Method for using upper nozzle

Abstract

With a view to adding, to an upper nozzle formed with a bore having a shape capable of creating a less energy loss or smooth (constant) molten steel flow to suppress the occurrence of adhesion of inclusions and metals in molten steel, a gas injection function to thereby further suppress the occurrence of the adhesion, the present invention provides a method of using an upper nozzle configured to have a cross-sectional shape of a wall surface defining the bore, taken along an axis of the bore, comprising a curve represented by the following formula: log(r (z))=(1/n)×log((H+L)/(H+z))+log(r (L)) (n=1.5 to 6), where: L is a length of the upper nozzle; H is a calculational hydrostatic head height; and r (z) is an inner radius of the bore at a position downwardly away from an upper edge of the bore by a distance z. The method comprises using the upper nozzle in such a manner as to satisfy the following relationship: R.sub.G≦4.3×V.sub.L, where R.sub.G is a gas rate defined as a volume ratio of a flow rate Q.sub.G (Nl/s) of injection gas to a flow rate Q.sub.L (l/s) of molten steel flowing through the bore (R.sub.G=(Q.sub.G/Q.sub.L)×100(%)), and V.sub.L is a flow speed of the molten steel at a lower edge of the upper nozzle.

Claims

1. A method comprising: providing an upper nozzle formed with a bore, the nozzle being fitted into a well block attached to a bottom of a tundish, the upper nozzle including a gas-permeable refractory member defining therein the bore, the nozzle further comprising: a cross-sectional shape of a wall surface defining the bore, taken along an axis of the bore, comprises a curve defined to have continuous differential values of r (z) with respect to z, between two curves represented by the following respective formulas: log (r (z))=(1/1.5)×log ((H+L)/(H+z))+log (r (L)); and log (r (z))=(1/6)×log ((H+L)/(H+z))+log (r (L)), where: L is a length of the upper nozzle; H is a calculational hydrostatic head height; and r (z) is an inner radius of the bore at a position downwardly away from an upper edge of the bore by a distance z, wherein: the calculational hydrostatic head height H is represented by the following formula: H=((r (L)/r (0)).sup.n×L)/(1−(r (L)/r (0).sup.n) (n=1.5 to 6); and the inner radius r (0) of the upper edge of the bore is equal to or greater than 1.5 times the inner radius r (L) of a lower edge of the bore; flowing molten steel through the bore of the upper nozzle with a flow rate of Q.sub.L (I/s); and injecting gas into the upper nozzle with a gas rate of R.sub.G, where R.sub.G≦4.3×V.sub.L, where R.sub.G is defined as a volume ratio of a flow rate Q.sub.G (Nl/s) of injection the injected gas to the flow rate Q.sub.L (I/s) of the molten steel flowing through the bore (R.sub.G=(Q.sub.G/Q.sub.L)×100(%)), and where V.sub.L is a flow speed of the molten steel at a lower edge of the upper nozzle, wherein injecting gas into the upper nozzle comprises: defining five regions in the wall surface defining the bore, the wall surface being evenly divided in a height direction of the upper nozzle to define the five regions; injecting the gas into at least three of the five regions of the wall surface, and injecting the gas such that a gas injection amount of the injected gas from each of the five regions of the wall surface is equal to or less than 60% of a total gas injection amount of the injected gas.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a conceptual diagram illustrating an axial section of a tundish and an upper nozzle.

(2) FIG. 2 presents one example of a result of computer simulation-based fluid analysis.

(3) FIG. 3 illustrates a graph obtained by plotting a relationship between a fluid flow speed V.sub.L (m/s), and a gas rate R.sub.G (%), i.e., a ratio of an injection gas flow rate Q.sub.G to a fluid flow rate Q.sub.L.

(4) FIG. 4A presents gas trajectories in a result of the computer simulation-based fluid analysis, obtained by changing a gas injection amount from each of five regions of the bore-defining wall surface evenly divided in a height direction of an upper nozzle.

(5) FIG. 4B presents gas trajectories in a result of the computer simulation-based fluid analysis, obtained by changing the gas injection amount from each of the five regions of the bore-defining wall surface evenly divided in the height direction of the upper nozzle.

