KR20090071221A - Apparatus and method for predicting clogging of submerged nozzle - Google Patents

Abstract

A prediction method of the nozzle clogging and a device thereof are provided to prevent the clogging and blow hole defect of the clogged nozzle. A prediction device of the nozzle clogging comprises: a vibration measuring unit(4) consecutively measuring the vibration of a clogged nozzle(3); a signal converter(5) converting a vibratory signal measured in the vibration measuring unit into a frequency signal; and a clogging detection unit(6). The vibration measuring unit is separately placed from the clogged nozzle surface and measures the vibration of the clogged nozzle surface. The clogging detection unit receives the frequency signal from the signal converter in order to calculate the thickness of the clogged nozzle.

Description

Apparatus and Method for predicting clogging of submerged nozzle}

The present invention relates to a method and apparatus for predicting clogging of an immersion nozzle in a continuous casting process, and more particularly, to a method and apparatus for accurately predicting a clogging amount of a nozzle by measuring vibration of an immersion nozzle and using its frequency change characteristic. It is about.

In general, the continuous casting process is a process of continuously casting liquid molten steel into a solid solid without any defect, and more specifically, a process in which molten steel of a ladle is transferred to a mold through a tundish and cast into a slab form. Proceeds to. In a continuous casting process, a submerged nozzle serves as a travel path through which molten steel is fed from the tundish to the mold. The immersion nozzle transfers the molten steel from the tundish to the mold in the state of being immersed in the molten steel in the mold in order to prevent oxidation and scattering of the molten steel generated when the molten steel is poured directly from the tundish into the mold. These immersion nozzles are made of refractory materials that can withstand high temperatures since they convey high temperature molten steel.

The immersion nozzle disposed between the tundish and the mold has a nozzle clogging phenomenon in which the nozzle inner diameter through which the molten steel passes decreases due to deoxidized inclusions mixed in the molten steel or an oxide formed by the refractory of the immersion nozzle and the molten steel. When the nozzle clogging occurs, the flow of molten steel is not constant, the height of the molten steel in the mold is unstable and the change in the hot water surface adversely affects the quality of the continuous cast product. In addition, the nozzle may be clogged, causing drift, and the mold flux may be mixed into the molten steel, thereby degrading the cleanliness of the molten steel. Moreover, when a part of the clogging substance (inclusion or oxide) adhering to the inner wall of the immersion nozzle falls, the part separated is mixed in the molten steel to worsen the cleanliness of the molten steel. If the nozzle is clogged, the casting process may be interrupted.

An inert gas blowing method is used as a method for preventing the nozzle clogging as described above. The inert gas blowing method is to inert an inert gas such as argon into the immersion nozzle and adhere to the nozzle inner wall to remove the clogging material. However, the gas blown into the immersion nozzle or the upper nozzle is discharged out of the molten steel in the continuous casting process, there is a problem causing a bubble defect when the inert gas is blown in a larger amount than necessary.

In order to remove the nozzle clogging material with an appropriate amount of inert gas at the appropriate time, it is necessary to detect the blockage of the immersion nozzle. As a method of detecting the immersion nozzle clogging, there is a detection method through the opening ratio of the sliding gate during the continuous casting process, and a method through the vibration obtained by the operator's touch by touching the iron rod on the wall of the immersion nozzle. However, the method of detecting the degree of blockage of the immersion nozzle according to the opening degree of the gate of the slide lamp is difficult to detect the blockage of the immersion nozzle until the inside of the nozzle is blocked about 50% or more. The way in which the operator touches the iron rod to detect vibrations with the touch of the hand has the limitation that the variation between the operators and the lack of accuracy and the real-time online measurement are difficult.

The present invention has been made in view of the above-described problems of the prior art, and the present invention has been made to solve the problem. By measuring the vibration of the immersion nozzle and using its frequency change characteristic, the immersion nozzle can be accurately predicted in real time in real time It provides a method and apparatus.

