WO2008078908A1

WO2008078908A1 - Temperature controlling method and apparatus in hot strip mill

Info

Publication number: WO2008078908A1
Application number: PCT/KR2007/006698
Authority: WO
Inventors: Cheol Jae Park; Pil-Jong Lee; Myung Jong Cho
Original assignee: Posco
Priority date: 2006-12-22
Filing date: 2007-12-20
Publication date: 2008-07-03
Also published as: KR20080058641A; KR100843842B1

Abstract

There is provided a method and apparatus for controlling temperature in a hot strip mill. In order to accurately control coiling temperature by using middle temperature, a method of controlling temperature in a hot strip mill includes correcting a learning coefficient of a coil previously processed, collecting finishing delivery temperature, coiling temperature, middle temperature, and moving speed of a strip, calculating an air cooling drop amount of temperature by using the finishing delivery temperature and calculating a water cooling drop amount of temperature by using the air cooling drop amount of temperature and a coiling temperature target value, calculating a first water cooling drop amount of temperature according to the water cooling drop amount of temperature and the middle temperature target value, and setting individual water injection amounts of first banks according to the first water cooling drop amount of temperature, and calculating a second water cooling drop amount of temperature according to the water cooling drop amount of temperature and the collected middle temperature, and setting individual water injection amounts of second banks according to the second water cooling drop amount of temperature. Accordingly, the middle temperature is controlled to be kept constant, and the coiling temperature is always kept constant, such that the strip has uniform material properties.

Description

TEMPERATURE CONTROLLING METHOD AND APPARATUS

IN HOT STRIP MILL

Technical Field

[1] The present invention relates to an apparatus and method of controlling temperature in a hot strip mill, and more particularly, to an apparatus for controlling temperature that can accurately control coiling temperature (CT) by using temperature measured by a middle thermometer for high quality steel requiring middle temperature control. Background Art

[2] In a cooling process on a run out table (ROT) in a hot strip mill according to the related art, a thermometer is not installed at an intermediate region of the ROT. The ROT is a device that transfers strips delivered from a finishing mill to a coiler.

[3] In order to manufacture high quality steel, such as a double phase (DP) steel, there is a need for a technique that accurately controls middle temperature. However, it is impossible to control the middle temperature. The performance of controlling the middle temperature as well as the coil temperature (CT) is relatively poor.

[4] This causes problems in high strength strips or steel grades that particularly require middle temperature control, and causes deviation of mechanical properties along a longitudinal direction. Therefore, in order to manufacture high quality steel, a problem of controlling temperature between banks needs to be solved by using middle temperature.

[5] Therefore, when feedforward control and feedback control are performed in a longitudinal direction of a coil by using middle temperature, a technique that accurately controls the middle temperature is required.

[6] FIG. 1 is a view illustrating a change in material properties of a steel grade according to temperature to show the importance of controlling middle temperature.

[7] When the temperature of a strip gradually decreases from finishing delivery temperature FDT and reaches middle temperature section MT, the strip has a ferrite phase. In the middle temperature section MT, a ferrite transformation ratio has a maximum value during the middle temperature section MT.

[8] When the temperature of the strip passes through the middle temperature section

MT and decreases more, the strip passes through a section of bainite and martensite Ms structures, and then the strip has coiling temperature CT.

[9] Steel grades that have the above-described metallurgical characteristics include a

DP steel and a transformation induced plasticity (TRIP) steel, and they are classified as high quality steel. The middle temperature control is an important factor that determines material properties of the steel grades. An air cooling time is another important factor that keeps middle temperature constant.

[10] FIG. 2 is a view illustrating a configuration of an apparatus for controlling temperature in a hot strip mill according to the related art.

[11] Referring to FIG. 2, an apparatus for controlling temperature includes an ROT 10, first to sixteenth banks Bl to B 16 that are formed above the ROT 10. The first to fourteenth banks Bl to B 14 are used as a feedforward bank FFB that controls a water injection amount according to temperature that is measured by a finishing delivery thermometer 12 installed at a delivery side of a finishing mill 11, and the fifteenth and sixteenth banks B 15 and B 16 are used as a feedback bank FBB that controls a water injection amount according to temperature that is measured by a coiling thermometer 13 installed at a side of a coiler (not shown).

