JPH0625756A - Method for controlling strip temperature in continuous annealing line - Google Patents

Abstract

PURPOSE:To keep the strip temperature jump within the permissible range without reducing the productive efficiency by rapidly changing the line speed within the permissible value when the strip size changing part passes the direct fire furnace of the continuous annealing line. CONSTITUTION:A strip 2 where the head end of the succeeding coil is welded to the tail end of the preceding coil is carried into a direct fire furnace 1 and heated and then, passed into a soaking furnace or the like to apply the necessary thermal cycle. The strip size changing part such as the strip thickness and the strip width is detected, the jumping quantity of the strip temperature on the furnace outlet side is calculated by a strip temperature control device 7. When this quantity exceeds the lower or upper permissible value of the strip temperature, the jumping quantity of the strip temperature is re-calculated by making an assumption that the line speed is arbitrarily changed while the strip is passing through the direct fire furnace 1. If the strip temperature when the jump of the strip temperature is observed is within the strip temperature permissible value, the strip temperature controlling device 7 gives an order to a line drive control device 9 so that the rapid change may be made to the corrective line speed which can control the strip temperature jump when the size changing part comes in the vicinity on the outlet side of the direct fire furnace 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate temperature control method for suppressing a plate temperature deviation occurring during passage through a direct furnace in a continuous annealing line having a direct furnace.

[0002]

2. Description of the Related Art At the entrance side of a continuous annealing line to an annealing furnace, as shown in FIG.
A preheating furnace 100 for heating the steel strip 2 by using (00 ° C.) is installed, and thereafter, a direct-fired burner is provided in the furnace and a direct-fired furnace 1 having a high heating capacity for directly heating the steel strip 2 by a burner flame is provided. Has been. After that, an RT heating furnace 101 that fills the furnace with reducing gas and uses indirect radiation heating by a radiant tube (hereinafter RT) is installed to heat the surface of the steel strip 2.

In the continuous annealing line as described above, since the steel strip 2 is continuously fed into the furnace, when the preceding coil and the following coil have different thicknesses and widths, the steel strips of different sizes are welded. By heating No. 2, the furnace outlet temperature becomes discontinuous before and after the welded portion while passing through each furnace, resulting in a plate temperature jump.

In particular, since the plate temperature jump amount on the outlet side of the direct furnace 1 is large, the plate temperature exceeds the allowable range and the plate temperature deviation occurs.
The temperature deviation of the direct furnace 1 causes the steel strip 2 to be oxidized,
If the plate temperature deviation is extreme due to the large size change,
The safety circuit of the direct-fired furnace control device works to cause an emergency combustion stop.

In order to reduce the plate temperature jump amount in the direct furnace 1, a method may be considered in which the steel plate size changing unit changes the speed while passing through the direct furnace 1, but the speed is common to all furnaces, and it is useless. Since it is considered that the change may cause disturbance to the plate temperature control of other furnaces, JP-A-60-
As in No. 70127 and No. 60-70128, a means for gradually changing the furnace temperature or speed is adopted.

Similarly, in Japanese Patent Laid-Open No. 1-92323, as shown in FIG. 9, the plate temperature is reduced as shown in FIG. [Adjust the sheet temperature slightly when changing from thin to thick, as shown in (a) in the figure, and slightly decrease as shown in (b) in the opposite case] Within the temperature tolerance (ΔTp1 and ΔTp2 between the lower limit and the upper limit)
A control method is employed in which the speed is reduced in advance to a plate temperature jump amount that can be accommodated in (1), and after passing through the size changing unit, the speed is increased to increase production efficiency.

[0007]

Of these, the latter control method employs a means of performing deceleration in advance and increasing the speed after the size changing section has passed through the entire furnace, so that the low speed state continues for a long time, and This will hinder the improvement of efficiency. Further, the former control method is premised on the high responsiveness of the direct furnace, and is difficult to apply in a plant where high responsiveness cannot be obtained due to O ₂ control in the exhaust gas of the direct furnace, combustion control restrictions, and the like.

The present invention was devised in view of the above problems of the prior art. When the size changing portion passes through the direct furnace, the plate temperature jump is kept within its allowable value without significantly lowering the production efficiency. The present invention aims to provide a plate temperature control method that can be accommodated in.

[0009]

Therefore, the plate temperature control method of the present invention is based on the fact that the line speed is rapidly changed within the allowable value while the steel plate size changing section is passing through the direct furnace of the continuous annealing line. Characteristic.

