CN117858775A

CN117858775A - Method and device for controlling continuous casting system

Info

Publication number: CN117858775A
Application number: CN202280057896.XA
Authority: CN
Inventors: 菲利普·维泽尔; 维特·胡默; 约瑟夫·瓦特辛格
Original assignee: Primetals Technologies Austria GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2021-08-25
Filing date: 2022-08-19
Publication date: 2024-04-09
Also published as: KR20240055000A; EP4140616A1; WO2023025669A1

Abstract

The invention relates to a method for controlling a continuous casting installation, wherein the continuous casting installation has a mould (1) and a strand guide (8) downstream of the mould (1), wherein liquid metal (3) is cast into the mould (1), in particular by means of an inflow device (4), wherein a metal strand (7) is pulled out of the mould (1) by means of spaced-apart rollers (8 b) of the strand guide (8), wherein a measured variable which is dependent on fluctuations in the casting level formed in the mould is determined, which measured variable is processed in conjunction with at least one calculation rule and is considered to be reduced in terms of fluctuations in the casting level (9), wherein the relative spacing of the mutually opposing rollers (8 b) of the strand guide is periodically changed in order to reduce the fluctuations in the casting level, i.e. the fluctuations in the casting level (9) are counteracted by periodically changing the roller spacing of the mutually opposing rollers (8 b) of the strand guide, wherein the frequency of the fluctuations in the casting level (9) is detected and at least one observer (25) is provided, and wherein an actual value of the actual roll spacing (ACT) is determined as a compensation value for the actual roll spacing (ACT) based on the target value of the frequency observer (8 b).

Description

Method and device for controlling continuous casting system

Technical Field

The present invention relates to a method for adjusting a continuous casting installation,

wherein the continuous casting installation has a mould and a strand guide downstream of the mould,

wherein liquid metal is cast into a mold, in particular via an inflow device, the liquid metal solidifying on the walls of the mold, thereby forming a metal strand with a solidified strand shell and a still liquid inner core,

wherein the metal strand is pulled out of the mold by means of spaced-apart rollers of a strand guide,

wherein a measurement variable relating to the fluctuation of the casting level formed in the mould is determined, which is processed in connection with at least one calculation rule and which is used to reduce the fluctuation of the casting level,

wherein the relative distance between the mutually opposite rollers of the strand guide, i.e. the distance between the rollers of the strand guide opposite to each other, is periodically changed before the complete solidification point, in order to reduce fluctuations in the casting level,

wherein the frequency of the fluctuation of the casting level is detected and at least one observer is provided, which determines a compensation value for the target value of the roll spacing of the rolls on the basis of the frequency.

The invention also comprises corresponding devices.

The method can be used in continuous casting of billets. In general, this method can be used advantageously in all casting methods at high casting speeds, since the necessity of high dynamic control of the casting level is increased here. The term casting blank casting includes casting of slabs and strips, in particular thin slab casting, for example direct-connection thin slab casting, i.e. connecting a continuous casting installation to a hot rolling system.

Background

In continuous casting, from a metallurgical point of view, a fluctuation in the casting level within the desired narrow tolerance range is generally of importance for the formation of a uniform, crack-free shell and a homogeneous, defect-free slab. Since the phenomena affecting the casting level are various, adjustments are required to keep the casting level constant. These phenomena include:

1. transient solution entering the mold through the inflow:

plugs of inflow devices, plugs of dip tubes or detachment and flushing of these plugs which can be designed as plugs or slides,

a change in the amount of flushing gas (if a blockage occurs, argon is usually injected into the centre of the blockage to create an overpressure in the dip tube (preventing air from being sucked in), which can cause turbulence in the molten steel bath in the mould),

Fluctuations in dispenser weight, for example due to non-ideal adjustment of ladle inflow in the dispenser (dispenser = intermediate vessel between ladle and mould). By this pressure variation, different flow rates will be created under the same plug opening, adjustments must be made to counteract the different flow rates,

for example, the viscosity of the steel changes when the ladle is replaced.

2. Change in volume of liquid steel in mold:

dimensional changes in the mould and,

casting level target value variation (e.g. to reduce signs of wear on the dip tube).

3. Instantaneous solution from the mold:

-a casting block pump,

the casting speed is varied and the casting speed is varied,

a bending roller is provided,

expected variation of the casting gap (e.g., slight drop).

All these mentioned phenomena lead to variations in the casting level and these variations have to be counteracted. Since many phenomena occur very suddenly and unexpectedly, the dynamics of the regulation play a very important role.

During continuous casting, the bath level rises and falls irregularly (=periodically), known as "casting pumps" ("bulging", "level oscillations"), more commonly found in special steel qualities (e.g. peritectic steel or ferritic stainless steel). In a casting pump, the correlation between a measured variable associated with the casting pump and the casting level movement can be determined. The periodically occurring disturbances are characterized in that the disturbances occur over a period time at a specific casting speed, which corresponds to at least one region of the strand guide in approximately the average roll pitch (that is to say the distance of the rolls in the transport direction of the strand). In continuous casting installations, in which the casting pump pumps out in a special range, the roll pitch in the strand guide over the longer sections is constant (i.e. a plurality of successive rolls in the transport direction of the strand have equal distances from one another). Harmonics occur in addition to the fundamental wave. It can also be determined that the casting block pump only occurs above an empirically determined critical casting speed, which in turn depends on the operating tool and operating method used. However, from the trend of increasing productivity, the limitation of the casting speed is unacceptable. Typical casting speeds (e.g. when casting thin slabs in direct connection) are up to 6m/min and higher.

The slab pump leads to irregular slab shell thicknesses, which can be problematic in direct bonding in particular when casting thin slabs, since the thickness of the cast slab is smaller and the casting speed is high compared to casting slabs.