[12] The apparatus for controlling temperature according to the related art transfers a strip by using the ROT 10. The strip is delivered from the finishing mill 11 and has finishing delivery temperature FDT. Tha apparatus gradually cools the strip by a water-injection operation of the feedforward bank FFB to reach the middle temperature section MT shown in FIG. 1. Further, after an air cooling time, the apparatus for controlling temperature resumes transferring the strip by the ROT 10 and gradually cools the strip by a water-injection operation of the feedforward bank FFB and the feedback bank FBB.

[13] However, it is difficult to control the coiling temperature CT by the method of controlling temperature according to the related art.

[14] FIG. 3 is a view illustrating a change in heat flux coefficient with a change in temperature. Referring to FIG. 3, it can be seen that a heat flux coefficient greatly changes according to rolling speed.

[15] Particularly, the heat flux coefficient greatly changes at low temperature. The DP steel of which temperature needs to be controlled in the exemplary embodiment of the invention has a low temperature of approximately 200°C. As mentioned above, since the heat flux coefficient greatly changes, it is very difficult to control the coiling temperature CT.

[16] FIG. 4 is a view illustrating a method of controlling temperature in the apparatus for controlling temperature shown in FIG. 2.

[17] In FIG. 4, a 590DP steel is used as an example of a steel grade. FDT refers to finishing delivery temperature, MT refers to middle temperature, LT refers to low coiling temperature, and CT refers to high coiling temperature.

[18] Referring to FIG. 4, the finishing delivery temperature FDT can be controlled to some degree, but the middle temperature MT hunts greatly in the middle. Therefore, the low coiling temperature LT also changes greatly and a deviation of approximately 300⁰C or more occurs between a maximum value and a minimum value of the low coiling temperature LT.

[19] Therefore, in order to increase the accuracy of coiling temperature control, a technique that controls the middle temperature by ensuring the air cooling time at middle temperature and is very important. Disclosure of Invention Technical Problem

[20] An aspect of the present invention provides a method and apparatus for controlling temperature in a hot strip mill that can accurately control middle temperature. Technical Solution

[21] According to an aspect of the present invention, there is provided a method of controlling temperature, the method including: correcting a learning coefficient of a coil previously processed, collecting finishing delivery temperature, coiling temperature, middle temperature, and moving speed of a strip, calculating an air cooling drop amount of temperature by using the finishing delivery temperature and calculating a water cooling drop amount of temperature by using the air cooling drop amount of temperature and a coiling temperature target value, calculating a first water cooling drop amount of temperature according to the water cooling drop amount of temperature and the middle temperature target value, and setting individual water injection amounts of first banks according to the first water cooling drop amount of temperature, and calculating a second water cooling drop amount of temperature according to using the water cooling drop amount of temperature and the collected middle temperature, and setting individual water injection amounts of second banks according to the second water cooling drop amount of temperature.

[22] According to another aspect of the present invention, there is provided a an apparatus for controlling temperature in a hot strip mill, the apparatus including: a learning coefficient correcting unit for correcting a learning coefficient of a coil previously processed, a measured data collecting unit for collecting finishing delivery temperature, coiling temperature, middle temperature, and moving speed of a strip, a middle target temperature setting unit for setting a middle temperature target value, a water cooling drop amount calculating unit for calculating an air cooling drop amount of temperature by using the finishing delivery temperature and calculating a water cooling drop amount of temperature by using the air cooling drop amount of temperature and a coiling temperature target value, and for calculating a first water cooling drop amount of temperature according to the water cooling drop amount of temperature and the middle temperature target value and calculating a second water cooling drop amount of temperature by using the water cooling drop amount of temperature and the collected middle temperature thereafter, a first water injection bank setting unit for setting idividual water injection amounts of first banks according to the first water cooling drop amount of temperature, a second water injection bank setting unit for setting individual water injection amounts of second banks according to the second water cooling drop amount of temperature, and a water injection control unit for controlling the water injection amount of each of the first and second water injection banks according to results set by the first water injection bank setting unit and the second water injection bank setting unit.

Advantageous Effects

[23] As set forth above, the apparatus and method of controlling temperature in a hot strip mill according to the exemplary embodiment of the invention measures middle temperature and uses the measured middle temperature to accurately control a water injection amount of a feedforward bank and a feedback bank, particularly, the water injection of the feedforward bank. Therefore, coiling temperature can be kept constant at all times, and the strip has uniform material properties.

