JPS6221850B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of a metal strip in an annealing zone of a continuous annealing furnace.

For example, in a continuous annealing furnace in a production line for hot-dip galvanized steel sheets, the ends of metal strips (hereinafter simply referred to as strips) of different sizes and materials are connected by welding depending on the required product type. Operations are underway. In this case, it is required to perform a precise annealing process commensurate with the dimensions and material of the strip. One type of slow cooling zone in such a continuous annealing furnace is to install a cooling tube inside the furnace through which air circulates, and remove the heat absorbed by the cooling tube from the strip with the air flowing inside the cooling tube. There is a type that cools the strip indirectly. The conventional method for controlling the temperature of the strip in the slow cooling zone is to measure the temperature of the strip at the exit side of the slow cooling zone, and change the rotation speed of the blower that absorbs the air in the cooling pipe depending on the deviation from the target temperature. A feedback system is used to adjust the air flow rate within the cooling pipe, and when changing the dimensions and material of the strip, the same method as above is used to change the rotation speed.

In this conventional control method, the feed
Because it is a back-up method, there is a delay in control, and precise strip temperature control is not possible. The amount of change in the blower rotation speed when changing the strip dimensions or material depends on the intuition of the operator, which results in inaccuracies.
There were drawbacks such as difficulty in adjusting to the target value within a predetermined time.

The purpose of the present invention is to solve these conventional problems and to provide a method for controlling the temperature of a metal strip in a cooling tube type slow cooling zone, which provides optimal cooling in response to changes in strip dimensions and materials. It is about providing. The method of the present invention to achieve this objective is as follows. That is, in a method in which the temperature of a metal strip in a continuous annealing furnace lehr zone having a cooling pipe through which air flows is controlled by changing the rotational speed of an air suction blower and adjusting the air flow rate in the cooling pipe, Using a calorific value calculation formula that includes the metal strip thickness, width, transfer speed, temperature at the entrance of the metal strip to the lehr-cooling zone, and target temperature at the outlet of the lehr-cooling zone, the metal strip is The amount of heat taken away by the air is predicted and calculated, and the air flow rate calculation formula in the cooling tube that includes the predicted amount of heat and the air temperature at the entrance side of the cooling tube is used to calculate the amount of heat necessary for the temperature at the exit side of the slow cooling zone of the metal strip to reach the target temperature. Calculate the air flow rate in the cooling pipe, calculate the required rotation speed of the blower from the predicted required air flow rate, set this as a set value, and adjust the transfer speed of the metal strip and the temperature of the metal strip during operation at the set blower rotation speed. , a method for controlling the temperature of a metal strip in a slow cooling zone of a continuous annealing furnace, which is characterized in that the temperature of the air is actually measured and the set value of the blower rotation speed is corrected based on these measured values, and in addition to the above control method. , Using the above-mentioned actual measurement values, find the actual value of the amount of heat taken away by the air while the metal strip passes through the slow cooling zone, and calculate the actual amount of heat, the air temperature on the inlet and outlet sides of the cooling pipe, and the blower rotation speed. This is a method for controlling the temperature of a metal strip in a slow cooling zone of a continuous annealing furnace, which is characterized by dynamically modifying the equation for calculating the air flow rate in the cooling tube using the actually measured value.

Hereinafter, the present invention will be explained by taking as an example a cooling tube type slow cooling zone of a continuous annealing furnace in a production line for hot-dip galvanized steel sheets. The amount of heat Q taken away by the air in the cooling tube while the strip passes through the slow cooling zone is expressed by the following equation.

