JP2008161920A - Immersed nozzle with japanese hand drum shape weir - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersed nozzle which can suppress drift currents in the directions of the thickness and width of a casting mold. <P>SOLUTION: The cylindrical immersed nozzle having a bottom is used for pouring molten steel to be held in a tundish into a casting mold. A pair of opposed molten steel discharging ports are formed on the peripheral wall of the immersed nozzle, and also a projecting portion is provided on the inside bottom surface so as to be parallel with the opening direction of the molten steel discharging ports in a bottom view. Further, the immersed nozzle satisfies the expression (1) of h/H=0.5 to 2.0 and the expression (2) of (a-b)/D=0.15 to 0.45, where h is the height of the upper surface of the projecting portion in the normal cross section for the elongating direction of the projecting portion; H is the distance between the lower end of the inner peripheral side opening edge of the molten steel discharging ports and the inside bottom surface; a is the width of the upper surface of the projecting portion of the immersed nozzle in a bottom view at the end portions of the projecting portion in the elongating direction; b is the width of the upper surface of the projecting portion of the immersed nozzle in a bottom view at the middle portion of the projecting portion in the elongating direction, and D is the inside diameter of the immersed nozzle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an immersion nozzle for continuous casting, and more particularly to an immersion nozzle for continuous casting in which a protrusion is provided at the bottom of the sump to suppress drift in the mold thickness direction and the width direction.

  In the conventional immersion nozzle, a hot water reservoir is formed at the nozzle bottom for the purpose of reducing splash at the start of casting. When a flow having a velocity gradient in the mold thickness direction occurs in the nozzle above the nozzle discharge hole, a flow across the nozzle bottom is generated from the pressure gradient in the hot water pool at the bottom of the nozzle, and the discharge hole is large with the discharge direction as the axis. A single rotating flow is generated. This drift occurs regardless of the opening / closing direction of the slide plate that adjusts the molten steel flow rate (see Non-Patent Document 1 and Non-Patent Document 2). This locally strong flow promotes remelting of the shell at the mold corner and causes a solidification delay. When this solidification delay is large, it leads to breakout of the slab.

  In order to suppress such drift, there is an invention in which a single ridge-like protrusion parallel to the discharge direction is installed on the inner bottom of the nozzle (see Patent Document 1).

  In addition, a protrusion is provided in the hot water reservoir, and the protrusion is inclined along a rectangular bottom surface, two vertical end surfaces of an isosceles triangle that are upright and opposed from the bottom surface, and a side of the vertical end surface. There is also an invention in which a triangular prism having two inclined surfaces facing each other is used, and the vertical surfaces are opposed to the discharge holes, respectively (see Patent Document 2).

Kenji Ichikawa and two others, “Flows in Immersion Nozzle Tubes [Water Model Experiment Results on Tundish SN; Third Report]”, Refractory, Refractory Technology Association, January 1990, Vol. 42, No. 1 , P.43-46 ARanderas, “Dynamics of two-phase downwards flow in submerged entry nozzle and its influence on the two- phase flow in the mold ”, Int. J. International Journal of Multiphase Flow, Netherlands, ELSEVIER, 2005, Vol. 31, p.643-665 International publication 2005/070589 pamphlet JP 2005-125389 A (see FIGS. 4 and 5)

  However, as described in Patent Documents 1 and 2, when the width of the protrusion is constant, the drift in the mold width direction appears remarkably. As a result, the solidification delay at the mold corner is not sufficiently suppressed by the drift in the width direction.

  This invention is made | formed in view of such various points, The main objective is to provide the immersion nozzle by which the drift of a mold thickness direction and a width direction is suppressed.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to the viewpoint of this invention, the immersion nozzle comprised as follows is provided. That is, it is a bottomed cylindrical immersion nozzle provided for pouring molten steel held in the tundish into the mold. A pair of opposed molten steel discharge holes are drilled in the peripheral wall of the immersion nozzle at a position away from the inner bottom surface of the immersion nozzle by a predetermined distance, and the molten steel discharge hole is viewed from the bottom surface of the immersion nozzle in the bottom view of the immersion nozzle. A protrusion extending in parallel with the perforating direction is provided, and further satisfies the following expressions (1) and (2).
h / H = 0.5-2.0 ... (1)
(ab) /D=0.15~0.45 ... (2)
However,
h: the height of the upper surface of the protrusion in a cross section perpendicular to the extending direction of the protrusion
H: Distance between the lower end of the inner peripheral opening edge of the molten steel discharge hole and the inner bottom surface
a: The width of the top surface of the protrusion in the bottom view of the immersion nozzle, and the width at the end of the protrusion in the extending direction
b: The width of the upper surface of the protrusion in the bottom view of the immersion nozzle, and the width of the protrusion in the center in the extending direction
D: Inner diameter of the immersion nozzle

  According to this configuration, it is possible to provide an immersion nozzle for continuous casting that suppresses the drift in the mold thickness direction and the width direction and reduces the splash at the start of casting.

