JPS619966A - Estimating method of amount of molten steel remaining in ladle - Google Patents

Abstract

PURPOSE:To estimate the amt. of the molten steel remaining in a ladle in real time with high accuracy with the change point of the induced magnetic field point according to the outflow of the molten steel as a reference position by disposing an excitation coil and magnetic field intensity detecting coil on the wall surface of the ladle so as to face each other and detecting the above-mentioned change point. CONSTITUTION:The induced magnetic field intensity of the excitation coil 14 in the outflow process of the molten steel 5 in the ladle 1 is measured by the detecting coil 15. At least the two change points among the change points of the magnetic field intensity i.e., the points A, B, C of the time when the molten steel surface 11 arrives at the top and bottom ends of the coils 14, 15 and the zero amt. of the molten steel remaining in the ladle 1 are detected and are stored in a calculator 20. The outflow rate of the molten steel 5 between the two points B and C is measured or determined by calculation (the amt. of the steel remaining at the change point C is zero) and the amt. of the molten steel at the point B is stored in the calculator 20 for the purpose of the succeeding measurement. The amt. of the above-mentioned steel 5 at the point B is preferably corrected by the estimated rate of erosion of furnace wall refractories 3 and is used as the estimated reference value at the point B in the next measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for estimating the remaining amount of molten steel in a ladle having a molten steel outlet at the bottom, such as a ladle used in continuous steel casting.

Generally, in continuous steel casting, a sliding gate 3 and a long nozzle 4 are attached to the molten steel outlet 2 provided at the bottom of the ladle as shown in FIG. Usually, the molten steel is injected into a tundish 6 through a gate 3 and a long nozzle 4, and then the molten steel in the tundish 6 is injected into a mold 7 and cast into a slab 8.

In the continuous casting of steel as described above, when the molten steel in the ladle 1 runs out, it is replaced with another ladle and continuous casting is continued. However, slag 9 exists on the surface of the molten steel 5 in the ladle 1, and at the end of the outflow of the molten steel in the ladle, the slab also starts to flow out, so the sliding gate 3 is opened only after the molten steel in the ladle is completely gone. If the ladle is closed, the slag 9 in the ladle may also flow into the tundish 6 and enter the slab 8 through the mold 7, causing internal defects in the slab.

Conventionally, an operator would empirically determine that the remaining amount of molten steel in the ladle was low and then open the sliding gate 3.
By closing the ladle, the slag in the ladle was prevented from flowing out. However, in reality, the amount of molten steel in the ladle cannot be visually observed, so the fact that the amount of molten steel in the ladle has decreased actually means that the slag 9 in the ladle has started to enter the tandy pipe 6 through the long nozzle 4. It cannot be determined until after that point. Therefore, in the operation based on experience as described above, it is almost inevitable that slag will flow into the tundish 6 and result in internal defects in the slab. Furthermore, in the actual ladle, the molten steel and slag are not completely separated, but are mixed to some extent, so in order to maintain good quality of the slab, it is necessary to adjust the ladle size and quality requirements. It is necessary to close the sliding gate while leaving the molten steel in the ladle in the range of about 1 to 20 tons.

Therefore, a method of estimating the amount of molten steel remaining in the ladle based on some data and closing the sliding gate based on the estimated amount of molten steel remaining has been considered. Several methods have been proposed to estimate the amount of remaining molten steel. However, all of the conventionally proposed methods for estimating the remaining amount of molten steel in a ladle have low accuracy and are insufficient for practical use.

In other words, the conventional method for estimating the remaining amount of molten steel in a ladle is to first calculate the amount of molten steel in the ladle by subtracting the actual casting amount based on the estimated production amount of molten steel for each ladle in the molten steel refining process. A method of calculating the remaining amount has been proposed, but in this case, the accuracy of the estimated value of ladle self-melting tj4Il is inevitably low, since there is actually a large variation in the production of molten steel in the refining process.

