JPH1080762A - Method for predicting flow-out of slag in molten steel ladle and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the flow-out of slag by continuously measuring just the upper part of a leading hole with microwave, detecting the point of time when the surface position starts the variation having short period, adding a prescribed time and judging as the slag flow-out timing. SOLUTION: The slag 3 is floated up on molten steel 2 in a molten steel ladle 1, and the molten steel 2 is flowed out from the leading hole 4 of the ladle 1 and a microwave level meter 10 is set at the upper part of the leading hole 4. The radiation heat from the molten steel surface is prevented with a heat insulating board 11. When the molten steel level becomes a specific level, the measured result of the level meter 10 is started to vary in the short period. When the molten steel in the ladle 10 becomes little, the molten steel is sucked into the leading hole 4 in a swirling state and the turbulence is developed on the surface level, and this turbulence remarkably appears in the molten steel having rich fluidity and does not remarkably appear in the slag having poor fluidity. The flow-out timing of the slag is obtd. by adding the prescribed time to the point of time when the variation is detected and the prescribed time is decided in consideration of the shape and the size of the ladle 10 and kind of the molten steel, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for predicting a slag outflow timing for discharging only molten steel except for slag when the molten steel is poured into a container in a next process.

[0002]

2. Description of the Related Art Generally, slag floats on the surface of molten steel during refining to prevent oxidation of the steel. The molten steel is discharged from the molten steel ladle to the receiving tray of the next process through the outlet provided at the bottom, and at this time, the molten steel having a large specific gravity flows out first. However, as the amount of molten steel decreases, slag having a low specific gravity is also involved and starts to flow out together (hereinafter referred to as co-flow). Since the co-leached slag reduces the quality and yield of steel, it is an important technique to quickly detect the co-flow of the slag and stop the discharge of molten steel.

Conventionally, in order to detect co-spill of slag,
Technology for detecting slag in the outlet pipe after passing through the outlet has been developed.

For example, in a slag detection device described in Japanese Patent Application Laid-Open No. Sho 61-30271, a reflected microwave is measured by transmitting a microwave through a waveguide to measure the difference between the reflectance of molten steel and the slag. Based on the above, the change in the reflectance that occurs when the slag starts to flow out is captured (hereinafter referred to as the reflectance method). FIG. 5 shows an outline of this apparatus. The molten steel 2 in the molten steel ladle 1 flows out of the outlet pipe 4 and transmits a microwave to this flow. The microwave oscillated by the oscillator 20 is guided and transmitted by the waveguide 23 through the circulator 21 and the stub tuner 22 for matching the impedance. The reflected wave is separated by the circulator 21 via the waveguide 23 and the stub tuner 22, and is guided to a measurement circuit. When the slag is mixed into the molten steel flow to some extent, the reflection coefficient changes, so that the change can be detected by measuring the reflected wave.

[0005] Japanese Patent Publication No. Hei 7-41402 discloses a technique in which a transmission coil and a reception coil are arranged around an outlet pipe, and slag is detected from a change in conductivity when slag is mixed. (Hereinafter, referred to as the conductivity method).

[0006]

However, in both the reflectance method and the conductivity method, the slag that reaches the outlet pipe is detected after the slag starts flowing out. Furthermore, since the closing of the outlet is performed by sliding the closing lid, it takes several seconds to close the outlet after detection. For this reason, there is a problem that not only the outflow of the slag cannot be prevented, but also the slag cannot be quickly prevented.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to predict the time of slag outflow before the slag reaches the outlet and prevent the outflow thereof.

[0008]

The first means for solving the above-mentioned problem is that when the molten steel in the molten steel pot in which the slag floats on the surface is discharged from the outlet provided on the bottom of the molten steel pot, the slag is discharged. This is a method for predicting the outflow start time of a slag of a molten steel ladle including the following steps (a) to (c). (A) a step of continuously measuring the surface position of the molten steel immediately above the outlet using microwaves; (b) a step of detecting a point in time when the surface position starts to change in a short cycle; (c) Calculating a slag outflow time by adding a predetermined time to the time point.

According to the first means, in order to measure the surface position of the molten steel, a measuring wave is transmitted and reflected on the surface of the molten steel to measure the distance from the transmitting position to the surface of the molten steel. Microwaves are most suitable at that wavelength. Dust is scattered in the molten steel pot. For example, a measurement wave having a short wavelength such as light has a high scattering rate before reaching the molten steel surface, and hardly transmits floating slag. On the other hand, a measurement wave having a long wavelength tends to be diffracted, is poor in directivity, is extremely attenuated, and further measures not only the level of molten steel immediately above the outlet but also the average level of the entire surface of the molten steel, thereby lowering the measurement sensitivity.

[0010] The microwave has a wavelength on the order of cm,
Microwave is used as the measurement wave because scattering by dust is small and the slag layer which is a dielectric is also transmitted.

When the molten steel is discharged from the outlet, the surface position of the molten steel in the molten steel pot (hereinafter, referred to as the molten steel level) is uniformly reduced over the entire surface. However, when the level is reduced to some extent, a spiral flow around the outlet occurs in the molten steel. When this spiral flow occurs, the molten steel level, which has been gradually decreasing until then, suddenly starts to fluctuate in a short period,
A different change appears in the transition of the measured value. At this point, the co-spill of the slag has not yet begun, but will soon commence.

When the measured value of the molten steel level is measured with the passage of time, the point at which the short-period fluctuation starts is detected.

When a predetermined time is added to the detected time, the outflow time of the slag is calculated. The predetermined time is determined in consideration of the shape and size of the molten steel pot and the type of the molten steel.

A second means for solving the above-mentioned problem is a method and an apparatus for predicting slag outflow of a slag of a molten steel ladle comprising the following components (a) to (c). (A) a microwave level meter installed above the outlet of the molten steel pot, (b) a heat shield provided on the microwave level meter, and (c) a signal from the microwave level meter over time. An arithmetic unit that detects a change point in time when a signal change has changed from a monotonous change to a short-period change, and adds a predetermined time to the change point to calculate a slag outflow timing.

According to the second means, the microwave level meter is installed above the molten steel pan, and the microwave is transmitted toward the molten steel. When the reflected wave is measured, the reflected wave on the slag surface and the reflected wave on the molten steel surface are measured. Is received. Then, the distance to these surfaces is determined by the time taken from transmission to reception.

Since the installed microwave level meter receives radiant heat directly from molten steel, a heat shield is provided to prevent this. Since microwaves pass through the dielectric, bricks or ceramics having excellent heat resistance can be used for the heat insulating plate.

The microwave level meter outputs a level measured every moment, and the output signal is input to an arithmetic unit.
The change over time is examined. By this investigation, the arithmetic unit detects a change point in time when the signal changes from a monotonous change to a short-period change.

The detected change point is input to a computing unit. The arithmetic unit calculates a predetermined time from the shape and dimensions of the molten steel pot and the molten steel stored in advance, and calculates the slag outflow timing in addition to the predetermined time at the input change point.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
When the level of the molten metal is measured using a microwave, a reflected wave shown in FIG. 2 is obtained. The microwave is transmitted from the directional antenna, but in order to measure the molten steel level by squeezing it just above the outlet, it is better to bring the level meter closer to the molten metal surface and a heat shield is required. In the figure, the vertical axis indicates the received wave height, and the horizontal axis indicates the position with reference to the level meter. The reflected waves are received at the R, S, and T positions. In these, R is a heat insulating plate, S is
Is the slag, and T is the surface position of the molten steel. Thus, the use of microwaves measures the slag level as well as the molten steel level.

FIG. 3 shows the change over time when the level of the molten metal during the discharge of molten steel is measured using this microwave. Both the slag level and the molten steel level monotonously decrease at a substantially constant rate until the point A. Then, at the time point A, the slag level slightly increases in speed, but the change time point is hard to catch instantaneously.

On the other hand, the molten steel level gradually decreases when reaching the point A, as in the case of the slag level, but in addition to this, it suddenly starts to fluctuate in a short cycle. This phenomenon is extremely remarkable, and the time point A can be detected immediately.

The speed at which the level of molten steel decreases has increased.
This is because the amount of molten steel in the molten steel pot was reduced and the surface level immediately above the outlet started to decrease. Also, the short-period fluctuation in the molten steel level is caused by a level disturbance due to the flow sucked into the outlet in a spiral shape. This turbulence is remarkable in molten steel with high fluidity, but not in slag with poor fluidity.

[0023]

EXAMPLE When molten steel was poured from a steel ladle into a tundish of a continuous casting machine, the outflow time of slag was predicted using the apparatus of the present invention.

