WO2012168005A1 - Method for regulating the height of the casting level in a mold of a continuous casting installation - Google Patents

Abstract

The invention relates to a method for regulating the height (h) of the casting level (1) in a mold (2) of a continuous casting installation (3), wherein liquid metal (4) flows into the mold (2), wherein the outflow of liquid metal (4) into the mold (2) can be controlled by a control element (8), the volume flow of liquid metal (4) flowing into the mold (2) being measured by a flow sensor (9), the volume flow being regulated in a first regulating circuit on the basis of a nominal value, the height (h) of the casting level (1) being regulated in a second regulating circuit on the basis of a nominal value or a nominal range (h_soll). According to the invention, a second controller (11) provides the first regulating circuit with a nominal value regarding the volume flow, wherein the determination of the actual height (h_ist) of the casting level (1) is carried out while taking into account a standing wave on the casting level (1) preferably by means of a number of optical waveguides (12). In this way, the height of the casting level can be kept constant in the mold in an improved manner.

Description

 Method for regulating the height of the casting mirror in a mold of a continuous casting plant

The invention relates to a method for regulating the height of the casting mirror in a mold of a continuous casting plant.

In the continuous casting of a metal strand, liquid metal is usually passed from a ladle via a shadow tube into an intermediate container (tundish). From the intermediate container then passes the liquid metal through a pouring tube into the mold. At the lower end of the mold, the cast strand is then discharged and deflected by means of a strand guide from the vertical to the horizontal.

It is important that the liquid metal is kept in the mold at a defined Gießspiegelhöhe to perform the continuous casting process of high quality. For this purpose, a certain height range is usually allowed, in which the casting level may be in the mold. The discharge from the intermediate container into the pouring tube may comprise a stopper which is arranged in a valve seat and by raising or lowering of which the volume flow of the liquid metal can be influenced. The plug position is influenced by a moving element, which is controlled by a controller to obtain a defined volume flow.

In the regulation of a desired constant volume flow in the pouring tube, the unknown transfer function of the plug is a disturbance variable; that is, it is not known per se how the volume flow of liquid metal changes when the plug is raised or lowered a defined amount. The problem arises from the fact that it is unknown how the transfer function changes if, due to clogging or erosion, a Change takes place at the seat of the plug in the outflow opening. Clogging describes the caking of material in the pouring tube or on the stopper; As a result, the plug must be raised further in order to achieve the same volume flow of metal. On the other hand, aggressive processes carry material from the stopper, so that in some steel grades, the stopper must be constantly fed further in order to obtain the same volume flow of metal. If there is an undesirable sudden breakdown of encrustation, there will be a corresponding change in the volume flow of the liquid metal and consequently a Gießspiegelschwankung in the mold. The regulation of the volume flow of liquid metal into the mold can be set at unknown transfer function, ie at unknown plug characteristic, usually only with a low gain of the controller, so that instabilities are prevented. However, a low gain reduces the adjustability of Gießspiegelschwankungen.

From DE 10 2009 057 861 A1 it is known to use a measuring device for the volume flow within the pouring tube for rapid regulation of the volume flow. Thus, a relatively fast regulation of the volume flow can take place. As an advantageous sensor for the volume flow, a solution has been proven, which is described in WO 00/58695 A1. Magnetic fields are used here to determine the volume flow quickly and accurately. By means of the sensor described here, a measured value can be recorded in the tenth of a second range; the resolution is also very precise, so that the actual volume flow can be detected accurately.

In addition to the constant regulation of the volume flow of liquid metal into the mold, another problem is that flow effects of the liquid metal also result in the mold itself, which make it difficult to stably maintain a defined pouring height in the mold. Furthermore, the behavior of the cast strand, as long as it is not yet solidified, a potential source of interference for keeping the pouring level constant. On the one hand, disturbances are the dynamic bulging of the strand between the strand guide rollers, ie the so-called bulging. This results in a pumping effect and a subsequent Gießspiegelschwankung. On the other hand, a Storeinfluss created by the fact that waves form on the mold surface, resulting from the pouring of the liquid metal into the mold. These waves fool a measuring device in the mold at shaft passage at the measuring point before a Gießspiegelschwankung, ie an apparent change in Gießspiegelhöhe, which does not exist.