The adjustment of the casting level by the arrangement of the inflow of the mould has only a low power, see for example WO 2007/042170A1, in which the measured value of the electrical consumption of the rolls of the strand guide is used to adjust the amount of steel fed into the strand casting mould. For example, frequencies greater than or equal to 0.6Hz, which occur during continuous casting of billets at speeds greater than or equal to 2m/min, cannot be counteracted, which may cause irregularities in the steel product and thus reduce the quality of the product. For example, WO 2018/108652A1 solves the problem of "high frequency ballooning", i.e. curvature compensation of the casting pump at a frequency greater than or equal to 0.6 Hz.

WO 2018/108652A1 therefore proposes a method of the initially mentioned type, in which fluctuations in the casting level are reduced by means of a periodic counter-movement of the inflow device (relatively low frequency) and a periodic counter-change in the roll spacing of the rolls of the strand guide (relatively high frequency).

It has been determined that with a defined compensation value for the roll distance of the rolls of the strand guide, the desired effect of reducing the fluctuation of the strand level is often not completely achieved if one inputs the compensation value into the adjustment device of the rolls.

Disclosure of Invention

The object of the present invention is therefore to overcome the disadvantages of the prior art and to propose a method for adjusting a continuous casting installation, by means of which fluctuations in the casting level of greater than or equal to 0.6Hz can be better reduced.

Description of the invention:

according to the invention, this object is solved by a method for adjusting a continuous casting installation according to claim 1,

It is proposed here that the actual value of the roll gap is used as one of the input variables of the observer in order to compensate for the phase shift and/or the amplitude of the actual value of the roll gap.

In principle, the movement of the adjustment fluctuations is thus effected by the calculation rules by means of the rollers of the adjustment strand guide. The relative distance between the opposing rolls (guiding the cast strand between the rolls) has a direct effect on the liquid core of the cast strand and changes the casting level directly, the fluctuations in the casting level being corrected immediately. This allows a more precise and dynamic adjustment of the casting level. The smaller fluctuations of the casting level again act on the quality improvement of the cast strand or of the slab product, for example, to reduce inclusions or to prevent cracks. Therefore, by changing the roller pitch, a higher frequency fluctuation can be generated at the correct phase as well. In contrast, the movement of the inflow device, which determines the amount of liquid metal entering the mould, is transferred to the casting level at a slower rate, because when the position of the inflow device changes, liquid metal still under the inflow device will flow into the mould. In this respect, a correct phase change of the inflow position can only be achieved by a lower frequency inflow or, due to this additional, uncompensated dynamics, only a lower regulator quality can be achieved.

According to the invention, the casting level can be controlled or regulated by varying the relative spacing between the rolls opposite each other. The cast strand is located between the rolls opposite each other. This method requires only adjustable rollers, which are arranged before the complete solidification point. The complete solidification point is the location along the strand guide where the core of the strand or the core of the slab has solidified. However, the casting level can only be adjusted or controlled before complete solidification, i.e. when the cast strand or slab is still in the liquid state at the core. Changing the relative spacing of the rolls to reduce the fluctuation in the casting level can be, but is not necessarily, a driven roll that pulls a metal strand from the mold.

According to the invention, the relative distance between the rollers of the strand guide that face each other is periodically varied. By "periodically varying" is meant that the rollers opposing each other periodically vary the distance relative to each other.

The method according to the invention can be used as the sole control method or control method of the casting level (in combination with the flow regulation of the inflow device) or also in combination with other control methods or control methods for the casting level by the inflow device. When combined with the regulating method or the control method, the individual regulating methods or control methods can be operated independently of one another.

Although in-phase reduction of fluctuations with higher frequency is successfully reduced in most cases with the method of WO 2018/108652 A1, in certain operating situations the behavior of the continuous casting plant (i.e. the adjustment of the rolls) deviates from the model stored in the observer. The adjusting device then cannot operate with the correct phase or with a predetermined amplitude. Reasons include, for example, wear of the mechanical and/or hydraulic components of the adjusting device, changes in the thickness of the cast strand or changes in the rigidity, friction of the hydraulic cylinders or mechanical components of the adjusting device and thermal deformations of the components of the adjusting device. Variations in the width of the cast strand, i.e. for example variations in the width of the sheet metal, can act on deviations of the mould, since the pressure in the hydraulic cylinders of the adjusting device must be increased as the width increases in order to maintain the same thickness of the cast strand.

In order to be able to achieve good compensation, in particular in the case of high-frequency casting level fluctuations, the actual value of the roll gap is taken into account in the calculation of the compensation value for the roll gap. This then yields the compensation value required for this unpredictable operating situation in order to compensate as much as possible for high-frequency casting level fluctuations.

In particular, if the (same) casting pumps ("bulge") should be compensated, the periodic variation in the frequency range can be up to greater than or equal to 0.6Hz, preferably up to 5Hz. The change in the roll spacing can also be carried out at a frequency which is also greater than or equal to 0.6Hz, in particular at a frequency up to 5Hz.

For example, if only an adjustment method or a control method for the roller is used, the periodic variation of the roller pitch in the frequency range can be 0 to 0.6Hz, 0 to 1Hz, 0 to 2Hz, 0 to 3Hz, 0 to 4Hz, or 0 to 5Hz. When the regulation method or control method according to the invention for reducing fluctuations of the casting level is combined with other regulation methods or control methods for reducing fluctuations of the casting level, one other method or some other method can cover a lower frequency range (e.g. 0 to 0.6 Hz), whereas the method according to the invention covers only a higher frequency range (e.g. 0.6 to 1Hz, 0.6 to 2Hz, 0.6 to 3Hz, 0.6 to 4Hz or 0.6 to 5 Hz).

