Method for evaluating the position of at least one mold level sensor and system for controlling the meniscus level in a mold

Abstract

The present invention relates to a method for evaluating the position of at least one mold level sensor in the mold of a continuous slab casting machine for molten metal, particularly molten steel, and to a system for controlling the meniscus level of molten metal in the mold of a continuous slab casting machine, and further to uses and computer programs related to the method.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the position of at least one mold level sensor in a mold of a continuous slab casting machine for molten metal, particularly molten steel, and a system for controlling the meniscus level of molten metal in the mold of a continuous slab casting machine. Furthermore, it relates to the use and computer program related to this method.

Background Art

[0002] In continuous slab casting, particularly in the continuous slab casting of steel, molten metal is supplied from a tundish through a submerged entry nozzle (SEN) into a mold, and the mold usually has a substantially rectangular horizontal cross-section. The mold is cooled, and as a result, the molten metal solidifies on the outside, thereby forming a solidification shell. The solidification shell is taken out from the bottom of the mold and guided by rollers while being further cooled so that a cast slab is continuously formed. During casting, the amount of molten metal supplied to the mold is carefully controlled, and the goal is to keep the meniscus level of the molten steel in the mold constant. To achieve this, usually, a mold level sensor is arranged in the mold, and the signal of the mold level sensor is used in a feedback loop to control the vertical position of the stopper of the submerged entry nozzle. The sensors used are often radiation measurement-based sensors such as those manufactured by Berthold Technologies GmbH & Co. KG, Bad Wildbad, Germany. In such a radiation measurement sensor, a point light source is arranged on one long side of the mold, and a long vertical X-ray sensor is arranged on the opposite long side of the mold. Depending on the height of the meniscus level, the intensity of the signal detected by the sensor varies in a known relationship, thereby enabling the determination of the meniscus level of the molten metal in the mold.

[0003] Quality issues during continuous slab casting include surface defects, which can occur when slag is incorporated into the molten metal rather than remaining on the surface of the molten metal pool within the mold. Other quality-related issues during casting in the mold include cracking and uneven solidification. Uneven solidification around the mold leads to uneven internal material properties of the casting. Therefore, a stable meniscus level is desirable to achieve good quality continuous castings. [Overview of the project] [Problems that the invention aims to solve]

[0004] Therefore, the object of the present invention is to optimize the meniscus level in the mold of a continuous slab casting machine and to provide an improved system for controlling the meniscus level of molten metal, which results in a more stable meniscus level and, consequently, improved casting quality. [Means for solving the problem]

[0005] These objectives are achieved or surpassed by the system described in claim 7 for controlling the meniscus level of molten metal in a mold of a continuous slab casting machine, by the method described in claim 1 for evaluating the position of at least one mold level sensor in a mold of a continuous slab casting machine of molten metal, particularly molten steel, by the use of such a system described in claim 12 and the computer program described in claim 13.

[0006] According to the first aspect, the present invention is A method for evaluating the position of at least one mold level sensor in the mold of a continuous slab casting machine for molten metal, particularly molten steel, The method is carried out within the caster arrangement configuration. The layout configuration of the casting machine is as follows: A mold having width and thickness, wherein the width is greater than the thickness, An immersion nozzle through which a liquid (e.g., molten metal or water) is supplied into a mold, and the immersion nozzle is positioned at least approximately in the center in the width direction of the mold, A valve that adjusts the flow of liquid through the immersion nozzle, This method provides a method that includes the following steps: (a) Placing at least one mold level sensor at a first position along the width of the mold to measure the meniscus level of the liquid, thereby generating at least one meniscus level signal; (b) A step of operating the casting machine's arrangement configuration while controlling a valve in a feedback loop in response to at least one meniscus level signal; (c) While operating the casting machine configuration over predetermined time intervals, the step of measuring the valve position and / or meniscus level at one or more positions along the width of the mold; (d) A step of calculating an index of fluctuations in the valve position and / or meniscus level measured over a predetermined time interval; (e) Placing at least one mold level sensor to measure the meniscus level of the liquid at a different position from the first position along the width of the mold, thereby generating at least one further meniscus level signal, and repeating steps (b) to (d) using at least one further meniscus level signal to control a valve; and (f) A step to determine the optimal position for at least one mold level sensor by selecting a position along the width of the mold where the index calculated in step (d) is smallest. Includes.

[0007] The present invention has found that the position of at least one mold level sensor affects mold level stability when the signal from the mold level sensor is used to control the flow of liquid into the mold and, consequently, the quality of the casting slab. Using a full-scale water model of the casting machine configuration (as done in one embodiment), it is possible to investigate mold level stability and the frequency of air bubble inclusion for various control positions of at least one mold level sensor in a safe environment, and it is believed that air bubble inclusion in the water model correlates with slag inclusion in an actual continuous casting machine. It has been found that mold level stability is extremely important for the quality of the casting. Since the meniscus level can vary differently at different positions in the mold, the placement of at least one mold level sensor is crucial for achieving the best meniscus level stability. Furthermore, the present invention has found that there is no single optimal position for at least one mold level sensor that fits all casting parameters. Rather, it is predicted that the optimal position of at least one mold level sensor may depend on the mold width, as well as the casting speed and the submergence depth (SD) of the immersion nozzle (SEN). Some continuous slab casting machines allow the mold width (MW) to vary during the ongoing, uninterrupted casting process, thereby allowing different positions of the mold level sensor to be optimal for different mold widths.

[0008] The present invention has found that the position of the mold level sensor is important for achieving meniscus level stability, and therefore, the method of the present invention makes it possible to evaluate the position of at least one mold level sensor. Thus, the method of the present invention makes it possible to investigate the dynamics of the meniscus level, and consequently slag inclusion and surface defects, using different control positions of one or more mold level sensors. The method of the present invention can be implemented in a water model of a continuous casting machine, for example, a full-scale model, or in an actual continuous casting machine using molten metal, in particular in an industrial-scale casting machine such as a continuous slab casting machine in a factory or foundry. The present invention is preferably applied to the continuous casting of steel.

