Breakout detection method, continuous casting equipment operation method, and cast slab manufacturing method

Abstract

To provide a detection method of breakout, an operation method of a continuous casting facility, and a manufacturing method of a casting piece, which are capable of quickly detecting breakout in a transient state just after starting casting and easily adjustable for optimization.SOLUTION: A detection method of breakout in a continuous casting facility 1 for steel continuously or intermittently measures, at a start timing of casting, a nozzle opening degree of a sliding nozzle 11 for adjusting the supply amount of molten steel 2 to be supplied into a mold 13, compares an opening degree value according to the measured nozzle opening degree with an allowable upper opening degree that is set according to a casting speed, a height change rate of molten steel in a mold, a mold width, a mold thickness and the weight of the molten steel in a tundish, and determines the occurrence of breakout when the opening degree value is greater than the allowable upper opening degree.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for detecting a breakout, a method for operating a continuous casting facility, and a method for producing a cast slab. [Background technology]

[0002] In conventional breakout detection methods for continuous steel casting equipment, as described in Patent Documents 1 and 2, a camera attached directly below the mold detects a breakout by judging changes in the amount of light captured by the camera using a threshold value, and measures are taken, such as quickly stopping the supply of molten steel.

[0003] Various methods have also been proposed for predicting breakout. For example, Patent Document 3 discloses a method using temperature measuring devices. In the method of Patent Document 3, temperature measuring rows, each with a plurality of temperature measuring devices arranged horizontally, are arranged in multiple stages in the pouring direction below the molten metal surface of the mold of a continuous casting machine, and for any two stages of the rows, the temperature measuring devices arranged in the upper stage and the temperature measuring devices arranged in the lower stage are arranged on the same line. The measured values ​​of the temperature measuring devices in the upper and lower stages, which are on the same line, are then transmitted to a computing device, and a breakout is determined using the relationship between these measured values. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-197352 [Patent Document 2] Japanese Patent Application Publication No. 2-235561 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-39644 Summary of the Invention [Problem to be solved by the invention]

[0005] In breakout detection technology, a higher detection rate when a breakout occurs is desirable because it reduces the damage caused by the breakout. Also, a lower false positive rate when a breakout does not occur is desirable because it reduces the frequency of interruptions to operations and increases productivity, and a shorter time from breakout occurrence to detection is desirable because it reduces the damage caused by the breakout.

[0006] The problem with breakout detection using a camera installed below the mold as in Patent Documents 1 and 2 is that it is difficult to detect breakouts immediately after casting begins when the amount of molten steel inside the mold is less than normal and the amount of light is insufficient.

[0007] Furthermore, detecting breakouts by measuring the temperature of the mold as in Patent Document 3 has the problem that it is difficult to detect breakouts immediately after the start of casting when the mold is in a transitional state of rising from room temperature.

[0008] Therefore, the present invention has been made in light of the above-mentioned problems, and an object of the present invention is to provide a breakout detection method, a continuous casting equipment operating method, and a slab manufacturing method, which are capable of quickly detecting a breakout even in a transient state immediately after the start of casting. [Means for solving the problem]

[0009] (1) According to one aspect of the present invention, there is provided a breakout detection method in continuous steel casting equipment, which continuously or intermittently measures the nozzle opening of a sliding nozzle that adjusts the amount of molten steel supplied into a mold at the start of casting, compares the measured nozzle opening value with an allowable upper limit opening value that is set in accordance with the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish, and determines that a breakout has occurred if the opening value exceeds the allowable upper limit opening value.

[0010] (2) In the configuration of (1) above, the allowable upper limit of the opening angle is expressed by a linear equation with a parameter x consisting of variables including the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish. (3) In the configuration of (2) above, the parameter x is expressed by the following equation (1).

[0011]

number

[0012] (6) In any one of the configurations (1) to (5) above, at least one of the level of the molten steel supplied into the mold at the start of casting and the opening deviation of the nozzle that adjusts the amount of the molten steel supplied into the mold is monitored, and when the level of the molten steel falls below the lower limit H0 of the allowable height over time after the start of casting, or when the opening deviation exceeds the upper limit S0 of the allowable deviation over time after the start of casting, and when the opening value exceeds the upper limit of the allowable opening, it is detected that a breakout has occurred.

[0013] (7) In the configuration of (6) above, the allowable height lower limit H0 is calculated by equation (8) based on multiple pieces of operational data from the start of past casting, and the allowable deviation upper limit S0 is calculated by equation (9) based on multiple pieces of operational data from the start of past casting. H0=H-Aσ1 (8) S0=S+Bσ2 (9) where: H0: Lower limit of allowable height H: Average value of the melt level from multiple past operation data A: Coefficient σ1: Standard deviation of the mold surface height from multiple past operational data S0: Upper limit of allowable deviation S: Average value of nozzle opening deviation from multiple past operation data B: Coefficient σ2: Standard deviation of nozzle opening deviation from multiple past operational data

[0014] (8) In any one of the configurations (1) to (5) above, at least one of the height of the surface of the molten steel supplied into the mold at the start of casting and the opening deviation of a nozzle that adjusts the amount of the molten steel supplied into the mold is monitored, When the molten metal level falls below the lower limit H0 of the allowable height over time after the start of casting, the opening deviation exceeds the upper limit S0 of the allowable deviation over time after the start of casting, and the opening value exceeds the upper limit of the allowable opening, it is detected that a breakout has occurred.

