JPS5830376B2 - Control method of continuous annealing furnace - Google Patents

Description

Detailed Description of the Invention The present invention provides a continuous annealing furnace in which a plurality of furnaces such as a heating furnace, a soaking furnace, a cooling furnace, and a reheating furnace are arranged continuously along the running direction of the strip. The present invention relates to a method of controlling a continuous annealing furnace when connecting coils of different strips and performing annealing treatment continuously.

In general, when the thickness change point of a strip of different thickness passes through multiple furnaces arranged in series along the running direction of the strip, if the furnace temperature and line speed are constant, the strip changes from thin to thick. When changing from a thick strip to a thin strip, the temperature of the strip decreases, and conversely, when changing from a thick strip to a thin strip, the sensitivity of the strip increases.

In a continuous annealing furnace, the strip temperature at the outlet of each furnace is to ensure uniform material quality, so the conventional control method in a continuous annealing furnace is to detect the material temperature with a thermometer installed at the furnace outlet and change the strip thickness. A control method is used to maintain the strip temperature constant by performing feedback control to cancel out the temperature changes that occur in the strip.

However, heating and cooling furnaces generally have a large furnace time constant, and the furnace temperature change rate is about 10°C/ytyx, so they do not have sufficient immediate response to changes in plate thickness.For this reason, conventional feedback control does not allow for changes in plate thickness. The response of the furnace temperature change to counteract the temperature change during the process was slow, temperature abnormalities often occurred, and there were drawbacks such as insufficient control when changing the plate thickness.

As a control technology to replace such feedback control, Japanese Patent Application No. 10450/1989 proposed by the same applicant
7.104508.104510.104512, etc., and there are no other technologies that can replace conventional feedback control.

The present invention was created as a development and improvement of the technology proposed as a control method for continuous annealing furnaces in place of the above-mentioned feedback control. In a continuous annealing furnace in which heating furnaces and the like are arranged in series, when the connection point of strips of different thickness unwound from the coil, that is, the point where the thickness changes, passes through the furnace,
It is an object of the present invention to provide a control method for a continuous annealing furnace that keeps the strip temperature at the furnace outlet within a predetermined allowable temperature range relative to the target temperature and ensures uniform material quality.

The form of the furnaces arranged in series along the line to be controlled by the present invention includes cases where the appearance is one furnace with a plurality of furnace temperature control zones, such as heating zones, equalization, etc. A furnace equipped with each group such as a tropical zone, a cooling zone, a reheating zone, and an overaging zone can also be controlled by the present invention as a continuous annealing furnace.

The control method of the present invention will be explained in detail below using the drawings.

The objects to be controlled in the present invention are roughly divided into two: line speed and furnace temperature.

In other words, there are two methods: a method in which the furnace temperature is operated as a reference and the line speed is primarily controlled based on this;
This is a method that mainly controls the furnace temperature based on this.

All of these controls are divided into the following three control processes.

AI 5TAGE: Preparation process to reach the plate thickness change point (hereinafter referred to as the preparation stage) A25TAGE: Control process while the plate thickness change point is passing through the continuous annealing furnace (hereinafter referred to as the plate thickness change side control stage) A3 STGE: Process of returning to steady plate thickness after the plate thickness change point passes through the continuous annealing furnace (hereinafter referred to as return stage) First, the case where the line speed is mainly controlled will be explained.

/%, I 5TAGE (preparation stage): There are the following four cases when adjusting the furnace temperature and line speed before the plate thickness change point enters the continuous furnace.

(1) If the line speed to be adjusted exceeds the upper limit speed,
The maximum line speed of a continuous furnace is limited by the specifications of the drive motor and the like.

Therefore, when changing the line speed when changing the plate thickness, if there is a possibility that the line speed after changing the plate thickness will exceed the maximum line speed, reduce the line speed in advance before reaching the point where the plate thickness changes. Prepare to ensure that the line speed after changing the plate thickness does not exceed the maximum speed.

Of course, the furnace temperature is also adjusted in response to the deceleration of the line speed.