According to an aspect of the present invention, a method of predicting clogging of an immersion nozzle includes continuously measuring vibration of a surface of a immersion nozzle for injection of molten steel from a tundish into a mold during continuous casting; Converting the measured vibration signal into a frequency signal; Obtaining, from the converted frequency signal, a duration that lasts in a frequency state that is less than or equal to a persistence frequency that is decreased at an initial frequency and lasts for a predetermined time; And calculating a clogging thickness of the immersion nozzle from the obtained duration using a predetermined experimental correlation between the duration and the clogging thickness of the immersion nozzle.

According to an embodiment of the present invention, in the step of calculating the clogging thickness of the immersion nozzle, using the correlation between the following duration T and the clogging thickness t of the immersion nozzle, The clogging thickness can be calculated.

If T ≥ b / a, t = aT-b

T = 0 for 0 ≤ T ≤ b / a

Here, a and b are constants greater than 0 and are experimental constants that vary depending on the length, thickness, and material of the immersion nozzle.

According to an embodiment of the present invention, the vibration measuring step of the immersion nozzle surface may be performed using a non-contact vibration measuring device spaced apart from the immersion nozzle surface. The converting the measured vibration signal into a frequency signal may include converting the measured vibration signal into a Fast Fourier Trasformation (FFT).

An apparatus for predicting the blockage of an immersion nozzle according to another aspect of the present invention is a device for predicting a blockage thickness of an immersion nozzle for injection of molten steel from a tundish into a mold during continuous casting, wherein the vibration of the surface of the immersion nozzle is continuously measured. Vibration measuring device for doing; A signal converter for converting the vibration signal measured by the vibration meter into a frequency signal; And receiving a frequency signal from the signal converter to obtain a duration that is reduced at an initial frequency and is maintained at a frequency that is less than or equal to a sustained frequency that is constant for a predetermined time, and establishes a predetermined experimental correlation between the duration and the blockage thickness of the immersion nozzle. And a blockage amount calculation unit configured to calculate a blockage thickness of the immersion nozzle from the obtained duration.

The vibration measuring device may be spaced apart from the immersion nozzle surface to measure the vibration of the immersion nozzle surface in a non-contact manner.

According to the present invention, it is possible to accurately and quantitatively predict the nozzle clogging thickness by measuring the vibration of the immersion nozzle. Accordingly, the amount of inert gas introduced into the immersion nozzle can be appropriately adjusted immediately, and the clogging phenomenon and the bubble defect of the immersion nozzle can be prevented in advance.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

1 is a view schematically showing an immersion nozzle prediction apparatus according to an embodiment of the present invention. In the continuous casting process, the molten steel contained in the tundish 1 is injected into the mold through the immersion nozzle 3. The molten steel flow to the immersion nozzle can be opened and closed by the sliding operation of the sliding gate connected to the cylinder.

Referring to FIG. 1, the immersion nozzle predicting apparatus includes a vibration measuring device 4, a signal converter 5, and a blockage calculating unit 6. Preferably, in order to continuously measure the vibration of the immersion nozzle 3 surface, the non-contact vibration measuring device 4 equipped with a laser sensor, an ultrasonic sensor, etc. is used and spaced apart from the immersion nozzle 3 surface. Since the temperature of the environment surrounding the immersion nozzle 3 is very high, the vibration measuring device 3 cools it with coolant or the like.

When molten steel starts to flow into the immersion nozzle 3 at the beginning of the continuous casting process, vibration occurs in the immersion nozzle 3. At this time, the vibration measuring device 4 measures the vibration of the surface of the immersion nozzle 3 during continuous casting to generate a vibration signal (see FIG. 3).

The signal converter 5 converts the vibration signal measured by the vibration meter 4 into a frequency signal. For example, a signal converter for generating an FFT converted signal (see FIG. 4) by converting the vibration signal of the vibration measuring device 4 into an FFT (Fast Fourier Transformaton) may be used. Through this frequency signal it is possible to know the frequency change characteristics.

Usually, the thickness of the nozzle clogging layer (nozzle clogging thickness) becomes thicker as the casting time elapses, and thus the vibration frequency of the nozzle is lowered. In the continuous casting process, the vibration frequency of the immersion nozzle 3 gradually decreases at the initial frequency fi and starts to become clogged, and thus has a characteristic that the vibration frequency of the immersion nozzle 3 lasts for a certain time at a specific sustain frequency fr. Here, the initial frequency (fi) and the reduced persistence frequency (fr) may vary depending on the length, thickness, material, etc. of the immersion nozzle (3). In the vibration frequency characteristic example of the immersion nozzle shown in FIG. 5, the initial frequency fi is 25 Hz, and the reduced persistence frequency fr is 20 Hz.

The inventors have found that the duration T of the frequency state below the reduced sustain frequency fr described above (including the sustain frequency) correlates with the plugging thickness t of the immersion nozzle. In particular, the plugging thickness (t) of the immersion nozzle increases linearly with the duration that lasts below the sustaining frequency (fr), and the nozzle plugging thickness (t) is substantially until a certain threshold time is reached after the start of casting. Is 0 and increases linearly with the duration thereafter (see FIG. 7).

Therefore, when the immersion nozzle plugging thickness t becomes greater than zero beyond the threshold time, the duration T and the duration T below the sustaining frequency and the plugging thickness t of the immersion nozzle are expressed by the following equation. Can be expressed as:

t = aT-b (T ≥ b / a)

Here, a and b are constants greater than 0 and are experimental constants that vary depending on the length, thickness, and material of the immersion nozzle.

Since the threshold time at which the nozzle clogging thickness starts to occur substantially can be obtained from a T value of t = 0 in the above equation, the threshold time can be set to b / a. Therefore, if the duration below the sustain frequency is greater than or equal to 0 and less than or equal to b / a (0 ≦ T ≦ b / a), it can be expected that the nozzle clogging thickness is substantially zero.

t = 0 (0 ≤ T ≤ b / a)

Based on this experimental fact, it is possible to experimentally derive a linear equation of the plugging thickness (t) and the duration (T) below the reduced persistence frequency (fr), and by setting up this experimental linear correlation, the plugging of the immersion nozzle The thickness can be accurately predicted.

The blockage calculator 6 is connected to the signal converter 6 to receive the frequency signal converted by the signal converter 6. The blockage calculation unit 6 obtains, from the frequency signal received from the signal converter 6, the duration To which continues in the frequency state which is less than or equal to the duration frequency fr, and the duration variable T and the immersion. Using a predetermined experimental correlation (particularly the above-described linear equation) between the clogging thickness parameters t of the nozzles, the clogging thickness of the immersion nozzle can be calculated in real time from the obtained duration To.

2 is a flowchart for explaining an immersion nozzle prediction method according to an embodiment of the present invention.

1 and 2, first, the vibration of the surface of the immersion nozzle 3 is continuously measured using the non-contact vibration measuring device 4 equipped with a laser sensor or the like (S210). Thereafter, the vibration signal of the immersion nozzle 3 is converted into a frequency signal by the signal converter 5 (S220). For example, the FFT conversion signal can be obtained by performing FFT conversion on the vibration signal of the immersion nozzle 3.

Then, the blockage calculation unit 6 obtains the duration To lasted in the frequency state which is less than or equal to the sustain frequency fr from the converted frequency signal (S230). Subsequently, the blockage calculation unit 6 uses the predetermined experimental correlation equation (t = aT−b) between the above-described duration (variable T) and the blockage thickness (variable t), thereby obtaining the obtained duration (To). ) The clogging thickness of the nozzle is calculated (S240). That is, when the obtained duration is To, the calculated nozzle clogging thickness is a × To−b (where To ≧ b / a). When calculating the nozzle clogging thickness, it can be said that there is no substantial clogging thickness until the critical time (b / a). Therefore, when the acquired duration time (To) is 0 ≦ To ≦ b / a, the clogging thickness of the immersion nozzle is It is expected to be substantially zero.

(Example)

As an example of the method of predicting the immersion nozzle clogging thickness described above, the inventors obtained the vibration signal and the FFT conversion signal as shown in FIGS. 3 and 4 after measuring the surface vibration of the immersion nozzle with a laser sensor (initial frequency (fi)). Is 25 Hz, and the reduced sustain frequency (fr) is represented by 20 Hz). 5 is a graph of frequency vs. time according to the FFT signal. As shown in FIG. 6, after the end of the casting, the immersion nozzles were discarded and the clogging thicknesses were measured.