In a further preferred embodiment of the method according to the invention, a plurality of roller segments are arranged along both sides of the strand guide (i.e. opposite each other for the strand), each roller segment having one or more rollers, at least one roller segment being adjusted in a direction perpendicular to the strand guide. The term roll section also includes so-called Grid (Grid) which is arranged in a typical manner directly underneath the mould. In this context, "in the direction perpendicular to the strand guide" means that each adjustment takes place essentially in the direction perpendicular to the strand guide. This case includes pivoting of the roller sections and parallel movement of the roller sections. The strand guide is generally divided in the direction of the strand guide into a plurality of sections, each section comprising two roll sections lying opposite one another.

Advantageously, the roller sections arranged close to the mould are adjusted. In this respect, it can be provided that at least one roller section of the first section is adjusted. It can also be provided that the uppermost, closest roller section to the mould is adjusted. The large enhancement of the directly intervening actuator makes maximum power feasible. Factors regarding the change in roll spacing and the effect of casting level at the uppermost section are typically about 1:10 to 1:13 (pivotable sections) or 1:20 (parallel travel sections). This means that an increase of 0.1mm in the roll spacing affects the casting level in the mould by approximately 1mm to 1.3mm or 1mm to 2mm. Only a small change in the roll spacing is required, which can be done in a short time to be able to compensate for the high frequency of the casting pumps up to 5 Hz.

By selective adjustment of the individual roller sections, each roller section has a plurality of rollers perpendicular to the direction of the strand guide, the distance between the oppositely arranged rollers decreasing in the opposite direction to the casting level fluctuation to compensate for the frequency of the casting level fluctuation. This compensation significantly increases the stability of the continuous casting strand casting and makes high casting speeds possible without changing the quality of the steel product.

Preferably, the method according to the invention provides according to an embodiment variant that at least one roller section is pivoted. Preferably, here the pivot axis is located closer to the mould, so that the part of the roller section remote from the mould deviates more. The outer roller sections, i.e. the outer roller sections located on the outwardly curved side of the strand guide, can be fixed, for example by means of a fixed outer frame. The opposite roller sections, i.e. the roller sections on the inwardly curved side of the strand guide, are pivoted. For this purpose, the roller section has, for example, an inner frame which carries the rollers and is mounted pivotably. However, it is also conceivable that the inner roller section is fixedly mounted and that the outer roller section is pivoted relative to the inner roller section.

Particularly good results of compensating for fluctuations in the casting level can be achieved if a plurality of roller sections, each having one or more rollers, are arranged on both sides along the strand guide, wherein at least the inner roller section closest to the mould is pivoted perpendicularly to the strand guide about the axis of rotation of the rollers of the roller section closest to the mould. The pivoting of the uppermost roll section has a particularly rapid effect on the casting level due to the small distance from the mould.

As an alternative to the pivoting of the roller sections, it can be provided that at least one roller section is adjustable in a direction parallel to the roller sections of the strand guide arrangement, which in turn makes it possible to selectively adjust the roller distance between the respective roller section and the roller. The outer roller sections, i.e. the outer roller sections located on the outwardly curved side of the strand guide, can be fixed, for example by means of a fixed outer frame. The opposite roll section, i.e. the roll section on the inwardly curved side of the strand guide, is then translated in the direction of the outer roll section. It is also conceivable here that, conversely, the inner roller section is fixed, while the opposite outer roller section is translationally movable.

By means of the distance between the rolls of the two opposing roll sections, the volume of liquid metal in the casting billet core can be determined and conclusions can be drawn about the relative change in the casting level.

According to a particularly preferred variant of the method according to the invention, the at least one roller section is adjusted by an adjusting device having at least one hydraulic or electromechanical actuator (e.g. a hydraulic cylinder or an electric spindle drive). In order to achieve an optimal response time for the roll gap adjustment taking into account fluctuations in the casting level, preferably a proportional valve is used for at least one hydraulic cylinder.

Embodiments of the invention provide that the frequency of the casting level fluctuations is detected in the frequency range of 0 to 5Hz and that the fluctuations are compensated for by cyclically varying the roll spacing of the rolls of the strand guide in opposite directions. In this embodiment variant, the fluctuations of the casting level are not counteracted by the inflow means for the mould.

An alternative embodiment of the present invention provides that,

detecting the frequency of the fluctuation of the casting level in a first frequency range and counteracting the fluctuation by a periodic counter-movement of the inflow device (mould), detecting the further frequency of the fluctuation of the casting level in a second frequency range and counteracting the fluctuation by a periodic variation in the opposite direction of the roll spacing of the rolls of the strand guide, wherein the second frequency range is larger than the first frequency range,

a first observer is provided, which determines a first compensation value for the target position of the inflow device on the basis of the frequency of the first frequency range,

a second observer is provided, which determines a second compensation value for a target value of the roll spacing of the rolls of the strand guide on the basis of the frequency of the second frequency range, wherein the actual value of the roll spacing is used as one of the input variables of the second observer.

The advantage of this variant embodiment is that it is possible to counteract the low-frequency fluctuations of the casting level by adjusting the inflow of the mould (for example, as has been done hitherto according to the prior art) while only the high-frequency fluctuations of the casting level are counteracted by adjusting the spacing between the rolls. It is therefore possible to improve the existing regulation for low-frequency fluctuations by means of an additional regulation of the roller spacing.

The adjustment of the inflow device and/or the adjustment of the roller distance can be achieved by means of a so-called observer, as is shown in AT 518461 A1. According to control techniques, a viewer is understood as a system which reconstructs variables (states) which cannot be measured from known input variables (e.g. manipulated variables or disturbance variables which can be measured) and output variables (measured variables) of a reference system under observation. To this end, the observer recreates the observed reference system as a model and uses the regulator to track the state variables that can be measured and thus compared with the reference system. This can prevent the model from generating errors that grow over time.