[0015] (9) In the configuration of (8) above, the allowable height lower limit H0 is calculated by equation (8) based on multiple pieces of operational data from the start of past casting, and the allowable deviation upper limit S0 is calculated by equation (9) based on multiple pieces of operational data from the start of past casting. H0=H-Aσ1 (8) S0=S+Bσ2 (9) where: H0: Lower limit of allowable height H: Average value of the melt level from multiple past operation data A: Coefficient σ1: Standard deviation of the mold surface height from multiple past operational data S0: Upper limit of allowable deviation S: Average value of nozzle opening deviation from multiple past operation data B: Coefficient σ2: Standard deviation of nozzle opening deviation from multiple past operational data

[0016] (10) According to one aspect of the present invention, there is provided a method for operating a continuous casting facility that continuously casts steel, the method comprising: detecting a breakout at the start of casting using the breakout detection method according to any one of the configurations (1) to (9) above; and interrupting the supply of molten steel to a mold when the breakout is detected. (11) According to one aspect of the present invention, there is provided a method for producing a slab by continuously casting steel using the method for operating continuous casting equipment as described in the configuration of (10) above. [Effects of the Invention]

[0017] According to one aspect of the present invention, there are provided a breakout detection method, a continuous casting equipment operating method, and a cast slab manufacturing method, which are capable of quickly detecting a breakout even in a transient state immediately after the start of casting. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a configuration diagram showing a continuous casting facility according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the state of the continuous casting equipment at the start of casting. [Figure 3] 10 is a graph showing the relationship between the parameter x and the normalized nozzle opening degree and the allowable upper limit opening degree. [Figure 4] 10 is a graph showing the relationship between the coefficient c and the number of detections. [Figure 5] 1 is a graph showing the allowable lower limit of height and the molten metal surface height at the time of breakout occurrence in an example. [Figure 6] 10 is a graph showing an upper limit of the allowable deviation and an opening deviation when a breakout occurs in an embodiment. [Figure 7] 10 is a graph showing the relationship between coefficient A and the number of detections in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, identical or similar parts are designated by identical or similar reference numerals, and redundant explanations will be omitted. The drawings are schematic and may differ from the actual product. Furthermore, the embodiments shown below exemplify devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not specify the materials, structure, arrangement, etc. of component parts as described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0020] First Embodiment (Device configuration) FIG. 1 is a schematic diagram showing a continuous steel casting system 1 according to a first embodiment of the present invention. The continuous casting system 1 includes a tundish 10, a sliding nozzle 11, a submerged nozzle 12, a mold 13, a plurality of support rolls 14, a molten steel level gauge 15, and a determination unit 16. In the continuous casting system 1, molten steel 2 contained in the tundish 10 is poured into the mold 13 via the sliding nozzle 11 and the submerged nozzle 12 and cooled to form a solidified shell at the interface between the mold 13 and the molten steel 2. The solidified shell is then withdrawn while supported by the support rolls 14 and further cooled with cooling water or the like to form a cast slab having a predetermined cross-sectional shape.

[0021] The sliding nozzle 11 has a plate 110 with holes formed therein, and controls the amount (feed rate) of molten steel 2 supplied from the tundish 10 to the mold 13 by sliding the plate 110. Specifically, the amount of molten steel 2 supplied is controlled by controlling the overlapping area between the holes in the plate 110 and the holes formed in the bottom of the tundish 10. The ratio of the amount of sliding based on the relative position of the plate 110 in the sliding direction with respect to the tundish 10 is referred to as the nozzle opening (%). For example, the nozzle opening may be 100% when the hole in the plate 110 and the hole in the bottom of the tundish 10 completely overlap in the sliding direction, and 0% when the two holes do not overlap.

[0022] The molten steel level gauge 15 is a measuring device that measures the height of the bath surface of the molten steel 2 in the mold 13. The measurement method of the molten steel level gauge 15 is not particularly limited as long as it is a known measurement method that can measure the height of the bath surface of the molten steel 2. For example, a vortex-type molten steel level gauge may be used as the molten steel level gauge 15. The height of the bath surface of the molten steel 2 is not particularly limited as long as it can determine the height position of the bath surface of the molten steel 2 in the mold 13, and may be, for example, the height (vertical distance) from the bottom surface of the mold 13 or a predetermined position inside the mold 13.

[0023] In the continuous casting equipment 1, the amount of molten steel 2 supplied to the mold 13 is adjusted by an adjustment mechanism (not shown). The adjustment of the amount of molten steel 2 supplied by this adjustment mechanism is performed by adjusting the nozzle opening based on the measurement result of the molten steel level gauge 15 so that the molten steel surface height is at a predetermined height.

[0024] The determination unit 16 is a calculation device such as a computer that detects breakout at the start of casting. The method of breakout detection by the determination unit 16 will be described in detail later.