[0009] The method of the present invention is carried out within a casting machine configuration. The casting machine configuration includes a mold having width and thickness, wherein the width is greater than the thickness; an immersion nozzle (SEN) through which liquid is supplied into the mold, the immersion nozzle being positioned at least approximately in the center in the width direction of the mold; and a valve for regulating the flow of liquid through the SEN. The casting machine configuration may be an industrial casting machine for molten metal, such as a continuous slab casting machine, including a thin slab casting machine, in which case the liquid is molten metal, particularly molten steel. The industrial casting machine may include a ladle and a tundish, as is common in the art. Alternatively, the casting machine configuration may be a model casting machine using a different liquid, such as oil, water, or aqueous solution. The casting machine model may also include a tundish and a liquid supply system. The liquid may be drawn out of the mold through a liquid outlet to simulate the drawing out of the solidified shell of the casting slab. It may be pumped back into the tundish above the mold. The model may be a full-scale model. It may also have a smaller scale (e.g., 1:5 to 1:1.5). Working in a model casting machine allows the use of molds made of transparent materials, such as glass or plexiglass, which simplifies the detection of the meniscus level, for example, by optical detection using a camera. Alternatively, an ultrasonic sensor (USS) may be used to measure the meniscus level. In industrial casting machines for molten metal, the mold level may be measured by radiometric sensors, such as radiometric sensors provided by Berthold Technologies GmbH & Co.KG, Bad Wildbad, Germany (hereinafter referred to as "Berthold Sensors") and described in DE_Whitepaper_Radiometrische-Messungen_DC00591PR1-01.pdf at www.berthold.com, or by electromagnetic sensors, such as eddy current sensors.

[0010] In both model casting and industrial casting machine configurations, the mold may have a substantially rectangular horizontal cross-section. The long sides of the rectangle extend in the width direction, and the short sides extend in the thickness direction. The substantially rectangular cross-section may have rounded corners. Each side of the rectangle may be straight or curved, in particular, convex. Liquid may be supplied into the mold through a SEN, and the amount of liquid is controlled by a valve. The valve may be any type of valve that is controllable to vary the flow rate of liquid flowing into the mold. The valve may be a position-controllable closure, such as a slide or pusher. The valve may be a stopper. In this case, the horizontal position of the stopper may be controlled to vary the flow rate of liquid. The valve may open and close the SEN, thereby controlling the flow rate of liquid into the mold. The flow rate may be controlled in a feedback loop in response to at least one meniscus level signal detected by at least one mold level sensor. Control may be carried out by a control unit and using control algorithms known in the art. Therefore, if the meniscus level falls below a predetermined set point, the flow of liquid through the SEN is increased by opening the valve (further). If the meniscus level exceeds the set point, the flow of liquid is reduced by closing the valve or reducing the flow through it. The valve may have several valve positions between fully open and fully closed. It may be continuously controllable between the fully open position and the fully closed position. Alternatively, it may be controllable only between a single open position and a single closed position.

[0011] According to the method of the present invention, at least one mold level sensor is positioned at a first position along the width of the mold to measure the meniscus level of the liquid, thereby generating at least one meniscus level signal. This at least one mold level sensor is used to control a valve and thereby regulate the flow of liquid. It is positioned at the first position, which is the position to be evaluated in this execution of the evaluation method. Other positions may also be tested. The casting machine configuration is then operated over a predetermined time interval while controlling the valve in response to the signal from at least one mold level sensor. The predetermined time interval may be 2 to 30 minutes, preferably 5 to 20 minutes. The time interval must be long enough to reproducibly capture the amount of variation in valve position and / or meniscus level within the casting machine configuration. The at least one mold level sensor may include one or more mold level sensors, in particular two mold level sensors.

[0012] While the casting machine's configuration is being operated, the meniscus level is measured at one or more locations along the width of the mold. This measurement may be performed using at least one mold level sensor, or another sensor, such as an optical camera. In addition to or instead of this, the valve position is measured over predetermined time intervals. The valve position and / or meniscus level may be measured at multiple points in time within predetermined time intervals. The sampling rate for this measurement, as well as the sampling rate for the measurement of the meniscus level signal used to control the valve, may be, for example, 1 to 500 Hz, preferably 5 to 30 Hz. Data processing methods, in particular filtering methods, may be applied to the time series of valve position or meniscus level measurements, for example, a low-pass filter may be applied. This can serve to filter out outlier measurements that do not contribute to the overall findings. The low-pass filter may also serve to approximate the measurement signal, for example, the measurement signal from an ultrasonic sensor (USS), to a measurement signal available in the foundry. The latter may be a radiometric sensor with a lower sampling rate than the USS.

[0013] In the next step, an index of the variation in valve position and / or meniscus level measured over a predetermined time interval is calculated. It was found that the variation in meniscus level correlates with the amount of surface defects in the casting. Therefore, the position of at least one mold level sensor can be evaluated in relation to the variation in mold level. It was further found that the variation in meniscus level correlates with the variation in valve position. Therefore, during the execution of this evaluation method, it is possible to measure the valve position in addition to or instead of the meniscus level in order to determine the amount of variation in meniscus level and consequently the predicted quality of the casting slab.

[0014] The index of variation can be determined by receiving a set of valve position and / or meniscus level values ​​measured at multiple points in time within a predetermined time interval and calculating an index of the amount of variation in the set of values. The set of values ​​may be all measurements of valve position and / or meniscus level measured at multiple points in time within a predetermined time interval. The set of values ​​may also be simply a subset of these measurements. The index of the amount of variation in the set of values ​​may be any index known in statistics to determine the amount of variation in the set of values. The index of the amount of variation may be the standard deviation. It may also be the variance, standard error, or interquartile range (IQR). Another index of the amount of variation may be the maximum wave amplitude, i.e., the distance from the peak to the trough of the wave, captured by a camera that measures the meniscus level over the full width of the mold. The present invention has shown that good results can be obtained when the standard deviation of the values ​​obtained for valve position and / or meniscus level over a predetermined time interval is calculated in step (d).

[0015] This method not only evaluates the position of at least one mold level sensor, but also provides a method for determining the optimal position of at least one mold level sensor. This can be done by placing at least one mold level sensor or at least one other mold level sensor at a different position along the width of the mold, different from the first position, thereby generating at least one meniscus level signal; repeating steps (b) to (d) of operating the casting machine configuration while controlling the valve in response to at least one meniscus level signal from the mold level sensors at different positions; and measuring the valve position and / or meniscus level and calculating an index of the variation of the measured values ​​over a predetermined time interval. The optimal position for at least one mold level sensor can then be obtained by selecting a position along the width of the mold where the index of variation is minimized. These steps allow for determining the optimal position of the mold level sensor to reduce meniscus level variation and, consequently, slag inclusion, while simultaneously allowing for adjustment of the casting speed and the mold width (MW) and SEN immersion depth (SD) to match any desired casting parameters. In prior art, the position of the mold level sensor is arbitrarily selected and not determined from measurements.

[0016] According to one embodiment, at least one mold level sensor includes a first mold level sensor and a second mold level sensor, the first and second mold level sensors being positioned at different locations along the width of the mold. According to this embodiment, the valve is controlled in a feedback loop in response to a combination of signals from the first and second (and optionally a third or further) mold level sensors. The inventors have found that variations in mold level can be reduced to very low levels when using two or more mold level sensors operating in parallel. In the prior art, only a single sensor was used. When using two or more sensors, the valve can be controlled in response to a combination of two or more meniscus level signals. The combination may be an algebraic function, e.g., a polynomial or linear function, in particular a linear combination, sum, weighted sum, or mean, e.g., an arithmetic mean, of the signal values ​​from the first and second (and optionally a third or further) mold level sensors.

