JPH0557412A - Method for predicting constrained breakout in continuous casting - Google Patents

Abstract

PURPOSE:To improve reliability of prediction of constrained breakout in continuous casting. CONSTITUTION:Temp. detected values are sampled from each of plural temp. detecting means embedded at mutually different positions in a mold wall, and standard deviation of temp. gradient in each detecting time is calculated, and alphatime of the standard deviation is made to a threshold value for discriminating breakage of solidified shell developed at the time of developing the constrained breakout.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to the prediction of constrained breakouts that can occur in continuous casting.

[0002]

2. Description of the Related Art There are various types of breakouts that occur in continuous casting, but restraint breakouts occur suddenly even when there is no apparent change in operating conditions. Prediction and prevention are difficult. Restraintable breakout is considered to occur when a part of the shell formed by solidification of molten steel is fixed to the mold and it is torn off, but until actually breakout occurs. No change in appearance is observed in the slab.

A method of predicting restraint breakout is as follows.
For example, it is disclosed in Japanese Patent Publication No. 63-47545. In this method, the temperature of each part of the mold is measured by a plurality of thermocouples embedded in the mold, and when the detected temperature of one thermocouple is higher than its average detected temperature and then decreased, it is adjacent. When a similar temperature change pattern is detected by another thermocouple, it is considered that there is a possibility of breakout.

[0004]

However, in the conventional constraint breakout prediction method, the prediction accuracy is relatively low, and even if breakout does not actually occur, it can be erroneously recognized as a breakout. It is highly likely. When the occurrence of restraint breakout is predicted in continuous casting, in order to prevent it, the drawing of the cast steel must be stopped immediately. However, the temporary stoppage of the withdrawal of the cast steel involves a partial change in the material quality of the cast steel, so the portion formed when the withdrawal is stopped cannot be made into a product, and the yield is reduced. Therefore, if the possibility of erroneous recognition of breakout is high, the yield will be reduced more than necessary.

When a plurality of temperature sensors are embedded in the side surface of the mold in the two-dimensional direction and the detected temperatures thereof are measured, if restraint breakout occurs, a temperature rise appears at a certain point in time series. Therefore, the inventors of the present invention have paid attention to such a phenomenon, and when the temperature rising points are detected and a series of them becomes a predetermined pattern and moves downward in essence in conjunction with the casting speed, the restraining blur is caused. -Provided a method of predicting that a quout will occur (Japanese Patent Application No. 1-276711 and Japanese Patent Application No. 2-30).
No. 6669). The present invention relates to an improvement in this type of restrictive breakout prediction method.

Conventionally, the time series change of the temperature data at each position is monitored, and the presence or absence of shell breakage is discriminated by whether or not the condition of the following expression (1) is satisfied.

T (t) −Ta (t ′) ≧ Ts (1) T (t): temperature (instantaneous value) at time t, Ta (t ′): movement one scan (2 seconds) before Average temperature, Ts: threshold value of temperature deviation.

The moving average temperature is obtained as an average value of all the instantaneous temperature values detected at the past n points at each time point. Number (1)
If the condition of the formula is satisfied, the following formula (2) and formula (3)
Whether or not a predetermined temperature drop appears within a predetermined time is identified by an expression.

[0009] [T (t) -T (t ' ) ] / 2 <b ··· (2) t 1 -t 0 ≦ c ··· (3) T (t): Temperature of time t (instantaneous value ), T (t '): temperature before one scan (2 seconds), t ₀ : time when the condition of expression (1) is satisfied, t ₁ : time when the condition of expression (2) is satisfied, b, c: a constant.

However, due to various operational factors, various temperatures appear data, and the patterns thereof vary, especially when the temperature fluctuates periodically due to an air gap or the like. When identification is performed by the conventional method, there are many cases in which temperature fluctuations unrelated to solidified shell rupture are identified as abnormal temperature rises. Further, since the falling portion of the time-series temperature change pattern is used as an identification element, there is a problem that the detection is delayed. The present invention aims to remedy this kind of problem.

