JP5123692B2 - Sliding nozzle plate life evaluation method - Google Patents

Description

The present invention relates to a method for determining the life of a sliding nozzle plate that constitutes a sliding nozzle device installed at the bottom of a molten metal container such as a ladle or tundish used in a continuous casting facility.

Damage to the sliding nozzle plate used to control the flow rate of molten steel includes edge melting Q (see Fig. 9 (A)) where the edge of the nozzle hole melts at the time of injection, and sliding operation of the sliding nozzle plate. Stroke damage R (see FIG. 9 (B)), which damages the sliding surface of the plate, is broadly classified, but in addition to these, sliding caused by structural deterioration due to oxidation, excessive sliding of the plate, pulling in the metal, etc. There is a rough surface.

Since these damages progress every time they are reused, the sliding nozzle plate has a limited number of uses. Conventionally, the life of a sliding nozzle plate is determined by visual inspection of an operator. However, since the visual inspection is qualitative, depending on the experience and skill of the worker who performs the visual inspection, the determination result may vary greatly depending on the worker.

Therefore, in Patent Document 1, one or a plurality of measured values related to the size, temperature, pressure and / or force of the slide plug are compared with a target value or a target value range to determine whether the slide plug can be used continuously. A method has been proposed. Further, in Patent Document 2, a step of inputting the pouring time, the number of relative movements, the limit wear amount of the orifice lip, etc., into the storage unit, a step of inputting information on the ladle and the heat-resistant plate through the input unit, The process of collecting the pouring time into the ladle, the weight of the ladle at a certain point in time, the number of movements, the hydraulic pressure of the cylinder, the position of the cylinder end at a certain point, and the limit value in the storage unit for the collected or calculated value There has been proposed a method having a comparison step for comparing with.

JP 2005-536349 A JP 2006-528070 Gazette

However, Patent Document 1 and Patent Document 2 only describe a measurement value or a collected value compared with a target value or a limit value, and completely describe how the target value or limit value should be set for an evaluation item. Absent. Further, the correlation between the damage of the sliding nozzle plate and the measured or collected data is not clear, and there are many problems in terms of practicality.

The present invention has been made in view of such circumstances, and a sliding nozzle capable of quantitatively evaluating the degree of damage of the sliding nozzle plate with clear correlation between the damage of the sliding nozzle plate and the measured data. An object of the present invention is to provide a method for determining the life of a plate.

In order to achieve the above object, the present invention is a method for determining the life of a sliding nozzle plate comprising a fixed plate and a sliding plate that slides in close contact with the fixed plate, and is fixed to the bottom of a molten metal container. A vibration meter is installed on the fixed metal frame that holds the fixed plate and / or the open / close metal frame that can be opened and closed with respect to the fixed metal frame, and the sliding plate slides in the opening direction. The vibration area is measured with the vibrometer, the waveform area is obtained from the time history data of the measured vibration waveform, the waveform area is compared with a preset determination reference value, and the waveform area is set to the determination reference value. When it exceeds, the sliding nozzle plate is determined as a defective product.

Here, the “open direction” means that the molten steel flows from the nozzle hole of the fixed plate through the nozzle hole of the sliding plate from the state where the nozzle hole of the fixed plate is blocked by the sliding plate. The sliding direction when the plate slides. The opposite direction is referred to as the “closing direction”.
The slide metal frame that holds and slides the sliding plate is more likely to move meandering in the closing direction than in the opening direction. For this reason, in this invention, the vibration waveform at the time of a sliding plate sliding to an opening direction is used for the lifetime determination of the plate for sliding nozzles. Furthermore, in the present invention, in order to avoid the influence of noise as much as possible, a vibrometer is installed on a fixed metal frame and / or an open / close metal frame that does not slide.

As will be described later, the vibration amplitude when the sliding nozzle plate slides in the opening direction has a high correlation with the degree of damage of the sliding nozzle plate. For this reason, the lifetime of the sliding nozzle plate can be quantitatively evaluated by comparing the waveform area of the vibration waveform with the determination reference value.

In the sliding nozzle plate life determination method according to the present invention, if the determination reference value is B, the waveform area by the sliding nozzle plate without damage is A, and the safety factor is α, then B = α · A and It is good also as (alpha) = 1.4-2.0.