[0017] The arrangement of two or more mold level sensors may be varied to find the optimal position for achieving the best meniscus level stability.

[0018] In one embodiment, two mold level sensors are positioned on one side of the width direction of the SEN, thereby controlling fluctuations in the meniscus level.

[0019] According to another embodiment, the first and second mold level sensors are positioned on opposite sides in the width direction of the SEN. This arrangement is advantageous because the inventors have found that when only one sensor is used in the control loop, the meniscus level may behave differently on the controlled and uncontrolled sides of the SEN, resulting in an asymmetrical mold level. Adding a second sensor to the other side of the SEN has been found to correct this asymmetry. When testing various sensor positions, it has been found that a very stable meniscus level is obtained when the two sensors are positioned symmetrically with respect to the SEN. In other words, in this embodiment, the first and second mold level sensors are positioned at least approximately equal distances from the center of the mold. "At least approximately" means that the distances are equal within a tolerance range of ±8%, preferably ±5%, and most preferably ±2%. In this context, the center of the mold means the center of the mold in the width direction extending along the long side of the mold.

[0020] According to one embodiment, the meniscus level is measured in step (c) at several locations along the width of the mold. Variation in the meniscus level can be calculated at each location where the meniscus level is measured. This provides valuable information about the variation in the meniscus level at different locations within the mold. In this case, the index of the variation in the meniscus level may be a combination of the variations in the meniscus level at each of these several locations, in particular, the average of a polynomial or linear combination, sum, weighted sum, or arithmetic mean. This is advantageous because it allows the meniscus level to be investigated not only at a single point but also across the width of the mold. In this embodiment, waves in the meniscus level profile can also be evaluated. In particular, the occurrence of standing waves or traveling waves, and especially the amplitude of traveling waves, can be investigated, and this too may be affected by the location of the mold level sensor. Some of the locations may be, for example, 4 to 80, preferably 8 to 20. The locations may exclude parts of the mold where the SEN is located. For practical reasons, it is rare for mold level sensors to be placed at the location of the SEN in a foundry. In particular, radiation measurement sensors do not function well when the SEN interferes with the radiation from the radiation source. Some positions may be equally spaced across the width of the mold, in which case the portion of the mold where the SEN is located may be excluded. For example, the meniscus level may be measured at eight positions, each spaced between 8% and 15% of the total width (MW) of the mold, while the position closest to the short side may be spaced, for example, between 4% and 8% (e.g., 5%) of MW from the short side.

[0021] At each of several locations, the meniscus level can be measured by a mold level sensor, such as an ultrasonic sensor, an electromagnetic sensor, or a radiometric sensor.

[0022] Measuring the meniscus level at several positions can be done especially when evaluating the mold level sensor position in the layout configuration of a mold casting machine. For example, several ultrasonic sensors, especially 4 to 16, preferably 6 to 12, for example 8 ultrasonic sensors can be arranged along the width of the mold. Half of the ultrasonic sensors (USS) can be arranged on either side of the SEN. In a preferred embodiment, the ultrasonic sensors can be arranged in a row on either side of the SEN, especially with equal spaces between adjacent sensors.

[0023] According to another embodiment, the meniscus level can be measured using a camera in step (c). This can be done using a water model of a continuous slab casting machine with a transparent mold. The camera can be installed, for example, on a stand and can view the mold level horizontally, or slightly obliquely from below or above. The camera aperture, field of view, and focus can be adjusted so that the meniscus level is visible in the captured image. To detect the meniscus level, the recorded image can be processed. For example, the contrast and light intensity can be adjusted to best capture the meniscus level. This can be done, for example, by using a min-max filter for adjusting the light intensity and a Laplacian filter for adjusting the contrast. In one embodiment, the meniscus level across the width of the mold can be extracted from the image using an edge detection method, especially an edge detection method focused on detecting horizontal features. Further image processing, especially morphological operations, can be used on the image to remove unwanted features. The image processing can be programmed with an algorithm, and at this time, MATLAB can be used. MATLAB is an abbreviation for "MATrix LABoratory" and is a commercially available multi-paradigm programming language and numerical computing environment.

[0024] In step (c), by measuring the meniscus level using a camera, it is possible to capture the meniscus level over the width of the mold with high image resolution, thereby enabling the meniscus level to be measured simultaneously at a plurality of positions spaced apart over the width of the mold. Thereby, the meniscus level can be measured at, for example, 10 to 3000 positions, preferably 100 to 1000 positions, spaced apart over the width of the mold. An indicator of the variation in the meniscus level can be calculated at fewer positions along the width of the mold, for example 8 to 100 positions, preferably 20 to 50 positions. This can be done by averaging the meniscus levels extracted from the camera image over several adjacent pixels along the width of the mold. The averaging helps to remove errors or outliers that may occur when extracting the meniscus level from the camera image using image processing techniques such as those described herein. The camera preferably records a time series of images at a rate of 10 to 500 images per second, preferably 20 to 60 images per second, and is consequently recorded as a video.

[0025] According to one embodiment, the index of variation calculated in step (d), which is used to evaluate the position of at least one mold level sensor responsible for controlling a valve, is an index of the amount of variation in valve position. In this embodiment, the meniscus level signal from at least one mold level sensor is used to control a valve that regulates the flow of liquid through the SEN, but the quality of control is evaluated from the variation in valve position rather than from the variation in meniscus level. It has been found that variations in valve position, in particular at the position of the stopper that controls the flow of liquid from the tundish through the SEN, behave the same as variations in meniscus level. An advantage of this embodiment is that it can be implemented in the arrangement configuration of an industrial casting machine using molten metal, for example, in a continuous slab casting machine used to cast slabs of steel or other metals for commercial purposes. Thus, a model casting machine using a different liquid is not required. Furthermore, the position of at least one mold level sensor can be determined more accurately because there is no difference between the model casting machine and the actual industrial casting machine that could distort the results. Since the valve position is controlled, its position is known, for example, within the control unit. Preferably, the valve position may fluctuate between fully open and fully closed, with 0 to 2000, preferably 10 to 500, valve positions existing within that range. The valve position may be recorded at multiple points in time within a predetermined time interval, for example, at a rate of 5 to 100 Hz, and an index of the amount of fluctuation is calculated from this set of values. The index of the amount of fluctuation may be the standard deviation. It may also be any other index from statistics, such as variance, standard error, or IQR.

