EP4061552B1 - Method, control device and rolling mill for the adjustment of an outlet temperature of a metal strip exiting a rolling train - Google Patents

Description

The invention relates to a method and a control device for setting an exit temperature of a metal strip exiting an at least two-stand rolling train. In addition, the invention relates to a rolling mill for rolling a metal strip, having at least one at least two-stand rolling train and at least one control device for setting an outlet temperature of the metal strip emerging from the rolling train.

Metal strips are rolled in rolling mills to a desired outlet thickness. The metal strip coming out of a rolling mill is wound up into a spool or coil. A temperature of the coiled metal strip is important for the quality of the respective metal strip, in particular for metal strips made from certain aluminum alloys. The temperature of such a metal strip must be kept within a relatively narrow temperature range in order to achieve specified mechanical properties of the metal strip.

DE 20 2014 011 231 U1 relates to a system having a first stand having a first pair of work rolls for reducing a thickness of a material to a first specified point, a second stand having a second pair of work rolls for reducing the thickness of the material to a second specified point, and a temperature sensor positioned to measure the temperature of the material as it exits the second rack. The system also includes a controller coupled to the temperature sensor, the first frame, and the second frame to adjust at least one of the first specified point and the second specified point based on the temperature of the material measured by the temperature sensor with the it exits the second rack.

EP 2 697 002 B1 relates to a control method for a rolling mill, wherein a temperature is determined for strip sections of a strip upstream of a first rolling stand of the rolling mill, which the strip sections have, with a strip model using the temperatures determined the temperatures of the strip sections for the time of rolling of the respective strip section in the first roll stand are predicted, with at least one respective control parameter for rolling the strip sections in the first roll stand being determined using the predicted temperatures of the strip sections, and with an adjusting device acting on the first roll stand during the rolling of the respective strip section, taking into account the respective determined Control parameter is controlled. The temperatures of the strip sections are forecast for the time of rolling of the respective strip section in the first roll stand using the strip model with a first forecast horizon. The first forecast horizon corresponds to a plurality of strip sections to be rolled in the first roll stand. A control variable curve for the control device is applied for the first forecast horizon. A profile of a roll gap formed by work rolls of the first roll stand is influenced by the course of the manipulated variable. By means of a roll stand model for the first roll stand, using the forecast temperatures of the strip sections and the set manipulated variable curve for the strip sections corresponding to the first forecast horizon, a respective roll gap profile is predicted, which the work rolls of the first roll stand form at the time of rolling the respective strip section. The set manipulated variable curve is optimized using the roll gap profile predicted for the strip sections and a respective target profile. The current value of the optimized manipulated variable profile corresponds to the control parameter and is specified as the manipulated variable for the actuating device.

EP 3 089 833 B1 relates to a system having a first stand having a first pair of work rolls to reduce a thickness of a material to a first set point, a second stand having a second pair of work rolls to reduce the thickness of the material to a second set point reduce, and one Temperature sensor arranged to measure the temperature of the material as it leaves the second stand. The system also includes a controller coupled to the temperature sensor, the first stand, and the second stand to set at least one of the first set point and the second set point based on the temperature of the material exiting the second stand as measured by the temperature sensor. set.

The item " Study on Temperature Prediction Model of Cold Rolling Strip", Chen Junyi et al., International Conference on Artificial Intelligence and Big Data, 2018 which forms the basis for the preamble of claim 1, discloses a temperature prediction model for a cold rolling process, wherein an outlet temperature of a metal strip rolled in a tandem rolling mill is calculated using parameters influencing the outlet temperature, which have been optimized in advance using a particle swarm optimization method.

Conventionally, when aluminum strip is cold-rolled in a rolling train, the strip temperature is measured directly, which is time-consuming and expensive. This temperature measurement can be disrupted or lost entirely due to a sensor error or misalignment of a sensor. In addition, a run-out thickness of the metal strip is briefly disrupted by changes in lead when the load is redistributed between rolling stands of a rolling train, since a thickness monitor control in the last rolling stand has dynamic disadvantages due to a transport dead time for the thickness measuring system. A conventional temperature controller therefore has to work very slowly in order to affect a target thickness of the metal strip as little as possible.