(Gauze) If the temperature change when changing the plate thickness is large, or if the rate of change in plate thickness given by the ratio of the plate thickness before and after the change is large, the temperature change in the strip will be large near the point where the plate thickness is changed.

Therefore, by lowering the furnace temperature and line speed to bring the strip temperature and furnace temperature closer together, it is possible to reduce the temperature difference at the plate thickness change point.

This physical explanation is made clear by the graph shown in FIG.

As is clear from the figure, various combinations of lie/speed and furnace temperature can be selected to ensure the same exit loss strip temperature, and the amount of temperature change when changing plate thickness is rate, target strip temperature, furnace temperature, and line speed.

Figure 1a shows the case where the plate thickness was changed from 1.0MM to Q, 9 ptytt, the furnace temperature was 850℃, and the line speed was 103℃.
The temperature change in the trip temperature is 40°C, which has a range of ±20°C with respect to the target strip temperature of 700°C.

Figure 1 shows the case where the same plate thickness was changed, the furnace temperature was 800QC, and the line speed was 77mpm, and the change in the temperature of the strip lost at this time was 28℃, and the target strip temperature was 7.
It has a width of ±14°C with respect to 00°C.

From this result, it can be seen that the temperature difference at the plate thickness change point is smaller when the line speed and furnace temperature are lowered.

At this time, since the annealing capacity is lowered by lowering the line speed, the lowering of the line speed should be kept to the minimum necessary level depending on the allowable limit of the strip temperature or the plate thickness change rate.

(3) In the case of heat load limit When the strip is wide or thick, the maximum gas flow rate is limited by the equipment, and the furnace atmosphere is affected before and after changing the plate thickness due to the capacity limit of the furnace main body. Even when constant control is performed, the furnace temperature may change.

For example, when the plate thickness changes from thin to thick, if the furnace temperature is saturated at the maximum gas flow rate, the furnace temperature will drop due to the change in plate thickness.

The idea here is to calculate the load after changing the plate thickness before changing the plate thickness, calculate the line speed after changing the plate thickness so that the load does not exceed the furnace capacity, and then calculate the line speed calculated after changing the plate thickness. The line speed and furnace temperature shall be adjusted before changing the plate thickness.

(4) When furnace temperature is restricted In a heating furnace, the maximum furnace temperature is restricted to protect the radiant tube, etc.

Therefore. If the line speed after changing the plate thickness exceeds the maximum line speed determined by the plate thickness after changing the plate thickness, the target strip temperature, and the maximum allowable furnace temperature, the line speed is reduced in advance. .

Additionally, in the preparation stage, fine adjustments are made to the furnace temperature.

This fine adjustment of the furnace temperature will be explained in detail in the explanation of Sakazuki 2 STAGE below, but since the temperature deviation that occurs when changing the plate thickness is proportioned equally to the target temperature, the furnace temperature can be adjusted before the plate thickness change point arrives. This is to finely adjust the temperature.

A25TAGE (plate thickness change control stage): Control in the plate thickness change control stage is performed based on the following basic principle.

In other words, the furnace temperature is kept constant, and the plate thickness before changing the plate thickness is hl,
The plate thickness after changing the plate thickness is h2, and the line speed before changing the plate thickness is V.
When the line speed after changing the plate thickness is V2, we obtain (d)=(±)−=r (1)1h2, and the line speed is controlled so that the first condition holds true after changing the plate thickness.

When many furnaces are arranged in series, the time constant for changing the furnace temperature is extremely slow, and it is impossible to cancel out the temperature change at the point where the plate thickness is changed. The occurrence of temperature changes is inevitable.

Therefore, the temperature change caused by changing the plate thickness and the change in line speed in this case are shown in FIGS. 2 and 3.

In Fig. 2, time t1 when the plate thickness change point reaches the entrance of the first furnace arranged in series, that is, the A1 heating furnace.
Then, the line speed is set as V=γVl (3) at the time when the plate passes through the final furnace where the plate thickness changing points are arranged in series, that is, the third heating furnace.

