Method for the open-loop or closed-loop control of the temperature of a steel strip during hot working in a hot strip mill

Abstract

A method for controlling or regulating the temperature of a steel strip in hot forming in a hot strip mill. A superordinate open-loop or closed-loop controller has a process model that predetermines the temperature development of the hot strip. The target values of the individual units are adjusted based on this predetermined temperature development.

Claims

1. A method for open-loop or closed-loop controlling a temperature of a steel strip with alloying elements TABLE-US-00002 in % by weight min max C 0 1 Mn 0 2.5 in hot forming of a preliminary product with a thickness between d.sub.V1 mm and d.sub.V300 mm into a hot strip with a hot strip thickness d.sub.WB25 mm and a hot strip width between b.sub.WB900 mm and b.sub.WB2100 mm, a target coiling temperature T.sub.H30 C. to T.sub.H750 C. in a hot strip mill, having at least one furnace for heating and temperature homogenization of the preliminary product, at least one roll stand for hot rolling the preliminary product, a cooling section for targeted cooling of the hot strip after forming, and a coiler for winding the hot strip to form a coil, with each individual unit having its own open-loop or closed-loop controller for the specified target values, wherein on a data processing system assigned to the hot strip mill, a superordinate process model exchanges and stores online target and actual values, including times, speeds, temperature, cooling rates and heating rates, with at least two open-loop or closed-loop controllers of the units; the superordinate process model, based on the exchanged target and actual values and stored values and using subordinate process models, predetermines the temperature of the steel strip online for at least one point before the hot strip is coiled; and the superordinate process model determines new target value specifications of the units at this point in case of deviations of the predetermined temperature from a target value specification, and transfers them to the open-loop or closed-loop controller of the unit in order to comply with the target value specification for the temperature of the steel strip; the determination of the new target value specifications is carried out by using an optimization algorithm including at least one subordinate process model; and controlling the temperature of the strip with the alloying elements using the new target value specification in response to the predetermined temperature deviations.

2. The method according to claim 1, wherein the preliminary product is a slab with a thickness d.sub.B50 mm to d.sub.B160 mm from a casting machine; and the superordinate process model takes into account a casting speed, preferably between v.sub.G4 m/min and v.sub.G6 m/min, more preferably v.sub.G5 m/min and v.sub.G6 m/min, and a casting machine outlet temperature, preferably T.sub.GE800 C., of the slab when determining the target specifications.

3. The method according to claim 1, wherein the optimization goal comprises energy consumption, production volume, process reliability, product properties, production costs and plant wear.

4. The method according to claim 1, wherein a subordinate process model determines the structure development of the steel strip in the hot strip mill for at least one point, preferably before the hot strip is coiled.

5. The method according to claim 1, wherein a roughing stand and a finishing stand are used in hot forming.

6. The method according to claim 4, wherein a temperature target value of T.sub.FS=850 C. to T.sub.FS=1050 C., preferably T.sub.FS=900 C. to T.sub.FS=1000 C., even more preferably T.sub.FS=900 C. to T.sub.FS=950 C. is specified by the superordinate process model for the target value of the inlet temperature into the finishing stand.

7. The method according to claim 4, wherein a temperature target value within T.sub.FE750 C. to T.sub.FE950 C., preferably T.sub.FE750 C. to T.sub.FE900 C., more preferably T.sub.FE800 C. to T.sub.FE850 C. is specified by the superordinate process model for the target value of the outlet temperature out of the finishing stand.

8. The method according to claim 4, wherein a speed target value of v.sub.F0.4 m/s to v.sub.F1 m/s is specified by the superordinate process model for the target value of the inlet speed into the finishing stand.

9. The method according to claim 4, wherein a temperature target value of T.sub.VS1000 C. to T.sub.VS1150 C. is specified by the superordinate process model for the target value of the inlet temperature into the roughing stand.

10. The method according to claim 4, wherein a temperature target value of T.sub.VE950 C. to T.sub.VE1100 C. is specified by the superordinate process model for the target value of the outlet temperature from the roughing stand.

11. The method according to claim 4, wherein a target value within d.sub.FS20 mm to d.sub.FS70 mm is specified by the superordinate process model for the target value of the entry thickness into the finishing stand.

12. The method according to claim 1, wherein a temperature target value of T.sub.H30 C. to T.sub.VE750 C., preferably T.sub.H450 C. to .sub.TH550 C. is specified by the superordinate process model for the target value of the coiling temperature.

13. The method according to claim 1, wherein the alloying element C is limited to a content of 0.03% by weight to 0.15% by weight and Mn to a content of 0.50% by weight to 2.00% by weight in the steel strip.

