KR20240055000A - Method and device for controlling a strand casting system - Google Patents

Abstract

The invention relates to a method for regulating a strand casting system, the strand casting system comprising a mold (1) and a strand guide (8) downstream of the mold (1), wherein - liquid metal (3) This is cast into the mold 1, in particular via the feeder device 4, and the metal strand 7 is extracted from the mold 1 using spaced apart rollers 8b of the strand guide 8. - a measurement variable that is correlated to the variation of the casting level formed in the mold is determined, said measurement variable being processed through the involvement of at least one calculation specification and used to reduce the variation of the casting level (9) , - In order to reduce fluctuations in the casting level, the mutual spacing of the opposing rollers 8b of the strand guide is adjusted, specifically in directions opposite to the fluctuations in the casting level 9, of the strand guide 8. By periodically changing the spacing of the opposing rollers 8b, which is periodically changed - the frequencies of the fluctuations of the casting level 9 are detected and based on this the setpoint value of the spacing of the rollers 8b ( At least one observer 25 is provided for determining a compensation value k' for SET), wherein the actual value of the roller spacing ACT is determined by determining the phase shift and/or amplitude of the actual value of the roller spacing ACT. To compensate, it is used as one of the input variables to the observer 25.

Description

Method and device for controlling a strand casting system

The present invention relates to a method for controlling a strand casting plant,

- The strand casting plant includes a mold and a strand guide downstream of the mold,

- In particular, liquid metal is poured into the mold through an inflow unit, which solidifies on the walls of the mold, resulting in a solidified strand shell and a metal strand with a still liquid core. formed,

- the metal strand is pulled out of the mold by rollers of the strand guides arranged spaced apart,

A measurement variable that is correlated with the variation of the casting level formed in the mold is determined, and this measurement variable is processed through the integration of at least one calculation rule and used to reduce the variation of the casting level,

- the mutual spacing of the opposing rollers of the strand guide is periodically adjusted before the point of complete solidification in order to reduce fluctuations in the casting level, i.e. the periodicity of the roller spacing of the opposing rollers of the strand guide is opposed to fluctuations in the casting level. changed by change,

- The frequencies of the fluctuations of the casting level are detected and, based on these frequencies, provided at least one observer that determines a compensation value for the target value of the roller spacing of the rollers.

The invention also includes corresponding devices.

The method can be used in continuous strand casting. In general, the method can be advantageously applied in all strand casting methods with high casting speeds, since highly dynamic regulation/control of the casting level is increasingly required here. The term “strand casting” includes the casting of slabs and strips, in particular the casting of thin slabs, for example in a direct combination, ie in a combination of a strand casting plant with a hot rolling mill.

In continuous strand casting, it is generally very important that the casting level variations are within the narrow tolerances required from the metallurgical regime for the formation of a uniform, crack-free strand shell and a homogeneous, defect-free slab. Because of the various phenomena that affect casting level, adjustments are necessary to keep it constant. These phenomena include:

1. Transient flows into the mold through the inlet unit:

- detaching and flushing with or without blockage of the immersion pipe, blockage of the inlet unit, which can be designed as a plug or slide,

- Variations in the amount of flushing gas (in the case of blockages, argon is usually injected into the center of the blockage, creating an overpressure in the immersion pipe (preventing the aspiration of air), which causes turbulence in the steel bath in the mold. may cause),

- Distributor weight fluctuations caused, for example, by non-ideal regulation of the inflow of the ladle in the distributor (distributor = intermediate vessel between ladle and mold). Due to these pressure changes, different flow rates are produced through the same plug opening, which must be compensated for by regulation.

- Changes in viscosity of steel, for example in the case of ladle changes.

2. Change in the volume of liquid steel in the mold:

- Change in mold format

- Change the casting level target value (e.g. to reduce the appearance of wear on the immersion pipe)

3. Transient flows out of the mold:

- Bulging

- Casting speed changes

- Curved rollers

- Intentional changes in casting gap (e.g. soft reduction)

All of these listed phenomena result in changes in casting level and these changes must be counteracted. Because many of the phenomena occur very suddenly and unexpectedly, the dynamic range of regulation plays a very large role.

In the case of special steel qualities, for example peritectic steels or ferritic rustproof steels, irregularly occurring rises and falls (= cyclic) of the bath level during the continuous strand casting procedure. Occurring increasingly, this is known as “bulging” or “mold level hunting”. During bulging, a determinable relationship can be established between casting level movements and measured variables that are correlated with bulging. This periodically occurring feature of disturbance occurs at a periodic duration that approximately corresponds to the average roller division (i.e. the spacing of the rollers in the direction of transport of the strand) of at least one region of the strand guide for a particular casting speed. It means doing it. Bulging occurs to a certain extent in strand casting plants where the roller splitting in the strand guide is constant over long sections (i.e. a number of successive rollers in the direction of transport of the strand are equally spaced with respect to each other). In addition to fundamental waves, harmonics also occur. It was possible to establish that bulging only occurs above a critical casting speed to be determined empirically, which ultimately depends on the equipment used and on the mode of operation. However, limiting the casting speed is not acceptable in view of the continued trend towards capacity increases. For example, in the casting of thin slabs in direct assembly, typical casting speeds are up to 6 m/min or more.

Bulging leads to irregular thickness of the strand shell, which can be particularly problematic in the casting of thin slabs in direct assembly due to the smaller thickness of the cast strand compared to the cast slab and high casting speeds.

Control of the casting level by setting the inlet unit of the mold has only a low dynamic range, see for example WO 2007/042170 A1, where the power consumption measurements of the rollers of the strand guide feeding the strand casting mould. It is used to set the amount of lecture. It is therefore impossible, for example, to cancel out frequencies above 0.6 Hz, which occur in continuous strand casting at speeds above 2 m/min and cause irregularities in the steel product and thus deteriorate its quality. This problem of “high-frequency bulging”, i.e. bulging compensation of bulging at frequencies above 0.6 Hz, is solved, for example, by WO 2018/108652 A1.