One object of the invention is to provide a method for adjusting an outlet temperature of a metal strip leaving a rolling mill that can be implemented more cost-effectively, with which a metal strip of higher quality can be produced. This object is solved by the independent patent claim. Advantageous configurations are in the following description and the dependent Patent claims reproduced, these configurations, each taken individually or in various combinations of at least two of these configurations with one another, can represent a further developing, in particular also preferred or advantageous, aspect of the invention.

According to a method according to the invention for setting an outlet temperature of a metal strip leaving an at least two-stand rolling train, the outlet temperature is determined by means of a process model, taking into account a relationship between a strip deformation and/or a cooling rate of the metal strip by at least one cooling medium and by the contact of the metal strip with at least one fixed Rolling train component and / or a rolling speed in a last roll stand of the rolling train on the one hand and the outlet temperature set on the other hand. In addition, after the process model has been used to determine an intervention-related deviation in strip forming and/or the rolling speed in the last rolling stand from the setting values for strip forming and/or the rolling speed in the last rolling stand contained in the context using the process model, a deviation with the intervention-related deviation associated deviation of the outlet temperature from a setpoint temperature contained in the context is determined, the strip forming in the last roll stand and in one or more upstream roll stands of the rolling mill being changed by means of the process model depending on the deviation in the outlet temperature such that the outlet temperature corresponds to the setpoint temperature.

The connection between the strip forming and/or the rolling speed in the last roll stand of the rolling train on the one hand and the outlet temperature, particularly at the respective operating point, on the other hand can be calculated using a higher-level pass schedule computer. A working point is to be understood as meaning all the setting values (relating to the physical properties of forming, thickness, speed, temperature) of an area within which rolling is carried out (target pass schedule), as well as the areas in between that are passed through to reach the area. There can be one or any number Operating points are taken into account. Four operating points are particularly favorable within the meaning of the invention, since they contain all the important key points of the rolling process without requiring too much computing time to determine them. The pass schedule computer is set up to define this relationship as a set state and to transfer coefficients corresponding to the set state to the (mathematical) process model. In addition, the pass schedule computer can be set up to transfer corresponding coefficients to a device for controlling actuators of the rolling train. These coefficients can consist of one or more terms or of terms composed of them, of the sizes listed below by way of example: $$\frac{\partial P}{\partial \mathit{\Delta T}},\frac{\partial f}{\partial \mathit{\Delta T}},\frac{\partial M}{\partial \mathit{\Delta T}},\frac{\partial v}{\partial \mathit{\Delta T}},\frac{\partial \dot{Q}}{\partial \mathit{\Delta T}},\frac{\partial T_f}{\partial \mathit{\Delta T}},\frac{\partial \mathit{\Delta h}}{\partial \mathit{\Delta T}},\frac{\partial f_v}{\partial \mathit{\Delta T}},\frac{\partial l_{\mathit{vn}}}{\partial \mathit{\Delta T}}.$$

where T is the temperature, P is the rolling power, F is the rolling force, M is the rolling torque, v is the rolling speed, Tf is the fluid temperature, Q is the fluid volume flow, h is the thickness of the rolling stock, Δh is the decrease, I _VN is the length of a strip at constant strip speed and _fv the advance.

The cooling medium can be air, water, oil or an emulsion, for example. The rolling train component can be, for example, a roll or a work roll.

