JPH02205634A - Method for controlling temperature of continuous annealing furnace - Google Patents

Abstract

PURPOSE:To control the temp. of a continuous annealing furnace to the annealing temp. of a succeeding steel strip in a short period of time at the time of annealing the welded steel strips consisting of different materials at different temps. in the furnace by holding the furnace temp. set value of the preceding steel strip for a prescribed period of time at the specific temp. corresponding to the furnace temp. set value of the succeeding steel strip, and then setting the temp. of the annealing furnace at the annealing temp. of the succeeding steel strip. CONSTITUTION:While the steel strip 2 formed by welding the steel strips consisting of the different materials is passed along many hearth rolls 3 in the continuous annealing furnace 1, the steel strip is continuously heated and annealed by plural radiant tubes 4. The temps. in various parts of the furnace are detected by plural furnace temp. detectors 5 and are fed to a furnace temp. controller 7. The controller 7 is connected to a furnace temp. setter 6 and a fuel flow rate controller 8. The setter 6 is connected further to a furnace temp. set pattern computing element 9. The furnace temp. is previously set at FR3 higher than FR2 in the case of FR2>FR1 and is then returned to the set temp. FR2 for annealing the succeeding steel strip at the time of changing the furnace temp. set value from FR1 to FR2 according to a change in the kinds of the steel strips, by which the annealing temp. of the steel strips different in steel kinds is set to the target annealing temp. in a short period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the furnace temperature of a radiant tube heating zone in a continuous annealing furnace.

[Conventional technology]

FIG. 4 is a schematic diagram showing a radiant tube heating zone and a furnace temperature control system in a conventional continuous annealing furnace. In the figure, 2 indicates a tuning zone which is a metal band to be continuously annealed. The steel strip 2 that has entered the heating furnace 1 of the continuous annealing furnace is driven by a plurality of drive devices such as a plurality of hearth rolls 3, 3, etc. arranged vertically and alternately in the transport direction, which is the longitudinal direction of the steel strip 2. , hearth roll 3.3
... is continuously transferred while being in contact with the upper or lower circumferential surface of about z-A, respectively. On the other hand, Hearth Roll 3.3...
- A plurality of radiant tubes 4, 4... for heating the steel strip 2 are provided around the steel strip 2 between them, and a fuel gas supply (not shown) is provided within the radiant tubes 4, 4... The radiant tubes 4,4... are heated by burning the fuel gas supplied from the source, and the steel strip 2 being transferred is heated by the radiant heat. The furnace temperature at this time is measured by a furnace temperature detector 5 installed at an appropriate position in each region when the inside of the heating furnace l is divided into, for example, four groups of regions.
．． 5... are detected as temperature signals in each region, and sent to the furnace temperature regulator 7 provided outside the heating furnace l. The furnace temperature controller 7 is connected to a furnace temperature setting device 6 in which a furnace temperature set value FR is set and a fuel flow rate controller 8 connected to a fuel gas supply source, and the furnace temperature detector 5 detects the temperature. A signal is sent to the fuel flow rate regulator 8 so that the value obtained becomes the furnace temperature set value F, thereby indirectly controlling the fuel gas supply amount and adjusting the furnace atmosphere temperature for each zone.

In such a continuous annealing furnace having a radiant tube heating zone, in order to heat-treat the steel strip continuously, the rear end of the steel strip 2 currently being processed and the tip of the steel strip 2 to be next processed are welded at the entrance of the furnace. Connected by If the dimensions, heat treatment conditions, or materials of each steel strip 2 to be connected are different before and after the weld,
It is necessary to change the furnace temperature actual value to the target furnace temperature set value, and conventionally, the furnace temperature set value F set in the furnace temperature setting device 6 in FIG. By changing the settings stepwise from the set value to the target furnace temperature set value for the next treatment steel strip 2 obtained in advance, the furnace temperature is changed by bringing the actual furnace temperature value asymptotically closer to the target furnace temperature set value. was.

