KR100965975B1 - The method on the prediction the falling of clogging material in the submerged entry nozzle and operation method of finishing line at continuous casting - Google Patents

Abstract

The present invention relates to the detection of dropping off of a clogging substance in a continuous casting immersion nozzle and a method for correcting operation using the same. In the continuous casting process of steel, the vibration characteristics of the immersion nozzle generated when the deposit inside the immersion nozzle is dropped. Continuous casting of steel by measuring and predicting the degree of dropping of deposits in the immersion nozzle and reducing the interfacial surface defects by increasing the number of scarfing treatments in the performance correction based on the maximum dropout index obtained for each slab. By measuring the vibration characteristics generated by the molten steel flowing in the immersion nozzle in the process, the dropping of the adhesion layer inside the immersion nozzle is predicted, and the correction process is performed based on this, thereby reducing the interfacial surface defect of the rolled product. There is a characteristic.

Immersion nozzle, inner layer, acceleration sensor, dropout index

Description

Drop detection of clogging material in immersion nozzles for continuous casting and operation of reclamation using the same {the method on the prediction the falling of clogging material in the submerged entry nozzle and operation method of finishing line at continuous casting}

1 is a block diagram of a device according to the present invention.

2 is a frequency analysis graph of the vibration signal according to the present invention.

3 is a graph showing the relationship between the dropout index of the present invention and the dropping time of deposits in the immersion nozzle.

4 is a graph showing the relationship between the incidence of interpositional surface defects according to the maximum dropping index for each cast.

5 is a graph showing the relationship between the steelmaking defect rate according to the average dropping index for each cast.

Figure 6 is a graph showing the change in the incidence of interpositional surface defects according to the performance correction scarping of the present invention.

<< Explanation of symbols for main part of drawing >>

1: Tundish 2: Mold

3: Tundish Iron Peel 4: Well Block                 

5: sliding gate 6: flow meter

7: upper nozzle 8: laser Doppler acceleration sensor

9: flow control valve 10: flow meter

11 pressure gauge 12 gas supply pipe

13: laser beam 21: low odor gas control calculator

22: acceleration sensor computing device 23: a computer (Computer)

The present invention relates to detection of dropout of a clogging substance in a continuous casting immersion nozzle and a method for correcting operation using the same.

In particular, the present invention measures the vibration characteristics of a submerged entry nozzle (SEN) for supplying molten steel of a tundish into a mold in a continuous casting process of the steel, by using it to the immersion nozzle wall surface during casting Detects whether the clogged material is dropped and predicts the amount of impurities (nonmetallic inclusions) mixed in the cast steel.In the case where a large amount of impurity is mixed above a specific value, a performance correction process is performed to generate an interference generated in the cold rolled coil. It relates to a method of minimizing the occurrence of physical defects (board scab).

In general, the continuous casting process of steel refers to a process of casting molten steel of a ladle into a mold through a tundish and casting it into a slab form. In this process, the immersion nozzle serves to supply molten steel from the tundish to the mold. In order to prevent the oxidation and scattering of molten steel that may occur when the molten steel of the tundish is poured directly into the mold, the immersion nozzle transfers molten steel in the molten steel in the mold. It is a necessary equipment. This immersion nozzle is made of refractory because it carries out the transfer of hot molten steel.

Such an immersion nozzle is a phenomenon in which the internal diameter of the nozzle decreases due to the oxide formed by the attachment of the deoxidant inclusions suspended in the molten steel or the reaction of the refractory and the molten steel in the immersion nozzle while the molten steel flows through the nozzle inner diameter. clogging). When the nozzle is clogged as described above, the flow of the molten metal is not constant, so fluctuation or drift of the height of the molten metal in the mold occurs, thereby causing mold plus or the like to enter the molten steel and deteriorate the cleanliness of the steel. . In addition, when a part of the clogging substance adhering to the inner wall of the immersion nozzle is dropped and mixed in the molten steel, this also acts as an impurity in the steel, deteriorating the cleanliness. When the clogging material is included in the cast slab as described above, it is drawn to the surface of the steel sheet of the inclusions in the rolling process to generate inclusion defects (linear scab). In the case of such a defect, the value as a product decreases and cannot be sold, and in severe cases, it may be disposed of as scrap.

