JPH0575503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the prediction of restrictive breakouts that may occur in continuous casting.

[Prior Art] There are various types of breakouts that occur in continuous casting, but restrictive breakouts occur suddenly even when there is no apparent change in operating conditions, so it is difficult to distinguish between them. Prediction and prevention are difficult. In other words, restraint breakout is thought to occur when a part of the shell formed by solidifying molten steel sticks to the mold and is torn off. There are no changes above.

A method for predicting restrictive breakout is disclosed, for example, in Japanese Patent Publication No. 47545/1983.
In this method, the temperature of each part of the mold is measured using multiple thermocouples embedded in the mold, and if the temperature detected by one thermocouple rises by one step above the average detected temperature, then falls. In addition, when a similar temperature change pattern is detected by other adjacent thermocouples, it is considered that there is a possibility of a breakout.

[Problem to be solved by the invention] However, in the conventional restrictive breakout prediction method, the prediction accuracy is relatively low, and even if a breakout does not actually occur, there is a high possibility that it will be mistakenly recognized as a breakout. .

If a restraining breakout is predicted to occur during continuous casting, in order to prevent it,
Drawing of cast steel shall be stopped immediately. However, temporary suspension of drawing of cast steel
Since this involves a partial change in the material of the cast steel, the portion formed by stopping the drawing cannot be made into a product, resulting in a decrease in yield. Therefore, if there is a high possibility of erroneous recognition of breakout, the yield will be reduced more than necessary.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to improve the prediction accuracy of a method for predicting restraint breakout in continuous casting, prevent breakout from occurring, and at the same time prevent a decrease in yield.

[Means for Solving the Problems] In order to solve the above problems, in a first aspect of the present invention, a plurality of temperature detection means embedded in mutually different positions of a mold wall of continuous casting equipment detect temperature detection means. in a method of monitoring the temperature at each location to predict a restrictive breakout: a first location, a second location above the first location, and a third location transverse to the first location. identify whether or not an increasing pattern of the detected temperature has been detected for each of the positions; when the increasing pattern is detected at all of the first, second, and third positions; a predetermined pattern of change in the detected temperature; detecting a time difference T12 between the first position and the second position with respect to the time when the detected temperature appears; detecting a time difference T13 between the first position and the third position with respect to the time when a predetermined change pattern appears in the detected temperature; A breakout is predicted when the time differences T12 and T13 are each within a predetermined time range depending on the drawing speed of the cast steel and the distance between each temperature detection position.

Moreover, in order to solve the above-mentioned problem, in a second aspect of the present invention, the temperature at each position detected by a plurality of temperature detection means embedded in mutually different positions of the mold wall of continuous casting equipment is In a method of monitoring and predicting a restrictive breakout: detecting at least each of a first position, a second position above the first position, and a third position transverse to the second position. identify whether or not a rising pattern of temperature has been detected; when the rising pattern is detected at all of the first, second, and third positions; detect a time difference T12 between the first position and the second position; detect a time difference T13 between the first position and the third position with respect to the time at which a predetermined change pattern appears in the detected temperature; the time difference T12 and T13 are A breakout is predicted if each temperature falls within a predetermined time range depending on the drawing speed of the cast steel and the distance between each temperature detection position.

[Function] In the present invention, the positional distribution pattern of the abnormal change in the temperature of the cast steel that appears prior to the restrictive breakout becomes V-shaped or U-shaped, and the positional distribution moves (generally downward). I'm paying attention to that. If both of these conditions are met, a breakout can be predicted with very high accuracy.

That is, in the first aspect, a temperature increase pattern is detected for three points: a reference point (first position), a point above the reference point (second position), and a point in the lateral direction of the reference point (third position). The time difference in which the temperature change pattern appears is measured between the first position and the second position and between the first position and the third position. By identifying the time difference, it is possible to detect the movement state of the abnormal temperature distribution and improve the detection accuracy of the position distribution pattern.

In the second aspect, a horizontal point at the second position is used as the third position in the first aspect. The rest is the same as in the first embodiment.

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

[Example] Figure 5a 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 the mold gradually solidifies within the mold as cooling progresses, and is slowly drawn out from below the mold at a constant speed. The casting width varies depending on the specifications of the product, but in this example, the maximum casting width is 222 cm.

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

The molten steel in the mold E solidifies sequentially from the portion along the inner wall of the mold that is cooled, forming a shell B. Since shell B is pulled out from below the mold, it progresses downward, and as it moves downward, it grows and becomes thicker. Since there is an inclusion called powder between shell B and mold E, shell B is separated from the wall surface of mold E. However, in the vicinity of meniscus F, part A of shell is sometimes attached to mold E. It may stick. The shell stuck to the mold E is restrained and will not move, so if you apply force to pull out the shell B from below, the shell will break midway and some of the shells A
While the shell remains fixed to the mold wall, the other parts of the shell B move downward (1).