(6) FIG. 4C presents gas trajectories in a result of the computer simulation-based fluid analysis, obtained by changing the gas injection amount from each of the five regions of the bore-defining wall surface evenly divided in the height direction of the upper nozzle.

(7) FIG. 4D presents gas trajectories in a result of the computer simulation-based fluid analysis, obtained by changing the gas injection amount from each of the five regions of the bore-defining wall surface evenly divided in the height direction of the upper nozzle.

(8) FIG. 5 illustrates the five regions of the bore-defining wall surface evenly divided in the height direction of the upper nozzle.

DESCRIPTION OF EMBODIMENTS

(9) The present invention will be described below, based on Examples.

Examples

(10) The present invention was applied to an actual tundish in a continuous casting facility. A result of the application will be described below. It should be noted that the following Inventive Examples are shown only by way of specific examples of the present invention, but the present invention is not limited thereto.

(11) Table 2 presents a result of a test performed by using, in an actual tundish, an upper nozzle under conditions, in each of Inventive Examples and Comparative Examples.

(12) TABLE-US-00002 TABLE 2 Inventive Inventive Inventive Inventive Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Example 3 Example 4 Nozzle shape Inventive Shape Conventional shape Inventive shape Fluid flow 1.7 1.8 1.8 1.2 1.7 1.2 1.1 0.5 speed V.sub.L m/s Injection gas flow 0.17 0.08 0.08 0.08 0.17 0.25 0.08 0.03 rate Q Nl/s Gas rate R.sub.G % 2.9 5.8 1.2 1.9 2.9 5.6 5.8 2.8 R.sub.G/V.sub.L 1.7 3.3 0.7 1.6 1.7 4.8 5.1 5.5 Situation of ○ Δ Δ Δ × × × × adhesion of inclusions and others Usable life >16 ch >10 ch >12 ch >8 ch 8 ch 8 ch 5 ch 5 ch (number of charges before nozzle change)

(13) The nozzle shape in each of Inventive Examples 1 to 4 and Comparative Examples 3 and 4 is the inventive shape illustrated in FIG. 2, and the nozzle shape in each of Comparative Examples 1 and 2 is the conventional shape illustrated in FIG. 2. As regards the situation of adhesion of inclusions and others, the collected used upper nozzle was cut into halves and the situation of the adhesion was visually evaluated. The marks “∘”, “Δ” and “x” denote, respectively, a situation where almost no adhesion of inclusion and others is observed, a situation where adhesion of inclusion and others is observed but slightly, and a situation where significant adhesion of inclusion and others is observed. As regards the number of charges before nozzle change in Table 2, for example, “>16 ch” means that although the nozzle was changed after 16 charges by another reason, the nozzle was further usable in terms of the situation of adhesion of inclusion and others. In all of Inventive Examples and Comparative Examples, the gas injection amount from each of the five regions of the bore-defining wall surface of the upper nozzle was evenly set.

(14) In Inventive Examples 1 to 4, the nozzle shape is the inventive shape satisfying the condition (1), and each upper nozzle is used in such a manner as to satisfy the condition (2): R.sub.G≦4.3×V.sub.L (R.sub.G/V.sub.L≦4.3). Almost no or slight adhesion of inclusions and others was observed, and each upper nozzle had sufficient usable life.

(15) On the other hand, in Comparative Example 1, the nozzle shape is the conventional shape which does not satisfy the condition (1), although the upper nozzle is used in such a manner as to satisfy the condition (2). In Comparative Example 2, the conditions (1) and (2) are not satisfied. In Comparative Examples 3 and 4, the condition (2) is not satisfied, although the condition (1) is satisfied. In all of Comparative Examples, significant adhesion of inclusions and others was observed, and each upper nozzle had short usable life.

(16) As above, in Inventive Examples, the adhesion of inclusions and others could be suppressed, and the usable life can be increased 1.5 to 2 times or more.

LIST OF REFERENCE SIGNS

(17) 1: upper nozzle 2: upper edge of upper nozzle 3: lower edge of upper nozzle 4: bore 5: large-diameter end edge of bore 6: small-diameter end edge of bore 7: bore-defining wall surface