In order to prevent such a phenomenon, there is a need for a method capable of measuring a phenomenon in which adhesion material inside the immersion nozzle is dropped during the actual operation. However, it is practically impossible because the naked eye cannot observe that the substance attached to the inside of the refractory is lost. As a method of predicting the degree of blockage of the immersion nozzle in the present continuous casting process, it is detected by the opening rate of the sliding gate during casting and the vibration obtained by the operator contacting the iron rod on the wall of the immersion nozzle. There is a way. Therefore, there are various problems in predicting that the blocked substance has been dropped when the blockage of the immersion nozzle suddenly decreases. For example, the method of estimating the degree of blockage of the immersion nozzle through the ruled rate of the sliding gate shows that the ruled rate decreases due to the difference in the average ruled rate according to the casting speed (discharge rate of molten steel) (opening rate is reduced). It is difficult to determine that the blocking substance inside the immersion nozzle has been removed. In addition, the manual measurement method of the operators there is a difference in the degree of measurement according to the operators, there is a problem that it is not clear whether the internal attachment is missing because it is difficult to quantify the degree of blockage.

In general, when the casting process is difficult because the amount of the adhesion material inside the immersion nozzle in the playing process is difficult to perform the operation of forcibly dropping the attachment material by pressing the inside of the immersion nozzle with an iron rod. In such a case, impurities in the slab increase. Such cast steel is not immediately put into the rolling process, but the surface of the rolled product is subjected to a scarfing process (operation for removing the specific thickness by using an oxygen lance) in the rolling process to be introduced into the rolling process so that defects on the surface of the rolled product ( The operation which suppresses generation | occurrence | production of a shipboard cap etc.) is performed. In such a case, it is possible to know that the adhesion layer inside the immersion nozzle has been dropped through the sticking in the performance.However, if it is not possible to recognize the time when the attachment substance dropped during casting, such a correction operation cannot be performed. Because of this, it is difficult to secure the surface quality of the rolled product.

An object of the present invention created to solve the above problems is to measure the vibration characteristics of the immersion nozzle generated by the molten steel flowing inside the immersion nozzle in a continuous casting operation, the laser Doppler Vibrometer (Laser Doppler Vibrometer) By measuring the vibration of the immersion nozzle and analyzing its vibration characteristics to quantify the degree of clogging of the nozzle, and controlling the amount of inert gas introduced into the upper nozzle and the immersion nozzle using the blockage index obtained by the above method. The present invention provides a method for detecting dropout of a blockage material in a continuous casting immersion nozzle which can prevent the blockage of an immersion nozzle without the occurrence of a retardation nozzle, and a method of correcting a play using the same.

The object of the present invention, in the continuous casting process of steel, by measuring the vibration characteristics of the immersion nozzle generated when the deposit inside the immersion nozzle is dropped, predicts the degree of dropping of the deposit inside the immersion nozzle, and obtained by the unit It is possible to achieve by the detection method of dropping of the blockage material in the continuous casting immersion nozzle and the reclamation operation method using the same, which increases the number of scarfing treatments in reclamation based on the maximum dropout index. Can be.

In the method of measuring the dropping of deposits in the immersion nozzle of the present invention, the vibration signal of the immersion nozzle is collected at least 256 times per second using a laser Doppler acceleration sensor, and frequency analysis is performed to obtain a frequency signal obtained in the frequency band of 1 Hz to 7 Hz. By integrating and summing vibration values,

The dropout index is preferably determined by the above equation.

