JPH0332457A - Method for detecting channeling flow of molten steel in continuous casting mold - Google Patents

Abstract

PURPOSE:To detect channeling flow of molten steel in a continuous casting mold with high accuracy by detecting temp. distributions on both wall faces in short sides at right and left, where the molten steel flows discharged from a submerged nozzle are made to directly collide, and comparing both distributions. CONSTITUTION:When the molten steel flow discharged from the discharging holes 3 in the submerged nozzle 2 is made to flow, the temps. of the molten steel flows 4, 5 are justly higher in comparison with temp. of the molten steel 6 at circumference already stored in the mold 1. The wall face part in each short side 1a, where the molten steel flows 4, 5 are made to directly collide, receive higher heat load in comparison with that of the other part and become high temp. This heat load is varied with the molten steel flow rate. Therefore, when there is some difference of the flow rate between the molten steel flows 4, 5, i.e., there is some channeling flow, the difference of temp. between the wall faces in the short sides 1a, where the molten steel flows 4, 5 are made to collide, is developed. Therefore, the temps. at right and left sides are detected with thermocouples 9a, 9b fitted to the wall faces in the short sides 1a, and by executing comparison-operation with an arithmetic device 12, the development of channeling flow in the molten steel can be detected.

Description

[Detailed description of the invention] <Industrial use! t> The present invention relates to a method for detecting drifting of molten steel in a continuous casting mold.

<Prior art> In general, non-metallic inclusions in molten steel during continuous casting are carried into the slab by the injection flow of molten steel, and most of them float to the surface, but the remaining part remains inside the slab. It will be m1lJN as it is. It is known that the amount of nonmetallic inclusions added to the filtrate varies greatly depending on the flow of molten steel in the slab during casting, and the flow of molten steel discharged from the immersion nozzle becomes large and deep over a wide range. As you can see, it is within an increasing territory.

Therefore, in continuous casting, the immersion nozzle is shaped to have a discharge hole on the side so that the molten steel flow discharged from the immersion nozzle does not reach deep into the slab. The discharge hole is oriented slightly downward in order to avoid getting the flux involved.

FIG. 6 is an explanatory diagram of the same, in which the immersion nozzle 2 is arranged in the center of the verse l in the slab continuous machine, and its discharge hole 3a,
3b! , are directed toward both short sides 1a of the mold 1, and the discharge holes 3
The molten steel flow discharged from a and 3b moves inside the mold l as indicated by the arrow 4.
It flows like 5. However, the molten steel flow from the discharge hole 3 decreases its speed while flowing through the t8 m 6 stored in the mold I, and reverses the flow by colliding with the side wall surface of each short side 1a of the mold I. These reversed flows are upward flows 4A and 5A heading towards the scene side on the one hand, and downward flows 4A and 5A heading downward on the other hand.
B and 5B, and as a result of being greatly decelerated during this time, the upward flows 4A and 5A do not involve the Franks on the scene in the vortex, and the downward flows 4B and 5B are prevented from reaching deep into the slab, and the casting is completed. A process is performed to improve the quality of the piece.

However, the relationship shown in FIG. 6 occurs when the molten steel flow from the amphoteric outlet holes 3a and 3b is uniform, and the aperture opening of the sliding nozzle (not shown) attached to the immersion nozzle 2 and the casting speed If the flow of molten steel descending through the immersion nozzle 2 fluctuates due to such reasons, or if non-metallic inclusions such as aluminum adhere to the inner wall of the immersion nozzle 2, the left and right discharge holes 3a, 3b The equality relationship breaks down, and the flow of molten steel from either side becomes stronger, resulting in so-called drifting.

When such a drift occurs, the upward flow or downward flow becomes stronger on the side of the mold S+ wave where strong flow occurs, resulting in flux entrainment or internal defects due to the downward flow being suitable deep inside the slab. This can cause quality deterioration.

Conventionally, as a means for detecting the above-described drifting of molten steel, for example, as disclosed in Japanese Patent Application Laid-open No. Sho (i2-93054), a plurality of thermocouples are arranged vertically on the walls of the left and right short sides of the tS type. By burying the steel at an interval of
As disclosed in Japanese Unexamined Patent Publication No. 197255/1983, two eddy current level meters are installed between the immersion nozzle and each short side of the mold on both sides to determine the level deviation, thereby determining the level deviation of the molten steel. Various methods for detecting drifting have been proposed.

