KR20000040931A - Dipping nozzle for continuously molding - Google Patents

Abstract

PURPOSE: A dipping nozzle for continuously molding is provided to decrease the process speed of molten steel and to secure more rising time of inclusion. CONSTITUTION: A jet thickness is increased fast since a molten steel starts to be expanded from the time when vented from a dipping nozzle. The vented molten steel is vented while expanded at a proper angle from the initial time. As a result, the molten steel is processed slower by making the expansion angle of molten steel jet flow. In addition, an inclusion secures more time to receive buoyancy. Herein, the molten steel expansion angle is formed larger than 0 degree and is not more than 60 degrees. When the expansion angle is more than 60 degrees, peeling occurs, and a desirable jet flow is not formed so that there is no effect in the promotion of inclusion.

Description

Immersion nozzle for continuous casting

The present invention relates to an immersion nozzle installed in a curved type machine having an electromagnetic braking device (hereinafter referred to as "EMBR"), and more particularly, the size of the discharge hole formed toward the mold short side is increased toward the outside and discharged therefrom. It relates to a continuous casting immersion nozzle that can improve the quality of the cast by reducing the speed of the molten steel to increase the jet thickness of the molten steel rapidly, thereby securing more floating time of the inclusions.

The continuous casting method of steel is an intermediate product production technology that has been introduced worldwide since the 1960s. Since it has many advantages over the general ingot method, it currently accounts for more than 60% of the world's crude steel production, especially 90% in Japan, Korea and Western Europe. The above has produced the slab by this continuous casting technique. Since the continuous casting method has been invented, new technologies have been constantly added, and have been changed very differently from the initial forms. In particular, the height of the instrument was gradually lowered for the purpose of producing various products and reducing the equipment cost.In the early stage, it was a vertical instrument in the vertical form from the start of solidification to the completion, whereas now it is bent horizontally by bending the cast slab from the start of solidification to a specific curvature radius Developed into a curved player 100 (see Fig. 1a) to be withdrawn.

However, the inclusion stack 160 is formed just below the upper surface of the cast steel 150 produced by the curved player 100, which includes the inclusions injected from the nozzle 110 is molten steel 150. It is caused by being attached to the curvature part of the solidification shell 140 as it rotates while rotating spirally under the influence of molten steel flow and the effect of buoyancy acting in the opposite direction to gravity when it is swept down to the lower part of the non-solidified slab. The inclusions accumulated on the inner upper surface of the cast steel are exposed to the surface during the rolling process and appear as surface defects of the product, or are inherent in the steel sheet and then undergo heat treatment such as annealing, It has a problem that appears as internal defects such as blow holes. Reference numeral 130 denotes a template.

Conventionally, in order to solve this problem and improve the quality of the cast steel, as shown in Figure 1b, by installing the vertical portion 170 of the appropriate length in the player 100A, the solidification shell even when the inclusion lowered to the lower portion of the cast steel is recycled A technique was used to allow the flotation to be separated by the floor without being attached to the surface. However, this vertical unit 170 installation method was not preferable in terms of economics by increasing the overall height of the installation.

Recently, a method of controlling molten steel by a relatively simple method without causing a large change in equipment is used. As shown in FIG. 2, an electromagnetic braking device (not shown) is applied to a local part around the immersion nozzle 110. (Electromagnetic Brake Ruler, 'EMBR') to control the flow of the molten steel 150 by using the Lorentz force caused by the magnetic field (Swedish patent SE 8,003,695, SE 9,100,184; US patent US 4,495,984, US 5,404,933; Gaepyeong 2-284750; Korean Patent Application No. 97-72370, 98-31788).

However, since recent methods using direct current electromagnetic fields are intended to reduce the penetration depth of inclusions or to improve the quality of castings by reducing the number of inclusions, there is a limit to the control of inclusions penetrated under the castings. It exists.

The present invention has been made to solve such a conventional problem, the object of which is to increase the jet thickness formed by the molten steel discharged to the mold short side portion to increase the speed of the molten steel to thereby further increase the floating time of the inclusions It is to provide a immersion nozzle for continuous casting that can secure a lot.

1A and 1B are schematic diagrams for explaining inclusion behavior in a general curved player.

Figure 2 is a flow diagram for explaining the molten steel flow in the general curved type player

Figure 3 is a flow diagram for explaining the molten steel flow in the case of removing the molten steel flow using an electromagnetic braking device in a general curved type player

Figures 4a and 4b is a view showing the shape of the immersion nozzle according to the prior art and the flow plane schematic diagram showing the shape of the molten steel jet flow thereby

Figures 5a and 5b is a view showing the shape of the immersion nozzle in accordance with the present invention and the flow plane schematic diagram showing the shape of the molten steel jet flow thereby

FIG. 6 shows numerical results of various cases (in the case of using the electromagnetic braking, in the case of the nozzle of the present invention) with respect to the number of inclusions accumulated in the equally divided sections of the slab width by 10. FIG. .

Explanation of symbols on the main parts of the drawings

10 ... Immersion nozzle 12 ... Molten steel discharge

130 ... mold 131 ... short edge

150 ... molten steel Z ... jets

As a technical configuration for achieving the above object, the present invention,

In the immersion nozzle provided in the player equipped with the electromagnetic brake (EMBR) to control the flow of molten steel discharged to the mold short side,

By providing a continuous casting immersion nozzle, characterized in that the size of the molten steel discharge port is gradually increased in the mold width direction with respect to the molten steel discharge direction.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

As shown in FIG. 2, molten steel discharged from the immersion nozzle 110 of the player 100B during continuous casting forms jets Z toward the short side portion 131 of the mold 130 (see FIG. 2A). ). The jet (Z) is divided into an upflow (U) and a downflow (D) while colliding with the short side portion 131 of the mold 130, which is also four types of circulation flow (U1) (U2) (D1) Divided into (D2). In this case, the speed of the molten steel that proceeds from the nozzle 110 to the short side portion 132 is closely related to the jet thickness 210 of the jet stream Z, and the speed of the inclusions discharged together with the molten steel is also related thereto.

