JPS591639A - Controlling method of plate temperature - Google Patents

Abstract

PURPOSE:To enable good following-up ability to a change in the temp. or thickness of a plate in a non-steady state and heating to about 900-950 deg.C in a method for heat treating continuously the plate material in a continuous furnace, by disposing the 2nd furnace wherein the response speed of heat is high on the outlet side of the 1st furnace. CONSTITUTION:An indirect heating furnace 1 heats a plate material S to about 850-900 deg.C, and a furnace 2 for IR heating or the like can heat the material to the higher temp. The target heating temps. Ta', Ta on the outlet sides of the furnaces 1, 2 in a steady state are determined with a control device 5 for plate temp. in accordance with the equation (tp: the rate of heating of the plate S (ton/hr), h: the thickness of the plate (mm.), f(tp. h): the max. heating rate in the furnace 2( deg.C). The temp. of the furnace 1 and the quantity of heat input of the furnace 2 are respectively controlled in such a way that the actually measuerd values of thermometers 41, 42 coincide with said targets. The coefft. in the 2nd term on the right side of the equation is 1/2, that is, the heating in the furnace 2 is 50% of the max. heating capacity and has an allowance in capacity; therefore, the furnace has a good following up ability. The information on the plate S in the furnace is obtd. from a process controlling computer in the non-steady time, the quantity of the heat to be inputted to the furnace 2 is determined by the equation and the temp. of the plate at the outlet of each furnace is so controlled that the heating in the furnace 2 resumes the mode in the steady state.

Description

Detailed Description of the Invention The present invention is particularly useful when changing the target plate temperature or changing the thickness of the treated plate when continuously feeding the plate to a continuous furnace such as a continuous annealing furnace to perform heat treatment such as annealing. The present invention provides a method for controlling plate temperature with good followability during unsteady conditions such as when

When manufacturing a cold rolled steel plate, a strip is cold rolled at an appropriate rolling rate, but the rolled strip is work hardened and has extremely poor workability. Therefore, in order to use this material for the subsequent forming step, the crystal grains are grown to an appropriate size after recrystallization, and softening annealing is performed for this purpose. This softening annealing can be carried out in a batch manner, but in order to improve its efficiency, it is carried out continuously in a continuous annealing furnace.

Various methods have been proposed to control the plate temperature in this continuous annealing furnace, but since heating in a continuous annealing furnace requires heating in a reducing atmosphere, an indirect heating furnace using a radiant tube is used as the heating device. However, since the thermal response speed of such indirect heating furnaces is slow, the optimum plate temperature control method that can be used in unsteady situations such as when changing the target plate temperature or changing the thickness of the processed plate is difficult. This is due to the fact that it has not yet been established.

In such a furnace with a slow thermal response speed, during unsteady situations such as changing the plate temperature or plate thickness, the heating temperature will deviate before and after the fulcrum point, causing problems such as deterioration of the quality of the plate. In extreme cases, defective products are likely to occur, resulting in a decrease in yield.

In addition, when heating with a normal radiant tube, 850
It is only possible to heat up to ~900°C, and indirect heating furnaces that can heat to temperatures higher than that are not practical due to equipment costs. Therefore, 9 from the top of the heat treatment specifications
When heating at about 00 to 950° C. is required, processing power ζ is generally carried out using a special batch furnace, but there is a problem in that the annealing cost for this is extremely high.

The present invention has been made in order to solve the above-mentioned problems, and is a method for continuously heat-treating plate materials in a continuous furnace. To provide a method that enables sheet temperature control with good followability even in unsteady situations such as when changing sheet temperature or sheet thickness, by using a continuous furnace, and also enables heating to about 900 to 950°C. The purpose is to

The plate temperature control method according to the present invention is a method of continuously feeding and heating plate materials to a continuous furnace, in which a furnace consisting of a second furnace with a slow thermal response speed is used as the continuous furnace, During normal conditions, the outlet plate temperature of the second furnace and second furnace is controlled so that the heating by the second furnace is less than its maximum heating capacity, and during unsteady conditions, the required heating amount is changed in the second furnace. After that, the second furnace is heated so that the heating by the second furnace returns to the steady state.
It is characterized by controlling outlet plate temperature of the furnace and the second furnace.