The above immersion nozzle may be further configured as follows. That is, the following formula (3) is satisfied.
s / S = 0.15-0.5 ... (3)
However,
s: Projected area of the upper surface of the protrusion in the bottom view of the immersion nozzle
S: Channel cross-sectional area of the immersion nozzle that can be conceived in the bottom view of the immersion nozzle

  According to this configuration, the splash suppression effect is effectively achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of an immersion nozzle according to an embodiment of the present invention. 2 is a cross-sectional view taken along line 2-2 in FIG. 3 is a cross-sectional view taken along line 3-3 in FIG.

  The immersion nozzle 1 shown in FIG. 1 has a bottomed cylindrical shape used for smoothly pouring molten steel held in a tundish into a mold in continuous casting of steel. The state is vertical.

  As shown in the figure, the immersion nozzle 1 is made of a hollow cylindrical refractory, and its lower end is closed. A pair of opposed molten steel discharge holes 3 are drilled in the peripheral wall of the immersion nozzle 1 at a position away from the inner bottom surface 2 of the immersion nozzle 1 by a predetermined distance (see also FIG. 2). Further, the inner bottom surface 2 is provided with a protrusion 4 extending in parallel with the drilling direction 3A of the molten steel discharge hole 3 in the bottom view of the immersion nozzle 1 (see FIG. 3). Specifically, it is as follows.

The thickness of the refractory on the peripheral wall of the immersion nozzle 1 (indicated by symbol g in FIG. 3) and the thickness of the refractory on the bottom wall are substantially the same. The molten steel discharge hole 3 is a hole for appropriately discharging the molten steel flowing from the tundish into the immersion nozzle 1 into the mold, and one end is connected to the inner peripheral surface of the immersion nozzle 1, and the other end is Connected to the outer peripheral surface of the immersion nozzle 1, and further, the molten steel discharge hole 3 is formed so that the drilling direction is slightly inclined downward in a vertical sectional view shown in FIG. Specifically, in the vertical sectional view shown in FIG. 2, the angle θ ₁ [deg] between the inner bottom surface 3g of the molten steel discharge hole 3 and the horizontal is set to −10 to 60. The inner peripheral opening edge 3a of the molten steel discharge hole 3 has a rectangular shape with a slightly rounded corner in the vertical sectional view shown in FIG. 1, and the same applies to the outer peripheral opening edge 3b of the molten steel discharge hole 3. The outer peripheral opening edge 3b of the molten steel discharge hole 3 is formed wider than the inner peripheral opening edge 3a, so that the molten steel discharge hole 3 has an outer periphery from the inner peripheral opening edge 3a in the bottom view shown in FIG. It forms so that it may expand gradually as it goes to the side opening edge 3b. The width of the inner periphery side opening edge 3a is indicated by a symbol f in the figure, and the width of the outer periphery side opening edge 3b is also indicated by a symbol e.

  The protrusion 4 has a so-called drum shape in which the center in the extending direction is narrowed in the bottom view shown in FIG. The shape of the protrusion 4 will be described in detail below.

As described above, the protrusion 4 extends in parallel with the drilling direction 3A of the molten steel discharge hole 3 in the bottom view shown in this figure, and its end is the inner periphery of the immersion nozzle 1 as shown in FIG. To the surface. The height of the upper surface of the protrusion 4 (height from the inner bottom surface 2) in the vertical cross section (vertical sectional view shown in FIG. 1) with respect to the extending direction of the protrusion 4 is considered by the symbol h, and the molten steel discharge hole When the distance between the lower end of the inner peripheral side opening edge 3a of 3 and the inner bottom surface 2 is considered by the symbol H, the following formula (1) is satisfied. However, the upper surface of the protrusion 4 does not necessarily have to be flat, and design changes such as forming a slight roundness at the corners are allowed. Further, the width of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1 shown in FIG. When the width at the center in the extending direction of 4 is considered by the symbol b, the following formula (2) is satisfied. In the following formula (2), the variable D means the inner diameter of the immersion nozzle 1.
h / H = 0.5-2.0 ... (1)
(ab) /D=0.15~0.45 ... (2)

The shape of the protrusion 4 will be described in more detail. That is, the projected area s of the top surface of the protrusion 4 in the bottom view (FIG. 3) of the immersion nozzle 1 (shown schematically by a two-dot chain line in this figure) and the flow path cross-sectional area S of the immersion nozzle 1 are as follows: Formula (3) is satisfied. The flow path cross-sectional area S is uniquely determined based on the inner diameter D of the immersion nozzle 1.
s / S = 0.15-0.5 ... (3)