Accordingly, WO 2018/108652 A1 is a result of the periodically opposing movements - at relatively low frequencies - of the inlet unit, as well as the periodic - at relatively high frequencies - of the roller spacing of the rollers of the strand guide. We propose a method as mentioned in the introduction to reduce fluctuations in casting level as a result of opposing changes.

Using a compensation value determined in the process for the roller spacing of the rollers of the strand guide, if this compensation value is supplied to the adjustment device of the rollers, the full range of expected reduction of fluctuations in the casting level often cannot be achieved. It turns out.

It is therefore the object of the present invention to overcome the shortcomings of the prior art and to propose a method for regulating a strand casting plant, by which fluctuations in the casting level above 0.6 Hz can be better reduced.

This object is achieved according to the invention by a method for regulating a strand casting plant as claimed in claim 1,

- The strand casting plant includes a mold and a strand guide downstream of the mold,

- liquid metal is poured into the mold, in particular through an inlet unit, which solidifies on the walls of the mold, resulting in the formation of a solidified strand shell and a metal strand with a still liquid core,

- the metal strand is pulled out of the mold by rollers of the strand guides arranged spaced apart,

A measurement variable that is correlated with the variation of the casting level formed in the mold is determined, and this measurement variable is processed through the integration of at least one calculation rule and used to reduce the variation of the casting level,

- the mutual spacing of the opposing rollers of the strand guide is periodically adjusted before the point of complete solidification in order to reduce fluctuations in the casting level, i.e. the periodicity of the roller spacing of the opposing rollers of the strand guide is opposed to fluctuations in the casting level. changed by change,

- The frequencies of the fluctuations of the casting level are detected and, based on these frequencies, provided at least one observer that determines a compensation value for the target value of the roller spacing of the rollers.

In this case, it is stipulated that the actual value of the roller spacing is used as one of the input variables to this observer, in order to compensate for the phase shift and/or amplitude of the actual value of the roller spacing.

Therefore, in principle, the movement to adjust the fluctuations is realized according to a calculation rule by means of adjusted rollers of the strand guide. The mutual spacing of the opposing rollers between which the strand is guided has a direct effect on the liquid core of the strand and directly changes the casting level, and variations in the casting level are immediately corrected. Therefore, more accurate and dynamic control of the casting level is possible. Smaller variations in casting level ultimately realize an improvement in the quality of the strand and/or slab final product, for example reduction of inclusions or prevention of cracks. Accordingly, in-phase oscillations with higher frequencies can also be generated by changes in roller spacing. In contrast, the movement of the inlet unit, which determines the amount of liquid metal entering the mold, is transmitted more slowly to the casting level because when the position of the inlet unit changes, the liquid metal positioned below the inlet unit still flows into the mold. Because. Therefore, an in-phase change of the position of the incoming unit can only be achieved at lower frequencies using the incoming unit and/or only a lower regulator quality can be achieved by this additional dynamic range, which cannot be canceled out.

According to the invention, control and/or regulation of the casting level can be achieved by varying the mutual spacing of opposing rollers. The strand is positioned between opposing rollers. The method requires only adjustable rollers arranged before the point of complete solidification. A fully solidified point is a location where the core of the strand or slab, when viewed along the strand guide, is already solid. Adjustment or control of the casting level is possible before complete solidification, but only if the strand or slab is still liquid in the core. The rollers, whose mutual spacing is varied to reduce variations in casting level, may, but need not, be the rollers driven to withdraw the metal strand from the mold.

The mutual spacing of the opposing rollers of the strand guide is periodically varied according to the invention. “Periodically varied” means that opposing rollers periodically change their mutual spacing with respect to each other.

In this case, the method according to the invention can be used as a single method of regulation and/or control of the casting level (in combination with flow rate regulation of the inlet unit) or as another adjustment and/or control of the casting level by the inlet unit. It can also be used in combination with control methods. In case of a combination of adjustment and/or control methods, the individual adjustment and/or control methods may be operated independently of each other.

Although the method of WO 2018/108652 A1 is most of the time sufficient to achieve in-phase reduction of vibrations with higher frequencies, models in which the behavior of the strand casting plant, i.e. the steering device relative to the rollers, are stored in the observer There are operating situations that deviate from . The regulating device then fails to operate in phase or with the intended amplitude. The reasons for this are, for example, wear of the mechanical and/or hydraulic components of the adjustment device, changes in the strand thickness or steel properties, friction in the mechanical parts of the adjustment device or in the hydraulic cylinder and friction in the adjustment device. Thermal deformation in the components of For example, changes in the strand width, i.e. the width of the thin slab, may also lead to deviations from the models, since in order to obtain the same strand thickness, as the width increases, the hydraulic cylinder of the adjustment device must be adjusted. This is because the pressure within the field must increase.

In order to be able to achieve good compensation of especially high-frequency casting level fluctuations also in these operating situations, the actual value of the roller spacing is taken into account in the calculation of the compensation value for the roller spacing. The necessary compensation values for this unpredictable operating situation are then generated so that the high-frequency casting level fluctuations are nevertheless compensated to the greatest extent possible.

In particular, if the bulging is (also) to be canceled, the periodic changes can be in a frequency range of at most 0.6 Hz or higher, preferably at most 5 Hz. Accordingly, changes in roller spacing can also occur at frequencies above 0.6 Hz, in particular up to 5 Hz.

Thus, for example, if only the regulation and/or control method acting on the rollers is applied, the periodic changes in the roller spacing may vary from 0 to 0.6 Hz, from 0 to 1 Hz, from 0 to 2 Hz. , may be within a frequency range of 0 to 3 Hz, 0 to 4 Hz, or 0 to 5 Hz. If the regulation and/or control method according to the invention for reducing fluctuations in the casting level is combined with other regulation and/or control methods for reducing fluctuations in the casting level, the other method or methods may therefore be (e.g. lower frequency ranges can be covered (e.g. 0 to 0.6 Hz), while the method according to the invention can cover lower frequency ranges (e.g. 0.6 to 1 Hz, 0.6 to 2 Hz, 0.6 to 3 Hz). It only covers the higher frequency range (from 0.6 to 4 Hz, or from 0.6 to 5 Hz).