Q=ρ・h・W・V・(Ci−Co)……(1) Here, Ci: Heat capacity corresponding to the strip temperature at the entrance side of the slow cooling zone Co: Heat capacity ρ corresponding to the strip temperature at the exit side of the slow cooling zone : Density of the strip h: Thickness of the strip W: Width of the strip V: Transport speed of the strip The air in the cooling pipe absorbs the above-mentioned amount of heat Q and its temperature rises, and the air temperature at the entrance side of the cooling pipe T _i (normally (atmospheric temperature) to the air temperature T _p on the outlet side of the cooling pipe. If the average temperature T _n of the air in the cooling pipe is T _n =T _i +T _p /2 (2), then the following equation holds true between the average air temperature T _n and the amount of heat Q.

T _n = B ₀ + B ₁・Q ………(3) However, B ₀ and B ₁ are constants. From equations (2) and (3) above, the air temperature T _p on the outlet side of the cooling pipe is T _p = 2・T It can be obtained predictively as _n −T _i ......(4).

Next, there is the following relationship between the amount of heat Q, the air flow rate F in the cooling pipe, and the air temperatures T _i and T _p on the inlet and outlet sides of the cooling pipe.

Q=(273/T _p +273・ρ _a )・(T _p −T _i )・
F・C _pa … …(5) Here, ρ _a : Density of air C _pa : Specific heat of air In equation (5), if 1/K=273・ρ _a・C _pa , then equation (5) is as follows. It is expressed as

F=Q・K・T _p +273/T _p −T _i・K _ln
......(6) However, K _ln is a learning coefficient that will be described later.Next, if the rotation speed of the blower that sucks air in the cooling pipe is N, the following formula holds true between it and the air flow rate F in the cooling pipe. .

N=A ₀ +A ₁・F (7) However, A ₀ and A ₁ are constants.The temperature control method of the present invention is a feed-forward control that allows changes in operating conditions, such as changes in strip dimensions and material. The number of revolutions of the blower required to achieve the strip target temperature on the exit side of the slow cooling zone when the point reaches the entrance side of the slow cooling zone is determined from (1) to (7) above.
Calculate and set using formulas, and as feed back control, use the actual measured values of the strip transfer speed, strip temperature, and air temperature to control the blower at regular intervals after the feed forward control. Correcting the rotation speed setting value,
And, for each feed back control, using the actual measurement value and the actual measurement value of the blower rotation speed (6)
This system is characterized by a learning control that dynamically modifies the cooling pipe air flow rate calculation formula.

Hereinafter, a method of calculating the required number of revolutions of the blower during each control will be explained.

(A) Feed forward control; First, calculate the predicted value Q _f of the amount of heat removed while the strip passes through the slow cooling zone using equation (1).
Here, the most recently measured speed and temperature are used for the transfer speed of the strip and the temperature at the entrance of the lehr, and the target temperature is used for the temperature of the strip at the outlet of the lehr. Next, the predicted value T _pc of the air temperature on the outlet side of the cooling pipe is calculated using equations (3) and (4), and the required air flow rate F _f in the cooling pipe is calculated using equation (6). Then, the blower rotation speed N _f necessary to obtain the air flow rate F _f is calculated using equation (7), and this blower rotation speed N _f is set in the blower control device. Note that, as the learning coefficient in equation (6), the coefficient obtained during the most recent learning control is used by the learning control method described later.

(B) Feedback control; Feedback control is activated at fixed time intervals after the completion of feedforward control, and there are the following two methods.

(B-a) Using the actual measured values of the strip transfer speed and temperature at the entrance of the lehr during feed back control, the temperature of the strip at the outlet of the lehr is adjusted to the target temperature using equation (1). Calculate the amount of heat Q _b that should be taken away while passing through the slow cooling zone, and use this amount of heat Q _b and the actual measured air temperatures at the inlet and outlet sides of the cooling pipe to calculate the required air flow rate F _b using equation (6). . Then, the blower rotation speed N _b necessary to obtain the air flow rate F _b is calculated using equation (7), and this blower rotation speed N _b is corrected and set in the blower control device. The learning coefficient in equation (6) uses the coefficient obtained during the most recent learning control.