The method variant with two frequency ranges preferably has a first observer, which determines a first compensation value for the target position of the inflow device on the basis of the frequency of the first frequency range, and a second observer, which determines a second compensation value for the target value for the roll spacing of the rolls of the strand guide on the basis of the frequency of the second frequency range, wherein the actual value of the roll spacing is likewise used as one of the input variables for the second observer.

The casting level in the mould is thus adjusted by flowing into the mould and guiding the metal strand (preferably the uppermost section after the mould). It is furthermore advantageous if the observers on the different actuators are separated (on the one hand, in the case of a first observer, a first compensation value for the target position of the inflow device and on the other hand, a second compensation value for the roller spacing of the rollers of the strand guide) so that no interference can occur between the observers and/or so that no negative influence can occur between the observers.

In a particularly preferred variant of the method with two frequency ranges, the first observer operates in a frequency range of less than or equal to 0.6Hz and the second observer operates in a frequency range of greater than or equal to 0.6Hz, preferably between 0.6Hz and 5 Hz. The advantage of the independent frequency ranges of the two observers is that, because the frequency windows can overlap, no interference occurs between the observers, which means that, for example, the target value of the casting level adjustment actuator remains equal (without curvature) or smaller than the target value without secondary compensation. As a result, the casting level fluctuations are additionally reduced and the mass loss of the steel product is greatly reduced. By using the method according to the invention, a high casting speed can be used in the case of high quality steel products, whereby the productivity for continuous casting systems, in particular for the production of directly connected continuous thin slabs, is significantly improved.

The possible means for carrying out the method according to the invention comprise means for introducing molten metal into the mould, a strand guide comprising rolls and measuring means for measuring fluctuations in the casting level, which measuring means are connected to the control means. An adjusting device is provided which is connected to the control device and is designed to reduce, in particular counteract, fluctuations in the casting level by periodically changing the roll distance of the opposing rolls of the casting strand guide in a direction opposite to the fluctuations in the casting level, wherein the control device comprises at least one observer which is designed to determine a compensation value for a target value for the roll distance of the rolls on the basis of the fluctuation frequency of the casting level, and the actual value of the roll distance is used as one of the input variables for the observer to compensate for the phase shift and/or the amplitude of the actual value of the roll distance.

As already discussed in connection with the method, it can be provided that the adjusting means are designed for periodically varying the roll distance in a frequency range of up to greater than or equal to 0.6Hz, preferably up to 5 Hz. The adjusting means can comprise at least one hydraulic actuator or an electromechanical actuator, for example a hydraulic cylinder or an electric spindle drive. Of course, the adjusting device can be designed to periodically vary the roll distance in the frequency range from 0Hz, preferably up to 5Hz, for example also with hydraulic or electromechanical actuators, for example hydraulic cylinders or motorized spindle drives.

As already mentioned in connection with the method, a plurality of roller segments can be provided, each having one or more rollers, which are arranged along both sides of the strand guide, wherein at least one roller segment can be adjusted in a direction perpendicular to the strand guide by means of an adjusting device.

For example, at least one roller section is adjustable in the top (i.e., first roller section). At least one roller section is pivotable. Or at least one roll section can be adjusted to be aligned parallel with respect to the opposing roll section arranged along the strand guide. Preferably, the roller sections are adjusted such that no abrupt section transitions (=thickness changes) occur, which is known as the "linkage method".

In a preferred embodiment, a plurality of roller segments (each roller segment having one or more rollers) are arranged on both sides along the strand guide, wherein at least the inner roller segment closest to the die is pivotable by means of the adjusting device in a direction perpendicular to the strand guide about the rotational axis of the rollers of the roller segment, which roller segment is located closest to the die.

In accordance with a variant of the method having two frequency ranges, the variant of the device according to the invention provides that the frequency of fluctuations of the casting level can be detected by the measuring device in a first frequency range and that these fluctuations can be counteracted by a periodic opposite movement of the inflow device of the mould, and that further frequencies of fluctuations of the casting level can be detected by the measuring device in a second frequency range, which is greater than the first frequency range, and that these fluctuations can be counteracted by means of the adjusting device by means of a periodic opposite change of the roll spacing of the rolls of the strand guide.

This can be performed again, for example, by means of the first viewer and/or the second viewer. The second observer comprises the same components as the first observer and functions similarly, except that it specifies a second compensation value, not an inflow for the mould, but an adjusting device, which is located (preferably in the uppermost section) at the strand guide.

The method according to the invention or the apparatus according to the invention can be used on existing continuous casting installations with the above requirements and represents a significant improvement in the quality of the continuous cast steel with a significantly higher casting speed, thus increasing the productivity. This new casting level adjustment enables to suppress high dynamic effects, such as high dynamic casting pumps with a frequency higher than 0.6Hz, when unforeseen operating conditions occur, such as wear or deformation of the adjustment means for the rolls, or undesired changes in the thickness of the casting or steel properties.

Drawings

The invention is further illustrated by means of examples. The drawings are exemplary and intended to illustrate the inventive concept, but are in no way intended to limit or even exhaustively represent the inventive concept. The drawings show:

Figure 1 shows an exemplary plan view of a part of a continuous casting installation according to the invention,

figure 2 shows an exemplary plan view of a blank guide according to the invention,

figure 3 shows an exemplary structure of a prior art control device,

figure 4 shows a detail view from the first viewer of figure 3,

figure 5 shows an exemplary control loop according to the invention comprising a first observer and a second observer,

figure 6 shows the time curves of the different variables of the continuous casting installation when it is adjusted,

fig. 7 shows a time profile of the roll gap and the casting level when the roll gap is not changed,

fig. 8 shows the time profile of the roll gap and the casting level when the roll gap is ideally kept constant,

fig. 9 shows a time curve of roll spacing and casting level when the roll spacing shows unusual behavior,

fig. 10 shows the time profile of the roll gap and the casting level when the unusual behaviour of the roll gap is ideally counteracted.