In a further preferred embodiment variant of the method according to the invention, it is provided that a plurality of roller segments, each having one or more rollers, are arranged on both sides (i.e. opposite each other in relation to the strand) along the strand guide. , where at least one roller segment is adjusted perpendicularly with respect to the strand guiding direction. The term roller segments also includes so-called grids, which are typically arranged directly beneath the mold. “Perpendicularly with respect to the strand guidance direction” means any adjustment extending essentially perpendicularly with respect to the strand guidance direction. This includes both rotation and also parallel displacement of the roller segments. The strand guide is generally divided along the strand guide direction into a number of segments, each segment comprising two opposing roller segments.

Roller segments arranged close to the mold are advantageously adjusted. Accordingly, it can be provided that at least one roller segment of the first segment is adjusted. Accordingly, it can be stipulated that the uppermost roller segment, ie the roller segment located closest to the mould, is adjusted. Maximum amplification of the directly engaged actuators allows for the highest dynamic range. The factor associated with changing the roller spacing in the uppermost segment and its effect on the casting level is typically approximately 1:10 to 1:13 (swivelable segments) or 1:20 (segments moving in parallel). This means that a lowering of the casting level in the mold of about 1 mm to 1.3 mm or 2 mm, respectively, is realized by an increase in the roller spacing by 0.1 mm. In this way, only very small changes in roller spacing are needed, which can be realized in a very short time to compensate for high frequencies of bulging of up to 5 Hz.

Due to the selective adjustment of the individual roller segments, each with a plurality of rollers perpendicular to the strand guiding direction, the spacing between the rollers located opposite each other is reduced against the fluctuations of the casting level, thereby reducing the variation of the casting level. cancel out the frequencies. Due to this compensation, the stability of continuous strand casting is greatly increased and high casting speeds are possible with uniform quality of the steel product.

According to one preferred embodiment variant of the method according to the invention, it is provided that at least one roller segment is pivoted. In this case, the pivot axis is preferably closer to the mold, with the result that the parts of the roller segments that are further away from the mold are deflected more strongly. The outer roller segment, ie the roller segment on the outwardly curved side of the strand guide, can in this case be stationary, for example it can be realized by a stationary outer frame. The opposing roller segment, ie the roller segment on the inwardly curved side of the strand guide, is pivoted. It has for this purpose, for example, an internal frame carrying rollers and pivotably mounted. It would also be conceivable for the inner roller segment to be fixedly attached and the outer roller segment to be pivotable with respect to the inner roller segment.

Particularly good results in compensation of casting level fluctuations can be achieved if a number of roller segments, each with one or more rollers, are arranged on both sides along the strand guide, wherein at least the inner roller segment, which is located closest to the mold, This roller segment, which is located closest to the mold, is pivoted perpendicularly with respect to the strand guidance direction about the axis of rotation of the roller. Thanks to the short distance from the mold, the rotation of the topmost roller segment affects the casting level particularly quickly.

Instead of turning the roller segments, at least one roller segment is adjusted in parallel alignment with respect to the opposing roller segment arranged along the strand guide, thereby providing selective control of the individual roller segments and the roller spacing between the rollers. It can be stipulated that adaptation becomes possible again. The outer roller segment, ie the roller segment on the outwardly curved side of the strand guide, can in this case be stationary, for example it can be realized by a stationary outer frame. The opposing roller segment, ie the roller segment on the inwardly curved side of the strand guide, is then translated translationally in the direction of the outer roller segment. Here, on the contrary, it would also be conceivable for the inner roller segment to be fixed, while the opposing outer roller segment is translationally displaced.

The volume of liquid metal in the core of the strand can be determined by the spacing of the rollers of the two opposing roller segments and thus inferences can be drawn regarding relative casting level changes.

According to one particularly preferred embodiment variant of the method according to the invention, at least one roller segment is moved by means of an adjustment device comprising at least one hydraulic or electromechanical actuator (for example a hydraulic cylinder or an electric spindle drive). It is adjusted. In order to enable an optimal response time for setting the roller gap with respect to casting level variations, it is desirable to use a proportional valve for at least one hydraulic cylinder.

One embodiment of the invention provides that the frequencies of fluctuations of the casting level in the frequency range from 0 to 5 Hz are detected and that the fluctuations are canceled by periodic opposing changes in the roller spacing of the rollers of the strand guide. Therefore, in this embodiment variant, there is no cancellation of variations in casting level by the inlet unit to the mold.

An alternative embodiment of the present invention provides:

- the frequencies of fluctuations of the casting level in a first frequency range are detected and the fluctuations are canceled by periodic counter movements of the inlet unit (of the mold), additional frequencies of fluctuations of the casting level in a second frequency range are detected and the strand The fluctuations are canceled out by periodic opposing changes in the roller spacing of the rollers of the guide, wherein the second frequency range is greater than the first frequency range,

- a first observer is provided that determines a first compensation value for the target position of the incoming unit based on the frequencies of the first frequency range,

- a second observer is provided which determines a second compensation value for the target value of the roller spacing of the rollers of the strand guide based on the frequencies of the second frequency range, where the actual value of the roller spacing is determined for this second observer. Used as one of the input variables.

This embodiment variant is such that, as already mentioned before according to the prior art, the lower frequency fluctuations of the casting level can be canceled out by adjusting the inlet unit of the mold, while the higher frequency fluctuations of the casting level This only has the advantage of being offset by adjustment of the spacing of the rollers. Therefore, there is the possibility of retrofitting existing regulators for lower frequency variations using an additional regulator of the spacing of the rollers.

