JPH03193826A - Method for controlling strip temperature in continuous annealing furnace - Google Patents

Abstract

PURPOSE:To execute high accurate control of strip temp. by using dynamic heat transfer model to the strip temp. in a furnace, deciding fuel set value corresponding to line speed and variation of strip condition at the prescribed control cycle and if necessary, resetting the control cycle. CONSTITUTION:The fuel rate supplied into a radiant tube set to heating zone in a continuous annealing furnace, is adjusted so as to become the fuel flow rate set value to control the strip temp. at outlet of the heating zone. In the above strip temp. control method, by using the preset dynamic heat transfer model to the strip temp. in the furnace, the optimum fuel flow rate time series is calculated at the prescribed control cycle. Then, for the variation of the current line speed and strip condition from the current to the prescribed time in further, calculation for causing the strip temp. to follow the target value with the min. deviation is executed. By this method, the above fuel flow rate set value is decided, outputted and this operation is repeated at every control cycle. Further, at the same time when the variation of line speed becomes the prescribed value or more, the above control cycle is reset, and immediately the same process as the above is executed. By this method, always the optimum fuel flow rate is calculated and the fuel flow rate set value is decided to maintain the variation of strip temp. to min.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling a plate temperature in a continuous annealing furnace, which controls the plate temperature by manipulating the flow rate of fuel supplied to a radiant tube.

C. Prior Art] A continuous annealing furnace is a process in which the trailing end of a thin plate coil after cold rolling is welded to the tip of the next coil, and the strip is continuously heated.
This is equipment that performs cooling heat treatment.

In other words, as shown in Figure 3, there are heating zone 2, soaking zone 3, and 1st zone.
It is composed of a secondary cooling zone 4, a secondary cooling zone 5, and a tertiary cooling zone 6, and a heat cycle as shown in FIG. 4 is realized in each zone.

FIG. 5 is a schematic diagram of the heating zone 2.

In the heating zone 2, a plurality of parallel rows of radiant tubes 11 are provided in the furnace, and fuel gas is combusted within the radiant tubes 11 for heating. That is, the strip 13 passing vertically between the rows of radiant tubes 11 while changing direction with the roll 12 is heated by radiant heat. Conventional plate temperature control in the heating zone 2 is performed indirectly by adjusting the fuel flow rate so that the furnace atmosphere temperature (furnace temperature) is at a predetermined value. That is, in FIG. 5, 14 is a furnace temperature detector, 15 is a furnace temperature controller, and 16 is a fuel flow rate controller, which control the furnace temperature control system A, B, etc. for each zone along the longitudinal direction.・－・・・・・・－ is comprised. Although not shown, the fuel flow rate for each zone is controlled by the control valve operation by the fuel flow rate controller 16 for each zone so that the fuel flow rate detected by the fuel flow rate detector becomes a predetermined value. Further, the operator corrects the furnace temperature setting so that the plate temperature detected by the plate temperature detector 22 becomes equal to the target value.

Furthermore, since the time constant of the furnace temperature is 20 minutes or more, a plate temperature control method that directly controls the fuel flow rate instead of the furnace temperature-fuel flow rate cascade control has been proposed in order to improve the responsiveness of the plate temperature.

For example, according to Japanese Patent Application Laid-Open No. 64-28329 filed by our company, a dynamic model of the furnace plate temperature is used to determine the annealing conditions (plate thickness, target plate temperature, line speed, etc.) of the target coil before annealing the target coil. A feedforward control method has been proposed that calculates and sets an optimal fuel flow rate time series that minimizes plate temperature deviation in response to changes in target values, etc.).

[Problem to be solved by the invention]

In conventional equipment, the process computer automatically calculates the line speed target value in order to obtain the maximum production volume, and since the line speed has not yet reached a settable operating level, the line speed is set by the operator. Also steel plate (strip)
Operators often manually slow down the speed to ensure welding time due to meandering or welding problems with the welding machine on the entry side.

Therefore, it is difficult to realize the feedforward control method in which the above-mentioned optimum fuel flow rate is calculated and set based on the line speed target value and its change timing as prerequisites before annealing the target coil. In other words, in order to perform practical plate temperature control at a conventional operating level, a control method is required that assumes that the line speed is manually set.

[Means to solve the problem]

The present invention takes the following measures to solve the above problems.