Detailed Description

The continuous casting installation according to fig. 1 has a mold 1. Liquid metal 3 is cast into the mould 1 via a dip tube 2, for example liquid steel or liquid aluminium. The inflow of liquid metal 3 into the mould 1 is regulated by means of the inflow device 4. Fig. 1 shows an embodiment of an inflow device 4 as a closure plug. In this case, the position p of the inflow device 4 corresponds to the stroke position of the closure plug. Alternatively, the inflow device 4 can be designed as a slide. In this case, the lock position p corresponds to the slider position.

The liquid metal 3 in the mould is cooled by means of cooling means (not shown) so that the liquid metal solidifies on the walls 1a of the mould 1 to form the cast slab shell. However, the core 6 is still liquid. The core solidifies later. Together, the shell 5 and the core 6 form a metal cast 7. The metal strand 7 is supported by a strand guide 8 and is pulled from a die 9. The strand guide 8 is located downstream of the mould 1. The strand guide has a plurality of roller segments 8a, which in turn have rollers 8b. Only some of the roller segments 8a and rollers 8b are shown in fig. 1. By means of the rolls 8b, the metal cast strand 7 is pulled out of the die 1 at a pull-out speed v.

The liquid metal 3 forms a casting level 9 in the mould 1. The casting level 9 should be kept as constant as possible. The position p of the inflow device 4 is thus tracked (in the prior art and in the variant of the present embodiment of the invention) in order to adjust the inflow of liquid metal 3 into the mould 1 accordingly. The height h of the casting level 9 is detected by means of a measuring device 10 (known per se). The height h is fed into a control device 11 of the continuous casting plant. The control device 11 determines the manipulated variable S of the inflow device 4 in accordance with an adjustment method, which will be explained in more detail below. The inflow device 4 is then correspondingly controlled by the control device 11 . In general, the control device 11 outputs the manipulated variable S to the regulating device 12 for the inflow device 4. For example, the adjusting device 12 can be a hydraulic cylinder unit. According to f=v _c /p _Roll * n determining and/or measuring the frequency of the casting block pump after the die, v _c Is the drawing speed of the casting blank, f is the curvature frequency, n is the number of harmonic frequencies (1, 2, etc.) and p _Roll Is the roll spacing.

By means of the pivot axis 23 and/or the adjusting device 24, a roller distance can be specifically adapted, which corresponds to the thickness d of the cast strand drawn. As shown in fig. 1, this makes it possible to provide at least one roller section 8a in the first section with a fixed outer frame, wherein, for example, this roller section 8a is located directly to the left below the mould 1. The oppositely arranged roller sections 8a or the inner frame supporting the roller sections can be pivoted about a pivot axis 23, which extends perpendicularly to the drawing plane. The pivot axis 23 can coincide with the rotation axis of the roller 8b, here with the rotation axis of the roller 8b above, but can of course also be arranged at another position. By pivoting, the roller spacing of the lower roller pair of the uppermost roller section 8a in fig. 1 changes, whereas the roller spacing of the upper roller pair remains unchanged. This is not disadvantageous, since by the method according to the invention the roll distance is typically only varied in the range of a few tenths of a millimeter to 2 millimeters.

Any guiding rollers directly connected to the mould and arranged above the uppermost shown roller section 8a are not shown in fig. 1. However, the guide rollers are generally not adjustable relative to one another and in a direction perpendicular to the strand guide.

As an alternative to pivoting, the left uppermost roller section 8a (i.e. approximately the outer frame of the roller section) can be fixed, while the right upper roller section 8a (i.e. approximately the inner frame of the roller section) can be moved in parallel to and away from the left roller section 8a perpendicular to the direction of the strand guide. Thereby, the roller pitches of all the roller pairs are each changed by the same value. This can also be achieved by means of one or more hydraulic cylinders (distributed along the width of the strand and/or in the direction of the strand guide).

In fig. 2 only the strand guide 8 is depicted, which may replace or also supplement (after the uppermost section) the strand guide 8 of fig. 1. In fig. 2, each of the three described sections in each roller section 8a has three rollers 8b on each side. However, each roller section 8a can also have only two or more than three rollers 8b. Continuing with fig. 1, there is depicted a solid cast slab shell 5 and a liquid core 6 of the cast slab up to the complete solidification point D. Up to the full freezing point D, the adjusting device 24 is correspondingly provided in all sections 8 a. The adjustment device 24 can adjust the roller section 8a by pivoting or by parallel displacement, respectively, as already explained in fig. 1. In the present example, the inner roller section 8a of the first (uppermost) section is adjusted by pivoting about a pivot axis 23, the inner roller section 8a of the second section being adjusted by parallel displacement by means of two adjusting devices 24. The connection of the regulating device 24 to the control device 11 is not shown here.

Furthermore (see fig. 3) the control device 11 executes a casting level regulator 13. The height h of the casting level 9 is fed into the casting level regulator 13. Furthermore, a target value h of the height h of the casting level 9 is input to the casting level regulator 13. In addition, other signals are input to the casting level regulator 13. Other signals can be, for example, the width and thickness of the cast metal strand 7 (or the cross section of the metal strand 7 in general), the withdrawal speed v (or the target value of the withdrawal speed), 1 and others. The casting level controller 13 then determines a temporary target position p' in particular for the inflow device 4 by means of the deviation of the height h of the casting level 9 from the target value h. The casting level controller 13 can take into account further signals for its parameterization and/or for determining the pre-control signal pV.