In this case, adjustments to the inlet unit and/or to the roller spacing can be implemented with the help of so-called observers, as disclosed in AT 518461 A1. According to the control technique, the observer detects unmeasurable variables (states) from known input variables (e.g. manipulated variables or measurable disturbance variables) and output variables (measured variables) of the observed reference system. It is understood as a system that reconstructs For this purpose, it simulates the observed reference system as a model and uses regulators to track measurable state variables, so that the measurable state variables are comparable to the reference system. Accordingly, the model is prevented from generating errors that increase over time.

A method variant with two frequency ranges preferably includes a first observer determining a first compensation value for the target position of the incoming unit based on frequencies in the first frequency range, and a first observer determining a first compensation value for the target position of the incoming unit based on frequencies in the first frequency range. a second observer determining a second compensation value for the target value of the roller spacing of the rollers of the strand guide on the basis of which the actual value of the roller spacing is one of the input variables for this second observer according to the invention. It is simply used as.

In this way, the casting level in the mold is controlled not only by the introduction into the mold, but also by the guidance of the metal strand, preferably in the uppermost segment behind the mold. Furthermore, due to the separation of the observer onto the various actuators (on the one hand, a first compensation value for the target position of the inlet unit in the case of the first observer, on the other hand, for the roller spacing of the rollers of the strand guide) second compensation value), it is advantageous that no interference between the observers and/or no negative influence of the observers on each other can occur.

In one particularly preferred embodiment variant of the method with two frequency ranges, the first observer operates in the frequency range below 0.6 Hz and the second observer operates at frequencies above 0.6 Hz, preferably between 0.6 and 5 Hz. It operates within a range. The advantage arises due to the separated frequency ranges of the two observers that no interference can occur between the observers due to the overlap of the frequency windows, whereby, for example, the target value for the actuator of the casting level adjustment is It remains the same (if there is no bulge) or smaller than if there is no secondary compensation. In this way, casting level fluctuations are further reduced and quality losses in the steel product are greatly reduced. Due to the use of the method according to the invention, high casting speeds can be used with high quality steel products, thereby increasing the productivity of plants for continuous strand casting, especially for the production of continuous thin slabs of direct combination. increases considerably.

One possible device for carrying out the method according to the invention comprises means for introducing the metal melt into the mold, a strand guide comprising rollers and a measuring unit for measuring fluctuations in the casting level, connected to a control unit. Includes. In this case, an adjusting device is provided, connected to the control unit, to reduce fluctuations in the casting level of the opposing rollers of the strand guide by periodic changes in the roller spacing, which oppose the fluctuations in the casting level, in particular offset. wherein the control unit comprises at least one observer designed in such a way that, based on the frequencies of the fluctuations of the casting level, a compensation value for the target value of the roller spacing of the rollers is determined, and the actual roller spacing of the rollers is determined. The value is used as one of the input variables to this observer to compensate for the phase shift and/or amplitude of the actual value of the roller spacing.

As already mentioned in connection with the method, it can be stipulated that the adjustment device is designed for periodic changes in the roller spacing in the frequency range of at most 0.6 Hz and above, preferably at most 5 Hz. The adjustment device may comprise at least one hydraulic or electromechanical actuator, such as a hydraulic cylinder or an electric spindle drive. Of course, the adjustment device can also use, for example, hydraulic or electromechanical actuators, such as hydraulic cylinders or electric spindle drives, for periodic changes in the roller spacing in the frequency range from 0 Hz, preferably up to 5 Hz. can be designed.

As already mentioned in connection with the method, it can be provided that a number of roller segments, each with one or more rollers, are arranged on both sides along the strand guide, where at least one roller segment is adjusted by means of an adjustment device. It is vertically adjustable with respect to the strand guidance direction.

For example, at least one roller segment may be adjustable at the top, ie first segment. In this case, at least one roller segment may be pivotable; Alternatively, the at least one roller segment is adjustable and aligned in parallel with respect to an opposing roller segment arranged along the strand guide. The roller segments are preferably adjusted in such a way that no sharp segment transitions (=thickness changes) occur, which is referred to as the “linked method”.

An embodiment is preferred in which a number of roller segments, each with one or more rollers, are arranged on both sides along the strand guide, wherein at least the inner roller segment located closest to the mold has a roller of this roller segment located closest to the mold. It is possible to pivot vertically with respect to the strand guidance direction by means of an adjustment device around its axis of rotation.

According to a method variant with two frequency ranges, one variant of the device according to the invention is such that the frequencies of fluctuations of the casting level within a first frequency range are detectable by the measuring unit, and these fluctuations are detected by the inlet unit of the mold. can be canceled out by periodic opposing movements of Can be offset by an opposite change, where the second frequency range is greater than the first frequency range.

This may again be carried out, for example, by the first and/or second observer. The second observer contains the same components as the first observer and functions similarly, but is not an entry unit to the mold, but rather provides a second compensation value for an adjustment device located in the strand guide - preferably its uppermost segment. There is a difference in being explicit.

The method according to the invention or the device according to the invention is applicable to existing strand casting plants with the requirements mentioned above and leads to a significantly higher casting speed and thus a significant improvement in the quality of continuously cast steel with increased productivity. represents. This new type of casting level adjustment even occurs when unexpected operating situations arise, for example as a result of wear or deformation of the adjustment device on the rollers, or simply unwanted changes in strand thickness or steel properties. , it becomes possible to suppress highly dynamic effects, for example by highly dynamic bulging at frequencies greater than 0.6 Hz.

The present invention will be explained in more detail based on exemplary embodiments. The drawings are exemplary and will illustrate the inventive concept, but will not limit the inventive concept in any way or even exhaustively reproduce the inventive concept. In the drawings:
1 shows a schematic diagram of part of a strand casting plant according to the invention,
Figure 2 shows a schematic diagram of a strand guide according to the invention;
3 shows a schematic configuration of a control unit of the prior art;
Figure 4 shows details of the first observer from Figure 3;
Figure 5 schematically shows a monitoring loop according to the invention comprising a first observer and a second observer;
Figure 6 shows time curves of various variables during regulation of the strand casting plant;
Figure 7 shows the time curves of roller spacing and casting level when the roller spacing is not changed;
Figure 8 shows the time curve of roller spacing and casting level when the roller spacing keeps the casting level ideally constant;
Figure 9 shows the time curves of roller spacing and casting level when the roller spacing shows abnormal behavior;
Figure 10 shows time curves of roller spacing and casting level when the abnormal behavior of the roller spacing is ideally canceled out.