Brief Description of the Drawings [24] FIG. 1 a view illustrating a change in material properties of a steel grade according to temperature to show the importance of controlling middle temperature; [25] FIG. 2 is a view illustrating a configuration of an apparatus for controlling temperature in a hot strip mill according to the related art; [26] FIG. 3 is a view illustrating a change in heat flux coefficient with a change in temperature; [27] FIG. 4 is a view illustrating a method of controlling temperature of the apparatus for controlling temperature shown in FIG. 2; [28] FIG. 5 is a view illustrating a method of controlling temperature in a hot strip mill according to an exemplary embodiment of the present invention; [29] FIG. 6 is a view illustrating a configuration of the apparatus for controlling in a hot strip mill according to an exemplary embodiment of the present invention; [30] FIG. 7 is a view illustrating a change in temperature of a strip by a hot strip mill according to an exemplary embodiment of the present invention; [31] FIG. 8 is an exterior view illustrating a middle thermometer according to an exemplary embodiment of the present invention; and [32] FIG. 9 is a view illustrating an example of a middle thermometer that is installed at an ROT shown in FIG. 8.

Best Mode for Carrying Out the Invention [33] Hereinafter, exemplary embodiments of the present invention by which those skilled in the art can easily implement the invention will now be described in detail with reference to the accompanying drawings. However, in description of operation principles associated with the embodiments of the present invention, detailed description of a known art or configuration is omitted because it may obscure the spirit of the present invention unnecessarily. In the following description, well-known functions or configurations are not described in detail since they would obscure the invention in unnecessary detail.

[34] Also, like reference numerals refer to like elements throughout the specification.

[35] FIG. 5 is a view illustrating a method of controlling temperature in a hot strip mil according to an exemplary embodiment of the present invention.

[36] First, in Step Sl, a learning coefficient fl of a coil previously processed is corrected. The learning coefficient of the coil is used to correct a heat flux coefficient (Q), such that a calorific value is accurately calculated and the accuracy of the control can be increased.

[37] At Step S2, finishing delivery temperature FDT, middle temperature MT, and coiling temperature CT are collected (S2). At Step S3, moving speed of a strip is collected (S3). In general, temperature control of an ROT section has an initial setup mode, a feedforward control mode, a feedback control mode, and a learning mode. In the feedforward control mode, the number of headers of banks that are controlled in the ROT section is determined by using the finishing delivery temperature FDT and the moving speed of the strip. In the feedback control mode, the number of headers of banks is determined by using the coiling temperature CT and the moving speed of the strip. Further, cooling patterns and rolling parameters are used in the above two modes.

[38] At Step S4, it is determined whether it is a general continuous cooling coil or a front and rear separate cooling coil (S4). General steels correspond to a continuous cooling coil. The number of headers of banks to be used is usually determined on the basis of cooling patterns of the coil. On the other hand, steel grades that require middle temperature control correspond to a front and rear separate cooling coil. The middle temperature may be used as a target value, while the temperature calculated using a temperature calculation model may be used as a measured value of the middle value. Alternatively, a thermometer may be directly mounted and the temperature measured by the thermometer may be used as the measured value.

[39] As a result of the determination at Step S4, if the coil is a front and rear separate cooling coil, an air cooling drop amount of temperature CT from the finishing air delivery temperature FDT to the coiling temperature CT is calculated according to

Equation 1 at Step S5. [40] [Equation 1]

[41] Γ_Ψ -Λ A*L , J 1 , o

^{C I <}* [ H^x V ^ (FDT- B) * 1

[42] B = FDT x a + b

[43] where a, b, and A are coefficients, L is a length of the ROT section, H is a thickness of the strip, and V is the moving speed of the strip.

[44] At Step S6, a temperature drop amount by actual water cooling except for the air cooling drop amount of temperature between the finishing delivery temperature FDT and the coiling temperature CT calculated at Step S5 is calculated. A first water cooling temperature drop amount of temperature ΔT is calculated according to Equation 2 (S6).

