EP1244816B1 - Method for controlling and/or regulating the cooling stretch of a hot strip rolling mill for rolling metal strip, and corresponding device - Google Patents

Abstract

A method and device for the automation of a cooling section in a hot strip rolling mill, wherein an individual course of cooling over time for each strip point of the metal strip is specified and whereby the cooling specifications can be determined from the desired properties of the steel, independent of variable process value.

Description

The invention relates to a method for control and / or control of the cooling section of a hot strip mill for Rolling of metal strip, the cooling properties of the structure of the rolled metal strip, especially one Steel strip. In addition, the Invention also on the associated device for performing of the procedure.

Especially in the steel industry, so-called slabs in the hot condition rolled into strips in a hot strip mill. After rolling, the sheet goes through a cooling section. The The cooling section of the hot strip mill is used to set the Structural properties of the rolled steel strips.

The structural properties of the tapes produced are So far mainly derived from the reel temperature, the through the cooling section automation on a given Setpoint is kept constant.

New materials, such as multi-phase steels, TRIP steels or the like, require a precisely defined heat treatment, i.e. the specification and monitoring of a temperature profile from the last roll stand to the reel.

From "Proceedings of ME FEC Congress 99", Düsseldorf, June 13 - 15, 1999 (Verlag Stahl Eisen GmbH) a proposal is known has become the automation of hot strip mills in which A model-based control system especially for the cooling section is available. The cooling is based on the idea that over the length of the entire cooling section Reference temperature can be specified and that the currently measured Temperature via an adaptive control unit to the given Values is adjusted. It is essential that about Enthalpy considerations and division of the cooling process in a series of smaller thermodynamic processes the influence of cooling in longitudinal and vertical Direction can be detected. In particular, there is a Calculation using the "finite element" method.

Starting from the latter, it is an object of the invention to improved process for the automation of cooling lines specify in hot rolling mills and the associated device to accomplish.

The task is according to the invention by the characteristic Features of claim 1 solved. Training courses are specified in the dependent claims. An associated device to carry out the procedure is by the features of claim 10 characterized.

The problem outlined at the beginning is now not like in the prior art by specifying the temperature profile along the cooling section, but by default one for each band point of the metal band temporal cooling process solved. It is advantageous in particular, that such a requirement is derived directly from the desired steel properties can be determined and regardless of variable process variables, such as the Belt speed remains.

In the method according to the invention it is therefore essential that for every so-called band point of the material to be cooled own time cooling process is specified. So that can the time functions determined in this way at any time for everyone Bandpoint compared with the predetermined time cooling curves become.

The process according to the invention has the advantage that cooling conditions can be specified, the actual Better meet practical requirements. advantageously, can now also variable cooling along the belt be specified, with which areas of the rolling strip are determined in particular Quality can be created in a targeted manner. This is now so-called dual-phase materials can also be produced, which is what State of the art was not possible.

Because the cooling process along for each band point of the entire cooling section is the control and / or regulation no longer tied to fixed switching locations; it are rather any valves for the supply of coolant at any time actuated. So that compliance with the specified Cooling down along the cooling section by the control and / or Regulation can be checked, according to the invention Including the model in real time with the belt in the cooling section. This provides the required strip temperatures on the Cooling section and is constantly measured temperature values corrected.

Overall, the method according to the invention allows one flexible specification of heat treatment for modern steels. This takes account of practical requirements.

With appropriate devices, each a cooling section include, which run through their entire length individually adjustable valves with coolants can be acted upon are means for specifying cooling curves available for the individual band points of the metal band. There are also units for calculating the cooling curves Correction of the determined cooling curves on the basis of measured temperatures, for comparison with the specification of the Cooling curves and for the generation of process control signals available. These units can be integrated into one software Calculator can be implemented.

Figur 1

den Aufbau einer der Walzstraße nachgeschalteten Kühlstrecke,

Figur 2

ein dreidimensionales Temperatur-Zeit/Bandlängen-Diagramm,

Figur 3

das Strukturbild der Steuerung/Regelung einschließlich Modellkorrektur für die Kühlstrecke gemäß Figur 1 und

Figur 4

im einzelnen die Berechnung der Modellkorrektur aus Figur 3.

Further details and advantages of the invention result from the following description of figures of exemplary embodiments with reference to the drawing in conjunction with further subclaims. Show it

Figure 1

the construction of a cooling line downstream of the rolling mill,

Figure 2

a three-dimensional temperature-time / band length diagram,

Figure 3

the structure of the control / regulation including model correction for the cooling section according to Figure 1 and

Figure 4

specifically the calculation of the model correction from FIG. 3.

The cooling of metal strip as part of the Hot rolling technology and in detail the function of the Cooling section illustrates. When hot rolling steel so-called slabs with an initial thickness of approx. 200 mm rolled into a strip from 1.5 to 20 mm. The processing temperature is 800 to 1200 ° C. The process end includes after rolling, cooling the strip with water in a Cooling section to 300 to 800 ° C.