  The upper end of the immersion nozzle 1 is connected to the bottom of the tundish via a molten steel flow rate adjusting unit for adjusting the discharge flow rate of the molten steel discharged from the immersion nozzle 1 into the mold. The molten steel flow rate control unit will be outlined below. Please refer to FIG. FIG. 4 is a longitudinal sectional view of a molten steel flow rate adjusting unit to which an immersion nozzle is connected. As shown in the figure, the molten steel flow rate adjustment unit 10 is formed in a substantially cylindrical shape, and has a slide plate 11 that can be opened and closed in the direction perpendicular to the paper surface at the center in the extending direction, and a porous shape at the upper part in the extending direction. A ring 12 is provided. This ring 12 serves as a gas ejection hole for injecting an inert gas typified by Ar gas into the molten steel flowing in the flow passage formed inside the immersion nozzle 1 and the molten steel flow rate adjusting unit 10. An appropriate blowing nozzle 13 is provided. With the above configuration, when an Ar gas supply device (not shown) is connected to the blowing nozzle 13, the Ar gas is appropriately supplied to the molten steel flowing in the immersion nozzle 1.

  And the immersion nozzle 1 comprised as mentioned above is a tundish (substantially) so that the piercing direction 3A (refer FIG. 3) of the molten steel discharge hole 3 pierced in the surrounding wall corresponds with the width direction of a casting_mold | template. Installed in the molten steel flow control unit 10).

  The effect produced by employing the immersion nozzle 1 having the above configuration will be described with reference to FIG. FIG. 5 is a diagram in which the flow of molten steel is imaged by curves and arrows. That is, the inventor of the present invention previously devised an immersion nozzle (comparative example) shown on the left side of the figure. This immersion nozzle is provided with a protrusion on the inner bottom surface that extends in parallel to the drilling direction of the molten steel discharge hole, and with this configuration, while maintaining the effect of suppressing splash at the start of casting, the mold in the molten steel discharge hole Generation | occurrence | production of the big single rotation flow which is the cause of the drift of thickness direction can be suppressed. However, as shown in the bottom view of the submerged nozzle shown in the upper left of the figure, the generation of a small-diameter vortex is confirmed along the extending direction of the protrusion, and the branch point of the vortex is the extending direction of the protrusion. It can be seen that it can be easily moved along. On the other hand, the immersion nozzle 1 according to the present embodiment is provided with a similar protrusion 4 on the inner bottom surface 2 thereof, and the protrusion 4 is narrowed at the center in the extending direction (also FIG. 3). reference). Due to this narrowed shape, the branch point of the vortex is strongly constrained at the center in the extending direction of the protrusion 4, so that the flow rate of the molten steel discharged from each of the pair of molten steel discharge holes 3 and 3 can be made substantially the same. it is conceivable that.

  Hereinafter, a test for confirming the technical effect of the immersion nozzle 1 according to the present embodiment will be described. Each numerical range described above is reasonably supported by the following confirmation test.

<First confirmation test>
This test is a test (water model test) for verifying the presence or absence of the drift suppression effect in the mold thickness direction. The test methods, test conditions, and test results are shown below.

(Test method)
See FIG. FIG. 6 is a schematic front view for explaining the test method of the first confirmation test. As shown in the figure, the flow velocity of the water flow discharged through the inside of the outer peripheral side opening edge 3b of the molten steel discharge hole 3 is measured with an electromagnetic current meter (model number: VM802H manufactured by Kennek). Specifically, the measuring elements of the electromagnetic current meter are installed at two locations near the lower left end and near the lower right end of the outer peripheral opening edge 3b. The flow velocity of the water flow measured by the electromagnetic current meter installed in the vicinity of the lower left end of the outer peripheral opening edge 3b is V1, and the flow rate of the water flow measured by the electromagnetic current meter installed in the vicinity of the lower right end of the outer peripheral opening edge 3b Using the flow velocity as V2, the thickness direction drift suppression rate [%] is obtained based on the following formula (4), and this is used as an evaluation object for verifying the presence or absence of the drift suppression effect in the mold thickness direction. Note that a sample in which the thickness direction drift suppression rate [%] is 80 or more is evaluated as “good (no thickness direction drift)”.
(Thickness direction drift suppression rate [%]) = 100 × (1−Speed difference / Speed sum) = 200 × V2 / (V1 + V2) (V1> V2) (4)