14. The method according to claim 1, wherein the optimized target value specifications are used for the production of a subsequent hot strip with the same production goals, including the mechanical properties.

15. A device for open-loop or closed-loop controlling the temperature of a steel strip according to a method according to claim 1, wherein on a data processing system assigned to the hot strip mill, target and actual values, including times, speeds, temperature, cooling rates and heating rates, can be exchanged and stored online with at least two open-loop or closed-loop controllers of the units by a superordinate process model; the superordinate process model, based on the exchanged target and actual values and stored values and using subordinate process models, can predetermine the temperature of the steel strip online for at least one point before the hot strip is coiled; and the superordinate process model determines new target value specifications of the respective units at this point in case of deviations of the predetermined temperature from a target value specification, and transfers them to the open-loop or closed-loop controller of the respective unit in order to comply with the target value specification for the temperature of the steel strip; and the determination of the new target value specifications is carried out by using an optimization algorithm including at least one subordinate process model.

16. The method according to claim 2, wherein the optimization goal comprises energy consumption, production volume, process reliability, product properties, production costs and plant wear.

17. The method according to claim 2, wherein a subordinate process model determines the structure development of the steel strip in the hot strip mill for at least one point, preferably before the hot strip is coiled.

18. The method according to claim 3, wherein a subordinate process model determines the structure development of the steel strip in the hot strip mill for at least one point, preferably before the hot strip is coiled.

19. The method according to claim 2, wherein a roughing stand and a finishing stand are used in hot forming.

20. The method according to claim 3, wherein a roughing stand and a finishing stand are used in hot forming.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The following three figures are attached to the description:

(2) FIG. 1: Plant diagram of the hot strip mill

(3) FIG. 2: Closed-loop control scheme with superordinate process model

(4) FIG. 3: Comparison of temperature profile target value, actual value

DETAILED DESCRIPTION

(5) FIG. 1 shows a possible plant diagram of a hot strip mill for the production of a hot strip in which the method according to the invention is used. The hot strip mill consists of a casting plant 1, two shears 2, 10, two furnaces 3, 6, two roughing stands 4, a transfer bar cooling 5, an inductive heating 7, three finishing stands 8, a cooling section 9 and a coiler 11 for winding up the hot strip. A superordinate data processing system 12 has an integrated temperature and structure model. Target and actual values are exchanged with the different plants or associated closed-loop controls, open-loop controls and/or measuring systems and stored, for example, in the form of a database.

(6) FIG. 2 shows a flowchart with an exemplary networking of two units or closed-loop controls of the two units with the respective process models. The superordinate data processing system I transfers target values to the superordinate process model II of the hot strip mill. From these target values, for example a strength, the superordinate process model II determines a number of target values or target value ranges, for example a temperature profile with minimum and maximum temperatures, which are transferred to the subordinate process models IIIa, b. The subordinate process models III a, b use these values to derive specific target values for the respective unit. For example, a specified temperature profile with assigned points in time becomes a target specification for burner control in a furnace 3 or a target specification for controlling the amount of water in a cooling section 9. These are passed on to the corresponding closed-loop controls of the respective units.

(7) If the values within the unit are not reached, the subordinate process model III a, b can adjust the target specification. Likewise, an automatic optimization of the process model IIIa, b can also take place here by means of a self-learning algorithm. If the actual target value deviates from the target value specification V of the superordinate process model II, the target values are recalculated on the superordinate level II and adjusted if necessary.

(8) FIG. 3 shows a diagram with a target temperature profile B and a measured and precalculated temperature profile A. The target temperature profile B begins at the end of the casting plant 1 and describes the course up to coiler 11. The actual values are plotted from the end of the casting plant 1 to the roughing stand 4. Here, the measured temperature is above the target temperature. From this point onwards, the superordinate process model II precalculates the temperatures at the various points in the hot strip mill. Based on this temperature profile, different target values can be newly specified at different points in order to correct the temperature deviation. Different process models, material or structure models and/or optimization algorithms can be used to determine the best adjustment strategy.

(9) TABLE-US-00001 TABLE 1 Reference numerals 1 casting plant 2 shear 3 oven 4 roughing stands 5 transfer bar cooling 6 oven 7 inductive heating 8 finishing stands 9 cooling section 10 shear 11 coiler 12 integrated temperature and structure model I data processing system II superordinate process model III a, b subordinate process model IV a, b control of the unit V target value specification A actual value profile or pre-calculated course A.sub.4 actual temperature of roughing stand B target value profile