The process model can be set up to monitor directly or indirectly whether a current state of the rolling train corresponds to the setting state. If this set condition is not reached during rolling operation due to other controller interventions, or if the strip forming and/or the cooling rate of the metal strip changes due to the application of a cooling medium to the metal strip and contact of the metal strip with at least one fixed rolling train component and/or the rolling speed in the roll gap of the last roll stand, for example due to interventions by operating personnel, the process model according to the invention can use the coefficients supplied by the pass schedule computer to determine the deviation of the strip forming and/or the rolling speed in the last roll stand from the related deviations caused by the intervention contained setting values for strip forming and / or the rolling speed in the last rolling stand determine a deviation associated with the intervention-related deviation of the outlet temperature from a setpoint temperature contained in the context. The process model is also set up to change the strip forming in the last rolling stand and in one or more rolling stands of the rolling train that are upstream with respect to a strip conveying direction through the rolling train, depending on the determined deviation of the outlet temperature, in such a way that the outlet temperature corresponds to the setpoint temperature. Consequently, the outlet temperature of the metal strip is set using the process model, taking into account the relationship described above. For this purpose, the process model can change the strip forming and/or the rolling speed and/or the cooling rate or the associated amount of coolant in the last roll stand and the one or more upstream roll stands such that the outlet temperature of the metal strip returns to the setpoint temperature.

The metal strip can be an aluminum strip or steel strip, for example. The rolling train can be a cold rolling tandem train, for example. The last rolling stand of the rolling train is the last rolling stand with regard to a mass flow or a direction of movement of the metal strip through the rolling train. The same applies to the at least one upstream roll stand of the rolling train. The rolling train has at least two, three or more roll stands. The direction of movement of the metal strip through the mill can also change, e.g. B. with a reversing stitch.

The model-based temperature setting according to the invention has the advantage that ideally it does not require any sensors. This reduces investment, commissioning and maintenance expenses. A simple off-line temperature measurement on the wound coil would be sufficient for process model validation. The process model also ensures that temperature setting and thickness control are decoupled, so that the quality of the end product can be increased by minimizing mutual interference between different controls. The Dynamics of the temperature setting is at a uniformly high level for different products thanks to the process model. The invention thus represents a model-based approach to a temperature setting that is fully integrated into a rolling mill control architecture, which requires less investment than the prior art, for example by eliminating the expensive thermal imaging camera that is customary with aluminum strips, less commissioning effort, lower operating costs, in particular maintenance costs and replacement costs , higher control quality and dynamics, better product quality and greater reliability.

An essential advantage of the invention compared to a conventional temperature controller is that the outlet temperature can already be set at an earlier point in time in the rolling process, particularly in the case of a plant in batch operation. In addition, it is advantageous that the method according to the invention works more evenly over the length of the strip and is more dynamic, since the process data are determined directly in the roll gap and are not subject to dead time due to the transport to the temperature measuring point. Another advantage is that the method according to the invention allows higher rates of change over time for setting the target temperature.

According to an advantageous embodiment, a change in a decrease in strip thickness of the metal strip in the last roll stand that is required to achieve the setpoint temperature is determined by means of the process model as a function of the deviation in the outlet temperature, and a roll gap height in one or more upstream roll stands is increased by one of the change in the strip thickness of the metal strip in changed in the opposite direction corresponding to the amount corresponding to the last stand. If, for example, the rolling speed of the pass schedule calculated by the pass schedule computer or setting condition is not reached, the outlet temperature of the metal strip is too low. The process model can then increase the strip deformation in the last roll stand in order to achieve a desired exit temperature of the metal strip even with the lower rolling speed. With the change of band reshaping in the However, the last roll stand alone would disrupt the target thickness of the metal strip. A thickness control of the rolling mill would compensate for this change in thickness and restore the initial state. To prevent this, the process model uses the coefficients supplied by the pass schedule computer to calculate a required change in strip forming in one or more upstream roll stands, so that, together with the strip forming required to set the desired exit temperature of the metal strip in the last roll stand, a desired exit thickness of the metal strip remains unchanged remains. If the process model calculates, for example, a percentage change in the decrease or reduction in the thickness of the metal strip in the last roll stand of +15% that is required to achieve the desired exit temperature of the metal strip, the decrease or reduction in the thickness of the metal strip in one or more upstream roll stands is as follows compensates that the total decrease remains constant. If the strip thickness of the metal strip is initially reduced, for example from 0.4 mm to 0.3 mm in the penultimate roll stand and from 0.3 mm to 0.2 mm in the last roll stand, and if there is a deviation in the exit temperature of the metal strip, this can Process model change the strip forming using the last two roll stands in such a way that the strip thickness is reduced from 0.4 mm to 0.345 mm with the penultimate roll stand and from 0.345 mm to 0.2 mm with the last roll stand, so that the outlet thickness of the metal strip is not affected becomes. The respective manipulated variable is the roll gap height of the respective roll stand calculated by the process model.