The second method is to weigh the ladle with a crane weigher, subtract the weight of the empty ladle to calculate the initial amount of molten steel in the ladle, and subtract the actual casting amount from that amount to calculate the amount of molten steel in the ladle. There is a method to estimate the amount of internal molten steel remaining. However, in addition to the molten steel, there is a considerable amount of slag in the ladle, and therefore, in this method, an error occurs due to the amount of slag. It is also possible to estimate the amount of slag and subtract it, but the slag layer varies widely during operation, and accurate estimation is difficult.
It is.

A third method is to install a distance sensor 10 above the ladle 1 to detect the level 11 of the molten steel 5, as shown in FIG. 2, and calculate the amount of molten steel #1. However, since slag 9 is present on the upper surface of the molten steel 5, the molten metal level 11 cannot often be detected correctly in this method.

Furthermore, even if the distance sensor 10 were to use II magnetic waves that can pass through the slag layer to correctly detect the scene level 11, it would not be possible to detect the scene level 11 correctly! i! ! The accuracy of estimating the amount of molten steel decreases due to the effects of erosion of refractories. That is, as the ladle-resistant material progresses, the inner volume of the ladle becomes larger, and even at the same scene level, the melt III becomes larger, and therefore the error from the actual amount of molten steel becomes larger.

As mentioned above, all of the conventional ladle-based methods for estimating the remaining amount of molten steel have large errors in relation to the actual amount of molten steel. Therefore, when determining the closing timing of the sliding gate using the conventional estimation method, it is necessary to estimate on the safe side. There was a problem in that the sliding gate had to be closed due to the residual amount of winter waste, which resulted in a large amount of scrap, resulting in high costs.

This invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for estimating the amount of molten steel in a ladle with high accuracy, regardless of the amount of slag in the ladle or the amount of corrosion damage of large ladle-resistant materials. The purpose is to

In other words, the method of the present invention, when estimating the remaining amount of molten steel in a ladle with a molten steel outlet provided at the bottom, requires that an excitation coil and a magnetic field detection coil be placed facing each other on refractories on opposing walls of the ladle. , measuring the intensity of the magnetic field induced from the excitation coil with a detection coil to detect at least two changing points of the intensity of the induced magnetic field during the outflow process of molten steel in the ladle;
The amount of molten steel flowing out in the ladle from the first changing point to the second changing point among those changing points is determined by measurement or calculation, and the amount of remaining steel at the second changing point is determined, and the calculated amount of flowing out is determined. The melt #lI at the first change point is determined from the remaining steel amount, and the first
The present invention is characterized in that the ladle self-melting copper coin is estimated based on the molten steel opening at the first changing point by detecting a changing point. In this way, the induced magnetic field of the excitation coil placed on the wall of the ladle is measured by the detection coil placed opposite to the excitation coil, the change point of the induced magnetic field is detected, and the remaining amount of molten steel is determined using the change point as a reference position. If estimated, the change point is almost unaffected by the presence of slag and the amount of slag, so the remaining amount of molten steel can be estimated with high accuracy without causing errors due to the influence of slag. In addition, when using the melt [1 at the first change point as the next reference amount, the furnace @I! If the reference amount [t is corrected by the melt weight when a refractory ladle is used once, it is possible to estimate the remaining melt W4 m without being affected by melting loss.

The estimation method of the present invention will be explained in detail below with reference to the drawings from FIG. 3 onwards.

FIG. 3 shows an example of a state in which the method of the present invention is carried out, in which there is mutual interaction between the furnace wall refractories 13 of the ladle 1, which is formed by lining the iron shell 12 with the furnace wall refractories 13. An excitation coil 14 and a detection coil 15 are embedded in opposing positions at positions opposite to each other. An AC excitation N current supplied from an AC excitation current generator 16 flows through the excitation coil 14 to induce an AC magnetic field within the ladle 1 . - The force detection coil 15 detects the magnetic field intensity at the detection coil position of the magnetic field induced by the excitation coil 14 as an electromotive force.