According to Figure 1, the strand casting plant comprises a mold (1). Liquid metal 3 is poured into mold 1 through an immersion pipe 2, for example molten steel or liquid aluminum. The inflow of liquid metal 3 into the mold 1 is established by the inlet unit 4. The design of the inlet unit 4 as a closure plug is illustrated in FIG. 1 . In this case, the position p of the inlet unit 4 corresponds to the stroke position of the closing plug. Alternatively, the inlet unit 4 can be designed as a slide. In this case, the closed position (p) corresponds to the slide position.

The liquid metal 3 placed in the mold is cooled by cooling units (not shown), so that it solidifies on the walls 1a of the mold 1 and thus forms a strand shell. However, the core 6 is still liquid. It only solidifies later. Strand shell 5 and core 6 together form metal strand 7. The metal strand (7) is supported by the strand guide (8) and drawn out of the mold (9). The strand guide (8) is downstream of the mold (1). It comprises a number of roller segments 8a, which in turn contain rollers 8b. In Figure 1 only a few of the roller segments 8a and rollers 8b are shown. The metal strand 7 is pulled out of the mold 1 by rollers 8b at a withdrawal speed v.

Liquid metal (3) forms a casting level (9) in mold (1). The casting level (9) should be kept as constant as possible. Thus - in the prior art but also in this embodiment variant of the invention - the position p of the inlet unit 4 is tracked and, correspondingly, sets the inflow of the liquid metal 3 into the mold 1. do. The height h of the casting level 9 is detected by means of a measuring unit 10 (known per se). The height h is supplied to the control unit 11 of the strand casting plant. The control unit 11 determines the operating variable S for the inlet unit 4 according to the regulation method, which is explained in more detail below. The inlet unit 4 is then correspondingly activated by the control unit 11 . In general, the control unit 11 outputs the manipulated variable S to the adjustment unit 12 for the inlet unit 4 . The adjustment unit 12 may be, for example, a hydraulic cylinder unit. The frequencies of bulging after molding are detected metrologically and/or determined according to f = v _c /p _Roll *n, where v _c corresponds to the withdrawal speed of the strand, f corresponds to the bulging frequency, and n Corresponds to the number of harmonic frequencies (1, 2, etc.), and p _Roll corresponds to the roller spacings.

The roller spacings corresponding to the strand thickness d shown can be intentionally adapted by means of the pivot axis 23 and/or the adjustment device 24 . This means, as shown here in FIG. 1 , an external frame to which at least one roller segment 8a is fixed in a first segment, for example the roller segment 8a here located on the left just below the mold 1 . This may occur because it is included. The opposing roller segments 8a, and/or the internal frame supporting them, are pivotable about a pivot axis 23 which extends perpendicularly with respect to the plane of the drawing. The pivot axis 23 can coincide with the axis of rotation of the roller 8b, here the axis of rotation of the upper roller 8b, but can of course also be provided at other points. Due to the turning, the roller spacing in the lower roller pair of the uppermost roller segment 8a in Figure 1 changes, while the roller spacing in the upper roller pair remains the same. This is not disadvantageous, since the change in roller spacing resulting from the method according to the invention is generally only in the range of several tens of millimeters and at most 2 mm.

Possible guide rollers that are directly connected to the mold and are arranged above the uppermost roller segment 8a shown here are not shown in FIG. 1 . However, these guide rollers are generally not vertically adjustable with respect to each other and with respect to the strand guiding direction.

Instead of pivoting, the upper left roller segment 8a, i.e. its outer frame, can be fixed and the upper right roller segment 8a, i.e. its inner frame, for example, can be fixed to the left roller segment. It can be displaced perpendicularly and parallel to the strand guidance direction towards (8a) and away from it. Accordingly, the roller spacing of all roller pairs changes in each case by the same absolute value. This can also be carried out using one or more hydraulic cylinders (distributed along the strand width and/or along the strand guidance direction).

In FIG. 2 , only one strand guide 8 is shown which can replace the strand guide 8 of FIG. 1 or - after the uppermost segment - also supplement it. In Figure 2, in each of the three illustrated segments, each roller segment 8a has three rollers 8b on each side. However, there may also be more rollers 8b than just two or three per roller segment 8a. Continuing with Figure 1, the fixed strand shell 5 and the liquid core 6 of the strand are illustrated here up to the point of complete solidification D. Accordingly, adjustment devices 24 are also provided in all segments 8a up to the point of complete solidification D. The adjustment devices 24 can adjust each of the roller segments 8a by rotation or by parallel displacement, as already explained in FIG. 1 . In this example, the inner roller segment 8a of the first (uppermost) segment is adjusted by pivoting around the pivot axis 23, and the inner roller segment 8a of the second segment is adjusted by means of two adjustment devices ( 24) is adjusted by the parallel displacement. The connection of the coordination devices 24 to the control unit 11 is not shown here.

The control unit 11 implements, inter alia, a casting level regulator 13 - see Figure 3. The height h of the casting level 9 is supplied to the casting level regulator 13. Furthermore, the target value h* for the height h of the casting level 9 is supplied to the casting level regulator 13. Furthermore, additional signals are supplied to the casting level regulator 13. Additional signals may be, for example, the width and thickness of the cast metal strand 7 (or more generally, the cross-section of the metal strand 7), the withdrawal speed v (or its target value), and others. It can be. The casting level regulator 13 then determines, in particular, a preliminary target position p'* for the inlet unit 4 based on the deviation of the height h of the casting level 9 from the target value h*. do. The casting level regulator 13 may use additional signals for its parameterization and/or for determining the pilot control signal pV.

