JP5458876B2 - Casting slab weight control method - Google Patents

Description

  The present invention relates to a cast slab weight control method for cutting a predetermined weight cast slab from a cast strand cast by continuous casting.

  The cutting length of the casting slab in continuous casting is determined according to the requirements of the lower process, but there is also variation in the weight of the casting slab or casting strand even in continuous casting. Generally, a margin that takes this into account is added. Cutting the line leads to a decrease in yield. Therefore, in Patent Document 1 below, the surface temperature of the cast strand is detected, and the cut length of the cast slab is corrected from the surface temperature and the actual cross-sectional shape of the cast strand.

Japanese Patent Publication No. 6-35034

However, in the casting slab cutting method described in Patent Document 1, the cutting length of the casting slab is only corrected based on the surface temperature of the casting strand. Variations are likely to occur.
The present invention has been made paying attention to the above-mentioned problems, and when cutting the cast slab to the target weight, the cast slab is cut using the crater end position having a high correlation with the average cross-sectional temperature of the cast strand. An object of the present invention is to provide a casting slab weight control method capable of suppressing weight variation by correcting the length.

In order to solve the above-mentioned problems, a cast slab weight control method according to the present invention is a method for controlling the weight of a cast slab obtained by cutting a cast strand cast by continuous casting, and includes a crater for a cast strand before cutting. Detect or estimate the end position, and correct the cutting length to achieve the target weight of the cast slab to be cut from the relationship between the detected or estimated crater end position and the cast strand weight per unit length determined in advance. The cast slab is cut with the corrected cutting length.
In the present invention, the slab before being cut is referred to as a cast strand, and the slab after being cut is referred to as a cast slab.

  Thus, according to the casting slab weight control method of the present invention, the crater end position is highly correlated with the cross-sectional average temperature at the cutting position of the cast strand, and the cross-sectional average temperature at the cutting position of the cast strand is equal to the cast strand per unit length. Since the correlation with the weight is high, the crater end position of the cast strand before cutting is detected or estimated, and the casting to be cut from the relationship between the detected or estimated crater end position and the previously determined cast strand weight per unit length Since the cutting length for achieving the target weight of the slab is corrected and the cast slab is cut with the corrected cutting length, the variation with respect to the target weight of the cut casting slab can be suppressed.

It is a schematic block diagram which shows one Embodiment of the continuous casting installation to which the casting slab weight control method of this invention was applied. It is explanatory drawing which shows the relationship between the cross-section average temperature in a crater end position and a torch (cutting) position. It is explanatory drawing which shows the relationship between the cross-sectional average temperature in a torch (cutting) position, and the average single weight of a cast strand. It is explanatory drawing which shows the relationship between a crater end position and the average single weight of a cast strand. It is explanatory drawing of the effect by the casting slab weight control method performed with the continuous casting installation of embodiment of FIG.

Next, an embodiment of the cast slab weight control method of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a continuous casting facility in which the casting slab weight control method of the present embodiment is implemented. The pig iron in the ladle 1 is fed to the tundish 3 via the refractory nozzle 2, and the pig iron in the tundish 3 is fed to the mold 5 via the refractory nozzle called the immersion nozzle 4. The mold 5 is vibrated so as not to be seized by a vibration device (not shown), and the cast strand 6 pulled out from the mold 5 is gradually drawn downward while being supported by the support roll 7. A secondary cooling zone (not shown) is formed in the vicinity of the support roll 7. In the secondary cooling zone, cooling water is sprayed from the spray nozzle in the form of a mist, thereby cooling the cast strand 6 from the outside. The cast strand 6 is cut into a cast slab 12 by the torch 8 after passing through the light pressure belt as necessary. The torch 8 is moved by the torch control device 9 according to the casting speed of the cast strand 6. In addition, the code | symbol 21 is a weighing machine which measures the weight of the cut casting slab 12. FIG.