Further, in the plate temperature control method of the second invention, the plate temperature is finely adjusted in advance just before the steel plate size changing portion enters the direct furnace of the continuous annealing line, and then the above line speed control is performed. Is.

In either method, when the steel plate size changing portion is a change from a thin material to a thick material, the line speed is reduced, and when the steel plate size changing portion is a change from a thick material to a thin material. , The line speed is changed by increasing the line speed.

Further, in the second invention method, the following adjustment may be made for the fine adjustment of the plate temperature. That is, when the steel plate size changing unit is a change from a thin material to a thick material,
The fine adjustment of the plate temperature is performed by raising the plate temperature by 1/2 of the allowable plate temperature jump amount. On the contrary, when the steel plate size changing portion is a change from thick to thin, the allowable plate temperature jump is performed. This is done by lowering the plate temperature by half of the amount.

In furnaces other than direct-fired furnaces, the change in the plate temperature in the transient state is small due to the thermal inertia of the hearth roll in the furnace, and if it is not too large, even if the line speed is changed at one time, the plate temperature is within the allowable value. Gaining new knowledge that it can be maintained,
Based on such knowledge, in the present invention, only in a direct furnace in which a large plate temperature jump occurs, the line speed is rapidly changed at once to reduce the plate temperature jump amount.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In FIG. 1, 1 is a direct furnace of a continuous annealing furnace, 2 is a steel strip which is a material to be annealed, 3 is a fuel supply pipe, 4 is a line drive motor, 5 is a plate temperature detector, 6 is a fuel flow rate detector, 7 Is a plate temperature control device, 8 is a furnace temperature control device, and 9 is a line drive control device.

A steel strip 2 formed into a continuous coil by welding the tip of the trailing coil to the tail end of the preceding coil with a welding machine (not shown) is passed through the entrance side looper (not shown) and is passed to the direct fire furnace 1. After being sent and heated to a predetermined temperature here, it is passed through a soaking furnace, a gas jet furnace, an overaging furnace, and a quenching furnace (not shown) to apply a necessary heat cycle. The fuel flow rate control of the burner 10 in the direct furnace 1 is performed by the fuel flow rate control valve 12, the fuel flow rate detector 6 and the fuel flow rate controller 11 installed in the fuel supply pipe 3. The line speed control is performed by controlling the rotation speed of the line drive motor 4 by a line speed detector (not shown) and the line drive controller 9.

In the present invention, when the steel plate size changing portion such as the plate thickness and the plate width is detected, the plate temperature control device 7
The plate temperature jump amount ΔT on the exit side of the furnace is calculated by [= (predicted value of trailing material plate temperature at trailing line speed-predicted value of preceding material plate temperature at leading line speed), and the change from thin to thick If it jumps to the descending side, otherwise jumps to the ascending side]. This plate temperature jump usually exceeds the plate temperature allowable lower limit value or upper limit value, but if it exceeds these, it is assumed that the line speed has been arbitrarily changed while passing through the direct furnace 1. , The plate temperature jump amount ΔT1 at that time is recalculated. If the plate temperature when there is a plate temperature jump of ΔT1 is within the plate temperature allowable value, the plate temperature control device 7 issues a command to the line drive control device 9 to change the rotation speed of the line drive motor 4. , Fig. 2
As shown in (a) and (b), when the size changing unit comes near the exit side of the direct furnace 1, the correction line speed is rapidly changed so that the plate temperature jump can be controlled [change from thin to thick (A) in the case, and (b) in the opposite case].

However, if it is attempted to bring the plate temperature within the allowable value only by changing the line speed, the speed change amount sometimes becomes large, and the influence on other furnaces may not be negligible.
In such a case, a plate temperature fine adjustment operation that can distribute the plate temperature change above and below the target plate temperature is performed to reduce the line speed change amount. That is, when the size changing portion is a change from a thin material to a thick material, as shown in FIG.
First, the plate temperature controller 7 calculates the allowable plate temperature jump amount ΔTp defined by the width of the allowable upper limit value and the lower limit value of the target plate temperature. Next, the plate temperature control device 7 issues a command to the furnace temperature control device 8, adjusts the fuel flow rate control valve 12 by the fuel flow rate controller 11 via the temperature instruction control system 13, and causes the plate temperature detector 5 to control. 1 / 2ΔTp based on the measured plate temperature
Only control so that the plate temperature rises. Then, the plate temperature gradually rises and reaches the plate temperature allowable upper limit value immediately before reaching the exit side of the direct furnace 1. On the other hand, the plate temperature control device 7 obtains the line speed of the trailing material for which 1/2 of the allowable plate temperature jump amount ΔTp is the plate temperature upper limit tolerance by a convergence calculation using a model formula and the plate temperature is above the allowable value. When the upper limit value is reached, a command is issued to the furnace temperature control device 8 and the line drive control device 9 to restore the plate temperature and change the line speed. In this way, the plate temperature is gradually raised by decreasing the plate temperature by the allowable plate temperature jump amount ΔTp, and then returns to the target plate temperature.