(B-b) Derived from equation (1) using the actual value of the transfer speed of the strip most recently during the current fee-back control and the difference between the actual value and target value of the temperature at the exit side of the strip lehr. The following formula ΔQ _b = ρ・h・W・V・(C _pa −C _pt )
......(1') Here, C _pa : The heat capacity corresponding to the actual measured temperature of the strip on the exit side of the slow cooling zone. C _pt : The heat capacity corresponding to the target temperature of the strip on the exit side of the slow cooling zone. Find the correction amount ΔQ _b of the amount _of heat that should be removed from the strip in order to
Using the actual measured values T _ia and T _pa of the air temperature on the inlet and outlet sides of the cooling pipe, the following formula is derived from equation (6): ΔF _b = ΔQ _b・K・T _pa +273/T _pa −T _ia
・K _ln ...... (6') Calculate the correction amount ΔF _b of the required air flow rate corresponding to the heat amount correction amount ΔQ _b . and
Calculate the blower rotational speed correction amount ΔN b corresponding to the air flow rate correction amount ΔF _b using the following formula derived from equation (7 ₎ : ΔN _b = A ₁ · ΔF _b (7')
The amount of correction of this rotation speed is the actual rotation speed N at that time.
The rotational speed N _b (=N _a +ΔN _b ) added to _a is corrected and set in the blower control device. The learning coefficient in equation (6') uses the coefficient obtained during the most recent learning control.

(C) Learning control; Using the actual measured values of the strip transfer speed and the temperature of the strip at the entrance and exit sides of the slow cooling zone, calculate the actual value _Q a of the amount of heat taken away from the strip while passing through the slow cooling zone using equation (1). is calculated, and the air flow rate calculation formula (6) is corrected using the measured values of the air temperature and blower rotation speed on the inlet and outlet sides of the cooling pipe, and the actual value Q _a of the amount of heat.

Specifically, for each feed back control, the actual value F _a of the air flow rate in the cooling pipe is calculated from equation (7) using the measured value N _a of the blower rotation speed, and this air flow rate actual value F _a and the above-mentioned The coefficient K _l is determined from the actual value Q _a of the amount of heat and the actual measured values T _ia and T _pa of the air temperature on the inlet and outlet sides of the cooling pipe using the following formula. That is, K _l =F _a /Q _a ·T _pa −T _ia /T _pa +
273・1/K……(8) Applying averaging processing to this coefficient K _l , K _ln =K _l ′ _n +G _kl・(K _l −K _l ′ _n )……(9) Here, K _ln : Current learning coefficient K _l ' _n : Learning coefficient at previous timing G _kl : Learning gain Using this learning coefficient K _ln , the air flow rate calculation formula is dynamically corrected.

Next, the structure and operation of the apparatus according to the embodiment of the present invention shown in FIG. 1 will be explained. In the figure, 1 is a setting device that sets the setting values necessary for each calculation, 2 to 11 are calculation units, S _f is a switch that closes during feed forward control and opens during feed back control,
_b is closed during feed back control;
A switch that opens during forward control, F _N is the slow cooling zone of the furnace, O ₁ to O ₄ are cooling pipes, P _t is a strip, D _i ,
D _p is a strip thermometer, PG is a strip velocimeter, B1 to B4 are suction blowers, BC1 to BC4
is a blower control device, TC1 to TC4 are cooling pipe outlet air temperature detectors, and TC is a cooling pipe inlet air temperature detector.