℃Problems to be Solved by the Invention] Figure 5 is a time chart of the furnace temperature set value and actual furnace temperature value in the conventional method of changing the furnace temperature set value in steps, and Figure 6 is It is a time chart of the steel strip temperature target value and the copper strip temperature actual value in . In addition, Fig. 5 and Fig. 6 show the furnace temperature setting values.

The copper strip temperature target value is shown by a solid line, and the furnace temperature actual value and copper strip temperature actual value are shown by a dashed line.

As shown in Fig. 5, when the furnace temperature setting value FR is changed stepwise from 820°C to 870°C, the actual furnace temperature value F
1 asymptotically approaches the furnace temperature set value F, and reaches 870''C, and it takes about 20 minutes, excluding dead time 17=2 minutes, to stabilize.

At this time, as shown in Figure 6, from 720°C to 760°C.
Copper strip temperature target value T set to °C.

On the other hand, since the copper strip temperature actual value T3 gradually converges like the furnace temperature actual value F, it also takes about 20 minutes excluding the dead time L=2 minutes until it stabilizes at 760°C. In this way, in the conventional method of changing the furnace temperature set value in steps, because the heat capacity of the heating zone is extremely large, the actual temperature value T, Since the steel strip temperature deviates from the steel strip temperature target value T, l, there was a problem in that the copper strip could not obtain predetermined mechanical properties during that time.

The present invention has been made in view of such circumstances, and after setting the furnace temperature setting value of the currently processed steel strip to a value higher than the target furnace temperature setting value of the next processing steel strip for a predetermined time, It is an object of the present invention to provide a furnace temperature control method for a continuous annealing furnace that can control the actual furnace temperature value to the target furnace temperature set value in a predetermined target response time by setting the furnace temperature set value. .

[Means to solve the problem]

The furnace temperature control method for a continuous annealing furnace according to the method of the present invention is such that when the heat treatment conditions of the metal strip are different before and after the joint between the currently treated metal strip and the next treated metal strip, the furnace temperature setting value of the currently treated metal strip is set to the next value. In a furnace temperature control method for a continuous annealing furnace, the furnace temperature is controlled to the target furnace temperature setting value by changing the target furnace temperature setting value of the processed metal strip,
The furnace temperature set value is set to be held at a value higher or lower than the target furnace temperature set value for a predetermined time, and then set to the target furnace temperature set value.

[Effect]

In the method of controlling the furnace temperature of a continuous annealing furnace according to the method of the present invention, the furnace temperature setting value of the currently processed metal strip is set to be held at a value higher or lower than the target setting value of the next processing metal strip for a predetermined time, and then the Since the target furnace temperature setting value is set, the furnace temperature actual value can be controlled to the target furnace temperature setting value in a predetermined target response time.

〔Example〕

Hereinafter, the method of the present invention will be specifically explained based on the drawings.

FIG. 1 is a time chart of the furnace temperature setting value according to the method of the present invention, and shows the case where the furnace temperature setting value is changed from F□ to F, □. If the target furnace temperature response time excluding dead time is, then from time 0 to tP+1. In order to stably change the actual furnace temperature (liF m) from the furnace temperature set value FRI to FR Temperature setting value F
R from FRI to F.

(F R3 > F * z), keep it constant as Fill until time tp, and then change the setting to return the furnace temperature setting F to Ftz in steps. This was clarified as a result of theoretical examination.

Here, the time t is based on the furnace temperature setting change timing, and for example, time 1=0 is when the welded portion of the currently treated steel strip and the next treated steel strip approaches the entrance of the continuous annealing furnace heating zone.

By the way, as in the past, the furnace temperature set value FII is changed from F□ to FR.
When the change is made in a stepwise manner up to expressed.

However, T: Time constant of response to furnace temperature change (minutes) L: Dead time of response to furnace temperature change (minutes) From equation (1), furnace temperature set value F is changed from Fall to F.
Actual furnace temperature value F1 (°
The response of C) can be predicted as shown in equation (2).

Fa (t+L)=e-”T-Fall (1e-”
”)...(2) However, t: FR or time based on the furnace temperature setting change timing, t≧0.

