JPS63168263A - Method for detecting variating molten surface level in mold - Google Patents

Abstract

PURPOSE:To enable an optimum treatment to take by directly observing molten surface by photoconductor arranged at the corresponding part of meniscus, finding the molten surface level boundary line, calculating variation by change with the lapse of time and detecting the molten surface variation. CONSTITUTION:The photoconductor is arranged in a penetrated hole bored at the corresponding part of meniscus in the long side or short side and the molten surface is observed by this photo conductor, to find the molten surface level 15. The variation of molten surface level 15 is successively calculated, to detect the variation of molten surface. That is, the prescribed interval from an inner wall face 1a of mold or the distance (l) to the prescribed position is put in abscissa and the molten surface level 15 is shown as ordinate (h). The difference h of molten surface level 15a after unit time passes, is calculated from the molten surface level 15 shown by (h) at some time to the prescribed abscissa (setting position), to find the molten surface variation per unit time. In the molten surface variation calculating device, the condition of variation of molten surface near the meniscus is quantitatively detected. In this way, the condition of variation of molten surface during casting, is quantitatively detected by on-line, and the suitable treatment is taken in accordance with this.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for accurately detecting the amount of variation in the level of molten metal in a mold during continuous casting.

[Prior Art] As is well known, a mold for continuous casting is composed of a combination of long sides and short sides, and molten steel is injected into this mold to form a solidified shell of a predetermined thickness on the surface in contact with the inner surface of the mold. After this, the slab is continuously pulled out from below to produce slabs. Therefore, the molten steel begins its initial solidification within the mold. This initial solidification state has a significant impact on the appearance of surface defects and other quality of the slab. In order to efficiently flow lubricant such as powder between the inner surface of the mold and the solidified shell, and to prevent seizure between the solidified shell and the inner surface of the mold, vibration is applied to the mold to reciprocate in the casting direction. ing.

By the way, if the lubricant supply conditions and vibration conditions mentioned above are not properly controlled, the solidified shell will seize on the inner surface of the mold, causing various casting defects, inducing breakout of binding and cracking, and making it impossible to operate. becomes. Also, the depth and shape of the oscillation marks formed on the surface of the slab become abnormal.
Defects such as bald spots, slipper scratches, and cracks on manufactured slabs (!
- appears. Particularly in recent years, the increase in casting speed and the direct connection of continuous casting and rolling processes (hereinafter referred to as direct rolling) have been actively promoted. It becomes a big obstacle.

However, conventionally, there is no way to directly detect whether the type of lubricant in the mold, its supply status, or vibration conditions such as the frequency and amplitude of the mold are properly controlled during casting. It was common practice to observe the surface properties of cast slabs after casting and use the results to judge the suitability of past casting conditions.

On the other hand, as a method for predicting casting defects such as seizure of the solidified shell and cracks caused by it, for example, Japanese Patent Application Laid-Open No. 57-1159
As shown in Publication No. 60, a plurality of temperature detection points are embedded in the wall surface of the mold in the casting direction, and the temperature values measured by these temperature detection points are compared with each other or with a reference value to prevent the occurrence of casting defects. A method for estimating
As shown in Publication No. 3, a method has been proposed in which the temperature values measured by multiple temperature detection terminals in the casting direction are Fourier-transformed to recognize patterns of temperature changes within the mold, and from this the type and location of casting defects can be estimated. , has been put into practical use in some areas.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional method, there is no way to directly detect the situation inside the mold, especially the fluctuation of the melt level near the meniscus. For this reason, even if, for example, fluctuations in the level of the molten metal, waves in the molten metal surface itself, insufficient supply of lubricant, uneven inflow, etc. occur during casting, these can be directly detected online. could not be detected.

Therefore, it has not been possible to implement appropriate controls corresponding to these, and the reality has been to rely on empirical operations based on past operational results.

In addition, many proposals have been made to detect various casting defects within a mold, and it has become possible to predict their occurrence with considerable accuracy. However, all of the conventional methods described above are indirect methods in which the temperature of the buried part is measured with a temperature detection end buried in the wall of the mold, and surface defects in the slab are estimated from the measured temperature value. . For this reason, even though no defects have occurred, it has often been mistakenly recognized as a surface defect, and there have been cases in which casting defects have been overlooked. Such erroneous recognition and oversight of casting defects have a great effect on direct rolling, and there is a major problem in that it cannot be carried out efficiently.

