KR20020001023A - Upper nozzle for preventing the re-oxidation of the hot metal in the tundish - Google Patents

Abstract

PURPOSE: A hot reusable upper nozzle is provided which blocks suction of external air by maintaining the space formed between the upper nozzle and a metal case on the bottom surface of a tundish under inert atmosphere. CONSTITUTION: In a hot reusable upper nozzle(20) mounted on the lower part of a tundish comprising a tubular body(21) having a certain shape made of porous ceramic and a metal case(23) which is mounted on the outer part of the tubular body, and on the lower part of which an inflow port of an inert gas is formed, the hot reusable upper nozzle is characterized in that plural holes are formed on the metal case, a partial inert gas blown into the tubular body through the inflow port is discharged through the holes so that the outer part of the metal case is maintained under the inert gas atmosphere, thereby preventing reoxidation of molten steel. In a hot reusable upper nozzle mounted on the lower part of a tundish comprising a tubular body having a certain shape made of porous ceramic and a metal case which is mounted on the outer part of the tubular body, and on the lower part of which an inflow port of an inert gas is formed, the hot reusable upper nozzle is characterized in that a supply ring capable of supplying of an Ar gas is installed at the upper outer part of the metal case, and plural holes(23a) are formed on the supply ring so that the outer part of the metal case is maintained under the inert gas atmosphere by the Ar gas supplied through the holes.

Description

Upper nozzle for preventing the re-oxidation of the hot metal in the tundish}

The present invention relates to a hot reuse upper nozzle for preventing re-molding of molten steel transferred from a tundish to a mold through a continuous hot water system from a tundish upper nozzle to an immersion nozzle during continuous casting operation. The space formed between the nozzle and the tundish bottom shell is maintained in an inert atmosphere, and relates to a hot reuse upper nozzle which can block the intake of external air.

In general, as shown in FIG. 1, the molten steel M transferred from the ladle 11 to the tundish 13 is transferred from the tundish upper nozzle 13a to the mold via the slitting gate 15. Through the continuous hot water supply system 17, it is continuously transferred from the tundish 13 to the mold. At this time, when a minute gap is formed between the tundish refractory material and the hot water supply system or at a connection portion in the hot water supply system, external air is sucked by a negative pressure formed around the hot water supply system. In this case, since the molten steel to be conveyed is reoxidized, it causes clogging of the tundish upper nozzle 13a, the sliding gate 15 and the immersion nozzle, and also lowers the cleanliness of the molten steel supplied to the mold 17.

As a result, the flow of molten steel in the mold 17 becomes abnormal, resulting in deterioration of the quality of the cast steel, resulting in defects such as scabs, dark lines and blow holes in the final product. .

That is, in the continuous casting process, a plurality of ladles 11 are sequentially provided, the molten steel M in the ladle 11 is supplied to the tundish 13, and the molten steel in the tundish 13 is formed in the mold 17. The casting is continued for several hours, so the casting takes place for several hours without interruption. However, when the nozzle is clogged by non-metallic inclusions present in the steel in the path where the molten steel moves from the tundish 13 to the mold 17, the molten steel cannot be supplied and casting cannot be continued for a long time.

Therefore, in order to continue casting, the discharge nozzle cleaning is generally performed at the top nozzle or the immersion nozzle in the upper nozzle area, but this operation also causes a defect in the cast steel and adversely affects the product quality.

On the other hand, since the problem described above occurs when the nozzle is clogged, various measures for suppressing the nozzle clogging have been applied. For example, argon (Ar), which is an inert gas, is blown through the upper nozzle 13a to prevent the inclusions in molten steel from adhering to the inside of the upper nozzle 13a or by blowing argon (Ar) through the inner wall of the immersion nozzle. It is known to prevent it from adhering to the immersion nozzle.

Referring to FIGS. 2 (a) and (b) in which a conventional upper nozzle shape is illustrated, the material of the upper nozzle 13a is made of porous ceramic (PC), and the outer surface of the upper nozzle 13a is made of MC. It is wrapped in a metal case. Argon gas introduced into the shell (MC) through the argon inlet (T: Ar tap) exposed to the outside is discharged into the molten steel inside the upper nozzle (13a) through the porous ceramic (PC).

On the other hand, in order to minimize the clogging of the upper nozzle (13a) in this way, the volume of the argon gas flowing through the argon inlet (T) is also optimized and managed. That is, when argon gas is excessively blown, when a large bubble formed by coalescing the bubbles of argon gas is introduced into the mold while passing through the immersion nozzle together with the molten steel, the fluctuation of the water surface in the mold 17 becomes severe, resulting in dark lines and blows. It will cause hole and scap defects. However, when the amount of argon gas blown is minimized, the effect is minimized by causing nozzle clogging due to failure of blocking the contact between the molten steel and the upper nozzle.

Thus, argon flow rates are typically maintained at levels of 5-10 l / min. As such, in order to minimize clogging of the upper nozzle, the amount of argon gas was strictly controlled, but the blocking of the upper nozzle or the immersion nozzle was not completely blocked.

On the other hand, the path of air intake along the tundish upper nozzle is likely to occur in the so-called hot reusable tundish, which uses the tundish to clean or replace only the upper nozzle cassette in a high temperature atmosphere and re-cast in a short time. high. That is, in the hot reusable tundish, the gap between the well block of the tundish bottom and the upper tundish nozzle is particularly high compared to the general tundish used for single use.

In normal tundish, the top nozzle is assembled to fit tightly on the tundish wall at the top, and the gap is well sealed with castable cement, so there is a small possibility that a gap is formed between the tundish bottom and the top nozzle. However, in the hot reuse tundish, it is impossible to seal the gap with castable cement because the upper nozzle is inserted outside the tundish bottom surface while the tundish refractory material is at a high temperature and the cassette is fixed to the shell of the tundish bottom.

Therefore, in the hot reuse tundish, a gap is generated between the upper nozzle and the well block, thereby increasing the possibility of intake of air. Therefore, clogging of the upper nozzle proceeds continuously, and when clogging proceeds excessively, inclusions dropped by the flow pressure of the molten steel flow into the mold and are caught by the solidification shell, thereby causing a cap defect.

In this case, referring to FIG. 3, which shows a graph of the clogging index of the upper nozzle which appears when casting while blowing argon gas into the upper nozzle according to the related art, the increase of the upper nozzle clogging index is due to reoxidation of molten steel. This phenomenon occurs when the non-metallic inclusions generated by the upper nozzle are attached to the upper nozzle, and the decrease in the blockage index means that the attached inclusions are dropped. In addition, the time when the upper nozzle blockage index gradually increases and then suddenly decreases indicates the moment when the inclusions blocking the upper nozzle are temporarily dropped. When the upper nozzle blockage index exceeds 0.2, the inclusions attached to the upper nozzle are frequently dropped. In order for the top nozzle to remain unblocked, the blockage index must remain below 0.1.

On the other hand, Figure 4 is a graph showing the clogging index of the upper nozzle during the casting using the hot reuse tundish, the probability of clogging the upper nozzle was found to be 25% as a result of a total of 502 castings. That is, according to the conventional embodiment, the clogging of the upper nozzle may not be effectively blocked by the process of blowing argon through the upper nozzle.

As described above, when performing casting by a conventionally known technique, when external air flows in, nozzle clogging is caused by the following chemical reaction in molten steel, and the cleanliness of molten steel is reduced. That is, oxygen in the introduced air preferentially reacts with the soluble aluminum or titanium component present in the molten steel to form an Al ₂ O ₃ or TiO ₂ compound.

2 [Al] + 3 [O] → Al ₂ O ₃

[Ti] + 2 [O] → TiO ₂

The Al ₂ O ₃ or TiO ₂ compound thus formed finally forms clusters having a particle size of several tens of micrometers, and these clusters cause clogging of the upper nozzle, sliding gate, and immersion nozzle. However, the cluster flowing into the mold does not float in the mold and is captured by the solidification shell, which causes dark lines, blow holes, and defects in the cold rolling process.

Therefore, in order to minimize the occurrence of such defects in the cold rolling process, it is necessary to suppress the phenomenon that molten steel is reoxidized by external air while moving from the tundish to the mold, and for this purpose, the external air is actively introduced into the upper nozzle. It needs to be blocked.

Accordingly, an object of the present invention is to prevent air from being sucked through the gap between the tundish well block and the upper nozzle, to prevent the upper nozzle, the sliding gate and the immersion nozzle from being blocked, and also to suppress the reoxidation of the molten steel in the mold. Hot re-use turn to prevent re-melting of molten steel to keep the flow pattern of molten steel in the normal state and to obtain good surface and internal quality of the cast steel and to minimize the occurrence of slap defects, dark line defects and blow hole defects. The upper nozzle is to provide a dish.

According to the present invention, the hot reuse upper nozzle mounted at the bottom of the tundish is formed of a tubular body of a predetermined shape made of porous ceramic, and a steel bar mounted outside the tubular body and having an inlet of an inert gas formed at the bottom thereof. The steel shell has a plurality of holes formed therein, and a portion of the inert gas blown into the tubular body through the inlet is discharged through the hole to create an inert atmosphere outside the steel shell to form molten steel by external air. It is characterized by preventing anger.

Figure 1 is a schematic diagram showing the supply of molten steel from ladle to the mold in a typical continuous casting machine.

2 is a view schematically showing an upper nozzle according to a conventional embodiment, (a) is a perspective view showing a state mounted on the upper plate, (b) is a cross-sectional view of the upper nozzle.

3 is a graph showing the blockage index of the upper nozzle according to the prior embodiment.

4 is a graph showing the blockage index of the upper nozzle according to the number of casting.

5 is a cross-sectional view of the upper nozzle according to the present invention.

6 is a graph showing the blockage index of the upper nozzle according to the present invention.

<Description of Symbols for Major Parts of Drawings>

20: Upper nozzle

21: tubular body

23: bar

23a: hole

Best Mode for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Figure 6 is a side cross-sectional view showing the shape of the upper nozzle according to the present invention, Figure 7 is a graph showing the blockage index of the upper nozzle according to the present invention.

Referring to Figure 6, the upper nozzle 20 according to the present invention is a tubular body 21 of a predetermined shape made of a porous ceramic, and is mounted on the outside of the tubular body 21 and the inlet T of the inert gas is It is made of a steel bar 23 formed at the lower end, a plurality of holes (23a) are formed in the steel bar (23). Therefore, the inert gas blown through the inlet T passes through the tubular body 21 and flows into the molten steel.

At this time, a part of the inert gas blown into the inlet (T) is discharged through the hole (23a) to create an inert atmosphere outside the shell 23, thereby preventing reoxidation of molten steel by the outside air. The inert gas is made of argon gas.

Therefore, in the upper nozzle 20 according to the present invention, a plurality of minute holes 23a are present in the shell 23, and some of the argon gas introduced into the argon inlet T flows through the molten steel of the upper nozzle 20. It is discharged to the space, the other part is discharged to the outside through the fine hole (23a) present in the shell 23.

Argon gas discharged to the outside of the shell 23 fills the gap between the upper nozzle 21 and the well block, and the empty space between the upper nozzle and the tundish bottom shell, and as a result, the outside of the shell 23 Composition in an inert atmosphere. At this time, the amount of argon gas discharged through the minute hole 23a of the shell 23 is adjusted to be maintained to be larger than the amount of argon gas sucked into the molten steel through the gap between the upper nozzle and the well block, so that the excess argon gas is turned. Allow the dish to drain out of the bottom of the dish.

As a result, the gases sucked into the molten steel through the upper nozzle and the tundish well block gap are all composed of only argon gas, so that the molten steel is not regenerated by the sucked gas. In addition, as described above, since the upper nozzle 23 is not blocked by molten steel reoxidation, molten steel flows into the mold while maintaining cleanliness, thereby causing blow holes and dark lines by non-metallic inclusions observed in the cold rolled coil. , Defects such as a scaffold are not generated.

Meanwhile, an ar ring is attached to the outer shell of the tundish upper nozzle to supply argon gas, and the argon gas supplied into the argon gas supply ring surrounds the outer shell through the hole drilled in the supply ring. Allow discharge in the circumferential direction. At this time, the supply ring is present above the tundish bottom surface, the amount of argon supplied is to be absorbed into the molten steel through the gap between the well block and the upper nozzle. Therefore, since molten steel is not reoxidized by external air, molten steel flows into a mold with the cleanness maintained, and a good quality product without surface defects can be obtained.

<Example>

In order to understand the inhibiting performance of the clogging of the upper nozzle provided by the present invention, as shown in Figure 6, the tubular body 21 of a predetermined shape inside the upper nozzle is made of a porous ceramic, 21, an outer nozzle 20 having a structure wrapped with a steel shell 23 in which a plurality of fine holes are formed was manufactured. The holes 23a formed in the shell 23 were arranged in six rows within a 1/6 to 5/6 section of the entire length of the upper nozzle iron shell 23, and each row had 10 in the circumferential direction. The size of the hole 23a was 2.0 mm in diameter.

These holes 23a were to be distributed over the entire bar 23, and the size area of the holes was 0.01 to 9 mm ² . In addition, when the upper nozzle 20 is assembled at the bottom of the tundish, the fine holes are concentrated in the 150 mm section from the portion where the bottom of the tundish is located among the bark 23 surrounding the porous ceramic part. In this case, the amount of argon gas is controlled through the inlet T so that the argon gas discharged through the hole 23a is at least one times or more larger than the amount introduced into the molten steel through the gap between the well block and the upper nozzle. .

The upper nozzle 20 manufactured as described above was mounted at the bottom of the tundish, and casting was performed while blowing argon gas of 10 l / min through two argon inlets (T). At this time, the measured top nozzle clogging index (clogging index) is shown in FIG. That is, the upper nozzle plugging index showed a value of 0.05 or less in the normal casting section except for the abnormal casting section at the end of the casting. This means that the upper nozzle plugging phenomenon appears at 0.1 or more. Means no blockage.

This is compared with FIG. 3 showing the blockage index of the upper nozzle when casting by using the upper nozzle shown in Figure 2 (b) produced by the conventional embodiment, it can be seen that the upper nozzle blockage index was kept significantly lower. . That is, clogging of the upper nozzle by the inclusions as shown in FIG. 3 and dropping out of the inclusions did not appear at all in the upper nozzle according to the present invention.

In addition, the suction of the air did not appear at all by the gap between the well block and the upper nozzle by the upper nozzle according to the present invention. It was effective in preventing nozzle clogging and maintaining cleanliness of molten steel by suppressing reoxidation of molten steel.

Therefore, according to the present invention, by maintaining the gap formed between the upper nozzle and the well block and the space formed between the upper nozzle and the tundish bottom shell in an argon atmosphere, even if gas is sucked into the molten steel through the gap. By making the gas into argon gas, reoxidation of molten steel is prevented from occurring, and clogging of the upper nozzle inner wall, sliding gate and immersion nozzle due to reoxidation of molten steel is prevented.

The foregoing is merely illustrative of the preferred embodiments of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. It should be recognized.

Claims (4)

In a hot tubular body formed of a porous ceramic and a steel shell mounted on the outside of the tubular body and the inlet of the inert gas is formed at the bottom, the hot reuse upper nozzle mounted on the bottom of the tundish, The steel shell is formed with a plurality of holes, a portion of the inert gas blown into the tubular body through the inlet is discharged through the hole to create an inert atmosphere outside the steel shell to reoxidize molten steel by external air Hot reusable top nozzle, characterized in that to prevent. The hot reuse upper nozzle of claim 1, wherein the total area of the holes is 0.01 to 9 mm ² . The method of claim 2, wherein the amount of argon gas discharged through the hole is adjusted to maintain the number of the hole so that the amount of the argon gas to be sucked into the molten steel through the gap between the upper nozzle and the well block. Reusable upper nozzle. In a hot tubular body made of porous ceramics and a steel bar mounted on the outside of the tubular body and formed with an inlet of an inert gas at the bottom thereof, the hot reuse upper nozzle mounted at the bottom of the tundish, A supply ring capable of supplying argon gas is provided at an outer upper end of the shell, and a plurality of holes are formed in the supply ring, and an inert atmosphere is formed outside the shell by argon gas supplied through the hole. Hot reusable top nozzle, characterized in that.