If α exceeds 2.0, it may be judged that a sliding nozzle plate that is severely damaged and cannot be used can be used, and if α is less than 1.4, the sliding nozzle can be reused with little damage. There is a risk of disabling the plate. As α increases, the safety decreases, and as α decreases, the cost increases. The above range is set in consideration of the balance between safety and cost.

In the sliding nozzle plate life determination method according to the present invention, the waveform area may be an area calculated from data obtained by performing a square moving average process after filtering the measured vibration waveform. Good.

When the sliding nozzle plate is damaged, vibrations in a specific frequency band are dominant. Therefore, in the present invention, the measured vibration waveform is filtered to obtain only the vibration waveform in a specific frequency band, thereby revealing the damage to the sliding nozzle plate. In order to clarify the pattern and tendency of the vibration waveform, the filtered vibration waveform is further subjected to the square moving average process so that the fluctuation of the vibration waveform is displayed smoothly.

The vibration waveform when the sliding plate constituting the sliding nozzle plate slides in the opening direction is highly correlated with the damage degree of the sliding nozzle plate, and the waveform area of the vibration waveform should be compared with the criterion value. Thus, the lifetime of the sliding nozzle plate can be quantitatively evaluated.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.

FIG. 1 is a schematic diagram of a sliding nozzle device 10 that uses a sliding nozzle plate life determination method according to an embodiment of the present invention. The following describes the case where the sliding nozzle plate is composed of two plates, an upper plate and a lower plate, but the upper plate (upper fixed plate), middle plate (sliding plate), and lower plate (lower fixed plate). The same applies to the case of comprising.

The sliding nozzle plate 11 has an upper plate 11u (fixed plate) in which a nozzle hole 12u connected to the upper nozzle 16 is formed, and a nozzle hole 12d connected to the lower nozzle 17, and is formed on the lower surface of the upper plate 11u. The lower plate 11d (sliding plate) slides in close contact with each other. The upper plate 11u is held by a fixed metal frame 13 fixed to the bottom of the molten metal container 20, and the lower plate 11d is disposed inside an open / close metal frame 15 provided to be openable and closable with respect to the fixed metal frame 13. The slide metal frame 14 is held. One end of the slide metal frame 14 is connected to a hydraulic cylinder 19 via an arm 18, and the hydraulic cylinder 19 is operated so that the slide metal frame 14 extends along the lower surface of the upper plate 11u while holding the lower plate 11d. Slide in one direction.

FIG. 2 shows the sliding nozzle device 10 with the opening / closing metal frame 15 opened as viewed from the bottom side of the molten metal container 20.
The upper plate 11 u in the fixed metal frame 13 is pressed so as not to move by a plate presser 22 attached to the tip of a plate fixing bolt 23 screwed into the fixed metal frame 13. A bracket 24 for fixing the fixed metal frame 13 to the molten metal container 20 is provided on the outer surface of the fixed metal frame 13, and a vibrometer 25 is installed on the bracket 24. As the vibrometer 25, an accelerometer, a speedometer, a displacement meter, or the like can be used.

FIG. 3 shows the sliding direction of the sliding nozzle plate 11. As shown in FIG. 3A, the nozzle hole 12d of the lower plate 11d is positioned directly below the nozzle hole 12u of the upper plate 11u from the state where the nozzle hole 12u of the upper plate 11u is blocked by the lower plate 11d. In addition, the sliding direction U when the lower plate 11d slides is referred to as “opening direction”. Further, as shown in FIG. 3B, the reverse direction S is referred to as a “closed direction”.
Compared to sliding in the opening direction U, sliding in the closing direction S is more likely to make the slide metal frame 14 meander. For this reason, when measuring the vibration of the sliding nozzle plate 11, the vibration waveform when the lower plate 11 d slides in the opening direction U is measured by the vibrometer 25.

The vibration waveform measured by the vibrometer 25 is subjected to filter processing, and a vibration waveform in a specific frequency band resulting from damage to the sliding nozzle plate 11 is extracted.
When performing the filtering process of the vibration waveform, it can be roughly divided into a method performed on the frequency axis and a method performed on the time axis.