The present invention aims to fundamentally solve the above-mentioned problems.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention attaches a light guide connected to an image processing device to a through hole drilled in a portion corresponding to a meniscus on a long side or a short side of a continuous casting mold. Directly observe the hot water level during casting with a conductor, and then binarize the observed image using a set standard brightness or wavelength to determine the hot water level boundary line, and calculate the amount of fluctuation per unit time from the change in this boundary line over time. This is a method for detecting the amount of variation in the level of molten metal in a mold, which is characterized by detecting the amount of variation in the molten metal level by calculation.

[Function] FIG. 1 is a cross-sectional structural diagram of the vicinity of a mold for explaining the basic configuration of the present invention, and FIG. 2 is a perspective view of the mold.

In the figure, 1 is a mold, which is composed of a long side 2 and a short side 3. In this example, a through hole 5 penetrating to the inside of the meniscus portion 4 of the long side 2 is bored. For example, as shown in the partial cross-sectional view of the mold in FIG.
It is also possible to provide it using a fastener 102 for attaching 1. That is, a hollow rod-shaped rod 103 is attached in place of the fastener 102 provided in the meniscus-corresponding portion 4, and a hole 10 that penetrates inside the corresponding inner wall 101 is installed.
4, and the hollow hole 103a of the rod 103 and the hole 104 constitute the through hole 5. The rod 103 may be fixed with a screw portion 104a formed in the hole 104 and a nut 105. .

A light guide 6 is attached to the through hole 5 with a heat-resistant glass 7 interposed therebetween. The light guide 6 uses, for example, an optical fiber, a combination of a spectrometer and a photomultiplier, a CCD element combined with a filter and a lens, an MO3 type element, an ITV camera, etc. that can detect the brightness and/or wavelength of light within the mold. Is possible. However, in the experience of the present inventors, an optical fiber that allows the diameter of the through hole 5 to be reduced and the observation field to be enlarged is the most excellent for effectively demonstrating the functions of the present invention. For example, the heat-resistant glass 7 is made of silicon glass, quartz glass, etc., which have both transparency and heat resistance, as shown in FIGS.
a, and the mold inner wall 10 is held via this fixing ring 7a.
1 is tightly fitted. Note that 7b indicates a set screw for fixing the fixing ring 7a to the inner wall 101 of the mold. Therefore, the heat-resistant glass prevents the molten steel 12 from leaking out of the mold, and also prevents the molten steel 12 from leaking out of the mold.
protects the light guide 6 from high heat. The light guide 6 is connected to an image processing device 21 whose functions will be described below.

In FIG. 1, numeral 9 denotes a vibration generator that applies vibration to the mold 1, and numeral 10 denotes a vibration control device that controls the frequency, amplitude, etc. of the vibration generator 9. In addition, 11 is a molten fiA in the mold 1.
12 is a nozzle for injecting a slab, 13 is a slab, and 14 is a solidified shell formed on the surface layer of the slab 13.

According to the present invention, the vicinity of the meniscus within the mold 1 can be directly observed using the observation image provided by the light guide 6. The image observed by the light guide 6 is binarized by the image processing device 21 based on a preset brightness or wavelength (hereinafter referred to as set reference brightness or set reference wavelength), and as a result, as shown in FIG. The boundary tilA15.15a between a portion brighter and darker than the set reference luminance, or between a portion longer and shorter than the set reference wavelength is determined. Therefore, if the set reference brightness or set reference wavelength is set to the brightness or wavelength emitted by the molten steel temperature, the boundary line 15 will be the hot water level, that is, the hot water level boundary line referred to in the present invention (hereinafter simply referred to as hot water level 15). ).

This hot water level 15 can be determined continuously or at an arbitrary period since images observed by the light guide 6 are continuously obtained, and its change over time can be determined. When this change over time is determined, the distance from a predetermined part in the observation field Y, for example, the mold inner surface 1a, is determined! By calculating the difference between the previous hot water level 15 and the next hot water level 15a at a distant site, it is possible to detect the amount of fluctuation in the hot water level per unit time at that site.