[0011]

In a method of predicting a constrained breakout by monitoring the temperature at each position detected by a plurality of temperature detecting means embedded in different positions on a mold wall of a continuous casting facility: (1) The features that appear at the shell rupture site can be classified into two types: rapid temperature rise and decrease after temperature rise. From the viewpoint of early detection, we focus on the rapid temperature rise that appears at the early stage of fracture occurrence, and not the temperature deviation. The level of the temperature gradient is judged,
(2) Statistical method is used to distinguish the temperature change due to fracture of solidification shell caused by various operation factors and the temperature change due to fracture of solidification shell. The fracture site of the solidified shell is identified by dynamically determining the threshold accordingly. That is, the detected value is sampled from each of the temperature detecting means,
The standard deviation of the temperature gradient at each detection time is calculated, and the standard deviation times α (coefficient) is used as the threshold value for determining the solidification shell rupture that occurs during the restraint breakout.

[0012]

The shell has a characteristic that the temperature of the thermocouple suddenly rises when the shell breaks, and the shell break can be detected by detecting this as an abnormal temperature. However, the behavior of the temperature obtained from the thermocouple in the casting mold during casting changes from moment to moment depending on various operating conditions. The behavior is represented by a temperature gradient, and the magnitude of the behavior is used at a certain time interval (32 seconds) by using an index called standard deviation, whereby an abnormal state of the value of the temperature gradient can be monitored. If the above-mentioned index is used as the value of the temperature gradient judgment, the threshold level is comparatively high when the temperature fluctuation is large, and a part of the fluctuation is not erroneously detected, and the threshold is detected when the temperature fluctuation is small. The level of the value becomes low, and the temperature abnormality can be detected with high sensitivity.

As described above, according to the present invention, the temperature abnormality can be detected regardless of the temperature behavior in the mold, and the accuracy of predicting the restraint breakout in continuous casting is improved. As a result, breakout is prevented in advance, and at the same time, reduction in yield is prevented.

Other objects and features of the present invention will become apparent from the following description of the embodiments with reference to the drawings.

[0015]

EXAMPLE FIG. 3 shows the appearance of a mold used in continuous casting. A cooling water passage is formed inside the wall of the mold, and the molten steel in the mold is cooled by the cooling water. The molten steel injected into this mold is gradually solidified in the mold as cooling progresses, and is slowly drawn out from below the mold at a constant speed. The casting width depends on the specifications of the product, but in this example the maximum casting width is 22
It is 2 cm.

Next, the progress of the process when the restrictive breakout occurs will be described with reference to FIG. In FIG. 6, the process is (1)-(2)-(3)-(4)-
Proceed in the order of (5).

The molten steel in the mold (mold) 1 is solidified sequentially from a portion along the inner wall of the mold which is cooled to form a shell B. Since the shell B is pulled out from the lower side of the mold, it progresses downward, grows downward, and its thickness increases. Since there is an inclusion called a powder between the shell B and the inner surface of the mold 1, the shell B is separated from the wall surface of the mold 1, but the meniscus F
In the vicinity of, a part of the shell A sometimes sticks to the inner surface of the mold 1. Since the shell fixed to the mold 1 is constrained and does not move, a force for pulling it out from below is applied to the shell B, so that the shell ruptures from the middle, and some shells A remain fixed to the mold wall, while shells of other parts remain. B progresses downward (1 in FIG. 1).

At the opening formed between the fractures of the shell (between shells A and B), the molten steel directly contacts the mold wall and is rapidly cooled, so that a new shell C is formed there (Fig. 1 of 2).

The new shell C adheres to both the lower shell B and the upper restrained shell A, but since the lower shell B moves downward, the new shell C having a small thickness is moved by its force. It is torn off and divided into a portion Cb fixed to the lower shell B and a portion Ca fixed to the upper shell A (3 in FIG. 1).

Molten steel again invades between the separated shells Ca-Cb and comes into contact with the mold wall, is cooled and forms a new shell, and the shell is torn off again. These processes are repeated (4 in FIG. 1).

The position where the new shell is formed gradually moves below the mold. When the position reaches the lower end of the mold 1, breakout occurs (5 in FIG. 4).

