JP3501054B2 - Method for preventing constraining breakout in continuous casting - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can predict a constraining breakout accurately during continuous casting and can effectively prevent the occurrence of breakout. The present invention relates to a method for preventing constraining breakout in casting. Conventionally, as a method for detecting a constraining breakout, for example, as disclosed in Japanese Patent Publication No. 5-75502, a plurality of thermocouples are arranged in the width direction and the vertical direction in a mold. The temperature of any one of the upper thermocouples and any one of the thermocouples adjacent to the thermocouple rises to 5 ° C. or more with respect to the peak value of each previous measurement, and the upper There is known a method of predicting a breakout when the lower thermocouple of a corresponding portion has risen by 5 ° C. or more with respect to the previous measured peak value of the lower thermocouple within 10 seconds. In Japanese Patent Publication No. 1-26791, the temperature in the width direction of a continuous casting mold is detected at a predetermined measurement position, and the detected temperatures at these measurement positions are compared to determine the mold. There has been proposed a method for preventing breakout by predicting a breakout sign due to a sudden change in temperature and adjusting the casting speed based on this. [0004] However, the method disclosed in the above Japanese Patent Publication No. 5-75502 only considers the temperature rise of the thermocouple adjacent to the upper stage, so that the typical restraint property is limited. The V-shaped break line of the breakout cannot be identified, and the temperature rise time difference between the upper and lower thermocouples is (the distance between the upper and lower thermocouples / casting speed), but the actual temperature rise time difference Is (distance between upper and lower thermocouples / (α ×
Casting speed) Here, α = 0.5 to 0.9), so it was predicted as a breakout, but it was not detected in spite of the occurrence of a breakout or a false detection that did not actually occur. However, it occurs frequently. In the method disclosed in Japanese Examined Patent Publication No. 1-26791, the temperature is measured only by the thermocouples arranged in a line in the width direction of the mold. As a result, it was not possible to accurately predict the breakout. [0006] The present invention advantageously solves the above problems, and can predict the sign of a breakout with much higher accuracy than before, and can effectively prevent the occurrence of a breakout. The purpose is to propose a method for preventing constraining breakout in continuous casting. Means for Solving the Problems Now, the inventors conducted a number of investigations on the form of occurrence of the constraining breakout in order to achieve the above object. We have found the fact that it is always V-shaped and its propagation speed is slower than the casting speed. The present invention
It was developed based on the above findings. That is, in the present invention, a plurality of upper and lower two-stage thermocouples are arranged in the width direction with respect to the continuous casting mold, and the following three thermocouples adjacent to each other between the thermocouples adjacent to each other are
The lower thermocouple directly below the thermocouple in which the sudden change in temperature is detected within the time (t ₁ ) satisfying the equation (1) and the first three sudden changes in temperature are detected. Is
This is a method for preventing a constraining breakout in continuous casting, wherein the casting speed is reduced when a sudden change in temperature occurs within a time (t ₂ ) that satisfies equation (2). W · tanθ _min / (α _max · Vc) ≤ t ₁ ≤ W · tan θ _max / (α _min · Vc) --- (1) H / (α _max · Vc) ≤ t ₂ ≤ H / (α _min・ Vc) --- (2) where W: distance between adjacent thermocouples (mm) H: distance between upper and lower thermocouples (mm) Vc: casting speed (m / min) α _{min ,} α _max : Minimum and maximum propagation speed ratio of constraining breakout break line to casting speed θ _{min ,} θ _max : Minimum constraining breakout break line,
Maximum propagation angle (°) Here, the propagation angle of the constraining breakout break line refers to an angle formed by the break line and the horizontal direction. DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. In the present invention, the reason for setting the upper temperature change detection position to three points is to recognize the passage of the V-shaped break line, which is the break line of the constraining breakout, as shown in FIG. This is because it is necessary to measure temperature at least three points. That is, when a V-shaped break line occurs, first, in this example, a sudden temperature change (specifically, a rapid temperature rise) occurs at the position A, and then both sides (B and C Position), the temperature rises after a predetermined time, and inevitably, the temperature rises also at the lower position directly under A, that is, the a position. Therefore, in the present invention, the temperature considered to pass the V-shaped break line that is the break line of the constraining breakout within a predetermined time between the adjacent thermocouples of the three adjacent thermocouples in the upper stage. When a change is detected and the thermocouple directly below the thermocouple where the temperature change is first detected among the above three thermocouples, the same temperature change occurs within the predetermined time. The casting speed is reduced as a sign of out. In this respect, even if the solidified shell is broken,
After the temperature rise is detected at the A position, the temperature rise does not occur within a predetermined time at the B or C position, or the temperature rise is detected at the lower a position although the temperature rise is detected at the B and C positions. If not, the breakout is not reached and the casting speed is not adjusted. In fact, in such a case, the damaged part is repaired after that and hardly reaches a breakout. Moreover, if it does as mentioned above, the exact judgment can be similarly made about the temperature change by disturbance, and false detection will be reduced markedly. Here, as the predetermined time t ₁ for detecting the temperature change between the upper thermocouples, the distance (W) between the thermocouples, the casting speed (Vc), the minimum with respect to the casting speed of the constraining breakout break line. In consideration of the maximum propagation velocity ratio (α _{min ,} α _max ) and the minimum and maximum propagation angles (θ _{min ,} θ _max ) of the constraining breakout break line, the range of the following equation (1) was adopted. _{W · tanθ min / (α max} · Vc) ≦ t 1 ≦ W · tanθ max / (α min · Vc) --- (1) [0012], for detecting the temperature change between the upper and lower thermocouples The predetermined time t ₂ is set in the range of the following equation (2) in consideration of the distance (H) between the upper and lower thermocouples. H / ( _αmax · Vc) ≦ t ₂ ≦ H / ( _αmin · Vc) --- (2) Further, the distance (W) between adjacent thermocouples illustrated in FIG. About 300 mm, the distance (H) between the upper and lower thermocouples is preferably about 100 to 500 mm. Here, in FIG. 2, W and H are equal pitches, but they are not necessarily equal pitches depending on design convenience. Further, according to the results of investigations by the inventors, the propagation angle (θ) and propagation speed ratio (α) of the fracture line in the vertical bending slab continuous casting machine are θ = 23 to 45, respectively.
°, α = about 0.5 to 0.9. Θ and α
However, it may be slightly different depending on individual continuous casting machines. Therefore, it is preferable to determine the optimum upper and lower limits in each continuous casting machine by analyzing past breakout marks. The casting speed (Vc) is usually 0.8 to 2.5.
Although it was about m / min, but when signs of breakout were predicted, the speed was reduced to about 0.3 to 0.5 m / min and the situation was observed. You can restore it back to its original speed later. If there is a time margin from the breakout prediction until the bottom end of the break line reaches the bottom end of the mold until the breakout occurs due to the mold shape, casting speed, and thermocouple spacing in the width direction. The accuracy can be further improved by setting the temperature increase at four points in the width direction as a condition for prediction. However, since the break line generally becomes more disturbed in the propagation angle and propagation speed as the distance from the center increases, it is not a good idea to increase it more than necessary. The reason why the breakout break line propagates at a speed slower than the casting speed is
This is because the breaking line breaks and propagates in the newly formed solidified shell for each oscillation. [Embodiment] Vertical bending type slab continuous casting machine (inner mold size, thickness:
When casting medium / low carbon steel and ultra-low carbon steel using 260 mm, width: 1900 mm), the method of the present invention and the conventional method (the method disclosed in Japanese Examined Patent Publication No. 1-26791) for about one month. A comparative experiment for predicting breakout was performed.
At that time, the actual number of detections, the number of undetected and the number of false detections,
This is shown in comparison with FIG. In the above experiment, 25 thermocouples are arranged in the upper and lower stages over the entire circumference of the mold, respectively. In the method of the present invention, the upper and lower two thermocouples are used.
On the other hand, the conventional method used the upper row of thermocouples to predict breakout according to each configuration. The distance (W) between adjacent thermocouples is 150 mm, the distance (H) between the upper and lower thermocouples is 200 mm, and the casting speed (Vc) is 1.0.
~ 2.0 m / min, also α _min = 0.5, α _max = 0.9, θ
_min = 23 ° and θ _max = 45 °. As shown in FIG. 3, according to the present invention, it is possible not only to significantly reduce false detections compared to the conventional method, but also to completely prevent the occurrence of undetected, and to predict breakouts with extremely high accuracy. It can be seen that breakout can be effectively prevented. Thus, according to the present invention, a sign of a breakout can be predicted with extremely high accuracy as compared with the prior art, and the occurrence of a breakout can be effectively prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a passage state (a) of a V-shaped break line, which is a break line of a restrictive breakout, and a temperature change (b) at each measurement point. FIG. 2 is a diagram showing the installation status of thermocouples. FIG. 3 is a graph comparing the actual number of detections, the number of undetections, and the number of false detections when predicting a breakout sign by the method of the present invention and the conventional method.