Furthermore, the control device 11 executes the first observer 14. The height h of the casting level 9 and its target value h, further signals and the final target position p for the inflow device 4 are fed to a first observer 14. The first observer 14 determines a first compensation value k. The first compensation value k is added to the temporary target position p' and thus the final target position p is determined. The manipulated variable S is then determined by means of the deviation of the actual position p from the final target position p, by means of which the inflow device 4 is actuated. In general, the control device 11 executes a low-order position regulator (not shown) here.

For good order, it is emphasized again that the first observer 14 and the second observer 25 are not persons, but function blocks which are executed in the control device 11.

The difference between the temporary target position p' and the final target position p corresponds to the first compensation value k determined by the first observer 14. Since the first compensation value k is determined by the first observer 14 and is thus known to the first observer 14, instead of the final target position p, the temporary target position p' can also be input to the first observer 14. Because, due to this, the first compensation value k is known to the first observer 14, furthermore the first observer 14 can determine the final target position p from the temporary target position p'. The taking point 15 taking (temporary or final) the target position p ', p can thus be located before or after the node 16, where the first compensation value k is added to the temporary target position p', as desired. However, the take point 15 should be located before the node 16', at which the pre-control signal pV is added.

The first observer 14 has an acknowledgement block 17. The height h of the casting level 9, other signals and the final target position p are input into a validation block 17. The validation block 17 has a model of the continuous casting facility. The validation block 17 determines the desired (i.e. calculated from the model support) height for the casting level 9 by means of the model by means of further signals and by means of the final target position p. The validation block 17 then determines a desired (i.e. model-supported calculated) fluctuation value δh, also called short-term fluctuation, for the height h of the casting level 9 by means of the desired height. For example, the validation block 17 can take an average of the height h of the casting level 9 and subtract the resulting average from the desired height. The determined fluctuation value δh thus reflects the desired fluctuation of the height h of the casting level 9. The validation chunk 17 thus determines the first compensation value k by means of the fluctuation value δh.

The procedure explained so far in connection with fig. 3 corresponds to the procedure of the prior art. This process is also employed in embodiments of the present invention. The first viewer 14 is again depicted in fig. 4 with a confirmation block 17. Within the framework of the invention, the validation chunk 17 is only one of the components of the first viewer 14, according to the description in fig. 4. Thus, the first observer 14 has, for example, additionally a first analysis element 18. The fluctuation value δh is input to the first analysis element 18. The first analysis element 18 determines therefrom the frequency component of the fluctuation value δh. A second analysis element 19 is preferably additionally present. The additional signal Z is input to the second analysis element 19. The second analysis element 19 thus determines the frequency component of the additional signal Z.

The additional signal Z can be a pull-out force F by means of which the metal strand 7 is pulled out of the rolls 8b of the strand guide 8 of the mold 1. The pull-out force F is directed in a direction parallel to the pull-out speed v. Alternatively it can be the pull-out speed v itself. Both alternatives are preferred. However, it is also possible for example for the force signal F' to be considered as an additional signal Z, which is applied to (at least) one of the roller sections 8a of the strand guide 8. The direction in which the force signal F' is directed is orthogonal to the pull-out speed v. Further alternatively, the additional signal Z can be a local casting thickness d, which is measured in the casting guide 8 by means of a measuring device 21 (see fig. 1). The first analysis element 18 inputs the frequency component determined by the first analysis element to the selection mechanism 22. This case also applies in the same way to the second analysis element 19, if present. The selection means 22 determine, in conjunction with the pull-out speed v, the relevant wavelength which coincides with the frequency component of the fluctuation value δh and, if necessary, also with the frequency component of the additional signal Z. For this purpose, the pull-out speed v is input to the first viewer 14 and to the selection mechanism 22 inside the first viewer 14. The selection means 22 determine the wavelength, wherein the associated frequency component of the fluctuation value δh and, if necessary, of the additional signal Z lies above the threshold values S1, S2. The respective threshold values S1, S2 can be determined on the one hand for the frequency components of the ripple value δh alone and on the other hand for the frequency components of the additional signal Z. The wavelength is preselected by the selection mechanism 22. Thus, the selection means 22 determines the wavelength λi (i=1, 2, 3 …) within the associated range of the preselected wavelength of the fluctuation value δh, respectively, wherein the respective frequency component of the fluctuation value δh has a maximum value. The number of wavelengths λi is not limited. The selection mechanism 22 (ultimately) selects these wavelengths λi. The selection mechanism 22 inputs the selected wavelength λi into the validation chunk 17. The validation block 17 performs a filtering of the height h of the casting level 9 and a filtering of the final target position p for the wavelength λi selected from the selection means 22. The validation block 17 determines the first compensation value k solely by means of the height h of the filtered casting level 9 and the filtered final target position p. In the framework of determining the first compensation value k, the validation block 17 does not take into account the further frequency component of the height h of the casting level 9 and the further frequency component of the final target position p. In addition, a predetermined wavelength range can be provided to the selection mechanism 22. The predetermined wavelength range in this case shows additional selection criteria. In particular, the wavelengths are selected only if they additionally lie within one of the predetermined wavelength ranges, wherein the associated frequency component of the ripple δh and, if appropriate, of the additional signal Z lie above the respective threshold value S1, S2. In addition, the associated frequency components of the ripple value δh are not selected if they also, if necessary, of the additional signal Z lie above the respective threshold values S1, S2.

As already mentioned before, the second observer 25 has the same components as the first observer 14, which analyzes the frequency of the casting block pump after the die 1 and predefines a second compensation value k', i.e. a compensation value for the target value SET for the roll gap, for the adjusting device 24. The target value SET is a static target value that generally corresponds to a desired thickness of the cast slab. In fig. 5 a control loop is depicted, which comprises a first observer 14 and a second observer 25. The first observer 14 presets a first compensation value k for the inflow 4 of the mold 1, so that the casting level 9 in the mold 1 is adjusted. In short, the first observer 14 together with the inflow 4 of the mold 1 shows a standard system for adjusting the casting level 9 of the mold 1, which is used in the first frequency range to compensate the frequency and thus shows a control 27 for the frequency of the first frequency range. A second observer 25 is connected to the adjusting device 24, which shows a control 26 for the frequencies of the second frequency range and predefines a second compensation value k'.

The second compensation value k' is fed to a regulator 28 for the roller adjustment, which calculates a control signal 29 for the roller distance from the target value SET and the actual value ACT and directs the control signal 29 to the regulating device 24. Additionally, the actual value ACT is only led to the second observer 25, which takes into account the actual value when calculating the second compensation value k'.

The first observer controls or adjusts the inflow 4 of the mould 1, and an additional adjustment method can be predetermined instead of the first observer 14.

It is also possible to prescribe only a single adjustment method, i.e. the inflow device 4 of the mold 1 is not used at all for the adjustment of the fluctuation of the casting level, only the adjustment device 24 of the roll 8 b. The only adjustment method can be the second observer 25. The second observer 25 here generally covers a larger frequency range than the two adjustment methods. The frequency range can cover frequencies of, for example, from 0 to 0.6Hz, from 0 to 1Hz, from 0 to 2Hz, from 0 to 3Hz, from 0 to 4Hz, or from 0 to 5 Hz.

Fig. 6 shows an example of suppressing the cycle fluctuation. The time t is plotted along the horizontal axis. In the first (uppermost) illustration, the position of the inflow device 4 is depicted along the vertical axis, indicated with "Pos (4)", the height of the casting level 9 in the mould 1 in the second image is indicated with "m_l" and the steel flow in the cast strand in the third image is indicated with "st_fl". For better understanding, the regulator "Comp" is not yet activated at the time point t=0 and is subsequently turned on, which describes the inactive regulator in the final image in the state "0" and "1" describes the active regulator. In the first three views, it can be well recognized that the position of the inflow device 4 changes periodically and that the height of the casting level 9 and subsequently the steel flow from the mould 1 also changes periodically. In this case, the periodic fluctuations of the casting level "m_l" are reduced with the activation of the regulator by changing the position "Pos (4)" of the inflow device 4. In the method according to the invention, in order to reduce the fluctuation of the casting level, in addition to or instead of the change of the position "Pos (4)" of the inflow device 4, one periodically changes the spacing of the opposite sides of the roller 8b in the uppermost section accordingly.

Fig. 7 to 10 each include two images: the upper graph shows the time profile of the casting level 9, wherein the casting level 9 ideally follows a horizontal center line. The following graph shows the time profile of the actual value ACT of the roll gap in dotted lines, wherein the time profile of the roll gap EST calculated beforehand using the observer model is shown in dashed lines and the time profile of the target value SET of the roll gap, which is modified by means of the second compensation value k', is shown in continuous lines. The target value SET of the roll spacing corresponds substantially to the desired casting thickness d. The second compensation value k' is then added to the target value and the resulting signal can be considered as a steering signal 29 for the roller spacing. The target value SET of the roll spacing is thus a static value, which is typically reduced and increased by periodically changing the second compensation value k' (and thus typically also periodically). Thus, the signal derived by adding the second compensation value k' to the static target value SET is the final target value.

Fig. 7 shows the time profile of the roll distance and the casting level 9 when the roll distance is not changed. The casting level 9 periodically changes the height of the casting level when the actual value ACT of the roll gap, the previously calculated roll gap EST and the final target value of the roll gap remain unchanged, in particular when no second compensation value k' is added to the static target value SET. The adjustment device 24 does not change the roller setting here.

Fig. 8 shows the time profile of the roll gap and the casting level 9 when the casting level 9 is maintained constant in the ideal state of the roll gap. For this purpose, a second compensation value k 'is added to the target value SET of the roll gap, which second compensation value k' varies with the same frequency as the unregulated casting level 9 (fig. 7) and generally with a corresponding phase shift to the casting level 9, thus yielding a common curve of the roll gap EST calculated in advance and the actual value ACT of the roll gap, which common curve has the same frequency as the target value SET plus the second compensation value k ', but which common curve is only phase shifted relative to the target value SET plus the second compensation value k'. Thus, the actual roller setting corresponds to the roller spacing EST calculated in advance.

Fig. 9 shows the time profile of the roll gap and the casting level when the actual roll gap shows an undesired behavior. Although the adjustment based on the target value SET plus the second compensation value k' results in a periodic fluctuation of the casting level 9. That is, everything is the same as in the previous fig. 8, but the result is different because the roller 8b is in an unexpected condition. Fig. 9 shows the difference in phase and amplitude between the actual value ACT of the roll gap and the roll gap EST calculated in advance.

Fig. 10 shows the time profile of the roll gap and the casting level when the undesired behavior of the roll gap from fig. 9 is ideally counteracted. By feedback of the actual value ACT at the second observer 25, the second observer can adapt to the second compensation value k' such that the undesired behavior is counteracted. It is seen that for this purpose the phase of the target value SET plus the second compensation value k' must be shifted with respect to fig. 9, whereby the casting level 9 is again ideally counteracted.

The typical slab thickness d is around 100mm in thin slab casting, with typical casting speeds between 2m/min and 6 m/min. The constant roll pitch in the transport direction via the longer sections of the strand guide lies in the typical range of approximately 200 mm. The frequency of the fundamental wave and the frequency of the harmonic wave of the oscillation of the casting level are then derived from the casting speed and the roll pitch, which are counteracted by means of the method according to the invention or the device according to the invention.