That is, as a method for controlling the plate temperature of a continuous annealing furnace, the plate temperature at the outlet of the heating zone is controlled by controlling the fuel flow rate supplied to the radiant tube arranged in the heating zone of the continuous annealing furnace so as to reach the fuel flow rate set value. , the current line speed and plate conditions (plate thickness, plate width, plate temperature target value) from now to a predetermined time in the future are calculated at a predetermined control cycle using a dynamic heat transfer model of plate temperature in the furnace created in advance. Determine the optimal fuel flow time series that allows the plate temperature to follow changes with the minimum deviation from the target value, determine the above fuel flow setting value, and
As soon as the change in line speed exceeds a predetermined value, the control cycle is reset and the same steps as described above are immediately performed.

[Effect]

When the change in line speed does not exceed a predetermined value by the above means, a dynamic heat transfer model of the furnace plate temperature created in advance is used to calculate the current line speed and the change from the present to a predetermined time in the future in a predetermined control cycle. The optimal fuel flow time series that allows the plate temperature to follow changes in plate conditions (plate thickness, plate width, plate temperature target value) with the minimum deviation from the target value is calculated, the fuel flow rate set value is determined, and the same The fuel flow rate is manipulated to reach the fuel flow set point. Further, the control cycle is reset as soon as the change in line speed exceeds a predetermined value,
Steps similar to those described above are immediately carried out.

In this way, even if the line speed is manually reduced, the optimal fuel flow rate is immediately calculated and the fuel flow rate set value is determined, so plate temperature fluctuations are kept small.

〔Example〕

An embodiment of the method of the present invention will be described with reference to FIGS. 1 and 2.

Note that the parts explained in the conventional example are given the same numbers and the explanation thereof is omitted, and the explanation will mainly be given to the parts related to the present invention.

In FIG. 1, a line speed detector 17 and an inlet plate temperature detector 21 are provided at the inlet of the heating zone 2. The output of the line speed detector 17 is sent to the first arithmetic unit 18. 1st
The output of the computing unit 18 is connected to the fuel flow rate controller 16 of each zone via a second computing unit 19 and a distributor 20. In addition, the model parameter estimator 23 includes an inlet plate temperature detector 21,
It inputs signals from the outlet plate temperature detector 22, line speed detector 17, etc., and sends its own output to the second computing unit 19.

In the above configuration, the arithmetic unit 18 uses the line speed detection value obtained by the line speed detector 17 to detect a manual line speed "change". For example, the method is as follows.

(a) Line speed is detected at a constant detection cycle.

(b) If the time rate of change of the line speed exceeds a predetermined value and satisfies equation (1), the optimum fuel flow rate time series calculation, which will be described later, is immediately started. Otherwise, return to (a).

V(t)−V(t−1)≧E−−−−−−・−m−−
--・(1) Δt where ν(t) second line speed detection value (current value) V(
t-1) Ni line speed detection value (previous value) Δt
: Detection period ε : Constant The second calculator 19 performs an optimum fuel flow rate time series calculation, which will be described later, at a constant control period, and outputs a fuel flow rate set value. The zone distributor 20 also distributes the output value to each zone at a predetermined ratio, and outputs it to the fuel flow rate controller 16 as a fuel flow rate set value for each zone. Note that as mentioned above, the first computing unit 1
8, if a change in line speed is detected, the control cycle is reset, the optimum fuel flow rate time series calculation is immediately performed, and the fuel flow rate setting value is output. Thereafter, the above process is repeated at a constant control cycle.

The optimum fuel flow rate time series calculation is to find a fuel flow rate time series that minimizes the plate temperature deviation due to the current line speed detection value and future changes in plate conditions.

Expressing it mathematically, for example, the number of evaluations J in equation (2) is
The goal is to find the fuel flow rate G, (t) (0≦t≦T) that is minimized under the constraints of equations (3) and (4).

However, G r (t) is a step function for each control period.

Ts(t)≧Tss(t)−ΔTSL(0≦t≦T)
-43) 1F≦CF (t)≦OF (0≦t
≦T) ---Isshin・-(4) Here, Ts(t)
: Plate temperature (0≦t≦T) Tss (t): Plate temperature target value (0≦t≦T) T: Target calculation interval (current time is 1-0) Gy (t): Fuel flow rate (O ≦t≦T)lF:
Lower limit value UF : Upper limit value ΔTSL : Plate temperature allowable deviation (low temperature side) The constraint condition of formula (3) is introduced because the allowable deviation of the heat cycle is usually larger on the high temperature side than on the low temperature side. Board conditions (
Future temporal changes in plate thickness, plate width, plate temperature target values) are known by line speed detection values and by tracking welding points using a welding point detector and a pulse generator attached to the roll (not shown). It can be calculated using this technique.

In addition, the solution method for optimal calculation is mathematical programming methods (maximum principle, dynamic programming, multiplier method, etc.) introduced in various conventional literature.
You can use either one.

For optimal calculations, a dynamic characteristic equation that expresses the relationship between the dynamic behavior of fuel flow rate, line speed, plate thickness, plate width, and plate temperature is required. For example, JP-A-64 filed by our company, etc.
-184233 proposes the following physical model.

(Tsx+273)') A,・φ・σ −・・・・ (5) Here, T: T's, l: ΔH: A,: L: d: ■: GF: C3: Ts: KF: Furnace Average plate temperature Strip enthalpy increase Strip heat transfer area (=WXLX2) Strip length W: Plate width Plate thickness Line speed Fuel flow rate Strip Specific heat strip Specific weight Stefan Boltzmann constant Constant C1φ: Use parameter formulas (5) and (6) For example, every control cycle or when the line speed changes, estimate T, , T, at that point + Ii (this is calculated in the previous control cycle).
is the initial value, and the current line speed V (becomes a constant).

), future board conditions (d(t), W(t) and Tss(
t) is given as a function of time by weld point tracking. ), the plate temperature behavior T s (t) can be calculated. Therefore, Gy(t) that minimizes the evaluation function of equation (2) is determined by optimal calculation and Gy(1) is output.

(Gy(1) is the fuel flow rate calculation value for one control period from the current point in Gy(t), which is a step function.) Figure 2 shows the plate temperature when the line speed is "low" according to this embodiment. This is an example of control. Even when the next coil with a thicker plate is passed several minutes later, the plate temperature does not fall below the lower limit, allowing operation with small plate temperature fluctuations.

Note that the model parameter estimator 23 is configured to improve model accuracy against modeling errors and process characteristic fluctuations.
Parameters are corrected using plate temperature detection values from the inlet plate temperature detector 21 and outlet plate temperature detector 22, and actual values of line speed, plate thickness, plate width, furnace temperature, and fuel flow rate.

For example, the parameter correction method is described in the above-mentioned Japanese Patent Application Laid-Open No. 64-184.
As proposed in 233, formulas (5) and (6) are used to minimize the error between the model calculation value and the actual value for a certain period of time.
) is corrected.

〔Effect of the invention〕

As explained above, according to the present invention, highly accurate plate temperature control can be performed by optimally controlling the fuel flow rate in response to changes in line speed and plate conditions (plate thickness, plate width, target plate temperature). Moreover, it is extremely practical because it can achieve highly accurate plate temperature control at operating levels where the line speed must be manually set.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a continuous annealing furnace heating zone and plate temperature control device B according to an embodiment of the present invention, Fig. 2 is a diagram showing an example of plate temperature control of the same embodiment, and Fig. 3 is a diagram showing a conventional continuous annealing furnace heating zone and plate temperature control device B. FIG. 4 is a diagram showing the overall configuration of the annealing furnace, FIG. 4 is a heat cycle diagram for heat treatment in the conventional continuous annealing furnace, and FIG. 5 is a configuration diagram of the conventional continuous annealing furnace heating zone and plate temperature control device. 2... Heating zone, 12... Radiant tube, 13... Strip, 16... Fuel flow rate controller, 17... Line speed detector, 18, 19... Actuator, 20... ...Zone distributor. Figure 1

Claims (1)

[Claims] In the method of controlling the plate temperature at the outlet of the heating zone by manipulating the fuel flow rate supplied to the radiant tube arranged in the heating zone of a continuous annealing furnace to the fuel flow rate set value, the dynamic Using a heat transfer model, the plate temperature is determined to be the minimum value compared to the target value based on the current line speed and changes in plate conditions (plate thickness, plate width, plate temperature target value) from the present to a predetermined time in the future at a predetermined control cycle using a heat transfer model. The optimum fuel flow rate time series to be followed when the limit is exceeded is calculated, the fuel flow rate set value is determined, and the control cycle is reset as soon as the change in line speed exceeds a predetermined value, and the same process as above is immediately performed. A method for controlling plate temperature in a continuous annealing furnace, characterized in that the method is carried out.