EP3515634B1 - Controlling the narrow-side conicity of a continuous casting mould: method and device - Google Patents

Description

The invention relates to a method for regulating the narrow side taper of a continuous casting mold based on the measurement of the forces applied to the narrow sides.

Furthermore, the invention relates to a continuous casting mold, the narrow side plates of which are set in accordance with the method according to the invention with the aid of actuators located at different distances from the pouring side.

Continuous casting molds are used when casting metal slabs, in particular when casting steel slabs. In this case, a continuous casting mold, in which the method according to the invention is used, consists of four individual metal plates, the so-called mold plates, which are arranged so as to be displaceable relative to one another and are preferably made from a copper alloy and essentially have a cuboid shape.

With respect to the casting direction of the continuous casting mold, all four mold plates have approximately the same extent, which is consequently referred to as mold height H. In addition, two of the mold plates each have the same dimension in the width direction. The mold plates of the pair with the larger dimension in the width direction are also referred to as broad side plates, those with the smaller dimension in the width direction as narrow side plates.

The four mold plates of a continuous casting mold are arranged at the same height in relation to the casting direction, the two broad side plate plates and the two narrow side plates each lying opposite one another. This creates a mold that is open on both sides, the openings of which are referred to as the pour-side or outlet-side end and which — with respect to a cutting plane that is normal to the casting direction — have a rectangular cross section.

The mold plates are arranged relative to one another in such a way that each of the two broad side plates contacts the two narrow side plates with their inner surface during the casting process, and conversely each narrow side plate with two opposite outer surfaces contacts the two broad side plates. The distance between the outlet-side ends of the narrow side plates is referred to as the casting width, since this distance defines the dimension of the cast metal strand when it emerges from the mold.

On the one hand, this arrangement enables the narrow side plates to be displaced parallel to the inner surfaces of the broad side plates even during the casting process. On the other hand, a clamping force can be exerted on the narrow side plates by mechanically positioning the wide side plates against the narrow side plates.

The space enclosed by the mold plates in relation to the direction of casting is referred to below as the interior of the mold, accordingly the surfaces of the mold plates facing the interior are referred to as their inner surfaces; analogously, the surfaces opposite the inner surfaces of the respective rectangular mold plates are also referred to as outer surfaces called the mold plates.

So-called back-up plates are generally attached to the outer surfaces of the mold plates, which on the one hand ensure sufficient mechanical stability of the mold plates and on the other hand contain a cooling device which dissipates the heat of the metal melt released during continuous casting from the mold plates. Such devices, e.g. Milling on the outer surfaces of the mold plates, which together with the backing plates form cooling channels through which water flows, are well known from the prior art.

The displaceable arrangement of the mold plates with respect to one another is carried out by corresponding actuators, which make it possible for individual Position mold plates spatially and thereby vary the cross-sectional area of the mold that is decisive for the dimension of the metal slab produced. Such actuators can be, for example, motor-driven spindles or hydraulic actuators, which are also known from the prior art.

During the casting process, a metal melt is introduced into the interior of the mold at the end on the pouring side, the metal melt starting to solidify in the contact area with the mold plates due to the heat being given off to the mold plates, and a so-called strand shell is formed in this area, the thickness of which is formed during the passage of the corresponding strand section continuously increased by the mold. The metal strand which is partially solidified in this way is extracted by appropriate pull-out devices, e.g. driven driver rollers in the roller table following the mold, pulled out of the mold at the outlet end thereof, this process being supported by mechanical oscillation movements of the mold itself.

The surface of the molten metal in the interior of the continuous casting mold is also referred to as a mold level. Accordingly, the so-called mold level height h is defined as the distance of the mold level from the exit end of the mold.

Furthermore, casting powder is applied to the molten metal at the pouring-in end of the mold, which is melted on the surface of the still molten metal melt by the heat given off and subsequently a sliding film between the strand shell that forms and the inner surfaces of the mold plates, which forms the mechanical Friction between the strand shell and the inside of the mold plates is reduced.

Despite the formation of a strand shell, the majority of the section of the metal strand located inside the mold remains in the liquid phase. A corresponding ferrostatic pressure therefore acts on the strand shell, which must be compensated for by a corresponding back pressure of the mold plates, since the strand shell itself cannot build up sufficient back pressure.

For this reason, a corresponding pressure force is applied to the narrow side plates in particular during the casting process by means of their actuators, since the clamping action which the broad side plates exert on the narrow side plates is generally not sufficient.

An actuator arranged on a narrow side plate has a point of application at which a force is transmitted to the narrow side plate and the narrow side plate is moved at this point by a spatial displacement of the point of application by the actuator. This point of attack can be designed to be articulated if, for example, the inclination of the narrow side plate changes during displacement by the actuator. In this sense, the point of attack is assigned a position which is displaceable in space and which is referred to below as the actuator position. Furthermore, an actuator comprises a sensor with which the current value of the actuator position is recorded, which is also referred to as the actual position of the actuator and which is transmitted to a control unit.

In the case of position control of the actuator, the control unit specifies a specific position value, which is also referred to below as the target position of the actuator. The actual position of the actuator is compared with its target position and the actuator is controlled by the control unit such that the actual position and target position match. This actuation takes place by applying a corresponding mechanical force to the actuator, which is transmitted to the narrow side plate via the point of application of the actuator and as a result of which the position of the narrow side plate is changed at this point. The actuation of the actuator with a mechanical force is also initiated by the control unit and can take place, for example, by changing the hydraulic pressure if the actuator is designed in the form of a hydraulic cylinder.

During the casting process, all actuators of the continuous casting mold are given individual target positions and the internal forces of the individual actuators are regulated in such a way that the interaction of all actuators during the casting process - with the exception of the process of adjusting the position of the narrow side plates - the outward forces of the Metal melt must be exactly balanced, otherwise the narrow side plates would move. There is therefore a balance of forces between the outward forces caused by the ferrostatic pressure of the molten metal and the inward forces of the actuators.

Since metal alloys experience a reduction in their spatial volume during their solidification and subsequent cooling, the cast metal strand shrinks accordingly as it passes through the mold. It is also known that, in order to achieve the highest possible quality result, the cast metal strand should have as large a mechanical contact as possible with the inner surfaces of the mold plates when they pass through the mold. However, if the strand shell lifts off from the inner surface of the mold due to thermal shrinkage, this significantly reduces the heat flow from the metal strand at the relevant point, which results in a non-uniform quality of the strand surface and, in extreme cases, can lead to the strand shell being torn open.

One measure to ensure that the metal strand passing through the mold is as large and uniform as possible is to specify a slight inclination between the opposing mold plates, so that the cross section of the mold from the pouring end to the outlet end corresponds to the shrinkage of the metal strand rejuvenated.

wird auch als Breitseitenkonizität bezeichnet.The inclination of the opposite broad side plates is usually determined by a trapezoidal shape of the narrow side plates achieved: since the narrow side plates contact the two broad side plates along their vertical extension, there is a different distance between the upper, pour-side ends of the two broad side plates than between the lower, outlet-side ends of the broad side plates. The quotient of the difference between the upper distances f and the lower distances d between the broad side plates and the mold height H accordingly $${\mathrm{K}}_{\mathrm{b}}=\left(\mathrm{f}-\mathrm{d}\right)/\mathrm{H}$$

is also called broadside taper.

definiert. Es sind jedoch auch andere Definitionen der Schmalseitenkonizität möglich, wobei wesentlich ist, dass diese dabei von der Neigung zumindest einer der Schmalseitenplatten in Bezug auf die Gießrichtung abhängen. So ist es denkbar, eine Definition für die Schmalseitenkonizität nur auf eine einzelne Schmalseitenplatte zu beziehen, beispielsweise $${\mathrm{K}}_{\mathrm{s},\mathrm{l}}=\begin{array}{cc}\left({\mathrm{e}}_{\mathrm{l}}-{\mathrm{b}}_{\mathrm{l}}\right)/{\mathrm{b}}_{\mathrm{l}}& \mathrm{mit}\mathrm{l}\in \left\{\mathrm{1,2}\right\},\end{array}$$

wobei der Index l die erste bzw. die zweite Schmalseitenplatte und e_l den eingießseitigen und b_l den austrittseitigen Normalabstand der Schmalseitenplatte l zur geometrischen Mittenlinie der Stranggusskokille bezeichnen. Im Fall einer derartigen, nur auf eine Schmalseitenplatte bezogenen Definition der Schmalseitenkonizität werden der Stranggusskokille folglich zwei Werte für die Schmalseitenkonizität zugeordnet.Similarly, the taper of the narrow side plates - hereinafter also referred to as narrow side taper K _s - is usually referred to as the difference between the distance e between the ends of the narrow side plates on the pouring side and the distance b between the ends of the narrow side plates on the outlet side, which is identical to the casting width b, according to $${\mathrm{K}}_{\mathrm{s}}=\left(\mathrm{e}-\mathrm{b}\right)/\mathrm{b}$$

Are defined. However, other definitions of the narrow side taper are also possible, it being essential that they depend on the inclination of at least one of the narrow side plates with respect to the casting direction. It is conceivable, for example, to refer to a definition for the narrow side taper only on a single narrow side plate $${\mathrm{K}}_{\mathrm{s},\mathrm{l}}=\begin{array}{cc}\left({\mathrm{e}}_{\mathrm{l}}-{\mathrm{b}}_{\mathrm{l}}\right)/{\mathrm{b}}_{\mathrm{l}}& \mathrm{With}\mathrm{l}\in \left\{1.2\right\},\end{array}$$

where the index l denotes the first or the second narrow side plate and e _l the pouring-side and b _l the outlet-side normal distance of the narrow side plate l to the geometric center line of the continuous casting mold. In the case of such a definition of the narrow side taper, which relates only to a narrow side plate, the continuous casting mold is consequently assigned two values for the narrow side taper.