Figure 2C shows the loss strip temperature of coal 1 heating furnace when the line speed is changed according to the plate thickness change rate γ, &3
The temperature of the loss strip leaving the heating furnace is shown in FIG. 2d.

As is clear from this figure, the temperature deviation before and after changing the plate thickness is equally distributed between positive and negative with respect to the target temperature 'I'so, and the temperature tolerance range shown by the broken line can be most effectively utilized.

FIG. 3 is a graph showing a characteristic diagram showing the control method of the present invention obtained by changing the line speed.

The change in line speed in this case is as shown in Figure 3.
The speed change is started at time t1 when the plate thickness change point reaches the 1st heating furnace population, and the final furnace where the plate thickness change points are arranged in series,
That is, the line speed is changed to the line speed according to equation (3) above so that the speed change ends exactly at the exit of the black 3 heating furnace.

In this case, the rate of speed change at the time when the plate thickness change point passes varies depending on the position of the furnaces arranged in series.

For example, in the No.1 heating furnace, the plate thickness change point reaches the furnace outlet before the speed is changed, but in the A3 heating furnace, which is the final furnace, the plate thickness change point arrives after the speed change has almost finished. will be reached.

FIG. 3C shows the temperature of the loss strip of fish 1 leaving the heating furnace when the line speed is changed as described above, and FIG. 3d shows the temperature of the loss strip of fish 3 leaving the heating furnace.

In this case, the strip temperature, as shown by the shaded area, exceeds the temperature tolerance range shown by the broken line, and the control of the present invention cannot be achieved satisfactorily.

Therefore, as shown in FIG. 4a, from before the time t1 when fish 1 reaches the heating furnace at the plate thickness change point, the time t when fish 3 leaves the heating furnace at the plate thickness change point.

From then on, by finely adjusting the furnace temperature by △TF in advance, the change in line speed shown in Figure 4
As shown in FIG. 4C, the A1 heating furnace loss strip temperature is the target strip temperature Ts.

It is possible to give a substantially equal distribution of temperature change to the positive and negative sides, and to keep the temperature change due to this distribution within the temperature tolerance range.

In this way, the control performed in the plate thickness change control stage (2nd STAGE) changes the line speed to γ (h
1/h2) and change the speed in two steps to the ratio of The speed change starts when the plate thickness change point reaches the furnace with the most paddy, and the speed is changed at a predetermined slope until it leaves the final furnace, and the temperature deviation exceeds the temperature tolerance due to the plate thickness variation rate γ. In this case, the furnace temperature is finely adjusted in advance, and the temperature deviation is distributed evenly between the positive and negative sides of the target temperature to keep it within the temperature tolerance range.

Fish 35TAGE (return stage): There are two cases of processing after the plate thickness change point passes through the final furnace.

(1) When the line speed is lowered in the speed correction preparation stage (AI STAGE), the line speed is accelerated until it reaches the maximum load of the reactor capacity.

At this time, the furnace temperature is adjusted as the line speed is changed, and the strip temperature is controlled to always stay within the allowable temperature range even when the line speed is being accelerated. After speed correction, the strip temperature is maintained at the target temperature. create a state.

(2) When the furnace temperature is finely adjusted in response to the speed change in the furnace temperature correction preparation stage (AI 5TAGE), the strip temperature after changing the plate thickness has an offset from the target value by the furnace temperature fine adjustment valve.

Therefore, the furnace temperature is changed using a fine adjustment valve to remove the offset, and the IJ tube temperature is controlled to the target temperature after passing the plate thickness change point.

FIG. 5 shows a flowchart of a method for controlling a continuous annealing furnace as described above, in which the line speed is mainly controlled.

The symbols used in the flowchart of FIG. 5 represent the following contents.

[Fish 1 ST'AGE] γ: Plate thickness change rate h1: Plate thickness after plate thickness change h2: Plate thickness after plate thickness change △T: Allowable temperature deviation limit LOADMAX: Furnace maximum capacity VMAX' Maximum line speed L7MAX: Maximum furnace temperature Ll: Line speed due to temperature deviation limit when changing plate thickness First, as a preparatory stage (AISTGE)
At 0, it is determined whether or not there is a change in plate thickness.

