JPH0734140A - Continuous strip annealing method - Google Patents

Abstract

(57) [Summary] In a continuous annealing furnace, the emissivity of the furnace is accurately maintained even when the furnace is in an unsteady state in order to secure the target strip temperature in response to changes in heat treatment conditions such as strip thickness and line speed. Is calculated to achieve precise strip temperature control. [Structure] In addition to the actual values of the furnace temperature, strip temperature, and line speed, the in-furnace roll temperature is further measured to calculate and set the emissivity of the furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous annealing method for strips in which the furnace temperature or line speed of a continuous annealing furnace is accurately calculated and annealed when a heat cycle, a line speed, a plate thickness or the like is changed.

[0002]

2. Description of the Related Art Generally, a heat cycle of a continuous annealing furnace,
To set the furnace temperature (hereinafter, furnace temperature) corresponding to changes in heat treatment conditions such as line speed or plate thickness, the furnace temperature is calculated using the heat balance formula in each furnace such as heating furnace and soaking furnace, There is a method of manually or automatically inputting this value into the arithmetic unit.

At this time, the temperature calculation method is as follows:
As disclosed in Japanese Patent Laid-Open No. 58-31372, there is a known method of calculating the emissivity from the operating results of the furnace by determining that the furnace is in a steady state and calculating the furnace temperature using this emissivity. Has been.

[0004]

However, in recent years, the annealing treatment of cold-rolled strip has been capable of producing a wide variety of products from high-strength steel sheets to drawing steel sheets at high speed and in a short time and in a small lot. Is required. For this reason, heat treatment conditions are frequently changed, and furnace temperature, line speed,
There is less opportunity to obtain a steady plate thickness, that is, a steady state of the furnace.

Therefore, in the method for calculating the emissivity from the operating results in the steady state of the furnace described in Japanese Patent Publication No. 58-31372, there is an opportunity to calculate (steady state).
However, there is a problem in that the emissivity cannot be estimated when it is necessary to estimate the emissivity and an appropriate furnace temperature is not set. As a method of dealing with this problem, there is a method of relaxing the determination condition of the steady state and increasing the number of times of emissivity calculation,
In this method, the accuracy of the emissivity is poor, so that there is a problem in that the actual strip temperature variations vary greatly.

The object of the present invention is to achieve a non-steady state,
An object of the present invention is to provide a continuous annealing method capable of calculating emissivity with higher accuracy and, moreover, capable of setting the strip temperature to a target value with higher accuracy.

[0007]

In order to solve the above problems, the present invention measures not only the actual furnace temperature value, the actual strip temperature value, the actual line speed value but also the temperature of the roll inside the furnace to measure the emissivity. Is calculated, and the thickness of the strip, the line speed, the furnace temperature and the line speed when changing the target strip temperature, or any one of them is calculated and set by using the calculated emissivity. .

That is, according to the present invention, when changing the heat treatment conditions of the continuous annealing furnace, the furnace temperature, the strip temperature and the line speed are measured, the emissivity is calculated using these measured values, and the emissivity is calculated by the furnace. Corrected according to the deviation between the inner roll temperature and the strip temperature, the furnace temperature target value and the line speed target value based on the corrected emissivity, or one of them is calculated and set. It is a continuous annealing method.

[0009]

The emissivity in the continuous annealing furnace is generally expressed by the following equation (1). ρ ・ Cp ・ t ・ LS ・ (dT _s / dx) = 2εσ (T _F ⁴ −T _S ⁴ ) ... (1) However, ρ: Strip density t: Plate thickness Cp: Specific heat LS: Line speed ε: Furnace Emissivity σ: Stefan-Boltzmann constant T _F : furnace temperature T _S : strip temperature X: line heating length.

Further, it is known that the equation (1) has the same value of the radiation ε only when the furnace is in a steady state (Japanese Patent Publication No. 58).
-31372 publication). Therefore, in the past, the emissivity could be calculated back only in the steady state. According to the present invention, when it is not in a steady state, the emissivity is obtained by correcting the emissivity by the measured value of the furnace temperature, and the furnace temperature and / or the line speed is calculated from the emissivity. Appropriate furnace temperature and line speed can be obtained even in the production of many kinds of small lots with many steady states.