  In the present embodiment, a transmitting transverse wave ultrasonic sensor 10 and a receiving transverse wave ultrasonic sensor 11 as crater end detection sensors for detecting a crater end in the cast strand 6 are arranged on the entrance side of the torch 8. Set up. Specifically, a plurality of pairs of transmission transverse wave electromagnetic ultrasonic sensors 10 and reception transverse wave electromagnetic ultrasonic sensors 11 sandwiching the cast strand 6 are arranged in the casting direction of the cast strand 6. The transmitting transverse wave electromagnetic ultrasonic sensor 10 and the receiving transverse wave electromagnetic ultrasonic sensor 11 are, for example, as described in Japanese Patent Application Laid-Open No. 2003-103351 previously proposed by the applicant of the present invention. It is suitable for detecting the position. As described in detail in the publication, the transverse wave of electromagnetic ultrasonic waves has a characteristic of not transmitting unless the inside of the cast strand 6 is solidified. By using this characteristic, the inside of the cast strand 6 is first solidified. Position, that is, the crater end position can be detected. That is, the transverse wave ultrasonic waves are transmitted from the transverse wave electromagnetic ultrasonic sensors 10 for transmission arranged in a plurality of pairs in the casting direction, and the position where the transverse wave electromagnetic ultrasonic waves can be received first by the receiving transverse wave electromagnetic ultrasonic sensor 11 is the crater. It will be the end position. Regarding the waveform, frequency, pulse width, etc. of the transverse wave of the electromagnetic ultrasonic wave, refer to the aforementioned patent publication. The number of crater end detection sensors is not limited to the above. For example, even one pair of crater end detection sensors can detect the crater end position, and it is preferable that a plurality of pairs are installed for more accurate crater end position detection.

  In the torch control device 9, the cutting position (cutting length) of the cast slab according to the crater end position detected by the crater end detection sensor comprising the transmitting transverse wave electromagnetic ultrasonic sensor 10 and the receiving transverse wave electromagnetic ultrasonic sensor 11. ) Is corrected. Incidentally, since the crater end position depends on the cooling rate of the cast strand, it can also be estimated from the continuous casting operation results such as the casting speed of the cast strand and the amount of secondary cooling water. In effect, the steel mill has a lot of data on continuous casting, so that the crater end position can be reasonably accurately estimated from these operational results. In addition, a combination with the above-described crater end position detection sensor is also possible. By doing so, the arrangement interval of the crater end position detection sensor is interpolated to detect or estimate the crater end position more accurately. Can do.

  Since the crater end is the final freezing point in the core of the cast strand, the crater end position depends on the cooling rate of the cast strand, more precisely the cooling rate and temperature distribution inside the cast strand. FIG. 2 shows the results of average cross-sectional temperatures at the crater end position and the torch position when the distance from the mold surface to the crater end is defined as the crater end position. The casting conditions are slab size: thickness 215 mm × width 2450 mm, casting speed: 0.75 to 0.86 m / min. As the crater end position is larger, that is, the farther the distance from directly under the mold is, the average cross-sectional temperature at the torch position is naturally higher. Both are highly correlated.

  A major cause of weight variation of the cast slab is that the amount of heat shrinkage of the cast strand at the time of cutting is unknown. That is, if the amount of heat shrinkage at the cutting position by the torch is large, the weight per unit length of the cast strand (hereinafter also referred to as single weight) is large, and if the heat shrinkage is small, the single weight of the cast strand is small. FIG. 3 shows the results of the average cross-sectional temperature at the torch position and the average unit weight of the cast strand. The lower the average cross-sectional temperature at the torch position, that is, the greater the amount of heat shrinkage at the cutting position, the higher the average single weight of the cast strand. Both are highly correlated.

  Therefore, the average unit weight of the cast strand can be obtained using the crater end position indicating the cooling performance of the cast strand. FIG. 4 shows the results of the crater end position of the cast strand and the average unit weight (torch position) of the cast strand. The closer the crater end position that appears as a result of cooling of the cast strand, the greater the average unit weight of the cast strand. Both are highly correlated.

