JPH0428687Y2 - - Google Patents

Description

[Detailed explanation of the idea]

<Industrial Application Field> The present invention relates to the structure of a submerged nozzle used for continuous casting of molten metal, particularly molten steel. <Prior Art> Conventionally, in continuous casting of molten steel, an immersion nozzle has been used to pour molten steel from a tundish into a mold. A typical example of this immersion nozzle is shown in Figure 3. Due to the constraints of the mold dimensions for continuous slab casting, the cross-sectional area of the central passage through which molten steel passes through the immersion nozzle is limited to the discharge holes provided on the left and right sides of the immersion nozzle. is designed to be smaller than the sum of the cross-sectional areas of Therefore, when the molten steel flowing down the central passage of the immersion nozzle at high speed is discharged into the mold from the wide discharge hole, a downward component of the momentum of the molten steel flowing down the molten steel central passage of the immersion nozzle at high speed remains. Non-metallic inclusions such as alumina and air bubbles carried along with the flow of molten steel penetrate deeply into the molten steel and become trapped in the solidification shell, causing deterioration in the quality of continuously cast slabs. Measures to prevent the above-mentioned downward component of molten steel include the following. It is conceivable to reduce the area of the discharge hole of the immersion nozzle, but in this case, the discharge speed of molten steel increases. For this reason, the molten steel discharged from the immersion nozzle collides with the short sides of the mold and changes to a downward flow, and nonmetallic inclusions such as alumina and air bubbles may be trapped in the solidified shell. Furthermore, it is possible to provide a current plate in order to stop the downward component of molten steel, but there is a problem that the current plate cannot withstand the flow of high-temperature molten steel at a high speed. Furthermore, it is conceivable to increase the cross-sectional area of the molten steel passage in the immersion nozzle, but this is limited by the thickness of the mold, and it becomes difficult to supply molten steel to the gap between the mold and the outer wall of the immersion nozzle. In addition, the immersion nozzle disclosed in Japanese Practical Publication No. 55-88347 has two discharge holes opened diagonally downward in the lower end of the nozzle and two discharge holes opened horizontally or diagonally upward in opposite directions. It is designed to cause the flowing molten steel to collide. The problem with this nozzle is that when the flow velocity of molten steel increases through the nozzle center passage, the molten steel flows out only from the discharge hole at the lower end, which instead promotes a fast downward flow and increases the penetration depth of the molten steel. There is. The purpose of the present invention is to prevent the downward component of molten steel seen in conventional immersion nozzles, and to prevent non-metallic inclusions such as alumina and air bubbles from being trapped in the slab. <Problems to be solved by the invention> The invention solves the problem that with conventional immersion nozzles, non-metallic inclusions such as alumina and air bubbles carried along with the downward flow of molten steel penetrate deep into the molten steel and become trapped in the solidified shell. Since the problem of degrading the quality of continuously cast slabs still remains, this was done in order to solve this problem and provide a submerged nozzle with less entrainment of nonmetallic inclusions and air bubbles. <Means for Solving the Problems> As a result of experiments, the inventors of the present invention found that simply providing a plurality of discharge holes in the immersion nozzle in the vertical direction of the immersion nozzle will cause the molten steel to be discharged from the lower discharge hole of the immersion nozzle. It was discovered that the flow force was strong and the flow rate of molten steel discharged from the top of the immersion nozzle was small. In order to prevent this phenomenon, it is possible to achieve a balance between the flow of molten steel discharged from the upper discharge hole and the lower discharge hole by narrowing the lower part of the molten steel central passage of the immersion nozzle. I understand. Furthermore, by tilting the bottom of the lower discharge hole downward, nonmetallic inclusions and air bubbles can be separated from the mainstream of molten steel and prevented from penetrating deeply into the molten steel, and the bottom of the lower discharge hole can be tilted downward. It was also found that nonmetallic inclusions and bubbles can be effectively separated by setting the angle to 5° or more and 50° or less. The present invention was developed based on the above findings. The present invention is an immersion nozzle that supplies molten metal from an intermediate container of a continuous casting machine into a mold, and has a plurality of symmetrically arranged discharge holes in the height direction of the bottomed nozzle, and the molten metal is placed in the center of the nozzle. Discharge holes are provided above and below the constriction part that reduces the cross-sectional area of the passage from the upper part, and the bottom surface of the lowest discharge hole part faces the outlet side and is angled downward by 5 degrees.
This immersion nozzle for continuous casting is characterized by having an inclination of 50° or less. <Function> As mentioned above, the present invention was made based on the knowledge obtained as a result of the experiment, and the present invention is to narrow the lower part of the molten steel central passage of the immersion nozzle, and to tilt the bottom surface of the lowest discharge hole downward. ,
This makes it possible to effectively separate nonmetallic inclusions and bubbles. In addition, the total cross-sectional area of the discharge holes of the immersion nozzle is
It is preferable that the cross-sectional area of the molten steel passage of the immersion nozzle be at least twice as large. In other words, if the total cross-sectional area of the discharge holes does not reach twice the cross-sectional area of the molten steel passage of the submerged nozzle, the velocity of the molten steel discharge flow is high, so the downward flow component becomes large and penetrates deeply into the mold. . Therefore, in order to make this sufficiently small, the total cross-sectional area of the discharge holes should be at least twice the cross-sectional area of the molten steel passage of the immersion nozzle. In this way, by reducing the upper and lower discharge flow velocities and tilting the bottom surface downward, inclusions and air bubbles are collected in the low pressure part above the lower discharge hole,
Can be floated and separated. Inclusions and bubbles that flow out of the upper discharge hole along with the flow of molten steel do not cause any harm because they float up while flowing out horizontally, or float up on the upward flow after colliding with the short sides. The reason why the bottom inclination is set to be 5° or more and 50° or less is as follows. In other words, if the bottom inclination is less than 5 degrees, a low-pressure part will be created above the lower discharge hole and air bubbles will be collected there, and if it is more than 50 degrees, the downward flow will be strong and the bubbles will not be separated and will flow deep into the molten steel. It will invade. Figure 2 shows the relationship between the downward angle of the bottom surface and the number of bubbles involved, which was investigated through a water model experiment. Here, the number of bubbles involved is the number of bubbles with a diameter of 2 mm or more that are entangled in the molten steel at a distance of 30 cm or less from the bottom of the discharge hole. From this result, the effect of the present invention is clear. Hereinafter, an example of the immersion nozzle of the present invention will be explained in detail based on FIG. 1. The immersed nozzle 4 shown in the figure is an example in which two discharge holes 8 and 8' are provided in the vertical direction of the nozzle, but the molten steel central passage 9 is the molten steel central passage (inverted truncated conical part) toward the bottom of the immersed nozzle 4. ) 9', the cross-sectional area decreases.
Discharge holes 8, 8' are provided above and below the constricted portion where the cross-sectional area of the molten steel central passage 9' is reduced. The bottom of the discharge hole 8' is inclined downward. This bottom surface causes the molten steel to flow downwardly, and furthermore, since the part directly hit by the flow from the molten steel central passage 9 is elevated, even if this part is slightly depressed, it will not affect the life of the immersion nozzle. <Example> (Example 1) Using a full-scale experimental apparatus, a conventional immersion nozzle shown in Fig. 3 and an immersion nozzle of the present invention shown in Fig. A comparison was made by adding air bubbles at a rate of 20/min. As a result, the maximum entrainment depth of a bubble with a diameter of 1 mm was approximately 120 cm in the conventional submerged nozzle, whereas it was approximately 72 cm in the submerged nozzle of the present invention. In addition, while the cross-sectional area of the discharge hole of the conventional immersion nozzle is approximately 1.8 times the cross-sectional area of the molten steel center passage, the cross-sectional area of the discharge hole of the immersion nozzle of the present invention is set to 3.0, and the position of the upper discharge hole of the immersion nozzle is The cross-sectional area of the molten steel passage at the position of the lower discharge hole of the immersion nozzle was set to 0.8 with respect to the cross-sectional area of the molten steel passage. In addition, the bottom downward angle of the lower discharge hole was set to 15°. (Example 2) When using the same nozzle of the present invention under the same conditions as Example 1 and setting the bottom downward angle of the lower discharge hole to 35°, the maximum entrainment depth of a bubble with a diameter of 1 mm is approximately
It was 68cm. Use the above immersion nozzle for continuous casting in actual operation.