It has been learned from past operational experience that when the vibration conditions of the mold are set to a small amplitude and a high frequency, the depth of the oscillation mark is reduced, its shape improves, and the surface quality of the slab improves. There is. However, it was conventionally thought that this was due to the following reasons. That is, mold 1
Taking as an example the case where the oscillation is sinusoidal as shown in Fig. 6, the amplitude of this oscillation is A, and the frequency is r.
, the casting speed is Vc, and the time is t, then the displacement X of the mold 1 is given by the following equation (1).

x=Asin (2πft) ”...” (1) The velocity Vm of mold 1 is obtained by differentiating equation (1) with respect to time t, and Vm=dx
/dt = 2 xf Acos (2πft) ”・
``(2).Here, if the descending speed Vm of the mold 1 is greater than the casting speed Vc, the slab will be pushed downward from the mold 1.The time during which the mold 1 is pushed downward (generally It is said that the smaller the negative strip time (hereinafter referred to as Ts waiting time), the better the surface and surface layer quality of the slab. is small and the frequency f
It can be seen that the larger the value, the smaller the 78 hours.

TN = (1/πf) ・cos-' (Vc/2π
fA)=-・"(3) 20 It is also known that in order to reduce the TN time, non-sinusoidal vibration may be used instead of the sinusoidal vibration.

However, such reasoning is based on the above-mentioned molten metal surface (in the present invention, the contact area between the inner surface of the mold 1a and the molten steel 12 shown in FIG. 5 is called the meniscus 6, and the molten steel surface at the set position in the mold is called the molten metal surface. Also, this continuous surface of the hot water is the boundary line,
In other words, it is the hot water surface level, hereinafter referred to as hot water surface level 15)
It is assumed that is stationary with respect to the absolute coordinates, that is, the molten metal level within the mold does not change even if the mold vibrates. It is common knowledge among those skilled in the art that in conventional molds, the inner surface of the mold and molten steel completely slip due to the action of lubricants, and that the molten steel level remains constant even when the mold moves up and down. The above reasoning was based on basic understanding.

However, the inventors of the present invention closely observed the inside of the mold from above the mold during actual continuous casting operations, and found that ripples were occurring on the surface of the mold even though the level was stable. Ta. This led us to question the conventional basic understanding and conducted various experimental studies on methods for detecting fluctuations in the level of hot water near the meniscus during actual operation. As a result, by using the device shown in FIG. 1, we succeeded in directly detecting the fluctuation of the hot water level. In other words, by attaching the light guide 6 to the through hole 5 drilled in the meniscus-equivalent part 4 of the long side 2 or the short side 3 so as to penetrate to the inner surface, the situation near the meniscus in the mold can be directly observed. did. As a result of repeatedly observing the fluctuations in the molten metal level using the light guide 6 in this way, we obtained new knowledge that the molten metal level is not static, but synchronized with the vibrations of the mold, which is completely different from the conventional basic understanding. It was done.

Based on this knowledge, the present invention continuously and quantitatively detects fluctuations in the molten metal level during casting, thereby preventing uneven inflow of lubricant and seizure of solidified shells during casting. This makes it possible to take prompt and accurate operational action when an abnormality occurs.

Now, an example of the processing mechanism in the image processing device 21 will be explained as follows.
This will be explained in further detail based on the figures. For example, if an optical fiber 6a is used as the light guide 6, the observed image detected by the optical fiber 6a is input to the RGB processing device 21a.

In this example, the number of pixels of the optical fiber 6a is 30,000, and the detection signal from each pixel input to the RGB processing device 21a is determined by the brightness set in advance by the binarization processing device 21b following the RGB processing device 21a. Alternatively, binarization processing is performed using a set reference luminance or wavelength (signal processing for luminance and wavelength is basically the same, so luminance will be explained below as a representative example) as a reference value of wavelength. As described above, the setting reference brightness can be set by expressing the brightness emitted by the temperature of the molten steel in the well-known lux or the like. That is, as shown in FIG. 7, the lubricant 17 supplied into the mold is
As it melts, it flows between the molten steel 12 and the mold inner surface 1a and exerts the aforementioned lubricating function. The temperature of this molten lubricant 17 is approximately 1400°C, which is slightly lower than that of the molten steel 12. However, the main components of the lubricant 17 are CaO and Sing, and since it has transparency like glass, the optical fiber 6
When observed at point a, the brightness is lower than that of the molten steel 12. Therefore, when the signal of the observed image is binarized using the brightness of the molten steel 12 as a reference, for example, parts with a brightness higher than the brightness of the molten steel 12 can be displayed white, and conversely, parts with a brightness lower than the brightness of the molten steel 12 can be displayed black for discrimination. can.