  Therefore, in the torch control device 9, the crater end position detected by the crater end detection sensor composed of the transmitting transverse wave electromagnetic ultrasonic sensor 10 and the receiving transverse wave electromagnetic ultrasonic sensor 11, or estimated from other operation results. Alternatively, based on the crater end position detected or estimated from both, the average unit weight of the cast strand at the torch position is obtained, and the cutting length of the cast slab is calculated by dividing the target cast slab weight by this average unit weight. Correct and cut the cast slab with the corrected cutting length. Thereby, the weight of the cut cast slab can be brought close to the target weight, and variations in the slab weight can be reduced.

  FIG. 5 shows the results of the cast slab added weight before and after the correction of the cast slab cutting length according to the crater end position. The additional weight is a weight added to the casting slab in the continuous casting process as a margin with respect to the required weight from the lower process, and it is desirable that the additional weight ratio with respect to the required weight from the lower process is constant. FIG. 5A is a result of casting slab additional weight before the casting slab cutting length correction by the crater end position, and the casting slab target weight with a margin is divided by a weighing correction coefficient to obtain a cutting length. For example, at the start of casting, the weighing correction coefficient is input according to the operator's empirical rule. For example, the operator corrects the weighing correction coefficient in accordance with the weighing results of 3 to 4 cast slabs, and then the additional weight is targeted. This is an operation method in which the operator continuously adjusts the weighing correction coefficient so as to approach the value. On the other hand, FIG. 5b is a cast slab added weight result after the casting slab cutting length correction by the crater end position. Here, the cutting length correction is performed almost automatically by the torch control device 9.

  The target value of the added weight ratio of the cast slab described as a result is 1.7% of the required weight from the lower process. As is clear from the figure, the added weight ratio after correction is 1.92%, which is significantly reduced compared to the added weight ratio 2.32% before the casting slab cutting length correction by the crater end position. Yield is improved. In addition, the standard deviation is 0.24% after the correction, compared with 0.38% before the correction, and the weight variation of the cast slab is greatly reduced.

  Thus, in the cast slab weight control method of the present embodiment, the crater end position is an average of the cross-section at the cut position of the cast strand 6 in controlling the weight of the cast slab obtained by cutting the cast strand cast by continuous casting. Since the correlation with temperature is high and the cross-sectional average temperature at the cutting position of the cast strand 6 is highly correlated with the single weight of the cast strand, the crater end position of the cast strand 6 before cutting is detected or estimated, and the detected or estimated crater By correcting the cutting length to achieve the target weight of the casting slab to be cut from the relationship between the end position and the casting strand single weight obtained in advance, by cutting the casting slab with the corrected cutting length, Variation in the target weight of the cut casting slab 12 can be suppressed.

  1 is a ladle, 2 is a refractory nozzle, 3 is a tundish, 4 is an immersion nozzle, 5 is a mold, 6 is a cast strand, 7 is a support roll, 8 is a torch, 9 is a torch control device, 10 is a transverse wave for transmission Electromagnetic ultrasonic sensor, 11 is a receiving transverse wave electromagnetic ultrasonic sensor, and 12 is a weighing instrument.

Claims (1)

A method for controlling the weight of a cast slab obtained by cutting a cast strand cast by continuous casting, the relationship between the cross-sectional average temperature at the crater end position and the torch position, and the cross-sectional average temperature and unit at the torch position From the relationship between the cast strand weight per length and the relationship between the crater end position and the cast strand weight per unit length in advance, the crater end position of the cast strand before cutting is detected or estimated, and the detected or estimated crater correcting the cut length to achieve the target weight of the cast slab to be cut from the relationship between the cast strand by weight of the previously obtained per unit length and the end position, cut the cast slab in the corrected cut length A casting slab weight control method comprising:

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