First, the case where the vibration waveform filtering process is performed on the frequency axis will be described. In the following description, for convenience of description, discrete data and continuous data will be described without particular distinction.
The measured vibration waveform x (t) is Fourier transformed to be converted into frequency data X (f). Here, t is time and f is frequency. A frequency response function H (f) consisting only of a specific frequency band is introduced, and only a specific frequency band is extracted for the measured vibration waveform by equation (1). Y (f) obtained by the equation (1) is subjected to inverse Fourier transform and converted to time history data y (t) consisting of only a specific frequency band.

FIG. 4 shows an example of a frequency response function H (f) consisting only of a specific frequency band. The frequency response function is not the normal distribution filter shown in FIG. 4, but a band pass filter whose amplitude is constant over a specific frequency band, a filter having only an integral multiple of the fundamental frequency, or the like. Can be used.

Next, a case where the vibration waveform filtering process is performed on the time axis will be described.
If h (t) is a weight function obtained by performing inverse Fourier transform on a frequency response function H (f) consisting only of a specific frequency band, y (t) consisting only of a specific frequency band is a convolution expressed by equation (2). It can be calculated using integration.

In the expression (2), when x (t) and h (t) are defined in a finite section, x (t) and h (t) are handled as periodic functions.
Note that wavelet transform may be used as another method for performing filtering processing of the vibration waveform on the time axis. In this case, the wavelet used as the basis function can be used according to the object such as a Gabor function or a Mexican hat function.

When the filter process is completed, the square moving average process is performed on the waveform after the filter process in order to clarify the pattern and tendency of the vibration waveform. In the square moving average process, each time history value is squared to be a positive value, and then, for each time history value, an average value of a constant section around the time is calculated. Variations can be displayed smoothly.

FIG. 5 shows an example of a result obtained by performing a square moving average process after filtering the acceleration waveform when the lower plate constituting the sliding nozzle plate slides in the opening direction. 5A shows the case where the sliding nozzle plate is new, FIG. 5B shows the case where the sliding nozzle plate is slightly damaged, and FIG. 5C shows the case where the sliding nozzle plate is heavily damaged. Shows the results. As can be seen from the graph, when (A) to (C) are compared for the data in the opening direction, the vibration amplitude increases as the damage to the sliding nozzle plate increases. That is, it can be seen that the vibration amplitude when the sliding nozzle plate slides in the opening direction is highly correlated with the degree of damage of the sliding nozzle plate.

When determining whether or not the sliding nozzle plate can be used using the vibration amplitude, the following is performed.
For the vibration waveform when the sliding nozzle plate slides in the opening direction, the waveform area of the data subjected to the filtering process and the square moving average process is obtained. When the waveform area exceeds the determination reference value, the sliding nozzle plate subjected to the data processing is determined as a defective product.
Here, B = α · A and α = 1.4 to 2.0, where B is the determination reference value, A is the waveform area of the sliding nozzle plate without damage, and α is the safety factor.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of matters described in the claims. Other possible embodiments and modifications are also included. For example, in the above embodiment, the vibrometer is installed in the bracket, but the vibrometer may be installed in another part of the fixed metal frame or in the opening / closing metal frame. In the above embodiment, one vibration meter is used. However, a plurality of vibration meters may be installed in the fixed metal frame and / or the opening / closing metal frame, and the average value thereof may be used.

An accelerometer was installed as a vibration meter on the fixed metal frame, and the acceleration waveform when the lower plate slid in the opening direction was measured for the five test bodies shown in FIG. In the test, an alumina carbon plate was used, and the shape of the plate was 350 mm in length, 200 mm in width, and 30 mm in thickness. The test body 1 is a new article, and the test bodies 2 to 5 are intentionally damaged for the test.
In addition, the surface pressure of the sliding nozzle apparatus used for the test is 8 tnf, and the stroke is 150 mm.

The accelerometer used was Model 376 / CC701HT manufactured by Wilcoxon Research. The main specifications of the accelerometer used are as follows. Maximum amplitude: 50 G, resonance frequency: 32.0 kHz, usable temperature: −50 to 260 ° C.

Table 1 shows the determination results made by skilled workers for each specimen. Evaluation is made in three stages, ◯ means damage degree: small, Δ means damage degree: medium, and X means damage degree: large.

