JPS62148066A - Estimation method for remaining molten steel in ladle for continuous casting - Google Patents

Abstract

PURPOSE:To surely prevent flow out of slag and to obtain a casting billet having high quality by detecting a molten steel level and also an erosion volume of refractory in a ladle and estimating remaining molten steel in the ladle at high accuracy. CONSTITUTION:At least two changed points in inducing magnetic field intensity of an exciting coil 11 by AC exciting current of a molten metal level measuring apparatus 13 is detected by a detecting coil 12 during flowing process of molten steel in the ladle 1, and molten steel flowing weight between the above- mentioned changed points is obtd. by a controlling device 14. That is, the device 14 is calculated by a tundish 6 weighing machine 15 and tundish 6 weight, pouring weight, etc., according to a length measuring instrument 16 for the above-mentioned flowing wt., and is detected for a change of the ladle sectional area in comparison with flowing weight at new-lining ladle 1 to detect erosion vol. of the ladle at arranged position of coil 11, 12. Then the remaining molten steel weight in the ladle is obtd. by changing of the above-mentioned magnetic field intensity as standard for the ladle 1 vol. compensated by the above- mentioned erosion vol.

Description

[Detailed description of the invention] <Object of the invention> Industrial field of application The present invention relates to a method for estimating residual molten steel in a ladle in continuous casting, and more specifically, to prevent outflow of converter slag mixed in the ladle. The present invention relates to a method for estimating the amount of residual molten steel in a ladle during continuous casting to improve the quality of continuously cast slabs.

Conventional technology In general, in continuous steel casting, a sliding gate 3 and a long nozzle 4 are attached to the FJ steel outlet 2 provided at the bottom of the trap A1, as shown in Fig. 6. Injecting the molten steel 5 in the pot into the tundish 6 via the sliding gate 3 and the long nozzle 4,
Further, the molten steel in the tundish 6 is usually injected into a mold 7 and cast to form 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, since slag 9 exists on the surface of the molten steel 5 in the ladle 1, and the slag also starts to flow out at the end of the flow of molten steel in the ladle, the sliding gate is opened only after the molten steel in the ladle is completely gone. 3 is closed, the slag 9 in the ladle also flows into the tundish 6 and enters the slab 8 through the mold 7. If converter slag is mixed in the slab, it will appear as non-gold layer inclusions as defects such as slivers even after rolling, damaging the product.

Therefore, conventionally, an operator has empirically determined that the remaining amount of molten steel in the ladle has become small and closed the sliding gate 3 to prevent the slag from flowing out of the ladle.

However, in reality, the molten tJAu in the ladle cannot be visually observed, so the fact that the molten steel in the ladle has decreased is actually due to the slag 9 in the ladle entering the tundish 6 through the long nozzle 4. You can't judge until after you start. 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 actual steel strips, molten steel and slag are not completely separated, but are mixed to some extent, so in order to maintain good quality of slabs, it is necessary to adjust the steel strip size and quality requirements. Depending on the amount of molten steel, it is necessary to close the sliding gate while leaving the molten steel in the range of about 1 to 20 tons.

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

In other words, as a conventional method for estimating the amount of molten steel remaining in the ladle, first, the estimated production value for each ladle of molten steel in the molten steel refining process is used as a standard, and the actual amount of tIa cast is subtracted to calculate the amount in the ladle. A method of calculating the remaining amount of molten steel has been proposed, but
In this case, since there is actually a large variation in the amount of molten steel produced in the refining process, the accuracy of the estimated value of the remaining molten steel in the ladle is inevitably low.

In addition, as a second method, the steel stock is weighed using a crane scale S, and the initial layer in the steel stock is calculated by subtracting the amount of stacked steel stock in an empty state. There is a method of estimating the residual melt in the ladle 1lffi by calculating the I output and subtracting the actual casting amount from that amount. However, in addition to molten steel, there is a considerable amount of slag in the steel strip, and therefore, in this method, an error occurs by the amount of slag. It is also possible to estimate the slag m and subtract it, but slag lifting involves large variations in work.
Accurate estimation is difficult.

As a third method, JP-A No. 55-95084, 53
There is a method of detecting the level of molten steel in a ladle using a molten steel level detection means disclosed in Japanese Patent Application No. 7359, and determining the amount of molten steel in its entirety. However, the accuracy of estimating the amount of molten steel decreases due to the influence of erosion of the large ladle-resistant material.

That is, as the melting loss of the large steel stock increases, the internal volume of the steel stock increases, and the amount of molten steel increases at the same level of molten steel, thus increasing the error from the actual amount of molten steel.

As mentioned above, all of the conventional methods for estimating the amount of molten steel remaining in the ladle have large errors with respect to the conventional molten uAm. Therefore, when determining the closing timing of the sliding gate using the conventional estimating method, it is necessary to be on the safe side. The sliding game 1 has to be closed with a large amount of remaining coral, which results in a large amount of coral being scrapped, resulting in high costs.

Problems to be Solved by the Invention The present invention aims to solve these problems, and specifically, detects the level of molten steel and detects the amount of corrosion loss of refractories in the steel stock, The purpose of the present invention is to provide a method for estimating the amount of remaining molten steel in a steel tap that is capable of estimating the remaining amount of molten steel in a steel tap with high accuracy.

<Structure of the Invention> Means for Solving the Problems and Their Effects The present invention provides an excitation coil and a magnetic field strength detection coil that are disposed facing each other in refractories on opposing walls of a ladle, and the magnetic field induced from the excitation coil is In the method for estimating the amount of molten steel remaining in the steel tap while measuring the strength of the molten steel with a detection coil and detecting the molten steel level, the induced magnetic field strength during the outflow process of the molten steel in the steel tap is Detect at least two changing points of the mouth, determine the flow rate of molten steel in the ladle between the changing points of the mouth by measurement or calculation, detect the amount of erosion of the refractory in the ladle, and based on the amount of erosion. The method is characterized in that the amount of remaining molten steel in the ladle is estimated from the change in magnetic field strength using the corrected steel volume as a reference.

Hereinafter, the structure and operation of the present invention will be explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing a method for estimating the residual molten steel in a ladle according to the present invention, FIG. 2 is a graph showing the relationship between the level of molten steel in a ladle and an output signal, and FIG. This is an explanatory diagram showing the configuration of the control system H, Fig. 4 is a graph showing the relationship between the bottom surface erosion and collapse of the ladle and the cross-sectional area ratio, and Fig. 5 is a graph showing the relationship between the target remaining steel amount and the actual remaining steel amount. Melting m! ! FIG. 6 is a graph showing the distribution of the difference between 1 and 1. FIG.

The present invention was developed based on the third method, and
The molten metal level measuring device uses the measuring device disclosed in Japanese Patent Laid-Open No. 55-95084. This control method is implemented with the apparatus shown in FIG. In Figure 1, 13 is JP-A No. 5
This is a molten metal level measuring device shown in No. 5-95084, and a pair of detection ends thereof are installed in a refractory in a steel stock. That is, an excitation coil 11 and a detection coil 12 are embedded in the refractory of the steel stock 1 in opposing positions at mutually opposing positions. An AC excitation current supplied from an AC excitation current generator (not shown) built in the level measuring device H13 flows through the excitation coil 11, and an AC magnetic field is induced in the steel stock 1. The -force detection coil 12 detects the magnetic field strength at the detection coil position of the alternating current magnetic field as an electromotive force.

The magnetic field distribution induced by the excitation coil 11 is strongly influenced by the molten steel in the steel drawer 1, and the magnetic field strength detected by the detection coil 12 changes depending on the level of the molten steel. By doing this, the level of the molten steel is detected, and the magnetic field strength is as follows.

First, when the hot water level is above the upper end of the coil 11.12, the magnetic field strength detected by the detection coil 12 is small because the space between the coils 11.12 is blocked by molten steel.

That is, the direct magnetic flux (primary magnetic field) from the excitation coil 11 does not reach the detection coil 12 and enters the molten steel, and only the magnetic flux (secondary Ia field) leaking from the molten steel is detected by the detection coil 12. The detected magnetic field strength will be small.