Since the inclusions 180 have a relatively small density compared to the molten steel 150, the inclusions 180 receive buoyancy in a direction opposite to the gravity of the earth while the inclusions proceed in the direction of the force vector of the force and buoyancy caused by the molten steel. Therefore, the slower the molten steel is, the more time is secured for the inclusions to receive buoyancy, and as the molten steel progresses from the nozzle 110 to the short side portion 131 of the mold 130, the molten steel rises more to the hot water surface.

In this principle, a player 100C (Korean Utility Model Registration Application No. 98-31788) equipped with an electromagnetic force braking device 190 was devised and disclosed. When the device is used for continuous casting, molten steel 150 is shown in FIG. As shown, the jet thickness 210A is greatly increased in the thickness direction of the mold 130, and the molten steel flow rate is drastically reduced, thereby increasing the time for the inclusions to rise while going to the short side portion 131, thereby improving the inclusion floating ability. It works.

However, until the molten steel diffuses in the mold thickness direction and the jet thickness 210A is sufficiently large, the diffusion distance 200 is necessary to some extent. This is because, as shown in the flow plan diagram of FIG. 4b, when producing slabs with a narrow width of about 970 mm, it is necessary to proceed up to the end of the slab width until the jet Z is sufficiently spread, so that there is not enough time for the inclusions to rise. Therefore, to ensure more time for the inclusions to float, it is necessary to reduce the required diffusion distance until the jet thickness becomes large enough.

The inventors of the present invention have started to diffuse the problem from the time when the molten steel is discharged from the immersion nozzle to increase the jet thickness more quickly, as shown in Figure 5a each of the molten steel discharge port 12 of the immersion nozzle 10 This is possible by being formed such that its width gradually increases toward the outside with respect to this radial direction. And, the shape of the molten steel discharge port 12 of the immersion nozzle 10 is compared with the conventional immersion nozzle 110 shown in Figure 4a having a molten steel discharge port 112 of the same size with respect to the radial direction.

That is, the immersion nozzle 10 of the present invention is discharged while the discharged molten steel is diffused at an appropriate angle θ from the beginning, and as a result, the molten steel is increased by increasing the diffusion angle of the molten steel jets Z as shown in FIG. 5B. It progresses more slowly toward the mold short edge, and the inclusions in it have more time to receive buoyancy.

The molten steel diffusion angle θ formed in the immersion nozzle 10 according to the present invention should be larger than 0 °, and the diffusion angle θ should not be greater than 60 ° or more, which means that the diffusion angle θ is 60 °. In the above case, since the separation of the flow occurs, the formation of desirable jets is difficult, and thus a great effect on the inclusion enhancement ability is not observed.

In order to examine the performance of the immersion nozzle of the present invention more quantitatively, computer simulation was performed for the case of θ = 15 °, and the variation of molten steel flow in the mold is shown in FIG. 5B, and the inclusion distribution in the slab is shown in FIG. 6. Indicated.

Looking at Figure 5b, by using the immersion nozzle 10 according to the present invention was able to visually determine that the molten steel is spread more quickly in the mold thickness direction, by the test piece width compared to the conventional immersion nozzle 110 by the test The quantitative characteristics were examined and the results are as follows.

That is, in the case of 970 mm, in the conventional immersion nozzle 110, the immersion nozzle 10 of the present invention has a relationship of "(diffusion distance) / (slab width / 2)>1". In the case of "(diffusion distance) / (slab width / 2) ≈ 0.45 ", and in the case of 1570 mm, in the conventional immersion nozzle 110," (diffusion distance) / (slab width / 2) ≈ On the other hand, in the immersion nozzle 10 of the present invention, "(diffusion distance) / (slab width) ≈ /2)0.25 "relationship.

This indicates that when the immersion nozzle 10 of the present invention is used, the diffusion distance required for the diffusion of molten steel in the mold thickness direction is reduced by about 55% or more as compared with the conventional immersion nozzle 110. there was.

FIG. 6 shows the numerical results of the number of inclusions accumulated in the divided sections of the slab width by 10 equal parts. The horizontal axis in the figure represents the slab width, and the vertical axis represents the number of inclusions. As shown in this figure, while using the conventional nozzle 110 and using electromagnetic braking while using the conventional nozzle 110, while exhibiting the effect of reducing the inclusions of about 35% In the case of using the nozzle 110 of the present invention and using electromagnetic braking, it was found that the inclusion reduction effect was about 60% or more.

As described above, according to the continuous casting immersion nozzle according to the present invention, the molten steel discharge port is formed to be larger and larger to diffuse as molten steel is discharged, thereby greatly reducing the diffusion distance required for the molten steel to sufficiently spread in the mold thickness direction. By reducing the flow rate of the molten steel toward the short side portion, the flotation resolution of the inclusions is improved, and thus, the inclusion accumulation in the slab is drastically reduced, so that defects in the slab are reduced.

Claims (2)

In the immersion nozzle provided in the player equipped with the electromagnetic brake (EMBR) to control the flow of molten steel discharged to the mold short side, Immersion nozzle for continuous casting, characterized in that the size of the molten steel discharge port 12 is gradually increased in the mold width direction with respect to the molten steel discharge direction. The method of claim 1, Immersion nozzle for continuous casting, characterized in that the diffusion angle (θ) indicating the size increase of the molten steel discharge port 12 is less than 60 °.