The reason why the accuracy of the emissivity in the unsteady state is increased by the measured value of the roll temperature in the furnace is as follows. That is, in the steady state, the strip temperature and the roll temperature are substantially equal to each other, but a temperature difference occurs during the non-steady state after passing the plate thickness change point. Generally, the heat capacity of the roll is large, and when there is a temperature difference, for example, when the strip temperature is higher than the roll temperature, the strip temperature is lowered by being absorbed by the roll, and the emissivity ε of the furnace is higher than the steady-state value. It gets smaller. Therefore, in the past, it was not possible to back-calculate in the non-steady state, but in the above case using the roll temperature according to the present invention, correct emissivity can be obtained by correcting the emissivity of the furnace to a larger side. Will be able to.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention. Reference numeral 1 is a first heating furnace, 2 is a second heating furnace, and 3 is a strip. Reference numeral 10 is a first heating furnace inlet side plate temperature detector, and the measured value is input to the arithmetic unit 11. Reference numeral 6 is a first heating furnace temperature detector, and 8 is a second heating furnace temperature detector, and the measured values are input to the arithmetic unit 11. Reference numerals 7 and 9 denote first and second heating furnace outlet side plate temperature detectors, respectively, and the measured values are input to the arithmetic unit 11. 13 is a line speed detection value by a line speed detector (not shown). 12 is the data about the constant and the length of the strip in the furnace,
Similarly, it is input to the arithmetic unit 11.

Next, the roll temperature detector 4 for the first heating furnace outlet side
And, each heating furnace outlet side roll temperature is measured by the second heating furnace outlet side roll temperature detector 5, and measured by the first heating furnace outlet side plate temperature detector 7 and the second heating furnace outlet side plate temperature detector 9. Using the difference between the strip temperature and the roll temperature on the outlet side of the heating furnace, the emissivity is corrected by the following equation (2) and the emissivity 17 is calculated back, and the value is used to set the furnace temperature from equation (15). Was calculated.

Ε ′ = ε + α (T _S −T _R ) + β (2) where ε ′ is the corrected emissivity of the furnace T _{R is the} roll temperature α and β are the control constants.

Although this embodiment shows an example in which the heating furnace has two stages, this drawing is an example of the present invention and the present invention is not limited to a two-stage furnace. Further, although the present embodiment has shown the example in which both the line speed 14 and the furnace temperature 15 are set, this is an example of the present invention, and only one of the line speed and the furnace temperature may be set. A graph showing the effect of the present invention is shown in FIG. Figure 2
In the figure, a is the plate temperature behavior according to the present invention, b is the plate temperature behavior according to the prior art, c is the plate temperature target value, and d is the roll temperature behavior when the present invention is carried out. In the present embodiment, in order to make the effects of the invention easy to understand, only the furnace temperature is set by the arithmetic unit, and the line speed is set manually by the operator.

By adopting the present invention, the plate thickness is 1.2
After the plate temperature was changed from 0.7 mm to 0.7 mm, the plate temperature satisfied the target value of 800 ° C in about 10 minutes, whereas it took about 17 minutes to meet the target value of 800 ° C using the conventional technology. I understand that This is because the plate temperature fluctuates in the present embodiment.
While the emissivity is already calculated back in 15 minutes, in the conventional technique, the furnace condition is stable for 15 to 18 minutes, 20
This is because the emissivity can be calculated backward only for ~ 23 minutes.

[0017]

According to the present invention, in the calculation of the emissivity of the continuous annealing furnace, since the roll temperature in the furnace is used, the emissivity can be calculated even when the furnace is not in a steady state.
It was possible to improve the setting accuracy of the furnace temperature and so on.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a graph showing the effect of the present invention.

[Explanation of symbols]

 1 1st heating furnace 2 2nd heating furnace 3 strip 4 1st heating furnace exit side roll temperature detector 5 2nd heating furnace exit side roll temperature detector 6 1st heating furnace furnace temperature detector 7 1st heating furnace exit side plate Temperature detector 8 Second heating furnace furnace temperature detector 9 Second heating furnace outlet side plate temperature detector 10 1st heating furnace inlet side plate temperature detector 11 Arithmetic unit 12 Constants on materials in furnace and data on furnace length 13 Line speed Signal from detector 14 Line speed setting signal 15 Furnace temperature setting signal 16 Setting line speed and furnace temperature computing device 17 Emissivity

Claims (1)

[Claims] 1. When changing the heat treatment conditions of a continuous annealing furnace, the furnace temperature, strip temperature and line speed are measured, and the emissivity is calculated using these measured values. A continuous annealing method for a strip, comprising: correcting according to the deviation of the strip temperature; and calculating and setting a furnace temperature target value and a line speed target value or any one of them based on the corrected emissivity.