Molten steel level control method

Abstract

To provide a molten steel surface level control method which can automatically detect the abnormality of level gauges caused by the sticking of splashes to continue monitoring.SOLUTION: A molten steel surface level control method for controlling a molten steel surface level so as to be a target value based on a measured molten steel surface level, includes the steps of: measuring a molten steel surface level with a first level gauge as one of plural level gauges install by two or more (S1); determining whether the first level gauge is abnormal or not based on the state of the molten steel surface level measured with the first level gauge (S2); and measuring the molten steel surface level by switching to a second level gauge, which is one of the plurality of level gauges other than the first level gauge when it is determined that the first level gauge is abnormal (S3).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a method for controlling the level of a molten steel mold, and more particularly to a method for controlling the level of a molten steel mold in the steel industry. [Background technology]

[0002] In continuous steel casting, maintaining a constant level of molten steel in the mold is an important technology for ensuring safety, stable production, and improving quality. Eddy current level gauges are generally used to measure the level of molten steel in the mold.

[0003] During continuous steel casting, molten steel splashes, known as "splash," can occur inside the mold. Due to the measurement principle of eddy current level meters, when molten steel adheres to the outer tube of the level meter, it indicates a certain level. This makes it impossible to monitor and maintain a constant level of molten steel inside the mold.

[0004] As a conventional solution to this problem, for example, Patent Document 1 discloses a method of ignoring the level indication when a monitoring camera is installed and splash is detected. Also, for example, Patent Document 2 discloses a method of installing a prevention plate inside the mold to prevent splash from adhering to the level gauge. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-351469 [Patent Document 2] Japanese Utility Model Application Publication No. 01-135327 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although Patent Document 1 proposes a method for reducing the impact when a splash occurs, it does not go so far as to suggest a method for reducing the impact when molten steel continues to adhere to the level gauge.

[0007] Furthermore, the method of Patent Document 2 cannot completely prevent splashes when the prevention plate deteriorates.

[0008] The object of the present disclosure, made in consideration of the above circumstances, is to provide a molten steel surface level control method that can automatically detect abnormalities in a level gauge caused by splash adhesion and continue monitoring. [Means for solving the problem]

[0009] (1) A method for controlling a molten steel surface level according to an embodiment of the present disclosure includes: A molten steel level control method for controlling the 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 meter which is one of two or more level meter installed; determining whether the first level meter is abnormal based on the state of the molten steel surface level measured by the first level meter; 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.

[0010] (2) As one 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.

[0011] (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.

[0012] (4) As an embodiment of the present disclosure, in any one of (1) to (3), Each of the plurality of level meters is an eddy current sensor. [Effects of the Invention]

[0013] According to the present disclosure, it is possible 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. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a system equipped with a molten steel level control device that executes a molten steel level control method according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a diagram illustrating the change in the measured value of the molten steel surface level. [Figure 2B] FIG. 2B is a diagram illustrating an example of changes in the set value of the molten steel surface level. [Figure 2C] FIG. 2C is a diagram illustrating an example of a change in the nozzle opening degree. [Figure 3] FIG. 3 is a diagram showing changes in the molten steel surface level measured by a plurality of level gauges in the example. [Figure 4] FIG. 4 is a flowchart showing the process of a molten steel surface level control method according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a method for controlling a molten steel level according to an embodiment of the present disclosure will be described with reference to the drawings. Here, the molten steel level refers to the level of the surface of molten steel poured into a mold.

[0016] 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 determination unit 7, and a level control unit 9, and executes a molten steel level control method according to an embodiment of the present disclosure. The determination unit 7 includes a calculation unit 8 that calculates the molten steel level, and a switch for switching the molten steel level to be 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, determination unit 7, calculation unit 8, and level control unit 9 will be described later.

[0017] 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 a mold 6 to a target value. In continuous steel casting, molten steel is supplied from a tundish 1 to a 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 entry nozzle 4 are provided below the tundish 1, and an amount of molten steel corresponding 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 a 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 height [mm] from the reference position or by relative height [%] where the height from the reference position to the upper limit position is set to 100%.

[0018] The level gauge 5, which measures the molten steel level in the mold 6, measures the molten steel 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. Eddy current sensors have excellent responsiveness and detection accuracy and are easy to handle. In a system performing the molten steel level control method according to this embodiment, two or more level gauges 5, i.e., a plurality of level gauges 5, are installed. Hereinafter, one of the plurality of level gauges 5 is referred to as a first level gauge 5A. Furthermore, the remaining one of the plurality of level gauges 5, excluding the first level gauge 5A, is referred to as a second level gauge 5B. The plurality of level gauges 5 may consist of two gauges, the first level gauge 5A and the second level gauge 5B, or may consist of three or more gauges including another level gauge 5. In this embodiment, each of the plurality of level gauges 5 measures the molten steel level.