(Test conditions)
Mold dimension [mm]: width 1260 x thickness 240
Casting speed [m / min]: 1.65
Molten steel superheat degree ΔT [° C]: −
Model type: Water model Molten steel flow rate (or water flow rate) [L / min]: Water flow rate 550
Ar gas flow rate (or air flow rate) [L / min]: Air flow rate 0
Slide plate opening / closing direction: Mold thickness direction
h [mm] (See Fig. 1): See Table 1 below
H [mm] (See Fig. 1): See Table 1 below
h / H: See Table 1 below
a [mm] (See Fig. 3): See Table 1 below
b [mm] (See Fig. 3): See Table 1 below
D [mm] (See Fig. 3): See Table 1 below
(ab) / D: See Table 1 below
s [mm ² ] (See Fig. 3): See Table 1 below
^{S (= πD 2/4)} [mm 2]: See Table 1 below
s / S: see Table 1 below θ ₁ [deg.] (see FIG. 2): 35
e [mm] (see Fig. 3): 100
f [mm] (see Fig. 3): 70
g [mm] (see Fig. 3): 30

(Test results)
The test results are shown in Table 1 below and FIG. In FIG. 7, “current product” corresponds to Comparative Example 2 in Table 1 (that is, no protrusions).

  According to Table 1 and FIG. 7 above, the presence of the protrusions is required in order to effectively exhibit the drift suppression effect in the mold thickness direction, while the magnitude of the variable (ab) / D is not limited. It turns out that there is no.

<Second confirmation test>
This test is a test (water model test) for verifying the presence or absence of the drift suppression effect in the mold thickness direction. The test methods, test conditions, and test results are shown below.

(Test method)
This is the same as the first confirmation test.

(Test conditions)
Mold dimension [mm]: width 1260 x thickness 240
Casting speed [m / min]: 1.65
Molten steel superheat degree ΔT [° C]: −
Model type: Water model Molten steel flow rate (or water flow rate) [L / min]: Water flow rate 550
Ar gas flow rate (or air flow rate) [L / min]: Air flow rate 0
Slide plate opening / closing direction: Mold thickness direction
h [mm] (See Fig. 1): See Table 2 below
H [mm] (See Fig. 1): See Table 2 below
h / H: See Table 2 below
a [mm] (See Fig. 3): See Table 2 below
b [mm] (See Fig. 3): See Table 2 below
D [mm] (See Fig. 3): See Table 2 below
(ab) / D: See Table 2 below
s [mm ² ] (See Fig. 3): See Table 2 below
^{S (= πD 2/4)} [mm 2]: Table 2 see
s / S: see Table 2 below θ ₁ [deg.] (see FIG. 2): 35
e [mm] (see Fig. 3): 100
f [mm] (see Fig. 3): 70
g [mm] (see Fig. 3): 30

(Test results)
The test results are shown in Table 2 below and FIG. In Table 2 below, the protrusion is not provided in Comparative Example 3.

  According to Table 2 and FIG. 8 described above, the presence of the protrusions is necessary for the effect of suppressing the drift in the mold thickness direction, and the above-described variable h / H satisfies the above equation (1). It turns out that satisfaction is required.

<Causal relationship between coagulation delay and breakout>
As described above, the effect expected by using the immersion nozzle 1 according to the above embodiment is mainly suppression of drift in the mold thickness direction and the mold width direction. By suppressing this drift, the object is to improve the so-called solidification delay and ultimately avoid the so-called breakout (a phenomenon in which molten steel in the solidified shell flows out of the solidified shell). Therefore, here, the degree of coagulation delay for quantitatively evaluating the coagulation delay is defined, and the causal relationship between the degree of coagulation delay and the breakout will be described.

  That is, “solidification delay” refers to partial growth delay of the solidified shell, and the degree of solidification delay is used for quantification. “Degree of coagulation delay” is based on the white band shown in FIG. The “white band” is a linear structure that appears when the solute in front of the shell being solidified is washed by the molten steel flow, and represents the growth of the solidified shell. If there is a difference in the thickness of the shell B at the corner and the shell A at the healthy part, the shrinkage amount due to solidification of the solidification delayed part and the healthy part will differ, and the tensile stress in the slab width direction will concentrate on the solidification delayed part. Cause vertical splitting. When the degree of vertical split increases, the molten steel in the solidified shell flows out of the solidified shell and breakout occurs. In past data (see Table 3 below), there is a record that breakout occurs when the solidification delay exceeds 40%, so the solidification delay was set to 40%.

<Quantification method of drift in mold width direction>
Next, a method for quantifying the drift in the mold width direction in actual machine casting will be described. Please refer to FIG. FIG. 10 is an explanatory diagram for explaining a method for quantifying the drift in the mold width direction in actual casting. That is, as shown in this figure, (1) the temperature distribution of the mold in the casting direction was measured using a thermocouple embedded in a vertical row at the center of the mold narrow surface, and (2) the inflection point of the temperature distribution was determined. (3) The difference Δh between the molten metal level on one side of the mold narrow surface (corresponding to the “right side molten metal surface”) and the molten metal level on the other side (corresponding to “left side molten metal surface”) is obtained. (4) The drift in the mold width direction was quantified based on the difference Δh.