When the point of change in strip size or material reaches the furnace entry side, switch S _f is closed and switch S _b is opened. The calculator 2 receives inputs from the setting device 1 (density ρ of the strip 1, plate thickness h, plate width W, target temperature t of the strip on the exit side of the annealing zone).
_pt ), the strip speed V measured by the strip speed meter _PG , and the strip temperature D _i at the entrance of the slow cooling zone, and the strip passes through the slow cooling zone according to equation (1). A predicted value Q _f of the amount of heat taken away by the air in the cooling pipe during this time is calculated. Based on the input Q _f from the calculator 2 and the air temperature T _ia (atmospheric temperature may be substituted) measured by the cooling pipe inlet air temperature detector TC, the calculator 3 calculates (3)
A predicted value T _pc of the air temperature at the exit side of the cooling pipe is calculated according to the equation and equation (4). The computing unit 4 calculates the value based on the input Q _f from the computing unit 2, the input T _pc from the computing unit 3, the cooling pipe inlet air temperature T _ia , and the learning coefficient K _ln obtained by the computing unit 11 during the most recent feed back control. Using equation (6), calculate the air flow rate F _f in the cooling tube required for the strip temperature on the outlet side of the slow cooling zone to reach the target temperature.
Based on this air flow rate F _f , the computing unit 5 calculates the necessary rotation speed N _f of the suction blower according to equation (7), and uses this rotation speed N _f as the blower rotation speed setting value at the time of feed forward. Control device
Set to BC1 to BC4. Blower control device BC
1 to BC4 act to suck and control the air in the cooling pipes _O1 to _O4 by known means. The above is feed forward control including learning control.

After a certain period of time has passed since the feed forward control, switch S _b is closed and switch S _f is opened. At this timing, the arithmetic unit 6 inputs the temperature t _i of the strip at the entrance of the slow cooling zone measured by the strip thermometer D _i , the strip speed V measured by the strip speed meter PG, and the inputs from the setting device 1 (ρ, h, W ,t
_pt ), the amount of heat Q _b that should be taken away by the strip while passing through the cooling zone is calculated according to equation (1). The computing unit 7 calculates the input Q _b from the computing unit 6, the input T _ia from the cooling pipe inlet air temperature detector TC (the atmospheric temperature may be substituted), and the cooling pipe outlet air temperature detector TC1. ~Based on the input T _pa from the TC4 and the learning coefficient K _ln obtained by the calculator 11 during the most recent feedback control, calculate the required temperature for the strip temperature at the outlet side of the slow cooling zone to reach the target temperature according to equation (6). Calculate the air flow rate F _b in the cooling pipe. The calculator 8 calculates the required number of rotations N _b of the suction blower according to equation (7) based on the input F _b from the calculator 7,
This rotational speed _Nb is set in the blower control devices BC1 to BC4 as a correction set value for the blower rotational speed during the feedback control. blower control device
BC1 to BC4 control the suction of air in the cooling pipes using new set values N _b instead of the previous set values N _f (or the revised set values used during the previous feedback control). Further, the series of calculations described above and the correction of the blower rotation speed setting value are repeated every predetermined period of time from the above timing. The above is the feedback control including learning control.

Note that a supplementary explanation will be provided regarding the functions of the computing units 9 to 11 for learning control. The calculator 9 calculates the strip temperatures t i _and t _p of the strip at the entrance and exit sides of the slow cooling zone measured by the strip thermometers D _i and D _p , the strip speed V measured by the strip speed meter PG, and the information from the setting device 1. Based on the inputs (ρ, h, W), (1)
The actual value Q _a of the amount of heat taken away by the strip while passing through the gradual cooling zone is calculated according to the formula. The calculator 10 calculates the actual value F _a of the air flow rate in the cooling pipe from the measured rotational speed N _a using equation (7). The computing unit 11 receives the actual measured value T _ia (or atmospheric temperature) of the air temperature on the inlet side of the cooling pipe, the actual measured value T _pa of the air temperature on the outlet side of the cooling pipe, the input Q _a from the computing unit 9, and the input F from the computing unit 10. Based on _a , the learning coefficient K _ln of equations (8) and (9) is calculated.