The appearance of the slab in which the constrained breakout occurred during casting is shown in FIG. Referring to FIG. 7, it can be seen that the portion where the restrictive breakout has occurred forms a substantially V-shape on the side surface. The part that causes breakout is
Due to the very thin thickness of the shell, the temperature at the mold wall will be higher than normal. The portion where such an abnormal temperature rise occurs (thick shell portion: V-shaped distribution) gradually moves downward. Therefore, in the invention of the above-mentioned patent application and the invention of the present application, the temperature is measured at each position of the mold, attention is paid to a portion where an abnormal temperature rise occurs, and the position distribution thereof is identified and By discriminating whether or not the vehicle advances at a predetermined speed, the restraint breakout is predicted.

In this embodiment, as shown in FIGS. 4 and 5, a large number of thermocouples TC are embedded in each of the four surfaces of the mold. Specifically, a rod made of constantan is covered with an insulating material except for the tip, and the rod is inserted and fixed in holes formed at respective positions of a copper plate constituting the mold.
By processing the electric signal obtained from each thermocouple, the temperature of each part can be measured.

Next, FIG. 1 shows an outline of the processing of predictive breakout prediction according to an embodiment of the present invention. An embodiment will be described below with reference to FIG. The processes P1 to P3 shown in FIG.
Is executed at a cycle Ts = 2 sec.

In process P1, the voltage output from each thermocouple mounted on the mold is sampled at predetermined intervals, and the obtained voltage is converted into digital data to obtain temperature information.
For each thermocouple whose temperature is sampled, the read value of this time and the read value of at least 16 times in the past are stored and held in the memory.

In process P2, the time series information of a large number of temperatures obtained in process P1 is processed by the present invention to detect the temperature abnormality at each point.

In process P3, regarding the point where the temperature abnormality is detected in process P2, the point is regarded as a fractured part, and the breakout is determined from the positional relationship of the fractured part.

The contents of the "temperature abnormality detection" P2 will be described with reference to FIG.

In process P21, the read value of this time and the read value of at least 16 times in the past are stored and held in the memory for each thermocouple whose temperature is sampled.

In process P22, the thermocouple effective this time is selected, and the process proceeds to the following.

When the temperature of the thermocouple is sampled as described above, the temperature abnormality is detected by the processing of P23 and below based on the read value of this time and the read value of at least 16 times in the past for each thermocouple (position) for which the temperature is sampled. I do.

In process P23, the temperature gradient ΔT (t) is calculated from the previous read value as follows: ΔT (t) = [Tb (t) -Tb (t-1)] / 2 (1) ΔT (t) ): Temperature gradient at time (t), Tb (t): detected temperature (instantaneous value) at time (t), Tb (t-1): detected temperature (instantaneous value) at time (t-1), Calculate by formula.

Next, in process P24, the standard deviation σ of the temperature gradient corresponding to the number of readings is calculated from the temperature gradient ΔT (t) obtained in P23.
To

[0034]

[Equation 2]

Σ: standard deviation of temperature gradient, ΔTa (t): moving average value of temperature gradient, n: number of readings.

In the next process P25, the threshold value ΔTs (t) for identifying the temperature abnormality is set for each scan time ΔTs (t) = α × σ (3) ΔTs (t): time The temperature gradient threshold value at t, α: coefficient, is calculated by the following equation.

In process P26, the first (1) is obtained from each position data.
Identify whether the temperature gradient determined by the equation satisfies the following equation (4). ΔT (t) -ΔTa (t)> ΔT (4) ΔT (t): temperature gradient at time t, ΔTs (t): temperature gradient at time t, ΔTa (t): moving average of temperature gradient value. When the expression (4) is satisfied, it is detected that the temperature is abnormal.

In process P27, the position distribution on the mold of the point (single or plural) where the temperature abnormality is detected in P26 is obtained to determine the shell breakage position.

When the above-described processing of P21 to P27, that is, "detection of temperature abnormality" P2 is completed, the process proceeds to breakout determination of P3.