<Causal relationship between solidification delay and drift in slab width direction>
Next, the causal relationship between the solidification delay and the drift in the slab width direction in actual machine operation will be described with reference to FIG. FIG. 11 is a diagram showing the relationship between the degree of solidification delay and the difference Δh in actual machine operation. However, in FIG. 11, the molten steel heating degree ΔT is set to 20 to 30. According to this figure, when the above difference Δh (corresponding to “melt level difference” in this figure) exceeds 10 mm, a solidification delay with a solidification delay degree of 40% or more may occur. I understand. Therefore, from the viewpoint of avoiding the breakout described above, the difference Δh [mm] is preferably suppressed to 10 or less.

<Conversion for convenience of verification experiment using water model>
The above-described method for quantifying the drift in the mold width direction utilizes the fact that molten steel is extremely hot, so that the quantification method is used for verification experiments using a water model to be performed instead of the actual machine. Cannot be applied directly. Therefore, a method for quantifying the drift in the mold width direction in a verification experiment using a water model, which has been devised with some contrivance for this quantification method, will be described. Reference is now made to FIG. FIG. 12 is an explanatory diagram for explaining a method of quantifying the drift in the mold width direction in the water model. That is, the difference Δh [m] can be expressed by the following equation (5).
Δh = ρ _m × U ₁ ² / (2 × g × (ρ _m -ρ _p ))-ρ _m × U ₂ ² / (2 × g × (ρ _m -ρ _p )) ... (5)
However,
ρ _m [kg / m ³ ]: Density of molten steel ρ _p [kg / m ³ ]: Density of mold powder
U ₁ [m / s]: Flow velocity of the upward flow of molten steel in the vicinity of one of the mold narrow surfaces
U ₂ [m / s]: Flow velocity of the upward flow of molten steel in the vicinity of the other narrow surface of the mold (U ₁ > U ₂ )
g [m / s ² ]: Gravity acceleration

For example, Δh [m] = 0.01, g [m / s ² ] = 9.8, ρ _m [kg / m ³ ] = 7000, ρ _p [kg / m ³ ] = 3000 is substituted for the above formula (5) Then, the following formula (6) is derived.
U ₁ ² -U ₂ ² = 0.1 ... (6)

<Definition of drift degree, no drift, no drift rate>
By the way, the flow velocity of the molten steel in the narrow mold surface is generally equal to the surface flow velocity of the molten steel in the vicinity of the narrow mold surface (Imamura et al .: Hydraulic study of molten steel flow in continuous casting, iron and steel Vol. 78, No. 3 (1992), p. 439-446), the surface velocity of water at a point 30 cm away from the mold narrow surface and 2 cm deep from the water surface as shown in FIG. Model No .: VM-802H manufactured by Kennek), and in the following description, the measured surface flow velocity is regarded as the variables U ₁ and U ₂ . In short, the drift in the mold width direction is evaluated by measuring the surface flow velocity of water.

Then, “the degree of drift” is defined as the following formula (7).
(Drift) = (U ₁ ² -U ₂ ² ) / (U ₁ ² -U ₂ ² ) _cr ... (7)
However, “(U ₁ ² −U ₂ ² ) _cr ” is the value of (U ₁ ² −U ₂ ² ) when the difference Δh [m] is 0.01 as shown in the equation (6) (that is, 0.1 ).

  When the absolute value of the drift rate defined by the above equation (7) is less than 1, it is defined as the `` no drift '' state, and the proportion of the `` no drift '' state in the flow velocity measurement time is `` no “Miscellaneous current rate” was defined, and when this “non-current drift rate” was 60% or more, it was evaluated as “effective in suppressing lateral drift”. Here, an example of the measurement result of the drift current is introduced in FIG. FIG. 13 is a graph showing the time transition of the drift degree. In the figure, “no drift portion” indicates a time region where the absolute value of the drift degree is less than one. The measurement conditions for the measurement according to FIG. 13 are as follows.