[0026] According to one embodiment, an index of variation in both valve position and / or meniscus level at any given position is calculated over a series of shorter time intervals within a predetermined time interval. For example, one shorter time interval may include, for example, a subset of 50 to 500 consecutive measurements, and the index of variation is calculated over this subset. The shorter time intervals may be 0.5 to 20 seconds, preferably 1 to 10 seconds. The shorter time intervals may overlap with each other within a predetermined time interval. In other words, the shorter time intervals may advance through a time series of measured data points, such as a slide window. Alternatively, the shorter time intervals may also be continuous with no overlap in the measurements.

[0027] In this embodiment, measured values ​​of valve position and / or meniscus level are divided into several subsets of values, each subset collected over one of shorter time periods, and an index of the amount of variation in each subset of values ​​is calculated. This allows for obtaining the temporal evolution of the amount of variation. Such investigation of mold level variations with higher temporal resolution has been shown to enable the detection of slag inclusion with high accuracy. In particular, the index of the amount of variation has been shown to exhibit fairly major peaks when calculated over shorter time periods and tracked over time, and by observing the meniscus level in the water model recorded by a camera, it can be seen that these major peaks correlate with the occurrence of bubble inclusion. In industrial-scale casting machines of molten metal, bubbles visible in the water model casting machine after, for example, a wave in the meniscus level has collapsed correspond to slag that has been incorporated into the solidified shell and subsequently taken up. Therefore, it is very valuable to detect variations at meniscus levels or stopper positions that are high enough for bubble inclusion to occur. Therefore, an overall indicator of meniscus level variation may be the number of major peaks observed when calculating an indicator of the amount of meniscus level variation measured over several shorter time periods within a predetermined time interval. "Major" may mean that the peak value exceeds a certain threshold, for example, a certain percentage of the mean.

[0028] An indicator of variation over a shorter time period may be the total path over which the meniscus level or valve position, particularly the stopper position, has moved. The difference between the meniscus level or valve position from one measurement to the next is then calculated, and the absolute values ​​of these differences are summed up for all measurements over a shorter time period.

[0029] The method of the present invention allows for the investigation of meniscus level dynamics and resulting slag inclusion using different control positions of one or more mold level sensors. It has been found that optical measurement of the meniscus level using a camera capable of tracking the meniscus level across the entire width of the mold can be advantageously used. The method of the present invention has shown that two mold level sensors can result in a more stable meniscus level and a more stable stopper position compared to a single control mold level sensor.

[0030] Furthermore, it was found that the control position, i.e., the position of at least one mold level sensor, has a significant impact on the meniscus level and valve stability. In particular, controlling at an inherently unstable position along the width of the mold increased meniscus level instability, while controlling at a point where the meniscus level is inherently more stable was found to be advantageous for the meniscus level and, consequently, for valve stability.

[0031] Furthermore, when using cameras to capture the meniscus level and evaluating the video recorded by the cameras, it was found that air bubble inclusion, which correlates with slag inclusion in commercial slab casting machines, correlates with large fluctuations in the meniscus level. These peaks can be identified by dividing a predetermined time interval into shorter time intervals and calculating an index of the fluctuation in the meniscus level during each shorter time interval. For example, the index could be the sum of the paths the meniscus level traveled over time. This allows the temporal evolution of the fluctuation in the meniscus level to be recorded. Counting the peaks in this signal may be an index of the stability of the meniscus level.

[0032] According to another embodiment, the present invention is A system for controlling the meniscus level of molten metal, preferably molten steel, in a mold of a continuous casting machine, Continuous casting machines are A mold having width and thickness, wherein the width is greater than the thickness, An immersion nozzle through which molten metal is supplied into the mold, and the immersion nozzle is positioned at least approximately in the center in the width direction of the mold, A valve that adjusts the flow of molten metal through the immersion nozzle, The present invention relates to a system comprising at least a first mold level sensor and a second mold level sensor, positioned at different locations along the width direction of the mold, for measuring the level of molten metal in the mold. The system may include more than two mold level sensors, e.g., three or four mold level sensors. The system further includes a control unit configured to receive at least first and second meniscus level signals from at least the first and second mold level sensors, respectively, calculate a combination of at least the first and second meniscus level signals, in particular the average, and control a valve in a feedback loop in response to the combination of meniscus level signals.

[0033] All features and advantages described in relation to the method of the present invention may also apply to the system, and vice versa. In particular, a continuous casting machine may have all the features of the arrangement configuration of an industrial casting machine that may be used to carry out the present method, and meniscus level measurement and signal processing may be carried out as described herein in relation to the method of the present invention. The system of the present invention is preferably suited to carrying out the method of the present invention. At least two mold level sensors may be radiation sensors or eddy current sensors.

[0034] In the system of the present invention, the valve is controlled in a feedback loop in response to a combination of signals from first and second (and optionally third or further) mold level sensors, particularly the mean. The inventors have found that variations in mold level can be reduced to very low levels when using at least two mold level sensors operating in parallel. When using two or more sensors, the valve may be controlled in response to a combination of two or more meniscus level signals. The combination may be an algebraic function of the two signals, e.g., a polynomial or a linear function, in particular a linear combination, sum, or weighted sum of the two or more signals. In a preferred embodiment, the valve is controlled in response to the mean of the two or more signals, e.g., the arithmetic mean.

[0035] This system may be part of an industrial continuous slab casting machine for molten metal, particularly a steel casting machine. Typically, molten metal is supplied from a tundish into the mold. The tundish itself may be supplied from a ladle. The mold of a continuous slab casting machine may have a width of about 800 to 1800 mm, preferably 1000 to 1600 mm. In one embodiment, the width of the mold may be varied, especially during the casting operation. The width of the mold may be adjusted, for example, to 800 to 1800 mm, preferably 1000 to 1500 mm. The thickness of the mold may be 80 to 600 mm, preferably 150 to 400 mm. The height of the mold may be 800 to 2000 mm. The mold may be made of a copper alloy, and the molten metal inside the mold may be cooled from the outside, resulting in the formation of a solidified shell as the mold descends, which is then removed from the bottom with the assistance of rollers. The control unit may be a digital processing unit, such as a central processing unit (CPU). It may be part of a control system for controlling the operation of a continuous slab casting machine. For example, the control unit may be part of a computing device such as a computer, personal computer (PC), laptop, or server. The computing device may have a user interface. The user interface may include a screen and / or input devices such as a keyboard and / or mouse for the user to input control commands for the control unit.

[0036] In a preferred embodiment, the positions of the first and second (and possibly further) mold level sensors are determined by a method according to a first aspect of the present invention. Thereafter, variations in the mold level can be evaluated at various positions of the first and second, or further, mold level sensors, and the best position can be determined. In one embodiment, the position is evaluated within the same mold and the same continuous casting machine in which a system for controlling the meniscus level is installed. Variations in valve position may be used to determine the best sensor position. Alternatively, signals may be captured from both sensors over a predetermined time interval, an index of the variation in each signal may be calculated, a combination of the two indices of variation, in particular the average, and a position along the width of the mold having the lowest average index of the meniscus level variation may be selected. Thereafter, the optimal positions for the first and second sensors can be determined. Thereafter, in particular, in embodiments in which the width of the mold can be adjusted, it is possible to determine the optimal positions for the first and second mold level sensors for different widths of the mold. In another embodiment, the position is evaluated within a model casting machine having the same or similar dimensions and casting parameters.

