WO2008078928A1

WO2008078928A1 - Temperature control apparatus and method in hot strip mill

Info

Publication number: WO2008078928A1
Application number: PCT/KR2007/006752
Authority: WO
Inventors: Cheol Jae Park; Pil Jong Lee; Myung Jong Cho; Jae Ryong Lee
Original assignee: Posco
Priority date: 2006-12-26
Filing date: 2007-12-21
Publication date: 2008-07-03
Also published as: KR100856284B1; KR20080060033A

Abstract

There are provided an apparatus and a method for precisely controlling a target temperature by compensating a time delay between a point in time of measuring a temperature and a point in time of controlling the temperature in a run out table (ROT) section of a hot strip mill. To precisely control a coiling temperature by compensating a measurement delay, the method including collecting a speed of the rolled steel strip and a temperature of the rolled steel strip at an outlet side of the ROT section; modeling a bank water injection measurement by considering a response delay of a feedback bank of the ROT; calculating a time delay between a point in time of measuring the temperature at the outlet side of the ROT section and a point in time of control in the feedback bank with respect to the measured temperature by using the modeled measurement; calculating a temperature deviation between the measured temperature and a preset target temperature by considering the calculated time delay; and controlling the water injection of the feedback bank according to the calculated temperature deviation.

Description

TEMPERATURE CONTROL APPARATUS AND METHOD IN

HOT STRIP MILL

Technical Field

[1] The present invention relates to an apparatus and method for controlling a temperature of a rolled steel strip at run out table (ROT) transferring a hot rolled steel strip to a winder.

[2]

Background Art

[3] A run out table (ROT) is a table roller transferring a rolled steel strip to a winder.

Cooling apparatuses are disposed at top and bottom of the ROT in parallel, thereby temperature control of the rolled steel strip is performed, in which the rolled steel strip transferred to the winder is cooled down to a target temperature.

[4] FIG. 1 is a schematic diagram illustrating an ROT section which is installed at an outlet of an F7 stand 10 disposed at an end of a hot strip mill, the top and bottom of which fourteen feedforward banks 13 and two feedback banks 14 are formed as cooling apparatuses. The feedforward banks 13 set water injection for controlling a temperature of a rolled steel strip by using a temperature measured at a first temperature measuring device 11 located at an outlet of the hot strip mill. The feedback banks 14 set and control water injection for controlling the temperature of the rolled steel strip by using a temperature measured at a second temperature measuring device located at an outlet of an ROT.

[5] However, there is a distance of about 19.067 m between a sixteenth bank 16 that is a final feedback bank and the second temperature measuring device 12. There occurs a time delay between measuring a temperature and controlling feedback. Such a measurement delay may have a serious effect on controlling the temperature of the rolled steel strip to be wounded by a winder.

[6] As shown in FIG. 2(a), in a temperature rise section, a temperature control corresponding to the deviation between a target temperature and a temperature deviation mesured by the second temperature measuring device 12 at a point in time ® is performed at a time ® after a measurement delay time τ. In this case, an amount of temperature control performed by the feedback banks is the deviation of the temperature measured at the point in time ®. However, an actual temperature deviation at the point in time © is greater than the deviation at the point in time ®. Accordingly, a temperature deviation is not reduced to 0 and still remains. In this case, when an actual response delay of banks is added thereto, responsiveness is more decreased and there is still maintained a deviation between the temperature of the rolled steel strip and the target temperature. [7] [8] On the other hand, in a temperature drop section, as shown in FIG. 2(b), a temperature control corresponding to a deviation between a temperature measured at a point in time © is performed by the feedback banks 14 at a point in time ® after the measuring delay time τ. The temperature control is performed greater than an actual temperature deviation. [9] Accordingly, in the rolled steel strip passing through a conventional ROT section, there are still present temperature deviations in a longitudinal direction. [10] FIG. 3 (a) illustrates intermediate temperature measurements of 590 DP steel, and

FIG. 3(b) illustrates temperature measurements performed at the second temperature measuring device 12.

[H]

[12] That is, in the case of the 590 DP steel that is a steel strip controlled to separately cool front and rear thereof, though an intermediate temperature is well controlled as shown in FIG. 3(a), a temperature of the 590 DP steel is seriously fluctuated after passing through the feedback banks 14, as shown in FIG. 3(b). This is metallurgical characteristics of the DP steel strip, in which temperature measurements and quality measurements greatly vary with water injections by only one or two of headers.