List of reference numerals

1. Mould

1a wall of a mould

2. Dipleg

3. Liquid metal

4. Inflow device

5. Casting shell

6. Kernel

7. Metal casting blank

8. Casting blank guide

8a roller section

8b roller

9. Casting level

10. Measuring device

11. Control device

12. Adjusting device

13. Casting level regulator

14. First viewer

15. Taking points

16. 16' node

17. Validation chunk

18. 19 analysis element

20. Temperature sensor

21. Measuring device

22. Selection mechanism

23. Pivot axis

24. Adjusting device

25. Second viewer

26. Controller for frequencies of a second frequency range

27. Controller for frequencies of a first frequency range

28. Regulator for roller arrangement

29. Control signal for roller distance

Actual value of ACT roll spacing

D complete freezing point

d thickness of casting blank

Roll spacing calculated in advance by EST

F pull-out force

F' force signal

h height of casting level

h is the target value of the height of the casting level

k first compensation value

k' second compensation value

p position of inflow device

p, p' target position

pV pre-control signal

S manipulated variable of inflow device 4

Target value of SET roller spacing

S1, S2 threshold

T temperature

v pull-out speed

Z additional signal

δh fluctuation value.

Claims

1. A method of adjusting a continuous casting installation,

wherein the continuous casting installation has a mould (1) and a strand guide (8) downstream of the mould (1),

wherein a liquid metal (3) is cast into the mould (1), in particular via an inflow device (4), which solidifies on the wall (1 a) of the mould (1) to form a metal cast strand (7) with a solidified cast strand shell (5) and a still liquid core (6),

wherein the metal strand (7) is pulled out of the mould (1) by means of spaced-apart rollers (8 b) of the strand guide (8),

wherein a measurement variable relating to the fluctuation of the casting level formed in the mould is determined, said measurement variable is processed in connection with at least one calculation rule and is used to reduce the fluctuation of the casting level (9),

wherein, in order to reduce the fluctuations in the casting level, the relative distance between the mutually opposite rollers (8 b) of the strand guide is periodically changed before the complete solidification point (D), i.e. by means of the periodic change in the roller distance of the mutually opposite rollers (8 b) of the strand guide (8) against the fluctuations in the casting level (9),

-wherein the frequency of the fluctuation of the casting level (9) is detected and at least one observer (25) is provided, based on which the observer determines a compensation value (k') for the target value (SET) of the roll spacing of the rolls (8 b), characterized in that, in order to compensate for the amplitude and/or the phase shift of the actual value (ACT) of the roll spacing, the actual value (ACT) of the roll spacing is used as one of the input variables of the observer (25).

2. Method according to claim 1, characterized in that the periodic variation is in a frequency range of up to greater than or equal to 0.6Hz, preferably up to 5 Hz.

3. Method according to claim 1 or 2, characterized in that a plurality of roller segments (8 a) are arranged along both sides of the strand guide (8), each of which roller segments has one or more of the rollers (8 b), wherein at least the inner roller segment (8 a) closest to the mould (1) is pivoted perpendicularly relative to the strand guiding direction about the axis of rotation of the roller closest to the roller segment of the mould (1).

4. A method according to any one of claims 1 to 3, characterized in that the frequency of the fluctuation of the casting level (9) is detected in the frequency range of 0 to 5Hz and the fluctuation is counteracted by means of a periodic opposite change of the roll spacing of the rolls (8 b) of the strand guide (8).

5. A method according to any one of claim 1 to 3, wherein,

detecting the frequency of the fluctuation of the casting level (9) in a first frequency range and counteracting the fluctuation by means of a periodic counter-movement of the inflow device (4), detecting the other frequency of the fluctuation of the casting level in a second frequency range and counteracting the fluctuation by means of a periodic counter-change of the roll spacing of the rolls (8 b) of the strand guide (8), wherein the second frequency range is larger than the first frequency range,

-providing a first observer (14) which determines a first compensation value (k) for a target position of the inflow device (4) on the basis of the frequencies of the first frequency range,

-providing a second observer (25) which determines a second compensation value (k') for the target value (SET) of the roll spacing of the rolls (8 b) of the casting blank guide on the basis of the frequency of the second frequency range, wherein the actual value (ACT) of the roll spacing is used as one of the input variables of the second observer (25).

6. An apparatus for carrying out the method according to any one of claims 1 to 5, comprising means for introducing a metal solution into the mould (1), a strand guide (8) comprising rolls (8 b), measuring means (10) for measuring fluctuations in the casting level, said measuring means being connected to control means (11),

-wherein an adjusting device (24) connected to the control device (11) is provided, which is designed for reducing, in particular counteracting, the fluctuation of the casting level (9) by a periodic change of the roll spacing of the rolls (8 b) of the strand guide (8) opposite each other against the fluctuation of the casting level, characterized in that the control device (11) comprises at least one observer (25) designed for determining a compensation value (k') for a target value (SET) of the roll spacing of the rolls (8 b) on the basis of the frequency of the fluctuation of the casting level (9) and for compensating for the amplitude and/or phase shift of the actual value (ACT) of the roll spacing, the actual value (ACT) of the roll spacing being used as one of the input variables of the observer (25).

7. The device according to claim 6, characterized in that the adjusting device (24) is designed to periodically vary the roll distance over a frequency range of up to greater than or equal to 0.6Hz, preferably up to 5 Hz.

8. The apparatus according to any one of claims 6 to 7, characterized in that a plurality of roller sections (8 a) are arranged along both sides of the strand guide (8), each roller section having one or more of the rollers (8 b), wherein at least the inner roller section (8 a) closest to the mould (1) is pivotable perpendicularly with respect to the strand guiding direction about the axis of rotation of the roller closest to the roller section of the mould (1) by means of the adjusting apparatus (24).