If there is a change in plate thickness, the plate thickness change rate γ is determined in step 12.

Then, at 14, line speed LH, L2 s L3 z L
4, find the minimum value of these in step 16, and calculate this as the line speed after changing the plate thickness.

shall be. At step 18, calculate the line speed after changing the plate thickness.

Find the line speed before changing the plate thickness to achieve this.

At step 20, the current line speed L7NOW is compared with L to determine whether the line speed should be reduced.

If deceleration is necessary, the line speed is decelerated to L while adjusting the furnace temperature, and at the same time control is performed to maintain the strip temperature at the target value.

If there is no need for deceleration control in 22 or deceleration, proceed to 24, and if fine adjustment of the furnace temperature is necessary by changing the speed when changing the plate thickness based on the plate thickness fluctuation rate γ, perform the furnace temperature adjustment. .

After the above processing steps, the preparation stage is completed, and the thickness change point control stage (where the thickness change point passes through the continuous annealing furnace)
& 2 STAGE).

In the plate thickness change point control stage indicated by 26, while the plate thickness change points pass through the volumes arranged in series, the line speed increases from the line speed before the plate thickness change to the line speed after the plate thickness change.

By changing the speed to , the temperature deviation of the strip that occurs when passing through the plate thickness change point is equally divided into positive and negative parts with respect to the target temperature, and control is carried out to keep the temperature within the permissible range.

In this line speed control, if the furnace temperature has been finely adjusted in the preparation stage 24, the line speed is changed as shown in FIG. The line speed is controlled as shown in FIG. 2a.

When the plate thickness change point passes through the final furnace, the process proceeds to the next return stage (35TAGE).

In the return stage, if the furnace temperature has been adjusted in 24 of the preparation stage, the furnace temperature is adjusted to return to the original value in 28.

Next, the line speed after changing the plate thickness at 30! L'1)
L 23 L 3 is determined, the minimum value of these is taken at 32, and this is set as the line speed L' after changing the plate thickness.

In step 34, this line speed L' is compared with the line speed LLo after changing the plate thickness obtained in step 16 of the preparation stage. At the same time, control to adjust the furnace temperature is carried out at step 36, the return stage is completed, and the continuous annealing furnace enters steady processing control after changing the plate thickness.The flowchart shown in Fig. 5 is related to heating control. However, cooling control can also be realized through a similar process, mainly changing the line speed.

Next, a method of controlling the thickness of the plate according to the present invention mainly by changing the furnace temperature will be explained.

Although the following description describes heating control, the same applies to cooling control, except that in the case of cooling control, the temperature pattern of the strip due to heating control is reversed.

In addition, when changing the furnace temperature mainly in response to changes in plate thickness,
Control is different between (thick material→thin material) and (thin material→thick material).

Even when changing the main stapling and furnace temperature,
5TAGE: Classified into three recovery stages.

(Preparation stage): As a preparatory action to adjust the furnace temperature and line speed before the plate thickness change point enters the continuous annealing furnace, if the plate thickness change rate is large and the temperature change is large, the furnace temperature Then, reduce the line speed, bring the strip temperature and furnace temperature closer together, and reduce the temperature difference at the point where the plate thickness changes.

This change in furnace temperature and line speed is carried out through the following process.

That is, the following four items are calculated.

(1) Line speed L1 to keep temperature fluctuations that occur when changing plate thickness within the temperature tolerance range, and this line speed L1
Furnace temperature T to obtain the target temperature of the strip at
Find 1.

('4 Maximum line speed L2 due to heat load limitation of the furnace,
The furnace temperature T2 for obtaining the target temperature of the strip at this maximum line speed L2 is determined.

(3) Limit line speed #L determined by the motor power installed in the continuous annealing furnace, and this limit line speed L3
The furnace temperature T4 is determined to obtain the target temperature of the strip.

(4) Furnace temperature limit T4, which is the maximum furnace temperature that is allowable due to the structure of the furnace, determined by the heat-resistant temperature limit of the radiant tube, etc.
seek.