(Test conditions)
Mold dimension [mm]: width 1260 x thickness 240
Casting speed [m / min]: 2.0
Molten steel superheat degree ΔT [° C]: −
Model type: Water model Molten steel flow rate (or water flow rate) [L / min]: Water flow rate 600
Ar gas flow rate (or air flow rate) [L / min]: Air flow rate 10
Slide plate opening / closing direction: Mold thickness direction
h [mm] (see Fig. 1): 20
H [mm] (see Fig. 1): 20
h / H: 1.0
a [mm] (see Fig. 3): 40
b [mm] (see Fig. 3): 15
D [mm] (see Fig. 3): 85
(ab) / D: 0.29
s [mm ² ] (see Fig. 3): 2332
^{S (= πD 2/4)} [mm 2]: 5675
s / S: 0.41
θ ₁ [deg.] (see Fig. 2): 35
e [mm] (see Fig. 3): 100
f [mm] (see Fig. 3): 70
g [mm] (see Fig. 3): 30

<Third confirmation test>
This test is a test (water model test) for verifying the presence or absence of the drift suppression effect in the mold width direction. The test methods, test conditions, and test results are shown below.

(Test method)
The method for measuring the non-flow rate is as described above. The measurement time is 2 hours.

(Test conditions)
Mold dimension [mm]: width 1260 x thickness 240
Casting speed [m / min]: 2.0
Molten steel superheat degree ΔT [° C]: −
Model type: Water model Molten steel flow rate (or water flow rate) [L / min]: Water flow rate 600
Ar gas flow rate (or air flow rate) [L / min]: See Table 4 below Slide plate opening / closing direction: Mold thickness direction
h [mm] (See Fig. 1): See Table 4 below
H [mm] (See Fig. 1): See Table 4 below
h / H: See Table 4 below
a [mm] (See Fig. 3): See Table 4 below
b [mm] (See Fig. 3): See Table 4 below
D [mm] (See Fig. 3): See Table 4 below
(ab) / D: See Table 4 below
s [mm ² ] (See Fig. 3): See Table 4 below
^{S (= πD 2/4)} [mm 2]: Table 4 refer
s / S: see Table 4 below θ ₁ [deg.] (see FIG. 2): 35
e [mm] (see Fig. 3): 100
f [mm] (see Fig. 3): 70
g [mm] (see Fig. 3): 30

(Test results)
The test results are shown in Table 4 below and FIG. In an actual machine, Ar gas is blown into the molten steel in order to suppress the inclusion adhesion in the immersion nozzle, and the flow rate is 5 to 20 NL / min. The Ar gas blown in the molten steel expands by a factor of 6.5 [273K → 1773K]. Furthermore, when Ar gas is blown from the top of the slide plate, the flow rate of Ar gas introduced into the mold is reported to be about 20% of the blown amount (Yamanaka et al .: Japan Society for the Promotion of Science, Steelmaking Committee 19 Solidification Process Study Group As the air flow rate is 10 [L / min] or 25 [L / min], Ar gas injection flow rate 7.7 [NL / min in the actual machine, respectively, because there is a document, 19 committee-12228, coagulation process IV40,2006) ] And 19.2 [NL / min].

  According to Table 4 and FIG. 14, it can be seen that when (a−b) / D is set to 0.15 to 0.45, the effect of suppressing the drift in the mold width direction is effectively exhibited.

As described above, in the above embodiment, the immersion nozzle 1 is configured as follows. That is, it is a bottomed cylindrical immersion nozzle 1 used for pouring molten steel held in a tundish into a mold. A pair of opposed molten steel discharge holes 3 are perforated in the peripheral wall of the immersion nozzle 1 at a position away from the inner bottom surface 2 of the immersion nozzle 1 by a predetermined distance, and the inner bottom surface 2 has a bottom surface of the immersion nozzle 1 As viewed, a protrusion 4 extending in parallel with the drilling direction 3A of the molten steel discharge hole 3 is provided, and further satisfies the following expressions (1) and (2).
h / H = 0.5-2.0 ... (1)
(ab) /D=0.15~0.45 ... (2)
However,
h: the height of the upper surface of the protrusion 4 in a cross section perpendicular to the extending direction of the protrusion 4
H: Distance between the lower end of the inner peripheral opening edge 3a of the molten steel discharge hole 3 and the inner bottom surface 2
a: The width of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1, and the width at the end of the protrusion 4 in the extending direction
b: The width of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1, and the width of the protrusion 4 in the center in the extending direction
D: Inner diameter of the immersion nozzle 1

  According to this configuration, it is possible to suppress the drift in the mold thickness direction and the width direction and reduce splash at the start of casting.

<Fourth confirmation experiment>
This test is a test (water model test) for verifying the presence or absence of the splash suppression effect. The test methods, test conditions, and test results are shown below.

(Test method)
Here, the `` splash '' mentioned above refers to a phenomenon in which molten steel poured into the immersion nozzle 1 at the start of casting is ejected so as to jump up by striking the inner bottom surface 2 without limitation. In addition, there is also a phenomenon that the molten steel is discharged from the molten steel discharge hole 3 of the immersion nozzle 1 downward and jumps up through the upper end surface of the dummy bar inserted in the mold and the narrow surface of the mold. It is a waste. This splash is not preferable because the productivity is lowered.