Although it is known from DE 10 2008 060 032 A1 as such, to detect the Gießspiegelhöhe in a mold, for which here optical waveguides are used, which are arranged in the mold. The temperature measurement takes place, for example, with the fiber Bragg grating method.

While insofar isolated measures are known which favor a constant maintenance of the level of the pouring material in the mold, it is still problematic to put the measures in a context in such a way that overall the result of the control can be improved.

It is therefore an object of the present invention to propose a method for controlling the height of the casting mirror in a mold of a continuous casting machine, which is characterized by an improved efficiency, ie. H. A method is to be proposed with which the level of the casting mirror can be kept as stable and as constant as possible at a predetermined value or in a predetermined range, even with the aforementioned influencing variable.

The solution of this problem by the invention is characterized in that liquid metal flows from a ladle or an intermediate container via at least one pouring tube into the mold, wherein the volume flow of liquid metal from the ladle or the intermediate container into the mold can be controlled by a control (stopper), wherein the volume flow of liquid metal flowing from the ladle or the intermediate container into the mold is measured by a flow sensor as the actual volume flow, the volume flow being determined according to a nominal value and taking into account the measured actual value. Volume control in a first control loop is controlled by a first controller, wherein the first controller acts on the control, wherein the height of the mold level in the mold after specification of a desired value or desired range and taking into account the actual height of the mold level in a second control loop with a second controller is controlled, wherein the second controller to the first control circuit sets a target value for the flow, wherein the determination of the actual height of the casting mirror takes into account a standing wave on the casting mirror, which is due to the inflow of liquid metal in the mold the Gießsp iegel is formed by a temperature profile over the height of the mold at a number of peripheral locations of the mold is detected and the measured temperature profiles are used in determining the effective height of the mold level.

Preferably, the determination of a temperature profile over the height of the mold by means of at least one optical waveguide, which is arranged vertically in the mold wall.

In this case, the temperature profile over the height of the mold can be detected for each optical waveguide and the maximum of the measured values can be used as a criterion for the position of the actual height of the mold level at the relevant peripheral point of the mold.

As a control, preferably a movable closure plug is used. As a flow sensor, a sensor is advantageously used, which determines the volume flow by induction of a magnetic field in the liquid metal. At least four optical waveguides, more preferably even at least eight or more optical waveguides, are preferably arranged around the circumference of the mold, each of which detects a temperature profile above the height of the mold.

Each optical waveguide can detect at least 5, preferably at least 20, measured temperature values over the height extent of the mold. The detection of up to 40 temperature values is possible.

As a target height for the liquid metal in the mold, a range is preferably set, which is located at a defined distance from the upper edge of the mold. In this case, it is particularly preferably provided that a distance from the upper edge of the mold between 90 and 1 10 mm is specified for the desired range.

In this case, no deviation is preferably reported to the second controller, as long as a value is determined for the actual height of the liquid metal which lies within the predetermined range. The first controller and the second controller are preferably designed so that the adjustment of the volume flow is faster than the adjustment of the height of the liquid metal in the mold.

Accordingly, the invention proposes that the integrative fraction of the fill level in the mold takes place by detecting the temperature distribution in the mold by means of optical waveguides and inference to the actual Gießspiegelhöhe, but then fast dynamic changes by flow measurement (volume flow measurement) are controlled at the pouring tube. The regulation of the liquid steel mirror in the mold, ie the regulation of the integrative component, is carried out - as mentioned - so that the Gießspiegelhöhe moves in a defined range. Provided for this purpose is a distributed measurement of the temperature profile over the mold height with the mentioned fiber optic methods. Here, in particular, in addition to the fiber Bragg grating method, the Optical Time Domain Reflectometry method or the Optical Frequency Domain Reflectometry method is used. The mold is in this case provided over the circumference with a plurality of optical waveguides which extend vertically in the mold wall and have up to 40 measuring points. In this case, a "heat lobe" is measured with each optical waveguide, ie a temperature profile above the mold height.These heat lobes can not be determined with thermocouples since thermocouples are not sensitive enough and provide too few measuring points above the mold height.

