KR100770339B1 - Submerged nozzle - Google Patents

Abstract

A submerged nozzle is provided to stabilize an edge of casting for improving yield by minimizing a skull generation and remelting residual skull generated. A submerged nozzle includes upper and lower nozzles(131,132). An upper part of the upper nozzle is connected to a turn-dish. A lower part of the upper nozzle is located above a baffle(133) passing through an upper cover of the lower nozzle. The upper cover of the lower nozzle completely encloses inside the lower nozzle. The baffle is installed above side and upper end discharging holes(141,242) for stably supplying molten steel. The side discharging holes are formed on a wall orienting a casting roll of the lower nozzle for supplying the molten steel from the turn-dish to a roll sump. The upper end discharging holes are formed on a wall orienting an edge dam and have a discharging angle ranging 0°~15°. A lower end discharging hole is formed below the upper end discharging holes and have the discharging angle ranging 10°~45°.

Description

Submerged nozzle

1 is a schematic diagram showing a conventional continuous sheet casting apparatus,

2 is a cross-sectional view showing a conventional immersion nozzle;

3 is a side view showing a skull generation situation in the conventional edge dam surface,

4 is a cross-sectional view showing a conventional immersion nozzle;

5 is a cross-sectional view showing an immersion nozzle according to the present invention;

6 is a schematic view showing an arrangement example of an upper surface discharge port and a lower surface discharge port according to the present invention;

7 is a plan view showing the flow surface of the hot water when the top surface discharge port is excessively large;

8 is a plan view showing the flow of the hot water surface when the area of the upper surface discharge port and the lower surface discharge port according to the present invention is properly combined;

9 is a skull mixing frequency result table according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

131: upper nozzle 132: lower nozzle

142: conventional end discharge port 160: edge dam

242: top discharge port according to the present invention

243: the lower surface discharge port according to the present invention

The present invention relates to an immersion nozzle, and more particularly, to an immersion nozzle attached to a tundish and consisting of an upper nozzle and a lower nozzle, a plurality of side discharge holes are formed on a side surface of the lower nozzle, and a cross section is provided. The upper and lower discharge ports are formed in the upper and lower sides, and a baffle is provided above the upper discharge port, and an edge dam surface and a roll roll close to the hot water surface are provided. The immersion nozzle is designed to minimize molting of the scull and re-dissolve the scull in this area by supplying molten steel to the edge dam near the nip. will be.

A schematic diagram of a conventional twin roll continuous sheet casting device 100 is shown in FIG. 1. The molten steel 150 supplied between the pair rolls 110 through the immersion nozzle 130 and the discharge port 140 attached to the tundish 120 forms a molten steel pool surrounded by the pair roll 110 and the edge dam 160. The molten steel 150 in contact with the twin roll 110 forms a solidification cell 170 on the surface of the roll 110 while losing heat in the direction of the center of the roll, and the formed slabs 180 rotate in opposite directions. The roll roll exits 110. On the upper surface of the molten steel, a meniscus shield 190 device is installed to block external air to prevent oxidation of the molten steel 150 by contact with the atmosphere, and the molten steel is provided through a gas supply nozzle 191 installed in the apparatus. By supplying an inert gas to the surface, the upper part of the bath surface is maintained in an inert atmosphere. In addition, since the momentum of the molten steel 150 discharged from the immersion nozzle 130 is considerably large, which may cause fluctuations in the surface of the molten steel, the weir 192 fixed to the meniscus shield 190 for the purpose of controlling the flow of the molten steel 150. Is installed. While casting tries to keep the atmosphere on the surface as inert as possible, it is difficult to secure 100% sealing and there is a possibility that oxides are partially formed on the surface. Weir 192 also serves as a kind of barrier (barrier) to prevent the oxide thus generated to reach the growing coagulation cell 170.

2 is a schematic view of the immersion nozzle 130 commonly used in the twin roll continuous sheet casting method of supplying the molten steel 150 to the lower nozzle 132 through the upper nozzle 131. Since the molten steel 150 supplied from the tundish 120 through the upper nozzle 131 has a large amount of its own momentum, the lower nozzle 132 is not provided without a molten steel supply control device such as a baffle 133 installed inside the lower nozzle 132. Turbulence and oscillation of the molten steel 150 is deepened in the inside and the uniform molten steel supply through the side discharge port 141 and the end discharge port 142 can not be expected. In addition, the lower nozzle 132 when the lower end of the upper nozzle 131 inserted through the upper cover 134 and inserted into the lower nozzle 132 is not sufficiently deposited in the molten steel because the height of the molten steel on the baffle 133 is not sufficient. ) Is present in the molten steel 150 is mixed into the molten steel 150, and when the molten steel 150 is supplied to the sump, the mixed gas enters into the coagulation cell 170 that finally enters and grows or oxidative inclusions in the sump. The probability of generating is increased. When such a phenomenon occurs, cast defects and cracks are generated inside and outside of the cast steel.

