the level gauge 5, which is an eddy current sensor, the molten steel level in the mold 6, which is the correct measurement target, cannot be measured, and a constant value continues to be output. Conventionally, when molten steel adheres due to splash, it is necessary to stop monitoring the molten steel level, which is a problem in that it interrupts the operation of continuous casting of steel. In this embodiment, the molten steel level control device executes the control method described below, so that it can automatically detect abnormalities in the level gauge 5 caused by splash adhesion and continue monitoring.

The molten steel surface level control device may perform the following steps (process a) to (process f). Here, the first level gauge 5A is for control and the second level gauge 5B is for backup.

As (Process a), the calculation unit 8 calculates the difference between the previous value and the current value of data (measurement values) indicating the molten steel surface level of the multiple level gauges 5 measured in a certain control cycle. The calculation unit 8 calculates the difference for at least the first level gauge 5A (control level gauge 5). The calculation unit 8 may calculate the difference for each of the multiple level gauges 5.

In (Process b), the calculation unit 8 determines whether the difference between the previous value and the current value of the first level gauge 5A exceeds a threshold value. The threshold value may be determined, for example, based on the change in the measurement value of the level gauge 5 when molten steel has adhered in the past. When comparing with the threshold value, the calculation unit 8 may read out the threshold value that has been stored in advance in the storage device from the storage device.

In (process c), the calculation unit 8 determines whether the difference between the previous value and the current value remains unchanged for a certain period of time after the difference exceeds the threshold value in (process b). The certain period of time may be, for example, a few seconds, but may be determined based on changes in the measurement values of the level gauge 5 when molten steel has adhered in the past.

In (process d), if the difference between the previous value and the current value does not change for a certain period of time in (process c), the judgment unit 7 judges that molten steel is attached to the first level gauge 5A, i.e., that the first level gauge 5A is abnormal. Here, if the difference does not exceed the threshold in (process b) or if the difference does not change for a certain period of time in (process c), the judgment unit 7 judges that the first level gauge 5A is normal. The normal first level gauge 5A continues to be used as the level gauge 5 for control.

In (process e), the determination unit 7 determines that the second level meter 5B is not abnormal. In other words, the determination unit 7 and the calculation unit 8 perform calculations and determinations similar to (process b) to (process d) with the second level meter 5B as the target. Here, (process e) can be omitted.

In (process f), the judgment unit 7 sets the second level gauge 5B as the new control level gauge 5. Therefore, the molten steel surface level output to the level control unit 9 is switched from the measurement value of the first level gauge 5A to the measurement value of the second level gauge 5B. At this time, the continuous steel casting operation continues without interruption.

When the second level gauge 5B is set as the new control level gauge 5, the molten steel surface level control device may replace the first level gauge 5A with the second level gauge 5B and perform steps (a) to (f) again.

When the control level gauge 5 is switched by the above (process f), the molten steel level control device implements the following sequence (control using a set level) to prevent a sudden change in the molten steel level and reduce the impact on operations.

As described above, the level control unit 9 adjusts the opening of the sliding nozzle 2 based on the acquired molten steel surface level so that the molten steel surface level becomes the target value. Here, due to individual differences between the multiple level gauges 5, the data (measurement values) indicating the molten steel surface level from each level gauge 5 may differ. FIG. 2A is a diagram illustrating an example of a change in the measurement value (measurement level) of the molten steel surface level acquired by the level control unit 9. In FIG. 2A, the vertical axis is the measurement level, and the horizontal axis is time. The measurement level changes significantly at the timing (Tc) when the control level gauge 5 is switched. In the example of FIG. 2A, the measurement level based on the measurement value of the first level gauge 5A is 40%, while the measurement level based on the measurement value of the second level gauge 5B is 35%. Also, in the example of FIG. 2A, the target value is preset to 40%.

When the level control unit 9 largely changes the opening degree of the sliding nozzle 2 so as to adjust the molten steel level to the target value after switching the control level gauge 5, the molten steel level also changes largely in a short time. A sudden change in the molten steel level is not preferable in the operation of continuous casting of steel. Therefore, the level control unit 9 changes the opening degree of the sliding nozzle 2 so as to adjust the molten steel level to the set level, not the target value. The set level is a set value of the molten steel level and functions as a temporary target. As shown in FIG. 2B, the set level is set so as to change stepwise (in a step-like manner) from the molten steel level at the timing (Tc) when the control level gauge 5 is switched to the target value. In FIG. 2B, the vertical axis is the set level, and the horizontal axis is the time. In the example of FIG. 2B, the set level is 35% at Tc, and then, after a certain time has passed, the set level gradually increases so as to approach the target value of 40%. The level control unit 9 starts control of the opening degree of the sliding nozzle 2 using the set level at the timing (Tc) when the control level gauge 5 is switched. The level control unit 9 adjusts the opening degree of the sliding nozzle 2 so that the molten steel surface level becomes the set level. Then, when the set level matches the target value, the level control unit 9 ends control using the set level.