The method for adjusting the number of scarfing treatments in the performance correction of the present invention determines the number of scarfings according to the range of the maximum dropping index per slab, the maximum dropping index is "2 or less", "2 to 4.5", "4.5 To 6 " and " 6 or more " are preferably " zero times ", " once ", " twice " and " three times "

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example 1

Example 1 relates to the configuration of an apparatus for measuring the vibration signal of an immersion nozzle used in the present invention and the signal processing of a sensor. In order to measure the vibration of the immersion nozzle, the apparatus of the present invention analyzes vibration characteristics based on the data of the signal processor 22 and the signal processor in order to measure the vibration of the laser doppler acceleration sensor 8 and the acceleration sensor. And a control calculator 21 for controlling the flow rate of the inert gas blown in. The signal processor 22 is composed of an amplifier used for amplifying a vibration signal of an immersion nozzle obtained from an acceleration sensor and an A / D converter for digitizing the signal.

The laser Doppler Vibrometr (model number 8329) of the OMETRON laser doppler acceleration sensor used in the present invention was used, and the signal processing system used a pulse system of B & K. The components shown herein are not limited to products that represent the respective functions, but must be configured with the above products to obtain the effects of the present invention. That is, the effects of the present invention can be obtained through other products having the same function.

Vibration signals from the accelerometer are collected at speeds of up to 256 times per second. Data collected for a specific time (for one second) can be obtained by frequency analysis (FFT; Fast Fourier Transformation). The frequency analysis graph obtained by the above method is shown in FIG.

In general, when an object falls freely in a fluid, vibration occurs in a low frequency region (10 Hz or less). Therefore, in the present invention, using the peak value of the low frequency region obtained from the frequency analysis graph was converted into a drop-off index in the following manner.

Equation 1 is an integral of the vibration amount of 1Hz to 7Hz in Fig. 2, the FFT analysis of the collected data for 1 second, in which f (x) refers to the FFT analysis value for x Hertz (Hertz) .

Example 2

Example 2 relates to the correlation between the dropout index obtained in Example 1 and the dropping of the adhesion layer inside the actual immersion nozzle. Since the degree of detachment of the adhesion layer inside the immersion nozzle generated during actual casting cannot be measured, in Example 2, the adhesion layer inside the immersion nozzle is dropped by randomly pushing at the time when the adhesion layer is formed on the immersion nozzle. The correlation of dropout index at time point was investigated. Figure 3 shows the change in dropping index with casting time. As shown in the figure, it was found that the dropout index increased when the sticking was performed.

Example 3

Example 3 relates to the correlation between the dropout index and the quality of the cast steel. In Example 2, it is possible to determine whether the deposit inside the immersion nozzle is dropped through the dropping index, but it is not possible to provide information about the dropping index and the size of the dropping attachment. In addition, when the dropped attachment is mixed into the cast steel, the size thereof cannot be measured. In general, when a large amount of deposits are dropped, the quality of cast steel at that point is deteriorated, and there is a high possibility of inclusion surface defects in the rolled product. Therefore, in this embodiment, by examining the correlation between the dropout index and the quality of the rolled product, the quality effect of dropping of the deposit was examined in an indirect manner.

In Example 3, the dropout index according to casting time was used to classify the maximum dropping index for each slab by 0.5 units, and the probability of occurrence of interfacial surface defects of the slab in each case is illustrated in FIG. 4. As shown in the figure, when the maximum dropout index per cast was 2 or more, the probability of inclusion surface defects in the rolling coil was 1.1% or more. In addition, the change in the steelmaking defect rate for each cast according to the average dropping index in the cast having interstitial surface defects is shown in FIG. As shown in FIG. 5, as the average dropout index increases, the steelmaking defect rate also increases, and there is a correlation between the two factors as follows.

Steelmaking defect rate (%) = 2.47 × EXP (1.54 × average dropout index)

In other words, if the deposit is dropped inside the immersion nozzle, the larger the size, the greater the probability of inclusion surface defects.In the case of inclusion surface defects, the steelmaking defect rate changes according to the size of the average dropping index for each cast. Able to know.