Furnace temperature T1. thus obtained. T2. T3. T.

The minimum value T.

Find the minimum value T of the current furnace temperature in the preparation stage.

If you increase the temperature, increase the furnace temperature to T.

This minimum value T. Change the line speed accordingly.

Even if the furnace temperature and line speed are changed in advance in the preparation stage in this way, if the furnace temperature is not controlled while the plate thickness change point is passing through the furnace, the temperature will exceed the allowable temperature range before and after the plate thickness change point. This will cause deviation.

For example, when a strip transitions from a thick material to a thin material, the strip temperature increases after the thickness change point.

This state is shown in FIG. That is, if the furnace temperature is only changed at the time t when the plate thickness change point leaves the final furnace as shown in Figure 6, the loss strip temperature of the fish 1 leaving the heating furnace will decrease as shown in Figure 6d. , a temperature deviation △TM occurs between the plate thickness change point 1 reaching the heating furnace exit time t1 and reaching the final furnace /Ex 3 DO heating furnace exit time t, and the temperature exceeds the allowable temperature range shown by the shaded area. Put it away.

Therefore, in order to eliminate this temperature deviation, the furnace temperature is lowered at or before the plate thickness change point reaches the black 1 heating furnace entrance.

The amount of change in the furnace temperature is set to a value sufficient and necessary to keep the temperature deviation that occurs at the time of changing the plate thickness within the allowable temperature range of the strip.

The amount of change in furnace temperature is given by the following equation.

Even if you change the furnace temperature by △TFI given by equation (4), there is no problem if the strip temperature is within the maximum allowable furnace temperature, but if it exceeds the maximum allowable furnace temperature, the furnace temperature must be changed. I can't.

In this case, the line speed is changed.

The amount of speed change in this case is given by the following equation.

In this way, the furnace temperature and line speed are changed before the plate thickness change point reaches the furnace, and while the plate thickness change point is passing through the continuous annealing furnace, the temperature fluctuation can be kept within the temperature tolerance range for the strip target temperature. I can do it.

Note that equations (4) and (5) above can be used in both cases of plate thickness change (thin material - thick material) or (thick material - thin material), and in the case of (thin material → thick material), the furnace Warmth (△TF1
)a, the line speed should be changed to (△V lower), and in the case of (thick material → thin material), the furnace temperature should be changed to (ΔTF
I' will be changed to a lower value and the line speed will be changed to a higher value (△V).

Also, in the case of the 4-fold process, the above-mentioned (4) t (5
) can be used, in which case the furnace temperature and line speed changes are exactly the opposite of the heating process described above.

2. 5TAGE (Plate Thickness Change Control Stage) When mainly changing the furnace temperature, control conditions for passing the plate thickness change point have already been given in the preparation stage, so no control is performed.

Fish 3 5TAGE (return stage) When the plate thickness change points have passed through each station arranged in series, the furnace temperature is changed based on the furnace temperature change amount △TF2I/c given by.

Figure 7 shows the furnace temperature change in the case of (thick material → thin material) in the fish 1 heating furnace. Adjust the furnace temperature with △T
Change the furnace temperature to lower it by F2.

At this time, the line speed is constant as shown in Fig. 7C, and the &1 heating furnace exit loss strip temperature shown in Fig. 7D is a temperature that falls within the temperature tolerance range that is equal in positive and negative directions with respect to the target temperature T'so. considered a deviation.

For each station of Fish 2 and Shi 3, the furnace temperature is similarly changed by ΔTF2 every time the board thickness change point passes.

In addition, in the preparation stage, the furnace temperature cannot be changed by △TF□ given by the above equation (4) due to the limit of the allowable maximum furnace temperature TMAX, and the line speed is changed by △V according to the above equation (5). (6) above.
The furnace temperature of ΔTF2 given by the formula is not changed.

Next, the plate thickness change point becomes the final furnace &3 When the sheet exits the heating furnace, the following three items are calculated.