[45] [Equation 2]

[46]

A T w= CT ^- CT r

[47]

A T ₁ ^ A T w- MT _x

[48] where ΔT^ is the first water cooling drop amount of temperture, and MT is a middle temperature target value. [49] At Step S7, a second water cooling drop amount of temperature ΔT is calculated according to Equation 3 (S7). [50] [Equation 3]

[51]

^ T₂ = MT _T- CT _τ

[52] where ΔT is the first water cooling drop amount of temperature, and CT is a

2 T coiling temperature target value.

[53] At Step S8, a water injection amount of first water injection banks (first to eight banks B 1 to B8), respectively, is determined on the basis of the first water cooling drop amount of temperature ΔT calculated at Step S6 and a water cooling temperature drop amount of temperature ΔT of each of the banks that is calculated according to Equation 4.

[54] [Equation 4]

[55]

^{1 bl ~} 3600* F*p^χ C*H ^ ¹ [56] where L is a length of each of the banks, C is specific heat, p is the boiling point, b and Q is a heat flux coefficient of a bank i.

[57] At Step S9, a water injection amount of second water injection banks (for example, ninth to fourteenth banks B9 to B 14), respectively, is determined on the basis of the second water cooling drop amount of temperature ΔT calculated at Step S7 and the water cooling temperature drop amount of temperature ΔT calculated according to bi

Equation 4.

[58] On the other hand, as a result of the determination at Step S4, when it is the continuous cooling coil, like the related art, the entire water injection amount is determined by using Equations 1, 2, and 3 at Step SlO. At Step 11, a water injection amount of each of the banks Bl to B 14 is deterimined.

[59] FIG. 6 is a view illustrating a configuration of an apparatus for controlling temperature in a hot strip mill according to an exemplary embodiment of the present invention.

[60] Referring to FIG. 6, the apparatus for controlling temperature according to an exemplary embodiment of the invention includes an ROT 10, a first feedforward bank FFBl comprising a first to an eighth banks Bl to B 8, a second feedforward bank FFB2 comprising a ninth to a fourteenth banks B9 to B 14, a feedback bank FBB that comprising a fifteenth and a sixteenth banks B 15 and B 16, a finishing delivery thermometer 12 installed at a delivery side of a finishing mill 11 to measure finishing delivery temperature FDT of a strip, a coiling thermometer 13 installed at a side of a coiler (not shown) to measure coiling temperature CT of a strip, a middle thermometer 20 installed in the middle of the ROT 10 to measure middle temperature MT of the strip, a learning coefficient correcting unit 30 to correct a heat flux learning coefficient fl, a measured data collecting unit 31 to collect the finishing delivery temperature FDT, the coiling temperature CT, the middle temperature MT, and the moving speed of the strip, a front and rear separate cooling determining unit 32 to determine whether the currently moving strip is a front and rear separate cooling coil, an air cooling drop amount calculating unit 33 to calculate an air cooling drop amount of temperature CT air according to Equation 1, a first water cooling drop amount calculating unit 34 to calculate a first water cooling drop amount of temperature ΔT according to Equation 2, a second water cooling drop amount calculating unit 35 to calculate a second water cooling drop amount of temperature ΔT according to Equation 3, a middle target temperature setting unit 36 to set a middle temperature target value MT , a first water injection bank setting unit 37 to set a first water injection amount by the first water injection banks Bl to B8 included in the first feedforward bank FFBl according to the first water cooling drop amount of temperature ΔT and a water cooling temperature drop amount of temperature ΔT bi of each of the banks calculated according to Equation 4, a second water injection bank setting unit 38 to set a second water injection amount ΔT by the second water injection banks B9 to B 14 included in the second feedforward bank FFB2 according to the second water cooling drop amount of temperature ΔT and the water cooling temperature drop amount of temperature ΔT

2 bi of each of the banks calculated according to Equation 4, and a water injection control unit 39 to substantially control the water injection amount of each of the first and second feedforward banks FFB 1 and FFB2 according to the set values of the first and second water injection bank setting units 37 and 38 so as to cool the strip. Preferably, the middle thermometer 20 has a structure as shown in FIG. 7, and is mounted to the ROT as shown in FIG. 8.

[61] As such, the ROT, shown in FIG. 6, measures the middle temperature MT of the strip and uses the measured middle temperature MT to accurately control the water injection amount of the first and second feedforward banks FFBl and FFB2. Therefore, the middle temperature MT is kept constant, and the coiling temperature CT is also kept constant.