Therefore, as shown in Fig. 1, at time 0, the furnace temperature set value FI
After changing I in a stepwise manner from F□ to F R3 (F 13 > F *z) and keeping it constant at Fll and I until time tP+L, the furnace temperature setting 4fJ F * was changed to Fllg.
From time 0 to t, p +
The response of the actual furnace temperature values F and ('C) during L can be predicted as shown in equation (3) as well as equation (2).

F, (LlL)=e-”7- F+u+ (1-e-”
”)...(3) However, 0≦t≦t, +L.

Furthermore, as mentioned above, at time t, +L, the furnace temperature actual value F
, ('C) to coincide with FIIg('C), the equation (4) is obtained from the equation (3).

F,, = e-tr't HF+u ten (1e-"")
・R13...(4) Furthermore, in equation (4), = (1-e-tp/
By setting KP > 1 (KP > 1), equation (5) is obtained.

Fa, I FRI=KF ・ (FIIg F□)
...(5) R3 As is clear from equation (5), ΔFm=FmzFill is the final setting change amount between time O and time tp+L.
However, if you change the furnace temperature set value by twice, the time tp +L
In this case, the actual furnace temperature value F can be made to match F□.

The arithmetic expressions for changing the furnace temperature set value FIl at each time are summarized as follows.

F R=F □
(Mu 〈 0 )...(6) F,=F□10KF ・ (Fa2 F□) (0
≦t≦L.

...(7) FR=F, l□ (tp+L<t
)...(8) However, K, = (1e - Ll>/T) -1.

Therefore, when changing the furnace temperature set value FR from Fll to FIIg in a stepwise manner, the time constant T of the response to the furnace temperature change determined experimentally in advance and the target furnace temperature response time L2 specified in advance. By using the data of <6), (7) and (8), and controlling the furnace temperature based on the values, the furnace temperature actual value F is set to the target furnace temperature response time (F+L). , the furnace temperature can be controlled to a desired set value FLll.

FIG. 2 is a schematic diagram showing a radiant tube heating zone and a furnace temperature control system in a continuous annealing furnace in which the method of the present invention is carried out, and 2 in the figure indicates a copper strip which is a metal strip to be continuously annealed.

The steel strip 2 that has entered the heating furnace 1 of the continuous annealing furnace is driven by a plurality of drive devices such as a plurality of hearth rolls 3, 3, etc. arranged vertically alternately in the transport direction, which is the longitudinal direction of the steel strip 2. The hearth rolls 3°3... are continuously transported while contacting the upper or lower circumferential surfaces of approximately X to 2, respectively. On the other hand, a plurality of radiant tubes 4, 4, . . . for heating the steel strip 2 are provided around the steel strip 2 between the hearth rolls 3, 3, . By burning fuel gas supplied from a fuel gas supply source (not shown) in the radiant tubes 4, 4...
The steel strip 2 being transferred is heated by the radiant heat. The furnace temperature at this time is determined by the furnace temperature detectors 5, 5, etc. installed at appropriate positions in each region when the inside of the heating furnace 1 is divided into, for example, four groups of regions. It is detected as a signal and sent to the furnace temperature regulator 7 provided outside the heating furnace 1. Furnace temperature controller 7 is furnace temperature setting device 6
and a fuel flow rate regulator 8 connected to a fuel gas supply source, and the furnace temperature setting device 6 further calculates the equations (6), (7), and (8) according to changes in the furnace temperature setting. It is connected to a furnace temperature setting pattern calculator 9 that performs calculations.

In the furnace temperature setting pattern calculator 9, when changing the furnace temperature setting value F, which is input therein, in a stepwise manner from I"Il+ to F., the time constant T of the response to a predetermined furnace temperature change and the target furnace The calculations of equations (6), (7), and (8) are performed as the temperature response time t.The calculation results are output to the furnace temperature setting device 6, and then sent to the furnace temperature controller 7.Then, the furnace temperature The regulator 7 determines that the value detected by the furnace temperature detector 5 is the target furnace temperature response time L.
Fuel flow so that the desired furnace temperature setting value Fll□ is reached at P! A signal is sent to the regulator 8 to indirectly control the fuel gas supply amount.