[0037] According to one embodiment, first and second mold level sensors are positioned on opposite sides of the SEN along the width direction of the mold. When the mold level is controlled using a signal from one side of the SEN, it has been found that the meniscus level may behave differently on both sides, and that the meniscus level tends to be more unstable on the uncontrolled side. Therefore, it has been found that using two sensors positioned on both sides of the SEN is beneficial for meniscus level stability. In particular, the first and second mold level sensors may be positioned at least approximately equal distances from the center of the mold. In other words, the two sensors are positioned symmetrically on both sides of the SEN which is approximately at the center of the mold. "At least approximately" means that the distance of each of the two sensors from the center of the mold may vary within a range of ±8%, preferably ±5%, and more preferably 2%.

[0038] In one embodiment of the present invention, the distance between the two sensors from the center of the mold is 9% to 20%, preferably 12% to 17%, of the width of the mold. In other words, it has been found that good results are obtained when the mold level sensor is placed close to the SEN. In this embodiment, it is preferable that the two sensors are placed at least approximately equal distances from the center of the mold.

[0039] According to one embodiment, the first and second sensors are arranged to be movable in the width direction. This embodiment is advantageous because it allows for adjustment of the positions of the first and second mold level sensors for different casting parameters, such as casting speed, SEN immersion depth, and mold width. Since the intrinsic stability of the meniscus level is expected to be a function of the meniscus level profile, which itself is a function of the mold width, the mold width is expected to have a significant impact on the optimal control position of the mold level sensors. The first and second mold level sensors may be mounted on a horizontal rail, thereby allowing them to be moved along the width direction, for example, using a cable or drive wheel.

[0040] Alternatively, the first and second mold level sensors may be selected from a plurality of mold level sensors spaced apart across the width of the mold. For example, the system may include 4 to 20, preferably 6 to 10, mold level sensors arranged at different positions along the width of the mold. They do not have to be equally spaced across the width of the mold, but can all be arranged at different positions that have proven suitable for controlling the flow of metal into the mold for different casting parameters. For example, they may be arranged at a distance from the center of the mold that is less than 50% of the width of the mold. Furthermore, the plurality of sensors may be arranged at least generally symmetrically around the center of the mold, for example, 2 to 8 mold level sensors may be arranged on both sides. In this embodiment, the system may select two of those mold level sensors for controlling the valve that have the best position for achieving low meniscus level fluctuations. Which two sensors are selected may depend not only on the width of the mold, but also on the casting speed and immersion depth.

[0041] According to one embodiment, the width of the mold is configured to be adjustable during the continuous casting process. This can result in different positions being optimal for the mold level sensors. Preferably, the first and second mold level sensors are configured to be automatically movable to positions along the width of the mold, particularly to opposing positions on both sides of the SEN along the width direction of the mold. In particular, the positions to which the first and second sensors are moved are determined to be preferable by using one embodiment of the method for minimizing meniscus level fluctuations and, consequently, the amount of slag inclusion. For example, the optimal position may be at a distance from the center of the mold that is 9% to 20%, preferably 12% to 17%, of the width of the mold. This embodiment makes it possible to still achieve optimal meniscus level stability and, consequently, product quality, by adjusting the width of the mold to reduce the amount of slag inclusion to a minimum.

[0042] According to one embodiment, the control unit is configured to filter out characteristic frequencies of meniscus level fluctuations from the signal used to control the valve. This is advantageous because, by analyzing video of the meniscus level across the width of the mold captured by a camera, it was found that the meniscus level exhibits the characteristics of a wave propagating along the width of the mold. Since these waves sometimes collapse, resulting in strong bubble inclusion and presumably slag inclusion in actual casting machines, attenuating the amplitude of such waves is an important objective. The waves were found to occur periodically. When plotting the meniscus level across the width of the mold as a function of time, it was possible to detect waves propagating toward the center of the mold on both sides of the SEN. When a wave reaches the center, another wave begins to propagate on the opposite side, thereby defining the cycle. To predict the frequency of this wave cycle, a power spectral analysis may be performed on the valve position and / or meniscus level measured over a predetermined time interval, for example, the meniscus level averaged across the width of the mold, measured by a camera. This can be done by performing a Fourlier analysis of the measured signal in the time domain. This yields a power spectral density (PSD) that can display one or more peaks correlated with characteristic frequencies. Such frequencies have been found to be 0.05–0.5 Hz, preferably 0.08–0.2 Hz, in the casting machine configuration used. Therefore, these frequencies can be filtered out from the signal used to control the valves. This is advantageous because these waves are not critical to the overall level of molten metal in the mold and therefore should not be used to control the valves, as this can result in meniscus level instability, particularly in the amplitude of the waves.

[0043] The present invention also relates to a continuous casting machine for molten metal, particularly steel, including a system according to the present invention. The continuous casting machine may be, in particular, an industrial continuous slab casting machine, for example, a thin slab casting machine. The present invention relates to the use of the system according to the present invention in a continuous casting machine, particularly a slab casting machine, for molten metal, particularly steel. All the features and advantages of the method and system of the present invention also apply to continuous slab casting machines and their use, and vice versa.

[0044] In an alternative embodiment, the present invention is A system for controlling the meniscus level of liquid in the mold of a model casting machine, A mold having width and thickness, wherein the width is greater than the thickness, An immersion nozzle through which liquid is supplied into the mold, and the immersion nozzle is positioned at least approximately in the center in the width direction of the mold, A valve that adjusts the flow of liquid through the immersion nozzle, The present invention relates to a system comprising at least a first mold level sensor and a second mold level sensor, positioned at different locations along the width of the mold, for measuring the meniscus level of the liquid in the mold. The system further comprises a control unit configured to receive at least first and second meniscus level signals from the first and second mold level sensors, respectively, calculate a combination of at least the first and second meniscus level signals, in particular the average, and control a valve in a feedback loop in response to the combination of meniscus level signals. In this alternative embodiment, the casting machine configuration is a casting machine model using a liquid such as water or oil. The mold level sensors may be USS or cameras. The system may be configured to measure valve positions and / or meniscus levels at one or more locations along the width of the mold while operating the casting machine configuration over predetermined time intervals, and to calculate an index of the variation in valve positions and / or meniscus levels measured over predetermined time intervals in a step. The system may include cameras for measuring meniscus levels across the width of those molds, as described herein. This system may be adapted to carry out the method of the present invention as described herein with respect to a model casting machine. All features described herein with respect to a model casting machine are applicable to systems according to alternative embodiments of the present invention, and vice versa. In this embodiment, the width of the mold may also be adjustable.