Here, the distribution of the magnetic field induced in the ladle 1 by the excitation coil 14 is strongly influenced by the molten steel 5 in the ladle. On the other hand, the slag 9 also has a slight effect on the magnetic field distribution, but it is much less than the effect of the molten steel 5, and therefore the magnetic field distribution in the ladle is substantially the same as in the case of only the molten steel 5 without the slag 9. The magnetic field distribution is as follows. In this way, the magnetic field distribution within the ladle 1 is influenced by the molten steel 5, and the magnetic field intensity detected by the detection coil 15 changes depending on the scene level 11 of the molten steel 5.

The change in magnetic field strength detected by the detection coil 15 is
Cancellation self-melting! FIGS. 4(A) to 4(D) show the changes in the wet surface level 11 due to the discharge of the liquid 45. In addition, Figure 4 (
In Δ) to (D), the electromotive force due to the magnetic field strength detected by the detection coil 15 is indicated by the pointer of the voltmeter 17. It is also assumed here that the upper ends of the 1illVa coil 14 and the detection coil 15 are at the same level, and that the upper ends are also at the same level.

As shown in FIG. 4(A), the corner level 11 is the coil 14.
．． 15, the coil 14.
15 is completely blocked by the molten steel 5, the magnetic field strength detected by the detection coil 15 is small. In other words, the direct magnetic flux (primary magnetic field) from the excitation coil 15 does not reach the detection coil 15, but only the magnetic flux (secondary magnetic field 19) that enters the molten steel 5 from the excitation coil 14 and leaks from the molten steel 5. is detected by the detection coil 15, but its secondary magnetic field 19 is 1
Since it is much weaker than the secondary magnetic field, the absolute level of the magnetic field strength detected by the detection coil 15 is low.

Next, as shown in FIG. 4(B), when the scene level 11 falls below the upper end of the coil 14.15 (but above the lower end of the coil 14.15), the excitation coil 14
A part of the primary magnetic field 18 from the magnetic field 18 comes to be detected by the detection coil 15.

As the scene level 11 decreases, the primary magnetic field strength from the excitation coil 14 increases, so as the scene level 11 decreases, the detection magnetic field strength of the detection coil 15 increases. In this process, the secondary magnetic field 19 from the excitation coil 14 via the molten steel 5 is also detected by the detection coil 15.

In this way, the primary magnetic field strength reaches its maximum when the hot water level 11 reaches the same level as the lower end of the coil 14.15, as shown in Fig. 4 (D). ), if the scene level 11 falls below the lower end of the coil 14.15, the primary magnetic field strength remains unchanged, but as the molten steel moves away from both the excitation coil 14 and the detection coil 15, the secondary magnetic field strength increases. It gradually decreases.

Therefore, as shown in FIG. 4(C), when the hot water level 11 reaches the lower end of the coil 14.15, the detection coil 15
The detected magnetic field strength (electromotive force) becomes maximum, and thereafter the detected magnetic field strength gradually decreases. And take f
Once the molten steel in s1 disappears, the magnetic field strength (electromotive force) detected by the detection coil 15 does not decrease any further.

The relationship between the hot water level 11 and the magnetic field strength detected by the detection coil 15 as described above can be summarized as shown in FIG. In Fig. 5, the horizontal axis represents the detected magnetic field strength (electromotive force) of the detection coil 15, and the vertical axis represents the level 1 of the melt #15.
1 corresponds to the position of coil 14.15.

As is clear from FIG. 5, when the hot water level 11 is above the upper end of the coil 14.
．． The electromotive force of the detection coil 15 is at an almost constant low level until it reaches the upper end of the coil 14.15, and from the time when the hot water level 11 reaches the upper end of the coil 14. The electromotive force of the detection coil 15 increases rapidly until the lower end of the coil 14.15 is reached, and the electromotive force reaches its maximum when the lower end of the coil 14. After 1 dB, the electromotive force gradually decreases until the melt level 11 reaches the bottom of the furnace, that is, the molten steel 5 in the ladle 1 is exhausted (this is defined as time C). Therefore, changes in the electromotive force of the detection coil 15 can be clearly detected at three points, A, B, and C. Also, since times A and B are determined by the positional relationship between the coil 14 and 15 and the molten metal level 11 of the molten metal 15, the slag 9
It always corresponds to a fixed position, regardless of the existence of refractories or the erosion of refractories. Moreover, since time C is the time when the molten steel is gone, this also corresponds to a fixed position regardless of the melting loss of the slag or refractory.