Next, the results of comparing the method of the present invention and the conventional method will be described. FIG. 3 is a time chart showing the actual furnace temperature values when changing the furnace temperature using the method of the present invention and the conventional method. - The dashed and dotted lines indicate the actual furnace temperature values obtained using the conventional method. In Figure 3, from the furnace temperature set point F□=820°C, Faz=
The results are shown when the furnace temperature setting was changed to 870℃.
In the method of the present invention, based on the results of experiments conducted in advance, the time constant T of the response to furnace temperature change is set to 6 minutes, and the target furnace temperature response time t.

is set to 5 minutes. As shown in Figure 3,
In the conventional method, it took 20 minutes, excluding the dead time L = 2 minutes, for the actual furnace temperature to asymptotically reach 870°C and stabilize, whereas the actual furnace temperature in the method of the present invention required 20 minutes to reach 870°C and stabilize. 87 at the same 5 minutes as the target furnace temperature response time except for time l7 = 2 minutes.
It is stable asymptotically reaching 0°C. This shows that by using the method of the present invention, the actual furnace temperature value can be controlled to a desired furnace temperature set value within a predetermined target furnace temperature response time.

In this example, the case where the target furnace temperature setting value for the next treatment steel strip is higher than the furnace temperature setting value for the currently treated steel strip is shown, but conversely, the target furnace temperature setting value for the next treatment steel strip is higher than the furnace temperature setting value for the currently treated steel strip. Needless to say, when the furnace temperature is lower than the target furnace temperature set value for the steel strip, the same effect can be obtained by setting the furnace temperature set value to be maintained at a value lower than the target furnace temperature set value for the next treatment steel strip for a predetermined period of time. .

〔effect〕

As detailed above, in the furnace temperature control method for a continuous annealing furnace according to the present invention, the furnace temperature setting value for the currently processed steel strip is set at a predetermined value higher or lower than the target furnace temperature setting value for the next processed steel strip. After the setting is made to hold the furnace temperature for a certain period of time, the furnace temperature is set to the target furnace temperature set value, which provides an excellent effect in that the actual furnace temperature value can be controlled to the desired furnace temperature set value within the predetermined target furnace temperature response time.

[Brief explanation of the drawing]

Fig. 1 is a time chart of furnace temperature setting values according to the method of the present invention, Fig. 2 is a schematic diagram showing the radiant tube heating zone and furnace temperature control system of a continuous annealing furnace implementing the method of the present invention, and Fig. 3 is a diagram of the furnace temperature control system according to the present invention. A time chart showing actual furnace temperature values when changing the furnace temperature using the method and conventional method. Figure 4 is a schematic diagram showing the radiant tube heating zone and furnace temperature control system in a conventional continuous annealing furnace. Figure 5 is a diagram showing the furnace temperature in the conventional continuous annealing furnace. Time chart of furnace temperature set value and furnace temperature actual value in the method of changing the set value in steps,
FIG. 6 is a time chart of the target zone temperature value and actual copper zone temperature value in FIG. 5. ■... Heating furnace 2... Steel strip 4... Radiant tube 5... Furnace temperature detector 6... Furnace temperature setting device 7
...Furnace temperature regulator 8...Fuel flow rate regulator 9...
Furnace temperature setting pattern calculator patent Applicant Sumitomo Metal Industries Co., Ltd. Representative Patent attorney Noboru Kono Figure R Figure L = 2 minutes diagram 870℃ L = 2 minutes diagram 760℃ Figure

Claims (1)

[Claims] 1. When the heat treatment conditions of the metal strip are different before and after the joint between the currently processed metal strip and the next processed metal strip, the furnace temperature setting value of the currently processed metal strip is set as the target furnace temperature of the next processed metal strip. A furnace temperature control method for a continuous annealing furnace in which the furnace temperature is controlled to a target furnace temperature set value by changing the set value to a set value, wherein the furnace temperature set value is maintained at a value higher or lower than the target furnace temperature set value for a predetermined time. A furnace temperature control method for a continuous annealing furnace, characterized in that the furnace temperature is set to the target furnace temperature set value after setting the target furnace temperature to the target furnace temperature.