FIG. 4 is a time chart showing a control procedure when the size changing portion changes from a thick material to a thin material, and the control is performed in a procedure substantially similar to the above case.

Further, FIG. 5 shows an example of control implemented in an actual plant.

In this embodiment, if the plate temperature jump is within the allowable plate temperature value when the first plate temperature jump amount ΔT is calculated, as shown in FIG. 6 and FIG. It was decided to fine-tune the plate temperature only by controlling the temperature.

[0021]

According to the method of the present invention described in detail above, since the size changing unit changes the line speed while passing through the direct furnace without changing the line speed in advance, the production efficiency of the line is significantly reduced. Therefore, it is possible to properly prevent the plate temperature from coming off.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an implementation configuration of the present invention.

FIG. 2 is a time chart showing a control procedure according to the method of the present invention and a state of a plate temperature jump at that time.

FIG. 3 is a time chart showing the state of the plate temperature jump when the plate temperature fine adjustment is also performed.

FIG. 4 is a time chart showing another plate temperature jump state when the plate temperature fine adjustment is hurriedly performed.

FIG. 5 is a time chart showing a control example when it is executed in an actual plant.

FIG. 6 is a time chart showing a control example when only plate temperature fine adjustment is performed by plate temperature control.

FIG. 7 is a time chart showing a control example when only plate temperature fine adjustment is performed by plate temperature control.

FIG. 8 is an explanatory diagram showing a line configuration of a continuous annealing line.

FIG. 9 is a time chart showing a conventional control example in which the line speed is changed in advance together with the fine adjustment of the plate temperature.

[Explanation of symbols]

 1 Direct Fire Furnace 2 Steel Strip 7 Plate Temperature Controller 8 Furnace Temperature Controller 9 Line Drive Controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noboru Taguchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (8)

[Claims] 1. A plate temperature control method in a continuous annealing line, wherein the line speed is rapidly changed within a permissible value while the steel plate size changing section is passing through a direct furnace of the continuous annealing line. 2. The plate temperature control method for a continuous annealing line according to claim 1, wherein the line speed is changed by decelerating when the steel plate size changing portion is a change from a thin product to a thick product. The plate temperature control method in the continuous annealing line according to claim 1. 3. The plate temperature control method for a continuous annealing line according to claim 1, wherein the line speed is changed by accelerating when the steel plate size changing portion is a change from a thick product to a thin product. The plate temperature control method in a continuous annealing line according to claim 1, characterized in that. 4. The plate temperature fine adjustment is performed in advance just before the steel plate size changing unit enters the continuous annealing line in the direct furnace, and the steel plate size changing unit keeps the line speed within the allowable value while passing through the direct furnace. A plate temperature control method in a continuous annealing line, which is characterized by rapidly changing. 5. The plate temperature control method for a continuous annealing line according to claim 4, wherein the line speed is changed by deceleration when the steel plate size changing portion is a change from a thin product to a thick product. The plate temperature control method in the continuous annealing line according to claim 4. 6. The plate temperature control method for a continuous annealing line according to claim 4, wherein the line speed is changed by increasing speed when the steel plate size changing portion changes from thick to thin. The plate temperature control method in the continuous annealing line according to claim 4, wherein. 7. The plate temperature control method for a continuous annealing line according to claim 4, wherein fine adjustment of the plate temperature is performed when the steel plate size changing portion is a change from a thin product to a thick product. 7. The method according to claim 4, wherein the plate temperature is raised by 1/2 of the allowable plate temperature jump amount.
A method for controlling the plate temperature in the continuous annealing line according to the item. 8. The plate temperature control method in the continuous annealing line according to claim 4, wherein when the steel plate size changing portion is a change from a thick material to a thin material, the fine adjustment of the plate temperature is performed. 7. The plate temperature is lowered by 1/2 of the allowable plate temperature jump amount.
A method for controlling the plate temperature in the continuous annealing line according to the item.