Then, the hot water level bell reaches the upper end of coil 11.12,
Furthermore, when going downward, excitation 11 coil 1
A portion of the primary magnetic field from 1 becomes detected by the detection coil 12, causing an increase in the magnetic field strength. Then, as the hot water level decreases, the strength of the primary magnetic field increases, so the strength of the magnetic field detected by the detection coil 12 becomes higher and higher. Note that the secondary magnetic field is also detected at the same time. This increase in the detected magnetic field strength continues until the scene level reaches the lower end of the coil 11.12, and when the lower end level is reached, the primary magnetic field strength reaches its maximum.

After that, if the scene level falls below the lower end of the coil 11.12, the primary magnetic field strength remains unchanged (the same), and the secondary magnetic field strength gradually decreases as the molten steel becomes the outlet where the molten steel moves away from the coil 11.12. , resulting in a decrease in the detected magnetic field strength. Then, once the molten steel in the ladle 1 is gone, the magnetic field strength does not decrease any further and becomes stable. This situation is shown in Figure 2.

In this way, it is clear that while the electromotive force changes due to the strength of the detected magnetic field of the detection coil 12, the change when the hot water level reaches the upper and lower ends of the coil 11.12 can be clearly detected. In the present invention, this fish is used to detect the amount of refractory erosion within the steel stock. Detection of this refractory erosion M is performed as follows.

The flow rate of molten steel between the two points from the upper end of the coil 11.12 until the molten metal level reaches the lower end is 1 weight,
Calculated from the casting weight, the change in the cross-sectional area of the ladle is detected in comparison with the flow rate when the ladle is new, and the amount of erosion in the area where the coils 11 and 12 are arranged is detected. Estimating the melting damage at the bottom of the ladle from the melting damage on the wall at the placement location, and calculating the amount of residual molten steel.

At this point, the corrosion of the refractory installed on the steel plate is determined by the receiving steel temperature,
The ladle wall surface,
It is clear that there is a correlation with the state of erosion on the bottom, etc., and an example is shown in FIG.

This will be explained in more detail below.

14 in Fig. 1 is the output of Fig. 2 and tanditshu weight 1! l
This is a control device that estimates the amount of remaining molten steel, which is the main focus of the present invention, and controls the injection of molten steel into a ladle based on this estimation, using the amount obtained from f15) and the casting amount. This control device 14 is constructed as shown in FIG. Control device! 11
The purpose of step 4 is to obtain the level signal obtained in step 13 and the amount of steel corrosion loss. This is because even if the distance between the bottom end of the coil and the surface of the molten steel is known, it is difficult to know the height of the molten steel itself because refractory corrosion occurs not only on the wall but also at the bottom, causing changes in the ladle depth. Because it is possible.

This correction method will be explained below.

In Fig. 3, a and b are peak detectors, c and d are storage devices,
e and h are a subtractor, ri is a consolidator, i is a JI calculator, f is a divider, and j is a comparison 'an' unit and a function setter, respectively.

In Fig. 3, peak detectors a and b are devices that detect points corresponding to the upper end and lower end of the coil, which are the changing points where the electromotive force clearly changes shown in Fig. 2, and the molten metal level measuring device The peak value of the electromotive force generated at the above change point is detected from the output of step 13. The estimated value of the remaining steel at this time is obtained from the following equation: steel production S - tanditshu heavy lifting - casting weight x unit weight of the slab. Based on S, use multiplier i to calculate casting length x slab unit weight, adder 0 to add 4 m of molten metal output from tanditshu weighing scale 15, and subtractor 11 from the known production structure. By subtracting the amount, the amount of remaining steel can be determined. These are stored in the memory devices @e and d, respectively, and the difference between them is determined in the subtractor e. At this time, even if there is an error in the amount of produced copper, it is offset by calculating the difference. By dividing this by the height of the coil [, the cross-sectional area of the new ladle, and the specific gravity of the molten steel γ using the divider, the cross-sectional area of the chain in use with respect to the new ladle, ^/A, is determined.Furthermore, the cross-sectional area ratio A
The amount of bottom surface melting loss can be determined from the relationship between /Ao and bottom surface melting loss ff1X. A/^0 vs.
The relationship is stored in the k function setter. Bottom melting f
By calculating f1X and the signal from the molten metal level measuring device 13, the molten steel level from the bottom can be determined (if you want to monitor with heavy M, you can multiply this by the cross-sectional area A). A comparator j compares this with a predetermined target remaining steel amount according to the steel stock size and quality requirements, and if they match, it is output to 17 as "injection end detection".