The present invention will be explained in detail below based on the drawings. FIG. 1 is a schematic side view showing the implementation state of the method of the present invention, in which 1 is a first furnace containing a radiant tube, and 2 is a second furnace containing an infrared heater or an induction heating device. Furnace 1
In this process, the strip S fed into the furnace from a previous process (not shown) is detoured and guided by a plurality of hearth rolls 3 placed at appropriate positions in the furnace, and is heated indirectly by a radiant tube. The reducing atmosphere is heated to a temperature of about 850-900'C. The second furnace 2 is
This furnace is capable of heating the strip S to a temperature higher than the maximum heating temperature of the furnace 1, and is connected to the rear stage of the first furnace 1, and together with the first furnace 1 constitutes a continuous annealing furnace. .

At an appropriate position on the exit side of the first furnace 1, that is, on the entrance side of the second furnace 2,
A thermometer 41 is installed to measure the surface temperature of the strip S, and a similar thermometer 42 is installed at an appropriate position on the outlet side of the second furnace 2, and data regarding the surface temperature of the strip S obtained by these thermometers 42 are installed. is input to the plate temperature control device 5.

Furthermore, a speed meter 6 is attached to the outlet side of the second furnace 2 in order to measure the running speed of the strip S running in the continuous annealing furnace, and the data obtained by the speed meter 6 also corresponds to the sheet temperature. It is input to the control device 5.

In addition to the data described above, data is also input to the plate temperature control device 5 from a process control computer 7 that tracks the strip S in the furnace. The specific data includes the material specifications such as the width, thickness, and material of the strip S at each position in the furnace, and the heating specifications such as the feeding speed and heating temperature given to the strip S. .

Note that these data are constant during steady state, but
Needless to say, it changes at unsteady times such as when changing the plate temperature or plate thickness.

The plate temperature control device i5 into which the various data have been inputted in this way determines the outlet side strip temperature setting values of the first furnace 1 and the second furnace 2 based on the various data, and adjusts the furnace temperature of the second furnace 1. The set values are output to the control device 8 and the furnace temperature control device 9 of the second furnace 2, respectively. The furnace temperature control device 8 controls the combustion of the first furnace 1 to maintain the given set value, and the furnace temperature control device @9 controls the amount of heat input to the second furnace 2 to maintain the given set value. Take control.

The control operation based on the above-mentioned plate temperature control device 5 will be explained in more detail. First, the control operation during steady state will be described. In this case, assuming that the target heating temperature on the outlet side of the second furnace 2 is Ta, the plate temperature control device 5 determines the target heating temperature Ta' on the outlet side of the second furnace 1 as shown in equation (1) below. .

Ta = Ta −7f (tp, h) ・” ・
” (1) However, t, Nistrip heating amount (tons/hour)
f(t,,h): Maximum temperature increase in the second furnace 2 ('C
) and the furnace temperature control system [8 is the temperature control device 8, which is a temperature control device (Ta) whose actual plate temperature on the outlet side of the first furnace 1 measured by the thermometer 41 is determined by equation (1).
The furnace temperature of the first furnace 1 is controlled so as to coincide with '.

This control is performed using the well-known P.1. D. Feedback control using control may be used. Further, the furnace temperature control device 9 controls the amount of heat input to the second furnace 2 so that the actual plate temperature value on the outlet side of the second furnace 2 measured by the thermometer 42 matches the target heating temperature Ta. This control is also performed using the well-known P, I, and D controls.

Feedback control using control may be used.

Note that instead of this control, feedforward control may be performed based on the actual plate temperature value on the outlet side of the second furnace 1 measured by the thermometer 41, but the strip length in the second furnace 2 is approximately 5 m. (The furnace time is about 1 to 4 seconds), so as is clear from FIG. Considering that the thermal response speed of
It can be seen that it is not necessarily necessary to perform feedforward control.

When controlling as described above, since the coefficient of the second term on the right side of equation (1) is set to 172, the heating by the second furnace 2 at steady state N4 is less than its maximum heating capacity, and specifically, This will be done at the maximum heating capacity of 5 liters. Therefore, even in unsteady situations such as when changing the plate temperature or plate thickness, the second furnace 2 has sufficient heating capacity to enable plate temperature control with good followability. The reason why the amount of heating by the second furnace 2 during steady state is set at 50% of its maximum heating capacity is that it is possible to This selection was made in order to maintain the same level of support even in cases where it is necessary to reduce the

Next, we will discuss control operations during unsteady conditions.

In the plate temperature control device 5, in-furnace strip information is obtained from the process control computer 7 at fixed time intervals Δ, and based on the strip specifications at the connection between the first furnace 1 and the second furnace 2 in the information, The target heating temperature Ta on the exit side of the first furnace 1 is determined using the above equation (1). Then, the furnace temperature control device [8 performs feedback control of the furnace temperature of the first furnace I, using Ta' determined as described above, as in the steady state. In addition, in the plate temperature control device 5, a plate temperature target value Ta′ on the outlet side of the first furnace 1, an actual plate temperature value Ts′ on the outlet side of the second furnace 1,
The amount of heat input to the second furnace 2 is Q (kc
a//R) is determined as shown in equation (2).

Q = y(Ta'-Ts'* Ta, tp,
h)+g(Ta-Ts, tp, h)...
・(2) However, y = required input heat amount to be fed forward to the second furnace 2 (kca 1 layer) ε: corrected amount of heat to be fed back to the second furnace 2 (kca
/ layer) Then, the furnace temperature control device 9 performs heating control of the second furnace 2 using the input heat ff1Q determined as described above.

In this way, in an unsteady state, for example, when changing the plate temperature target value Ta on the outlet side of the second furnace 2 in a stepwise manner, the plate temperature target value Ta' on the outlet side of the second furnace 1 is also changed according to equation (1). However, as mentioned above, since the thermal response speed of the first furnace 1 is slow, the plate temperature at the exit side of the first furnace 1 will be changed until the actual measured value Ts' matches the target value Ta'. It takes a long time. So (2
) As shown in the first term on the right side of the equation, by controlling the heating amount of the second furnace 2 in a feedforward manner according to the deviation between Ts' and Ta', the plate temperature at the exit side of the second furnace 2 can be adjusted to the target value. It is made to match the value Ta. The error in the required input heat amount 2 to be fed forward to the second furnace 2 is calculated by the plate temperature target value Ta on the outlet side of the second furnace 2, as shown in the second term on the right side of equation (2).
Since this occurs as a deviation between the measured value Ts and the actual measurement value Ts, correction is made in a feedback manner using the corrected amount of heat.

The subsequent control is performed so that the heating by the second furnace 2 returns to the steady state, that is, the state wA below its maximum heating capacity (for example, the state of 5 sieves with the maximum heating capacity).

Specifically, such control is performed as follows, for example. That is, (i) control based on the above equation (2) is started at the timing when the plate thickness change point of the IJ tube S leaves the first furnace l. For example, if the thickness of the subsequent strip S is thick, and the second value is 2
If it is not necessary to change the plate temperature target value Ta on the outlet side, Ta
The difference between 2 and Ts' becomes larger, and in order to correct this using the second value 2, y(Ta'i8') is used.

The input heat amount is increased by the second value 2 using feedforward control using Ta, tp, h), and the response delay of the second value 2 is increased using feedback control using ε(Ta - Ts, tp, h). It will be supplemented.

On the other hand, in Furnace 1, Ta' is changed as tp is changed, and initially Ts' is a force that cannot follow this (Ts' eventually becomes Ta', and in this state, the second value 2 becomes The amount of heat input is 50% of its maximum heating capacity.

Note that the tail end of the leading strip S and part of the tip of the trailing strip S may be out of specification, but the length is 10 m or less, and the previous one is 60 to 70 m.
It's quite short compared to the length of time.

In addition, although the target of the control to return to the normal mode was set to 5 bites, which is the maximum heating capacity, in the above explanation, it may be set according to the specifications of the strip S to be fed next. For example, if the thickness of the next strip S to be fed is thicker than the thickness of the previous strip S, when the change point in the thickness of the strip S passes the outlet side of the first furnace 1, Since the measured value Ts' of the plate temperature on the outlet side tends to decrease, in order to make it match the target temperature Ta, it is necessary to rapidly increase the amount of heating based on the second value 2. Therefore, if heating in a steady state according to the second value 2 is performed in advance, for example, in a state of 4 sieves with the maximum heating capacity, when looking at the second value 2, the margin for the increase in the amount of input heat will increase to 5 sieves of the maximum heating capacity. It is possible to perform control with a slight overshoot, and to further improve the followability of the second value 2.

In the above explanation, the amount of heat Q (kca//ll) input to the second value 2 in the plate temperature control device 5 is determined based on the above equation (2), but it is determined based on the following equation (3). You may decide.

Q = y(Ta - Ts', tp, h) + g(
Ta - Ts, tp, h)... - (a) This is because the relationship between Ta and Ta' is defined by equation (1) above, so the feedforward difference between Ta' and Ts' is This is because there is no substantial difference even if the portion related to is replaced by the difference between Ta and Ts'.

When heating the strip S while controlling the plate temperature as described above, if it is necessary to suddenly change the target heating temperature of the strip S to be processed, the thickness of the fed strip S is changed. Heating control with extremely good followability is possible even in unsteady situations such as when

Incidentally, the control of the second value 2 in a steady state may be performed using the result shown by the above equation (2), and the control of the second value 2 in an unsteady state may be performed by simple feedback control. It is possible.

Next, the method of the present invention will be explained based on drawings showing an example of its effects. In Fig. 3, (4) shows the case where the plate temperature is controlled by the conventional method (feedback type control using an indirect heating furnace with radiant tubes), and (4) shows the case where the plate temperature is controlled by the method of the present invention. Indicates when control is performed. (A) e) In both cases, time is plotted on the horizontal axis and temperature is plotted on the vertical axis, and changes over time in the target plate temperature value (solid line) and the measured plate temperature value (dashed line) on the output side of the second value 2. This is what is shown.

From the figure, it can be seen that the method of the present invention enables heating control with extremely good followability compared to the conventional method, confirming the excellent effects of the method of the present invention.

As detailed above, in the present invention, in the method of continuously feeding and heating plate materials to a continuous furnace, a second value having a fast thermal response rate is arranged on the outlet side of the first furnace having a slow thermal response rate. Using a continuous furnace with Since the outlet plate temperature of the first furnace and the second value is controlled so as to return to the normal mode, plate temperature heating control with extremely good followability is possible. Furthermore, according to the present invention, a continuous furnace capable of heating to 900°C or higher can be easily realized, so that it becomes possible to heat treat steel plates, which have conventionally been treated using a batch furnace, using a continuous furnace. etc., the benefits of the present invention are extremely high.

[Brief explanation of the drawing]

Fig. 1 is a schematic side view showing the implementation state of the method of the present invention, Fig. 2 is a graph showing the relationship between the amount of temperature increase and the amount of heating of the strip, and Fig. 3 is a graph showing the effect of the method of the present invention. It is. DESCRIPTION OF SYMBOLS 1... First furnace, 2... Second furnace, 41.42... Thermometer, 5... Plate temperature control device, 6... Speed needle, 7...
- Process control computer, S... strip. Patent Applicant Sumitomo Metal Industries Co., Ltd. Patent Attorney Tosuke Kono
(tons/hour) Figure 2

Claims (1)

[Claims] 1. In a method of continuously feeding and heating plate materials to a continuous furnace, the continuous furnace includes a first furnace with a slow thermal response speed and a second furnace with a fast thermal response speed arranged on the outlet side of the first furnace. The outlet plate temperature of the first furnace and the second furnace is controlled so that the heating by the second furnace is less than its maximum heating capacity during steady state, and the required heating amount is changed during unsteady state. 1. A plate temperature control method comprising controlling outlet plate temperatures of the first furnace and the second furnace so that the heating by the second furnace returns to a steady state after being carried out in the second furnace.