Example 4

Example 4 relates to a method of performing a performance correction operation based on the correlation between the dropout index obtained in Examples 2 and 3 and the quality. In Example 4, as in Example 3, the occurrence rate of interfacial surface defects of the rolled product was examined by changing the number of scarpings in the performance correction to 1 to 3 based on the maximum dropping index of the cast unit.

As described above, the occurrence rate of interpositional surface defects of the rolled product in the case of scarfing and in the case of the performance correction is shown in FIG. 6. As shown in the figure, in the case of performing the scarfing in the performance correction, it was found that the incidence of intervening surface defects was reduced even at the same dropout index. However, the effect of reducing the surface defects according to the number of scarfing appears differently depending on the range of the maximum dropout index. In other words, when the maximum dropout index is 2 or less, there is almost no difference in the surface defect occurrence rate according to the number of scarfings, and in the region where the maximum dropout index is 2 to 4.5, the effect of reducing the defect occurrence rate is reduced even if only one scarfing is performed. It can be seen, but the reduction effect is insignificant when the number of scarfing increases. On the other hand, in the case of the maximum dropout index of 4.5 to 6, the occurrence of interfering surface defects decreases when the number of scarfings is two or more times, and in the case of the maximum dropout index of six or more, three scarfings are performed. In this case, the effect of reducing the defect rate could be seen.

As shown in FIG. 6, as the number of scarfing treatments increases, inclusion surface defects in the rolled product are reduced. However, there is a limit to randomly increasing the number of scarfing to achieve this effect. In other words, in the case of scarfing, the weight of the slabs is reduced by removing the surface of the slab, thereby reducing the error rate of obtaining the rolled product from the slab, and also by the time required for scarfing. An increase in the temperature load of the hot-rolling furnace and the stock of the cast steel may occur due to the cooling of the cast steel temperature. Therefore, in the present invention, based on the maximum dropout index for each cast, a method of treating the scarfing number of times as 0 to 3 is used as shown in Table 1 below. Here, Table 1 shows the number of scarfing in the performance correction according to the maximum dropout index for each cast.

Although the present invention described above is limited to one embodiment, the present invention is not limited thereto, and the present invention may be easily modified by those of ordinary skill in the art to which the present invention pertains. It is obvious that it belongs to the technical idea.

According to the present invention having the above configuration, by measuring the vibration characteristics generated by the molten steel flowing in the immersion nozzle in the continuous casting process of steel to predict the detachment of the adhesion layer inside the immersion nozzle, and based on this, performing a correction process, rolled products There is an advantage that can reduce the intervening surface defects.

Claims (5)

Collect the vibration signal of the immersion nozzle at least 256 times per second, and integrate the frequency signal obtained in the frequency band of 1Hz to 7Hz and add the vibration values according to the following formula to determine the degree of dropping of the attachment to the cast steel inside the immersion nozzle in units of 1 second. Predicting; And

Reducing intervening surface defects by adjusting the number of scarfing treatments in the performance correction based on the maximum value of the dropout indexes over a period of time. Drop detection of the clogging material in the continuous casting immersion nozzle comprising a and a correction operation method using the same. (Where f (x) is the frequency analysis for x Hz) delete The method of claim 1, wherein the number of scarfing treatment, Dropping detection of the clogging material in the continuous casting immersion nozzle, characterized in that it is carried out 0 times when the maximum value of the dropout index is 2 or less, and the performance correction operation method using the same. The method of claim 1, wherein the number of scarfing treatment, Dropping detection of the clogging material in the continuous casting immersion nozzle, characterized in that performed once when the maximum value of the dropout index is 2 to 4.5, and the performance correction operation method using the same. The method of claim 1, wherein the number of scarfing treatment, Dropping detection of the clogging material in the continuous casting immersion nozzle, characterized in that performed twice when the maximum value of the drop-out index is 4.5 to 6, and the performance correction operation method using the same.

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