In the opening (between A and B) formed by the fracture of the shell, the molten steel directly contacts the mold wall and is rapidly cooled, so a new shell C is formed in that area (2).

The new shell C sticks to both the lower shell B and the upper restrained shell A, but as the lower shell B moves downward, the new shell C, which is thinner, is torn off by the force. The part Ca fixed to the lower shell B and the upper shell A
It is divided into a part Cb and a part Cb that is fixed to (3).

Molten steel again enters between the separated shells Ca and Cb, contacts the mold wall, is cooled, and forms a new shell, which is then torn off again. These processes are repeated (4).

The position where the new shell is formed gradually moves below the mold. Breakout occurs when the position reaches the lower end of mold E (5).

FIG. 7 shows the appearance of a slab that suffered a restrictive breakout during casting. Referring to FIG. 7, it can be seen that the portion where the restrictive breakout has occurred forms a substantially V-shape. Because the thickness of the shell is very thin where breakout occurs, the temperature at the mold wall is higher than normal. The portion where such an abnormal temperature rise occurs (thin portion of the shell) gradually moves downward.

Therefore, in this invention, the temperature is measured at each position of the mold, attention is paid to the part where an abnormal temperature rise has occurred, the position distribution is identified, and whether or not it progresses downward at a predetermined speed is determined. By identifying this, we are able to predict restrictive breakouts.

In this embodiment, a number of thermocouples are provided on each of the four sides of the mold, as shown in Figures 5b and 5c.
TC is buried. Specifically, a rod made of constantan is covered with an insulating material except for the tip, and the rod is inserted and fixed into holes formed at various positions on a copper plate constituting the mold. By processing the electrical signals obtained from each thermocouple, the temperature of each part can be measured.

In the method of the present invention, in order to identify the position distribution pattern of abnormal temperature, a reference point, an upwardly related point, a laterally related point,
We are focusing on four types of points: and upward horizontal related points. However, the three points actually used to identify breakouts are the reference point, upward related point, and horizontal related point, and the reference point, upward related point, and upward related point. It's either one or the other.

Next, each point of interest will be explained.

Reference point: The necessary conditions for the reference point are: (a) It must not be in the hot water level affected area (b) It must not be in the air gap generation area (c) It must be inside the slab width (d) There may be a direction-related point and a lateral-related point, or an upward-related point and an upward-laterally related point, and in this example, the position of the thermocouple in the area AR1 shown in Figure 2a is a necessary condition for the reference point. I am satisfied.

The identification condition (sufficient condition) for the reference point is expressed by the following equation (1) (see Figure 2b).

Tb(t)−Tba(t′)≧Ts……(1) Tb(t): Current detected temperature (instantaneous value) Tba(t′): Moving average temperature one cycle (2 seconds) ago Ts: Temperature Deviation Threshold The moving average temperature is determined at each point in time as the average value of all instantaneous temperatures detected at n points in the past (in this example, the average over n=16:32 seconds).

When the detected temperature of the thermocouple at each position shown in Figure 2b satisfies the above standard point conditions, each of them is regarded as a reference point, and the state is maintained for a predetermined period of time (Tbh: 28 seconds) from the time of detection Tbo. ) to be memorized and retained.

Upward related point: The necessary conditions for the upward related point are: (a) It must not be in the hot water level influence area (b) It must not be in the air gap generation area (c) It must be inside the slab width (d) It must be at that point On the other hand, there is a reference point and there may be a horizontally related point or an upper horizontally related point (e) The horizontal spread angle (θ in Figure 3a) with respect to the reference point is within 55 degrees. However, if the second stage thermocouple becomes the reference point due to restrictions on the number of thermocouples actually arranged, the positions on both sides of the position directly above the reference point shall satisfy the condition.

If each point satisfies all of the conditions (a) to (e) above, check all identification conditions (sufficient conditions) shown in equations (2), (3), and (4) below ( (See Figure 3b).

Tr(t)−Tra(t′)≧Ts ……(2) (Tr(t)−Tr(t′))/2<b ……(3) tr ₁ −tr ₀ ≦c ……(4) Tr(t): Current detected temperature (instantaneous value) Tr(t′): Previous detected temperature (instantaneous value) Tra(t′): Moving average temperature one cycle (2 seconds) ago tr ₁ : The (3rd) ) when the condition of equation (2) is satisfied tr ₀ : when the condition of equation (2) is satisfied b, c: constant Equations (3) and (4) are only applied after equation (2) is satisfied. ) formula must continuously satisfy the conditions for a predetermined period of time. When all of the necessary conditions (a) to (e) above and formulas (2), (3), and (4) are satisfied, point that point in the upward direction. Considered as a related point. When an upward related point is detected, its state is stored and held for a predetermined period of time.