Typically, in the case of a twin roll continuous sheet casting process, the material of the edge dam 160 is ceramic and is kept lower than the molten steel 150 temperature during casting. Therefore, as shown schematically in FIG. 3, a large skull 151 grows under and above the edge dam 160 during casting, and when the size of the skull 151 becomes a certain degree or more, it leaves the edge dam 160 and grows. Incorporation into the solidification cell 170 causes problems such as reduced slab edge quality, reduced error rate, roll damage and, in extreme cases, casting interruption. Therefore, in order to suppress the occurrence of this phenomenon, as shown in FIG. 4, a method of supplying hot molten steel in the edge dam direction by machining the end discharge port 142 at the end is also used, but when the supply amount is excessively excessive, the slag edge is not solidified. If the phenomenon is aggravated or too small, there is no effect of inhibiting skull generation. In addition, depending on the angle (θ) of the end discharge port may not be desired flow, and the effect of suppressing the generation of the skull appears only in a very limited area can not minimize the damage caused by the skull as a whole.

The present invention is to overcome the above-mentioned conventional problems, an object of the present invention is that when the molten steel is supplied to the lower nozzle through the upper nozzle and exits the lower nozzle discharge port and supplied to the roll sump and the upper surface discharge port of the lower nozzle Since the size and angle of the bottom discharge port have a very important influence on the solidification pattern of the solidification cell growing on the roll surface, the size and angle of the top and bottom discharge ports of the lower nozzle are appropriately applied. It is possible to easily suppress the occurrence of skulls growing near the top and the surface, and as a result, it is possible to minimize the generation of skulls and to re-dissolve the grown skulls, and to immerse nozzles to improve the casting error rate by stabilizing cast edges and stabilizing castings. To provide.

The present invention is attached to a tundish and in the immersion nozzle consisting of the upper nozzle 131 and the lower nozzle 132, a plurality of side discharge port 141 is formed on the side portion of the lower nozzle 132 and the upper and lower end in the cross section A surface discharge port 242 and a lower surface discharge port 243 are formed, and a baffle is provided inside the upper surface discharge port 242, and the edge dam 160 close to the surface of the water is formed. By supplying molten steel 150 to the edge dam near to the roll and rolls, it is possible to minimize the occurrence of skull and re-dissolve the grown skull in this area, and to improve the error rate of cast through stabilization of cast edge and casting stabilization. will be.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

5, a cross-sectional view of an immersion nozzle according to the present invention is shown.

Immersion nozzle 130 is composed of a two-piece (piece) of the upper nozzle 131 and the lower nozzle 132, the upper portion of the upper nozzle 131 is connected to the tundish and the lower portion of the upper portion of the lower nozzle 132 The cover 134 is positioned at a predetermined position on the baffle 133. The inside of the lower nozzle 132 is completely sealed by the upper cover 134, and the baffle 133 is installed at the side discharge port 141 and the upper surface discharge port 242 to provide stable molten steel. In the lower part of the baffle 133, in order to supply molten steel introduced from the tundish to the roll sump, the side discharge port 141 is formed in the wall of the lower nozzle 132 in the casting roll direction. In addition, one to three top surface discharge holes 242 are formed in the edge dam direction wall surface of the lower nozzle 132 toward the hot water surface, and one bottom surface discharge hole 243 is formed in the bottom of the top surface discharge hole.

The discharge angle θ ₁ of the top discharge port and the discharge angle θ ₂ of the bottom discharge port may be the same or different from each other. In this case, the discharge angle θ ₁ of the top discharge port is 0 °. ₁ ≤θ ≤15 °, and the range of the ejection angle (θ ₂₎ of the lower end face the discharge port is 10 ° ≤θ ₂ ≤45 °. However, the discharge direction is directed toward the edge dam.

At this time, when the discharge angle θ ₁ of the upper surface discharge port is larger than 15 °, the flow of molten steel is directed downward rather than toward the surface of the molten steel, and thus it is not effective in reducing the scull scull. Therefore, the discharge angle θ ₁ of the upper surface discharge port is maintained in the range of 0 ° ≦ θ ₁ ≦ 15 °.

In addition, if the discharge angle (θ ₂ ) of the lower surface discharge port is smaller than 10 °, the flow of molten steel is directed to the surface of the molten steel, so that molten steel cannot be supplied to the edge dam close to the roll,. It goes to the roll 닢 instead of finely, so it is not effective in reducing the skull generation. Therefore, the discharge angle θ ₂ of the lower surface discharge port is maintained in the range of 10 ° ≦ θ ₂ ≦ 45 °.

6 (a), 6 (b) and 6 (c) show schematic diagrams showing possible arrangement examples of the top surface discharge port 242 and the bottom surface discharge port 243.

By the above configuration, the immersion nozzle according to the present invention functions as follows.

Referring to FIG. 5, the molten steel supplied through the baffle 133 may supply molten steel to the roll sump through the side discharge port 141, the top surface discharge port 242, and the bottom surface discharge port 243. The molten steel supplied through the upper surface discharge port 242 mainly reaches the edge dam 160 while being supplied toward the surface of the melt, resulting in minimization and re-dissolution of the skull size, resulting in the surface of the edge dam near the surface of the melt. This will minimize the generation of skulls. The hot molten steel supplied through the lower surface discharge port 243 is mainly supplied to the lower side of the edge dam, which also causes the skull size to grow in this region and minimizes the re-dissolution of the generated skull. At this time, the top surface of the ejection angle (θ ₁₎ and when the bottom side discharge port discharge angle (θ ₂₎ wrong selection of the discharge angle of the upper surface discharge port because the skull incidence of the target area can not reduce (θ ₁₎ of the outlet range is 0 ° ≤θ ₁ in ≤15 °, range of the ejection angle (θ ₂₎ of the lower end face a discharge port, it is necessary that the relative optimum angle selected for each other in the 10 ° ≤θ ₂ ≤45 °.

On the other hand, the relative sizes of the top surface discharge port 242 and the bottom surface discharge port 243 is also very important, if the size of the top surface discharge port 242 is excessively large compared to the size of the bottom surface discharge port 243, the flow direction is not desired Will appear. A plan view thereof is shown in FIG. 7.

7 is an undesired flow of scum which is formed between the weir 192 and the roll 110 when the top surface discharge port 242 is excessively large in size. If it is. The scum that has not escaped between the weir 192 and the weir 192 is very likely to be incorporated into the growing coagulation cell, and the mixed scum causes the difference in coagulation capacity, causing cast defects.

In contrast, FIG. 8 is a conceptual view illustrating the flow of the hot water when the areas of the top discharge port 242 and the bottom discharge port 243 are properly combined, and the scum generated between the weir 192 and the roll 110 is molten steel. It is a case where the surface of the water flow which is easy to remove scum is formed by being collected between the weir and the weir by the flow.

The area ratio of the upper surface discharge port 242 and the lower surface discharge port 243 is obtained by the following equation, and the value is maintained within the range of 0.7 to 1.3.

End discharge area ratio = Top discharge port / Bottom discharge port

On the other hand, when the sum of the areas of the upper surface discharge port 242 and the lower surface discharge port 243 becomes more than 45% of the total discharge area (stage discharge port + side discharge port), the slag edge unsolidification occurs severely. It is essential for slab edge stabilization.

<Example>

Using a twin roll continuous sheet casting apparatus, a thin plate was produced in this example.

Conduct common condition

Target steel grade: stainless steel (STS304), casting speed: 50m / min

Sheet Size: Thickness 3.5mm, Width 1300mm,

Roll diameter: 1250mm,

Roll width: 1300mm,

End Discharge Area Ratio: Upper Discharge Outlet / Lower Discharge Outlet = 1.12

Area Ratio: (Top Discharge Outlet + Lower Discharge Outlet) / Total Discharge Area X 100 = 25%

Example: θ ₁ = 0 °, θ ₂ = 20 °

Comparative Example: θ = 0 °

9 is a result table according to the embodiment of the present invention. As shown, it can be seen that the frequency of the occurrence of the skull sharply reduced compared to the comparative example, in particular, the frequency of the upper scull (face scull) is less than the frequency of the occurrence of the lower scull (skull generated near the roll)). Able to know.

As described above, the immersion nozzle according to the present invention allows molten steel to be supplied to the edge dam surface close to the water surface and the edge dam side close to the roll surface, thereby minimizing scull occurrence and re-dissolving of the grown skull, and the slab edge. Stabilization and casting stabilization improve cast error rate.

Claims (4)

In the immersion nozzle attached to the tundish and consisting of the upper nozzle 131 and the lower nozzle 132, A plurality of side discharge holes 141 are formed in the side portion of the lower nozzle 132, and an upper end discharge hole 242 and a lower end discharge hole 243 are formed in an upper and lower sides of the lower nozzle 132, and a baffle is formed above the upper end discharge hole. An immersion nozzle is used in a twin roll sheet metal casting process, wherein an area ratio of the upper surface discharge port 242 and the lower surface discharge port 243 is 0.7 to 1.3. delete The method of claim 1, The discharge angle (θ ₁₎ of the upper discharge port surface is 0 ° ≤θ ₁ ≤15 °, and the discharge angle of the lower end face discharge opening (θ ₂₎ is a pair, characterized in that 10 ° ≤θ ₂ ≤45 ° roll type sheet Immersion nozzle used in casting process. The method of claim 1, The sum of the area of the upper and lower discharge ports is an immersion nozzle for use in a twin roll sheet metal casting process, characterized in that maintained at 45% or less of the total discharge area.

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