[Table] <Effects of the invention> As explained above, according to the invention, the amount of non-metallic inclusions and air bubbles trapped inside the continuously cast slab is reduced, and the quality of the slab is significantly improved.

[Brief explanation of the drawing]

FIG. 1 shows a front view of the immersion nozzle a according to the present invention;
b is a side view thereof, c is a sectional view thereof, FIG. 2 is a graph showing the relationship between the downward angle of the bottom surface of the lower discharge hole and the number of air bubbles entrained in it, and FIG. 3 is a drawing showing a conventional immersion nozzle. A is a front view, b is a side view, and c is a plan sectional view. 1... Conventional immersion nozzle, 4... Immersion nozzle according to the present invention, 8, 8'... Discharge hole, 9... Molten metal central passage, 9'... Molten metal central passage (throttled part).

Claims (1)

[Scope of utility model registration request] A submerged nozzle that supplies molten metal from an intermediate container of a continuous casting device into a mold, with a plurality of symmetrically arranged discharge holes in the height direction of the bottomed nozzle, and a cross-sectional area of the molten metal central passage of the nozzle. An immersion nozzle for continuous casting, characterized in that discharge holes are provided above and below a constriction part that reduces the flow rate from the upper part, and the bottom surface of the lowest discharge hole part has an inclination of 5 degrees or more and 50 degrees or less downward toward the outlet side. .