JPH079117A - Automatic closing method of ladle sliding nozzle - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a sliding nozzle automatic closing method that can both prevent the outflow of molten slag and reduce the amount of residual steel in the ladle. [Composition] Molten steel in the ladle is passed through a sliding nozzle,
Pour into tundish under a protective atmosphere. At the end of injection, the slag mixture rate measuring sensor 6A provided around the upper nozzle measures the slag mixture rate, and the slag outflow detector 6 determines the level. Then, when the slag mixture ratio is within the range of 2 to 10%, the pulse generator 7 alternately and repeatedly generates the closing pulse and the opening pulse, and the sliding nozzle opening / closing controller 3A narrows the control of the nozzle opening. After that, when the slag mixing ratio is in the range of 10 to 30%, the nozzle is closed by the closing continuous signal. [Effect] It is possible to omit slag work, prevent slag outflow, improve casting yield by reducing the amount of residual steel, and reduce steel quality defects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents secondary oxidation of an injection flow and outflow of slag into a tundish, etc. when pouring molten steel from a ladle into a tundish, etc.
The present invention relates to a method for automatically closing a ladle sliding nozzle capable of reducing the amount of residual steel in the ladle.

[0002]

2. Description of the Related Art An outflow state of a slag of a ladle is generally judged by an operator by monitoring the pouring flow through a gap between the ladle and the tundish, which is generally called a slag. FIG. 4 is a cross-sectional view illustrating a conventional ladle to tundish injection state at the end of molten steel injection.

When the molten steel 8 is injected from the ladle 1 into the tundish 4, the injection flow 8A from the sliding nozzle 2 comes into contact with the atmosphere and the molten steel 8 undergoes secondary oxidation. For this reason, the tundish 4 is covered with a tundish lid 4A, an injection pipe 5 immersed in the molten steel 8 in the tundish and an injection pipe lid 5A for circulating a protective gas (for example, Ar gas) are provided immediately below the sliding nozzle 2, and the sliding nozzle 4A is provided. 2 is lowered to the inside of the injection pipe lid 5A and the molten steel 8 is injected under Ar atmosphere to prevent the secondary oxidation of the injection flow 8A. However, since the molten slag 9 on the molten steel 8 in the ladle flows out at the end of the injection, it is necessary to close the sliding nozzle 2 using the hydraulic cylinder 3 at the same time as the slag outflow, and the lower end of the sliding nozzle 2 is injected. The tube is removed from the tube lid 5A, and the above-mentioned inspection is performed.

At this time, since the injection flow 8A comes into contact with the atmosphere, secondary oxidation is unavoidable, and the oxide acts as an inclusion to impair the steel quality.

On the other hand, application of slag outflow detection means has been considered in order to omit the scavenging work in which the secondary oxidation of the injection flow is unavoidable. For example, the slag outflow detector of AMEPA, Germany, is not used. It has become possible to detect slag outflow.

FIG. 5 is a diagram showing the measuring principle of the slag outflow detector. The slag mixing rate measuring sensor 6A is composed of a transmitting coil 6A-1 and a receiving coil 6A-2 which are provided in the refractory of the upper nozzle 2A at the bottom of the ladle so as to surround the injection flow 8. A constant current is supplied from the transmitter coil 6A-1, an induced magnetic field 10 is formed in the injection flow 8A, and the molten metal 8 of the injection flow 8A is melted into the molten steel 8 due to the change in the induced electromotive force generated in the reception coil 6A-2. Can be measured.

However, if the slag outflow detector detects the slag outflow and at the same time the sliding nozzle is closed, the residual steel in the ladle increases and the casting yield decreases. On the other hand, if the sliding nozzle is closed when the slag mixing ratio reaches 30%, for example, the sliding nozzle causes a time lag until it is completely closed due to its sliding resistance, and a large amount of slag flows into the tundish. As a result, the composition of molten steel changes and the quality of steel deteriorates.

[0008]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving the above problems in a method of automatically closing a ladle sliding nozzle by using a slag outflow detector. The closed pulse signal and the open pulse signal are alternately transmitted by adjusting the pulse number according to the slag mixing rate level of the slag, and by automatically closing while controlling the opening of the sliding nozzle switch, the secondary oxidation of the injection flow and An object of the present invention is to provide a method for preventing the slag from flowing into the tundish and reducing the amount of residual steel in the ladle.

[0009]

In order to achieve the above object, the method for automatically closing a ladle sliding nozzle according to the present invention has a slag mixing ratio detected by a slag outflow detecting means provided in the ladle sliding nozzle. When it is in the range of 2 to 10%, a closing pulse signal and an opening pulse signal having an equal pulse width and an equal pulse repetition interval are alternately repeated to be transmitted to the sliding nozzle opening / closing control means, and the closing pulse signal The sliding nozzle opening is narrowed down by adjusting the number of pal with the open pulse signal, and when the slag mixing ratio is within the range of 10 to 30%, a closing continuous signal is transmitted to the sliding nozzle opening / closing control means. It is characterized in that the nozzle is closed.

[0010]

FIG. 1 is a sectional view showing an example of a molten steel pouring device and a ladle sliding nozzle automatic closing device used for carrying out the method of the present invention, and FIG. 2 is a block diagram showing the essential points of the method of the present invention. Hereinafter, the method of the present invention will be specifically described with reference to these drawings.

To carry out the method of the present invention, a conventional ladle pouring device is provided with a ladle sliding nozzle automatic closing device as shown in FIG. This automatic nozzle closing device is used for injecting a flow 8 into the refractory of the upper nozzle 2A attached to the bottom of the ladle 1.
It is composed of a slag mixture rate measuring sensor 6A composed of a transmitting coil and a receiving coil provided so as to surround the slag, a slag outflow detector 6, a pulse generator 7, a sliding nozzle opening / closing controller 3A, a hydraulic cylinder 3 and a sliding nozzle 2. There is.

The operation of the molten steel pouring device is the same as the conventional pouring operation described with reference to FIG.

The features of the operation of the automatic nozzle closing device according to the method of the present invention are as follows. As shown in FIG. 2, the slag outflow detector 6 converts the induced electromotive force analog value of the receiving coil of the slag mixing ratio measurement sensor 6A into the slag mixing ratio analog value. Then, the slag mixture rate level is determined, and the slag mixture rate is 2 to
Within the range of 10%, the pulse generator 7 alternately and repeatedly generates the closing pulse signal and the opening pulse signal for the sliding nozzle opening / closing control having the same pulse width and pulse repetition interval.

At this time, the sliding nozzle opening / closing controller 3 is adjusted by adjusting the number of pulses of the closed pulse signal and the open pulse signal.
A is transmitted to A and the hydraulic cylinder 3 is pulse-switching closed / opened to sequentially narrow the nozzle opening. Adjust the number of pulses so that the number of pulses of the closed pulse signal to be transmitted first is greater than the number of pulses of the open pulse signal to be transmitted next, and the difference in each pulse number is It is preferable that the difference is larger than the difference in the number of pulses from the open pulse signal. That is, it is desirable that the degree of narrowing of the nozzle opening be large at first and then gradually decreased.

As described above, when the slag outflow detector 6 detects and determines that the slag mixture ratio is within the range of 10 to 30% while the nozzles are successively narrowed down, the pulse generator 7 outputs an infinite number of pulses. A large closing pulse signal, that is, a closing continuous signal is generated and transmitted to the sliding nozzle opening / closing controller 3A to close the hydraulic cylinder 3 to close the nozzle.

According to the method of the present invention, the mixing ratio of slag is 2 to 10%.
Within the range of, the nozzle opening is controlled and narrowed down to 10 to 30
The reason why the nozzle is clogged within the range of% is as follows.

As shown in FIG. 1, at the final stage of fully opening the sliding nozzle 2 and injecting the molten steel 8 from the ladle 1 into the tundish 4, the molten steel 8 in the ladle 1 is immediately above the upper nozzle 2A. A vortex 8B is formed. And swirl 8
Since the molten slag 9 is present on the molten steel surface of B, the slag outflow is detected when the amount of residual steel in the ladle is large. Therefore, if the sliding nozzle 2 is closed immediately after detecting the outflow of a slag having a slag mixing ratio of 10% or less, the amount of residual steel in the ladle increases and the ingot yield decreases.