Figure 2C is a diagram illustrating an example of changes in the opening degree of the sliding nozzle 2. In Figure 2C, the vertical axis represents the opening degree of the sliding nozzle 2 (nozzle opening degree), and the horizontal axis represents time. The level control unit 9 executes control using the set level shown in Figure 2B, so that the opening degree does not change suddenly even at Tc. In the example of Figure 2C, the opening degree of the sliding nozzle 2 changes gently within the range of 70% to 90%. And, as shown in Figure 2A, the measurement level gently approaches the target value of 40%.

Figure 3 shows the change in the measured value of the molten steel surface level by two level gauges 5, which are eddy current type sensors, in one embodiment. The two level gauges 5 are the first level gauge 5A and the second level gauge 5B, as described above. First, the first level gauge 5A is assigned for control, and the second level gauge 5B is assigned for backup. In the example of Figure 3, when the time reaches 2 [seconds], the first level gauge 5A reaches a constant value, indicating an abnormality. Since the molten steel surface level has been constant for a certain period of time (C), the molten steel surface level control device assigns the second level gauge 5B for control at Tc. In this way, the molten steel surface level control device automatically switches the level gauge 5 for control, so that the continuous casting operation of steel is not interrupted. In this embodiment, the operation is interrupted only when the molten steel surface level reaches a constant value for all of the multiple level gauges 5, and the operation continues as long as at least one level gauge 5 is normal.

Figure 4 is a flowchart showing the process of the molten steel surface level control method according to this embodiment. In the molten steel surface level control method according to this embodiment, at least the processes of steps S1 to S3 in Figure 4 are executed.

First, the molten steel surface level is measured by the first level gauge 5A (step S1). That is, the calculation unit 8 acquires the data measured by the first level gauge 5A and calculates the molten steel surface level.

Then, based on the state of the molten steel surface level measured by the first level gauge 5A, it is determined whether the first level gauge 5A is abnormal. In this embodiment, if a certain time has passed without the molten steel surface level measured by the first level gauge 5A changing (Yes in step S2), it is determined that the first level gauge 5A is abnormal. If the certain time has not passed without the molten steel surface level changing (No in step S2), it is determined that there is no abnormality in the first level gauge 5A, and the process returns to step S1.

If it is determined that the first level gauge 5A is abnormal, the molten steel surface level is measured by the second level gauge 5B. That is, the determination unit 7 changes the control level gauge 5 from the first level gauge 5A to the second level gauge 5B (step S3). Then, the process returns to step S1, and measurement is performed by the second level gauge 5B. That is, the calculation unit 8 acquires the data measured by the second level gauge 5B and calculates the molten steel surface level.

Here, when the control level gauge 5 is switched, the level control unit 9 performs control using the set level. In other words, when the molten steel level is measured by the second level gauge 2B, which has been switched from the first level gauge 5A, the level control unit 9 adjusts the set level so that the molten steel level gradually approaches the target value.

As described above, the molten steel surface level control method according to this embodiment can automatically detect abnormalities in the level gauge 5 caused by splash adhesion and continue to monitor the molten steel surface level due to the above-mentioned configuration. If the first level gauge 5A is abnormal, the second level gauge 5B continues to measure the molten steel surface level, enabling stable operations such as continuous casting. Furthermore, the number of multiple level gauges 5 may be more than two, and in this case, two or more backup level gauges 5 are prepared, making it possible to further stabilize the casting operation.

Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications or amendments based on the present disclosure. Therefore, it should be noted that these modifications or amendments are included in the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. The embodiments of the present disclosure can also be realized as a program executed by a processor included in the device or a storage medium having a program recorded thereon. It should be understood that these are also included in the scope of the present disclosure.

REFERENCE SIGNS LIST 1 Tundish 2 Sliding nozzle 3 Cylinder 4 Submerged nozzle 5 Level gauge 5A First level gauge 5B Second level gauge 6 Mold 7 Judging unit 8 Calculating unit 9 Level control unit

Claims (4)

A molten steel level control method for controlling a molten steel level to be a target value based on a measured molten steel level, comprising:
measuring the molten steel surface level with a first level gauge which is one of two or more level gauges installed;
determining whether the first level gauge is abnormal based on a state of the molten steel surface level measured by the first level gauge;
and when it is determined that the first level gauge is abnormal, switching to a second level gauge, which is one of the plurality of level gauges other than the first level gauge, to measure the molten steel surface level. The molten steel level control method according to claim 1, wherein the first level gauge is determined to be abnormal if the molten steel level measured by the first level gauge does not change for a certain period of time. The molten steel level control method according to claim 1 or 2, further comprising: adjusting a set level so that the molten steel level gradually approaches the target value when the molten steel level is measured by the second level gauge switched from the first level gauge. The molten steel surface level control method according to claim 1 or 2, wherein each of the plurality of level gauges is an eddy current sensor.

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