On the other hand, the thickness of the lubricant 17 is thin, and there are cases in which there is no actual harm even if the surface of the lubricant 17 is at the level of the hot water level. There is a significant brightness difference between the molten lubricant 17 and the undissolved lubricant 17a. Therefore, in such a case, the brightness of the lubricant 17 may be used as the setting reference brightness. In addition, the human observed image is divided into any number of blocks, and vertical and horizontal differential calculations are performed on the image between each block. Is it more than or less than 2? In other words, there is a method of binarizing the brightness difference as the set standard brightness, or a method of binarizing the brightness difference as the set standard brightness, or a method of binarizing the brightness difference as the set standard brightness.
It is possible to adopt a method of converting the data into values. The processing in the binarization processing device 21b is a general term for such methods. The signal processed by the binarization processing device 21b is used to calculate the boundary line between the molten steel 12 and the lubricant 17 by the boundary line calculation device 21c, and the molten metal level 15 is determined. The hot water surface level 15 calculated by the boundary line calculation device 21c can be smoothed using a well-known filter, for example, and displayed on the monitor 28 as a smooth level display, and the fluctuation status of the hot water surface level 15 can be monitored. By doing so, it is possible to grasp the macroscopic situation of the molten metal level in the mold.

However, in the present invention, in order to grasp the fluctuation situation of the hot water level more accurately and quantitatively, the amount of fluctuation in the hot water level is further calculated from the hot water level 15. Once the hot water level 15 within the observation field Y of the optical fiber 6a is determined continuously or at an arbitrary period, the amount of change in the hot water level 15 at a preset location is calculated sequentially to determine the hot water level at that location. The amount of surface variation can be detected. FIG. 8 shows an example of a specific calculation method, where the abscissa represents the distance l from the mold inner wall surface 1a to a predetermined interval or a set point, and the molten metal level 15 is represented as the ordinate. By calculating the difference Δh between the hot water level 15 and the hot water level 15a after a unit time has elapsed, which is expressed by the time h for a predetermined abscissa (setting part), the amount of hot water level fluctuation per unit time can be calculated. Desired. In FIG. 1, reference numeral 22 denotes a hot water level fluctuation amount calculation device for calculating this hot water level fluctuation amount. The liquid level fluctuation calculation device 22 performs the above-mentioned calculations, for example, at intervals of 1 to 3 IINIn from the inner wall surface of the mold, or at intervals of 3 f from the inner wall surface of the mold.
By performing this at a 10 mm distance, it becomes possible to quantitatively detect the fluctuation state of the hot water level near the meniscus.

The unit time for calculating the amount of fluctuation in the hot water level is arbitrary, and may be determined to be an optimal value depending on the operating conditions. Furthermore, if this unit time is set to, for example, 1/4 of the mold period, it is also possible to detect the amount of fluctuation in the molten metal level corresponding to the maximum value and minimum value of mold displacement.

The amount of variation in the level of the hot water can, for example, be expressed not only as a relative amount of variation, but also as an amount of absolute variation obtained by subtracting the amount of vibration of the mold from the amount of relative variation.

As described above, it has become possible to quantitatively detect the fluctuations in the melt level during casting online, making it possible to accurately grasp the initial solidification state inside the mold. Therefore, it is now possible to select the most suitable lubricant for the operation according to the situation, and to take appropriate measures in the event of insufficient supply, uneven inflow, etc. When the amount of variation becomes large, pinholes and inclusions are generated in the solidified shell 14, which appear as surface defects in the manufactured slab. In other words, it can be said that the above-mentioned amount of fluctuation in the hot water level is large. On the other hand, the fact that the amount of fluctuation in the melt level is small means that the initial solidification is stable. Therefore, stable initial solidification can be achieved by controlling the amount of fluctuation in the level of the melt to be small.