<Invention tries to solve! ! ! However, when using the former thermocouple of JP-A No. 62-93054, based on the difference in melt flow due to uneven flow,
As mentioned above, the mechanism of generating the 8wJ level difference is the partial uplift of the molten steel scene due to the upward flow of 1mA and 5A generated when the molten steel flow from the discharge holes 3a and 3b collides with each short side 1a, and Since the level on one side does not change uniformly over the entire surface, it is difficult to easily detect it as a level difference.

That is, for example, if the flow of molten M from the discharge hole 3b on the right side of the immersion nozzle 2 is strong, as shown in FIG. A5A
As a result, a raised portion 8 is generated on the molten steel bath surface, and a level difference Δh occurs compared to the molten steel bath surface on the left side of the immersion nozzle 2. However, this raised portion 8 is not generated along the wall surface of the short side 1a of the gong type 1, but is generated at the position where the upward flow 5A reaches the TA steel bath surface, and is usually separated from the wall surface as shown in the figure. This will occur in the area where the

Therefore, if you try to detect the level difference using the thermocouple 9b buried in the wall surface, it will only be possible when the raised part 8 due to the upward flow 5A reaches the wall surface, so it will not be possible to detect the level difference until it reaches that stage. There is a problem that detection is not possible, and even if detection is possible, the accuracy is poor.

In addition, when using the latter eddy current level meter disclosed in JP-A No. 62-197255, it is a prerequisite that the level meter must always be installed at the location where the amount of upheaval is greatest, but in practice the following It is technically difficult for several reasons.

In other words, in continuous casting, it is necessary to change the casting width frequently, but if the level meter is installed in a fixed position, it will not necessarily match the position of the ridge, so it will be possible to accurately measure the height of the ridge. This means that it cannot be detected. Therefore, if the level meter is made to be movable to accommodate changes in the width of the mold, the level meter will have to be reinstalled each time, making installation difficult. There is a risk of a decline.

In addition, when processing measurement signals using a two-to-one eddy current level meter, it is assumed that the absolute measured value is a loss, so it is essential to improve the absolute surface area of each level meter for measurement purposes. becomes. However, the measurement conditions of the level meters actually used are generally slightly different, and the locations where they are installed are in adverse environments with extremely high temperatures, so immediate measurements cannot be made.
The current situation is such that there is no major impact on the situation.

Therefore, since it is difficult to maintain the level of the four units at the same level and with a high level of sensitivity, when such a level meter is used, the sensitivity of detecting drifting flow is dominated by the surface area of the measurement surface. Therefore, it is difficult to achieve accurate detection.

It is possible to increase the number of eddy current type level needles installed to cope with the variation in the position of the maximum protrusion due to changes in the width of the mold. This is not an appropriate countermeasure as there is a problem of mutual interference.

The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a method that can detect drifting of molten steel with high accuracy in a continuous casting mold.

Means for Solving the Problems> A first aspect of the present invention is to detect the temperature distribution or heat flux distribution of both short side wall surfaces with which the molten steel flow discharged from the immersion nozzle collides in the continuous casting mold. A second aspect of the present invention is a method for detecting uneven flow of molten steel in a continuous casting mold, which is characterized by determining the presence or absence of uneven flow of molten steel by comparing temperature distribution or heat flux distribution. Detecting the temperature distribution or heat flux distribution in the width direction of the long side wall surface in the casting mold, and comparing the right half pattern and the left half pattern of the temperature distribution or heat flux distribution with respect to the center of the mold. This is a method for detecting drifting of molten steel in a continuous casting mold, characterized by determining whether or not drifting of molten steel has occurred.

Furthermore, the third aspect B of the present invention is to detect the temperature distribution or heat flux distribution in the width direction of the short side wall surface and the long side wall surface with which the molten tR flow discharged from the dipping nozzle collides in the continuous casting mold. The continuous V# forming mold is characterized in that the presence or absence of uneven flow of molten steel is determined by comparing the right half pattern and the left half pattern with respect to the center part of the mold of the temperature distribution or heat flux distribution. This is a method for detecting drifting of molten steel within a vessel.