From the data in Table 1, a scatter plot of the actual clogging thickness and duration below the sustain frequency fr as shown in FIG. 7 can be obtained. From the scatter plot data, a linear correlation between the blockage thickness (t) and the duration (T) was obtained as in the following equation.

t (mm) = 0.0028171 × T (sec)-8.62157

The above correlation can be effectively applied to immersion nozzles of the same family in the foundry. When the casting equipment is changed and the length, thickness, material, etc. of the immersion nozzle are changed, a linear correlation with respect to the changed immersion nozzle is derived through the above-described method.

The present invention is not limited to the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims, and that various modifications can be made without departing from the spirit of the invention described in the claims. It will be apparent to one of ordinary skill in the art.

1 is a schematic diagram showing an installation state of an immersion nozzle prediction apparatus for executing an immersion nozzle prediction method according to an embodiment of the present invention.

2 is a flowchart for explaining an immersion nozzle prediction method according to an embodiment of the present invention.

3 is a graph showing a vibration signal obtained according to an embodiment of the present invention.

4 is a graph showing an FFT transform frequency signal obtained by fast Fourier transform (FFT) transform the vibration signal of FIG.

5 is a graph showing a change in the vibration frequency of the immersion nozzle with time.

Figure 6 is a photograph showing a cross section of the immersion nozzle and the blocked state.

7 is a scatter plot of the actual clogging thickness of a immersion nozzle and a duration of 20 Hz.

<Description of the symbols for the main parts of the drawings>

1: tundish 2: sliding gate

3: immersion nozzle 4: vibration measuring instrument

5: signal converter 6: blockage calculator

11: cylinder

Claims (6)

Continuously measuring vibration of the surface of the deposition nozzle for injection of molten steel from the tundish into the mold during continuous casting; Converting the measured vibration signal into a frequency signal; Obtaining, from the converted frequency signal, a duration that lasts in a frequency state that is less than or equal to a persistence frequency that is decreased at an initial frequency and lasts for a predetermined time; And Calculating a blockage thickness of the immersion nozzle from the obtained duration using a predetermined experimental correlation between the duration and the blockage thickness of the immersion nozzle. The method of claim 1, In the step of calculating the blockage thickness of the immersion nozzle, the blockage thickness of the immersion nozzle is calculated from the obtained duration using the correlation between the following duration T and the blockage thickness t of the immersion nozzle. To predict the blockage of the immersion nozzle If T ≥ b / a, t = aT-b T = 0 for 0 ≤ T ≤ b / a Here, a and b are constants greater than 0, which are experimental constants depending on the length, thickness, and material of the immersion nozzle. The method of claim 1, The vibration measuring step of the immersion nozzle surface, the method of predicting the clogging of the immersion nozzle, characterized in that performed using a non-contact vibration measuring device disposed spaced apart from the immersion nozzle surface. The method of claim 1, The converting of the measured vibration signal into a frequency signal, FFT conversion of the measured vibration signal comprising the immersion nozzle clogging prediction method. An apparatus for predicting the blockage thickness of an immersion nozzle for injection of molten steel from a tundish into a mold during continuous casting, Vibration measuring device for continuously measuring the vibration of the immersion nozzle surface; A signal converter for converting the vibration signal measured by the vibration meter into a frequency signal; And Receiving a frequency signal from the signal converter, obtaining a duration that is reduced to an initial frequency and is maintained at a frequency that is less than or equal to a sustained frequency that is constant for a certain time, and uses a predetermined experimental correlation between the duration and the clogging thickness of the immersion nozzle. And a blockage calculation unit for calculating a blockage thickness of the immersion nozzle from the obtained duration. The method of claim 5, The vibration measuring device is spaced apart from the surface of the immersion nozzle, it is non-contact measuring the vibration of the immersion nozzle surface, characterized in that the immersion nozzle clogging prediction apparatus.

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