JP2936082B2 - How to open the tundish injection nozzle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for opening a tundish injection nozzle when a closed start of a continuous casting operation has failed.

[0002]

2. Description of the Related Art In a continuous casting operation, generally at the start of casting, molten steel 13 is poured from a ladle 11 into a tundish 12 as shown in FIG. 2, and the molten steel 13 in the tundish reaches a predetermined amount. Slide valve 14 from tundish 12 at time
Is opened and molten steel 13 is poured into mold 15. However, at the start of casting, molten steel is oxidized by oxygen in the air present in the tundish and inclusions are easily generated,
In addition, if the timing of starting the injection from the tundish to the mold is early, sufficient time to separate and float the inclusions in the tundish cannot be secured. Is generally inferior. .

[0003] In order to prevent this, the molten steel is held in the tundish until the level of the molten steel in the tundish poured from the ladle reaches near the capacity limit of the tundish,
A so-called closed start method for starting the injection of molten steel from a tundish into a mold after a sufficient time for flotation and separation of inclusions in the tundish is ensured is performed.

On the other hand, as a flow control device for injecting molten steel from a tundish into a mold, a slide valve made of a refractory as shown in FIG. 3 is generally used below an injection nozzle of the tundish, While holding the molten steel in the tundish, the Ar gas 7 flows from the pores 6 incorporated in the middle slide plate 3 out of the three-layer plate brick, so that the Ar gas 7 flows in the insert nozzle 1 or the bottom plate 2. It prevents the molten steel from solidifying.

[0005]

However, since the temperature of the molten steel in the tundish is controlled to a solidification temperature of about +20 to 30 ° C., the molten steel is easy to solidify. When pouring molten steel into the steel, the molten steel may solidify in the insert nozzle or the bottom plate, and casting may not be started.

At this time, in order to open the nozzle, an operator inserts an oxygen pipe into the nozzle from the top of the tundish and melts the solidified steel in the nozzle with oxygen. Not only is the danger itself, but there is also molten steel in the tundish, so when the nozzle cannot be seen from the top and the oxygen pipe could not be inserted into the nozzle well, the oxygen will melt the refractory around the nozzle, Furthermore, since a large amount of oxygen must be supplied to the molten steel, the molten steel is severely oxidized and the level of inclusions is significantly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a nozzle of a tundish clogged with solidified steel is supplied with oxygen by a slide valve for controlling a flow rate of molten steel.
By blowing a gas mixture of Ar gas into
An object of the present invention is to melt solidified steel in a nozzle and open a hole without melting a surrounding refractory .

[0008]

The present invention SUMMARY OF THE INVENTION, in continuous casting operation, incorporating a slide valve for controlling the molten steel flow to be injected from the tundish into the mold pores or a porous refractory than oxygen equivalent amount of Ar gas Mixed gas
This is a method for opening a tundish injection nozzle that blows and melts solidified steel in the nozzle without melting the surrounding refractory .

[0009]

The slide valve attached to the tundish is of a two-layer type or a three-layer type. Here, a more general three-layer type slide valve will be described as an example. As shown in FIG. 1, the slide valve used in the method of the present invention has a bottom plate 2 below an insert nozzle 1, and a slide plate 3 provided between the bottom plate 2 and a seal plate 4. The slide plate 3 slides between the bottom plate 2 and the seal plate 4 by the operation of the cylinder 5 for controlling the flow rate of molten steel. A pore 8 or a porous refractory (not shown) is incorporated in the bottom plate 2, and a pipe 9 for gas supply is connected to the pore 8 or the porous refractory. The slide plate 3 incorporates pores 6 or a porous refractory (not shown), and a pipe 7 for gas supply is connected to the pores 6 or the porous refractory.

As shown in FIG. 4, when the closed start fails, the molten steel is cooled by Ar gas 7 blown from pores 6 incorporated in the slide plate 3 and solidified steel 10 is cooled.
Is formed, and the inside of the nozzle is closed. At this time, the pores 6 incorporated for the closed start are often closed, and it is often difficult to blow a sufficient amount of gas from here to melt the solidified steel 10. In this case, separately from the slide plate , an equal amount of Ar gas is mixed with oxygen through the pores 8 incorporated in the bottom plate 2.
The mixed gas is blown to melt the solidified steel 10.

According to the method of the present invention , an equivalent amount of oxygen is
Mixed gas to mix the Ar gas
The oxygen in the medium reacts with the solidified steel efficiently, and the solidified steel can be dissolved with a very small amount of oxygen. It is desirable that the pores 8 face downward toward the solidified steel 10.

At this time, a large amount of heat is generated in the reaction between the oxygen and the molten steel or the solidified steel. Therefore, when the oxygen is blown for a long time, the heat of reaction causes the pores 8 and the surrounding refractories to be melted and damaged. Sometimes. In order to prevent this, Ar gas which does not react with the molten steel is mixed with oxygen, and heat of oxidation reaction is taken as sensible heat of Ar gas . When mixing Ar gas, by mixing an equal amount of Ar gas with oxygen, the local temperature rise due to the heat of oxidation reaction is reduced by a factor,
The solidified steel in the nozzle can be melted without melting the refractories around the pores 8 and the surroundings.

[0013]

The present invention will be described below with reference to examples. A mixed gas obtained by mixing an equal amount of Ar gas with oxygen is used for the opening of the tundish injection nozzle closed due to failure of the closed start, and this gas is blown from the pores of the bottom plate to remove the solidified steel. Upon melting, the nozzle was opened. At this time, the amount of oxygen used in the conventional method of inserting an oxygen pipe into the molten steel from the upper part of the tundish to melt the solidified steel in the nozzle required an average of 100 liters of oxygen, but the invention method required an average of 5 liters.
The nozzle could be opened with oxygen.

Further, as a result of examining the amount of oxides generated in the molten steel due to oxygen used for the opening, as shown in FIG. 5, the amount of Al ₂ O ₃ in the ladle after the completion of the molten steel treatment and the conventional nozzle while observed a large difference between the amount of Al ₂ O ₃ in the tundish after opening, little difference between the amount of Al ₂ O ₃ in the tundish after the nozzle opening according to the present invention method unacceptable. From this result, it is clear that even if the method of the present invention fails in closed start, it is possible to safely open the nozzle without contaminating the molten steel.

In the above embodiment, in the closed start method in which Ar gas is blown from the pores of the slide plate,
Mix an equal amount of Ar gas with oxygen through the pores of the bottom plate.
In the closed start method in which Ar gas is blown from the fine holes of the bottom plate, the mixed gas may be blown from the fine holes of the slide plate.

Further, in the closed start method in which Ar gas is blown from the fine holes of the slide plate and the bottom plate, another fine hole for blowing a mixed gas obtained by mixing an equal amount of Ar gas with oxygen can be provided. said Ar gas
It is also possible to open the nozzle by switching to a mixed gas . However, in this method, since the front surface of the pores is covered with the solidified steel due to the failure of the closed start, the mixed gas often does not flow sufficiently, and it takes time to open the nozzle.

[0017]

According to the present invention, a solidified steel in a nozzle of a tundish clogged with solidified steel is blown into a nozzle of a tundish clogged with solidified steel by blowing a mixed gas obtained by mixing an equal amount of Ar gas with oxygen from a slide valve for controlling the flow rate of molten steel. According to this method, the nozzle can be safely opened without refractory damage around the nozzle and without contaminating the molten steel.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a slide valve used in the method of the present invention.

FIG. 2 is an explanatory diagram of a continuous casting operation.

FIG. 3 is an explanatory diagram of a conventional technique.

FIG. 4 is an explanatory diagram of an example of nozzle blockage.

FIG. 5 is a diagram showing a relationship between a nozzle opening method and an amount of Al ₂ O _{3 in} molten steel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insert nozzle, 2 ... Bottom plate, 3 ... Slide plate, 4 ... Seal plate, 5 ... Cylinder,
6 ... pore, 7 ... pipe, 8 ... pore, 9 ... pipe, 10 ... solidified steel, 11 ... ladle, 12 ... tundish, 13 ... molten steel, 14 ...
Slide valve, 15 ... mold.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B22D 11/10 340 B22D 41/42

Claims (1)

(57) [Claims] 1. In a continuous casting operation, an equivalent amount of oxygen from pores or a porous refractory incorporated in a slide valve for controlling a flow rate of molten steel injected from a tundish into a mold.
Blow a mixture of Ar gas and remove surrounding refractories.
A method for opening a tundish injection nozzle, wherein the solidified steel in the nozzle is melted without melting .