The acceleration for 20 seconds from when the nozzle hole was fully opened to when it was fully closed and fully opened was measured, and data processing was performed for the section where the nozzle hole was fully closed and fully open. The sampling frequency during A / D conversion was 25 kHz.

As shown in FIG. 7, the weighting function h (t) gradually increases from zero to the positive direction, reverses at the positive peak to become a negative peak, and gradually increases again in the positive direction to zero. A triangular wave having the shape This weight function h (t) has a frequency characteristic of a normal distribution as shown in FIG. 4, where the dominant frequency is P, the frequency band is P / 2 to 2P, and the main frequency band is 3P / 4 to 3P. / 2. In this test, filtering was performed with the dominant frequency set to 6.25 kHz.
In the square moving average process, a moving average value was calculated for every 100 data.

FIG. 8 shows the waveform area of each specimen together with the criterion value. Here, the determination reference value is obtained by multiplying the waveform area 58.0 of the specimen 1 by α = 1.4 and α = 2.0.
From the figure, it can be seen that the specimen 1 can be reused, and the specimens 3 to 5 cannot be reused, which is consistent with the determination result made by the skilled worker. The specimen 2 is reusable when the safety factor α is 2.0, and is not reusable when α is 1.4. Regarding the test body 2, the judgment results made by the skilled workers are also “◯” and “Δ”, and the judgment is divided.

It is the schematic diagram which showed the structure of the sliding nozzle apparatus which uses the lifetime determination method of the plate for sliding nozzles concerning one embodiment of this invention. It is the schematic diagram which showed the state which installed the vibrometer in the sliding nozzle apparatus. It is explanatory drawing which shows the sliding direction of the plate for sliding nozzles, Comprising: (A) is a case where the plate for sliding nozzles slides in an opening direction, (B) is a case where a plate for sliding nozzles slides in a closing direction. is there. It is a spectrum figure which shows an example of the frequency response function H (f) which consists only of a specific frequency band. It is explanatory drawing which shows an example of the result of having performed the square moving average process after filtering the measured acceleration waveform, Comprising: When (A) is a new article, (B) is a slight damage, (C) Is when the damage is significant. It is the top view which showed the state of the sliding surface of one plate of each test body. It is a time history waveform diagram of the used weight function h (t). It is the bar graph which showed the determination result of the plate for sliding nozzles. (A) is a side cross-sectional view of the plate showing edge melting of the sliding nozzle plate, and (B) is a side cross-sectional view of the plate showing stroke damage of the sliding nozzle plate.

Explanation of symbols

10: Sliding nozzle device, 11: Plate for sliding nozzle, 11u: Upper plate (fixed plate), 11d: Lower plate (sliding plate), 12u, 12d: Nozzle hole, 13: Fixed metal frame, 14: Slide metal frame 15: Opening / closing metal frame, 16: Upper nozzle, 17: Lower nozzle, 18: Arm, 19: Hydraulic cylinder, 20: Molten metal container, 22: Plate holder, 23: Plate fixing bolt, 24: Bracket, 25: Vibration meter

Claims (3)

A method for determining the life of a sliding nozzle plate comprising a fixed plate and a sliding plate that slides in close contact with the fixed plate,
A vibration meter is installed on a fixed metal frame that is fixed to the bottom of a molten metal container and holds the fixed plate and / or an open / close metal frame that can be opened and closed with respect to the fixed metal frame, and the sliding plate Measure the vibration waveform when sliding in the opening direction with the vibrometer, obtain the waveform area from the time history data of the measured vibration waveform, compare the waveform area with a preset criterion value, A sliding nozzle plate life determination method, wherein the sliding nozzle plate is determined to be defective when the area exceeds the determination reference value. 2. The sliding nozzle plate life determination method according to claim 1, wherein B = α · A and α, where B is the determination reference value, A is the waveform area of the sliding nozzle plate without damage, and α is the safety factor. = Lifetime determination method of sliding nozzle plate that is 1.4 to 2.0. 3. The sliding nozzle plate life determination method according to claim 1, wherein the waveform area is obtained by performing a square moving average process after filtering the measured vibration waveform. 4. A method for determining the life of a sliding nozzle plate having an area calculated from

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