Therefore, in the method of the present invention, the mixing ratio of slag is 2 to 10
Within the range of%, the nozzle is not immediately closed and the hydraulic cylinder 3 is pulse-switched closed and opened to overcome the sliding resistance between the upper plate 2B, the lower plate 2C and the lower nozzle 2D, and in a short time. Make accurate control of the nozzle opening. As a result, the formation of the vortex 8B is weakened and the entrainment of the molten slag 9 is suppressed, so that the molten steel 8 can be poured into the tundish 4 without rapidly increasing the slag mixing rate, and the residual steel amount in the ladle can be reduced. Can be reduced.

Noise may be generated in the slag mixing rate measuring sensor 6A due to an arc in an electric furnace near the pouring work place or welding work. When the slag mixing rate is less than 2%, the nozzle opening is narrowed down. Doing so will cause a malfunction and will not be narrowed down.

When the slag mixing ratio is 10% or more and the control of the nozzle opening is continued and narrowed down, the molten slag 9 becomes caught in the vortex 8B, and when the slag mixing ratio further increases, it flows out to the tundish 4. Like Therefore, in the method of the present invention, when the mixture ratio of slag falls within the range of 10 to 30%, the nozzle opening is narrowed and the nozzle is closed. At this time, a part of the nozzle cross section is already closed, and the sliding nozzle 2 slides smoothly, so that the time lag until complete closing can be reduced. Therefore, the nozzle can be closed immediately after the sliding nozzle opening / closing controller 3A receives the closing continuous signal. As a result, the outflow of the molten slag 9 into the tundish 4 can be prevented, and the compositional change of the molten steel 8 in the tundish 4 and the deterioration of the steel quality can be avoided. If the slag mixing ratio exceeds 30%, the slag 9 flows out into the tundish 4, so it is necessary to close the nozzle when the slag mixing ratio is 30% or less.

As described above, according to the method of the present invention, the outflow of slag can be quantitatively detected, and the nozzle opening can be narrowed down and the nozzle closed. As a result, it is possible to omit scrutiny, prevent secondary oxidation of the injection flow 8A, and prevent occurrence of steel quality defects.

The effects of the present invention will be specifically described below with reference to examples.

[0023]

[Example 1] Low carbon stainless molten steel melted in a VOD furnace and an AOD furnace was Ar (argon) from a ladle to a tundish by using the pouring device and the ladle sliding nozzle automatic closing device shown in Fig. 1. Injected under atmosphere.

The automatic closing of the sliding nozzle was performed according to the block diagram shown in FIG. The pulse width of the closing pulse and the opening pulse of the sliding nozzle opening / closing control signal was 0.5 seconds, and the pulse repetition interval was 0.1 seconds. And within the range of 2 to 10% of slag mixture, 5 closed pulses, 2 open pulses, 2 closed pulses,
Open pulses were generated in the order of 1 pulse at 1 second intervals to narrow down the control of the nozzle opening. Next, the slag mixing rate is 10-30
In the range of%, a closed pulse with an infinite number of pulses, that is, a closed continuous signal was generated to close the nozzle.

After closing the nozzle and moving the ladle, the presence or absence of the outflow of slag on the surface of the molten steel in the tundish in the injection pipe was visually judged and the amount of residual steel in the ladle was investigated.

[0026]

[Comparative Examples 1 and 2] At the end of injection, the lower end of the lower nozzle was pulled out from the lid of the injection tube and a scrutin was observed to visually determine the presence or absence of slag outflow. Then, when the slag mixing ratio reached 5% in Comparative Example 1 and 35% in Comparative Example 2, the nozzle closing was performed by immediately generating a closed continuous signal without performing control narrowing of the nozzle opening. Except for this, the same injection as in Example 1 was performed.

FIG. 3 is a diagram showing the change over time in the mixing ratio of slag at the final stage of injection. FIG. 3 (a) shows Example 1, and FIGS. 3 (b) and (c) show Comparative Example 1 and Comparative Example 2, respectively. Indicates.

Table 1 shows the presence / absence of slag outflow, the ratio of the amount of residual steel to the amount of steel output, the amount of oxygen and nitrogen picked up in the molten steel injected, and the coil maintenance rate due to a bald flaw, as determined by the naked eye.