[13]

[14] Accordingly, in manufacturing high quality steel, the measurement delay is very critical with respect to temperature control in the ROT section.

[15] However, in conventional hot strip mill facilities, a second temperature measuring device (CT thermometer) installed at an outlet of an ROT is separated from a final feedback bank at a considerable distance. According to this, it is possible to measure an appropriate temperature, not affected by cooling water staying in a strip when feedback banks inject water. However, as described above, there occurs a time difference between a point in time of measurement and a point in time of control. Accordingly, an error occurs, in which controlling a temperature of a rolled steel strip is performed differently from an actual temperature of the rolled steel strip. This causes a characteristic deviation in a longitudinal direction in steel seriously affected by a temperature deviation, such as high strength thin steel.

[16] Prior art related with this will be described.

[17] Japanese Patent Laid-Open Publication No. Hei 10-43808 discloses a method of controlling a hot rolling finish temperature, the method including calculating an average temperature from rolling mill load at a hot rolling final stand, detecting a surface temperature of a rolled steel strip by using a surface temperature sensor at a descaling device in hot strip mill, calculating a center temperature in a thickness direction from the average temperature and the surface temperature, setting an adjustment coefficient according to how much the center temperature is higher than the surface temperature, and determining an amount of injected cooling water. However, in rolling mill for a thin steel, it is difficult to calculate the average temperature using the rolling mill load. Particularly, in the case of rolling a thin steel of high strength steel strip, since rolling load is great, it is difficult to measure and control a temperature using the rolling load, thereby causing a defects on passing ability when cooling the thin steel.

[18] Japanese Patent Laid-Open Publication No. 1997-192722 discloses a method controlling water injection and cooling a steel strip, the method including determining whether a surface temperature of the steel strip is about to be less than a boiling temperature by injecting water by injection nozzles when injecting water to an end portion of the steel strip until the end portion of the steel strip is transferred to a winding apparatus, obtaining a distance where the surface temperature of the steel strip is retrieved to a temperature more than the boiling temperature when the surface temperature is about to be less than the boiling temperature, and injecting the cooling water by the injection nozzle located in a position separated from the injection nozzle at the distance for retrieving the temperature. In this case, the temperature is controlled by obtaining the distance retrieving the temperature where the surface temperature of the steel strip is retrieved to the boiling temperature when the surface temperature is about to be less than the boiling temperature. Actually, it is difficult to install a thermometer at a distance where the surface temperature is retrieved to a temperature more than the boiling temperature in each ROT section. Accordingly, it may be difficult to appropriately control the temperature.

[19]

Disclosure of Invention Technical Problem

[20] An aspect of the present invention provides an apparatus and a method for controlling a temperature of a rolled steel strip in a run out table (ROT) section in a hot rolling mill, the apparatus and method capable of precisely controlling a target temperature by compensating a delay between a point in time of measuring a temperature and a point in time of controlling the temperature in the ROT section.

[21]

Technical Solution

[22] According to an aspect of the present invention, there is provided a method of controlling a temperature of a rolled steel strip in a run out table (ROT) section, the method including: collecting a speed of the rolled steel strip and a temperature of the rolled steel strip at an outlet side of the ROT section; modeling a bank water injection measurement by considering a response delay of a feedback bank of the ROT; calculating a time delay between a point in time of measuring the temperature at the outlet side of the ROT section and a point in time of control in the feedback bank with respect to the measured temperature by using the modeled measurement; calculating a temperature deviation between the measured temperature and a preset target temperature by considering the calculated time delay; and controlling the water injection of the feedback bank according to the calculated temperature deviation.

[23]

[24] The modeling of the bank water injection measurement may include calculating the bank water injection measurement according to a following equation σco— s f +- a. where G(s) indicates the bank water injection measurement, a=Tr/2.2, and Tr indicates a point in time of reaching 90% of a normal state response.

[25] The calculating of the time delay comprises calculating the time delay (τ) for the rolled steel strip to be transfered from a final feedback bank of the ROT section to a temperature measuring device as shown in a following equation

D

where V indicates the speed of the rolled steel strip [mpm] and D indicates a distance from the final feedback bank to the temperature measuring device [m]. [26] The calculating of the temperature deviation may include calculating the temperature deviation according to a following equation

R_PID=K_P{ 1 + -^- +sT_a

where K p , T i , and T d indicate proportion, integration, and differential control gains, re- spectively.