(1) Find the maximum line speed L'2 due to furnace heat load limitation and the furnace temperature τ2 to obtain the target temperature of the strip at this maximum line speed L'2.

(2) Find the limit line speed L'3 and the furnace temperature T/3 to obtain the target temperature of the strip at this L/.

(3) Furnace temperature limit T which is the maximum furnace temperature allowable due to the furnace structure
Find /.

Find the minimum value T'o of these furnace temperatures T/, , T/, , T/, and calculate the current furnace temperature T after passing the plate thickness change point.
If 'MOW is equal to or less than the minimum value T'o, then the furnace temperature is set to the minimum value T.

Change the line speed to the minimum value T.

Change the speed to take the strip target temperature at .

With the above, the control of the continuous annealing furnace for passing through the plate thickness change point is completed, and the steady annealing process is performed on the strip after the plate thickness change.

8 and 9 are flowcharts mainly showing the control method of the present invention for changing the furnace temperature.

The symbols shown in FIGS. 8 and 9 represent the following contents.

[Fish I 5TAGE] Ll: Line speed L2 due to temperature deviation limit when changing plate thickness: Maximum line speed due to heat load limit of heating furnace, line speed limit T1 Furnace temperature T2 to obtain target strip temperature at line speed L1 Furnace temperature T to obtain the target strip temperature when the second line speed is L2, Furnace temperature T4 to obtain the target strip temperature when the second line speed is 13: Furnace temperature limit TNOW: Current furnace temperature △T'p'it△TF2: Furnace temperature Change amount △V Ni line speed change amount (A3 5TAGE) L'2 Maximum line speed due to heat load limit of near JO furnace [,/, Ni line speed limit T'2 Ni line speed L/, To obtain the target strip temperature when Furnace temperature T3 Niline speed T/, furnace temperature for obtaining the target strip temperature, and processing details of the block codes used are the same as in the case of FIG.

In FIG. 8, it is determined at 50 whether there is a change in the plate thickness, and if there is a change in the plate thickness, the plate thickness change rate γ is determined at 52, and the line speed L is determined at 54 using this plate thickness change rate γ as a calculation parameter.
1*L2 s L3 and T15T2. T5. T4 is required.

For these furnace temperatures, a minimum value is taken at 56, which is T.

It is said that

Next, in step 58, a comparison is made with the current furnace temperature TNOW, and the current furnace temperature TNOW is set to the minimum value T.

If it is equal to or less than that, go to the next process.If it is thick, set it to 60 and set the furnace temperature to the minimum value T.

At the same time, take the strip target temperature at To and change it to the line speed obtained at 54. Next, at 62, calculate the above equation (4) to find △TF1, and at 64, set the furnace temperature as △TFI. It is determined whether the change exceeds the furnace temperature limit TMAX, and if the change exceeds the furnace temperature limit TMAX, △■ of the above formula (5) is determined at 66.
The line speed is changed in step 68 to find the value, and if the line speed is not exceeded, the furnace temperature is changed in step 68 by ΔTFI.

The above process completes the preparation stage (/Fix I
S TAGE ) ends.

No control is performed at 70, which is the plate thickness changing stage (A, 2 STAGE).

Next, the return stage (Fish 3 STAGE) shown in Figure 9
to go into.

In FIG. 9, first, at 72, it is determined whether or not the line speed has been changed at 68 shown in FIG.

If not, it is determined in step 74 whether or not the plate thickness change point has passed through the applicable furnace, and at the time of passing, △TF of the above equation (6) is determined.
2 is determined at 76, and the furnace temperature is changed by ΔTF2 at 78.

At this time, if the furnace temperature exceeds the furnace temperature limit by changing the furnace temperature to ΔTF2, the furnace temperature is changed to TMAX.

At 80, it is determined whether the plate thickness change point has passed through all stations.

72 to 80 if it is determined that the line speed has changed at 72
processing is not performed.

When the plate thickness change point leaves the final furnace, the line speed after plate thickness change L'2. L'3 and furnace @T',.

T;, T', are determined, and the minimum value of these furnace temperatures is taken at 84 and is designated as T'o.