Laterally related point: The conditions for a laterally related point are: (a) a reference point exists for that point; and (b) it is at least one position on either side of the reference point. Points that satisfy these requirements (Article 4a)
(see figure), the following identification conditions (sufficient conditions)
(See Figure 4b).

Tw(t)−Twa(t′)≧Ts ……(5) (Tw(t)−Tw(t′))/2<b ……(6) tw ₁ −tw ₀ ≦c ……(7) Tw(t): Current detected temperature (instantaneous value) Tw(t′): Previous detected temperature (instantaneous value) Twa(t′): Moving average temperature one cycle (2 seconds) ago tw ₁ : The (6th) ) when the condition of formula (5) is satisfied tw ₀ : when the condition of formula (5) is satisfied b, c: constant Equations (6) and (7) are only applied after formula (5) is satisfied. ) formula must satisfy the condition continuously for a predetermined period of time If all of the necessary conditions (a) and (b) above and formulas (5), (6), and (7) are satisfied, then cross that point. Considered as a direction-related point. When a horizontally related point is detected, its state is stored and held for a predetermined time (twh).

Upward horizontal related point: The necessary conditions for the upward horizontal related point are (a) the presence of an upward related point, and (b) the position of at least one of both sides of the upward related point. Points that satisfy these requirements (Article 4a)
(see figure), the following identification conditions (sufficient conditions)
(See Figure 4c).

Tu(t)−Tua(t′)≧Ts ……(8) (Tu(t)−Tu(t′))/2<b ……(9) tu ₁ −tu ₀ ≦c ……(10) Tu(t): Current detected temperature (instantaneous value) Tu(t′): Previous detected temperature (instantaneous value) Tua(t′): Moving average temperature one cycle (2 seconds) ago tu ₁ : The (9th) ) when the condition of equation (8) is satisfied tu ₀ : when the condition of equation (8) is satisfied b, c: constant Equations (9) and (10) are only applied after equation (8) is satisfied. ) formula must satisfy the condition continuously for a specified period of time If all of the necessary conditions (a) and (b) and formulas (8), (9), and (10) are satisfied, then the point is Considered as a direction-related point. When a horizontally related point is detected, its state is stored and held for a predetermined time (tuh).

Note that when detecting each of the above points, different surfaces on the mold are also expanded and considered as being continuous. Therefore, for example, the reference point may exist on the L plane and the laterally related point may exist on the E plane.

Next, a method for predicting breakout will be explained. The conditions for predicting a breakout are:
There are two ways:

Condition 1: (A) There is at least one reference point. (B) There is at least one upwardly related point to the reference point in (A). (C) Laterally related point to the reference point in (A). (D) Each point (A), (B), and (C) must satisfy the following conditions (1) and (2). (1) The reference point and the upward direction The progression time of the shell rupture point (abnormal temperature detection point) between the related points is within the specified range,
That is, the following equation (11) must be satisfied.

(2) The progression time of the shell rupture point (abnormal temperature detection point) between the reference point and the lateral related point is within the specified range;
That is, the following equation (12) must be satisfied.

UL ₁ ≧tbo−tro≧LL ₁ …(11) UL ₂ ≧tbo−two≧LL ₂ …(12) UL ₁ = Lbr/(a ₁・Vz(tbo)) LL ₁ = Lbr/(a ₂・Vz(tbo)) UL ₂ = Lbw/(a ₃・Vz(tbo)) LL ₂ =Lbw/(a ₄・Vz(tbo)) Lbr: Reference point - Distance between upward related points Lbw: Reference point - Distance a ₁ to _{a 4} between horizontally related points: Constant (a ₁ < a ₂ , a ₃ < a ₄ ) tbo: Time at which the condition of equation (1) is satisfied tro: The condition of equation (2) is satisfied Time two: Time when the condition of equation (5) is satisfied Vz (tbo): Slab pulling speed condition 2 at tbo: (E) At least one reference point exists (F) Criteria for (E) There is at least one upward related point to the point (G) There is at least one upward horizontal related point to the upward related point of (F) (H) (E), (F), (G ) must both satisfy the following conditions (1) and (2): (1) The progression time of the shell breakage point (abnormal temperature detection point) between the reference point and the upward related point must be within the specified range. Inside,
That is, the above formula (11) should be satisfied.