Since the broadside cone is determined solely by the geometric shape of the narrow side plates, no influence can be exerted on it during the casting operation. In order to improve the contact of the inside of the mold with the strand shell during the casting process, solutions are known from the prior art which influence the shape of the narrow side plates of a mold.

The formation of the strand shell when the metal strand passes through the continuous casting mold depends on various factors, such as the casting speed, the composition of the molten metal itself, the properties of the casting powder or the cooling capacity of the cooling device of the mold, which also influence the heat transfer from the cast metal strand to the mold and thus the mechanical contact of the metal strand with the mold.

From the JP 2010 253548 A A construction for continuous casting molds is known, which proposes to mechanically bend the narrow side plates during the casting depending on the casting speed, the carbon content of the molten metal or the heat flow passing from the metal strand to the mold, the heat flow from temperature values of the cooling water of the cooling device of the mold is calculated. The aim of this invention is to keep both the solidification profile of the strand shell and the frictional forces that occur on the inner surfaces of the mold plates as constant as possible, even with changing casting conditions, by the targeted bending of the narrow side plates, and thus to avoid the formation of longitudinal cracks in the cast metal strand . A complex bending mechanism according to FIGS. 15 and 18 is used to apply the required bending forces.

The JP H03 210953 A proposes a continuous casting mold, the narrow side plates of which each have a groove 15 running in the horizontal direction perpendicular to the casting direction, which is why a kink occurs at this point under the action of force corresponding Fig. 1 trains. The control of this force action takes place as a function of temperature values measured by means of a thermocouple in the vicinity of the outlet-side end of the narrow side plates. The grooves of the narrow side plates represent a mechanical weak point.

The JP H02 247059 A suggests bending the narrow side plates together with the backing plates attached to them, depending on the measured heat flow or the casting speed. The bending forces required for this are very high, the inner surfaces of the narrow side plates assume a curve along the casting direction.

A disadvantage of all the publications mentioned above is that high mechanical forces or correspondingly complex trades are required to bend the narrow side plates.

In addition, in the publications mentioned, a hypothetical solidification process of the strand shell is assumed, for which a physical modeling is necessary, which in turn depends on various influencing factors and is therefore subject to the corresponding uncertainties, since there is no direct measurement of the actual contact area between the strand shell and the inner surfaces of the mold plate .

Another disadvantage of the above-mentioned publications is that a control system which is based on a measured temperature value or a measured heat flow has a correspondingly inherent inertia and therefore cannot react quickly enough to rapidly changing production conditions.

In order to avoid disadvantageous mechanical loads on the narrow side plates, the present invention therefore proposes, instead of bending the narrow side plates, to change their spatial position during the casting operation by guiding them along the inner sides of the wide side plates. This happens because the clamping force, which exert the broad side plates on the narrow side plates is reduced, then the narrow side plates are adjusted accordingly using appropriate position-controlled actuators and finally the contact pressure of the broad side plates is reset to the original value. Such an adjustment process takes place in a controlled manner and in such a way that there is no sudden tearing of the strand shell despite the outward forces of the liquid metal melt.

In particular, the narrow side taper can be adapted to the shrinkage of the metal strand resulting from the formation of the strand shell, so that the contact area of the narrow side plates with the strand shell is as large as possible. No forces are applied for the bending of the narrow side plates themselves and the frictional forces between the strand shell and the inner surfaces of the mold plates are not increased unnecessarily.

If the narrow side taper is optimal in this sense, the setting of the narrow sides of the mold corresponds exactly to the shrinkage of the strand, which is caused by the growth of the strand shell. Typical values of the narrow side taper are between 0.9% and 1.3% of the pouring width according to the above definition.

Excessive taper of the narrow side plates, which causes the strand to be squeezed by the mold, causes increased wear on the mold surface and increases the friction between the mold and the strand. Under certain circumstances, when the metal strand passes through the continuous casting mold in the edge area where the narrow side plates and the wide side plates meet, the strand shell can also bulge inwards, which in turn leads to longitudinal defects in the metal strand.

On the other hand, too little taper on the narrow side creates a gap between the strand shell and the narrow side plates of the mold, which leads to reduced strand shell growth due to insufficient heat dissipation through the mold walls. A resulting bulging of the strand in the mold can, in addition to an increased probability of breakdown, also lead to quality problems in the edge region of the metal strand.

The optimal narrow side taper depends on various production parameters, e.g. the shrinkage characteristics of the cast metal melt or also from the actual heat dissipation, which is determined, among other things, by the properties of the mold powder and the casting speed. It is therefore advisable to dynamically adapt the narrow side taper to the prevailing casting conditions during casting.

The setting of the narrow side taper of a continuous casting mold during the casting operation as a function of a production parameter is known from the prior art. In order to ensure rapid adjustment of the narrow side, the wide side plates can be permanently clamped, for example, by means of a preset spring clamp, the clamping action of which is only briefly opened by a corresponding unclamping device during the adjustment of the narrow side taper by actuators of the unclamping device canceling the clamping force of the spring clamp.

So describes the DE 10 2014 227 013 A1 the adjustment of the narrow side taper of a continuous casting mold depending on a temperature distribution in the mold plates and the mechanical contact of the strand shell derived therefrom to the inner surfaces of the mold plates. The temperature distribution is preferably determined with the aid of optical waveguide sensors, with conclusions being drawn about the mechanical contact or the formation of air gaps from the ratio of measured values between centrally located and near-edge temperature sensors.

For one, it is in the DE 10 2014 227 013 A1 described temperature-based control of the narrow side cone relative slow - for example, the lifting of the strand shell can only be detected with a corresponding time delay. On the other hand, this control method is only based on the heat flow from the cast metal strand to the mold plates and the associated temperature changes, but without taking friction forces into account, and is therefore only an indirect method for determining the appropriate conicity, which is subject to corresponding inaccuracies.

The JP S56 119646 A describes a continuous casting mold, the plates of which are moved under pressure control during casting. The narrow side plates are each movably connected at their pour-side end to a base plate which can be moved and fixed in the horizontal direction. The point of application of a pressure-controlled actuator, e.g. a hydraulic cylinder, which presses the narrow side plates against the cast metal strand, lies near the end of the narrow side plates on the casting outlet side, with a small gap of 0.1-0.2 mm in the casting direction between the narrow side plates and the wide side plates to enable their relative movement .

Although this invention allows a quick reaction to changing production conditions with regard to the contact of the narrow side plates with the metal strand due to the pressure-controlled actuation of the lower actuators, the movements of the actuators simultaneously adjust the narrow side cone itself, so that the contact behavior of the narrow side plates on the one hand and on the other hand, the optimal value of the narrow side cone cannot be set independently of one another. In addition, a uniform pouring width cannot be maintained, since during a control process the narrow side plates are tilted at their lower end and, moreover, it cannot be guaranteed that the narrow side cone is identical on both sides, which can lead to non-uniform growth of the strand shell.

It is also common to use known production parameters such as the composition of the molten metal, the casting width, the current casting speed or a heat flow calculated from measured temperature values, to calculate a value for the narrow side taper and to specify this value manually using the automation system of the relevant continuous casting plant. This procedure is based either on empirical values or a model assumption with regard to strand shell growth and is therefore subject to a corresponding number of uncertainties, and there is no precise reproducibility due to the manual intervention.

It is therefore an object of the present invention to overcome the disadvantages of the aforementioned methods and to disclose a method for regulating the narrow side taper of a continuous casting mold which, depending on the current process conditions, allows the optimum value of the narrow side taper to be set as quickly and reproducibly as possible in the sense of the greatest possible Contact surface between the strand shell and the inside of the mold is allowed without unnecessarily increasing the frictional forces.

The object is achieved by the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

In the following, a continuous casting mold is assumed, the narrow side plates of which can be moved along the inner sides of the broad side plates via at least two mechanical actuators, and as a result of which an inward force is exerted on the continuous shell of the cast metal strand in order to prevent the ferrostatic pressure acting on the outside from occurring to counteract solidified metal melt, since the clamping effect of the narrow side plates by the broad side plates and the intrinsic cohesive force of the strand shell itself are not sufficient to prevent the strand from tearing open. These forces transmitted from the narrow side plates to the strand shell are referred to below as narrow side forces.

It is assumed that the casting direction of the continuous casting mold 1 is oriented essentially in the direction of the acceleration due to gravity; therefore, the ferrostatic pressure of the molten metal introduced into the mold 1 increases linearly in the casting direction in accordance with the behavior of a liquid with the distance to the surface of the molten metal which is located in the casting direction at a distance corresponding to the level of the mold level above the outlet-side ends of the mold plates.

The increase in pressure within the molten metal melt naturally also continues below the outlet end of the continuous casting mold. A good approximation of a deviation from the linear rise behavior due to the temperature dependence of the density of the molten metal can be neglected, since the temperature of the melt introduced into the mold is only slightly above the solidification temperature.

The ferrostatic pressure of the molten metal causes outward forces that have to be compensated by corresponding inward counter forces to prevent the strand shell from tearing open.