Based on the measured heat lobe can be calculated by experiments on the actual pouring mirror back. The pouring mirror is mainly described by the position of the maximum of the heat lobe. The distributed measurement of up to 32 heat lobes distributed over the circumference of the chill mold creates a "mountain range" along the outer boundary of the chill mold so that the shape and size of a so-called "standing wave" in the chill mold can be determined. H. a quasi-stationary wave structure on the casting mirror, which results from the pouring of liquid metal into the mold.

All fluctuations of this standing wave are detected by the determination of the ridge; the standing wave can thus be recorded and displayed online. Accordingly, by the proposed approach by means of the distributed optical fiber measurement, the actual effective Gießspiegelschwankung - It has to be corrected - to be distinguished from the fluctuation caused by the standing wave.

This makes it possible to restrict control interventions to the actual Gießspiegelhöhenschwankungen.

This control over the distributed measurement in the mold thus serves to adjust the integrative content in the mold. It should be prevented the runaway of the casting mirror from a target area. In order to prevent "erosion" of the pouring tube at one point, a target range of, for example, 90 to 110 mm (measured from the upper edge of the copper mold) is determined for controlling the integrative fraction in the mold In this range and has no strong fluctuations, there are no control interventions with respect to the integrative level.

If there are strong fluctuations in the mold, they can be specifically assigned to the dip tube or the mold, so that the proposed control strategy can compensate for this purpose. The number of optical fibers can be selected expertly. In principle, it is also possible to work with only a single optical waveguide, of course with a loss of accuracy. The optical waveguide would be preferred in this case z. B. vertically beckupfert in a narrow side or broadside or arranged in a hole in the mold.

The optical waveguide is preferably laid in a cladding tube. The cladding tube has, for example, an outer diameter of 0.5 to 2 mm and an inner diameter of 0.4 to 1, 8 mm and is made of stainless steel. The introduction into the mold is carried out by insertion into a bore made for this purpose or by incorporation in a layer of copper or nickel. The temperature rise times for the optical waveguide in the cladding tube are very short (after a time well below one second, a considerable part of the final temperature value is reached). A resolution of up to 1 ° C is possible. Accordingly, the overall result is an effective control of the rapidly changing portion by a very rapid flow measurement at the pouring tube and a control based on the control of the volume flow of liquid metal, which is conveyed into the mold. The further control of the integrative component in the mold is, however, by observing a confidence interval (target range) for the level of the pouring mold in the mold, for which the distributed optical fiber measurement is used, with which a Höhengebirgszug the so-called. Standing wave is detected. Effects such as bulging can hereby be recorded and corrected. The technology of measuring temperatures by optical waveguides is known as such, to which reference is made to WO 2004/015349 A2 and to WO 2007/079894 A1.

In the drawing, an embodiment of the invention is shown. Show it:

Fig. 1 shows schematically a continuous casting, wherein in addition to a ladle, an intermediate container and a mold and a control scheme is outlined, Fig. 2 shows the section A-B of FIG. 1 by the mold and

Fig. 3 shows schematically the course of a measured temperature above the height of the mold. In Fig. 1, a part of a continuous casting plant 3 is outlined, which has a ladle 5 for receiving molten steel 4 in a known manner. About a shadow tube 13, the liquid metal 4 passes into an intermediate container 6. From this in turn, the liquid metal 4 is passed through a pouring tube 7 in the mold 2. In the mold 2, the liquid metal 4 forms a pouring mirror. 1

The height h of the pouring mirror 1 should remain as constant as possible during continuous casting and, in any case, be in a range which is away from the upper edge of the mold 2 by a defined distance x. Specifically, it has proven useful if the casting mirror 1 remains at a distance x of 90 to 1 10 mm from the upper edge of the mold 2.

The volume flow V of liquid metal 4, which is supplied to the mold 2, can be influenced by a control element 8, which - formed as a plug - can be moved via an actuating element in the direction of the double arrow in FIG. Accordingly, more or less volume of liquid metal 4 can be passed into the mold 2 per time.