In Figure 1 there is the last rolling stand of a hot strip mill designated 1. The mill stand 1 is followed by a finishing mill measuring station 2, after cooling a reel measuring station 3 each of which measures the temperature of the strip, and then an underfloor reel 4 for reeling the metal strip to a coil. Between finished road measuring station 2 and Haspelmeßplatz 3 is in the present context Cooling section 10 generally referred to as a system.

A rolled hot strip made of steel is 100 in FIG designated. It runs through the cooling section 10 and is by both sides via valves with a cooling medium, in particular Water, chilled. Individual valves can be grouped together be, for example, valve groups 11, 11 ', ..., 12, 12 ', ..., 13, 13', ... and 14, 14 ', ... are shown.

The cooling of the strip 100 to be recorded by control technology is usually a one-dimensional unsteady heat conduction equation based. With the mathematical description is made of an isolated rod that is just beginning and End - according to the top and bottom of the band - one Carried out heat exchange with the environment.

Specially for heat conduction in the strip is from the model acceptance assumed that the heat conduction in the longitudinal and transverse directions disappears and that in the width of the band the enthalpy is constant. This allows the problem to be one-dimensional reduce transient heat conduction problem, where the initial conditions and the boundary conditions are defined Need to become.

According to the latter model, the band 100 can have individual band points are described in which heat conduction in Rod is done. This is known, for what purpose Technical literature is referred.

There are generally no temperatures in the cooling section 10 measurable. The temperature is, however, at measuring station 2 in front of the cooling section and especially measured at the reel measuring station 3. about the mathematical model is the heat exchange in band 100 according to the above requirements. It will that is, a model of the cooling section is created, which is shown in FIG is denoted by 15. If about the model 15 the temperatures are available at any location implement a control to the specified cooling profile.

In Figure 2 is based on a three-dimensional temperature band length / time diagram the specification of a cooling process shown: If one of a cooling start (t = 0) one Band point, there is a predetermined value over time t Cooling profile 300 as a time function. From Figure 2 is a separate cooling curve for each band point of the metal band 100 removable. An example is for a specific band point at left the curve 300 is represented, whereby for this band point results in its own time function.

For example, after a certain cooling time t _i , the temperature profile for the band point i should have a predetermined temperature Ti, in particular the reel temperature T _H. There are corresponding specifications for the remaining band points. If all the specified reel temperatures of the individual strip points are connected, curve 400 is drawn in FIG.

If you consider everyone's specifications in an instant currently lying in the cooling section 10 band points and connects if you get these band points, you get a curve 500, which represents the cooling profile over the length of the cooling section. This cooling curve is also shown in FIG. 1 in unit 30. It is essential that according to the specified technical teaching the curve 500 in the event of disruptions in the manufacturing process, for example with variable belt speed, is automatically dynamically adjusted. This leaves them Disruptions - in contrast to the prior art - without any Effects on the given cooling process every band point.

So it is important in the described method that for everyone Bandpoint own cooling curves 300, 310, 311, 312 etc. specified become. For example, a for the first point Cooling curve with an initially steep drop and then given a shallower drop while in the middle Cooling curves with almost constant temperature gradients result. Overall, this is what is described Profile 400 reached.

Other cooling profiles can also be created. In particular if you start from the structure as a target, the profile be specified so that largely constant structural properties on the finished belt. But it can also deliberately changing the structural properties for certain Band areas are provided. For example, can also change the structure due to the longer lay time of the rear Strip sections balanced again before further rolling become.

Since the structural properties the mechanical properties and to determine the quality of steel strips in particular, can be desired through targeted structural changes Achieve material properties. In this respect it results from the described method has an increased potential in the Production of finished tape.

In Figure 3, the cooling section is designated as the actual system with 10. 1 is expressed here by a so-called real-time model 20, by means of which the temperatures T and _i at the individual band points i of the band 100 are determined.

The calculated reel temperature T and _H , which has an error, is compared with the temperature T _H measured on the reel 3 and the resulting error is fed to a unit 25 for model correction. The latter unit 25 is also supplied with the entire cooling process calculated by the real-time model 20. The unit 25 uses this data to determine a correction of the cooling process, which is applied to the calculated cooling process. The corrected cooling curve determined in this way is compared with the target cooling and the resulting control deviation is fed to the controller 33. From this and by means of the gain factors determined by the unit 25, the valve positions are generated as process control signals, which are both implemented on the system and fed back to the real-time model 20 as information.

If there is no valid measured value, the calculation is omitted a corrected cooling process. The correction will then be made assumed to be zero.

The controller 33 can because of the entered control deviation and the other values with a predetermined algorithm operate. Such algorithms become software predetermined and let the control of any pattern of Valves too. In particular, the controller can be used at any time the valves 11, 11 ', ..., 12, 12', ..., 13,13 ', ..., 14, 14', ... can be activated by the controller in any combination at the same time.

The cooling along the metal strip is described in detail the enthalpy and the temperature curve depending on considered the enthalpy.