  The presence or absence of the splash suppression effect is evaluated based on measurement of “scattering height” and “bubble dive depth”. The “scattering height” is related to the former phenomenon, and the “bubble dive depth” is related to the latter phenomenon. The latter phenomenon is indirectly evaluated by evaluating the strength of the water flow discharged downward from the molten steel discharge hole 3 (bubble dive depth).

  The measurement of the “scattering height” is performed as follows. FIG. 15 is a side view of the immersion nozzle. That is, as shown in this figure, the arrival height of water droplets discharged and scattered upward from the molten steel discharge hole of the immersion nozzle is measured visually with reference to the upper side of the outer peripheral opening edge of the molten steel discharge hole.

  On the other hand, the measurement of the “bubble dive depth” is performed as follows. That is, as shown in the figure, a water tank whose water surface height is adjusted so that the vertical distance to the lower end of the immersion nozzle is 5 cm is installed below the immersion nozzle and is directed downward from the molten steel discharge hole of the immersion nozzle. The depth of arrival of the bubbles in which the water discharge flow ejected vigorously is measured visually with reference to the water surface. In addition, the observation object which records this reach | attainment depth is limited to the thing whose diameter is 5 mm or more among the bubbles entrained by the water discharge flow.

  Then, when the splash height of the water droplet is less than 15 cm and the bubble dive depth is less than 35 cm, it is evaluated as “with splash suppression effect”.

(Test conditions)
Mold dimension [mm]: width 1260 x thickness 240
Casting speed [m / min]: 2.0
Molten steel superheat degree ΔT [° C]: −
Model type: Water model molten steel flow rate (or water flow rate) [L / min]: Water flow rate 800 (equivalent to start of casting in actual machine)
Ar gas flow rate (or air flow rate) [L / min]: Air flow rate 0
Opening and closing direction of slide plate 11: mold thickness direction
h [mm] (See Fig. 1): See Table 5 below
H [mm] (See Fig. 1): See Table 5 below
h / H: See Table 5 below
a [mm] (See Fig. 3): See Table 5 below
b [mm] (See Fig. 3): See Table 5 below
D [mm] (See Fig. 3): See Table 5 below
(ab) / D: See Table 5 below
s [mm ² ] (See Fig. 3): See Table 5 below
^{S (= πD 2/4)} [mm 2]: Table 5 refer
s / S: see Table 5 below θ ₁ [deg.] (see FIG. 2): 35
e [mm] (see Fig. 3): 100
f [mm] (see Fig. 3): 70
g [mm] (see Fig. 3): 30

(Test results)
The test results are shown in Table 5 below and FIG.

  According to Table 5 and FIG. 16, it can be seen that the above-described variable s / S needs to satisfy the above formula (3) in order for the splash suppression effect to be effectively achieved.

  Further, from the viewpoint of difficulty in manufacturing the protrusion 4, it is preferable to secure the variable b (see FIG. 3) of 10 mm or more. When the inner diameter D of the immersion nozzle 1 is 120 mm, (a−b) /D=0.15, and b = 10 mm, s / S = 0.15. From this point, it can be said that the lower limit of s / S should be 0.15. In addition, if s / S = 0.15 to 0.5 and (ab) /D=0.15 to 0.5 are satisfied at the same time, considering that the inner diameter D of the immersion nozzle 1 used in the actual machine is 60 to 120 mm, b / D is 0.08 to 0.33.

As described above, in the above embodiment, the immersion nozzle 1 is further configured as follows. That is, the following formula (3) is satisfied.
s / S = 0.15-0.5 ... (3)
However,
s: projected area of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1
S: Channel cross-sectional area of the immersion nozzle 1 that can be conceived in the bottom view of the immersion nozzle 1

  According to this configuration, the splash suppression effect is effectively achieved.

  Although the preferred embodiments of the present invention have been described above, the present invention can be implemented with the following modifications.

That is, in the above embodiment, the molten steel discharge hole 3 is formed so as to expand from the inner peripheral side toward the outer peripheral side as shown in FIG. The opening cross-sectional areas of the inner peripheral opening and the outer peripheral opening may be the same.

◆ The protrusion 4 may have the shape shown in FIG. FIG. 17 is a view similar to FIG. That is, the protrusion 4 has a substantially trapezoidal shape narrowed upward in a longitudinal sectional view (displayed on the lower side of the figure: corresponding to the AA cross section), and at the intersection of the upper side and the side side of the trapezoid. The radius R2 is rounded, and the intersection of the side of the trapezoid and the inner bottom surface 2 is rounded with the radius R1, and the side of the trapezoid forms an angle θ3 with respect to the inner bottom surface 2, The bottom surface width a2 of the protrusion 4 that is considered by the intersection of the virtual extension line of the side and the inner bottom surface 2 is the width a of the top surface (in the shape shown in FIG. 17, the virtual extension line of the side and the virtual surface of the top surface The shape may be larger than the point of intersection with the extension line. The technical effect when the protrusion 4 is formed in this shape has been sufficiently proved experimentally as shown in Table 6 below.

