Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
TITLE OF INVENTION
Immersion nozzle
TECHNICAL FIELD
[0001]
The present invention relates to an immersion nozzle for use in continuous
casting to pour
molten steel from tundish into a mold, and more particularly to an immersion
nozzle, such as those
used for continuous casting of a thin slab, a medium-thick slab or the like,
which is flat in terms
of transverse cross-section (cross-section in a direction perpendicular to a
vertical direction) near
a discharge port of the immersion nozzle.
BACKGROUND ART
[0002]
In a continuous casting process for forming a slab having a given shape by
continuously
subjecting molten steel to cooling and solidification, molten steel is poured
into a mold via an
immersion nozzle for continuous casting (hereinafter also referred to simply
as "immersion
nozzle") installed with respect to the bottom of a tundish.
[0003]
Generally, the immersion nozzle is composed of a bottomed tubular body which
has an upper
end serving as an inlet of molten steel, and a molten steel flow passage
(inner bore) internally
formed to extend downwardly from the molten steel inlet, wherein a pair of
discharge ports
communicated with the molten steel flow passage (inner bore) are formed in a
lateral wall of a
lower portion of the tubular body in opposed relation to each other. The
immersion nozzle is
used in a state in which the lower portion thereof is immersed in molten steel
in a mold. This is
intended to prevent scattering of poured molten steel, and further block
contact of the molten steel
with the atmosphere, thereby preventing oxidation thereof. Further, the use of
the immersion
nozzle is intended to allow the flow of molten steel in the mold to be
straightened, thereby
preventing impurities such as slag or non-metal inclusions floating on the
surface of the molten
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steel from being entrained into the molten steel.
[0004]
In recent years, there has been a growing tendency toward manufacturing
thinned slabs such
as a thin slab and a medium-thick slab during continuous casting. In order to
cope with a thin
mold for this type of continuous casting, the immersion nozzle needs to be
flattened. For
example, the below-mentioned Patent Document 1 discloses a flat immersion
nozzle in which a
discharge port is provided in a short-side lateral wall; and in the below-
mentioned Patent
Document 2 discloses a flat immersion nozzle in which a discharge port is
further provided in a
lower end wall. Generally, such a flat immersion nozzle is configured such
that the width of an
inner bore thereof is increased between a molten steel inlet thereof and the
discharge port in a
direction from the molten steel inlet toward a mold.
[0005]
However, when the inner bore has a region where it is increased in terms of
width, and
flattened, the flow of molten steel inside the immersion nozzle becomes more
likely to be
disordered, and thus a discharge flow toward the mold also becomes more likely
to be disordered.
Resulting turbulence of the molten steel flow becomes a factor causing
defective quality of slabs,
an increase in danger during casting operation, etc., such as an increase in
fluctuation of the surface
of (molten steel) bath in the mold (in-mold bath surface), entrainment of a
mold powder into a
slab, or unevenness in temperature. Therefore, it is necessary to stabilize a
molten steel flow
inside the immersion nozzle and a molten steel flow during discharge.
[0006]
With a view to stabilizing the above molten steel flows, for example, the
below-mentioned
Patent Document 3 discloses an immersion nozzle formed with at least two
bending facets
extending from a point (center) on a plane in a lower region of an inner bore
toward a lower edge
of a discharge port. The Patent Document 3 also discloses an immersion nozzle
comprising a
flow divider for dividing a molten steel flow into two streams. In the flat
immersion nozzle
disclosed in the Patent Document 3, the stability of the molten steel flow
inside the immersion
nozzle are enhanced, as compared with the immersion nozzles disclosed in the
Patent Documents
1 and 2, in which there is not any means to change a flow direction/pattern in
an internal space
thereof.
[0007]
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However, the means to divide the molten steel flow in a right-left direction
is still likely to
cause a situation where the fluctuation of the molten steel discharge flow
between right and left
discharge ports is increased, and thereby the fluctuation of the in-mold bath
surface is increased.
[0008]
Under the above background, the present inventors have invented a flat
immersion nozzle
disclosed in the below-mentioned Patent Document 4, thereby contributing to
stabilizing an in-
mold bath surface, etc.
CITATION LIST
[Patent Document]
[0009]
Patent Document 1: JP-A H11-005145
Patent Document 2: JP-A H11-047897
Patent Document 3: JP-A 2001-501132
Patent Document 4: WO-A 2017/081934
SUMMARY OF INVENTION
[Technical Problem]
[0010]
However, the present inventors has found that, in continuous casting carried
out under casting
conditions, particularly, a condition of a molten steel flow rate of about
0.04 (t / (min=cm2)) or
more, as measured with reference to the position of minimum cross-sectional
area in a region
around an upper end of the immersion nozzle where a transverse cross-section
of the inner bore is
a circular shape, even the flat immersion nozzle disclosed in the Patent
Document 4 is still
insufficient in terms of the intended effects such as stabilization of an in-
mold bath surface.
[0011]
Therefore, a problem to be solved by the present invention is to provide a
flat immersion
nozzle capable of stabilizing an in-mold bath surface, i.e., reducing the
fluctuation of the in-mold
bath surface.
[Solution to Technical Problem]
[0012]
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In the flat immersion nozzle disclosed in the Patent Document 4, primarily, a
protrusion
(protruding portion) is provide in a central region of an inner bore (inner
hole) of the nozzle, as a
basic configuration, and optionally a protrusion having a protruding thickness
equal to or less than
that of the central protrusion is provide beside the central protrusion to
finely adjust a discharge
flow direction, a discharge flow/pattern, or the like.
Differently, in the present invention, symmetrical lateral (laterally-offset)
protrusions are
provided, wherein a space having no protrusion is defined between the lateral
protrusions, as a
basic configuration, and optionally a protrusion having a protruding length
less than that of each
of the lateral protrusion is provided.
[0013]
In the structure of the flat immersion nozzle disclosed in the Patent Document
4, the molten
steel flow inside the inner bore is guided such that the flow rate thereof
becomes larger in a lateral
direction (which means a width direction of a flat portion of the nozzle. this
is also applied to the
following description) than in a central and vertically downward direction. In
this case, the flow
velocity of molten steel discharged from the discharge port tends to be
increased, and, under the
condition that a molten steel flow rate per unit time or per unit area is
relatively large, the
fluctuation of the in-mold bath surface is likely to be increased.
Differently, in the structure of the flat immersion nozzle of the present
invention, the molten
steel flow inside the inner bore is guided, while being adjusted to increase
the flow rate thereof in
the central and vertically downward direction, thereby relatively reducing the
flow rate thereof in
the lateral direction. In other words, the ratio of the flow rate in the
central and vertically
downward direction / the flow rate in the lateral direction is relatively
increased as compared with
that in the structure of the flat immersion nozzle disclosed in the Patent
Document 4.
It should be noted here that the above adjustment is made in relation to the
ratio of the flow
rate in the central and vertically downward direction / the flow rate in the
lateral direction, but is
not necessarily made to establish the relationship of the central and
vertically downward direction
> the flow rate in the lateral direction.
[0014]
The present invention intended to obtain the above flow pattern provides a
flat immersion
nozzle having features described in the following sections 1 to 8.
1. An immersion nozzle having a flat portion whose inner bore has a thickness
Tn and a width
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Wn greater than the thickness Tn, and which comprises opposed short-side
lateral walls and
opposed long-side walls extending in a width direction of the flat portion,
wherein a pair of
discharge ports are provided, respectively, in lower parts of the short-side
lateral walls. The
immersion nozzle comprises two portions provided on each of the width-
directionally extending
walls, and arranged at axial symmetrical positions with respect to a
longitudinal central axis of the
width-directionally extending walls, in pairs, wherein each of the portions
extends obliquely
downwardly in the width direction and protruding in a thickness direction of
the flat portion (the
portion will hereinafter be referred to as "lateral protrusion"), wherein two
pairs of the lateral
protrusions are arranged, respectively, on the width-directionally extending
walls, in opposed
relation, and wherein two sets of opposed lateral protrusions in the two pairs
of lateral protrusions
have a same value falling within a range of 0.18 to 0.90 in terms of a total
protruding length Ts in
the thickness direction, expressed as an index on the basis of 1 indicative of
a thickness of the
inner bore at a position where the opposed lateral protrusions are provided.
2. The immersion nozzle as described in the section 1, which further comprises
a protrusion
provided on each of the width-directionally extending walls at a position
between two lateral
protrusions in each of the two pairs of lateral protrusions (this protrusion
will hereinafter be
referred to as "central protrusion"), wherein the central protrusion has a
thickness-directional
protruding length less than that of the lateral protrusion, and wherein two
central protrusions in
the two pairs of lateral protrusions have a value of 0.40 or less (not
including zero) in terms of a
total protruding length Tp in the thickness-direction, expressed as an index
on the basis of 1
indicative of the thickness of the inner bore at the position where the
opposed lateral protrusions
are provided.
3. The immersion nozzle as described in the section 2, wherein an upper end
surface of the
central protrusion has one selected from the group consisting of a shape
extending horizontally in
the width direction, a curved shape having a top at a midpoint thereof, and an
upwardly protruding
shape including a bending point.
4. The immersion nozzle as described in any one of the sections 1 to 3,
wherein an upper end
surface of the lateral protrusion or the central protrusion has a shape
extending horizontally in a
direction toward a center of the inner bore, or a planar or curved shape
extending obliquely
downwardly in the direction toward the center of the inner bore.
5. The immersion nozzle as described in any one of the sections 1 to 4,
wherein one or each
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of the lateral protrusion and the central protrusion has a shape in which the
thickness-directional
protruding length thereof is constant, or becomes shorter linearly,
curvilinearly or stepwisely in a
direction toward a center of the width-directionally extending wall.