[0025] In the first embodiment, the period during which continuous casting is performed will be described by dividing it into a casting start time and a steady casting time. The casting start time is the period from immediately after the start of continuous casting until the casting speed reaches the steady casting speed. The steady casting time is the period after the casting start time, that is, the period after the casting speed reaches the steady casting speed.

[0026] At the start of casting, continuous casting begins in the state shown in Fig. 2. As shown in Fig. 2, at the start of continuous casting, a dummy bar 17 is inserted into the continuous casting equipment 1, and the tip of the dummy bar 17 (dummy bar head) is placed in the mold 13. Then, with the tip of the dummy bar 17 positioned at the bottom of the mold 13, molten steel 2 is poured into the mold 13, thereby starting continuous casting. Then, after a predetermined time has elapsed since the molten steel 2 was poured, the dummy bar 17 is withdrawn. Then, the dummy bar 17 is separated from the slab at a predetermined position, and the casting speed is increased to a steady-state pouring speed.

[0027] At the start of casting, the determination unit 16 continuously or intermittently determines whether or not a breakout has occurred, thereby detecting a breakout. Note that, since a breakout cannot occur while the dummy bar 17 is present inside the mold 13, breakout detection is performed after the dummy bar 17 is withdrawn from the mold 13. If a breakout is detected, the supply of molten steel 2 to the mold 13 is stopped and casting is suspended. On the other hand, if a breakout is not detected, casting continues, and breakout detection is also continued. The steady-state casting period is not particularly limited, and continuous casting is performed at a steady-state casting speed using a known continuous casting method.

[0028] (How to detect a breakout) A breakout detection method according to the first embodiment will be described. In the first embodiment, at the start of casting, the nozzle opening, which is the opening value of the sliding nozzle 11 that controls the amount of molten steel 2 supplied into the mold 13, is measured continuously or intermittently.

[0029] Next, the determination unit 16 compares the measured nozzle opening value with the allowable upper limit of the nozzle opening, which is set based on the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish. If the nozzle opening value exceeds the allowable upper limit of the nozzle opening, it is determined that a breakout has occurred. If the nozzle opening value is equal to or less than the allowable upper limit of the nozzle opening, it is determined that a breakout has not occurred. The determination of whether a breakout has occurred is made continuously or intermittently depending on the timing of the nozzle opening measurement.

[0030] The allowable upper limit opening angle is preferably expressed by a linear equation with a parameter x consisting of variables including the casting speed, the rate of change of the meniscus level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish. The parameter x can be expressed by the following equation (1). The rate of change of the meniscus level in the mold is the amount of change in meniscus level per minute (m / min).

[0031]

number

[0032] Specifically, the allowable upper limit opening degree M is expressed by the following equation (2), which is a linear expression of the parameter x. In the first embodiment, the determination unit 16 calculates the parameter x from the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish at the timing when the nozzle opening degree is measured, and calculates the allowable upper limit opening degree M from the obtained parameter x and equation (2). The determination unit 16 then determines whether or not a breakout has occurred by determining whether or not the calculated opening degree value exceeds the allowable upper limit opening degree M. This determination is the same as determining whether or not the nozzle opening degree value satisfies equation (3).

[0033] M = a(xX) + b (2) (sn-SN)-a(xX)-b>0.0 (3) where: sn: Nozzle opening (%) SN: Average nozzle opening rate for 50 seconds from the start of casting (%) X: Average value of parameter x for 50 seconds from the start of casting a: a constant corresponding to the gradient of the linear equation b: constant corresponding to the intercept of the linear equation

[0034] In the first embodiment, the nozzle aperture value corresponding to the nozzle aperture is calculated by subtracting the average nozzle aperture value for 50 seconds from the start of casting (also referred to as the standardized nozzle aperture or aperture deviation). Furthermore, the linear equation uses the value calculated by subtracting the average value of parameter x for 50 seconds from the start of casting (also referred to as the standardized parameter x) from the measured parameter x. The parameter x and the nozzle aperture are not constant due to various conditions, such as differences in tundish shape and the state of ingot adhesion in the tundish 10. However, by using standardized values ​​for the nozzle aperture and parameter x and determining the deviation from the average value for the casting chance from the start of casting to 50 seconds, breakout can be detected using the same criteria regardless of the casting conditions. The time from the start of casting for calculating the average values ​​SN and X of the nozzle aperture and parameter x is preferably 50 seconds. Although a similar effect can be obtained even if the time from the start of casting is longer than 50 seconds, a shorter time is preferable to maximize breakout detection.

[0035] Furthermore, constants a and b are preset values, and are preferably set based on multiple pieces of past operational data in which no breakout has occurred. This operational data preferably includes multiple data, each containing multiple opening values ​​and multiple parameters x at the time the opening values ​​were measured. Specifically, constant a is calculated using a regression equation expressed as a linear equation in Equation (4) below, based on the multiple opening values ​​included in the multiple pieces of operational data and the multiple parameters x at the time the opening values ​​were measured. Constant b is calculated using Equation (5), which uses constant b' calculated in Equation (4). Furthermore, the linear relationship between parameter x and nozzle opening is not constant in practice, but varies within a certain range. To evaluate this variation, it is generally preferable to collect 50 or more pieces of past operational data. However, to address changes in the proportional relationship due to long-term fluctuations, it is preferable to collect 200 or fewer pieces of past operational data.