During the process of restraint breakout, the shell formed along the wall of the mold has a partial breakage, which is V-shaped as shown in FIG. 7.
At least 3 points at different positions, for example, Japanese Patent Application No. 1
-276711, the reference point, the upward direction related point, and the lateral direction related point, or the reference point, the upward direction related point, and the lateral direction lateral related point, the presence or absence of the breakage portion and the timing difference at which it occurs. , It is possible to determine whether or not it is the position distribution pattern associated with the constrained breakout. In addition, it is possible to detect the movement speed of the shell rupture region from the deviation of the timing at which the abnormal temperature rise occurs between the points and the distance between the points, and determine whether or not it is related to the restrictive breakout. In the breakout judgment of P3, the predictive judgment of the restrictive breakout is performed by the time series processing of the shell break position information obtained in "Detection of temperature abnormality" P2.

[0041]

[Effect] As described above, according to the present invention, the threshold value is dynamically determined according to the temperature fluctuation condition of the thermocouple in the mold to identify the presence or absence of temperature abnormality, that is, the presence or absence of shell breakage. Even in the steady temperature fluctuation occurrence region which may occur due to various operation factors, the temperature abnormality is detected with high accuracy and early, and the accuracy of the constraint breakout prediction in the continuous casting becomes high. As a result, breakout is prevented in advance, and at the same time, reduction in yield due to erroneous detection is prevented.

FIGS. 8 and 9 show the temperature gradient and the threshold value expressed by the expressions (1) to (3) based on the detected values obtained from the thermocouple in the casting mold.
It is calculated by an equation and is shown in a time series with a broken line and a solid line. The unit of time on the horizontal axis is seconds, and the unit of temperature gradient on the vertical axis is ° C / sec. In FIGS. 8 and 9, the time point when the temperature gradient shown by the broken line exceeds the threshold value shown by the alternate long and short dash line is the time point when the fracture detection of the shell is established. Figure 8 is -2 on the horizontal axis
At time 0, the shell is broken, and FIG. 9 shows that the temperature is fluctuating due to some factor other than the shell break. In this case, the temperature fluctuates significantly, but the fracture is not detected. Like this
By determining the presence or absence of breakage based on the threshold value obtained by the equation (3), the probability of erroneously detecting temperature fluctuation other than shell breakage as shell breakage is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a process for predicting restrictive breakout according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the content of “detection of temperature abnormality” P2 shown in FIG.

FIG. 3 is a perspective view showing an appearance of a mold for carrying out the present invention in one aspect.

FIG. 4 is a plan view showing outer surfaces of F and L surfaces of the mold 1 shown in FIG.

5 is a plan view showing outer surfaces of E and W surfaces of the mold 1 shown in FIG.

FIG. 6 is a vertical cross-sectional view in a mold showing a process of generating a constrained breakout.

FIG. 7 is a perspective view showing the external appearance of a slab having a constrained breakout.

FIG. 8 is a graph showing an example of a time series transition of a threshold value obtained by the present invention, in which the horizontal axis represents time and the vertical axis represents temperature gradient.

FIG. 9 is a graph showing another example of time series transition of threshold values obtained by the present invention, in which the horizontal axis represents time,
The vertical axis represents the temperature gradient.

[Explanation of symbols]

 1: mold 2, TC: thermocouple

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[Procedure amendment]

[Submission date] October 9, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

[0034]

[Equation 2]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

In process P26, the first (1) is obtained from each position data.
Identify whether the temperature gradient determined by the equation satisfies the following equation (4). ΔT (t) -ΔTa (t)> ΔTs (t) (4) ΔT (t): temperature gradient at time t, ΔTs (t): threshold value of temperature gradient at time t . ΔTa (t): moving average of temperature gradient. When the expression (4) is satisfied, it is detected that the temperature is abnormal.

Claims (1)

[Claims] 1. A method for predicting a constrained breakout by monitoring the temperature at each position detected by a plurality of temperature detecting means embedded in different positions on a mold wall of a continuous casting facility: Each detected temperature is sampled, the standard deviation of the temperature gradient at each detection time is calculated, and the value obtained by multiplying the standard deviation by a predetermined coefficient α is a threshold value for determining the solidification shell rupture that occurs at the time of restraint breakout. A method for predicting a constrained breakout in continuous casting, characterized by: