JPH0337824B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a molten metal flow path through which molten metal flows and a discharge hole from which the molten metal is discharged, and a gas is supplied to the molten metal flow path. The present invention relates to an immersion nozzle that injects molten metal by immersing its discharge hole into molten metal in a mold.

[Prior art] In continuous steel casting, a nozzle attached to the bottom of a tundish is immersed in molten steel inside the mold.
Molten steel is injected into the mold from the tundish while adjusting the opening degree of this nozzle by moving the stopper up and down. In this case, if injection continues for a long time, non-metallic inclusions such as alumina will adhere to the inner wall of the nozzle, causing nozzle clogging. Argon gas is also ejected from the nozzle to prevent inclusions from adhering to the inner wall of the nozzle.

A conventional gas blow nozzle (immersion nozzle) 2 will be explained with reference to FIG. The upper end of the cylindrical gas blow nozzle 2 is connected to the injection hole 25 at the bottom of the tundish 1, and the lower end of the nozzle 2 is immersed in the molten steel 30 in the mold 3. This nozzle wall 5 is equipped with argon gas supply pipes 4 and 6. The supply port of the gas supply pipe 4 is introduced into the nozzle wall 5, and is connected to a porous brick 12 at the upper end of the nozzle wall through a slit 8 formed around the entire circumference of the nozzle wall. Similarly, the supply port of the gas supply pipe 6 is also introduced into the nozzle wall 5, and a slit 10 is formed around the entire circumference of the nozzle wall 5.
It is connected to the lower porous brick 14 via. Note that a plurality of discharge holes 26 for discharging molten steel are opened laterally at the lower end of the nozzle 2.
On the other hand, the stopper 20 is arranged at a position aligned with the injection hole 25, and its vertical movement causes the injection hole 25 to be aligned with the injection hole 25.
5 is opened and closed, and the amount of molten steel injected is adjusted. A gas passage 22 is formed at the axial center of this stopper 20.

In such a gas blow nozzle 2, argon gas is supplied from the gas passage 22 of the stopper 20 in the direction of the arrow 24 and is ejected into the molten steel passage of the nozzle 2, and is also ejected from the gas supply pipes 4 and 6 in the direction of the arrow 1.
Argon gas is supplied in directions 6 and 18 and is ejected through the slits 8 and 10 and the porous bricks 12 and 14 into the molten steel passage. The argon gas ejected from the gas passage 22 becomes a gas flow that descends in the center area of the molten steel passage, while the porous bricks 12,
The gas supplied through the nozzle 2 becomes bubbles near the inner surface of the nozzle 2 . For this reason, the descending gas flow and air bubbles coexist in the molten steel flow path, suppressing the adhesion of inclusions to the nozzle inner wall, and preventing the occurrence of nozzle clogging.

[Problems to be Solved by the Invention] By the way, in the conventional gas blow nozzle 2, in order to improve the effect of preventing nonmetallic inclusions from adhering to the inner wall of the nozzle, the gas passage 22 and the gas supply pipes 4 and 6 are It is necessary to increase the amount of argon gas supplied. However, this gas supply amount is
/min or more, a large amount of gas 28 will be ejected from the discharge hole 26 at the bottom end of the nozzle, and this gas 28 will blow into the mold 3.
This disturbs the molten steel flow and the molten metal surface (meniscus) in the molten metal, causing so-called molten surface cracks. When this surface crack occurs, the thickness of the solidified shell 31 formed on the inner wall of the mold 3 becomes uneven, and the molten steel surface is exposed and the molten steel 30 becomes uneven.
is oxidized, and the slag 32 covering the molten metal surface mixes into the molten steel 30 and is trapped in the solidified shell 31, which causes a problem that the quality of the slab deteriorates. For this reason, there are restrictions on the amount of gas supplied to the molten steel flow path, and conventionally it has not been possible to effectively prevent nozzle clogging. There is a problem in that it is not possible to increase the number of continuous casting operations.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an immersion nozzle that can effectively prevent nozzle clogging without disturbing the molten metal and the molten metal surface within the mold.

[Means for Solving the Problems] The immersion nozzle according to the present invention has a molten metal flow path through which molten metal flows and a discharge hole through which molten metal is discharged,
In the immersion nozzle, which injects the molten metal by immersing the discharge hole into the molten metal in the mold while supplying gas to the molten metal passage, gas is supplied to the molten metal passage through the supply passage formed in the nozzle wall. The present invention is characterized by comprising a gas supply means and a gas discharge means for discharging gas from the molten metal channel through a discharge passage formed in the nozzle wall.

[Function] In the immersion nozzle according to the present invention, the gas supply means supplies gas to the molten metal flow passage through the supply passage formed in the nozzle wall, and the gas discharge means supplies gas through the discharge passage formed in the nozzle wall. Since the gas is discharged from the molten metal passage through the molten metal passage, even if the amount of gas supplied to the molten metal passage is increased, the gas in the molten metal passage is discharged by the gas discharge means, and a large amount of gas is discharged from the discharge hole at the lower end of the nozzle. This avoids the situation where the water spouts out. Thereby, nozzle clogging can be effectively prevented without disturbing the molten metal flow and the molten metal level in the mold. Note that it is preferable to allow a certain amount of gas to flow out from the discharge hole into the mold by adjusting the gas supply amount and gas discharge amount in the molten metal passage.

[Example] If the amount of argon gas supplied to the molten steel flow path is reduced to prevent the above-mentioned molten metal surface from flaring, and the gas is prevented from flowing out from the discharge hole, inclusions tend to adhere to the discharge hole. . Therefore, it is considered necessary to allow an appropriate amount of gas to flow out from the discharge hole into the mold in order to suppress the adhesion of inclusions over the entire surface of the inner wall of the nozzle. Therefore, in order to suppress the amount of gas flowing out from the discharge hole into the mold while maintaining a predetermined amount of argon gas supply, a pore is formed in the lower part of the inner surface of the nozzle, and a molten steel flow path is formed through this pore. The argon gas supplied to the molten steel was discharged, and the discharge pressure was further adjusted to control the internal pressure of the molten steel passage to a predetermined pressure, and good results were obtained. In addition,
It has been found that porous bricks have a low porosity and are therefore not suitable as a member for gas discharge in molten steel passageways.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

1 and 2 are schematic diagrams showing a first embodiment of the present invention. A tundish 1 containing molten steel is disposed above a mold 3 for continuous casting. A stopper 20 is disposed at a position aligned with the injection hole 64 at the bottom of the tundish 1, and the stopper 20 is supported so as to be movable up and down, and is provided with appropriate up-and-down driving means (not shown).
By moving the stopper 20 up and down, the nozzle inlet 64 is opened and closed, and the amount of molten steel injected is adjusted. A gas passage 22 opening at the lower end is formed at the axial center of the stopper 20, and the gas passage 22 is connected to an argon gas supply source (not shown). A cylindrical refractory nozzle body 42 is provided between the tundish 1 and the mold 3, and its upper end is connected to the injection hole 64 at the bottom of the tundish 1, and its lower end is connected to the molten steel 30 in the mold 3. is immersed in. The surface of this molten steel 30 is covered with slag 32. Further, a solidified shell 31 is formed in contact with the water-cooled casting wall of the mold 3. A stainless steel gas supply pipe 44 is attached to the nozzle body 42, and a stainless steel gas exhaust pipe 46 is attached below it. Both the gas supply pipe 44 and the gas discharge pipe 46 are substantially perpendicular to the axis of the nozzle body 42 . Gas supply pipe 44
The supply port is introduced into the nozzle body 42 and connected to the porous brick 50 via the slit 48. Further, the outlet of the gas exhaust pipe 46 is also introduced into the nozzle body 42 and connected to the through-hole brick 54 via the slit 52. slit 48,
52 is formed around the entire circumference of the wall of the nozzle body 42 at a position approximately half the thickness of the wall, for example,
It is 0.4mm. Further, the porous brick 50 is provided over the entire circumference of the upper end of the nozzle body 42.
On the other hand, the through-hole brick 54 has a thickness that is approximately half the thickness of the wall of the nozzle body 42, and is fitted into the wall of the nozzle body 42 below. This through-hole brick 54
The plurality of through holes formed in the nozzle have an opening substantially perpendicular to the inner wall of the nozzle, and have an inner diameter of, for example, 0.4 mm. On the other hand, the gas supply side of the gas supply pipe 44 is connected to an argon gas supply source (not shown). Additionally, the gas exhaust pipe 46 has a pressure control mechanism (not shown).
The outlet side of the pump 60 is further connected to an argon gas recovery container (not shown) through a pipe 62.
Further, a plurality of discharge holes 66 for discharging molten steel are branched at the lower end of the nozzle body 42, and are each opened laterally.

In the immersion nozzle 40 configured in this way, when the stopper 20 is pulled up to open the injection hole 64 and molten steel begins to flow from the tundish 1 into the mold 3 via the molten steel flow path of the nozzle body 42, the gas passage 22 For example, argon gas is supplied in the direction of arrow 24 at a supply rate of 12/min. Then,
The argon gas descends through the molten steel passageway, and a gas flow is formed in the nozzle body 42 that reaches the lower part.
On the other hand, at this time, argon gas is supplied to the gas supply pipe 44 in the direction of the arrow 56, and the gas is ejected into the molten steel passage through the porous brick 50, and the suction pump 60 is driven to supply the gas through the through-hole brick 54. The gas in the molten steel flow path is discharged in the direction of arrow 58.
The gas supplied through the porous brick 50 becomes bubbles, and the gas flow ejected from the gas passage 22 of the stopper 20 entrains these bubbles. Then, the gas flow containing the bubbles descends along with the molten steel through the molten steel flow path, and a portion thereof becomes a gas film that covers the inner wall of the nozzle, thereby suppressing the adhesion of inclusions to the inner wall of the nozzle.
When the gas is ejected into the molten steel flow path of the nozzle body 42, the internal pressure of the nozzle body 42 becomes higher than 1 atmosphere. On the other hand, the discharge pressure (suction force) of the pump 60
The gas in the molten steel passage is discharged by controlling the pressure to a pressure range of 1 atm or higher and lower than the nozzle internal pressure. Since the gas discharge pressure is controlled in this manner, the gas in the molten steel passage can be discharged while preventing the molten steel from entering the slit 52.

FIG. 3 shows a second embodiment of the invention. In this second embodiment, instead of the through-hole brick 54 of the first embodiment, a slit 74 is formed as a gas exhaust means, approximately parallel to the inner wall of the nozzle body 72, and extending around the entire circumference of the nozzle. It is connected to the gas exhaust pipe 46 and opens downward to the molten steel flow path. Even in this case, the argon gas in the molten steel passage can be effectively discharged through the slit 74. Further, since the slit 74 is open toward the bottom of the molten steel flow path, it is possible to effectively prevent molten steel from entering into the slit 74.

FIG. 4 is a graph showing the effect of the submerged nozzle according to the embodiment of the present invention, with the nozzle clogging index of the conventional gas blow nozzle plotted on the horizontal axis and the nozzle clogging index of the submerged nozzle of the present invention plotted on the vertical axis. It is a diagram.
Continuous casting conditions are carried out simultaneously for each continuous casting,
In the conventional gas blow nozzle, the argon gas supply rate is 8/min, and in the submerged nozzle of this embodiment, the argon gas supply rate is 12/min. The gas blow nozzle gas supply rate was set to 8/min.
This is because if the amount is less than /min, the molten metal level in the mold 3 is quiet, and if the gas supply amount exceeds this amount, a large amount of gas will be ejected from the discharge hole 66, disturbing the molten steel flow and the molten metal level. As is clear from FIG. 4, the nozzle clogging index of this embodiment is lower than that of the prior art, and nozzle clogging is less likely to occur.

Figure 5 shows the amount of argon gas supplied on the horizontal axis.
It is a graph diagram showing a comparison between a conventional gas blow nozzle and a submerged nozzle according to an embodiment of the present invention, with a nozzle clogging index and a melt surface roughness index plotted on the vertical axis. In the figure, □ indicates the results obtained using the immersion nozzle of the present invention, △ indicates the results obtained using the conventional gas blow nozzle, and ◯ indicates the nozzle clogging index at each gas flow rate. As is clear from this Figure 5,
The immersion nozzle of this example can increase the amount of argon gas supplied by more than 70% compared to the conventional gas blow nozzle, dramatically reducing the occurrence of nozzle clogging, and reducing the flow of molten steel. Slag 32 to solidified shell 31 without surface disturbance
can be prevented from becoming entangled. Therefore, the number of times of casting can be increased without degrading the quality of the slab.

Note that the above-described embodiments are not limited to those for a tundish immersion nozzle that adjusts the flow rate using a stopper, but the present invention can also be applied to a tundish immersion nozzle that uses a sliding nozzle to adjust the flow rate. .

[Effects of the Invention] According to the immersion nozzle of the present invention, the gas supplied to the molten metal passage by the gas supply means is discharged by the gas exhaust means, so when the amount of gas supplied to the molten metal passage is increased. However, the situation in which a large amount of gas is blown out from the discharge hole immersed in the molten metal in the mold can be avoided. Therefore, nozzle clogging can be effectively prevented without disturbing the molten metal flow and the molten metal level in the mold.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention, FIG. 2 is a partially enlarged view of FIG. 1, and FIG.
FIG. 4 is a graph showing a comparison between the nozzle clogging of the immersion nozzle according to the example and the conventional nozzle, and FIG. 5 is a schematic diagram showing the immersion nozzle according to the example and the conventional nozzle. FIG. 6 is a graph showing the relationship between the nozzle clogging index, the hot water surface roughness index, and the argon gas supply amount for a gas blow nozzle. FIG. 6 is a schematic diagram showing a conventional gas blow nozzle. 20; stopper, 22; gas passage, 40; immersion nozzle, 42; nozzle body, 44; gas supply pipe, 46; gas discharge pipe, 48, 52, 74; slit, 50; porous brick, 54; through-hole brick, 60; pump; 66; discharge hole.

Claims (1)

[Claims] 1 Immersion, which has a molten metal passage through which molten metal flows and a discharge hole from which molten metal is discharged, and in which the molten metal is poured by immersing the discharge hole into the molten metal in the mold while supplying gas to the molten metal passage. In the nozzle, a gas supply means for supplying gas to the molten metal passage through a supply passage formed in the nozzle wall, and a gas discharge means for discharging gas from the molten metal passage through a discharge passage formed in the nozzle wall. An immersion nozzle comprising: means.