[0036] (sn-SN)=a(xX)+b' (4) b=b'+c·σ (5) where: b': constant corresponding to the intercept of the regression equation c: Coefficient between 5.0 and 10.0 σ: Standard deviation of the regression equation

[0037] Furthermore, as shown in equation (5), the constant b is set to the average value μ b’ The coefficient c is set to 5.0 to 10.0, i.e., 5.0 to 10.0, which is calculated by adding 5.0 to 10.0 times the standard deviation to the above. In this way, by detecting a breakout only when there is a variation of 5 to 10 times the standard deviation, it is possible to determine a breakout without false positives. If the coefficient c is small, less than 5.0, the nozzle opening will frequently exceed the upper allowable opening limit M even when a breakout has not occurred, resulting in many false positives. On the other hand, if the coefficient c is large, greater than 10.0, there is a high possibility that a breakout will not be detected even when it has occurred.

[0038] The parameter x corresponds to the ratio of the volume fluctuation of the molten steel 2 in the mold 13 to the volume fluctuation of the molten steel 2 in the tundish 10. The inventors have noticed that when casting is performed normally, the parameter x and the nozzle opening have a linear relationship expressed by a first-order equation. They have found that breakout can be detected with high accuracy by using the allowable upper limit of the nozzle opening, which is set based on the parameter x, as a threshold value.

[0039] Specifically, the inventors came up with the idea for the present invention by approximating the physical model equation shown in equation (6) as being proportional to the head height H and the weight of molten steel in the tundish TD, which results in the proportional equation shown in equation (7). In the physical model shown in equation (6), molten steel 2 in the tundish 10 falls freely from the head height (H) from the bottom of the tundish 10 to the surface of the molten steel through the sliding nozzle 11 according to the gravitational acceleration g and flows into the mold 13. Then, the casting speed V c The sliding nozzle 11 has a nozzle cross-sectional area of ​​A snThe nozzle opening is sn, and the mold 13 has a width w and a thickness d.

[0040]

number

[0041] When a breakout occurs, the nozzle opening increases so as to maintain a constant level of molten steel in the mold 13. On the other hand, the slide nozzle of the ladle, which adjusts the supply of molten steel 2 from the ladle to the tundish 10, also opens its nozzle opening as the amount of molten steel in the tundish 10 decreases, so that the weight of molten steel in the tundish remains constant, and therefore the parameter x does not change significantly. The detection method in the first embodiment utilizes this response difference to detect a breakout.

[0042] In the first embodiment, the nozzle aperture of a sliding nozzle, which adjusts the amount of molten steel supplied to the mold at the start of casting, is continuously or intermittently measured. The allowable upper limit of the nozzle aperture is then calculated continuously or intermittently depending on the timing of the nozzle aperture measurement. A breakout is determined to have occurred when the calculated allowable upper limit of the nozzle aperture exceeds an aperture value corresponding to the nozzle aperture. Because this detection method does not use a camera, it is possible to detect a breakout immediately after the start of casting, when the amount of molten steel in the mold 13 is lower than usual and the amount of light is insufficient. Furthermore, because the temperature of the mold 13 is not used, it is possible to detect a breakout immediately after the start of casting, when the mold 13 is in a transitional state of rising from room temperature. Furthermore, since this detection method provides more direct detection than methods such as mold temperature measurement, it is possible to perform detection without missing any breakouts.

[0043] In the first embodiment, the occurrence of a breakout is determined using equation (3), which is based on a linear expression of the parameter x. This makes it easy to adjust for optimization, since there are only two constants to be set: a and b.

[0044] Second Embodiment Next, a second embodiment of the present invention will be described. The second embodiment is similar to the first embodiment in terms of the apparatus configuration, the operation method of the continuous casting equipment, and the manufacturing method of the cast slab, but differs in terms of the method of detecting breakouts. Therefore, in the following description, only the method of detecting breakouts will be described.

[0045] In the second embodiment, in addition to the breakout detection (first detection) in the first embodiment, a breakout detection (second detection) is performed based on at least one of the molten metal surface height and the opening deviation at the start of casting. If a breakout is detected in both the first and second detections, it is determined that a breakout has actually occurred.

[0046] [Breakout detection method (secondary detection)] In the second detection in the second embodiment, the nozzle opening, which is the opening value of the sliding nozzle 11 that controls the amount of molten steel 2 supplied into the mold 13, is measured continuously or intermittently at the start of casting. Furthermore, the determination unit 16 calculates the opening deviation, which is the difference (fluctuation value) between the average value of the nozzle opening for a certain period from the start of casting and the nozzle opening thereafter. The certain period for calculating the average value of the nozzle opening is not particularly limited, but is preferably about 50 seconds.

[0047] (Detection method based on the height of the molten metal surface) A method for detecting breakout based on the molten steel level height in the second detection will now be described. In the detection method based on the molten steel level height, first, once continuous casting has started, the molten steel level meter 15 continuously measures the molten steel level height, and the measurement results are sent to the determination unit 16, thereby monitoring the molten steel level height. Note that the molten steel level height may be measured using an actual distance (mm), or an output value (%) of the molten steel level meter 15 corresponding to the actual distance.