[27]

[28] According to another aspect of the present invention, there is provided an apparatus for controlling a temperature of a rolled steel strip in an ROT section in which cooling equipment including a plurality of feedforward banks and feedback banks for cooling down the rolled steel strip is disposed in parallel and a temperature measuring device measuring the temperature of the rolled steel strip is disposed at an outlet side thereof, the apparatus including: a measurement data collector collecting the temperature of the rolled steel strip at the outlet side of the ROT section from the temperature measuring device and a speed of the rolled steel strip at the ROT section; a model developing unit modeling measurements collected by the measurement data collector by considering a response delay of the feedback banks; a time delay calculator calculating a time delay between the temperature measuring device and a final feedback bank; a target temperature setter setting a target temperature of the rolled steel strip discharged from the ROT section; a temperature deviation calculator calculating a deviation between the measured temperature and the target temperature by considering the time delay calculated by the time delay calculator; a water injection commanding value calculator calculating a water injection commanding value for controlling the calculated temperature deviation; and a water injection controller controlling an actual water injection at the feedback banks in the ROT section according to the water injection commanding value outputted from the water injection commanding value calculator. [29]

Advantageous Effects

[30] As described above, according to the present invention, a time delay between a point in time of measuring a temperature and a point in time of controlling the temperature in a run out table (ROT) section is precisely calculated and water injection is accurately controlled by compensating the time delay, thereby precisely controlling a

CT temperature of a rolled steel strip. Therefore, characteristics in a longitudinal direction of a rolled coil may be controlled to be uniform. [31]

Brief Description of the Drawings [32] FIG. 1 is a schematic diagram illustrating a run out table (ROT) in a hot strip mill process; [33] FIGS. 2(a) and 2(b) are graphs for illustrating problems caused by a temperature measurement delay in an ROT section; [34] FIGS. 3 (a) and 3(b) are graphs illustrating measured temperature controls due to a temperature measurement delay in the ROT section; [35] FIG. 4 is a flowchart illustrating a method of controlling a temperature of a rolled steel strip at an ROT section according to an exemplary embodiment of the present invention; [36] FIG. 5 is a configuration diagram illustrating an apparatus for controlling a temperature in an ROT section according to an exemplary embodiment of the present invention; [37] FIG. 6 is a block diagram illustrating a method of calculating a temperature deviation by considering a measurement delay according to an exemplary embodiment of the present invention; and

[38] FIGS. 7(a) and 7(b) are graphs illustrating results of controlling the temperature according to an exemplary embodiment of the present invention.

[39]

Best Mode for Carrying Out the Invention

[40] Hereinafter, exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Only, in describing operations of the exemplary embodiments in detail, when it is considered that a detailed description on related well-known functions or constitutions unnecessarily may make essential points of the present invention be unclear, the detailed description will be omitted.

[41] Also, in the drawings, the same reference numerals are used throughout to designate the same or similar components.

[42] In addition, throughout the specification, when it is describe that a part is

"connected to" another part, this includes not only a case of "being directly connected to" but also a case of "being electrically connected to , interposing another device therebetween. Also, when it is described that an apparatus "includes" an element and there is no opposite description thereof, this does not designate that the apparatus excludes other elements but designates that the apparatus may further include other elements.

[43] FIG. 4 is a flowchart illustrating a method of controlling a temperature of a rolled steel strip in a run out table (ROT) section, according to an exemplary embodiment of the present invention.

[44] Referring to FIG. 4, to precisely calculate a time delay occurring in the ROT section and precisely control a CT temperature by separating a time delay from a controller, a speed of a rolled steel strip and a temperature at an outlet side of the ROT section, that is CT temperature measurements are collected (SlOO).

[45] The collected measurements are modeled according to a response delay of a feedback bank,(S200). A time delay between the second temperature measuring device 12 and the final feedback bank 14 by using the modeled measurements (S300).

[46] A temperature deviation between the measured temperature and a predetermined target temperature is calculated according to the calculated time delay (S400). Water injection of the feedback bank is controlled according to the calculated temperature deviation (S500).