[0045] The present invention also, A computer program that includes computer executable code, Computer-executable code, when executed by a computer, follows these steps: A step of receiving a set of multiple values ​​representing the valve position or meniscus level at one or more locations along the width of the mold, measured over predetermined time intervals; The steps include: calculating an index of the amount of variation for each value in the set; and Steps to determine the optimal set of values ​​that have the lowest amount of variation in the indicators. This invention relates to a computer program for implementing the method and system of the present invention. All features and advantages of the method and system of the present invention also apply to the computer program, and vice versa. In particular, the computer program may implement a method for determining the optimal position of a mold level sensor by processing the measured values ​​of valve position and / or meniscus level obtained from the method of the present invention. The computer program may run on any computing unit or computer, such as a server, cloud computer, mobile device, laptop, or PC.

[0046] The present invention also relates to a computer program product, which includes a computer program. The computer program product may be supplied in a downloadable format on a server or provided on a digital storage medium.

[0047] The present invention also relates to a non-temporary digital storage medium containing a computer program. The storage medium may be optical, solid-state, or magnetic storage medium. It may be, for example, a hard disk on a mobile device such as a laptop, tablet, or mobile phone, an SD card, an SSD card, a USB stick, a cloud computer, or any other digital storage medium.

[0048] The present invention will be described below with reference to the attached drawings, illustrating the embodiments. [Brief explanation of the drawing]

[0049] [Figure 1] Figure 1 is a schematic cross-sectional view of a continuous slab casting machine. [Figure 2] Figure 2 is a simplified diagram of the arrangement of a model casting machine that may be used in an embodiment of this method. [Figure 3] Figure 3 is a side view of the mold shown in Figure 2, indicating the sensor position. [Figure 4]Figure 4 shows the meniscus level measured by a camera with a low-pass filter applied and by a USS. [Figure 5] Figure 5 shows the standard deviation of the meniscus level according to the control position, using single control and mean control. [Figure 6] Figure 6 shows the standard deviation of the meniscus level measured optically using single control and average control. [Figure 7] Figure 7 shows the standard deviation of the stopper position for different control positions using single control and average control. [Figure 8] Figure 8 shows the power spectral density at the stopper position. [Figure 9] Figure 9 shows the path taken by the optically measured meniscus level over a predetermined time interval. [Figure 10] Figure 10 is a flowchart of a method according to one embodiment of the present invention. [Modes for carrying out the invention]

[0050] Figure 1 shows a cross-section of a continuous slab casting machine 1 according to one embodiment of the present invention. In the continuous slab casting machine, molten metal 8, in particular steel, is held in a ladle 7 and transferred from there to a tundish 6. From the tundish 6, the liquid metal is supplied into the mold 2 through an immersion nozzle 3. The flow of molten steel is controlled by a valve 5, which in this embodiment is a stopper, and this stopper can be moved upward or downward (in this embodiment), and its movement is controlled by a control unit 28. The molten steel forms a liquid pool 12 in the mold 2. The meniscus level of the liquid pool 12 is indicated by 4, and a mold level sensor 10 can measure the height of the meniscus level. The sensor 10 may be, for example, a radiation sensor or an eddy current sensor. The mold 2 may be cooled by spray cooling 18, as a result the steel forms a solidified shell 16. This solidified shell 16 is drawn from the bottom of the mold while still being spray cooled by a water spray 18 and guided to horizontal alignment by rollers 14. In step 24, the fully solidified strand can be cut to form a slab 20. In another embodiment, the strand is fed directly into a hot rolling mill, thereby continuously producing hot-rolled steel products, such as steel sheets. [Examples]

[0051] Figure 2 shows a portion of the configuration of a model casting machine, also referred to as a thin-slab casting machine water model, used to conduct experiments using a method according to one embodiment of the present invention. It includes a tundish (not shown), a supply system 3, and a mold 2 corresponding to the mold of the thin-slab casting machine. The mold 2 is made of a transparent material such as glass or plexiglass. It has a mold width MW and a mold thickness MT. SEN 3 is positioned approximately in the center of MW and reaches into the liquid 9, which may be water, at an immersion depth SD. The meniscus level 4 of the liquid 9 can be measured by an ultrasonic sensor USS (not shown in Figure 2) and / or by a camera 30. The casting speed, as well as the mold width and immersion depth, can be adjusted in the foundry to match the desired casting parameters. The meniscus level is controlled via a feedback loop, the input parameter of the feedback loop being the meniscus level signal acquired by one or two ultrasonic sensors (USS) not shown in Figure 2. Because the USS acquires signals at a higher rate than the radiation sensors in the factory, a low-pass filter is used on the signals acquired by the USS to mimic the Berthold sensors used in the factory. The camera can acquire video, i.e., a time series of images, of at least the field of view 32, which includes images of meniscus level 4 across the full width of the mold. Meniscus level 4 is controlled to be located at the mold level setting point indicated by 33.

[0052] Camera 30 can be mounted on a stand (not shown) so that its height is the same as or slightly above the meniscus level 4. This allows for a clear view of the meniscus level at any time and in any location. Image processing-based algorithms, developed within MATLAB, were used to track and measure the meniscus level.

[0053] The results presented herein were obtained using a fixed set of casting parameters: a casting speed of 5.4 m / min, an immersion depth (SD) of 290 mm, and a mold width of 1500 mm. The predetermined time interval was 15 minutes. In other words, each measurement was performed over a 15-minute duration to achieve data convergence.

[0054] Eight different equidistant positions of the USS were investigated. These positions are shown in Figure 3, which shows a schematic side view of the thin slab casting machine water model mold 2. The width MW of the mold is 1500 mm, and SEN3 is indicated at the center 34 of mold 2. The eight different positions of the USS are arranged symmetrically with respect to the centerline 36 of mold 2. For the experiment, two USS 10a and 10b were placed at equal distances from the symmetry axis 36 of the mold, specifically at one of the four symmetric positions 1L1R, 2L2R, 3L3R, or 4L4R. The distance between positions 1, 2, 3, and 4 was 150 mm, the distance between positions 4L and 4R from the symmetry axis 36 was 215 mm, and the distance between positions 1L and 1R to the short side of the mold was 85 mm. For each position (1, 2, 3, or 4), sensors were used independently in several experiments to control the liquid flow. In other words, only the left sensor "L" or the right sensor "R" was used in the control loop, while the other sensor was only measuring the meniscus level. In other experiments, the average signal of the two sensors was used in the control loop. These control strategies are also referred to herein as "single control" and "average control." In other embodiments not reported herein, the two sensors were not symmetrically arranged, for example, the sensor positions were 1L2R, 3L4R, 4L3R, etc.