[0048] Next, the determination unit 16 determines whether the measured molten metal level becomes less than the allowable height lower limit H0 over time after the start of casting. The determination unit 16 determines that a breakout has occurred if the molten metal level becomes less than the allowable height lower limit H0, and determines that a breakout has not occurred if the molten metal level becomes equal to or greater than the allowable height lower limit H0.

[0049] When a breakout occurs, the molten steel 2 breaks through the solidified shell and leaks out inside the continuous casting equipment 1, and the amount of molten steel 2 discharged from the mold 13 becomes greater than the amount of molten steel 2 supplied from the tundish 10, causing a drop in the molten steel surface height. Therefore, by setting a lower allowable height limit H0 as a threshold value for detecting a breakout, it is possible to detect a breakout in the early stages of casting. The lower allowable height limit H0 is a value obtained over time after the start of casting and is set for each elapsed time. For example, the lower allowable height limit H0 may be set for each measurement time interval of the molten steel surface height.

[0050] Furthermore, the allowable height lower limit H0 is preferably calculated using equation (8) based on multiple pieces of operational data from the start of past casting. The multiple pieces of operational data from the past are from conditions where no breakout occurred. Furthermore, the coefficient A is preferably between 2.0 and 7.0. H0=H-Aσ1 (8) where: H0: Lower limit of allowable height H: Average value of the melt level from multiple past operation data A: Coefficient σ1: Standard deviation of the mold surface height from multiple past operational data

[0051] The number of past operational data is preferably 50 or more in order to evaluate the variation (standard deviation) of the molten metal level height, while the number of past operational data is preferably 200 or less in order to deal with changes in patterns due to long-term fluctuations.

[0052] (Detection method based on opening deviation) Next, a method for detecting breakout based on the opening deviation in the second detection will be described. In the detection method based on the opening deviation, first, when continuous casting starts, the determination unit 16 continuously acquires the nozzle opening of the sliding nozzle 11 and calculates the opening deviation, thereby monitoring the opening deviation.

[0053] Next, the determination unit 16 determines whether the obtained opening deviation exceeds the upper limit of allowable deviation S0 over time after the start of casting. If the opening deviation exceeds the upper limit of allowable deviation S0, the determination unit 16 determines that a breakout has occurred, and if the opening deviation is equal to or less than the upper limit of allowable deviation S0, the determination unit 16 determines that a breakout has not occurred.

[0054] When a breakout occurs, the molten steel level drops as described above, and control is performed to increase the nozzle opening to increase the amount of molten steel 2 supplied from the tundish 10. The supply amount at this time is greater than when no breakout occurs, and the nozzle opening and opening deviation are also greater than usual. For this reason, by setting an allowable deviation upper limit S0 as a threshold value for detecting a breakout, it is possible to detect a breakout in the early stages of casting. Furthermore, the allowable deviation upper limit S0 is a value at the time elapsed after the start of casting, and is set for each elapsed time. For example, the allowable deviation upper limit S0 may be set for each time interval at which the molten steel level height is measured.

[0055] Furthermore, the allowable deviation upper limit S0 is preferably calculated using equation (9) based on multiple pieces of operational data from the start of past casting. The multiple pieces of operational data from the past are from conditions where no breakout occurred. Furthermore, the coefficient B is preferably between 2.0 and 10.0. S0=S+Bσ2 (9) where: S0: Upper limit of allowable deviation (%) S: Average value (%) of the opening deviation of multiple past operation data B: Coefficient σ2: Standard deviation of the opening deviation of multiple past operation data

[0056] Furthermore, the number of past operational data is preferably 50 or more in order to evaluate the variation (standard deviation) of the opening deviation, while the number of past operational data is preferably 200 or less in order to deal with changes in patterns due to long-term fluctuations.

[0057] (Detection method based on the level of the molten metal and the deviation of the opening) Furthermore, in the second detection, a breakout may be detected based on both the molten metal level height and the opening deviation. In this case, the judgment unit 16 monitors both the molten metal level height and the opening deviation, and determines that a breakout has occurred if the molten metal level height is below the lower limit H0 of the allowable height and the opening deviation exceeds the upper limit S0 of the allowable deviation. On the other hand, if the molten metal level height is below the lower limit H0 of the allowable height and the opening deviation does not exceed the upper limit S0 of the allowable deviation, the judgment unit 16 determines that a breakout has not occurred. Note that it is also possible to monitor both the molten metal level height and the opening deviation, and determine that a breakout has occurred if the molten metal level height is below the lower limit H0 of the allowable height or the opening deviation exceeds the upper limit S0 of the allowable deviation.

[0058] As described above, in the second detection, the occurrence of a breakout is detected by making a judgment based on at least one of the molten metal level height and the nozzle opening deviation. The judgment of the occurrence of a breakout is made based on at least one of the lower limit H0 of the allowable height and the upper limit S0 of the allowable deviation over time after the start of casting, so that the judgment can be made more accurately even in the transient state immediately after the start of casting than when making a judgment based on a fixed threshold value for the molten metal level height or the nozzle opening.