Furthermore, the control unit 11 implements the first observer 14 . The height h of the casting level 9 and its target value h*, additional signals for the inlet unit 4 and the final target position p* are supplied to the first observer 14. The first observer 14 determines the first compensation value k. The first compensation value (k) is added to the preliminary target position (p'*) and thus the final target position (p*) is determined. The manipulated variable S - with which the inflow unit 4 is activated - is then determined based on the deviation of the actual setting p from the final target position p*. Typically, the control unit 11 implements a lower-order position regulator (not shown) for this purpose.

For the sake of good order, it should be emphasized once again that the first and second observers 14 , 25 are not people, but rather functional blocks implemented in the control unit 11 .

The difference between the preliminary target position (p'*) and the final target position (p*) corresponds to the first compensation value (k) determined by the first observer (14). The first compensation value k is determined by the first observer 14 and, therefore, instead of the final target position p*, since it is known to the first observer 14, the preliminary target position p'* ) may also be provided as the first observer 14. Due to the situation where the first compensation value k is known to the first observer 14, the first observer 14 can therefore easily determine the final target position p* from the preliminary target position p'*. there is. Accordingly, the tapping point 15 at which the (preliminary or final) target position p'*, p* is tapped is, as required, the first compensation value k at the preliminary target position p'*. It may be positioned before or after the node point 16 being added. The tapping point 15 should be located before the node point 16' to which the pilot control signal pV is added.

The first observer 14 includes a decision block 17 . The height h of the casting level 9, additional signals and the final target position p* are supplied to the decision block 17. Decision block 17 contains a model of a strand casting plant. By means of the model, the decision block 17 determines the expected height for the casting level 9 (i.e. calculated via model support) based on the additional signals and the final target position p*. Based on the expected height, decision block 17 then determines the expected variation value δh (i.e. calculated with model support) for the height h of the casting level 9, i.e. the short-term variation. Decide. For example, the decision block 17 can perform averaging of the heights h of the casting levels 9 and subtract the resulting average value from the expected height. Therefore, the determined variation value δh reflects the expected variation in the height h of the casting level 9. Based on the variation value δh, decision block 17 then determines the first compensation value k.

The procedure previously described in connection with Figure 3 corresponds to the procedure of the prior art. It is also used in this embodiment variant of the invention. The first observer 14 with decision block 17 is illustrated once again in FIG. 4 . However, within the scope of the invention, the decision block 17 is only one of a number of components of the first observer 14 according to the example of FIG. 4 . Thus, for example, the first observer 14 additionally includes a first analysis element 18 . The variation value δh is supplied to the first analysis element 18 . The first analysis element 18 determines therefrom the frequency components of the variation value δh. Additionally, a second analysis element 19 is preferably also provided. The secondary signal (Z) is supplied to the second analysis element (19). The second analysis element 19 determines therefrom the frequency components of the secondary signal Z.

The secondary signal Z may be the pulling force F, with which the metal strand 7 is pulled out of the mold 1 by the rollers 8b of the strand guide 8. The pull-out force (F) is oriented parallel to the pull-out speed (v). Alternatively, it could be the retrieval rate (v) itself. These two alternatives are preferred. However, it is also possible to use as secondary signal Z a force signal F', for example applied to (at least) one of the roller segments 8a of the strand guide 8. The direction with which the force signal (F') is related is orthogonal to the withdrawal velocity (v). The secondary signal Z may again alternatively be the local strand thickness d measured by measuring unit 21 (see Figure 1) in the strand guide 8. The first analysis element 18 supplies the frequency components determined by it to the selection element 22. If provided, this also applies in a similar way to the second analysis element 19 . The selection element 22 determines, in conjunction with the fetch rate v, the associated wavelengths corresponding to the frequency components of the variation value δh and possibly also of the secondary signal Z. The withdrawal speed v is supplied for this purpose to the first observer 14 and to the selection element 22 in the first observer 14 . The selection element 22 determines wavelengths for which the associated frequency component of the variation value δh and possibly also the associated frequency component of the secondary signal Z is greater than the threshold values S1, S2. The individual threshold values S1, S2 can be defined separately, on the one hand, for the frequency components of the variation value δh and, on the other hand, for the frequency components of the secondary signal Z. . These wavelengths are preselected by selection element 22. Within the ranges of preselected wavelengths of the variation value δh, each of which is itself coherent, the selection element 22 then determines the range at which the individual frequency component of the variation value δh assumes a maximum. Determine the wavelengths (λi(i = 1, 2, 3,...)). The number of wavelengths λi is not limited. The selection element 22 (finally) selects these wavelengths λi. The selection element 22 supplies the selected wavelengths λi to the decision block 17. The decision block 17 performs filtering of the height h of the casting level 9 and the final target position p* for the wavelengths λi selected by the selection element 22. The decision block 17 determines the first compensation value k based solely on the filtered height h of the casting level 9 and the filtered final target position p*. The decision block 17 leaves the height h of the casting level 9 and other frequency components of the final target position p* not taken into account within the scope of the determination of the first compensation value k. Furthermore, predetermined wavelength ranges may be specified to the selection element 22. In this case, predetermined wavelength ranges represent additional selection criteria. In particular, the wavelengths at which the associated frequency component of the variation value δh and possibly also the associated frequency component of the secondary signal Z exceed the respective threshold values S1, S2, if they are additionally within one of the predetermined wavelength ranges. Selected only if present. Otherwise, they are not selected even if the associated frequency component of the variation value δh and perhaps also the associated frequency component of the secondary signal Z are greater than the respective threshold values S1, S2.