One of the important influences on initial solidification is whether the lubricant is suitable for the operation in question. This problem can also be effectively solved by detecting the amount of fluctuation in the hot water level described above. An example of the results will be described below.

Figure 9 shows the viscosity of 1 using the apparatus shown in Figure 1.
poise lubricant 17 (1), 2 poise lubricant 17 (2), 3 potse lubricant 17 (3)
FIG. 3 is a diagram showing the results of investigating the amount of fluctuation in the hot water level using the method. In this example, the casting speed is 1.6m/min and the mold vibration frequency is 126c.
This is an example of casting low-grade aluminum killed steel with pm and mold amplitude of ±6 mm, and the vertical axis in Figure 9 is 3.
The amount of fluctuation in the hot water level at the location m is expressed by the type of lubricant by converting the above-mentioned average value of the absolute amount of fluctuation in the hot water level into an index. The larger the hot water level fluctuation index means the larger the hot water level fluctuation, and it can be seen that under the same casting conditions, the hot water level fluctuation varies greatly depending on the type of lubricant, especially its viscosity. Further, FIG. 10 shows the occurrence of surface defects in slabs manufactured under the conditions, and FIG. 11 shows an example of the investigation results of the incidence of breakouts during the same operation. The occurrence of surface defects is expressed as an index of the number of surface defects such as pinholes and inclusions per meter of slab (number of defects/m), and the breakout occurrence rate is expressed as the number of surface defects such as pinholes and inclusions per meter of slab. The number of occurrences is expressed as an index. From these results, it is possible to detect the amount of liquid level fluctuation during casting, and if there is a tendency or phenomenon that the fluctuation becomes larger than during stable operation in the past, select and use a lubricant that will reduce the fluctuation. This makes it possible to stabilize the initial solidification state and reduce surface defects, breakouts, etc.

〔Example〕

The present invention was carried out in a curved continuous casting machine with a monthly production capacity of 160,000 tons.

Table 1 The casting conditions in this example are as shown in Table 1.
Using the apparatus shown in FIG. 1, through holes of 13 nn were drilled in the meniscus-equivalent portions of the parts that join the short sides of the long sides of the mold (4 locations at each corner where surface defects are likely to occur). An optical fiber with 50,000 pixels and a diameter of 12 mm was attached to this through hole, and the observation field of the optical fiber was set to 50'. Silicon glass with a thickness of 10IrI11 was fitted onto the inner surface of the mold in the through hole to prevent leakage of molten steel and to protect the optical fiber. 5 during continuous casting in this equipment.
Continuous observation was carried out for 0 minutes, and during this period the vibration frequency of the mold was consciously changed to detect the fluctuation of the melt level at that time. 1st
Figure 2 shows an example where the casting speed is 0.53m1m:n, the mold frequency is 68.6 cps, and the amplitude is ±6mn+. Figure 12 (a) shows the variation of the mold, and Figure 12 (b) shows Figure 12 (C) shows the relative fluctuation amount of the hot water level, and the absolute fluctuation amount of the hot water level. During this operation, the condition of the molten metal surface was visually observed from above the mold, and it was confirmed that it was smooth with almost no ripples.

FIG. 12(b) and FIG. 12(C) continuously represent the amount of fluctuation in the hot water level detected by the method of the present invention over time.
The waveform was smooth.

Next, FIG. 13 shows an example in which the casting speed was 1.6 m/min, the vibration frequency of the mold was 126.4 cpm, and the amplitude was ±6 degrees, and as a result of visual observation of the mold, ripples were generated. In this way, if ripples are generated even though the vibration is higher than in the example shown in Fig. 12, the actual detected amount of water level fluctuation will also change over time as shown in Figs. 13 (b) and (C). As shown in the waveform of the amount of fluctuation in the hot water level continuously expressed in , it was confirmed that there was a large disturbance, and that the amount of fluctuation tended to rise to the right. As a result, the slab produced in the embodiment shown in FIG. 13 had more surface defects and was of poor quality compared to the slab produced in the embodiment shown in FIG.