[0029]

[Table 1]

As shown in FIG. 3 (a), in the first embodiment, when the slag inclusion ratio is detected and judged to be within the range of 2 to 10%, the control aperture of the nozzle opening is narrowed down. This suppresses the formation of vortices in the molten steel directly above the upper nozzle, and the molten steel is preferentially injected, so that the amount of residual steel in the ladle can be reduced. After that, when the mixture ratio of slag is detected to be in the range of 10 to 30% and the determination is made, the nozzle is blocked. At this time, the nozzle opening has already been narrowed down, and the sliding nozzle operates smoothly. Therefore, the time lag until complete blockage is reduced, and slag outflow can be effectively prevented.

Further, in Example 1, since the slag outflow is detected by using the slag mixing ratio measuring sensor, the slag watching operation can be omitted, and the amount of oxygen and nitrogen picked up in the molten steel to be poured is reduced. . For this reason, surface defects and ground defects are reduced, and the coil maintenance rate due to the bald defects is lowered.

On the other hand, in Comparative Example 1 shown in FIG. 3 (b), the nozzle mixture is immediately closed after determining the slag mixing ratio of 5% detected in the slag existing on the vortex surface formed in the molten steel. For this reason, as shown in Table 1, the outflow of slag can be prevented, but the amount of residual steel in the ladle increases, and the casting yield decreases.

Further, in Comparative Example 2 shown in FIG. 3 (c), the nozzle is closed at the time when the slag mixing ratio of 35% is detected and determined, so that the slag mixing ratio rapidly increases due to the time lag until complete blockage. Is blocked. Therefore, as shown in Table 1, the amount of residual steel in the ladle can be made relatively low, but a large amount of slag flows into the tundish, which often causes fluctuations in the molten steel composition in the tundish and the occurrence of steel quality defects.

[0034]

EFFECTS OF THE INVENTION According to the method of the present invention, at the end of molten steel injection from a ladle to a tundish, which is carried out under an antioxidant atmosphere, the measuring sensor detects the mixing ratio of slag in the injection flow. It can be omitted, and secondary oxidation of the injection flow and steel quality defects can be prevented. Moreover, when the slag mixing ratio is in the low level range, the nozzle opening is controlled and narrowed down, so that molten steel can be preferentially injected, and the amount of residual steel in the ladle can be reduced to increase the casting yield. Further, since the nozzle is closed immediately when the slag mixing ratio exceeds the low level range, the time lag until complete closing is reduced, and slag outflow can be effectively prevented. Therefore,
It is possible to manufacture a high-quality steel ingot with few surface defects and ground defects.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a molten steel pouring device and a ladle sliding nozzle automatic closing device used for carrying out the method of the present invention.

FIG. 2 is a block diagram showing the main points of the method of the present invention.

FIG. 3 is a diagram showing a change with time of a slag mixing rate at the final stage of injection, in which (a) is an example, (b) is a comparative example 1, and (c) is a comparative example.

FIG. 4 is a cross-sectional view for explaining an injection state at the final stage of injecting molten steel from a conventional ladle to a tundish.

FIG. 5 is a diagram showing a measurement principle of a slag outflow detector.

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[Procedure amendment]

[Submission date] October 26, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is a diagram showing a change with time of a slag mixing rate at the final stage of injection.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneyoshi Onodera 1850 Minato Minato, Wakayama, Wakayama Japan Stainless Steel Co., Ltd. Wakayama Steel Works

Claims (1)

[Claims] 1. A closed pulse signal having an equal pulse width and an equal pulse repetition interval when the slag mixture ratio detected by the slag outflow detection means provided in the ladle sliding nozzle is in the range of 2 to 10%. An open pulse signal is alternately repeated and transmitted to the sliding nozzle opening / closing control means, the number of pulses of the closing pulse signal and the opening pulse signal is adjusted to sequentially narrow the sliding nozzle opening, and the slag mixture rate is 10
When it is within the range of -30%, a closing continuous signal is transmitted to the sliding nozzle opening / closing control means to close the nozzle, thereby automatically closing the ladle sliding nozzle.