As already mentioned, the second observer 25 comprises the same components as the first observer 14 and analyzes the frequencies of bulging after the mold 1 and determines a second compensation value for the adjustment device 24 (k'), that is, specifies the compensation value for the target value (SET) of the roller spacing. This target value (SET) is generally a static target value corresponding to the desired strand thickness. A monitoring loop comprising first and second observers 14, 25 is shown in Figure 5. The first observer 14 specifies a first compensation value k for the inlet unit 4 of the mold 1, by which the casting level 9 in the mold 1 is adjusted. Stated in simplified terms, the first observer 14 and the inlet unit 4 of the mold 1 together represent a standard system for regulating the casting level 9 of the mold 1, which It is used for compensation of frequencies within the 1 frequency range and thus represents a controller 27 for frequencies of the first frequency range. A second observer 25 connected to the adjustment device 24 represents the controller 26 for the frequencies of the second frequency range and specifies a second compensation value k'.

This second compensation value k' is supplied to the regulator 28 for roller adjustment, which outputs a manipulated signal 29 for the roller gap from the target value SET and the actual value ACT. Calculates and transmits this manipulated signal (29) to the regulating device (24). In addition, the actual value ACT is then also passed to the second observer 25, which takes this into account in the calculation of the second compensation value k'.

Instead of the first observer 14 controlling and/or regulating the inlet unit 4 of the mold 1, other adjustment methods may be provided.

It can also be provided that only a single adjustment method controls and/or regulates only the adjustment device 24 of the rollers 8b, while the inlet unit 4 of the mold 1 is used to adjust variations in the casting level. Not used at all. This single control method may be the second observer 25. In this case, the second observer 25 will generally cover a larger frequency range than in the case of both adjustment methods. This frequency range can then be, for example, frequencies from 0 to 0.6 Hz, 0 to 1 Hz, 0 to 2 Hz, 0 to 3 Hz, 0 to 4 Hz, or 0 to 5 Hz. It can be inclusive.

Figure 6 shows an example of suppression of periodic oscillations. Time (t) is plotted along the horizontal axis. The position of the inlet unit (4), written as "Pos (4)", is illustrated along the vertical axis in the first (top) example, and the casting level (9) in the mold (1), written as "M_L" in the second figure. ) is illustrated, and the river flow in the strand, recorded as "St_Fl" in the third figure, is illustrated. For better understanding, the regulation ("Comp") is still deactivated at the time (t = 0) and then switched on, which is the state ("0") for the disabled regulation and the state ("0") for the activated regulation. This is illustrated in the last figure with state (“1”). It is well recognizable in the first three examples that the position of the inlet unit 4 changes periodically, as well as the height of the casting level 9 and consequently the river flows out of the mold 1 . Here, by changing the position (“Pos(4)”) of the inlet unit (4), the periodic fluctuations of the casting level (“M_L”) are reduced along with the activation of the regulation. In the method according to the invention, additionally or alternatively to changing the position (“Pos(4)”) of the inlet unit (4), the mutual spacing of the rollers (8b) in the uppermost segment is periodically varied; Correspondingly, it will reduce fluctuations in casting level.

7 to 10 each contain two examples: the upper example shows the time curve of the casting level 9, which in this case ideally follows the horizontal center line. In the subexample, the dotted line shows the time curve of the actual value of the roller gap (ACT), the dashed line shows the time curve of the roller gap (EST) as pre-calculated by the model of the observer, , the solid line shows the time curve of the target value (SET) of the roller spacing corrected using the second compensation value (k'). The target value of roller spacing (SET) corresponds substantially to the desired strand thickness (d). A second compensation value k' is added to the target value and the resulting signal can then be used as a manipulated signal 29 for the roller spacing. Accordingly, the target value SET of the roller spacing is a static value over which the second compensation value k' decreases and increases, which varies, generally periodically, and is therefore generally also periodic. Accordingly, the signal resulting from the addition of the second compensation value k' to the static target value SET is, so to speak, the final target value.

Figure 7 shows the time curve of roller spacing and casting level 9 when the roller spacing is not changed. If the actual value of the roller spacing (ACT), the pre-calculated roller spacing (EST) and the final target value of the roller spacing remain constant, i.e. in particular any second compensation value (k') will not be applied to the static target value (SET). ), the casting level (9) periodically changes its height. Therefore, the adjustment device 24 here does not change the roller adjustment.

Figure 8 shows the time curve of roller spacing and casting level 9 when the roller spacing keeps the casting level 9 ideally constant. For this purpose, a second compensation value (k') added to the target value (SET) of the roller spacing has the same frequency as the unadjusted casting level (9) (Figure 7) and is generally equal to the casting level (9). must be changed with a corresponding phase shift in relation to, thus resulting in a common curve of the pre-calculated roller spacing (EST) and the actual value of the roller spacing (ACT), which is the second compensation value (k' ) has the same frequency as the added target value SET, but only the phase is shifted with respect to the added target value SET to the second compensation value k'. Therefore, the actual roller adjustment corresponds to the pre-calculated roller spacing (EST).

Figure 9 shows time curves of roller spacing and casting level when the actual roller spacing shows abnormal behavior. Despite the adjustment based on the target value SET plus the second compensation value k', periodic fluctuations in the casting level 9 occur. In other words, everything is done the same as in Figure 8 before, but the result is different because the rollers 8b behave unexpectedly. Therefore, Figure 9 shows the difference in both phase and amplitude between the actual value of the roller spacing (ACT) and the pre-calculated roller spacing (EST).

Figure 10 shows time curves of roller spacing and casting level when the abnormal behavior of the roller spacing from Figure 9 is ideally canceled out. As a result of the feedback of the actual value ACT to the second observer 25, the second observer 25 can adapt the second compensation value k' in such a way that this abnormal behavior is also canceled out. For this purpose, it is clear that the phase of the target value SET to which the second compensation value k' is added must be shifted relative to FIG. 9 so that the casting level 9 is ideally offset again.

Typical strand thicknesses (d) during thin slab casting are around 100 mm and typical casting speeds are between 2 and 6 m/min. The constant roller splitting over the relatively long portions of the strand guide in the transport direction is typically in the range of about 200 mm. The casting speed and roller splitting then yield the frequencies of the fundamental and harmonic waves of the oscillations of the casting level to be canceled by the method according to the invention and the device according to the invention.