To regulate the volume flow V, a first control loop is provided, which consists of a first regulator 10 and the first controlled system 14 influenced by it (see the schematic representation in FIG. Given the first control loop is a setpoint for the flow rate V _So u. The actual

Volume flow VM is detected by a flow sensor 9, which is arranged in or on the pouring tube 7. As used herein, a sensor is included that includes a magnet whose force is detected by a weighing device. This force is influenced by the flow of the liquid metal so that the volume flow can be measured. The deviation V _So u - V is given to the first controller 10, which then actuates the control element 8 accordingly. Superimposed in cascade on the first control loop is a second control loop which has a second regulator 11 and a second control path 15. Here, the manipulated variable is the nominal height of the casting mirror h _S0 ii, which - as explained - should be at a predetermined value or in a predetermined range. The desired height or the desired height range is specified for the control. The second controller 1 1 is the second controlled system 15 before the control signal, in which case the first control loop is interposed (cascade control). The actual height h | _St is subtracted from the desired height h _S0 ii, so that at a given control difference, the second controller 1 1 causes the necessary.

In this case, the determination of the actual height of the pouring mirror in 1 of the mold 2 is correspondingly important. Due to the inflow of liquid metal 4 into the mold 2, a so-called standing wave forms here, which is indicated in FIG. 1 in the mold. Also sketched are some flow arrows in the melt. The flow is responsible for the fact that it comes to said standing wave.

It is important to recognize the "mountain elevation" of this standing wave and to take into account in determining the effective height h of the casting mirror 1 in the mold 2.

The procedure is as follows:

Over the circumference of the mold 2 - as can be seen in Fig. 2 - a plurality of optical waveguides 12 are arranged. Each optical fiber 12 is located in a vertical bore which is introduced in the mold wall. About the circumference up to 32 optical fibers 12 are placed.

Each optical waveguide 12 can detect the temperature profile over the height h of the mold 2, for example, via the fiber Bragg grating method explained in more detail below. For this purpose, reference is made to Fig. 3, where qualitatively such a course T = f (h) is sketched in the form of a "heat lobe" Maximum of the temperature T. This maximum is a sure indication of the actual position of the casting level 1 at this circumferential point of the mold 2. Thus, it is possible in a simple manner to detect the shape of the standing wave in the mold by evaluating all detected "heat lobes" For example, by means of appropriate averaging, the effective position of the pouring mirror 1 can be detected, quasi-adjusted for the standing wave .This value is then the actual value h | _St , which is used as the basis for the control.

The optical waveguide 12 typically has a diameter of z. B. 0.12 mm; with cladding usually results in a diameter in the range of 0.5 mm to 2.0 mm. The optical waveguide 12 can withstand temperatures up to 800 ° C continuous load.

The optical waveguides 12 are connected to a temperature detection system, not shown. By means of the detection system laser light is generated, which is fed into the optical waveguide 12. The data collected by the optical fiber 12 are converted into temperatures by means of the detection system and assigned to the various measurement locations.

The evaluation can be carried out, for example, according to the so-called fiber Bragg grating method (FBG method). In this case, suitable optical waveguides are used, the measuring points with a periodic variation of the refractive index or grating get impressed with such variations. This periodic variation of the refractive index leads to the fact that the optical waveguide represents a dielectric mirror as a function of the periodicity for specific wavelengths at the measuring points. By changing the temperature at one point, the Bragg wavelength is changed and exactly this is reflected. Light that does not meet the Bragg condition is not significantly affected by the Bragg grating. The different signals of the different measuring points can then be distinguished from one another on the basis of propagation time differences. Of the Detailed structure of such fiber Bragg gratings and the corresponding evaluation units are well known. The accuracy of the spatial resolution is given by the number of impressed measuring points. The size of a measuring point can be, for example, in the range of 1 mm to 5 mm.

Alternatively, the "Optical Frequency Domain Reflectometry" method (OFDR method) or the "Optical Time Domain Reflectometry" method (OTDR method) can be used to measure the temperature. These methods are based on the principle of fiber optic Raman backscatter, taking advantage of the fact that a temperature change at the point of a light guide causes a change in the Raman backscatter of the optical waveguide material. By means of the evaluation unit (eg a Raman reflectometer), the temperature values along a fiber can then be determined in a spatially resolved manner, with this method averaging over a specific length of the conductor. This length is about a few centimeters. The different measuring points are in turn separated by differences in transit time. The construction of such systems for evaluation according to the said methods is well known, as are the necessary lasers which generate the laser light within the optical waveguide.