Next, T'o and the current furnace temperature T' are compared and determined, and if the current furnace OV @T/NOw is equal to or smaller than the minimum value T'o, the furnace temperature is changed to T'o at 88, At this T'o, the target temperature of the strip is taken and the line speed determined in step 82 is changed, and the current furnace temperature T'NOV is the minimum value T'.

If it is thicker, control is terminated.

As explained above, the method for controlling a continuous annealing furnace of the present invention is such that when the thickness change point of the strip passes through a plurality of rods arranged in series, the line speed and furnace temperature are controlled by a predetermined control process. By equally distributing the temperature change that occurs in the target strip temperature in positive and negative directions, it is possible to keep the humidity deviation within the specified strip temperature tolerance range, and even before and after the point where the plate thickness changes, the steady annealing process It was possible to obtain an annealed product of the same quality as that obtained, improve the operating efficiency and equipment capacity of the continuous annealing furnace, and reduce the cost of the product.

In addition, when the control method of the present invention is actually carried out in a continuous annealing furnace, the control is fully automated by computer control that executes the control process of the present invention.

[Brief explanation of the drawing]

Figure 1 is a graph showing the difference in strip temperature variation when the plate thickness change point passes through the furnace with respect to line speed and furnace temperature, and Figure 2 shows changes mainly in line speed. Figure 3 is a graph showing the change in strip temperature at the furnace outlet when the line speed is changed stepwise in the control method of the present invention. Figure 4 is a graph showing the change in the furnace exit loss strip temperature when changing the time gradient, and Figure 4 shows the graph when the furnace temperature is finely adjusted to eliminate the temperature deviation exceeding the temperature tolerance that occurred in Figure 3. A graph showing changes in furnace temperature, line speed, and furnace exit loss strip temperature. Figure 5 is a flowchart showing the processing process by the control method of the present invention that mainly changes line speed. Figure 6 is a graph showing changes in furnace temperature, line speed, and furnace exit loss strip temperature. FIG. 7 is a graph showing a control in which a temperature deviation exceeding the temperature tolerance range occurred due to a temperature change, and FIG. The graphs showing the changes in FIGS. 8 and 9 are flowcharts mainly showing the process of the control method of the present invention when changing the furnace temperature. T...Strip target temperature, TSI...Gan 1 furnace outlet O strip concentration, TS3...Fish 3 furnace exit loss strip temperature, tl...Plate thickness change point 1 furnace inlet arrival time, t2.
・・Plate thickness change point 1 Furnace exit arrival time, t ・・Plate thickness change point 3 Furnace exit arrival time, △TF ・・・Fine adjustment furnace temperature, △
TM...Amount of strip temperature change when changing plate thickness, △TF2
)△TF2... Furnace temperature change amount, ■... Line speed.

Claims (1)

[Claims] 1. A continuous annealing furnace having a plurality of furnaces or furnace zones arranged in series along the running direction of the strip (strips of different thicknesses)
In a method of controlling a continuous annealing furnace that performs annealing treatment when passing a plate thickness change point where an IJ tube is welded, the control process is a preparation stage for reaching a plate thickness change point,
The process is divided into a thickness change control stage during which the plate thickness change point is passing through the furnace, and a return stage after the plate thickness change point has passed through the furnace. The line speed and/or furnace temperature are changed so that the temperature fluctuations that occur when passing through the strip are distributed equally between the positive and negative values with respect to the strip target temperature, and the line speed and/or furnace temperature are kept within a predetermined temperature tolerance range. The line speed is controlled in accordance with the changed line speed and/or furnace temperature, and in the return stage, the line speed is changed to a value corresponding to the strip after the thickness change, and the furnace maintains the strip target temperature at the changed line speed. A method for controlling a continuous annealing furnace, characterized by changing the temperature to a continuous annealing furnace. 2. In the preparation stage, the line speed is determined by the temperature deviation, which is a predetermined temperature target range for the target temperature when changing the plate thickness, the maximum line speed is determined by the furnace heat load limit, and the maximum line speed and furnace temperature limit determined by the characteristics of the drive motor, etc. Find the minimum value of the maximum line speeds, divide the minimum line speed by the plate thickness variation rate to find the predicted line speed, and if the predicted line speed is less than the current line speed, change the plate thickness. changing the line speed to the predicted line speed at or before the point reaches the furnace inlet, and changing the furnace temperature to a strip target temperature at the changed line speed;
If the predicted line speed exceeds the current line speed, finely adjust the furnace temperature according to the plate thickness change rate; maintain the line speed and furnace temperature changed in the preparation stage in the plate thickness change control stage; In the return stage, the minimum value of the maximum line speed due to the furnace heat load limit, the maximum line speed determined by the characteristics of the drive motor, etc., and the maximum line speed due to the furnace temperature limit is obtained for the strip after the thickness change, and the current line speed is determined. is less than the minimum value, the line speed is changed to the minimum value when the plate thickness change point passes through the furnace, and the furnace temperature is changed to a target temperature of the strip at the changed line speed. A method for controlling a continuous annealing furnace according to claim 1. 3 In the preparation stage, based on the plate thickness change rate, the line speed is determined to ensure that the temperature fluctuations that occur when the plate thickness change point passes through the furnace are equally distributed between the positive and negative parts of the strip target temperature and within a predetermined temperature tolerance range. If the plate thickness change rate exceeds a predetermined value, fine adjustment of the furnace temperature is performed; in the plate thickness change control stage, the furnace temperature is changed from the time when the plate thickness change point reaches the furnace inlet to the time when it exits the final furnace. In the passing section, the line speed obtained in the preparation stage is changed with a gradient for a predetermined time; in the return stage, the line speed is changed to a line speed corresponding to the strip after the plate thickness has been changed, and the strip target temperature is adjusted at the line speed after the change. A method of controlling a continuous annealing furnace according to claim 1, characterized in that the furnace temperature is changed to a temperature that takes . 4. In the preparation stage, the furnace temperature at the line speed is determined by limiting the temperature deviation when changing plate thickness, the furnace temperature is determined by the maximum line speed due to heat load restrictions, the furnace temperature is determined by the maximum line speed determined by the characteristics of the drive motor, etc., and the furnace temperature is determined by the furnace capacity. The minimum value of the temperature limits is determined as the predicted furnace temperature, and if the predicted furnace temperature exceeds the current furnace temperature, the furnace temperature is changed to the predicted furnace temperature, and the line speed is changed in accordance with the predicted furnace temperature. Fine adjustment of the furnace temperature and/or line speed is performed using the relational expression to prevent temperature deviations that occur during passage through the furnace at the plate thickness change point; In the plate thickness change control stage, the furnace temperature and line speed obtained in the preparation stage are maintained. ; In the return stage, the amount of fine adjustment of the furnace temperature and/or line speed made in the preparation stage is returned to the original value each time the plate thickness change point passes through each furnace, and the plate thickness is changed after the plate thickness change point passes through all furnaces. The minimum value of the furnace temperature at the maximum line speed determined by the heat load restriction for the subsequent strip, the furnace temperature at the maximum line speed determined by the characteristics of the drive motor, etc., and the maximum furnace temperature determined by the furnace capacity is determined as the predicted return furnace temperature. , if the predicted return furnace temperature exceeds the current furnace temperature, the furnace temperature is changed to the predicted return furnace temperature, and the line speed is changed in accordance with the predicted return furnace temperature. A method of controlling the continuous annealing furnace described above. 5 As a fine adjustment of the furnace temperature and/or line speed in the preparation stage, the furnace temperature adjustment amount △TFI is obtained and the furnace temperature is finely adjusted.If the furnace temperature cannot be changed by △TF1, the line speed adjustment amount △V However, TMAX" is the maximum allowable furnace temperature T'yi. The furnace temperature V immediately before the two-furnace temperature adjustment is obtained at the two-line speed, and the furnace temperature is adjusted by △TF□ and the line speed is finely adjusted by △V. Claim No. 4
A method of controlling a continuous annealing furnace described in Section 1.