Kusaku Kawa> According to the present invention, by detecting the temperature distribution or heat flux distribution of the left and right short side wall surfaces with which the molten steel flow discharged from the immersion nozzle directly collides and comparing the two, it is possible to detect the uneven flow of molten steel in the mold. The presence or absence of occurrence can be determined.

In addition, by measuring the temperature or heat flux in the width direction of the long side and comparing the temperature or heat flux patterns on the left and right sides with respect to the center of the long side in the width direction, it is possible to generate uneven flow of molten steel in the mold. It is possible to determine the presence or absence of

Furthermore, in addition to detecting the temperature or heat flux on each short side wall surface described above, the temperature or heat flux in the width direction of the long side is also measured. Alternatively, by comparing heat flux patterns, it is possible to detect drifting of molten steel with even higher accuracy.

<Examples> Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention. In addition, in the figure, the same parts as in the conventional example are given the same reference numerals.

As shown in the figure, a plurality of thermocouples 9a and 9b are installed at equal intervals in the height direction of the wall surface of both the left and right short sides 1a of the mold l, and the molten steel temperature signal detected by these thermocouples 9a and 9b is For example, an input device such as an A/D converter Wl l
It is then manually processed by an arithmetic device 12 such as a microcomputer, and the arithmetic results are displayed on a CRT, for example.
It is displayed on a display device 13 such as.

Therefore, when the molten steel flow discharged from the discharge hole 3 of the immersion nozzle 2 flows in the mold l as shown by the arrow 4.5, the molten steel flow 4.
5 is the temperature of the surrounding melt 11 already stored in the mold l.
Since the temperature is naturally higher than G, the molten steel flow is 4.5
As shown in FIG. 2, for example, the wall surface portion of each short side 1a where 11i directly protrudes receives a higher heat load than other portions and becomes high temperature.

It is obvious that this heat load changes depending on the amount of molten steel. Therefore, if there is a difference in flow rate, that is, a drift, between the molten steel flows 4 and 5, the force of each of the molten steel flows 4 and 5 will be Since a difference occurs in the temperature or heat flux on the wall surface of the molten steel, it is detected by the thermocouples 9a and 9b attached to the wall surface of each short side 1a, and the presence or absence of a drift of molten steel is detected by comparing and calculating with the arithmetic unit 12. It is possible to do so.

In addition, in the above-described embodiment, the thermocouple 9a.

By using a heat flux meter instead of 9b, a change in the amount of heat that the wall surface receives from the molten steel may be detected as a heat flux.

Further, according to this embodiment, even if the upward flow of the molten steel flow that collides with the wall surface of each short side 1a and reverses does not have the strength to reach the molten steel surface, the presence or absence of drift can be detected at an early stage. I can do it.

Next, as shown in FIG. 3, a plurality of thermocouples (or heat flux meters) 10a to 10e are attached in the width direction of one long side 1b, and temperature changes (or heat flux meters) in the width direction of the long side 1b are measured. It is also possible to detect the presence or absence of drift in the i8 steel by measuring the change in the flow rate.

That is, since the molten steel flow 4.5 discharged from the discharge hole 3 of the immersion nozzle 2 flows across the long piece tb of the mold 1, the long piece ib is subjected to a thermal load due to the flow of the molten steel flow 4.5. This induces a change in temperature or heat flux in the width direction. Therefore, if a flow rate difference or drift occurs between the molten steel fi4.5, the heat load will change, and a difference will occur in the temperature or heat flux on the wall surface in the width direction of the long piece tb. The presence or absence can be detected.

Furthermore, in addition to the temperature detection by the plurality of thermocouples 10a to 10e attached in the width direction of the long side 1b of this embodiment, the temperature detection is performed by the thermocouples 9a and 9b attached to the wall surface of each short side 1a of the above-mentioned embodiment. If the temperature change is measured by adding the temperature change, it is possible to detect the drift of the molten steel even more clearly.

Note that the number of thermocouples in the above embodiment is not particularly limited, and the arrangement thereof is not limited to one row, but may be in multiple rows, and furthermore, they may be attached to both long sides, respectively.