LIST OF REFERENCE NUMBERS

5

 1 pouring mirror

 2 mold

 3 continuous casting plant

 4 liquid metal (steel flames)

10 5 ladle

 6 intermediate tanks (Tundish)

 7 pouring tube (SEN - submerged entry nozzle)

8 control

 9 flow sensor

15 10 first controller

 1 1 second controller

 12 optical fibers

 13 shadow tube

 14 first controlled system

20 15 second controlled system

Height of the water level

 Target height of the pouring mirror Actual height of the pouring mirror

30 V volume flow of the liquid metal Setpoint for the volumetric flow Actual value for the volumetric flow

T (h) Temperature profile over the height of the mold x distance

Claims

claims: 1 . Method for regulating the height (h) of the casting mirror (1) in a mold (2) of a continuous casting installation (3), wherein liquid metal (4) flows from a ladle (5) or an intermediate container (6) via at least one pouring pipe (7) flows into the mold (2), wherein the volume flow (V) of liquid metal (4) from the ladle (5) or the intermediate container (6) into the mold (2) by a control element (8) can be controlled, wherein the of the ladle (5) or the Between the container (6) in the mold (2) flowing volume flow (V) of liquid metal (4) by a flow sensor (9) is measured as an actual volume flow (Vi _st ), wherein the volume flow (V) after specification of a setpoint (V _So u) and under Considering the measured actual volume flow (Vi _st ) is controlled in a first control loop with a first controller (10), wherein the first controller (10) acts on the control element (8), wherein the height (h) of the pouring mirror (1) in the mold after setting a desired value or desired range (h _so n) and taking into account the actual height of the casting mirror in a second control loop with a second controller (1 1) is regulated, wherein the second controller (1 1) the first control loop a Specifies the setpoint for the flow rate (V _So u), wherein the determination of the actual height (h | _St ) of the casting mirror (1) taking into account a standing wave on the casting mirror (1), which is due to the inflow of liquid metal (4) into the mold (2) on the casting mirror (1) is formed by detecting a temperature profile (T (h)) over the height (h) of the mold (2) at a number of circumferential locations of the mold (2) and the measured temperature profiles (T (h)) in determining the effective height (h | _St ) of the pouring mirror (1) are taken as the basis. 2. The method according to claim 1, characterized in that the determination of a temperature profile (T (h)) over the height of the mold (2) by means of at least one optical waveguide (12), which is arranged vertically in the mold wall. 3. The method according to claim 1 or 2, characterized in that for each optical waveguide (12) the temperature profile (T (h)) over the height (h) of the mold (2) is detected and the maximum of the measured values as a criterion for the position the actual height (h) of the pouring mirror at the respective circumferential point of the mold (2) is taken as the basis. 4. The method according to any one of claims 1 to 3, characterized in that a movable sealing plug is used as the control element (8). 5. The method according to any one of claims 1 to 4, characterized in that as a flow sensor (9), a sensor is used, which determines the volume flow (V) by induction of a magnetic field in the liquid metal. 6. The method according to any one of claims 1 to 5, characterized in that at least four optical waveguides (12), preferably at least eight optical waveguides (12) around the circumference of the mold (2) are arranged around, each having a temperature profile (T (h )) above the height (h) of the mold (2). 7. The method according to any one of claims 1 to 6, characterized in that each optical waveguide (12) over the height extent of the mold (2) detects at least 5, preferably at least 20, temperature readings. 8. The method according to any one of claims 1 to 7, characterized in that as a predetermined height (h _So ii) for the liquid metal (4) in the mold (2) a range is set, which at a defined distance from the upper edge of the mold (2), wherein for the desired range, preferably a distance (x) from the upper edge of the mold (2) between 90 and 1 10 mm is specified. 9. The method according to claim 8, characterized in that the second controller (1 1) no deviation is reported, as long as for the actual height (h | _St ) of the liquid metal (4) a value is determined, which is in the predetermined range lies. 10. The method according to any one of claims 1 to 9, characterized in that the first controller (10) and the second controller (1 1) are designed so that the adjustment of the volume flow (V) is faster than the adjustment of the height (h ) of the liquid metal (4) in the mold (2).