The contents of the calculation are shown in the following equation.

h=Jo-Z+X 2=αV+β However, h... Molten steel depth! .・・・・・・Length from the bottom end of the coil to the bottom of the new pot (constant) ... Output signals α, β of the molten metal level measuring device ... Constants Of course, the system shown in Figure 3 can also be configured by processing it in software using a microcomputer or minicomputer. It is.

Example: Applying the method of estimating the amount of remaining molten steel of the present invention to continuous & R construction, controlling the injection end and achieving the target remaining amount! ! The distribution of the difference between 4@ and the actual remaining molten steel is shown in a bar graph in Figure 5. As is clear from the figure, the error was within about 1 ton, indicating that the present invention is effective. Furthermore, when the present invention is applied to the closing timing control of a sliding nozzle, there are no cases where slag intrudes into the slab as it flows out into the steel plate.

<Effects of the Invention> The present invention detects at least two changing points of the induced magnetic field intensity during the outflow process of solid molten steel in the ladle, and determines the outflow of molten steel in the ladle between the changing points at the mouth by measurement or calculation.
It is characterized by detecting melting loss a of the refractory in the ladle, and estimating the remaining amount of molten steel in the ladle from the change in magnetic field strength using the ladle volume corrected based on the amount of melting damage as a reference. Residual melt in steel plate 1
According to the present invention, it is possible to reduce the H1 constant error of the residual melt tMffi in the ladle due to the progress of melting of the refractory. In addition, if applied to the closing control of sliding nozzles, the amount of remaining molten steel can be estimated with high accuracy, and as a result, it is possible to reliably prevent slag from flowing out and obtain high-quality slabs. Now you can.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the ni standard method for the residual molten steel a in the steel withdrawal according to the present invention, Fig. 2 is a graph showing the relationship between the ladle solid molten steel level and the output signal, and Fig. 3 is a diagram showing the relationship between the ladle solid molten steel level and the output signal. An explanatory diagram showing the configuration, Fig. 4 is a graph showing the relationship between the amount of erosion on the bottom surface of the steel plate and the cross-sectional area ratio, Fig. 5 is a graph showing the distribution of the difference between the target remaining w4m and the actual remaining molten steel surface. FIG. 6 is a sectional view of the vicinity of the ladle in normal continuous casting. Code 1... Ladle 2... Molten steel outlet 3... Sliding gate 4... Long nozzle 5... Molten steel 6.
...Tandisht...Mold 8...Slab 9...
...Slug 11 ...Exciting coil 1
2...Detection coil 13... Molten metal level measuring device 14...
...Residual molten steel amount control device 15...Tandish weight scale 1G...
・Length measuring device

Claims (1)

[Claims] An excitation coil and a magnetic field strength detection coil are arranged facing each other in the refractories on opposing walls of the ladle, and the strength of the magnetic field induced by the excitation coil is measured by the detection coil to detect the molten steel level while detecting the molten steel in the ladle. A method for estimating the remaining amount of molten steel in the ladle includes detecting at least two changing points of the induced magnetic field strength during the outflow process of the molten steel in the ladle, and calculating the amount of molten steel flowing out in the ladle between these changing points. Determined by measurement or calculation, detecting the amount of erosion of the refractory in the ladle, and estimating the remaining amount of molten steel in the ladle from the change in magnetic field strength with the ladle volume corrected based on the amount of erosion as a reference. A method for estimating the amount of remaining molten steel in a ladle, characterized by: