JPH05200507A - Long nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To form molten metal stream flowing in a horizontal direction near the molten metal surface in a tundish, to lengthen a retention time of the molten metal in the tundish and to promote floatation/separation of the non-metallic inclusions. CONSTITUTION:In a long nozzle 10, molten metal discharging holes 13a, 13b inclined upward in the side surface 12 of the nozzle body are formed near the closed lower end part 11. The upward inclining angle in the molten metal discharging holes 13a, 13b to the direction at the right angle to the axis of the nozzle body is preferably set in the range of 5-30 deg. angle. The molten metal 50 in a ladle 20 flows into the tundish 30 from the molten metal discharging holes 13a, 13b is slightly upward stream toward the neighborhood of the surface of the molten metal 51 and becomes the molten metal stream 52 flowing in the horizontal direction near the molten metal surface, and the non-metallic inclusions are floated up and separated in the condition of low static pressure of the molten metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long nozzle for efficiently floating and separating non-metallic inclusions from molten metal such as molten steel poured in a tundish.

[0002]

2. Description of the Related Art When a slab or other slab is produced by a continuous casting method, molten metal contained in a ladle is poured into a tundish and then cast into a continuous casting mold. The tundish has the function of supplying a required amount of molten metal to a plurality of continuous casting molds and also serves to float and separate non-metallic inclusions. The non-metallic inclusions in this case are deoxidation products already contained in the molten metal in the ladle, and are generated by air oxidation of the molten metal stream when pouring from the ladle into the tundish. There are oxides, etc.

During the process of tapping the ladle from the ladle to the tundish, the floating of the non-metallic inclusions is greatly affected by the flow state of the molten metal tapped. Above all, the residence time of the molten metal in the tundish greatly affects the floating separation of non-metallic inclusions. That is, as shown in FIG. 1, the longer the molten metal poured from the ladle stays in the tundish while being poured into the continuous casting mold, the more non-metallic inclusions are floated and separated from the molten metal. The amount tends to increase.

By promoting the floating separation of non-metallic inclusions, clean molten metal is fed into the continuous casting mold, and a slab with high cleanliness is produced. For example, when continuously casting Al-killed steel or the like, non-metallic inclusions such as alumina clusters remaining in the slab significantly impair the quality of the slab. Non-metallic inclusions such as alumina clusters are derived from deoxidation products contained in the ladle, alumina and the like generated by reoxidation of molten steel between the ladle and the tundish. There is a limit to floating separation of this kind of non-metallic inclusions in the continuous casting mold, so as to send clean molten steel after separating the non-metallic inclusions in the tundish to the continuous casting mold, Conventionally, various means have been proposed.

For example, Japanese Laid-Open Patent Publication No. 1-2224152 introduces a weir provided inside a tundish to form a flow of molten metal effective for floating separation of non-metallic inclusions. Further, Japanese Patent Laid-Open No. 63-157745 proposes to promote floating separation of nonmetallic inclusions by blowing an inert gas into a tundish provided with a weir.

[0006]

By providing the weir inside the tundish, the residence time of the molten metal becomes long, and a large amount of the non-metallic inclusions floats and separates accordingly. However, since the inside of the tundish is exposed to severe erosion by the molten metal, frequent relining work of the lining is required. In this respect, if there are protrusions such as weirs inside the tundish, the re-attachment work becomes troublesome.

Further, the erosion by the molten metal poured into the tundish is large in the portion of the weir which is an obstacle to the flow of the molten metal. As a result, the weir is more prone to melting damage than the tundish body, and the lining work itself becomes more frequent because the original function of the weir is secured.

Even in the method of promoting floating separation of non-metallic inclusions by blowing an inert gas, damage to the gas blowing pipe cannot be avoided. In addition, it is necessary to attach extra equipment for gas injection.

As described above, the conventional method is the construction, repair,
It is not practical because the workability such as maintenance is poor, or an extra equipment burden is required. Moreover, it is only an auxiliary means for promoting the floating of the non-metallic inclusions on the molten metal surface, and is not a very effective means for prolonging the residence time of the molten metal in the tundish.

The present invention has been devised to solve such a problem, and by devising a long nozzle for pouring molten metal from a ladle to a tundish,
An object of the present invention is to extend the residence time of the molten metal in the tundish and effectively float and separate non-metallic inclusions without incurring extra equipment load.

[0011]

In order to achieve the object, a long nozzle for continuous casting of the present invention is a long nozzle for pouring molten metal from a ladle to a tundish.
It is characterized in that it is attached to a bottom wall of the ladle, a lower end portion thereof facing the inside of the tundish is closed, and an upward molten metal discharge port is formed on a side surface near the lower end. The molten metal outlet is preferably formed on the nozzle side surface near the lower end at an upward angle of 5 to 30 degrees.

[0012]

[Operation] Hereinafter, the present invention will be specifically described together with its operation with reference to the drawings. As shown in FIG. 2, the long nozzle 10 according to the present invention has its upper end connected to a molten metal outflow hole 21 provided in the bottom wall of the ladle 20, and its lower end faces the inside of the tundish 30. An appropriate number of pouring holes 31a and 31b are formed in the bottom wall of the tundish 30, and the immersion nozzle 32 is provided in each of the pouring holes 31a and 31b.
a and 32b are connected. And the immersion nozzle 32
The a and 32b are arranged on the upper part of the continuous casting molds 40a and 40b, respectively.

As shown in FIG. 3, the long nozzle 10 has molten metal discharge ports 13a and 13b formed in the side surface 12 of the nozzle body in the vicinity of the closed lower end 11 so that the nozzle hole 14 communicates with the outside. ing. The molten metal discharge ports 13a and 13b are
Although it may be singular or plural, two or more are preferable from the viewpoint of causing the molten metal to flow in a wide range in the tundish 20. Multiple melt outlets 1
When 3a and 13b are provided, the molten metal discharge ports 13a and 13b are arranged on the side surface 12 of the nozzle body at equal intervals in the circumferential direction.

The molten metal discharge ports 13a and 13b are inclined upward at an angle α with respect to the direction perpendicular to the axis of the nozzle body. The upward inclination angle α is preferably set in the range of 5 to 30 degrees in consideration of the flow state of the molten metal sent into the tundish 20.

When the molten metal 50 is fed into the tundish 30 from the ladle 20 equipped with the long nozzle 10, the molten metal 50 descending through the nozzle hole 14 collides with the inner surface of the lower end 11 and then has an upward inclination angle α. Correspondingly, it is sent out from the molten metal discharge port 13 to the tundish 30 as a flow having a slightly upward directional component. At this time, ladle 20
The molten steel static pressure and the falling energy from the molten metal to the tundish 30 act to convert the molten metal flowing out from the molten metal discharge port 13 to the floating upstream.

The molten metal discharged from the long nozzle 10 flows out toward the molten metal surface of the molten metal 51 in the tundish 30, and a molten metal flow 52 shown by an arrow in FIG. The molten metal flow 52 flows horizontally near the surface of the molten metal 51, and the molten metal 5 is added.
The static pressure of 1 is small. Therefore, the molten metal 51
The non-metallic inclusion having a smaller specific gravity than that of (1) is easily floated and separated from the discharged molten metal. As a result, clean molten metal 51 from which non-metallic inclusions have been removed is supplied to the pouring holes 31a and 31b of the tundish 30.

On the other hand, when the molten metal 50 is discharged from the ladle 20 to the tundish 30 using the conventional long nozzle 15 having the molten metal discharge port 16 formed at right angles to the axial direction of the nozzle body, As shown in FIG. 4, a molten metal flow 55 having a downward directional component is generated. The molten metal flow 55 is
Since the molten metal 51 in the tundish 30 flows in a relatively deep portion, the static pressure applied to the molten metal 51 increases. Therefore, the rise in the non-metallic inclusions that are about to float due to the difference in specific gravity is suppressed.

Further, the outflow destination of the molten metal flow 55 is the pouring hole 31.
Since they are located relatively close to a and 31b, they do not stay in the tundish 30 for a long time,
It flows out from 31b to continuous casting molds 40a and 40b. As a result, the molten metal in the continuous casting molds 40a and 40b has low cleanliness containing a large amount of non-metallic inclusions.

Molten metal flow 52 in the tundish 30
As is clear from the comparison between the molten metal flow 55 and the molten metal flow 55, the long nozzle 10 according to the present invention promotes the floating separation of the non-metallic inclusions and the molten metal 51 in the tundish 30.
Is also effective for staying for a long time. As a result, molten metal having high cleanliness can be poured into the continuous casting molds 40a and 40b.

The long nozzle 10 has a melt discharge port 13a,
It is preferable that the side surface 12 on which the 13b is formed faces the short side wall of the tundish 30 and is arranged in the tundish 30. With this arrangement, the molten metal flow 52 flowing near the molten metal 51 is turned into a long horizontal flow parallel to the longitudinal direction of the tundish 30 over a wide range from the long nozzle 10 to the short side wall. As a result, the floating separation of non-metallic inclusions is further promoted.

The upward inclination angle α of the molten metal discharge ports 13a and 13b can be set in the range of 5 to 30 degrees in order to enhance the floating separation action of the non-metallic inclusions by the molten metal flow 52 mainly in the horizontal direction. preferable. When maintaining the upward inclination angle α in this range, an effective molten metal flow 52 is formed over a wide range of the tundish 30. And the molten metal flow 52
Goes down along the short side wall of the tundish 30 and the pouring hole 3
The flow has a long residence time up to 1a and 31b.

When the upward inclination angle α is less than 5 degrees, the action of inclining the molten metal discharge ports 13a and 13b upward becomes small. That is, the flow of the molten metal discharged is close to the molten metal flow 55 shown in FIG. 4, which is mainly a downward flow, and the flow of the molten metal 51 toward the molten metal surface decreases.
As a result, the non-metallic inclusions are sent to the continuous casting molds 40a and 40b along with the molten metal without being floated and separated.

On the other hand, at an upward inclination angle α of more than 30 degrees, the molten metal 51 already in the tundish 30 acts as a resistance against the molten metal discharged from the molten metal discharge ports 13a and 13b, and immediately near the long nozzle 10. It is easy to turn into a downward flow. Therefore, the molten metal flow 52 in a wide range of the tundish 30 is not formed, and a sufficient opportunity for the non-metallic inclusions to float and separate cannot be obtained. Therefore, the molten metal is likely to be fed into the continuous casting molds 40a and 40b in a state of low cleanliness. However, even in this case, as compared with the conventional long nozzle in which the single-hole molten metal discharge port is provided in the bottom portion, the floating separation of non-metallic inclusions is significantly different.

[0024]

EXAMPLE A long nozzle 10 having two molten metal discharge ports 13a and 13b was used to flow low carbon Al killed steel into a tundish 30 at an injection rate of 8 ton / min.
In addition, as the long nozzle 10, the melt discharge port 13a,
13b having an upward inclination angle α of 15 degrees was used. Further, taking the long nozzle 15 (FIG. 4) in which the molten metal discharge port 16 is bored without providing the upward tilt angle α as a conventional example, the molten metal discharge port 13 has an upward tilt angle α of 45 degrees.
The long nozzle 10 formed with a and 13b was used as a comparative example. In each example, the tundish 10 having the same shape and the same size was used.

Low carbon Al killed steel is cast from the ladle 20 through the tundish 30 into the continuous casting molds 40a and 40b.
A slab having a cross section of 1325 mm × 250 mm was manufactured. The dispersed state of the non-metallic inclusions in the obtained cast piece was investigated.
FIG. 5 is a graph showing the amount of non-metallic inclusions as a non-metallic inclusion index. As is apparent from FIG. 5, when continuous casting is performed using the long nozzle 10 in which the molten metal discharge ports 13a and 13b having the upward inclination angle α = 15 degrees are used for continuous casting, it is incorporated in the manufactured slab. It can be seen that the non-metallic inclusions are greatly reduced.

[0026]

As described above, in the long nozzle for continuous casting of the present invention, the flow state of the molten metal in the tundish is a flow mainly in the horizontal direction near the molten metal surface. Therefore, the molten metal static pressure applied to the molten metal sent to the tundish is small, and the floating separation of non-metallic inclusions is promoted. Further, the molten metal flow generated in the tundish has a relatively wide range, and the molten metal is retained in the tundish for a long time. This also causes the floating separation of the non-metallic inclusions. Therefore, the non-metallic inclusions contained in the molten metal cast into the continuous casting mold are small, and a slab with high cleanliness is manufactured. Moreover, it is not necessary to provide a weir inside the tundish that causes a molten metal flow that adversely affects the lining refractory, or to blow an inert gas into the molten metal in the tundish, simply by replacing the long nozzle. Equipment can be used.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the residence time of molten metal in a tundish and the levitation rate of nonmetallic inclusions.

FIG. 2 Pouring part for continuous casting incorporating a long nozzle according to the present invention

FIG. 3 Long nozzle according to the invention

FIG. 4 Pouring part for continuous casting incorporating a conventional long nozzle

FIG. 5 is a graph showing the influence of the upward inclination angle of the molten metal discharge port on the index of non-metallic inclusions in the slab.

[Explanation of symbols]

10 Long Nozzle 11 Closed Lower End 12 Side of Nozzle Body 13a, 13b Molten Metal Discharge Port 20 Ladle 30 Tundish 50 Molten Metal 52 Molten Metal Flow in Tundish α Molten Metal Discharge Port Upward Inclination Angle

Claims (2)

[Claims] 1. A long nozzle for pouring molten metal from a ladle to a tundish, which is mounted on a bottom wall of the ladle and has a lower end portion facing the inside of the tundish closed and near the lower end. A long nozzle for continuous casting characterized in that an upward molten metal discharge port is formed on the side surface. 2. The molten metal discharge port according to claim 1, wherein the molten metal discharge port is 5 to 30.
Long nozzle for continuous casting, characterized in that it is formed on the side surface of the nozzle near the lower end at an upward angle of 10 degrees.