The calculation of the model correction for the controller is illustrated in detail in FIG. 4: the enthalpies e and the temperatures T are determined as a function of the enthalpy e. The real-time model 20 delivers a calculated enthalpy value ê , from which the value T and ( ê ) is formed in a unit 21. From this, the temperature values T and for any band points can be calculated. Specifically, the calculated temperature value T and _H for the reel temperature is compared with the measured reel temperature T _H , which results in a value ΔT _H.

From the real-time model 20 enthalpy signals are equally fed to a unit 22 in which the partial derivative of the enthalpy is formed according to the heat conduction coefficient ∂ ê / ∂ _κ . The heat conduction coefficient represents a correction factor to a certain extent. The valve positions of the system continue to be included in both units 20 and 22.

The output signal of the unit 22 results in calculated values ∂ ê / ∂ _κ . In unit 23, the signal is subjected to dT and / dê , from which a signal ∂ T and / ∂ _κ can be determined by forming partial derivatives according to the chain rule.

In particular, the value for the reel ∂ T and _H / wird _κ is considered and the previously determined temperature error ΔT _{H is divided} by this value, which results in the Δκ. The latter value Δκ is multiplied by ∂ ê / ∂ _κ so that the model correction Δe is available as the initial value. The model correction of the unit 25 from FIG. 3 is thus implemented.

When calculating the model correction Δe according to FIG. 4, ∂ ê / ∂ _κ therefore represents a sensitivity model.

It has been shown that with the above procedure and consideration the cooling curves for the individual band points the conditions can be better modeled in practice. The approach is based on the knowledge that the heat treatment of modern steels by direct specification of the Target curves for the temperature curve of the actual cooling curve individually specified for each band point can be. In this respect, the interface for the tax and / or control the model calculated in real time and is the associated correction algorithm is an essential component of the described method.

This approach ideally takes into account the Guideline for the manufactured material, as they are part of the System limits - regardless of the belt speed - Guaranteed the setting of the required quality.

Claims (14)

1. Method for the open-loop and/or closed-loop control of the cooling section of a hot strip rolling mill for rolling metal strip, in particular a steel strip, the microstructural properties of the rolled metal strip being adjusted by cooling, with the following method steps:

   for each strip point of the metal strip, a course of cooling over time is specified,

   in addition, for each strip point of the metal strip, the actual cooling curve is determined as a function of time,

   the determined time function of the actual course of cooling is compared with the specification of the course of cooling over time for each strip point of the metal strip;

   process control signals for the open-loop and/or closed-loop control of the cooling section are derived from the deviations of the determined time curves from the actual course of cooling.
2. Method according to Claim 1, characterized in that different cooling curves are specified for individual strip points of the metal strip.
3. Method according to Claim 1 or Claim 2, characterized in that desired microstructural properties are adjusted on the basis of the specified cooling curves for each strip point of the metal strip.
4. Method according to Claim 3, characterized in that such cooling curves that undesired changes in the microstructural properties occurring on account of external influences are offset are specified for the individual strip points of the metal strip.
5. Method according to Claim 3, characterized in that the cooling curves for the individual strip points of the metal strip are specified in such a way that predetermined, possibly different, microstructural properties are obtained for different strip points of the metal strip.
6. Method according to Claim 5, characterized in that the mechanical properties of the metal strip are specified on the basis of the specifically selective influencing of the microstructural properties.
7. Method according to one of the preceding claims, characterized in that the time functions or individual values at the given instant in time of the course of cooling of individual strip points are fed to a controller and lead to the generation of the process control signals.
8. Method according to Claim 7, it being possible to use the controller for activating valves for coolant for cooling the metal strip, characterized in that any desired valves can be simultaneously activated by the controller at any point in time.
9. Method according to one of the preceding claims, characterized in that the measured time function of the coiling temperature is used as the comparison temperature with respect to the cooling curves of individual strip points.
10. Device for carrying out the method according to Claim 1 or one of Claims 2 to 9, with a cooling section, in which the metal strip running through can be subjected to coolant by means of adjustable valves (11, ..., 14), and a unit for determining the temperature-time functions of each individual strip point of the metal strip and with a process control unit (30) for obtaining process control signals for the open-loop and/or closed-loop control of the cooling in accordance with specified criteria, where the process control unit for the open-loop and/or closed-loop control of the cooling is based on a real-time model (20) with a model correction (25), from which the input signals for a controller (33) for activating the individual valves (11, 11', ... to 14, 14 ', ...) are derived.
11. Device according to Claim 10, characterized in that, with the process control unit (30), each of the individual valves (11, 11', ... to 13, 13', ...) for supplying coolant can be activated at any time.
12. Device according to Claim 10, characterized in that the criteria comprise a cooling profile along the metal strip in accordance with desired microstructural properties.
13. Device according to Claim 10, characterized in that the measured coiling temperature (T_H) is used for the model correction.
14. Device according to Claim 10, characterized in that the system deviation for the controller (33) is formed from a corrected course of cooling and the setpoint cooling.

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