[62] FIG. 7 is a view illustrating a change in temperature of the strip by the apparatus for controlling temperature in a hot strip mill according to the exemplary embodiment of the present invention.

[63] Like FIG. 4, a 590DP is used as an example of a steel grade. FDT refers to finishing delivery temperature, MT refers to middle temperature, LT refers to low coiling temperature, and CT refers to high coiling temperature.

[64] Referring to FIG. 7, the middle temperature MT as well as the finishing mill delivery temperature FDT is controlled to be kept constant. It can be seen that the low coiling temperature LT becomes constant by the middle temperature MT.

[65] 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 temperature, the method comprising: correcting a learning coefficient of a coil previously processed; collecting finishing delivery temperature, coiling temperature, middle temperature, and moving speed of a strip; calculating an air cooling drop amount of temperature by using the finishing delivery temperature and calculating a water cooling drop amount of temperature by using the air cooling drop amount of temperature and a coiling temperature target value; calculating a first water cooling drop amount of temperature according to the water cooling drop amount of temperature and the middle temperature target value, and setting individual water injection amounts of first banks according to the first water cooling drop amount of temperature; and calculating a second water cooling drop amount of temperature according to the water cooling drop amount of temperature and the collected middle temperature, and setting individual water injection amounts of second banks according to the second water cooling drop amount of temperature.

[2] The method according to claim 1, wherein the air cooling drop amount of temperature is calculated by Equation of

_ J-

L Hx V (FDT- B)

the water cooling drop amount of temperature is calculated by subtracting the coiling temperature target value from the air cooling drop amount of temperature, the first water cooling drop amount of temperature is calculated by subtracting the middle temperature target value from the water cooling drop amount of temperature, the second water cooling drop amount of temperature is calculated by subtracting the coiling temperature target value from the collected middle temperature, and the water cooling drop amount of temperature of each of the banks is calculated by Equation of

3600^χ F^χρ^χ Cx H ^{W i}

where B is FDT x a + b, FDT is finishing delivery temperature, a, b, and A are coefficients, L is a length of an ROT, H is a thickness of a strip, V is moving speed of the strip, Lb is a length of each of the banks, C is specific heat, p is the boiling point, and Q is a heat flux coefficient of a bank i.

[3] An apparatus for controlling temperature in a hot strip mill, the apparatus comprising: a learning coefficient correcting unit for correcting a learning coefficient of a coil previously processed; a measured data collecting unit for collecting finishing delivery temperature, coiling temperature, middle temperature, and moving speed of a strip; a middle target temperature setting unit for setting a middle temperature target value; a water cooling drop amount calculating unit for calculating an air cooling drop amount of temperature by using the finishing delivery temperature and calculating a water cooling drop amount of temperature by using the air cooling drop amount of temperature and a coiling temperature target value, and for calculating a first water cooling drop amount of temperature according to the water cooling drop amount of temperature and the middle temperature target value and calculating a second water cooling drop amount of temperature by using the water cooling drop amount of temperature and the collected middle temperature thereafter; a first water injection bank for setting unit setting individual water injection amounts of first banks according to the first water cooling drop amount of temperature; a second water injection bank for setting unit setting individual water injection amounts of second banks according to the second water cooling drop amount of temperature; and a water injection control unit for controlling the water injection amount of each of the first and second water injection banks according to results set by the first water injection bank setting unit and the second water injection bank setting unit.

[4] The apparatus according to claim 3, wherein the calculating unit comprises: an air cooling drop amount for calculating unit calculating the air cooling drop amount of temperature; a first water cooling drop calculating unit for calculating the first water cooling drop amount of temperature; and a second water cooling drop calculating unit for calculating the second water cooling drop amount of temperature.

[5] The apparatus according to claim 3, wherein the air cooling drop amount of temperature is calculated by equation of AxL + _π\ 3 + B

L Hx V (FDT- B)

the water cooling drop amount of temperature is calculated by subtracting the coiling temperature target value from the air cooling drop amount, the first water cooling drop amount of temperature is calculated by subtracting the middle temperature target value from the water cooling drop amount, and the second water cooling drop amount of temperature is calculated by subtracting the coiling temperature target value from the middle temperature, the water cooling drop amount of temperature of each of the banks is calculated by Equation of