[47] The modeling, the calculating the time delay, and the calculating the temperature deviation in S200 to 400 will be described in detail later.

[48] FIG. 5 is a schematic diagram illustrating an apparatus for controlling a temperature of a rolled steel strip in an ROT section, according to an exemplary embodiment of the present invention.

[49] Referring to FIG. 5, the apparatus includes a measurement data collector 20 collecting a CT temperature of the rolled steel strip at an outlet side of the ROT section and a speed of the rolled steel strip, a model developing unit 21 calculating actual bank water injection measurements by using a model considering a response delay of the feedback bank 14 from measurements collected by the measurement data collector 20, a time delay calculator 22 calculating a time delay between the second temperature measuring device 12 and the final feedback bank 14, a target temperature setter 24 setting a target temperature of a rolled steel strip discharged from an ROT, a temperature deviation calculator 23 calculating a temperature deviation from the target temperature considering the time delay calculated by the time delay calculator 22, a water injection commanding value calculator 25 calculating a water injection commanding value for controlling the calculated temperature deviation, and a water injection controller 26 controlling an actual water injection in the feedback banks of the ROT section according to a water injection commanding value outputted from the water injection commanding value calculator 25.

[50] The temperature control process according to an exemplary embodiment of the present invention will be described in detail.

[51] The CT temperature measured at the second temperature measuring device 12 located at the outlet side of the ROT and the measured speed of the rolled steel strip are collected from the measurement data collector 20. The measurement data collector 20 is embodied as a programmable logic controller (PLC).

[52] The model developing unit 21 calculates actual bank water injection measurements by using a model considering a response delay of the feedback bank from the measurements collected from the measurement data collector 20. A model for analyzing response characteristics of the feedback bank is generally modeled as a first delay system, which may be shown as Equation 1.

[53]

... Equation (1)

[54] where G(s) indicates the bank water injection measurement.

[55] Rising time T indicates a point in time of reaching 90% of a normal state response.

Generally, T r =2.2/a. Accordingly, a=2.2/T r . In the present embodiment, when the rising time T of the feedback bank is given about 1 second, according to the definition of the rising time T , a=2.2. In this case, a response model of the feedback bank may be shown as Equation 2. [56]

s+2.2

... Equation (2) [57] The time delay calculator 22 calculates a time delay τ for the rolled steel strip to be transfered from a final feedback bank #16 to the second temperature measuring device

12. The time delay τ is calculated as shown in Equation (3). [58]

D

... Equation (3) [59] where V indicates the speed [mpm] of the rolled steel strip measured at the measurement data collector 20 and D indicates a distance [m] from the final feedback bank #16 to the temperature measuring device 12. For example, D may be, but not limited to be, 19,067 m. [60] The temperature deviation calculator 23 calculates a temperature deviation considering the calculated time delay. In detail, the temperature deviation may be calculated from the target temperature set by the target temperature setter 24, considering the time delay. [61] FIGS. 6(a), 6(b), and 6(c) illustrates block diagrams of the temperature deviation calculator 23. [62] Referring to FIG. 6(a), the temperature deviation calculator 23 includes a controller

R (S), a process P(s), and a process model P (s). The controller R (S) controls the

PID m PID process P(s). In the process P(s), a time delay e ^st is modeled. The process model P (s) is modeled as shown in Equation 2. Accurately, the process model P (s) also includes a time delay term. [63] The temperature deviation calculator 23 may be reconfigured as shown in FIG.

6(b). [64] When a degree of modeling is similar to a field process (P(s)=P m (s)), as shown in

FIG. 69c), since G(s) included in modeling is separated from the time delay term G(s)e s^t, the controller R (s) may be controlled regardless of the time delay term. Accordingly, a degree of controlling a temperature is increased. In this case, the R may be as shown in Equation 4 and a transfer function shown in FIG. 6(c) may be as shown in Equation 5. [65] R_PIΩ=K_Pl 1 + ^7" ÷sTA

... Equation (4) [66] where K , T , and T indicate proportion, integration, and differential control gains, p i d respectively. [67]

Y(s) R_PID(s)P(s)

V^" .0, -Sl

1 W l +R_P!D(s)G_m(s)( l -e l+R_PIDP(s)

[68] ... Equation (5)

[69] The temperature deviation calculator 23 calculates a temperature deviation considering a time delay by using Equations 4 and 5 and transfers the time deviation to the water injection commanding value calculator 25. The water injection commanding value calculator 25 calculates a water injection commanding value capable of solving the temperature deviation considering the time delay and transfers the water injection commanding value to the water injection controller 26. The water injection controller 26 controls water injection of each of the feedback banks 14 according to the water injection commanding value.

[70]

[71] FIG. 7 (a) is a graph illustrating input temperature deviations of a case of estimating a time delay and a case of without estimation, respectively. FIG. 7(b) is a graph illustrating comparison between CT temperatures measured after a rolled steel strip inputted with the temperature deviation of FIG. 7 (a) passes through the feedback bank that is temperature-controlled according to an exemplary embodiment of the present invention.

[72] Referring to FIG. 7(b), when the time delay is precisely estimated (delay correct estimation), a temperature deviation is improved by 10 degrees more than two cases where the time delay is not precisely estimated.

[73] While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[1] A method of controlling a temperature of a rolled steel strip in a run out table

(ROT) section, the method comprising: collecting a speed of the rolled steel strip and a temperature of the rolled steel strip at an outlet side of the ROT section; modeling a bank water injection measurement by considering a response delay of a feedback bank of the ROT; calculating a time delay between a point in time of measuring the temperature at the outlet side of the ROT section and a point in time of control in the feedback bank with respect to the measured temperature by using the modeled measurement; calculating a temperature deviation between the measured temperature and a preset target temperature by considering the calculated time delay; and controlling the water injection of the feedback bank according to the calculated temperature deviation. [2] The method of claim 1, wherein the modeling of the bank water injection measurement comprises calculating the bank water injection measurement according to a following equation

G(» — — s + a. where G(s) indicates the bank water injection measurement, a=Tr/2.

2, and Tr indicates a point in time of reaching 90% of a normal state response.

[3] The method of claim 1, wherein the calculating of the time delay comprises calculating the time delay (τ) for the rolled steel strip to be transfered from a final feedback bank of the ROT section to a temperature measuring device as shown in a following equation

_ D τ

V where V indicates the speed [mpm] of the rolled steel strip and D indicates a distance [m] from the final feedback bank to the temperature measuring device.

[4] The method of claim 1, wherein the calculating of the temperature deviation comprises calculating the temperature deviation according to a following equation

where K , T , and T indicate proportion, integration, and differential control p i d gains, respectively.

[5] An apparatus for controlling a temperature of a rolled steel strip in an ROT section in which cooling equipment comprising a plurality of feedforward banks and feedback banks for cooling down the rolled steel strip is disposed in parallel and a temperature measuring device measuring the temperature of the rolled steel strip is disposed at an outlet side thereof, the apparatus comprising: a measurement data collector collecting the temperature of the rolled steel strip at the outlet side of the ROT section from the temperature measuring device and a speed of the rolled steel strip at the ROT section; a model developing unit modeling measurements collected by the measurement data collector by considering a response delay of the feedback banks; a time delay calculator calculating a time delay between the temperature measuring device and a final feedback bank; a target temperature setter setting a target temperature of the rolled steel strip discharged from the ROT section; a temperature deviation calculator calculating a deviation between the measured temperature and the target temperature by considering the time delay calculated by the time delay calculator; a water injection commanding value calculator calculating a water injection commanding value for controlling the calculated temperature deviation; and a water injection controller controlling an actual water injection at the feedback banks in the ROT section according to the water injection commanding value outputted from the water injection commanding value calculator.

[6] The method of claim 5, wherein the model developing unit calculates a bank water injection measurement according to a following equation

GO) s — + — a. where G(s) indicates the bank water injection measurement, a=Tr/2.2, and Tr indicates a point in time of reaching 90% of a normal state response.

[7] The method of claim 5, wherein the time delay calculator calculates a time delay for the rolled steel strip to be transferred from the final feedback bank in the ROT section to the temperature measuring device as shown in a following equation

D where V indicates the speed [mpm] of the rolled steel strip and D indicates a distance [m] from the final feedback bank to the temperature measuring device. [8] The method of claim 5, wherein the temperature deviation calculator calculates the temperature deviation by using a controller according to a following equation

Λ P pIrDn TC IPF₁ ^+sT° where K , T , and T indicate proportion, integration, and differential control p i d gains, respectively.