[0019] 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, computer memory). When the program stored in the storage device is read by the processor, it causes the processor to function as a determination unit 7, a calculation unit 8, and a level control unit 9.

[0020] 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 may acquire 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, if the target value is set as a relative height [%] from the reference position of the mold 6, the calculation unit 8 may convert the value measured by the level gauges 5 into a molten steel surface level expressed as a relative height [%].

[0021] The determination 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 use, and the others are assigned for backup use. The determination unit 7 sets a switch so that the molten steel surface level based on data measured by the control level gauge 5 is output to the level control unit 9. When the determination unit 7 determines 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 determination unit 7 switches the switch so that the molten steel surface level based on 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 assigned to the new control level gauge 5 may be determined according to a predetermined priority order, or may be determined randomly.

[0022] 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 a 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.

[0023] During continuous casting of steel, splashes (spattering of molten steel) may occur within the mold 6. If molten steel adheres to the level gauge 5 due to splashes, the level gauge 5 will detect the adhered molten steel, making accurate measurement impossible. For example, because eddy current sensors react to magnetic materials, if molten steel, which is a magnetic material, adheres to the outer casing 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 the level gauge 5 will continue to output a constant value. Conventionally, when molten steel adhesion due to splashes occurs, it is necessary to stop monitoring the molten steel level, which poses a problem of interrupting the continuous casting operation of steel. In this embodiment, the molten steel level control device executes the control method described below, thereby automatically detecting an abnormality in the level gauge 5 due to splashes and continuing monitoring.

[0024] The molten steel surface level control device may perform the following (Process a) to (Process f): Here, it is assumed that the first level gauge 5A is for control and the second level gauge 5B is for backup.

[0025] In (process a), the calculation unit 8 calculates the difference between the previous value and the current value of data (measured values) indicating the molten steel surface level measured by the plurality of level gauges 5 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 plurality of level gauges 5.

[0026] In (process b), the calculation unit 8 determines whether the difference between the previous value and the current value of the first level meter 5A exceeds a threshold value. The threshold value may be determined based on, for example, changes in the measured values of the level meter 5 when molten steel has adhered in the past. When comparing with the threshold value, the calculation unit 8 may read out a threshold value stored in advance in the storage device from the storage device.

[0027] In (process c), the calculation unit 8 determines whether the difference between the previous value and the current value has remained unchanged for a certain period of time after the difference exceeded the threshold in (process b). The certain period of time may be, for example, several seconds, and may be determined based on changes in the measured values of the level meter 5 when molten steel adhered in the past.

[0028] In (process d), if the difference between the previous value and the current value in (process c) remains unchanged for a certain period of time, the judgment unit 7 judges that molten steel has adhered to the first level meter 5A, i.e., that the first level meter 5A is abnormal. Here, the judgment unit 7 judges that the first level meter 5A is normal if the difference does not exceed the threshold in (process b) or if the difference does not remain unchanged for a certain period of time in (process c). The normal first level meter 5A continues to be used as the level meter 5 for control.

[0029] In (process e), the determination unit 7 determines that the second level meter 5B is not abnormal. That is, 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.

[0030] In (process f), the determination unit 7 sets the second level meter 5B as the new control level meter 5. Therefore, the molten steel surface level output to the level control unit 9 is switched from the value measured by the first level meter 5A to the value measured by the second level meter 5B. At this time, the continuous steel casting operation continues without interruption.

[0031] When the second level gauge 5B is set as a 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 then perform (process a) to (process f) again.

[0032] When the control level meter 5 is switched by the above (process f), the molten steel surface level control device performs the following sequence (control using a set level) to prevent a sudden change in the molten steel surface level and reduce the impact on operations.

[0033] As described above, the level control unit 9 adjusts the opening degree of the sliding nozzle 2 based on the acquired molten steel level so that the molten steel level reaches the target value. Here, due to individual differences between the multiple level gauges 5, the data (measured values) indicating the molten steel level from each level gauge 5 may differ. FIG. 2A is a diagram illustrating an example of changes in the measured molten steel level (measured level) acquired by the level control unit 9. In FIG. 2A, the vertical axis represents the measured level, and the horizontal axis represents time. The measured level changes significantly at the timing (Tc) when the control level gauge 5 is switched. In the example of FIG. 2A, the measured level based on the measured value of the first level gauge 5A is 40%, while the measured level based on the measured value of the second level gauge 5B is 35%. In the example of FIG. 2A, the target value is preset to 40%.