[0059] Furthermore, breakouts can be detected with high accuracy by setting the allowable height lower limit H0 using multiple past operational data and Equation (1), or by setting the allowable deviation upper limit S0 using multiple past operational data and Equation (2). Although the mold surface height is automatically controlled to a constant value, it is not constant and fluctuates within a certain range. Immediately after the start of casting, the speed pattern is similar due to constant operation. However, the mold surface is prone to hunting immediately after the casting speed is increased or immediately after the casting speed is stabilized. Therefore, the average and variation of the mold surface height depend on the passage of time. Therefore, setting the allowable height lower limit H0 and the allowable deviation upper limit S0 for each elapsed time enables more accurate breakout detection. Furthermore, increased detection accuracy prevents false detections and improves productivity. Furthermore, breakouts can be detected more quickly than with conventional detection methods, thereby reducing the impact of breakouts on production. Furthermore, breakouts can be detected more directly than with detection methods based on mold temperature, ensuring accurate detection.

[0060] Furthermore, unlike the molten metal surface height, the nozzle opening degree is not constant and depends on the size (width and thickness) of the mold 13 and various other conditions. For this reason, by making a judgment using the opening deviation, which is the fluctuation value from the average value for a certain period of time from the start of casting during the chance (unit of continuous casting) at which the judgment is made, it becomes possible to detect breakout using the same judgment criteria regardless of the size of the mold 13.

[0061] Furthermore, by detecting a breakout based on both the molten metal surface height and the opening deviation, it is possible to detect a breakout with higher accuracy.

[0062] Furthermore, in the second detection, it is preferable to set the coefficients A and B in equations (8) and (9) to 2.0 or more and 7.0 or less, in other words, to detect a breakout when there is a fluctuation of 5 to 10 times the standard deviation of the mold level height and opening deviation of the past operational data. By doing so, it is possible to determine a breakout without false detection.

[0063] In the second embodiment, if a breakout is detected in the first detection and then again in the second detection, it is detected that a breakout has actually occurred. This reduces false positives compared to when a breakout is detected only in the first detection, and since detection can be performed without any omissions, it is possible to improve detection accuracy.

[0064] Furthermore, in the second embodiment, the number of constants to be set is as small as four at most: a, b, A, and B. This makes adjustments for optimization easier than when there are many constant thresholds to be set.

[0065] <Modification> Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention that include various modifications in addition to the disclosed embodiments will be apparent to those skilled in the art. Therefore, it should be understood that the embodiments of the invention set forth in the claims also encompass embodiments that include these modifications described herein, either alone or in combination.

[0066] For example, while the first and second embodiments have described methods for detecting breakouts, the present invention is not limited to such examples. The present invention can also be applied to methods for operating continuous casting equipment and methods for producing slabs. A method for operating continuous casting equipment according to one aspect of the present invention is a method for operating continuous casting equipment 1 that continuously casts steel, in which a breakout is detected at the start of casting using the breakout detection method according to the first or second embodiment. If a breakout is detected, the supply of molten steel 2 to the mold 13 is interrupted, and if no breakout is detected, the supply of molten steel 2 to the mold 13 is continued. Furthermore, a method for producing slabs according to one aspect of the present invention continuously casts steel using the method for operating continuous casting equipment 1 described above.

[0067] In the first embodiment, the standardized nozzle opening and the standardized parameter x are used as the opening value, but the present invention is not limited to this example. If the influence of various conditions, such as differences in tundish shape and the state of metal adhesion in the tundish 10, among continuous casting machines is small, the measured nozzle opening may be used as the opening value, and the parameter x calculated by equation (1) may be used as is without standardization. [Example]

[0068] An example conducted by the present inventors will be described. In this example, the allowable upper limit of opening was determined from the data of 200 past operations. The allowable upper limit of opening was determined using equation (2). Figure 3 shows a plot of the past operation data, the determined allowable upper limit of opening (dashed straight line), and the regression equation determined using equation (4) (solid straight line). In addition, in Figure 3, the horizontal axis represents the parameter x determined using equation (1), and the vertical axis represents the opening value, which is the standardized nozzle opening. In the example of Figure 3, the coefficient c used in equation (5) when determining the allowable upper limit of opening was set to 7.

[0069] Furthermore, Figure 3 plots the data for the opening value and parameter x for the two charges where a breakout actually occurred, with a line. In the example shown in Figure 3, it was confirmed that a breakout can be detected 5 to 10 seconds earlier than with the current breakout detection method that relies on the operator.

[0070] Furthermore, Figure 4 shows the relationship between the coefficient c used in equation (5) and the number of detections. As can be seen from Figure 4, decreasing the coefficient c eliminates missed detections, but increases the number of false positives, resulting in a higher number of detections. Increasing the coefficient c also reduces false positives, but increases the occurrence of missed detections. For this reason, it was found that it is preferable to set the coefficient c between 5.0 and 10.0.

[0071] Furthermore, in the example, the lower limit of the allowable height H0 and the upper limit of the allowable deviation S0 were calculated from the past operation data of 200 operations using equations (8) and (9), and the molten metal surface height and the opening deviation when a breakout occurred for two chances were compared.