──────────────────────────────────────────────────── ─── Continuation of front page (56) References Japanese Patent Laid-Open No. 7-112259 (JP, A) Japanese Patent Laid-Open No. 1-143748 (JP, A) (58) Fields studied (Int.Cl. ⁷ , DB name) B22D 11/16 B22D 11/16 104 B22D 11/20

Claims (1)

(57) [Claims] [Claim 1] A plurality of upper and lower two-stage thermocouples are arranged in the width direction with respect to a continuous casting mold, and the upper three adjacent thermocouples are adjacent to each other. A sudden change in temperature is detected within the time (t ₁ ) that satisfies the following equation (1), and the upper 3
Among the thermocouples at the point, the time (t) when the lower thermocouple directly under the thermocouple where the sudden temperature change is detected first satisfies the following equation (2)
₂ ) A method for preventing a constraining breakout in continuous casting, wherein the casting speed is reduced when a sudden change in temperature occurs. W · tanθ _min / (α _max · Vc) ≤ t ₁ ≤ W · tan θ _max / (α _min · Vc) --- (1) H / (α _max · Vc) ≤ t ₂ ≤ H / (α _min・ Vc) --- (2) where W: distance between adjacent thermocouples (mm) H: distance between upper and lower thermocouples (mm) Vc: casting speed (m / min) α _{min ,} α _max : Minimum and maximum propagation speed ratio of constraining breakout break line to casting speed θ _{min ,} θ _max : Minimum constraining breakout break line,
Maximum propagation angle (°)