FIG. 2 is a diagram showing the configuration of another embodiment of the device of the present invention. In the figure, computing units 12, 13 and 1
Since the components other than 4 are the same as those shown in FIG. 1, only the calculation procedures of the calculation units 12 to 14, that is, the feed back control procedure will be described here. After a certain period of time has passed since the feed forward control, switch S _b is closed and switch S _f is opened. At this timing, the arithmetic unit 12 inputs the temperature t _p of the strip at the outlet side of the lehr measured by the strip thermometer D _p , the strip speed V measured by the strip speed meter PG, and the input from the setting device 1 (ρ, h, W, t
_pt ), the correction amount ΔQ _b of the amount of heat to be removed while the strip passes through the cooling zone is calculated according to equation (1'). Arithmetic unit 13 receives input ΔQ from arithmetic unit 12
_b and input from cooling pipe inlet air temperature sensor TC T _ia
(atmospheric temperature may be substituted), input T _pa from the cooling pipe outlet air temperature detectors TC1 to TC4, and the computing unit 11 during the most recent feedback control.
Based on the learning coefficient K _ln obtained in , the correction amount ΔF _b of the required air flow rate is calculated according to equation (6'). Based on the input ΔF _b from the calculator 13, the calculator 14 calculates the blower rotational speed correction amount Δ according to equation (7').
N _b is calculated, and this correction amount ΔN _b is calculated as the actual rotation speed N _a
The rotation speed N _b added to the rotation speed N b is set in the blower control devices BC1 to BC4 as a correction set value for the blower rotation speed during the feedback control.

As explained above, according to the present invention, the rotation speed of the air suction blower can be accurately set and corrected at the point where the dimensions and material of the strip are changed in the slow cooling zone of a continuous annealing furnace using the cooling tube method. temperature control can be performed optimally.

Although the above explanation has been made by taking as an example a continuous annealing furnace in a production line for hot-dip galvanized steel sheets, the present invention can be applied to continuous annealing furnaces for other general metal strips, and the present invention can also be applied to continuous annealing furnaces for other general metal strips. The device configuration for carrying out is not limited to the device configuration shown in the examples. For example, in the devices shown in FIGS. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of another embodiment of the apparatus according to the present invention. 1: Setting device, 2 to 14: Arithmetic unit, S _f : Feed forward control switch, S _b : Feed back control switch, D _i , D _p : Strip thermometer, PG: Strip speed meter, TC, T.C.
1, TC2, TC3, TC4: Air temperature sensor, F
_N : Annealing zone of continuous annealing furnace, P _t : Strip, B
1, B2, B3, B4: Blower, BC1, BC
2, BC3, BC4: Blower control device, O ₁ ,
O ₂ , O ₃ , O ₄ : Cooling pipe.

Claims (1)