[0072] Figure 5 shows the behavior of the mold surface height at the calculated lower limit H0 of the allowable height and the two chances of breakout versus time. In Figure 5, the vertical axis represents the mold surface height, and the horizontal axis represents the elapsed time (sec) from the start of dummy bar withdrawal. The mold surface height on the vertical axis represents the output value (%) of the molten steel level gauge 15 corresponding to the actual distance, and is controlled to be 45%. The horizontal axis represents the elapsed time from the start of pouring molten steel 2 into the mold 13 at -50 sec and from the start of dummy bar withdrawal at 0 sec. In the example shown in Figure 5, coefficient A is set to 7, i.e., the threshold value is set to 7 times the standard deviation of the average mold surface height. In the example shown in Figure 5, the timing when the mold surface height falls below the lower limit H0 of the allowable height occurs 10 to 20 seconds before the breakout detection that currently relies on the operator. This confirms that breakout detection can be performed accurately and quickly.

[0073] Furthermore, in the example shown in Figure 5, it was confirmed that the threshold value fluctuates over time, reaching a maximum approximately 20 seconds after the start of casting. This is because the casting speed is changed approximately 20 seconds after the start of casting, causing large variations in the molten metal surface height. However, it was confirmed that the value subsequently settles down to about one-third of the peak. Here, with conventional detection methods, detection is performed using a constant threshold value that matches the peak of the variation, so the threshold value must be set large throughout the entire time period. However, with the second detection method, the optimal threshold value is selected based on past operational data over time, making it possible to detect breakouts more quickly than conventional detection methods.

[0074] Figure 6 shows the behavior of the calculated allowable deviation upper limit S0 and the opening deviation at the time of two chances of breakout occurrence with respect to elapsed time. In Figure 6, the vertical axis represents the opening deviation, and the horizontal axis represents the elapsed time (sec) from the start of dummy bar withdrawal, as in Figure 3. The opening deviation on the vertical axis represents the difference from the average nozzle opening from -50 sec to 0 sec, and is shown for times after 0 sec. In the example shown in Figure 6, coefficient B is set to 4, i.e., a threshold value four times the standard deviation of the average opening deviation is assigned. Furthermore, the breakout occurrence chance in Figure 6 is the same as that in Figure 5. As is clear from Figure 6, it was confirmed that breakout can be detected more quickly when opening deviation is used than when using the molten metal level.

[0075] Furthermore, we investigated the effects of coefficients A and B in equations (1) and (2) on detection accuracy and the occurrence of false positives. Figure 7 shows the relationship between coefficients A and B and the number of breakout detections when coefficients A and B are varied from 1.0 to 10.0. In Figure 5, the graph labeled "Both" represents the case where both the mold surface height and nozzle opening deviation detection methods were used. A breakout was detected only when a breakout was detected based on both the mold surface height and nozzle opening. In this investigation, the actual number of breakouts was two. It was confirmed that decreasing coefficients A and B reduced false positives but increased overdetection, while increasing coefficients A and B reduced overdetection but increased false positives. Therefore, it was confirmed that coefficients A and B between 2.0 and 7.0 were appropriate for the equipment used in this example. Furthermore, in this example, when coefficients A and B were set to 4 and coefficient c was set to 7, the number of detections was two under the combined conditions of first and second detection, confirming that there were no overdetection or false positives. In the example shown in Figure 6, it was confirmed that compared to the current breakout detection method that relies on the operator, breakouts can be detected 9 seconds before the breakout occurrence chance (1) and 4 seconds before the breakout occurrence chance (2). Therefore, it was confirmed that breakout occurrences can be detected with high accuracy by detecting using both the mold surface height and the opening deviation.

[0076] From the above results, it was confirmed that by combining the first and second detections, it is possible to reduce over-detection and false detection, and to detect breakouts with high accuracy. [Explanation of symbols]

[0077] 1. Continuous casting equipment 10 Tundish 11 Sliding Nozzle 110 Plate 12 Submerged Entry Nozzle 13 Mold 14 Support Roll 15 Molten steel level gauge 16 Judgment section 17 Dummyba 2. Molten steel

Claims

1. In continuous steel casting equipment, Continuously or intermittently measure the nozzle opening of a sliding nozzle that adjusts the amount of molten steel supplied into the mold at the start of casting, The method for detecting a breakout comprises: comparing an opening value, which is obtained by subtracting an average value of the nozzle opening over a predetermined time period from the start of casting, from the nozzle opening value; with an allowable upper limit opening, which is an upper limit value predetermined by a linear function of parameters including the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of molten steel in the tundish; and determining that a breakout has occurred if the opening value exceeds the allowable upper limit opening.

2. 2. The breakout detection method according to claim 1, wherein the allowable upper limit opening is expressed by a linear equation with a parameter x consisting of variables including the casting speed, the rate of change of the molten steel level in the mold, the mold width, the mold thickness, and the weight of the molten steel in the tundish.