FIG. 1 shows the apparatus used. In the molten steel pot 1, the slag 3 floats on the molten steel 2, and the molten steel 2 flows out from the outlet 4. The microwave level meter 10 was installed above the outlet 4, the radiant heat from the hot water surface was prevented by the heat insulating plate 11, and the temperature was kept at about 40 ° C. or lower by sending cool air. Then, the measurement signal was sent to the arithmetic unit 12, the signal was processed by the arithmetic unit 12, and the outflow start time of the slag 3 was predicted based on the processing result. Reference numeral 4 'denotes an outlet pipe.

The microwave level meter was a transmission / reception integrated type, and a horn type antenna was used. Transmission frequency is 5.8GH
z. A plate made of alumina (AI ₂ O ₃ : 92 wt%) and having a thickness of about 9 mm was used as the heat insulating plate. The test was also performed at a transmission frequency of 10 GHz. In this case, a heat shield plate of about 5 mm was used.

The arithmetic unit 12 calculates the slag layer thickness and the molten steel outflow velocity necessary for the prediction at intervals of one second in addition to the slag level and the molten steel level. Based on the information provided, a prediction was made.
The prediction result was sent to a process computer (not shown), and when the timing of stopping molten steel outflow came, the outlet 4 was closed by the closing plate 5 to stop the injection of molten steel.

The prediction result is similar between the case where the transmission frequency is 5.8 GHz and the case where the transmission frequency is 10 GHz, and is 5.8 GHz.
FIG. 4 shows the results in the case of (1). The figure also shows the slag outflow measured by the conventional reflectance method measured at the same time. The left vertical axis in the figure is the level of the molten metal according to the method of the present invention, the right vertical axis is the slag outflow, and the horizontal axis is the time axis.

In the present invention, a point P at 40 seconds after point A at which a short-period fluctuation in the molten steel level appears was predicted to be a slag outflow start time.

On the other hand, in the reflectance measurement method, co-flow of slag was detected at the time point Q, and thereafter, it was measured that the slag flow rate rapidly increased. This measured slag outflow curve S
Was extrapolated and indicated by the dotted line, which was in good agreement with the predicted P time point.

[0030]

As described above, according to the present invention, when the molten steel is discharged, the level of the molten steel is measured immediately above the outlet of the molten steel ladle, and the level decrease curve is short before the slag flows out at the end of the molten steel outflow. A time point that fluctuates in a cycle is detected, and a slag outflow start time is predicted based on this. Therefore, it is possible to completely prevent the slag from flowing out, and the quality and yield of steel are greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a slag outflow prediction device used in an embodiment of the present invention.

FIG. 2 is a diagram showing a received wave height of a reflected wave of a transmitted microwave.

FIG. 3 is a diagram showing a change curve of a slag level and a molten steel level for explaining the principle of the invention.

FIG. 4 is a diagram showing a slag outflow start time predicted in the embodiment of the present invention.

FIG. 5 is a schematic diagram of a conventional slag detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molten steel pot 2 Molten steel 3 Slag 4 Outlet 5 Closing plate 10 Microwave level meter 11 Heat insulation plate 12 Arithmetic unit.

Continuing on the front page (72) Inventor Tetsuo Taniguchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Takashi Itakura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In company

Claims (2)

[Claims] 1. A method for predicting the start time of slag outflow when molten steel in a molten steel pot in which slag floats on the surface is discharged from an outlet provided in the bottom face of the molten steel pot.
A method for predicting slag outflow of a molten steel ladle, comprising the step (c). (A) a step of continuously measuring the surface position of the molten steel immediately above the outlet using a microwave, (b) a step of detecting a point in time when the surface position starts to change in a short period from the measurement result, (C) calculating a slag outflow time by adding a predetermined time to the time point. 2. An apparatus for predicting slag outflow of a molten steel ladle, having the following components (a) to (c). (A) a microwave level meter installed above the outlet of the molten steel pot and measuring the position of the molten steel surface immediately above the outlet,
(B) a heat shield provided on the microwave level meter;
(C) processing the signal from the microwave level meter over time to detect a change time point at which the signal change changes from a monotonous change to a short-period change, and add a predetermined time to the change time to add a slug; An arithmetic unit that calculates the outflow time.