When the molten metal passes through the continuous casting mold, a cooling shell is formed along the inner surfaces of the mold plates due to the cooling effect. The strand shell has an inherent strength, which depends locally on its thickness and which partially compensates for the ferrostatic pressure of the molten metal acting outwards. The remaining part of the ferrostatic pressure inside the continuous casting mold must be compensated for by appropriate counterpressure of the mold plates in order to avoid tearing the strand shell.

While the corresponding back pressure is automatically set due to the fixed clamping of the broad side plates, the back pressure must be along the narrow side plates be actively regulated, as there is no complete clamping effect of the narrow side panels through the wide side panels. The spatial position and orientation of the narrow side plates is therefore carried out by active position control of the mechanical actuators moving the narrow side plates.

After the metal strand emerges from the continuous casting mold, the strand shell has already grown to such an extent that the ferrostatic pressure exceeding the intrinsic strength of the strand shell can be easily compensated for by spatially fixed or position-controlled strand guide rollers, the strand guide rollers directly supporting the surface of the extended metal strand.

Experiments show that the narrow side forces with decreasing casting speed (less than 0.6 meters per minute) always decrease due to the formation of the strand shell and the associated strand shrinkage, until the metal strand at very low casting speeds (0 to 0.2 meters per minute) comes into contact with loses the mold narrow sides almost completely and the narrow side forces tend towards zero.

Tests also show that adjusting the narrow side taper has a direct influence on the required narrow side forces.

There is therefore an empirical relationship between the narrow side forces and the casting speed. There is also a connection between the narrow side forces and the narrow side taper.

• ein Referenzdruck P_ref als Führungsgröße und
• eine mittlere Flächenpressung P_med zwischen den Schmalseitenplatten und dem Metallstrang als Regelgröße, wobei die mittlere Flächenpressung P_med aus den in Wirkrichtung der Aktoren auftretenden Kräften ermittelt wird,

herangezogen werden und dass

• ein Regler in Abhängigkeit von einer Regelabweichung P_dif = P_ref - P_med als Eingangsgröße die Schmalseitenkonizität K_s als Stellgröße des Regelkreises ermittelt und dass
• über eine Regelstrecke mittels der Aktoren die Position der ersten und/oder der zweiten Schmalseitenplatte entsprechend der Schmalseitenkonizität K_s eingestellt wird.

The present invention for setting a value of the narrow side taper that is as optimal as possible, in which the placement of the narrow side plates against the strand shell that is being formed exactly compensates for the shrinkage of the metal strand, is based on the use of this relationship and is effective
A method for setting a narrow side taper K _{s of} a continuous casting mold for the production of a metal strand using at least one control circuit, the continuous casting mold comprising a first and a second narrow side plate, on each of which at least two position-controlled actuators for positioning the respective narrow side plate at different distances from the end on the casting side the continuous casting mold is arranged and corresponding forces occur in the direction of action of each actuator during operation of the continuous casting mold,
characterized in that during a cycle run through the at least one control loop

• a reference pressure P _ref as a reference variable and
• an average surface pressure P _med between the narrow side plates and the metal strand as a control variable, the average surface pressure P _{med being determined} from the forces occurring in the direction of action of the actuators,

be used and that

• a controller as a function of a control deviation P _dif = P _ref - P _med as the input variable determines the narrow side taper K _s as the manipulated variable of the control loop and that
• The position of the first and / or the second narrow side plate is set according to the narrow side taper K _s over a controlled system by means of the actuators.

According to the invention, each of the two narrow side plates of the continuous casting mold can be positioned by a separate, independent control circuit which only controls the actuators of the respective narrow side plate. In this case, the manipulated variable of the control loop in question depends on the inclination of the respective narrow side plate in relation to the casting direction, and the method according to the invention thus comprises two independent values for the narrow side conicity - in each case one value for the first and one value for the second narrow side plate - the continuous casting mold .

Alternatively, however, a common control loop can also be used for both narrow side plates, which accordingly controls the actuators of both narrow side plates. In this case, the method according to the invention comprises a common value for the narrow side taper of the continuous casting mold, the definition of which depends equally on the inclinations of both narrow side plates with respect to the casting direction.

Furthermore, the controller of the control loop can also contain filterings that either process the input signal for a control regulation contained in the control loop or process the signal determined by the control regulation before it is fed to the controlled system.

The method according to the invention enables a quick reaction to changing process conditions, since the detection of the narrow side forces which are influenced by the process conditions, in contrast to methods which are based on temperature or heat flow measurements, takes place practically in real time.

The method according to the invention is also based on an empirical relationship between the narrow side forces on the one hand and the current casting parameters, such as the casting speed, the behavior of the casting powder or the composition of the molten metal on the other hand, this empirical relationship being modeled by the behavior of the controller. Therefore, the method according to the invention does not require any physical modeling of the effects of the various influencing variables, but rather is based on the measurement of the direct reaction of the casting parameters in the form of the narrow side forces, so that the effects of all relevant casting parameters are taken into account equally and equally quickly.

For example, a lifting of the strand shell from the inside of the narrow side plates, caused, for example, by excessive cooling and associated strand shrinkage, can be detected immediately because the narrow side forces to be applied for a specific control position decrease accordingly. Likewise, an increase in the narrow side forces, which would cause the strand to be crushed and is caused, for example, by an insufficient cooling capacity of the metal strand, can be compensated for directly. In this way, an optimal force distribution of the actuators and correspondingly the largest possible contact area between the strand shell and the inner surfaces of the narrow side plates is achieved without the frictional forces between the strand shell and the inner surfaces of the continuous casting mold being unnecessarily increased.

Furthermore, the method according to the invention ensures good reproducibility, since the adaptation of the narrow side taper to the current production conditions does not require any operator intervention, but only depends on the preset parameters of the controller or on any filtering carried out in the controller.

In a further preferred embodiment of the method _according to the invention, the reference _pressure P _{ref is} a function of the density of the molten metal ρ _liq , a mold level h and a dimensionless correction factor S.

The density ρ _{liq of} the molten metal is to be understood as the material density of the liquid melt, the physical unit of which is given, for example, in kg / m ³ . The reference _pressure P _ref depends on the density of the molten metal ρ _liq and on the level of the mold level h, which is defined as the distance between the mold _level and the _exit end of the mold, and also contains another dimensionless correction factor S that can be specified.

The reference pressure P _ref is a parameter of the control process and can also be used, for example, during the casting process if required by an operator or by another control system, to change the characteristic of the control loop. This makes it possible to take into account a change in the mold level h during the casting process or to react flexibly to changes in the casting parameters, such as a change in the composition of the molten metal, the casting powder or in the heat dissipation of the mold.

An adaptation of the reference pressure can be based, for example, on empirical values based on the recorded casting parameters, as a result of which an advantageous driving style of the continuous casting mold, once determined under certain casting conditions, can be reproduced.

bestimmt werden, wobei g der Wert der Erdbeschleunigung und P_fer den ferrostatischen Druck der Metallschmelze im Inneren des gegossenen Metallstranges am austrittseitigen Ende der Stranggusskokille bezeichnen. Da aufgrund der physikalischen Gesetzmäßigkeiten der ferrostatische Druck P_fer linear in Gießrichtung ansteigt, entspricht der über die Gießspiegelhöhe h gemittelte ferrostatische Druck, der als mittlere Flächenpressung P_med bezeichnet wird, dem halben Wert des lokalen ferrostatischen Drucks P_fer am Fuß der Flüssigkeitssäule der Höhe h am austrittseitigen Ende der Kokille. Eine temperaturbedingte Änderung der Dichte ρ_liq kann hierbei unberücksichtigt bleiben, wenn die Eingießtemperatur der Metallschmelze nur wenige Grad über ihrer Erstarrungstemperatur liegt.The reference pressure P _ref can, for example, by the expression $${\mathrm{P}}_{\mathrm{ref}}=\mathrm{S}\cdot {\mathrm{P}}_{\mathrm{fer}}/\mathrm{2nd}=\mathrm{S}\cdot {\mathrm{\rho }}_{\mathrm{liq}}\cdot \mathrm{G}\cdot \mathrm{H}/\mathrm{2nd}$$

are determined, where g is the value of the acceleration due to gravity and P _fer the ferrostatic pressure of the molten metal in the interior of the cast metal strand at the outlet end of the continuous casting mold. Since, due to the laws of physics, the ferrostatic pressure P _{fer increases} linearly in the pouring direction, the ferrostatic pressure averaged over the mold level h, which is referred to as the mean surface pressure P _med , corresponds to half the value of the local ferrostatic pressure P _fer at the foot of the liquid column of height h at the exit end of the mold. A temperature- _related change in density ρ _liq can be disregarded if the pouring temperature of the molten metal is only a few degrees above its solidification temperature.

The correction factor S preferably has a value range of 0.7 - 3 and takes into account the inherent load-bearing capacity of the strand shell that forms, which weakens the effect of the outwardly directed ferrostatic pressure P _{fer of} the molten metal, furthermore the effect of the frictional forces between the narrow side plates and the broad side plates, which differ from those of counteract the forces applied to the actuators of the narrow side plates and reduce them accordingly, and the friction between the strand shell and the narrow side plates, which due to the narrow side conicity has an outward force component in the width direction of the continuous casting mold and depends on the value of the narrow side conicity. In addition, the correction factor S can depend on the chosen casting speed v, because in particular the friction between the strand shell and the narrow side plates represents sliding friction and therefore the friction forces that occur depend on the relative speed between the surfaces involved.

With values of S <1, the self-supporting capacity of the strand shell outweighs the frictional forces between the narrow-side and broad-side plates or between the narrow-side plates and the strand shell and is used, for example, in an operating mode in which the broad-side plates are only applied with very little clamping action against the narrow-side plates what is also known as soft clamping.

In contrast, values of S> 1 mean that the frictional forces between the narrow-side and broad-side plates or between the narrow-side plates and the strand shell predominate and must be compensated accordingly by the actuators of the narrow-side plates.

The dependence of the correction factor S on the casting speed v can be described, for example, by a table model based on empirical values. S can also be influenced by other factors, e.g. depend on the composition of the molten metal or the casting powder, which can also be shown in an empirically determined table model.

The above-mentioned definition of the reference pressure P _ref offers the advantage that it is an easy-to-use empirical model of the command variable of the control loop according to the invention which, in addition to the correction factor S, depends only on process parameters which are known in any case and which can therefore be expanded in a simple manner by means of the correction factor S, for example in relation to new compositions of the molten metal or the casting powder, and does not require any complex physical simulations.

bestimmt, wobei

F_1,i

die von einem Messglied des Regelkreises erfasste, am Aktor i der ersten Schmalseitenplatte auftretende Kraft,

F_2,j

die von einem Messglied des Regelkreises erfasste, am Aktor j der zweiten Schmalseitenplatte auftretende Kraft,

N1

die Anzahl der Aktoren der ersten Schmalseitenplatte,

N2

die Anzahl der Aktoren der zweiten Schmalseitenplatte,

h

die Gießspiegelhöhe und

d

die Gießdicke

bezeichnen.In a further preferred embodiment of the method according to the invention, the mean surface pressure P _{med is given} by the expression $${\mathrm{P}}_{\mathrm{med}}=\left[{\displaystyle \sum _{\mathrm{i}=1}^{\mathrm{N}1}\left({\mathrm{<figure-callout\; id="1"\; label="F"\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">F</figure-callout>}}_{1,\mathrm{i}}\right)+{\displaystyle \sum _{\mathrm{j}=1}^{\mathrm{N}\mathrm{2nd}}\left({\mathrm{F}}_{\mathrm{2nd},\mathrm{j}}\right)}}\right]/\left(\mathrm{2nd}\cdot \mathrm{H}\cdot \mathrm{d}\right)$$

determined where

F _{1, i}

the force detected by a measuring element of the control circuit and occurring at the actuator i of the first narrow side plate,

F _{2, j}

the force detected by a measuring element of the control loop and occurring at the actuator j of the second narrow side plate,

N1

the number of actuators of the first narrow side plate,

N2

the number of actuators of the second narrow side plate,

H

the mold level and

d

the casting thickness

describe.

The mean surface pressure P _med represents an averaging over the forces of all actuators of the two narrow side plates which the actuators exert on the narrow side plates. These forces can advantageously be measured very simply and quickly using methods known from the prior art, as a result of which the control loop detects control deviations very quickly can react. In particular, it is possible to control control deviations much more quickly than would be the case with temperature or heat flow-based controls, since force measurements can be carried out within fractions of a second.

In a preferred embodiment of the method according to the invention, the setting of a common narrow side taper for both narrow side plates takes place symmetrically with respect to the casting direction of the continuous casting mold, with the spatial position of the center line of the metal strand in relation to the wide side plates and a value for the casting width b.

For each of the two narrow side plates, by means of the actuators acting in the width direction of the continuous casting mold, whose spatial arrangement is known, the inclination of the narrow side plate with respect to the casting direction and an absolute spatial position can be specified, which - based on the entire continuous casting mold - has four mechanical ones Represents degrees of freedom.

If the position of the center line of the produced metal strand with respect to the broad side plates is kept constant by appropriate positioning of the narrow side plates so that the metal strand does not drift in the width direction relative to the broad side plates, this reduces the number of degrees of freedom by one. An additional specification of a distance between the narrow side plates to one another - for example the distance between the ends of the narrow side plates on the casting outlet side, which by definition is identical to the casting width b of the continuous casting mold - reduces the degrees of freedom by another. Furthermore, if the inclinations of the two narrow side plates are set symmetrically with respect to the casting direction, this represents a restriction to only a single degree of mechanical freedom of the narrow side plates, which is represented by a correspondingly unique value for the narrow side conicity. This means that there is a clear connection between a value for the narrow-side taper K _s and the position values of the individual actuators of both the first and the second narrow-side plates, so that corresponding position values of the actuators of both narrow-side plates can be determined uniquely from a preset value for the narrow-side taper K _s . In this case, the two narrow side plates of the continuous casting mold are no longer positioned independently of one another, but instead are positioned by a single control loop.

In this context, it is also possible to change the casting width b during the execution of the control process or to leave it constant and to specify a starting value for the target positions of the individual actuators when they first pass through the control circuit. A constant value of the casting width b during the casting process is particularly desirable with regard to the quality of the cast metal strand, since subsequently complex measures for adjusting the width of the metal strand, such as e.g. Flame cutting or side upsetting can be omitted.

In a preferred embodiment of the method according to the invention, the controller of the at least one control circuit comprises a control specification with an input variable derived from the control deviation and an output variable and the actual positions {X _{1, i} , X _{2, j} } of the at least one control circuit are generated in each cycle Actuators of at least one of the first or the second narrow side plates are detected and an actual value I _s for the narrow side taper K _{s is} derived therefrom and this by specifying corresponding target positions {Y _{1, i} , Y _{2, j} } for the actuators of at least one of the first or the second Narrow side plate in a controlled system of the at least one control loop that reproduces the effect of the narrow side taper on the mean surface pressure only if there is a difference to the determined actual value.

The detected actual positions of the actuators of the narrow side plates thus represent input variables and the determined target positions for the actuators at least correspond to output variables represents a control loop, which are determined anew each time through the at least one control loop.

If the actual value I _{s of} the narrow side taper and the manipulated variable determined in the current cycle of the at least one control loop, which is identical to the nominal value of the narrow side taper K _s , then there is no need to adjust the narrow side taper over the controlled system. This is particularly advantageous if, when adjusting the narrow side plates, the clamping mechanism for the wide side plates usually has to be actuated, which in this case can be omitted. Such a control cycle can therefore be run through correspondingly quickly, ie within a few milliseconds or less.

wobei

P_dif'

eine aus einer Regelabweichung P_dif des Regelkreises abgeleitete Größe,

K_s'

eine von der Regelvorschrift des Regelkreises ermittelte Größe zur Ermittlung der Stellgröße K_s und

k

ein Proportionalitätsfaktor mit einem Wertebereich von 0.001 bis 0.1, bevorzugt von 0.005 bis 0.02

sind.In a further preferred embodiment of the method according to the invention, there is a rule specification of the controller $${\mathrm{K}}_{\mathrm{s}}\prime ={\mathrm{I.}}_{\mathrm{s}}-\mathrm{k}\cdot {\mathrm{P}}_{\mathrm{dif}}\prime$$

in which

P _dif '

a variable derived from a control deviation P _{dif of} the control loop,

K _s '

a variable determined by the regulation of the control loop for determining the manipulated variable K _s and

k

a proportionality factor with a range of values from 0.001 to 0.1, preferably from 0.005 to 0.02

are.

The rule specification describes the behavior of the control loop as a function of the control deviation and is used to determine the output variable; the meaning and role of the regulation are to be understood in the context of a classic control loop and are therefore well known to the person skilled in the art.

With this rule specification, control deviations can be parameterized in a very simple manner: if the proportionality factor k has a value less than 1, this means that the determined control deviation is weakened into the correction of the output variable of the control specification, while for values greater than 1, the control deviation is amplified.

wobei

{P_dif} _τ

eine Menge von über eine Zeitspanne τ zurückreichenden, gespeicherten Werten der Regelabweichung P_dif aus vorangegangenen Zyklen des Regelkreises und

P_dif'

eine vom zeitbezogenen Filter Φ_T ermittelte Eingangsgröße für die Regelvorschrift des Regelkreises

sind.In a further preferred embodiment of the method according to the invention, the control deviation P _{dif of} the control circuit is first _filtered by means of a time-related filter Φ _T according to $${\mathrm{P}}_{\mathrm{dif}}\prime ={\mathrm{\Phi }}_{\mathrm{T}}\left({\mathrm{P}}_{\mathrm{dif}},{\left\{{\mathrm{P}}_{\mathrm{dif}}\right\}}_{\mathrm{\tau }}\right),$$

in which

{P _dif } _τ

a set of over a period τ reaching back, stored values of the control deviation P _dif from previous cycles of the control circuit and

P _dif '

an input variable determined by the time-related filter Φ _T for the control specification of the control loop

are.

This filtering can consist, for example, of a simple averaging of all the values of the control deviation used. However, it is also conceivable to weight current values more strongly than values from earlier times. For example, the historical values of the control deviation are preferably taken into account over a period of time t = 5-10 seconds.

This temporal filtering of the control deviation eliminates high-frequency fluctuations in the measurement signal, which can be caused, for example, by incorrect measurements. suppressed. This prevents incorrect adjustment of the narrow side plates due to incorrect measured values or due to high-frequency interference and helps to stabilize the continuous casting process.

In the event that an adjustment of the narrow side taper is triggered, this can be carried out quickly since, because of the first filtering, which filters out large fluctuations in the control deviation, usually only small changes in the manipulated variable have to be carried out. For example, a change of 0.1% of the narrow side taper at a casting width of 2000mm in a conventional continuous casting mold, the level of which is typically less than 1000mm, only causes an adjustment of less than 2mm in the area of the cast-side actuators. The entire process of such an adjustment, including releasing the clamping of the broad side plates, moving the narrow side plates by means of the actuators and then clamping the broad side plates again, can therefore usually be carried out within a second or even faster, so that a very fast control process is provided.

wobei

K_s"

eine mittels des Sättigungsfilter Φ_S abgeleiteter Wert zur Ermittlung der Stellgröße K_s,

K_s,min

ein unterer Grenzwert für die Schmalseitenkonizität K_s und

K_s,max

ein oberer Grenzwert für die Schmalseitenkonizität K_s

sind.In a further preferred embodiment of the method according to the invention, the output variable K _s ' is filtered a second time by means of a saturation filter Φ _S according to $${\mathrm{K}}_{\mathrm{s}}"={\mathrm{\Phi }}_{\mathrm{S}}\left({\mathrm{K}}_{\mathrm{s}}\prime ,{\mathrm{K}}_{\mathrm{s},\min },{\mathrm{K}}_{\mathrm{s},\mathrm{Max}}\right),$$

in which

K _s "

a value derived by means of the saturation filter Φ _S for determining the manipulated variable K _s ,

K _{s, min}

a lower limit for the narrow side taper K _s and

K _{s, max}

an upper limit for the narrow side taper K _s

are.

The saturation filter Φ _S ensures that the narrow side taper K _s regulated by the control loop remains within the permitted range defined by the limit values K _{s, min} and K _{s, max} , for example within 1.1 to 1.2. The limit values K _{s, min} and K _{s, max are} parameters of the control process, which are usually preset, but which can also be changed during the casting process. For example, the limit values K _{s, min} and K _{s, max can} be changed by an operator or by a control system when changing between two metal batches, if a changed composition of the molten metal requires this.

ermittelt, wobei | | die Bildung des numerischen Absolutwerts und λ den Schwellwert des Hysteresefilters bezeichnen und der abgeleitete Wert K_s" einer der dritten Filterung vorangegangenen signaltechnischen Behandlung der Ausgangsgröße K_s' der Regelvorschrift entspricht.In a further preferred embodiment of the method according to the invention, the narrow side taper K _{s is} correspondingly filtered by a third filtering of a value K _s "derived from the output variable K _s ' of the regulation by means of a hysteresis filter Φ _H $${\mathrm{K}}_{\mathrm{s}}={\mathrm{\Phi }}_{\mathrm{H}}\left(\left|{\mathrm{K}}_{\mathrm{s}}"-{\mathrm{I.}}_{\mathrm{s}}\right|,\mathrm{\lambda }\right),$$

determined, where | | the formation of the numerical absolute value and λ denote the threshold value of the hysteresis filter and the derived value K _s "corresponds to a signal-technical treatment of the output variable K _s ' preceding the third filtering of the regulation.

According to a two-point controller, the manipulated variable of the control loop is only changed if the value K _s determined in the current cycle of the control loop differs in amount by at least the value λ from the current actual value I _{s of} the narrow side taper. This means that the actuators of the narrow side plates are only adjusted if the newly calculated default value for the narrow side taper differs from the existing value by more than 0.05, for example, so that, for example, only slight fluctuations in production conditions affect the quality of the metal strand produced have no effect, do not unnecessarily adjust the narrow side plates and in particular do not release the clamping of the broad side plates must, which contributes to a constant stability of the continuous casting process and to the speed of the control process.

• einen Referenzdruck P_ref als Führungsgröße,
• eine mittlere Flächenpressung P_med zwischen den Schmalseitenplatten und dem Metallstrang als Regelgröße, wobei die mittlere Flächenpressung P_med aus den in Wirkrichtung der Aktoren auftretenden Kräften ermittelbar ist,
• einen Regler, durch den in Abhängigkeit von einer Regelabweichung P_dif = P_ref - P_med als Eingangsgröße die Schmalseitenkonizität K_s als Stellgröße des Regelkreises ermittelbar ist, und
• eine Regelstrecke, über die mittels der Aktoren die Position der ersten und/oder der zweiten Schmalseitenplatte entsprechend der Schmalseitenkonizität K_s einstellbar ist,

aufweist.The invention further relates to a
Device for setting a narrow side taper K _{s of} a continuous casting mold for the production of a metal strand, in particular for carrying out one of the methods described, the continuous casting mold comprising a first and a second narrow side plate, on each of which at least two position-controlled actuators for positioning the respective narrow side plate at different distances from the are arranged on the pour-side end of the continuous casting mold and the device has a control unit and devices for detecting the forces occurring in the direction of action of each actuator during operation of the continuous casting mold,
characterized in that
the control unit is set up for a control loop, the control loop

• a reference pressure P _ref as a reference variable,
• an average surface pressure P _med between the narrow side plates and the metal strand as a controlled variable, the average surface pressure P _{med being able to be determined} from the forces occurring in the direction of action of the actuators,
• a controller, by means of which, depending on a control deviation P _dif = P _ref - P _med, the narrow side taper K _s as the manipulated variable of the control loop can be determined as an input variable, and
• a controlled system, via which the position of the first and / or the second narrow side plate can be adjusted according to the narrow side taper K _s by means of the actuators,

having.

The advantageous configurations of the device according to the invention for setting a narrow side taper of a continuous casting mold essentially correspond to those of the method according to the invention.

In a preferred embodiment of the device according to the invention, at least one of the actuators is a hydraulically moved actuator.

Such actuators can be moved very quickly since no gear is required and are sufficiently known from the prior art.

In a particularly preferred embodiment of the device according to the invention, at least one of the hydraulically moved actuators is a double-acting hydraulic cylinder.

Double-acting hydraulic cylinders offer the advantage that the force applied by the respective actuator can be determined very easily by two pressure sensors per actuator, since the force is determined by the differential pressure between the two chambers and the cross-sectional area of the piston of the double-acting hydraulic cylinder. It is therefore also possible to retrofit an existing continuous casting mold, which already has such hydraulic cylinders for adjusting the narrow side plates, to carry out the method according to the invention in a simple and cost-effective manner, since only sensors for detecting the corresponding pressures and the travel positions of the corresponding actuators have to be installed.

In a further embodiment of the device according to the invention, at least one of the actuators has an electrical rotary drive.

Such actuators allow simple determination of the actuator position on the basis of the position of the drive axis of the electrically operated motor or an axis of the transmission, that is usually used between the motor and the linearly moving point of application of the actuator in question. The forces that occur at the points of application of the actuators can be measured, for example, using strain gauges.

In a further preferred embodiment of the device according to the invention, at least one of the electrically driven actuators is a linear motor.

Linear motors do not require a gear and therefore have no mechanical play. They also offer the advantage that the force occurring can be determined directly from the force-speed characteristic or from the force-current characteristic without additional force sensors.

FIG 1a

eine perspektivische Darstellung einer Stranggusskokille,

FIG 1b

einen Schnitt durch eine Stranggusskokille normal zur Breitenrichtung,

FIG 1c

einen Schnitt durch eine Stranggusskokille normal zur Dickenrichtung,

FIG 2

schematisch die in Breitenrichtung der Kokille auftretenden Kräfte,

FIG 3

den Signalfluss einer Schmalseitenplatte eines erfindungsgemäßen Regelkreises und

FIG 4

den schematischen Aufbau eines erfindungsgemäßen Regelkreises einer Schmalseitenplatte mit zwei Aktoren.

The above-described properties, features and advantages of this invention and the manner in which they are achieved can be more clearly understood in connection with the following description of exemplary embodiments, which are explained in more detail in connection with the drawings. Show

FIG 1a

a perspective view of a continuous casting mold,

1b

a section through a continuous casting mold normal to the width direction,

1c

a section through a continuous casting mold normal to the thickness direction,

FIG 2

schematically the forces occurring in the width direction of the mold,

FIG 3

the signal flow of a narrow side plate of a control circuit according to the invention and

FIG 4

the schematic structure of a control circuit according to the invention of a narrow side plate with two actuators.

FIG 1a shows an oblique view of the arrangement of the broad side plates 2, 2 'and the first and second narrow side plates 4 and 4' of a continuous casting mold 1, the two narrow side plates 4, 4 'being slidably arranged along the inner surfaces of the broad side plates 2, 2'. The back-up plates of the individual mold plates and the actuators for adjusting the narrow side plates are not shown in this view.

Furthermore are in FIG 1a the direction vectors of the thickness direction D, the width direction B and the casting direction G are shown in their spatial position in relation to the continuous casting mold 1, the vectors D, B and G forming an orthogonal, right-handed coordinate system.

At the end 3 on the pouring side, molten metal is added with the addition of casting powder into the interior of the continuous casting mold 1, where the molten metal is transported further in the casting direction G and is withdrawn from the mold 1 at the exit end 3 'in the form of a partially solidified metal strand 5. The metal strand 5 has a rectangular cross section with respect to the normal plane to the casting direction G, the short side of which is oriented in the thickness direction D and the long side in the width direction B.

1b shows a section through the continuous casting mold 1 FIG 1a normal to the width direction B, in which the broad side plates 2, 2 'inclined relative to the casting direction G with the backing plates 7, 7' attached to them and the trapezoidal shape of the second narrow side plate 4 'can be seen.

The distance f between the inner surfaces of the broad side plates 2, 2 'at the end 3 on the pouring side is greater than the corresponding distance d at the end 3' of the continuous casting mold 1, where d is also referred to as the casting thickness, since the cast metal strand 5 (in 1b not shown) with this thickness from the interior enclosed by the continuous casting mold 1 exit.

In 1c is a section through the continuous casting mold 1 from FIG 1a shown normal to the thickness direction D. The narrow side plates 4, 4 ', which are inclined relative to the casting direction G, can be seen, with the backing plates 6, 6' attached to them, and the rectangular shape of the wide side plate 2 can also be seen, along the inside of which the narrow side plates 4, 4 'can be moved.

The distance e between the inner surfaces of the narrow side plates 4, 4 'at the end 3 on the pouring side is in turn greater than the corresponding distance b at the end 3' of the continuous casting mold 1 at the outlet side, b being referred to as the casting width.

On the outer sides of the narrow side plates 4, 4 ', an upper actuator A _1.1 or A _2.1 engages near the pour-side end 3 of the continuous casting mold 1 and a lower actuator A _1.2 or A _2.2 near the outlet side End 3 'of the continuous casting mold 1. By means of the actuators A _{1, 1} or A _{1, 2} acting in the width direction B, the first narrow side plate 4 can be moved or held in a certain position with respect to its inclination to the casting direction G and its position in the width direction B, with the upper actuator A _{1 , 2} the force F _1.1 and at the lower actuator A _1.2 the force F _{1.2 occurs} along the effective direction of the respective actuator. Accordingly, the inclination and the position of the second narrow side plate 4 'are set or maintained by means of the actuators A _2.1 and A _2.2, the force F _2.1 on the upper actuator A _{2.1 and} the force on the lower actuator A _{2 , 2} the force F _{2.2 occurs} in the effective direction of the respective actuator.

$${\mathrm{K}}_{\mathrm{s}}=\left(\mathrm{e}-\mathrm{b}\right)\times 100/\mathrm{b}$$

With the above definitions and in 1b and 1c The distances shown are the broadside taper K _b and the narrow side taper K _s as a dimensionless quantity, in each case in percent, in the present example $${\mathrm{K}}_{\mathrm{b}}=\left(\mathrm{f}-\mathrm{d}\right)\times 100/\mathrm{H}$$

$${\mathrm{K}}_{\mathrm{s}}=\left(\mathrm{e}-\mathrm{b}\right)\times 100/\mathrm{b}$$

However, other calculation rules for the taper are also conceivable, for example the narrow side taper K _{s can} also be related to the mold height H.

FIG 2 shows a section normal to the thickness direction D through a continuous casting mold 1, the first and second narrow side plates 4 and 4 'of which each have two actuators (A _1.1 , A _1.2 ) and (A _2.1 , A _2.2 ) are, however, the inclination of the narrow side plates 4 and 4 'is not shown. Along the inner surface of the first narrow side plate 4, the course of the ferrostatic pressure P _{fer of} the metal melt 10, which increases linearly in the casting direction G, is shown schematically, while along the inner surface of the second narrow side plate 4 'the strand shell 13 growing in the casting direction G can be seen. Furthermore, the center line M denotes the line of symmetry of the metal strand 5 with respect to the width direction B of the continuous casting mold 1.

Near the pouring-side end 3 of the continuous casting mold 1, the surface of the cast metal melt 10 is also referred to as a casting level 12, which is located at a distance h - the so-called casting level - above the exit-side end 3 'of the continuous casting mold 1. At the outlet end 3 ', the partially solidified metal strand 5 is pulled out of the continuous casting mold 1, the strand shell 13 already formed being supported in the width direction B by lateral strand guide rollers 14 and 14'.

With F _1.1 and F _2.1 are as in 1c the forces of the upper actuators A _1.1 and A _2.1 (in FIG 2 not shown) referred to, which are transferred near the pouring end 3 to the respective narrow side plate 4 or 4 '. Correspondingly, F _1.2 and F _2.2 symbolize the forces of the outlet-side actuators A _1.2 and A _2.2 .

In FIG 3 is normal to the thickness direction D in a section Half of a continuous casting mold 1 according to the invention up to the center line M as well as the control connection to a control unit 8 are shown, the first narrow side plate 4 being able to be moved with the aid of two actuators A _1,1 and A _1,2 . The other half of the continuous casting mold 1, which comprises the second narrow side plate 4 'and corresponding actuators A _2.1 and A _2.2 , is connected to the control unit 8 in a manner corresponding to the first half shown, but in FIG FIG 3 not shown. In addition, in the specific example, the actuators A _1.1 and A _{1.2 are designed} as double-acting hydraulic cylinders.

The liquid metal melt 10, which is introduced into the continuous casting mold 1 during the continuous casting near the upper, casting-side end 3, forms with its surface the casting level 12 at a distance corresponding to the level of the casting level h above the lower, exit-side end 3 'of the continuous casting mold 1. In the casting direction G below the first narrow side plate 4, the solidified strand shell 13 is supported by lateral strand guide rollers 14.

The actuator A ₁ , ₁ engages near the upper, casting-side end 3 of the continuous casting mold 1 on the first narrow side plate 4 and can move it at this point of attack in the width direction B; Similarly, the first narrow side plate 4 can also be moved in the width direction B by the actuator A 1, ₂ , which engages the first narrow side plate 4 in the vicinity of the lower, outlet-side end 3 '.

For detecting the instantaneous position of the first narrow side plate 4 are of the actuators A _1.1 and A _1.2 the respective position values X and _1.1 X transmitted to the control unit 8 _1,2, which are determined by the corresponding position sensors 16 of the respective actuator . In addition, the pressures of the two chambers of each double-acting hydraulic cylinder are detected by means of corresponding pressure sensors 11 and transmitted to the control unit 8. The forces F _1.1 and F _1.2 with which the actuators A _1.1 and A _{1.2 act} on the first narrow side plate 4 can be determined from the difference between these pressures. Furthermore, the actuators A _1.1 and A _{1.2 are} acted upon by hydraulic drive units 9 with corresponding amounts of hydraulic fluid, so that the pistons of the actuators are moved in accordance with the desired positions Y _1,1 and Y _1,2 determined by the control unit 8. The hydraulic drive units 9 can be, for example, hydraulic pumps or hydraulic valves which provide the volume of hydraulic fluid required in each case. For those in FIG 3 The second narrow side plate 4 '(not shown), the explanations apply mutatis mutandis with respect to the actual positions X _2.1 and X _2.2 and the forces F _2.1 and F _{2.2 of} the actuators A _2.1 and A _2.2 and for the setpoints Y _2.1 and Y _2.2 specified by the control unit 8.

FIG 4 shows an embodiment of a control circuit 15 for setting the narrow side taper K _s according to the inventive method, the control circuit 15 in addition to the actual regulation 25 a first time filtering 22 of the control deviation P _dif , and a second filtering 23 with respect to the allowable maximum values and a third filtering 24 with regard to a desired hysteresis behavior of K _s .

• Die von den Aktoren A_1,i an die erste Schmalseitenplatte 4 übertragenen Kräfte F_1,i und die von den Aktoren A_2,j an die zweite Schmalseitenplatte 4' übertragenen Kräfte F_2,j werden in einem Messglied 26 erfasst, woraus zusammen mit den Werten der Gießspiegelhöhe h und der Gießdicke d die Regelgröße des Regelkreises 15 in Form einer mittlere Flächenpressung P_med (mit Druck als physikalischer Einheit) ermittelt wird. Die Indizes i bzw. j umfassen dabei den Wertebereich {1, ... N1} bzw. {1, ... N2}, wobei N1 bzw. N2 die Anzahl der Aktoren an der ersten bzw. zweiten Schmalseitenplatte 4 bzw. 4' bezeichnen.
• Als Führungsgröße des Regelkreises 15 wird ein Referenzdruck P_ref aus der Dichte der flüssigen Metallschmelze ρ_liq, der Gießspiegelhöhe h und einem dimensionslosen Korrekturfaktor S herangezogen. Dabei können die Werte von h, ρ_liq und S für jede gegossenen Charge entweder fest vorgegeben werden oder auch während des Gießvorganges geändert werden. Insbesondere kann die aktuelle Gießspiegelhöhe h messtechnisch erfasst und der erhaltene Momentanwert dem Regelkreis 15 übermittelt werden.
• Es wird der aktuelle Wert der Regelabweichung P_dif des Regelkreises 15 gemäß $${\mathrm{P}}_{\mathrm{diff}}={\mathrm{P}}_{\mathrm{ref}}-{\mathrm{P}}_{\mathrm{med}}$$
  
  bestimmt und in einer Regeleinheit 8 (in FIG 4 nicht dargestellt) gespeichert und dem Regler 21 des Regelkreises 15 zugeleitet, wobei der Regler 21 neben der eigentlichen Regelvorschrift 25 im vorliegenden Beispiel eine erste, zweite und dritte Filterung 22, 23 und 24 beinhaltet.
• Im nächsten Schritt wird aus dem aktuellen Wert von P_dif zusammen mit gespeicherten Werten der Regelabweichung aus früheren Durchläufen durch den Regelkreis 15 mittels einer ersten Filterung 22, die einen zeitbezogenen Filter Φ_T verwendet, der eine zurückliegende Zeitspanne τ umspannt, ein gefilterter Wert P_dif' aus der Regelabweichung bestimmt, wobei der Filter Φ_T dazu dient, kurzzeitige Abweichungen und hochfrequente Störeinflüsse auszufiltern und so einen zeitlich geglätteten Wert der Regelabweichung zu ermitteln.
• In der Regelvorschrift 25 des Regelkreises werden die Istwerte der Positionen X_1,i der Aktoren A_1,i der ersten Schmalseitenplatte 4 und die Istwerte der Positionen X_2,j der Aktoren A_2,j der zweiten Schmalseitenplatte 4' mit Hilfe von Positionssensoren 16 (in FIG 4 nicht dargestellt) erfasst und daraus entsprechend den geometrischen Verhältnissen der Stranggusskokille 1 ein Istwert I_s für die Schmalseitenkonizität der Stranggusskokille 1 bestimmt. Aus dem Istwert I_s und aus dem zeitlich gefilterten Wert P_dif' wird eine Ausgangsgröße K_s' der Regelvorschrift 25 derart bestimmt, dass über die Wirkung der Aktoren A_1,i bzw. A_2,j in der Regelstrecke 20 der Regelabweichung P_dif entgegengewirkt wird.
• Anschließend wird in einer zweiten Filterung 23 mittels eines Sättigungsfilters Φ_S, der die erlaubte Untergrenze K_s,min bzw. Obergrenze K_s,max als Parameter für die Schmalseitenkonizität K_s beinhaltet, aus der Ausgangsgröße K_s' der Regelvorschrift 25 ein abgeleiteter Wert K_s" bestimmt. Dadurch wird verhindert, dass die Schmalseitenkonizität K_s die vorgegebenen Grenzwerte bei großer oder permanent andauernder Regelabweichung P_dif über- oder unterschreitet, was insbesondere bei einer Proportionalregelung in der Regelvorschrift 25 bewirkt würde.
• Danach wird in einer dritten Filterung 24 mittels eines Hysteresefilters Φ_H aus dem abgeleiteten Wert K_s" der neu einzustellende Wert für die Schmalseitenkonizität K_s bestimmt, der gleichzeitig die Stellgröße des Regelkreises 15 darstellt. Der Hysteresefilter Φ_H beinhaltet dabei einen Parameter λ, der den Schwellwert des Hysteresefilters beschreibt. Dieser Parameter legt die minimale Differenz zwischen der Stellgröße K_s und dem zugehörigen Istwert I_s fest, ab der eine Verstellung der Schmalseitenplatten 4 bzw. 4' tatsächlich durchgeführt wird. Differenzen unterhalb des Schwellwertes λ werden vom Hysteresefilter Φ_H unterdrückt, indem die Stellgröße K_s dem Istwert I_s gleichgesetzt wird.
• In der Regelstrecke 20 des Regelkreises 15 werden aus dem neuen Vorgabewert für die Schmalseitenkonizität K_s und aus der Gießbreite b die entsprechenden Sollpositionen Y_1,i bzw. Y_2,j der Aktoren A_1,i bzw. A_2,j der ersten bzw. zweiten Schmalseitenplatte 4 bzw. 4' ermittelt und eine Verstellung der Schmalseitenplatten durch entsprechende Anstellung der Aktoren veranlasst, wobei die Verstellung nur dann durchgeführt wird, wenn sich die Stellgröße K_s und der zugehörige Istwert I_s unterscheiden.

A cycle of the control circuit 15 runs as follows for a continuous casting mold 1 comprising a first and a second narrow side plate 4 and 4 ':

• The forces F _{1, i} transmitted by the actuators A _{1, i} to the first narrow side plate 4 and the forces F _{2, j} transmitted by the actuators A _{2, j} to the second narrow side plate 4 'are recorded in a measuring element 26, which together with the controlled variable of the control circuit 15 is determined in the form of an average surface pressure P _med (with pressure as the physical unit), the values of the mold level h and the casting thickness d. The indices i and j comprise the value range {1, ... N1} or {1, ... N2}, where N1 or N2 is the number of actuators on the first or second narrow side plate 4 or 4 ' describe.
• A reference pressure is used as the reference variable of the control circuit 15 P _ref from the density of the molten metal ρ _liq , the casting _{level height} h and a dimensionless correction factor S. The values of h, ρ _liq and S for each cast batch can either be specified or changed during the casting process. In particular, the current mold level h can be measured and the instantaneous value obtained can be transmitted to the control circuit 15.
• The current value of the control deviation P _{dif of} the control circuit 15 is shown in FIG $${\mathrm{P}}_{\mathrm{diff}}={\mathrm{P}}_{\mathrm{ref}}-{\mathrm{P}}_{\mathrm{med}}$$
  
  determined and in a control unit 8 (in FIG 4 not shown) stored and fed to the controller 21 of the control circuit 15, the controller 21 in addition to the actual regulation 25 in the present example including a first, second and third filtering 22, 23 and 24.
• In the next step, a filtered value P _dif is made from the current value of P _dif together with stored values of the control deviation from previous runs through the control circuit 15 by means of a first filtering 22, which uses a time-related filter Φ _T that spans a past time period τ 'determined from the control deviation, the filter Φ _T being used to filter out short-term deviations and high-frequency interference and thus to determine a time-smoothed value of the control deviation.
• In the regulation 25 of the control loop, the actual values of the positions X _{1, i of} the actuators A _{1, i of} the first narrow side plate 4 and the actual values of the positions X _{2, j of} the actuators A _{2, j of} the second narrow side plate 4 'are made with the help of position sensors 16 (in FIG 4 not shown) recorded and an actual value I _s for the narrow side taper of the continuous casting mold 1 is determined therefrom in accordance with the geometric conditions of the continuous casting mold 1. The actual value I _s and the time-filtered value P _dif 'becomes an output variable K _s ' of the regulation 25 is determined such that the effect of the actuators A _{1, i} or A _{2, j} in the controlled system 20 counteracts the control deviation P _dif .
• Subsequently, the control law in a second filtering 23 by a saturation filter Φ _{S, S min is} the allowed lower limit of _K, or the upper limit K _{s, max} as a parameter for Schmalseitenkonizität K _s includes, from the output of K _s' 25 is a derived value K _s "is determined. This will prevent that the Schmalseitenkonizität K _s, which would be caused particularly in a proportional control in the control law 25 _dif exceed the predetermined limit values at high or permanently persistent control deviation P or below.
• Then, in a third filtering 24, a hysteresis filter Φ _{H is used to determine} the newly set value for the narrow side conicity K _s from the derived value K _s ″, which value simultaneously represents the manipulated variable of the control circuit 15. The hysteresis filter Φ _{H contains} a parameter λ which This parameter defines the minimum difference between the manipulated variable K _s and the associated actual value I _s , from which adjustment of the narrow side plates 4 or 4 'is actually carried out. Differences below the threshold value λ are caused by the hysteresis filter Φ _H suppressed by setting the manipulated variable K _{s to} the actual value I _s .
• In the control path 20 of the loop 15 are out of the new default value for the Schmalseitenkonizität K _s and from the casting width b the corresponding desired positions Y _{1, i,} Y _{2, j} of the actuators A _{1, i,} A _{2, j} of the first or The second narrow side plate 4 or 4 'is determined and the narrow side plates are adjusted by adjusting the actuators accordingly, the adjustment being carried out only if the manipulated variable K _s and the associated actual value I _s differ.

Reference symbol list

1

Continuous casting mold

2, 2 '

Broad side plate

3rd

pour end

3 '

exit end

4th

first narrow side plate

4 '

second narrow side plate

5

Metal strand

6, 6 '

Back plate narrow side

7, 7 '

Back plate broadside

8th

Control unit

9

hydraulic drive unit

10th

Molten metal

11

Pressure sensor, device for force detection

12

Casting level

13

Strand shell

14, 14 '

Strand guide rollers

15

Control loop

16

Position sensor

20th

Controlled system

21st

Regulator

22

first filtering

23

second filtering

24th

third filtering

25th

Regulation

26

Measuring element

A _{1, i}

Actuator i of the first narrow side plate

A _{2, j}

Actuator j of the second narrow side plate

A _1.1

pouring-side actuator of the first narrow side plate

A _1.2

outlet-side actuator of the first narrow side plate

A _2.1

pouring-side actuator of the second narrow side plate

A _2.2

outlet-side actuator of the second narrow side plate

b

Casting width

B

Width direction

d

Casting thickness

D

Thickness direction

e

distance on the pouring side of the narrow side plates

f

distance on the casting side of the wide side plates

F _{1, i}

Force on actuator i of the first narrow side plate

F _{2, j}

Force on actuator j of the second narrow side plate

F _1.1

Force on the casting-side actuator of the first narrow side plate

F _1.2

Force on the outlet-side actuator of the first narrow side plate

F _2.1

Force on the casting-side actuator of the second narrow side plate

F _2.2

Force on the outlet side actuator of the second narrow side plate

Φ _H

Hysteresis filter

Φ _p

Saturation filter

Φ _T

time-related filter

G

Pouring direction

H

Casting level height

H

Mold height

i

Index regarding the first narrow side plate

I _s

Actual value of the narrow side taper

j

Index regarding the second narrow side plate

K _s

Narrow side taper, manipulated variable

K _s '

Initial size of the rule

K _s "

derived value

K _{s, min}

lower limit for narrow side taper

K _{s, max}

upper limit for narrow side taper

λ

Threshold

M

Center line

N1

Number of actuators on the first narrow side plate

N2

Number of actuators on the second narrow side plate

P _dif

Control deviation

P _dif '

filtered value of the control deviation, input variable of the control regulation

P _med

medium surface pressure, controlled variable

P _ref

Reference pressure, reference variable

ρ _liq

Density of the molten metal

S

dimensionless correction factor

τ

Period of time

X _{1, i}

Actual position of the actuator i of the first narrow side plate

X _{2, j}

Actual position of the actuator j of the second narrow side plate

X _1.1

Actual position of the casting-side actuator of the first narrow side plate

X _1.2

Actual position of the outlet-side actuator of the first narrow side plate

X _2.1

Actual position of the casting-side actuator of the second narrow side plate

X _2.2

Actual position of the outlet-side actuator of the second narrow side plate

Y _{1, i}

Target position of the actuator i of the first narrow side plate

Y _{2, j}

Target position of the actuator j of the second narrow side plate

Y _1.1

Target position of the casting-side actuator of the first narrow side plate

Y _1.2

Target position of the outlet-side actuator of the first narrow side plate

Y _2.1

Target position of the casting-side actuator of the second narrow side plate

Y _2.2

Target position of the outlet-side actuator of the second narrow side plate

Claims (14)

1. Method for setting a narrow-side conicity (K_s) of a continuous casting mould (1) for the production of a metal strand (5) with the aid of at least one closed-loop control circuit (15), the continuous casting mould (1) comprising a first narrow-side plate (4) and a second narrow-side plate (4'),

   - wherein a plurality (N1) of positionally controlled actuators (A_1,i), with i∈{1,...,N1}, for positioning the first narrow-side plate (4) are arranged on the first narrow-side plate (4) and a plurality (N2) of positionally controlled actuators (A_2,j), with j∈{1,...,N2}, for positioning the second narrow-side plate (4') are arranged on the second narrow-side plate (4'), in each case at a different distance from the charging-side end (3) of the continuous casting mould (1), and

   - wherein, during the operation of the continuous casting mould (1), corresponding forces (F_1,i, F_2,j), with i∈{1,...,N1} and j∈{1,...,N2}, occur in the effective direction of each actuator (A_1,i, A_2,j),

   characterized in that, the cycle through the at least one closed-loop control circuit (15) uses

   - a reference pressure (P_ref) as a reference variable and

   - an average surface pressure (P_med) between the narrow side plates (4, 4') and the metal strand (5) as a controlled variable, wherein the average surface pressure (P_med) is determined from the forces (F_1,i, F_2,j),

   and in that

   - a controller (21) determines the narrow-side conicity (K_s) as a manipulated variable of the closed-loop control circuit (15) in dependence on a system deviation (P_dif) = (P_ref) - (P_med) as an input variable and in that

   - a controlled system (20) is used to set the position of the first and/or the second narrow-side plate (4, 4') in a way corresponding to the narrow-side conicity (K_s) by means of the actuators (A_1,i, A_2,j) .
2. Method according to Claim 1, in which the reference pressure (P_ref) is a function of the density (ρ_liq) of the liquid molten metal (10), a casting level height (h) and a dimensionless correction factor (S).
3. Method according to one of the preceding claims, in which the average surface pressure (P_med) is determined by the expression $${\mathrm{P}}_{\mathrm{med}}=\left[{\displaystyle \sum _{\mathrm{i}=1}^{\mathrm{N}1}\left({\mathrm{F}}_{1,\mathrm{i}}\right)+{\displaystyle \sum _{\mathrm{j}=1}^{\mathrm{N}2}\left({\mathrm{F}}_{2,\mathrm{j}}\right)}}\right]/\left(2\cdot \mathrm{h}\cdot \mathrm{d}\right)$$

   

   with a casting level height (h) and a casting thickness (d) of the continuous casting mould (1).
4. Method according to one of the preceding claims, in which the setting of a common narrow-side conicity (K_s) for the first and second narrow-side plates (4, 4') is performed symmetrically with respect to the casting direction (G) of the continuous casting mould (1), with the spatial position of the centre line (M) of the metal strand (5) being preset with respect to the wide-side plates (2, 2') and also the casting width (b).
5. Method according to one of the preceding claims, in which the controller (21) comprises a control specification (25) with an input variable (P_dif'), derived from the system deviation (P_dif), and an output variable (K_s') and wherein

   - in each cycle of the closed-loop control circuit (15), the actual positions (X_1,i, X_2,j) of the actuators (A_1,i, A_2,j) of at least one of the first or second narrow-side plate (4, 4') are sensed,

   - an actual value (I_s) of the narrow-side conicity (K_s) is derived therefrom and

   - in a controlled system (20) of the closed-loop control circuit (15), which replicates the effect of the narrow-side conicity (K_s) on the average surface pressure (P_med), the narrow-side conicity (K_s) is only newly set by presetting corresponding setpoint positions (Y_1,i, Y_2,j) for the actuators (A_1,i, A_2,j) at least of one of the first or second narrow-side plate (4, 4') whenever there is a difference from the determined actual value (I_s).
6. Method according to Claim 5, in which the control specification (25) is K_s' = I_s - k · P_dif', where k is a proportionality factor with a range of values from 0.001 to 0.1.
7. Method according to either of Claims 5 and 6, in which the input variable (P_dif') of the control specification (25) is determined from the system deviation (P_dif) by a first filtering (22) by means of a time-based filter (Φ_T) according to $${\mathrm{P}}_{\mathrm{dif}}\prime ={\mathrm{\Phi }}_{\mathrm{T}}\left({\mathrm{P}}_{\mathrm{dif}},{\left\{{\mathrm{P}}_{\mathrm{dif}}\right\}}_{\mathrm{\tau }}\right),$$

   

   where {P_dif}_τ is a set of stored values of the system deviation (P_dif), reaching back over a time period τ, from previous cycles of the closed-loop control circuit (15).
8. Method according to one of Claims 5 to 7, in which a derived value (K_s") is determined from the output variable (K_s') of the control specification (25) by a second filtering (23) by means of a saturation filter (Φ_S) according to $${\mathrm{K}}_{\mathrm{s}}"={\mathrm{\Phi }}_{\mathrm{S}}\left({\mathrm{K}}_{\mathrm{s}}\prime ,{\mathrm{K}}_{\mathrm{s},\min },{\mathrm{K}}_{\mathrm{s},\max }\right),$$

   

   where K_s,min is a lower limit value and K_s,max is an upper limit value for the narrow-side conicity (K_s).
9. Method according to one of Claims 5 to 8, in which the narrow-side conicity (K_s) is determined by a third filtering (24) of a value (K_s"), derived from the output variable (K_s') of the control specification (25), by means of a hysteresis filter (Φ_H) according to $${\mathrm{K}}_{\mathrm{s}}={\mathrm{\Phi }}_{\mathrm{H}}\left(\left|{\mathrm{K}}_{\mathrm{s}}"-{\mathrm{I}}_{\mathrm{s}}\right|,\mathrm{\lambda }\right),$$

   

   where | | denotes the formation of the numerical absolute value and λ denotes the threshold value of the hysteresis filter (Φ_H).
10. Device for setting at least one narrow-side conicity (K_s) of a continuous casting mould (1) for the production of a metal strand (5), in particular for carrying out a method according to Claims 1 to 9, wherein the continuous casting mould (1) comprises a first narrow-side plate (4) and a second narrow-side plate (4'),

    - wherein a plurality (N1) of positionally controlled actuators (A_1,i), with i∈{1,...,N1}, for positioning the first narrow-side plate (4) are arranged on the first narrow-side plate (4) and a plurality (N2) of positionally controlled actuators (A_2,j), with j∈{1,...,N2}, for positioning the second narrow-side plate (4') are arranged on the second narrow-side plate (4'), at a different distance in each case from the charging-side end (3) of the continuous casting mould (1), and

    - wherein the device has a closed-loop control unit (8) and devices (11) for sensing the forces (F_1,i, F_2,j) occurring during the operation of the continuous casting mould (1) in the direction of effect of the respective actuators (A_1,i, A_2,j), with i∈{1,...,N1} and j∈{1,...,N2},

    characterized in that
    the closed-loop control unit (8) is designed for at least one closed-loop control circuit (15), wherein the closed-loop control circuit (15) has

    - a reference pressure (P_ref) as a reference variable and

    - an average surface pressure (P_med) between the narrow-side plates (4, 4') and the metal strand (5) as a controlled variable, wherein the average surface pressure (P_med) can be determined from the forces (F_1,i, F_2,j),

    - a controller (21), by which the narrow-side conicity (K_s) can be determined as a manipulated variable of the closed-loop control circuit (15) in dependence on a system deviation (P_dif) = (P_ref) - (P_med) as an input variable, and

    - a controlled system (20), by way of which the position of the first and/or the second narrow-side plate (4, 4') can be set in a way corresponding to the narrow-side conicity (K_s) by means of the actuators (A_1,i, A_2,j).
11. Device according to Claim 10, in which at least one of the actuators (A_1,i, A_2,j) is a hydraulically moved actuator.
12. Device according to Claim 11, in which at least one of the hydraulically moved actuators (A_1,i, A_2,j) is a double-acting hydraulic cylinder.
13. Device according to Claim 11, in which at least one of the actuators (A_1,i, A_2,j) has an electrical rotary drive.
14. Device according to Claim 11, in which at least one of the electrically driven actuators (A_1,i, A_2,j) is a linear motor.

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