1 mold
1a Mold walls
2 Immersion Pipe
3 liquid metal
4 inlet units
5 strand shell
6 cores
7 metal strands
8 strand guide
8a roller segments
8b rollers
9 casting levels
10 measuring units
11 control unit
12 adjustment units
13 Casting level regulator
14 1st observation period
15 tapping points
16, 16' node points
17 decision blocks
18, 19 analysis elements
20 temperature sensor
21 measuring units
22 selection elements
23 pivot axis
24 adjustment device
25 Second observation period
26 Controller for frequencies in the second frequency range
27 Controller for frequencies in the first frequency range
Regulator for adjusting 28 rollers
29 Manipulated signals for roller spacing
Actual value of ACT roller gap
D Full solidification point
d strand thickness
EST pre-calculated roller spacing
F withdrawal force
F' force signal
h Height of casting level
h* Target value for the height of the casting level
k first compensation value
k' second compensation value
p Position of inflow unit
p*, p'* target positions
pV pilot control signal
Manipulated variables for S inflow unit (4)
Target value of SET roller gap
S1, S2 thresholds
T-temperature
v withdrawal speed
Z secondary signal
δh fluctuation value

Claims (8)

A method for controlling a strand casting plant, comprising:
- the strand casting plant comprises a mold (1) and a strand guide (8) downstream of the mold (1),
- In particular, liquid metal 3 is poured into the mold 1 via an inflow unit 4, which solidifies on the walls 1a of the mold 1, resulting in solidification. A metal strand (7) is formed with a strand shell (5) and a still liquid core (6),
- the metal strand (7) is pulled out of the mold (1) by rollers (8b) of the strand guide (8) arranged spaced apart,
- a measurement variable correlated with the variation of the casting level formed in the mold is determined, the measurement variable being processed through the integration of at least one calculation rule and used to reduce the variation of the casting level 9 ,
- the mutual spacing of the opposing rollers 8b of the strand guide is periodically adjusted before the point of complete solidification D in order to reduce the fluctuations of the casting level, i.e. the opposing rollers of the strand guide 8 of the fields (8b) are varied by periodic changes in the roller spacing, as opposed to the variations of the casting level (9),
- the frequencies of the fluctuations of the casting level 9 are detected and, on the basis of these frequencies, a compensation value k' is determined for the target value SET of the roller spacing of the rollers 8b. At least one observer (25) is provided,
The actual value of the roller spacing (ACT) is used as one of the input variables to the observer 25 to compensate for the phase shift and/or amplitude of the actual value (ACT) of the roller spacing. felled,
Methods for regulating a strand casting plant. According to claim 1,
Said periodic changes are within a frequency range of at most 0.6 Hz or higher, preferably at most 5 Hz.
Methods for regulating a strand casting plant. According to claim 1 or 2,
A plurality of roller segments (8a) each having one or more rollers (8b) are arranged on both sides along the strand guide (8),
At least the inner roller segment (8a) located closest to the mold (1) is pivoted perpendicularly with respect to the strand guiding direction about the axis of rotation of the roller of the roller segment that is located closest to the mold (1). ,
Methods for regulating a strand casting plant. According to any one of claims 1 to 3,
The frequencies of the fluctuations of the casting level 9 in the frequency range from 0 to 5 Hz are detected, the fluctuations corresponding to periodic opposing changes in the roller spacing of the rollers 8b of the strand guide 8. offset by
Methods for regulating a strand casting plant. According to any one of claims 1 to 3,
- the frequencies of the fluctuations of the main level 9 in a first frequency range are detected and the fluctuations are canceled by periodic counter movements of the inlet unit 4, and the frequencies of the fluctuations of the main level 9 in a second frequency range are detected and the fluctuations of the main level 9 in a first frequency range are detected. Additional frequencies of the fluctuations are detected and canceled by periodic opposite changes in the roller spacing of the rollers 8b of the strand guide 8, the second frequency range being further than the first frequency range. big,
- a first observer (14) is provided, which determines a first compensation value (k) for the target position of the inflow unit (4) based on the frequencies of the first frequency range,
- a second observer (25) for determining a second compensation value (k') for the target value (SET) of the roller spacing of the rollers (8b) of the strand guide based on the frequencies of the second frequency range. ) is provided, and the actual value (ACT) of the roller spacing is used as one of the input variables for the second observer (25),
Methods for regulating a strand casting plant. The method according to any one of claims 1 to 5,
means for introducing the metal melt into the mold (1), a strand guide (8) comprising rollers (8b), a measuring unit (10) for measuring the variations in the casting level, which is connected to a control unit (11). It includes and is connected to the control unit 11,
to reduce the fluctuations of the casting level (9) by periodic changes of the roller spacing of the opposing rollers (8b) of the strand guide (8), as opposed to the fluctuations of the casting level, An adjustment device (24) designed to offset is provided,
The control unit 11 determines, based on the frequencies of fluctuations of the casting level 9, a compensation value k' for the target value SET of the roller spacing of the rollers 8b. at least one observer (25) designed in such a way, that the actual value (ACT) of the roller spacing is configured to compensate for the phase shift and/or amplitude of the actual value (ACT) of the roller spacing, used as one of the input variables for the observer 25,
Methods for regulating a strand casting plant. According to clause 6,
The adjustment device 24 is designed for periodic changes in the roller spacing in the frequency range of at most 0.6 Hz and above, preferably at most 5 Hz.
Methods for regulating a strand casting plant. According to claim 6 or 7,
A plurality of roller segments (8a) each having one or more rollers (8b) are arranged on both sides along the strand guide (8),
At least the inner roller segment 8a, which is located closest to the mold 1, is adjusted by the adjustment device 24 around the axis of rotation of the roller of the roller segment, which is located closest to the mold 1. Capable of turning vertically with respect to the guidance direction,
Methods for regulating a strand casting plant.