[0055] Figure 4 shows the meniscus level signals with a low-pass filter applied to the signal, measured over a 2-minute interval using an optical camera (line 38) and an ultrasonic sensor (line 40). Figure 4 shows the meniscus level at one of the eight locations shown in Figure 3. The agreement between the USS and camera measurements is very satisfactory. The small difference between the two measurement techniques can be explained by the fact that the camera measurement is slightly less accurate than the USS. Furthermore, the two techniques are not measuring at exactly the same location, as the USS measures at the center of the mold in the direction of the mold signal, while the camera measures the meniscus level at the transparent sidewall.

[0056] Using the settings described above, the standard deviation of the meniscus level was measured and calculated using different positions (also called "control positions") of the mold level sensors that control the liquid flow. Figure 5 shows the standard deviation of the meniscus level according to the control positions. In the corresponding experiment, USS10a and 10b were placed at four different positions, specifically 1L1R, 2L2R, 3L3R, and 4L4R, arranged symmetrically around axis 36. The casting machine configuration was then operated either using the signal from one USS42 or using the average signal from both sensors 44 in the control loop. The variation in the meniscus level was obtained by calculating the standard deviation of the meniscus level measured by each of the two USS10a and 10b over a predetermined time interval, and then taking the average of these two standard deviations.

[0057] First, Figure 5 shows that the standard deviation of meniscus level variation is always considerably smaller when using average control 44 compared to single-sensor control 42. In fact, meniscus level variation is reduced by approximately 15-25% when two sensors are used in the control for each control position. Furthermore, it can be seen that the maximum standard deviation is obtained at position 3L3R. The minimum standard deviation is obtained at position 4L4R.

[0058] Figure 6 shows the standard deviation of the overall meniscus level measured by the camera using single control 45 and average control 46. The results are the same as the meniscus level measured by USS, and average control always yields better results than single control. The lowest standard deviation was obtained by two ultrasonic sensors at control position 4L4R, i.e., 215 mm from the center line 36 of the mold or approximately 14% of the width of the mold.

[0059] This means that the mold level stability benefits from a control position relatively close to the SEN. However, the highest level fluctuations can be found at position 3, which appears to result from the fact that the traveling wave collapses at this position. The mold appears to be inherently more unstable at this position.

[0060] Figure 7 shows the standard deviation of the stopper position for different control positions, again using single control 48 or average control 50. The bar graph strictly follows the behavior of the meniscus level variation 10 in Figures 5 and 6. This shows that the method of the present invention can also be carried out by evaluating the position of the mold level sensor through the amount of variation in the stopper position, which is highly advantageous because it makes it possible to carry out the method in industrial slab casting machines as well.

[0061] Wave generation within the mold was also analyzed by analyzing the meniscus level across the mold width as a function of time, as recorded by the camera. Specifically, the waves propagate toward the SEN (Single Energy Line). When a wave reaches the center, another wave begins propagating on the opposite side of the SEN. This defines the cycle. The duration of the cycle was observed to be approximately 5–15 seconds. The phase velocity of the waves was approximately 0.12 m / s.

[0062] To detect the frequency of this wave cycle, power spectral analysis was performed on the measurement data collected by this method, particularly the complete meniscus level measured by a camera, the stopper position, or the meniscus level measured at two symmetrical positions by an ultrasonic sensor. As an example, Figure 8 shows the power spectral density normalized by the standard deviation of the signal for the stopper position. The power spectral density (PSD) shows a characteristic frequency f1 corresponding to the frequency of the wave cycle. This frequency was approximately 0.11 Hz. In some experiments, additional characteristic frequencies were found corresponding to the first and second mode oscillations of gravity waves, where the wavelength is twice the width of the mold. Therefore, the control loop was designed to intentionally filter out these characteristic frequencies because gravity waves do not alter the mean meniscus level. Frequency analysis can be further used to predict when inclusions originating from surface wave contamination may occur within the casting slab.

[0063] Finally, Figure 9 shows an embodiment in which an index of valve position and / or meniscus level fluctuations is calculated over a shorter time series. This yields the time evolution 54 of the meniscus level fluctuations over a predetermined time interval (in this example, 900 seconds = 15 minutes). Figure 9 specifically shows the time evolution of the level of meniscus level fluctuations averaged over the width of the entire mold, as detected by the camera. In this case, the shorter time intervals overlap, and the index of fluctuations was the sum of the absolute values ​​of the differences between meniscus levels from one measurement point to the next (the path traveled). The dashed line indicates the point in time when bubble inclusion was observed in the video recorded by the camera. Major peaks 56 in the signal in Figure 9 are indicated by black triangles. It can be seen that the peak positions are very strongly correlated with bubble inclusion. Not all peaks result in bubble inclusion, but nevertheless, the peaks indicate strong meniscus level fluctuations. Therefore, the number of peaks is a good indicator for evaluating the control position when using at least one mold level sensor to control the flow of liquid into the mold. Using this method, a significant reduction in the number of peaks can be observed when using the average control compared to the single control, particularly when the number of peaks was reduced by 20–50%. It can be further found that position 3 was the control position that resulted in the most unstable meniscus level with respect to potential bubble inclusion, while positions 1 and 4 appeared to be the most preferable.

[0064] Finally, Figure 10 illustrates the method according to the present invention. In step 60, the casting machine assembly is set up, and at least one, preferably two, mold level sensors are positioned at specific locations along the width of the mold to measure the meniscus level at those locations. In step 62, the casting machine arrangement configuration is operated while controlling the valves and feedback loop in response to the meniscus level signals from at least one mold level sensor. In step 64, while the casting machine arrangement configuration is operating in this manner, the valve positions and / or meniscus levels at one or more locations along the width of the mold are measured. This can be done for the meniscus level using a camera, or using at least one mold level sensor, or using more mold level sensors. The stopper position can also be measured using an existing mechanism for controlling the stopper position.

[0065] When this is done over a predetermined period of time, for example, 5 to 20 minutes, an index of the variation in valve position and / or meniscus level is calculated in step 66. This could be, for example, the standard deviation.