Therefore, in the method of the present invention, at least two change points among time points A, 8, and C during the first measurement, for example, B,
C) is detected, and among the detected change points, the flow rate of molten steel is measured from the point where the hot water level is higher (e.g. B) to the point where the hot water level is lower (e.g. C). In addition to estimating or calculating from the casting amount etc., the amount of remaining steel at the change point (C) where the molten metal surface level is lower is determined, and from these values, the melt t! at the change point (8) where the shoulder surface level is higher. Seek AI. At the next measurement,
Detect the change point (B) where melt [1 was determined during the previous measurement,
Using the change point (B) as a reference, the amount of self-molten steel in the ladle after the change point (B) is estimated from the actual casting amount, etc.

To simplify the explanation, an example will be described below in which the changing points at time points B and C are detected during the first measurement.

During the process of outflow of molten steel from the drawer 11, the magnetic field strength is measured by the detection coil 15 as described above, and the detection coil 1
The electromotive force data of No. 5 is input to the computing unit 20, and the point of time when the electromotive force becomes maximum is detected as a change point 8. The point in time when the outflow from the ladle 1 progresses and the molten steel 5 in the ladle WA1 disappears is detected as a change point C, and the electromotive force ■0 at that change point C is stored. Simultaneously with or after such detection, the flow rate of molten steel from change point B to C is determined. This amount of molten steel flowing out can be obtained by integrating the casting speed of continuous casting from change point A to C. Here, since the amount of remaining steel at the change point C is zero, the amount of molten steel flowing out between the change points 8 and 0 obtained as described above is equal to the amount of ladle self-melting 81 at the change point B.
This corresponds to 41. Therefore, the amount of molten steel at this change point B is stored in the calculator 20 for the next measurement.

For the next measurement, the amount of molten steel at change point B obtained during the previous measurement may be used as the estimated reference value, but in order to reduce estimation errors due to melting of the refractory, it is necessary to The melting loss B of the refractory due to one use is investigated in advance, and the amount of molten steel obtained by adding the amount of increase in the internal volume of the ladle 1 due to the melting of the refractory as a correction value is determined as the change point B at the next measurement. It is desirable to use this as the estimated reference value. During this measurement, the magnetic field strength is measured by the detection coil 15 at the same time as the previous measurement, and a point of change (change point 8N) is detected when the electromotive force of the detection coil 15 reaches its maximum.This change point B'
Since the warm blood level at is the same as the level at change point B during the previous measurement, as the estimated value of the amount of molten steel at change point B-, the molten mfl at change point B during the previous measurement is used as the estimated value of the molten steel amount at change point B-. Use the value corrected by the amount of erosion. After the change point B-, the casting speed is integrated in real time and subtracted from the estimated value at the change point B' to calculate the amount of molten steel in real time. By doing this, the amount of remaining molten steel in the ladle after the change point B- can be estimated in real time, so for example, in the ladle of a continuous casting machine, the estimated amount of molten steel will depend on the ladle size, quality requirements, etc. The sliding gate may be closed when a predetermined number of people to remain is reached.

In the above example, change points B and C were detected, and the next measurement was based on the estimated amount of molten steel at the time corresponding to change point B, but if change points A and C or change point A1B were detected, Of course, the estimated amount of molten steel at the time corresponding to the change point may be used as a reference for the next measurement.

It goes without saying that the method of the present invention is applicable not only to ladles in continuous casting, but also to any estimation of the remaining amount of molten steel in a ladle having a molten steel outlet at the bottom.

The fruiting results obtained by the method of this invention are described below.

In order to perform precision weighing using the estimation method of this invention, the estimated molten steel volume in the ladle using the method of this invention is 2.4.6.8.1
When the weight reaches 0.12 tons, the sliding gate is closed, the slag and molten steel in the ladle are separated and cooled and solidified, and then only the steel ingot is weighed to measure the actual amount of molten steel remaining in the ladle. did. The results of this experiment are shown in FIG. According to FIG. 6, the error in the estimated l with respect to the actual melt tsm is about 1 ton, and while in the conventional method mentioned above, the error was about 3 ton even in the case of maximum a11 degrees, the estimation of the present invention It is clear that the method achieved a significant improvement in accuracy.