  (A) Note that, as a result of R being added to the corner as in the shape shown in FIG. 17, (i) the width of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1, and the protrusion (Ii) the width of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1, the width at the center of the protrusion 4 in the extending direction, (iii) When the projected area of the upper surface of the protrusion 4 in the bottom view of the immersion nozzle 1 cannot be directly considered (i) to (iii), the "projection 4 It is reasonable to think of (i) to (iii) based on the “upper surface”. (B) There is no plane portion on the side surface of the protrusion 4 shown in FIG. 17 (the surface represented by the contour line extending obliquely upward from the inner bottom surface 2 in the AA cross section shown in the lower side of the figure). As a reason, when the “upper surface of the protrusion 4” cannot be considered even before the R is attached, the above is based on the virtual side surface having the normal of the side surface at the inflection point of the contour line of the side surface. It is reasonable to think of the “upper surface of the protrusion 4” by the method (A). (C) Even if no inflection point is found in the contour line of the side surface in (B) above, it has a normal line of the side surface at the intersection point of the contour line of the side surface and the inner bottom surface 2, and the intersection point is It is reasonable to think of the “upper surface of the protrusion 4” by the method (A) based on the virtual side surface included in the surface.

◆ The protrusion 4 may have a shape shown in FIG. FIG. 18 is a view similar to FIG. That is, the protrusion 4 may have a shape that is smoothly narrowed from both ends in the extending direction toward the center in the extending direction. Although the protrusion 4 shown in the drawing has a side surface perpendicular to the inner bottom surface 2, the present invention is not limited to this, and there is no problem even if an appropriate taper is provided as shown in FIG. 17.

The longitudinal cross-sectional view of the immersion nozzle which concerns on one Embodiment of this invention Sectional view taken along line 2-2 in FIG. Cross-sectional view taken along line 3-3 in FIG. Longitudinal section of molten steel flow control unit connected with immersion nozzle Figure depicting the flow of molten steel with curves and arrows Front schematic diagram for explaining the test method of the first confirmation test The figure which shows the test result of the first confirmation test The figure which shows the test result of the second confirmation test Vertical sectional view of the slab in the casting direction Explanatory drawing for demonstrating the quantification method of the drift in the mold width direction in actual machine casting Diagram showing the relationship between the degree of solidification delay and the difference Δh in actual machine operation Explanatory diagram for explaining the method for quantifying the drift in the mold width direction in the water model Graph showing time transition of drift current The figure which shows the test result of the third confirmation test Side view of immersion nozzle The figure which shows the test result of the 4th confirmation test It is a figure similar to FIG. 3, Comprising: The figure which shows a modification It is a figure similar to FIG. 3, Comprising: The figure which shows a modification

Explanation of symbols

1 Immersion nozzle
2 Inside bottom
3 Molten steel discharge hole
3A Drilling direction
4 Projections
D Inner diameter

Claims (2)

In a bottomed cylindrical immersion nozzle provided for pouring molten steel held in a tundish into a mold, the peripheral wall of the immersion nozzle is spaced apart from the inner bottom surface of the immersion nozzle by a predetermined distance. A pair of opposed molten steel discharge holes are drilled, and the inner bottom surface is provided with a protrusion extending in parallel with the drilling direction of the molten steel discharge hole in the bottom view of the immersion nozzle, and further includes the following formula (1) And an immersion nozzle satisfying (2).
h / H = 0.5-2.0 ... (1)
(ab) /D=0.15~0.45 ... (2)
However,
h: the height of the upper surface of the protrusion in a cross section perpendicular to the extending direction of the protrusion
H: Distance between the lower end of the inner peripheral opening edge of the molten steel discharge hole and the inner bottom surface
a: The width of the top surface of the protrusion in the bottom view of the immersion nozzle, and the width at the end of the protrusion in the extending direction
b: The width of the upper surface of the protrusion in the bottom view of the immersion nozzle, and the width of the protrusion in the center in the extending direction
D: Inner diameter of the immersion nozzle The immersion nozzle according to claim 1, wherein the following formula (3) is satisfied.
s / S = 0.15-0.5 ... (3)
However,
s: Projected area of the upper surface of the protrusion in the bottom view of the immersion nozzle
S: Channel cross-sectional area of the immersion nozzle that can be conceived in the bottom view of the immersion nozzle

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