[0034] If the level control unit 9 significantly changes the aperture of the sliding nozzle 2 to adjust the molten steel level to the target value after switching the control level meter 5, the molten steel level also changes significantly in a short period of time. Rapid changes in the molten steel level are undesirable in continuous steel casting operations. Therefore, the level control unit 9 changes the aperture of the sliding nozzle 2 to adjust the molten steel level to a preset level rather than a target value. The preset level is a set value for the molten steel level and functions as a temporary target. As shown in FIG. 2B, the preset level is set to change in stages (stepwise) from the molten steel level at the time (Tc) when the control level meter 5 is switched to the target value. In FIG. 2B, the vertical axis represents the preset level, and the horizontal axis represents time. In the example of FIG. 2B, the preset level is 35% at Tc, and then gradually increases over time to approach the target value of 40%. The level control unit 9 starts control of the opening of the sliding nozzle 2 using the set level at the timing (Tc) when the control level meter 5 is switched. The level control unit 9 adjusts the opening 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 the control using the set level.

[0035] FIG. 2C is a diagram illustrating an example of changes in the opening degree of the sliding nozzle 2. In FIG. 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 FIG. 2B, so that the opening degree does not change suddenly even at Tc. In the example of FIG. 2C, the opening degree of the sliding nozzle 2 changes gradually within the range of 70% to 90%. Then, as shown in FIG. 2A, the measurement level gradually approaches the target value of 40%.

[0036] FIG. 3 shows changes in the molten steel level measured by two level gauges 5, which are eddy current sensors, in one embodiment. The two level gauges 5 are, as described above, a first level gauge 5A and a second level gauge 5B. Initially, the first level gauge 5A is assigned for control, and the second level gauge 5B is assigned for backup. In the example shown in FIG. 3, when the time reaches 2 seconds, the first level gauge 5A reaches a constant value, indicating an abnormality. Since the molten steel level remains constant for a certain period of time (C), the molten steel level control device assigns the second level gauge 5B to control at time Tc. In this way, the molten steel level control device automatically switches the control level gauge 5, thereby preventing interruptions to the continuous steel casting operation. In this embodiment, operation is interrupted only when the molten steel level measured by all of the level gauges 5 reaches a constant value. Operation continues as long as at least one level gauge 5 is normal.

[0037] 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 FIG.

[0038] First, the level of the molten steel surface 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 level of the molten steel surface.

[0039] 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.

[0040] 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.

[0041] Here, when the control level meter 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 meter 2B, which has been switched from the first level meter 5A, the level control unit 9 adjusts the set level so that the molten steel level gradually approaches the target value.

[0042] As described above, the molten steel surface level control method according to this embodiment is configured to automatically detect an abnormality in the level gauge 5 due to the adhesion of splashes and continue to monitor the molten steel surface level. 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 level gauges 5 may be more than two, and in this case, two or more backup level gauges 5 are provided, making it possible to further stabilize casting operations.

[0043] 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 alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within 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 an apparatus or a storage medium on which a program is recorded. It should be understood that these are also included within the scope of the present disclosure. [Explanation of symbols]

[0044] 1 tundish 2 sliding nozzle 3 cylinders 4 Submerged Entry Nozzle 5 Level gauge 5A 1st level meter 5B Secondary Level Gauge 6. Mold 7 Judgment section 8 Arithmetic section 9 Level control section

Claims

1. A molten steel level control method for controlling a molten steel level based on a measured molten steel level so that the molten steel level is at a preset target value, comprising: measuring the molten steel surface level with a first level meter which is one of two or more level meter installed; determining whether the first level meter is abnormal based on the state of the molten steel surface level measured by the first level meter; when it is determined that the first level meter is abnormal, switching to a second level meter, which is one of the plurality of level meter other than the first level meter, to measure the molten steel surface level; 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 meter switched from the first level meter, each of the plurality of level meters is an eddy current sensor; The set level functions as a temporary target and is adjusted so as to change stepwise from the molten steel level measured by the second level meter to the target value at the timing of switching.

2. 2. The molten steel level control method according to claim 1, wherein the first level meter is determined to be abnormal when the molten steel level measured by the first level meter does not change for a certain period of time.

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