Furthermore, FIG. 6 shows the effect of controlling the closing timing of the sliding gate by applying the method of the present invention to an actual continuous casting operation. Figure 6 shows a case where the method of the present invention is applied to the sliding gate closing timing control in continuous casting of a steel type with strong internal quality requirements, and a case where the gate is closed empirically without applying the method of the present invention. This figure shows a comparison of the defective rates of slabs. When this invention is not applied to the method, the slag in the ladle flows into the tundish, and in many cases remains in the slab as non-metallic inclusions, resulting in defects. On the other hand, after applying the method of the present invention, the above-mentioned cases disappeared, and only a few defects were caused by other factors, and it was confirmed that this greatly contributed to improving the quality and yield of steel materials.

As is clear from the above explanation, the ladle residual bath WI of this invention!
According to the estimation method, the remaining amount of molten steel in the ladle can be estimated with high accuracy in real time without being affected by slag on the molten steel surface, and therefore it is possible to estimate the remaining amount of molten steel in the ladle with high precision in real time. If the method of the present invention is applied to the closing timing of the sliding gate of a ladle, it is possible to reliably prevent slag from flowing out and obtain high-quality slabs, and at the same time, it is possible to prevent excessive slag from flowing out after the sliding gate is closed. It is possible to prevent a large amount of molten steel from remaining in the ladle, thereby improving the operating rate.In addition, in particular, the estimated molten steel of the refractory on the wall of the ladle can be
According to the embodiment in which the correction is made by l, the estimation error due to the influence of the melting loss of the refractory is reduced, and the amount of molten steel can be estimated with even higher accuracy.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram schematically showing a general example of continuous casting equipment to which the method of the present invention is applied, and Fig. 2 is a schematic diagram showing a situation in which an example of the conventional estimation method is implemented. It is. FIG. 3 is a schematic diagram showing an example of a situation in which the method of the present invention is implemented, and FIGS. 4 (A) to (D) show the level of molten steel in the ladle and the detection coil when implementing the method of the present invention. Figure 5 is a diagram showing the relationship between the detected magnetic field strength (electromotive force) of the detection coil in stages, and Figure 6 is a diagram showing the relationship between the first plane level and the detected magnetic field strength (electromotive force) of the detection coil. Figure 7 is a diagram showing the accuracy of the amount of remaining molten steel in the ladle estimated by the method of the invention, and shows the slab defect rate when the method of the invention is applied to the sliding gate closing timing control of continuous casting equipment. FIG. 11 is a comparison diagram showing a case where the method of the present invention is not applied. DESCRIPTION OF SYMBOLS 1... Ladle, 2... Molten steel outlet, 3... Sliding gate, 5... Molten steel, 9... Slag, 14... Excitation coil, 15... Detection coil,
A, B, C...change points.

Claims (2)

[Claims] (1) When estimating the remaining amount of molten steel in a ladle with a molten steel outlet at the bottom, an excitation coil and a magnetic field strength detection coil are placed facing each other in the refractories on the opposing walls of the ladle, and The intensity of the magnetic field induced from the coil is measured with a detection coil to detect at least two changing points of the induced magnetic field intensity during the outflow process of the molten steel in the ladle, and the The flow rate of molten steel in the ladle up to the second change point is determined by measurement or calculation, and the amount of remaining steel at the second change point is determined, and the amount of molten steel at the first change point is determined from the determined flow rate and remaining steel amount. is determined, and at the next time of measurement, the first change point is detected and the remaining amount of molten steel in the ladle is estimated based on the amount of molten steel at the first change point. Method for estimating the amount of remaining molten steel. (2) As the amount of molten steel at the first change point used in the next measurement, a value corrected by the estimated amount of corrosion loss of the refractories on the inner wall of the ladle is used. Method for estimating the amount of molten steel.