3. 3. The breakout detection method according to claim 2, wherein the parameter x is expressed by the following equation (1): [Equation 1] where: V ｃ : Casting speed (m / min) Δh: rate of change of molten metal surface height in the mold (m / min) w: mold width (m) d: mold thickness (m) TD: Weight of molten steel in tundish (t)

4. The breakout detection method according to claim 3 , wherein it is determined that the breakout has occurred when the following formula (3) is satisfied: (sn-SN)-a(xx-X)-b>0.0...(3) where: sn: Nozzle opening (%) SN: Average value (%) of nozzle opening for 50 seconds from the start of casting X: Average value of parameter x for 50 seconds from the start of casting a: a constant corresponding to the gradient of the linear equation b: A constant corresponding to the intercept of the linear equation

5. Constants a and b are set based on multiple pieces of past operation data from 50 to 200 times, The constant a is calculated from the plurality of opening values ​​included in the plurality of operational data and the plurality of parameters x at the time of measurement of the opening values ​​by a regression equation expressed as a linear equation in the following equation (4):

5. The breakout detection method according to claim 4, wherein the constant b is calculated by equation (5) using a constant b' calculated by equation (4). (sn-SN)=a(x-X)+b'...(4) b=b'+c・σ...(5) where: b': constant corresponding to the intercept of the regression equation c: a constant between 5.0 and 10.0 σ: Standard deviation of the regression equation

6. monitoring at least one of the level of the molten steel supplied into the mold at the start of casting and the opening deviation of a nozzle that adjusts the amount of the molten steel supplied into the mold; The molten metal level is lower than the allowable height lower limit H ０ If the opening deviation is less than the upper limit S of the allowable deviation over time after the start of casting, ０ and when the opening value exceeds the allowable upper limit opening, the occurrence of a breakout is detected. The breakout detection method according to any one of claims 1 to 5, wherein the nozzle opening deviation is determined as the difference between the average nozzle opening for a predetermined period from the start of casting and the nozzle opening at the current time.

7. The allowable height lower limit H ０ is calculated by the formula (8) based on multiple operational data from the start of past casting, and the allowable deviation upper limit S ０ The breakout detection method according to claim 6, wherein is calculated using equation (9) based on a plurality of operation data from the start of past casting. H ０ =H-Aσ １ ・・・(8) S ０ =S+Bσ ２ ・・・(9) where: H ０ : Lower limit of allowable height H: Average value of the molten metal surface height from multiple past operation data A: Coefficient σ １ : Standard deviation of the mold level height from multiple past operation data S ０ : Upper limit of allowable deviation S: Average value of nozzle opening deviation from multiple past operation data B: Coefficient σ ２ : Standard deviation of nozzle opening deviation from multiple past operational data

8. monitoring at least one of the level of the molten steel supplied into the mold at the start of casting and the opening deviation of a nozzle that adjusts the amount of the molten steel supplied into the mold; The molten metal level is lower than the allowable height lower limit H ０ The opening deviation is less than the upper limit S of the allowable deviation over time after the start of casting. ０ When the opening value exceeds the allowable upper limit opening, it is detected that a breakout has occurred, The breakout detection method according to any one of claims 1 to 5, wherein the nozzle opening deviation is determined as the difference between the average nozzle opening for a predetermined period from the start of casting and the nozzle opening at the current time.

9. The allowable height lower limit H ０ is calculated by the formula (8) based on multiple operational data from the start of past casting, and the allowable deviation upper limit S ０ The breakout detection method according to claim 8, wherein is calculated using equation (9) based on a plurality of operation data from the start of past casting. H ０ =H-Aσ １ ・・・(8) S ０ =S+Bσ ２ ・・・(9) where: H ０ : Lower limit of allowable height H: Average value of the molten metal surface height from multiple past operation data A: Coefficient σ １ : Standard deviation of the mold level height from multiple past operation data S ０ : Upper limit of allowable deviation S: Average value of nozzle opening deviation from multiple past operation data B: Coefficient σ ２ : Standard deviation of nozzle opening deviation from multiple past operational data

10. A method for operating a continuous casting facility for continuously casting steel, comprising: At the start of casting, the breakout is detected using the breakout detection method according to any one of claims 1 to 5, A method for operating a continuous casting facility, comprising interrupting the supply of molten steel to the mold when the breakout is detected.

11. A method for producing a slab by continuously casting steel using the method for operating continuous casting equipment according to claim 10.

12. A method for operating a continuous casting facility for continuously casting steel, comprising: Detecting the breakout at the start of casting using the breakout detection method according to claim 6; A method for operating a continuous casting facility, comprising interrupting the supply of molten steel to the mold when the breakout is detected.

13. A method for producing a cast slab, comprising producing a cast slab by continuously casting steel using the method for operating continuous casting equipment according to claim 12.

14. A method for operating a continuous casting facility for continuously casting steel, comprising: Detecting the breakout at the start of casting using the breakout detection method according to claim 8; A method for operating a continuous casting facility, comprising interrupting the supply of molten steel to the mold when the breakout is detected.

15. A method for producing a cast slab, comprising producing a cast slab by continuously casting steel using the method for operating continuous casting equipment according to claim 14.

16. A method for operating a continuous casting facility for continuously casting steel, comprising: Detecting the breakout at the start of casting using the breakout detection method according to claim 9; A method for operating a continuous casting facility, comprising interrupting the supply of molten steel to the mold when the breakout is detected.

17. A method for producing a slab by continuously casting steel using the method for operating continuous casting equipment according to claim 16.

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