From the above, the following knowledge regarding the behavior of the molten metal surface inside the mold was confirmed in actual operation, and based on this knowledge, it has become possible to accurately predict casting abnormalities and surface defects. That is, (1) The hot water level is not static, but fluctuates over time, and this level fluctuation is not only due to the balance between the amount of molten steel injected into the mold and the withdrawal of slabs, but also due to the change in the mold temperature. (2) The relative motion of the melt surface to the mold (referring to the movement of the melt surface obtained by the light guide 6 attached to the mold) has the same period as shown in Figure 5. (3) The absolute motion of the hot water surface relative to the mold (meaning the movement of the hot water surface with the earth as an absolute reference, canceling mold vibration from the relative motion) is the same as shown in Figure 6. The period and phase are the same, and the amplitude of the molten metal surface is 70 to 80% of the mold amplitude.

〔Effect of the invention〕

By carrying out the present invention, it becomes possible to accurately and quantitatively detect the amount of fluctuation in the level of the molten metal in the mold, especially in the vicinity of the meniscus, on-line. As a result, it becomes possible to quickly and accurately predict various casting abnormalities during casting, the occurrence of surface defects in slabs, etc., and appropriate operational actions can be taken accordingly.

As described above, the practical effects of the present invention are very large.

[Brief explanation of the drawing]

Each figure is an example based on the present invention, in which Figure 1 is a cross-sectional structural diagram near the mold to explain the basic configuration of the present invention, Figure 2 is a perspective view of the mold, and Figure 3 Figure 4 is a side view of the heat-resistant glass shown in Figure 3, and Figure 5 is an example of the display of the molten metal level within the observation field of the optical fiber. Figure 6 is a diagram illustrating an example of the displacement situation of the mold, Figure 7 is a partial sectional view near the meniscus, Figure 8 is a diagram illustrating an example of a specific method for calculating the amount of fluid level fluctuation, Figure 9 shows the results of investigating the relationship between the type of lubricant and the amount of variation in the metal level under the same operating conditions. Figure 10 shows the surface defects that occurred in the slab produced in the example shown in Figure 9. FIG. 11 is a diagram showing an example of the investigation results of the occurrence rate of Pleikuau I in the example of FIG. 9, and FIGS. FIG. 3 is a diagram illustrating an example of the results of detecting the amount of fluid level fluctuation based on the casting speed, mold frequency, and amplitude while changing the casting speed, mold frequency, and amplitude, respectively. 1... Mold, 1a... Mold inner surface, 2... Long side, 3
... short side, 4 ... meniscus equivalent part, 5 ... through hole, 6 ... light guide, 6a ... optical fiber, 7 ...
・Heat-resistant glass, 9... Vibration generator, 10... Vibration control device, 11... Nozzle, 12... Molten steel, 13.
... Slab, 14... Solidified shell, 15.15a... Molten metal level, 16... Meniscus, 17.17a... Lubricant, 21... Image processing device, 21a... RGB Processing device, 21b... Binarization processing device, 21c... Boundary line calculation device, 22... Hot water level fluctuation amount calculation device, 23.
... Comparator, 24... Process control device, 25...
Data collection device, 26...Recording device, 27...Alarm device, 28...Monitor, 100...Mold body, 1
01... Mold inner wall, 102... Fastener, 103...
- Rod body, 104...hole, 105...nut. Agent: Patent Attorney Masamitsu Aki Sawa and 1 other person 21″ 6 Figure π 9 Figure 5 & l Synovial fluid / 7 (+) ρrv / home) Tonshi Nu
/7(+) /7(2) /7(3) Anthem/
7ω n(z)/7(3) Ord figure vT interval (Sec) Valve 13 figure k M <sec>

Claims (1)

[Claims] (1) A light guide connected to an image processing device is attached to a through hole drilled in the meniscus-equivalent part of the long side or short side of the continuous casting mold, and this light guide directly monitors the molten metal surface during casting. While observing, the observed image is binarized using a set standard brightness or wavelength to obtain the hot water level boundary line, and the amount of change in the hot water level is calculated by calculating the amount of change per unit time from the change in this boundary line over time. A method for detecting the amount of variation in the level of molten metal in a mold.