When there is no difference in the flow of the melt w4 discharged from the discharge hole 3 of the immersion nozzle 2, as shown in FIG. 4(a), an example of the measurement result is shown in FIG. vs 10
A groove is formed in a substantially symmetrical curved pattern centered on point c, but if drift occurs, as shown in Figure 4(b),
This phenomenon is caused by a change in the temperature distribution in the width direction of the long side 1b of the mold due to the difference in fil'l of the molten steel flow.

Therefore, by comparing the temperature distribution patterns on the left and right sides with the widthwise center C of the long side tb as a boundary, it is possible to determine whether there is a drift of molten steel.

In addition, as one of the simple methods for determining drift, the temperature distribution obtained always draws a figure-9 pattern, and the arithmetic unit 12 ranks each measurement position according to the temperature value. By performing the processing, determination can be made by converting the temperature distribution into an index.

That is, as shown in FIGS. 5(a) and (b), for the temperature distribution obtained in FIGS. 4(a) and (b), an integer "l" is added to the lowest temperature measurement value. The measured value is given as an integer that increases as the value increases.

First, in FIG. 5(a) where there is no drift, 1"
The rank sum on the left side is 12 (-2-) 4 + 6), while the rank sum on the right side is 15 (-3-) 5 + 7), and the difference between the two is 3, so the temperature distribution on the left and right sides is No significant difference was observed, so it can be determined that there is "no drift."

On the other hand, in FIG. 5(b) where there is a drift, "l
”, the rank sum on the left side is 9 (-2+4+6), while the rank sum on the right side is 18 (-5+6+7), and the difference between the two is 9, so there is clearly a significant difference between the left and right temperature distributions. Since it is recognized, it can be determined that there is a "biased flow".In addition, when making this determination, it is necessary to give a threshold value in advance to the difference between the two rank sums and compare it with the calculated value of the difference. It is..

It will be more accurate to determine that there is a drift after confirming that the condition exceeding the threshold continues for a predetermined period of, for example, several seconds.

When the method of the present invention was applied to pouring in continuous casting to determine the presence or absence of drifting, and when the drifting was detected, the casting speed was reduced and the amount of molten steel discharged was reduced. It was possible to suppress the defect occurrence rate to 3%, which was significantly lower than the conventional rate of 12%.

<Effects of the Invention> As explained above, according to the present invention, drifting can be easily detected using a simple method, which greatly contributes to improving the quality of products.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the drift detection device according to the method of the present invention, FIG. 2 is a graph showing the advantages of temperature measurement by the drift flow detection device, and FIG. 3 is a diagram showing other implementations of temperature measurement. FIG. 4(a) is a perspective view showing the main part of the example. 5(b) is a graph showing an example of a temperature distribution pattern, FIGS. 5(a) and 5(b) are explanatory diagrams showing an example of indexing a temperature distribution pattern, and FIGS. It is an explanatory diagram showing an example. l...mold, la...short side. 1b...Long side, 2...Immersion nozzle. 3...Discharge hole, 6... Molten steel. 9.10...Thermocouple, 11...Input device. 12... Arithmetic device. 13...Display device.

Claims (1)

[Claims] 1. Detecting the temperature distribution or heat flux distribution of both short side wall surfaces that collide with the molten steel flow discharged from the immersion nozzle in the continuous casting mold, and comparing the temperature distribution or heat flux distribution. A method for detecting drifting of molten steel in a continuous casting mold, the method comprising: determining the presence or absence of drifting of molten steel. 2. Detect the temperature distribution or heat flux distribution in the width direction of the long side walls in the continuous casting mold, and determine the right half pattern and left half pattern of the temperature distribution or heat flux distribution with respect to the center of the mold. A method for detecting drifting of molten steel in a continuous casting mold, the method comprising determining whether or not drifting of molten steel has occurred through comparison. 3. Detect the temperature distribution or heat flux distribution in the width direction of the short side wall surface and the long side wall surface that collide with the molten steel flow discharged from the immersion nozzle in the continuous casting mold, and determine the temperature distribution or heat flux distribution of the mold. 1. A method for detecting drifting of molten steel in a continuous casting mold, the method comprising: determining the presence or absence of drifting of molten steel by comparing a pattern on the right half and a pattern on the left half of the center.