JP2001162358A - Method for preventing restrictive breakout in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent development of breakout by predicting a sign of the breakout with a remarkable accuracy in comparison with the conventional method. SOLUTION: In thermocouple lines disposed in two steps at the upper and the lower parts in the width direction of a mold for continuous casting, when detecting rapid change in the temperature within a time (t1) satisfying the following formula (1) between the mutually adjacent thermocouples in the adjacent three points of the thermocouples at the upper step and also, when developing the rapid change of the temperature within a time (t2) satisfying the following formula (2) to the lower step thermocouple just below the thermocouple firstly detecting the rapid change in the upper step three point thermocouples, the casting speed is reduced. W.tanθmin/(αmax.Vc)<=t1<=W.tanθmax/(αmin.Vc)...(1), H/(αmax.Vc)<=t2<=H/(αmin.Vc)...(2). Wherein, W: The distance (mm) between the mutually adjacent thermocouples, H: The distance (mm) between the thermocouples at the upper and the lower steps, Vc: Casting speed (m/min), αmin and αmax: The minimum and the maximum propagation speed rates to the casting speed of the above break line respectively and θmin and θmax: The minimum and the maximum propagation angles ( deg.) in the above break line, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing restraint breakout in continuous casting, which can accurately predict restraint breakout during continuous casting and effectively prevent the occurrence of breakout. Things.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting a restraint breakout, a plurality of thermocouples are arranged in a width direction and a vertical direction in a mold as disclosed in Japanese Patent Publication No. 5-75502, for example. The temperature of any one of the upper thermocouples and the temperature of any thermocouple adjacent to the thermocouple rises to 5 ° C. or more with respect to the peak value of each of the previous measurements, and There is known a method of predicting a breakout when a temperature of the lower thermocouple rises by 5 ° C. or more within 10 seconds with respect to the previously measured peak value of the lower thermocouple.

[0003] In addition, Japanese Patent Publication No. 1-26791 discloses that the temperature in the width direction of a continuous casting mold is detected at predetermined measurement positions, and the detected temperatures at these measurement positions are compared with each other. A method has been proposed in which a sign of breakout is predicted by a sudden change in temperature, and the casting speed is adjusted based on this to prevent breakout.

[0004]

However, the method disclosed in Japanese Patent Publication No. 5-75502 described above only considers the temperature rise of the thermocouple adjacent to the upper stage, and thus has a typical constraint breakout. The V-shaped break line 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 (upper And lower thermocouple distance / (α ×
Casting speed) Here, since α = 0.5 to 0.9), it is predicted as a breakout, but is incorrectly detected without any abnormal occurrence, or undetected, which cannot be predicted even though a breakout has occurred. But it happens frequently.

In the method disclosed in Japanese Patent Publication No. 1-26791, the temperature is measured only by thermocouples arranged in a line in the width direction of the mold. The character-shaped break line could not be accurately identified, and as a result, accurate prediction of breakout could not be expected.

The present invention advantageously solves the above-mentioned problem, and can predict the sign of a breakout much more accurately than in the past, and effectively prevent the occurrence of a breakout. An object of the present invention is to propose a method for preventing restraint breakout in continuous casting.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted a number of investigations on the mode of occurrence of the restrictive breakout in order to achieve the above object. And found that the propagation speed was lower than the casting speed. The present invention
It was developed based on the above findings.

That is, according to the present invention, a plurality of upper and lower two-stage thermocouples are arranged in a width direction with respect to a continuous casting mold, and the following three thermocouples of the upper stage are disposed between adjacent thermocouples.
A rapid change in temperature is detected within the time (t ₁ ) satisfying the expression (1), and a lower thermocouple immediately below the thermocouple for which a sudden change in temperature is first detected among the above three thermocouples at the upper stage. Is below
This is a method for preventing a constrained breakout in continuous casting, characterized by reducing the casting speed when a sudden change in temperature occurs within a time (t ₂ ) satisfying the expression (2). Note W tan θ _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 : ratio of minimum and maximum propagation speed to the casting speed of the constraint breakout break line θ _{min ,} θ _max : minimum of the constraint breakout break line,
Maximum propagation angle (°) Here, the propagation angle of the restrictive breakout break line refers to the angle between the break line and the horizontal direction.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. In the present invention, the reason for setting three points for detecting the temperature change in the upper stage is that in order to recognize the passage of the V-shaped break line which is the break line of the restrictive breakout, as shown in FIG. This is because temperature measurement at at least three points is required. That is, when a V-shaped break line occurs, a sudden change in temperature (specifically, a sharp rise in temperature) occurs at the position A in this example, and then both sides thereof (B and C). In the position (a), the temperature rises after a lapse of a predetermined time, and inevitably, the temperature also rises in the lower position immediately below A, that is, the position a. Therefore, in the present invention, the temperature which is considered to pass through the V-shaped break line, which is the break line of the restrictive 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 immediately below the thermocouple for which the temperature change is first detected among the three thermocouples in the upper stage produces a similar temperature change within a predetermined time, a break occurs. The casting speed is reduced as a sign of an out.