According to a further advantageous embodiment, a separate stand model contained in the process model is used for the last roll stand and for one or more upstream roll stands, which is adapted at time intervals by forcing the respective roll stand without metal strip. The (mathematical) framework model is a framework model calibrated by the impression (calibration process). The work rolls of the respective roll stand are brought into contact with one another during the bucking, with adjustment paths, forces and the like being able to be recorded, for example by means of the process model, in order to adapt the stand model.

According to a further advantageous embodiment, a cooling model contained in the process model is used, with which a cooling of the metal strip through optional application of different coolants and a cooling of the metal strip due to contact with work rolls is calculated. The various coolants can be air, water, oil or an emulsion, for example. The contact of the metal strip with the work rolls results in a flow of heat, via which heat flows away from the metal strip via the work rolls, so that the metal strip is cooled. When calculating the respective cooling of the metal strip, the cooling model can take into account the flow temperatures, volume flows and residence times in the relevant parts of the plant. The cooling capacity can be calculated using coefficients that are determined by the pass schedule calculator.

According to a further advantageous embodiment, an inlet temperature level of a coil made from the metal strip before it enters the rolling train is taken into account in the process model. This information is also required for setting up the system. The primary distinction to be made here is whether it is a coil that has been cooled to room temperature or a coil that has been heated above room temperature as a result of hot rolling or annealing processes. This can be done by manually or inline measuring the temperature in the infeed of the rolling train or by calculating the cooling based on data from process steps over time from production planning.

According to a further advantageous embodiment, changes in the strip deformations in the last roll stand and one or more upstream roll stands are precontrolled by means of a tracking module, in that the respective change in strip thickness is shifted into the respective roll stand with a respectively measured strip speed. The tracking module ensures that the variations in the manipulated variables calculated by the coefficients in the downstream roll stands occur at the right time, so that when the correct exit temperature is set, there are never any disturbances in the thickness. The tracking module can be used in a transient range in which the thickness of the Changes metal strips, redistribute the strip forming in the nips of the last roll stand and one or more upstream roll stands, so that a desired outlet thickness of the metal strip is not disturbed. Since the respective change in the strip thickness of the metal strip is shifted with the measured strip speed into the following, in particular last, rolling stand, a change in the adjustment in the roll gap of the following rolling stand is time-correct in the following rolling stand as in the preceding, in particular one or more upstream, Rolling stand(s) started.

According to a further advantageous embodiment, the temperature change based on the rolled strip length as a function of the strip speed is determined by means of the process model.

According to a further advantageous embodiment, changes in roll gap heights in the last roll stand and one or more upstream roll stands are compensated by means of the process model by changes in the speeds of work rolls of the last roll stand or the one or more upstream roll stands, the speeds being determined using a or the mass flow contained in the process model through the rolling mill can be determined. The changes in overfeeds and strip thicknesses can be pre-controlled by the redistribution of forming in such a way that, ideally, the thickness control downstream of the last roll stand does not interfere. This can be achieved, for example, in that a change in the adjustment in the last roll stand and in one or more upstream roll stands is compensated for by the change in speed in the affected roll stand(s) that corresponds to the mass flow. As a result, a strip tension remains unchanged, regardless of whether a tension control affects the adjustment or the stand speed.