[0066] This is repeated for several different control positions, i.e., different positions of at least one mold level sensor, for as many different positions as there are to be tested. This is indicated by arrow 68. Finally, once all positions have been tested, in step 70, the calculated index of the amount of variation is compared among the different control positions, and the control position with the lowest index of variation is selected as the optimal control position. [Explanation of Symbols]

[0067] 1. Continuous slab casting machine 2. Mold 3. Immersion nozzle (SEN) 4 Meniscus Level 5 valves 6 Tan Dish 7 Ladle 8 Molten steel 9 liquid 10. Mold level sensor 12 Liquid pools 14 Support Rolls 16 Solidified Shell 18. Spray cooling 20 slabs 24 Cutting point 28 Control Unit 30 Cameras 32 field of view 33. Mold level setting point MW mold width MT mold thickness SD Immersion Depth 1L, 2L, 3L, 4L: Sensor position on the left side 1R, 2R, 3R, 4R Right-side sensor position 34 Center of the mold in the width direction 36 Axis of Symmetry 38 Meniscus level measured by camera 40 Meniscus level measured by ultrasonic sensor 42. Meniscus-level standard deviation using a single control. 44 Meniscus-level standard deviation using two symmetric control sensors 5. Standard deviation of mold level using optical measurement with single-sensor control. 46. ​​Standard deviation of meniscus level measured by optical measurement using two symmetric control sensors. 48 Standard deviation of stopper position during single-sensor control 50 Standard deviation of stopper position during control of two sensors 52 Power spectrum at stopper position 54 Graph of changes in mold level over time 60-70 Method Steps

[0068] None of the reference numerals in the claims should be construed as limiting the scope of the attached claims.

Claims

1. A method for evaluating the position of at least one mold level sensor (10) in the mold of a continuous slab casting machine (1) for molten metal, particularly molten steel, The above method is carried out within the arrangement configuration (1) of the casting machine. The arrangement configuration (1) of the casting machine is as follows: A mold (2) having a width (MW) and a thickness (MT), wherein the width is greater than the thickness, An immersion nozzle (3) through which liquid is supplied into the mold (2), and the immersion nozzle (3) is positioned at least approximately in the center (34) in the width direction of the mold, A valve (5) that adjusts the flow of liquid through the immersion nozzle (3), Includes, The above method involves the following steps: (a) Placing at least one mold level sensor (10) at a first position along the width of the mold to measure the meniscus level (4) of the liquid, thereby generating at least one meniscus level signal; (b) A step of operating the casting machine configuration (1) while controlling the valve (5) in a feedback loop in response to the at least one meniscus level signal; (c) While operating the arrangement configuration of the casting machine over predetermined time intervals, measure the position of the valve and / or measure the meniscus level (4) at one or more positions (1L, 2L, 3L, 4L, 1R, 2R, 3R, 4R) along the width of the mold; (d) A step of calculating an index of the variation in the position of the valve and / or the meniscus level measured over the predetermined time interval in step (c); (e) Placing at least one mold level sensor (10) to measure the meniscus level of the liquid at a different position from the first position along the width of the mold, thereby generating at least one further meniscus level signal, and repeating steps (b) to (d) using the at least one further meniscus level signal to control the valve (5); and (f) A step of determining the optimal position for the at least one mold level sensor (10) by selecting the position along the width of the mold where the index calculated in step (d) is smallest. The method, including the method described above.

2. The at least one mold level sensor (10) includes at least a first mold level sensor (10a) and a second mold level sensor (10b), The at least first and second mold level sensors are arranged at different positions (1L, 2L, 3L, 4L, 1R, 2R, 3R, 4R) along the width of the mold, The method according to claim 1, wherein the valve (5) is controlled in a feedback loop in response to a combination of signals from at least the first and second mold level sensors (10a, 10b), particularly the average.

3. The method according to claim 2, wherein the first and second mold level sensors (10a, 10b) are arranged on opposite sides of the immersion nozzle (3) along the width direction (MW) of the mold, and in particular are arranged at at least approximately equal distances from the center (34) of the mold.

4. The meniscus level (4) is measured in step (c) at several positions (4L, 4R) spaced apart across the width (MW) of the mold. The method according to any one of claims 1 to 3, wherein the index of the variation in the meniscus level is a combination, in particular the average, of the variation in the meniscus level (4) at each of the several locations.

5. The method according to any one of claims 1 to 4, wherein the meniscus level (4) is measured using a camera (32) in step (c).

6. The index of the fluctuations in the position and / or meniscus level of the valve is calculated over a plurality of shorter time intervals within the predetermined time interval. The method according to any one of claims 1 to 5, wherein the index of variation includes a plurality of peaks (56) in the index of variation observed over a plurality of shorter time periods (54).

7. A system for controlling the meniscus level of molten metal, preferably molten steel, in a mold (2) of a continuous casting machine (1), The aforementioned continuous casting machine is A mold (2) having a width (MW) and a thickness (MT), wherein the width is greater than the thickness, An immersion nozzle (3) through which molten metal is supplied into the mold, and the immersion nozzle (3) is positioned at least approximately in the center (34) in the width direction of the mold, A valve (5) that adjusts the flow of molten metal through the immersion nozzle (3), Includes, The aforementioned system, At least a first mold level sensor (10a) and a second mold level sensor (10b) are arranged at different positions along the width direction of the mold for measuring the level of molten metal in the mold (2), A control unit (28) is configured to receive at least first and second meniscus level signals from at least first and second mold level sensors (10a, 10b), respectively, calculate a combination of the at least first and second meniscus level signals, particularly the average, and control the valve (5) in a feedback loop in response to the combination of the meniscus level signals, Includes, The system wherein the positions of at least the first and second mold level sensors (10a, 10b) are determined by the method described in any one of claims 1 to 6.

8. The system according to claim 7, wherein the first and second mold level sensors (10a, 10b) are arranged on opposite sides of the immersion nozzle (3) along the width direction of the mold, and in particular are arranged at a distance of at least approximately equal distance from the center (34) of the mold, and more particularly at a distance of 9% to 20%, preferably 12% to 17%, of the width of the mold.

9. The system according to claim 7 or 8, wherein at least the first and second mold level sensors (10a, 10b) are arranged to be movable along the width direction.

10. The width of the mold (2) is configured to be adjustable during the continuous casting process. The system according to claim 9, wherein the first and second sensors (10a, 10b) are configured to be automatically movable during the continuous casting process to positions along the width of the mold, in particular to positions on both sides of the immersion nozzle (3) that are opposed to each other, and which are determined to be optimized for the parameters of the continuous casting process, in particular for the current width of the mold.

11. The system according to any one of claims 7 to 10, wherein the control unit (28) is configured to filter out characteristic frequencies of meniscus level fluctuations from the signal used to control the valve (5).

12. Use of the system according to any one of claims 7 to 11 in a continuous slab casting machine (1) for molten metal, particularly molten steel.

13. A computer program for carrying out the method described in any one of claims 1 to 7, The computer program includes computer executable code, When the aforementioned computer executable code is executed by a computer, the following steps occur: Steps include receiving a set of values ​​representing the position of the valve and / or the meniscus level at one or more locations along the width of the mold, measured over predetermined time intervals; A step of calculating an index of the amount of variation for each of the aforementioned set of values; The step of determining the optimal set of values ​​that has the lowest indicator of the amount of variation. The computer program that performs the above.

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