[0010] In this regard, even if the solidified shell is broken,
After the temperature rise is detected at the position A, the temperature rise does not occur within a predetermined time at the position B or C, or the temperature rise is detected at the position a at the lower stage where the temperature rise is detected at the positions B and C. If not, the breakout is not reached and the casting speed is not adjusted. In fact, in such a case, the breakage is subsequently repaired and it is unlikely that a breakout will occur. Further, according to the above-described method, it is possible to make an accurate determination on a temperature change due to disturbance in the same manner, and erroneous detection is significantly reduced.

Here, as the predetermined time t ₁ for detecting a temperature change between the upper thermocouples, the minimum (the distance (W) between the thermocouples, the casting speed (Vc), the casting speed of the restraining breakout break line relative to the casting speed) is set. In consideration of the maximum propagation speed ratio (α _{min ,} α _max ) and the minimum and maximum propagation angles (θ _{min ,} θ _max ) of the restrictive breakout breaking line, the range of the following equation (1) is set. W · tanθ _min / (α _max · Vc) ≤ t ₁ ≤ W · tan θ _max / (α _min · Vc) --- (1)

Further, as the predetermined time t ₂ for detecting a temperature change between the upper and lower thermocouples, taking into account the distance (H) between the upper and lower thermocouples, the following equation (2) is used. Range. H / (α _max · Vc) ≦ t ₂ ≦ H / (α _min · Vc) --- (2)

Further, as shown in FIG. 2, the distance (W) between the adjacent thermocouples is about 50 to 300 mm, and the distance (H) between the upper thermocouple and the lower thermocouple is about 100 to 500 mm. Is preferred. Here, in FIG. 2, W and H are equal pitches, but they need not necessarily be equal pitches depending on design convenience. According to the results of the investigations by the inventors, the propagation angle (θ) and the propagation speed ratio (α) of the breaking line in the vertical bending type slab continuous caster are θ = 23 to 45, respectively.
°, α = about 0.5 to 0.9. Note that θ and α
May vary slightly depending on the individual continuous casting machine. 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.
m / min, but if signs of breakout were predicted, the speed was reduced to about 0.3-0.5 m / min to see the situation, after which it was determined that the damage to the solidified shell had been repaired Later, you can restore the original speed.

In the case where there is a margin of time from the prediction of breakout to the time when the lowermost end of the breaking line reaches the lower end of the mold and reaches the breakout due to the prediction of the breakout due to the shape of the mold, the casting speed, and the thermocouple interval in the width direction. By setting the temperature rise at four points in the width direction as a condition for prediction, the accuracy can be further improved. However, the more the distance from the center of the break line is, the more the propagation angle and the propagation velocity are disturbed. Therefore, it is not advisable to increase the break line more than necessary. Also, the reason that the breakout break line propagates at a speed lower than the casting speed is
This is because the breaking line breaks and propagates in the newly formed solidified shell with each oscillation.

[0016]

[Example] Vertical bending type continuous slab casting machine (mold inner dimensions, thickness:
The method of the present invention and the conventional method (method disclosed in Japanese Patent Publication No. 1-26791) were applied for about one month when casting medium- and low-carbon steels and ultra-low carbon steels using 260 mm and a width of 1900 mm. A comparative experiment of breakout prediction was performed according to the following.
At that time, the actual detected count, undetected count and false detected count are
This is shown in comparison with FIG. In the above experiment, the upper and lower thermocouples were arranged 25 each over the entire circumference of the mold. In the method of the present invention, the upper and lower two thermocouples were used.
On the other hand, in the conventional method, breakout was predicted according to each configuration using thermocouples in the upper row. 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, 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, not only the erroneous detection can be remarkably reduced as compared with the conventional method, but also the occurrence of the undetected state can be completely prevented, and the breakout can be predicted with extremely high accuracy. It can be seen that the occurrence of breakout can be effectively prevented.

[0018]

As described above, according to the present invention, it is possible to predict the sign of breakout with extremely high accuracy as compared with the related art, and it is possible to effectively prevent the occurrence of breakout.

[Brief description of the drawings]

FIG. 1 is a diagram showing a passing 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 a setting state of a thermocouple.

FIG. 3 is a graph showing a comparison between the actual number of detections, the number of undetected detections, and the number of false detections when a sign of breakout is predicted by the method of the present invention and the conventional method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Sakai 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term (reference) 4E004 MC05 MC12

Claims (1)

[Claims] 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 following three formulas are satisfied between the three adjacent thermocouples in the upper stage. Abrupt change in temperature is detected within the time (t ₁ )
Of the thermocouples at the point, the lower thermocouple immediately below the thermocouple at which the sudden change in temperature was first detected satisfies the following equation (2) (t
₂ ) A method for preventing restraint breakout in continuous casting, wherein the casting speed is reduced when a sudden change in temperature occurs. Note W tan θ _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 : ratio of minimum and maximum propagation velocity to the casting speed of the constraint breakout break line θ _{min ,} θ _max : minimum of the constraint breakout break line,
Maximum propagation angle (°)