(2) The progression time of the shell rupture point (abnormal temperature detection point) between the upward related point and the upward horizontal related point is within the specified range, that is, satisfies equation (12) above.

UL ₃ ≧tro−tuo≧LL ₃ ...(13) UL ₃ = Lru/(a ₅・Vz(tbo)) LL ₃ =Lru/(a ₆・Vz(tbo)) Lru: Upward related point − top Distance of direction-horizontal related points a ₅ , a ₆ : Constant (a ₅ < a ₆ ) tuo : Time when the condition of equation (8) is satisfied If either condition 1 or condition 2 above is satisfied, It can be predicted as a restrictive breakout. In other words, during the process of restraint breakout, a partial break occurs in the shell formed along the mold wall, and the temperature of the mold wall facing that part increases abnormally compared to before. . As is clear from the shape of the slab shown in FIG. 7, the portion where this abnormal temperature rise occurs forms a V-shaped or U-shaped positional distribution pattern. This position distribution pattern is
As shown in FIG. 6, a restrictive breakout occurs when progressing progressively downward.

at least three points at mutually different positions, namely the aforementioned reference point, an upwardly related point, and a laterally related point;
Or, by identifying the presence or absence of an abnormal temperature rise and the timing difference in its occurrence at the reference point, upward related point, and upward lateral related point, it is possible to determine whether it is a position distribution pattern related to a restrictive breakout. It can be determined whether or not. Furthermore, it is possible to detect the moving speed of the shell rupture region from the difference in the timing at which abnormal temperature increases occur between each point and the distance between each point, and determine whether or not this is related to a restraining breakout.

In reality, when a restrictive breakout occurs, the temperature changes at each measurement point will have a pattern as shown in FIG.

[Effects] As described above, according to the present invention, the presence or absence of an abnormal temperature rise is detected at three types of points at different positions, and when an abnormal temperature rise is detected, the deviation in the timing of abnormal temperature rise between each point is detected. On the basis of the,
Since the position distribution pattern of the broken portion of the shell and the speed of its progress are identified, and a restrictive breakout is predicted based on these results, extremely highly accurate prediction is possible.

[Brief explanation of the drawing]

FIG. 1 is a timing chart showing temperature changes at various points when a restrictive breakout occurs. Figures 2a, 3a, and 4a are, respectively,
FIG. 2 is a schematic diagram of a thermocouple array on a mold showing an example of each measurement point that can be a reference point, an upwardly related point, a laterally related point, and an upwardly laterally related point. FIGS. 2b, 3b, 4b, and 4c are timing charts showing temperature changes at abnormal temperature increases at each point. Figures 5a, 5b, and 5c are a perspective view, a front view, and a side view, respectively, showing the appearance of the mold of the example. FIG. 6 is a longitudinal cross-sectional view showing the process of generating a restrictive breakout. FIG. 7 is a perspective view showing the appearance of a slab in which a restraining breakout has occurred. TC: thermocouple, AR1: range that can be a reference point,
tbo-tro: (T12), tbo-two: (T13), tbo
-tuo: (T13).

Claims (1)

[Claims] 1. A method for predicting a restrictive breakout by monitoring the temperature at each position detected by a plurality of temperature detection means embedded at different positions on a mold wall of continuous casting equipment: identifying the presence or absence of detection of at least a pattern of increase in detected temperature for each of a first position, a second position above the first position, and a third position transverse to the first position; When a rising pattern is detected at all of the first position, second position, and third position; detect the time difference T12 between the first position and the second position regarding the time at which a predetermined change pattern appears in the detected temperature; ; detecting a time difference T13 between the first position and the third position regarding the time when a predetermined change pattern appears in the detected temperature; A continuous casting constraint breakout prediction method that predicts a breakout if it is within a predetermined time range depending on the distance of the continuous casting. 2. In a method for predicting a restrictive breakout by monitoring the temperature at each position detected by a plurality of temperature detection means embedded at different positions in a mold wall of continuous casting equipment: a first position, the first position; identifying the presence or absence of detection of at least a pattern of increase in detected temperature for each of a second position above the first position and a third position transverse to the second position; When the rising pattern is detected at both the position and the third position; detect the time difference T12 between the first position and the second position regarding the time at which a predetermined change pattern appears in the detected temperature; A time difference T13 between the first position and the third position is detected regarding the time at which the change pattern appears; the time differences T12 and T13 are predetermined depending on the drawing speed of the cast steel and the distance between each temperature detection position, respectively. A constraint breakout prediction method for continuous casting that predicts a breakout if it is within a time range of .