According to a further advantageous embodiment, changes in the overfeed of the metal strip are made by means of the process model when the strip speed is corrected taken into account when the process model has determined a deviation in the strip forming and/or the rolling speed in the last rolling stand due to an intervention by an actuator of another control device of the rolling train. The lead changes can be taken into account, for example, via difference quotients of the pass schedule model when correcting the speed. If the process model detects a deviation in strip forming from the set state due to the intervention of an actuator, for example a thickness control or tension control, the process model can apply the speed correction analogously. Since the process model can work continuously and the strip forming can be continuously distributed between the roll stands and advance changes can also be pre-controlled, ideally there is no disruption to a desired exit thickness of the metal strip. If, for example, the reduction in the last rolling stand is less than that provided for in the settlement (input variables: outlet thickness, rolling torque and rolling force in the last rolling stand), then the reduction in one or more upstream rolling stands is reduced, so that the reduction in the last rolling stand can be increased. The greater deformation then leads to the desired increase in the outlet temperature. The changes in speed and overfeed that occur during the rearrangement are pre-controlled by the changed mass flow balance and overfeed coefficients doverfeed/dreduction in the roll stands concerned, so that tension and thickness disturbances do not occur during the rearrangement.

According to a further advantageous embodiment, the connection between the strip forming and/or the cooling rate of the metal strip by at least one cooling medium and by at least one fixed rolling train component and/or the rolling speed in the last rolling stand on the one hand and the exit temperature on the other hand is determined with the aid of temperature measurements at the end of the rolling train expiring metal band adapted. For example, the actual coil temperature can be measured with a hand-held measuring device at the end of a rolling program. Inline temperature measurement is more convenient but more complex. The measured values of the respective temperature measurement can be sent automatically to the pass schedule computer, which calculates and compares the measured temperature with a calculated temperature value and adapts the calculated temperature value to the measured value. In this case, other model parameters can also be adapted.

A control device according to the invention for setting an exit temperature of a metal strip exiting an at least two-stand rolling train is set up in such a way that it carries out the method according to one of the above-mentioned configurations.

The advantages mentioned above in relation to the method are correspondingly associated with the control device. The control device can be given as a separate device or can be realized by a software implementation in existing system electronics of a rolling mill. The control device can be used as a predictive temperature controller of a rolling mill based on a process model.

A rolling mill according to the invention for rolling a metal strip has at least one at least two-stand rolling train and at least one above-mentioned control device for setting an outlet temperature of the metal strip emerging from the tandem rolling train, the rolling train having at least one fixed rolling train component for contact with the rolled strip and means for loading the metal strip having a coolant medium.

The advantages mentioned above in relation to the method are correspondingly associated with the rolling plant. The rolling mill can be designed as a multi-stand cold rolling tandem train, in particular for the production of aluminum strip.

Figur 1

eine schematische Darstellung eines Ausführungsbeispiels für eine erfindungsgemäße Walzanlage;

Figur 2

eine schematische Darstellung eines weiteren Ausführungsbeispiels für eine erfindungsgemäße Walzanlage;

Figur 3A

eine schematische Darstellung eines Gerüstmodells eines Ausführungsbeispiels für ein erfindungsgemäßes Prozessmodell;

Figur 3B

eine schematische Darstellung eines Kühlmodells eines Ausführungsbeispiels für ein erfindungsgemäßes Prozessmodell; und

Figur 3C

eine schematische Darstellung eines Trackingmoduls eines Ausführungsbeispiels für ein erfindungsgemäßes Prozessmodell.

In the following, the invention is explained by way of example with reference to the enclosed figures using preferred embodiments, with the features explained below being able to represent an advantageous or further developing aspect of the invention both individually and in combination with at least two of these features. Show it:

figure 1

a schematic representation of an embodiment of a rolling mill according to the invention;

figure 2

a schematic representation of a further embodiment of a rolling mill according to the invention;

Figure 3A

a schematic representation of a framework model of an embodiment of a process model according to the invention;

Figure 3B

a schematic representation of a cooling model of an embodiment of a process model according to the invention; and

Figure 3C

a schematic representation of a tracking module of an embodiment of a process model according to the invention.

Identical or functionally identical components are provided with the same reference symbols in the figures. Repeated description of these components may be omitted.

figure 1 shows a schematic representation of an exemplary embodiment of a rolling mill 1 according to the invention for rolling a metal strip 2. The rolling mill 1 has a three-stand rolling train 3 and a control device 4, shown symbolically, for setting an outlet temperature of the metal strip 2 emerging from the rolling train 3. The control device 4 is set up to carry out a method according to the invention for setting the exit temperature of the metal strip 2 exiting the rolling train 3 .

In figure 1 different variables and their relationships are shown. P ₁ is the target rolling capacity of the first roll stand 5 and P' ₁ is the actual rolling capacity of the first roll stand 5. h ₁₀ is the inlet thickness of the rolled strip 2 entering the first roll stand 5 and h ₁₁ is the outlet thickness of the first roll stand 5 expiring rolled strip 2, where Δh ₁ , the decrease in the thickness of Rolled strip 2 in the first roll stand 5 is. v ₁ is the strip speed of the rolled strip 2 leaving the first roll stand 5 and S ₁₂ is the strip tension in the rolled strip 2 between the first roll stand 5 and a second roll stand 6 downstream of the first roll stand 5.

P ₂ is the target rolling capacity of the second rolling stand 6 and P' ₂ is the actual rolling capacity of the second rolling stand 6. h ₂₀ is the entry thickness of the rolled strip 2 entering the second rolling stand 6 and h ₂₁ is the exit thickness of the rolling strip 2 exiting the second rolling stand 6 Rolled strip 2, where Δh ₂ is the decrease in the thickness of the rolled strip 2 in the second roll stand 6. v ₂ is the strip speed of the rolled strip 2 leaving the second roll stand 6 and S ₂₃ is the strip tension in the rolled strip 2 between the second roll stand 6 and a third or last roll stand 7 downstream of the second roll stand 6.

P ₃ is the target rolling capacity of the third rolling stand 7 and P' ₃ is the actual rolling capacity of the third rolling stand 7. h ₃₀ is the entry thickness of the rolled strip 2 entering the third rolling stand 7 and h ₃₁ is the exit thickness of the rolling strip 2 exiting the third rolling stand 7 Rolled strip 2, where Δh ₃ is the decrease in the thickness of the rolled strip 2 in the third roll stand 7. v ₃ is the strip speed of the rolled strip 2 leaving the third roll stand 7.

T is the target temperature of the cold or hot strip 2 leaving the rolling train 3 and T' is the actual temperature of the cold or hot strip 2 leaving the rolling train 3, where ΔT is the temperature difference between the target temperature and the actual temperature is.

In the lower area of figure 1 shows the relationships between the variables mentioned above, which allow the outlet temperature T′ to be set according to the invention.

figure 2 shows a schematic representation of a further embodiment of a rolling mill according to the invention for rolling a metal strip, not shown, of the rolling mill, only a pass schedule computer 8 and the process model 9 with reference to a roll stand n are shown.

An inlet temperature T0 of the hot strip, an outlet temperature T of the hot strip, a reduction in thickness Δh within the roll stand n and material and system data A are fed to the pass schedule computer 8 . From this, the pass schedule calculator 8 determines on the right in figure 2 shown coefficients and setting values, which are fed to the process model 9 together.

The process model 9 is also given the current rolling power P(n) of roll stand n, a current rolling torque M(n) of roll stand n, a current rolling force F(n) of roll stand n, a current rolling speed v(n) of roll stand n, a current roll deformation Δh(n) in roll stand n, a current coolant temperature Tf(n) at roll stand n and a current coolant volume flow Q(n) at roll stand n. Furthermore, optionally calibration curves K(n) of the roll stand n and optionally a measured actual temperature T are supplied to the process model 9 . From this, the process model 9 determines a rolling speed change Δv(n) over time t and a decrease change Δh(n) over time t for the roll stand n. For this purpose, the process model 9 has a stand model 10, a cooling model 11 and a tracking module 12 .

Figure 3A shows a schematic representation of a framework model 10 of an embodiment of a process model according to the invention. The stand model 10 is supplied with the current rolling force F(n) of a roll stand n and a current roll deformation Δh(n) in the roll stand n. Furthermore, a framework module G(n) and a belt module B(n) are supplied to the framework model 10 . From this, the stand model 10 determines a setting position deviation Δs(n) from a setting value s(n) of the roll stand n. The stand model 10 can be used in the process model figure 2 be implemented.

Figure 3B shows a schematic representation of a cooling model 11 of an exemplary embodiment of a process model according to the invention. The cooling model 11 a current rolling speed v(n) of roll stand n, a current coolant temperature Tf(n) at roll stand n and a current coolant volume flow Q(n) at roll stand n are supplied. Furthermore, the cooling model 11 system data A (n) are supplied. From this, the cooling model 11 determines a strip temperature deviation ΔT(n) from a set value T(n) at the roll stand n. The cooling model 11 can be included in the process model figure 2 be implemented.

Figure 3C shows a schematic representation of a tracking module 12 of an embodiment of a process model according to the invention. The tracking module 12 receives the data from the skeleton model Figure 3A determined adjustment position deviation Δs(n) of roll stand n and the current rolling speed v(n) of roll stand n. Furthermore, the tracking module 12 system data A (n) are supplied. From this, tracking module 12 determines a change in rolling speed Δv(n) over time t and a change in decrease Δh(n) over time t for roll stand n. Tracking module 12 can be found in the process model figure 2 be implemented.

Reference List

1

rolling mill

2

rolled strip

3

rolling mill

4

control device

5

first (upstream) roll stand

6

second (upstream) roll stand

7

third (last) roll stand

8th

pass schedule calculator

9

process model

10

scaffold model

11

cooling model

12

tracking module

Claims (13)

1. Method for setting an exit temperature of a metal strip (2) exiting an at least two-stand rolling train (3), wherein the exit temperature is set by means of a process model (9) with consideration of a correlation between a strip reshaping and/or a rate of cooling down of the metal strip (2) by at least one cooling medium and by contact of the metal strip (2) with at least one fixed rolling train component and/or a rolling speed in a last roll stand (7) of the rolling train (3) on the one hand and the exit temperature on the other hand,
   characterised in that
   after determination, which is carried out with use of the process model (9), of a deviation, which is caused by engagement, of the strip reshaping and/or the rolling speed in the last roll stand (7) from set values, which are present in the correlation, for the strip reshaping and/or the rolling speed in the last roll stand (7), by means of the process model (9), a deviation, which is connected with the deviation caused by engagement, of the exit temperature from a target temperature, which is present in the correlation, is determined, wherein the strip reshaping in the last roll stand (7) and in one or more upstream roll stands (5, 6) of the rolling train (3) is changed in such a way by means of the process model (9) in dependence on a deviation of the exit temperature that the exit temperature corresponds with the target temperature.
2. Method according to claim 1, characterised in that a change, which is required for achieving the target temperature, in a decrease of strip thickness of the metal strip (2) in the last roll stand (7) is determined by means of the process model (9) in dependence on the deviation of the exit temperature, and a rolling gap height in one or more upstream roll stands (5, 6) is changed by an amount, which corresponds with the change of the strip thickness of the metal strip (2) in the last roll stand (7), in opposite direction.
3. Method according to claim 1 or 2, characterised in that for the last roll stand (7) and for one or more upstream roll stands (5, 6) in each instance use is made of an individual stand model (10) which is present in the process model (9) and which is adapted at intervals in time by pressing down the respective roll stand (5, 6, 7) without metal strip (2).
4. Method according to any one of claims 1 to 3, characterised in that use is made of a cooling model (11) which is present in the process model (9) and by which cooling down of the metal strip (2) by selectable loading with different cooling media and a cooling down of the metal strip (2) due to contact with work rolls are calculated.
5. Method according to any one of claims 1 to 4, characterised in that an entry temperature level of a coil consisting of the metal strip (2) prior to entry into the rolling train (3) is taken into consideration in the process model (9).
6. Method according to any one of claims 1 to 5, characterised in that changes in the strip reshapings in the last roll stand (7) and in one or more upstream roll stands (5, 6) are pre-controlled by means of a tracking module (12) in that the respective change in the strip thickness is displaced into the respective roll stand (5, 6, 7) at a respective measured strip speed.
7. Method according to any one of claims 1 to 6, characterised in that the temperature change due to the rolled strip length is determined by means of the process model (9) as a function of the strip speed.
8. Method according to any one of claims 1 to 7, characterised in that compensation for changes in rolling gap heights in the last roll stand (7) and in one or more upstream roll stand (5, 6) is made by means of the process model (9) through changes of rotational speeds of work rolls of the last roll stand (7) or of the one or more upstream roll stands (5, 6), wherein the rotational speeds are determined with use of a mass flow, which is determined or is present in the process model (9), through the rolling train (3).
9. Method according to any one of claims 1 to 8, characterised in that advance changes of the metal strip (2) in the case of correction of the strip speed are taken into consideration by means of the process model (9) when the process model (9) has determined a deviation of the strip reshaping and/or the rolling speed in the last roll stand (7) due to intervention of a setting element of another regulating device of the rolling train (3).
10. Method according to any one of claims 1 to 9, characterised in that the correlation between the strip reshaping and/or the rate of cooling down of the metal strip (2) by at least one cooling medium and by at least one fixed rolling train component and/or the rolling speed in the last roll stand (7) on the one hand and the exit temperature on the other hand is adapted with the help of the temperature measurements of the metal strip (2) exiting the rolling train (3).
11. Control device (4) for setting an exit temperature of a metal strip (2) exiting an at least two-stand rolling train (3), characterised in that the control device (4) is so arranged for performing the method according to claim 1 that the exit temperature is set by means of a process model (9) with consideration of a correlation between a strip reshaping and/or a rate of cooling down of the metal strip (2) by at least one cooling medium and by contact of the metal strip (2) with at least one fixed rolling train component and/or a rolling speed in a last roll stand (7) of the rolling train (3) on the one hand and the exit temperature on the other hand, wherein after determination, which is carried out with use of the process model (9), of a deviation, which is caused by engagement, of the strip reshaping and/or the rolling speed in the last roll stand (7) from set values, which are present in the correlation, for the strip reshaping and/or the rolling speed in the last roll stand (7) a deviation, which is connected with the deviation caused by the engagement, of the exit temperature from a target temperature, which is present in the correlation, is determined by means of the process model (9), wherein the strip reshaping in the last roll stand (7) and in one or more upstream roll stands (5, 6) of the rolling train (3) is changed in such a way by means of the process model (9) in dependence on the deviation of the exit temperature that the exit temperature corresponds with the target temperature.
12. Control device (4) according to claim 11, characterised in that the control device is so arranged that the method according to any one of claims 2 to 10 is performed.
13. Rolling mill (1) for rolling a metal strip (2), comprising an at least two-stand rolling train (3) and at least one control device (4) for setting an exit temperature of the metal strip (2) exiting the rolling train (3), wherein the rolling train comprises at least one fixed rolling train component for contact with the rolled strip (2) and means for loading the metal strip (2) with the coolant medium, characterised in that the control device (4) is constructed according to claim 11 or 12.

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