[Scope of Claims] 1. Temperature control of a metal strip in a slow cooling zone of a continuous annealing furnace having a cooling pipe through which air flows is controlled by changing the rotational speed of an air suction blower to adjust the air flow rate in the cooling pipe. In the method carried out by
Using a calorific value calculation formula that includes the metal strip thickness, width, transfer speed, temperature at the entrance of the metal strip to the lehr-cooling zone, and target temperature at the outlet of the lehr-cooling zone, the metal strip is The amount of heat taken away by the air is predicted and calculated, and the air flow rate calculation formula in the cooling tube that includes the predicted amount of heat and the air temperature at the entrance side of the cooling tube is used to calculate the amount of heat necessary for the temperature at the exit side of the slow cooling zone of the metal strip to reach the target temperature. Calculate the air flow rate in the cooling pipe, calculate the required rotation speed of the blower from the predicted required air flow rate, set this as a set value, and adjust the transfer speed of the metal strip and the temperature of the metal strip during operation at the set blower rotation speed. . A method for controlling the temperature of a metal strip in a continuous annealing furnace slowing zone, characterized in that the temperature of the air is actually measured, and the set value of the blower rotation speed is corrected based on these measured values. 2. The method for correcting the set value of the blower rotation speed uses the transfer speed of the metal strip and the measured value of the temperature at the entrance of the lehr to make the temperature of the strip at the outlet of the lehr to reach the target temperature. The amount of heat that should be taken away by the air while passing through the slow cooling zone is calculated, and the required air flow rate in the cooling tube is calculated using the calculated amount of heat and the actual air temperature values at the inlet and outlet sides of the cooling tube. 2. A method for controlling the temperature of a metal strip in a continuous annealing furnace lehr as claimed in claim 1, wherein the required number of revolutions of a blower is calculated from the flow rate and used as a corrected setting value. 3. The method for correcting the set value of the blower rotation speed is based on the difference between the measured value of the transfer speed of the metal strip, the actual temperature on the exit side of the slow cooling zone of the metal strip, and the target temperature, and the air on the inlet and outlet sides of the cooling pipe. Using the actual measured temperature value, calculate the correction amount of the air flow rate in the cooling pipe necessary for the temperature at the exit side of the slow cooling zone of the metal strip to match the target temperature, and calculate the correction amount of the blower rotation speed from the correction amount of the air flow rate. Temperature control of a metal strip in a continuous annealing furnace lehr as claimed in claim 1, wherein the correction amount of the blower rotation speed is added to the measured value of the blower rotation speed to obtain a corrected setting value. Method. 4. A method for controlling the temperature of a metal strip in a slow cooling zone of a continuous annealing furnace having a cooling pipe through which air circulates by adjusting the air flow rate in the cooling pipe by changing the rotational speed of an air suction blower,
Using a calorific value calculation formula that includes the metal strip thickness, width, transfer speed, temperature at the entrance of the metal strip to the lehr-cooling zone, and target temperature at the outlet of the lehr-cooling zone, the metal strip is The amount of heat taken away by the air is predicted and calculated, and the air flow rate calculation formula in the cooling tube that includes the predicted amount of heat and the air temperature at the entrance side of the cooling tube is used to calculate the amount of heat necessary for the temperature at the exit side of the slow cooling zone of the metal strip to reach the target temperature. Calculate the air flow rate in the cooling pipe, calculate the required rotation speed of the blower from the predicted required air flow rate, set this as a set value, and adjust the transfer speed of the metal strip and the temperature of the metal strip during operation at the set blower rotation speed. , the temperature of the air is actually measured, the set value of the blower rotation speed is corrected based on these measured values, and the temperature of the metal strip is determined by the air while passing through the slow cooling zone using the measured value. Continuous annealing characterized by determining the actual value of heat quantity and dynamically correcting the formula for calculating the air flow rate in the cooling pipe using the actual value of heat quantity, the air temperature on the inlet and outlet sides of the cooling pipe, and the actual measured values of the blower rotation speed. A method for controlling the temperature of metal strips in the furnace slow cooling zone. 5 The method for correcting the set value of the blower rotation speed uses the transfer speed of the metal strip and the actual value of the temperature at the entrance of the lehr to bring the temperature of the strip at the outlet of the lehr to the target temperature. The amount of heat that should be taken away by the air while passing through the slow cooling zone is calculated, and the required air flow rate in the cooling tube is calculated using the calculated amount of heat and the actual air temperature values at the inlet and outlet sides of the cooling tube. 5. A method for controlling the temperature of a metal strip in an annealing zone of a continuous annealing furnace according to claim 4, wherein the required number of revolutions of a blower is calculated from the flow rate and used as a corrected setting value. 6. The method of correcting the set value of the blower rotation speed is based on the difference between the actual value of the transfer speed of the metal strip, the actual measured temperature on the exit side of the slow cooling zone of the metal strip, and the target temperature, and the air temperature on the inlet and outlet sides of the cooling pipe. Using the actual measured value of A method for controlling the temperature of a metal strip in a continuous annealing furnace lehr as set forth in claim 4, which is a method of calculating and adding the correction amount of the blower rotation speed to the measured value of the blower rotation speed to obtain a corrected setting value. .