6. The immersion nozzle as described in any one of the sections 1 to 5,
wherein one or each
of the lateral protrusion, and the lateral protrusion combined with the
central protrusion is provided
plurally in an up-down direction.
7. The immersion nozzle as described in any one of the sections 1 to 6, which
comprises a
protrusion provided around a center of a bottom of the inner bore to protrude
upwardly.
8. The immersion nozzle as described in any one of the sections 1 to 7, which
is used for
continuous casting carried out under conditions including a molten steel flow
rate of 0.04 (t /
(min=cm2)) or more, as measured with reference to a position of minimum cross-
sectional area in
a region around an upper end of the immersion nozzle where a transverse cross-
section of the inner
bore has a circular shape.
[0015]
In the present invention, the terms "width Wn" and "thickness Tn" of the inner
bore means,
respectively, a width (length in a long-side direction) and a thickness
(length in a short-side
direction) at positions of upper ends of the pair of discharge ports provided
in the short-side lateral
wall of the immersion nozzle.
[Effect of Invention]
[0016]
The flat immersion nozzle of the present invention can control a molten steel
flow to
gradually increase/reduce the flow rate thereof in a continuous manner,
without fixedly or
completely separating the direction of the molten steel flow over the range
from a central region
to a lateral region inside the immersion nozzle, thereby ensuring an
appropriate balance of molten
steel flows within the immersion nozzle. Thus, even in continuous casting
carried out under
casting conditions, particularly, a condition of a molten steel flow rate of
about 0.04 (t/ (min=cm2))
or more, as measured with reference to the position of minimum cross-sectional
area in a region
around an upper end of the immersion nozzle where a transverse cross-section
of the inner bore is
a circular shape, wherein the continuous casting tends to cause a situation
where a high-speed or
high-volume molten steel flow is generated on the side of each of the lateral
discharge ports, it
becomes possible to appropriately suppress the flow velocity or flow rate of
molten steel
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discharged from the discharge ports to stabilize the in-mold bath surface or
the like, i.e., reduce
the fluctuation of the in-mold bath surface or the like.
Then, since the fluctuation of the in-mold bath surface is suppressed, it
becomes possible to
reduce entrainment of a mold powder or the like into the mold, and promote
floating of in-molten
steel inclusions, thereby improving quality of slabs. Further, since an
excessive molten steel flow
toward lateral walls of the mold is suppressed, it becomes possible to reduce
a risk of the
occurrence of accident such as breakout.
BRIEF DESCRIPTION OF DRAWINGS
[0017]
FIG. 1 is a conceptual diagram showing an example of an immersion nozzle of
the present
invention (an immersion nozzle according to a first embodiment of the present
invention), which
is provided with two pairs of lateral protrusions, wherein FIG. 1(a) is a
schematic sectional view
taken along a vertical plane passing through the center of a short side of a
flat portion of the
immersion nozzle, and FIG. 1(b) is a schematic sectional view taken along a
vertical plane passing
through the center of a long side of the flat portion (taken along the line A-
A in FIG. 1(a)).
FIG. 2 is a conceptual diagram showing another example of the immersion nozzle
of the
present invention (an immersion nozzle according to a second embodiment of the
present
invention), which is provided with the two pairs of lateral protrusions (lower
lateral protrusions)
in FIG. 1 and two pairs of upper lateral protrusions each at a position on the
upper side of a
respective one of the two pairs of lower lateral protrusions, wherein FIG.
2(a) is a schematic
sectional view taken along a vertical plane passing through the center of a
short side of a flat
portion of the immersion nozzle, and FIG. 2(b) is a schematic sectional view
taken along a vertical
plane passing through the center of a long side of the flat portion (taken
along the line A-A in FIG.
2(a)).
FIG. 3 is a conceptual diagram showing yet another example of the immersion
nozzle of the
present invention (an immersion nozzle according to a third embodiment of the
present invention),
which is provided with the two pairs of lateral protrusions in FIG. 1 and two
central protrusions
each at a position between a respective one of the two pairs of lateral
protrusions, wherein FIG.
3(a) is a schematic sectional view taken along a vertical plane passing
through the center of a short
side of a flat portion of the immersion nozzle, and FIG. 3(b) is a schematic
sectional view taken
along a vertical plane passing through the center of a long side of the flat
portion (taken along the
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line A-A in FIG. 3(a)).
FIG. 4 is a conceptual diagram showing still another example of the immersion
nozzle of the
present invention (an immersion nozzle according to a fourth embodiment of the
present
invention), which is provided with the two pairs of lateral protrusions (lower
lateral protrusions)
and the two central protrusions in FIG. 3 and two pair of upper lateral
protrusions each at a position
on the upper side of a respective one of the pair of lower lateral
protrusions, wherein FIG. 4(a) is
a schematic sectional view taken along a vertical plane passing through the
center of a short side
of a flat portion of the immersion nozzle, and FIG. 4(b) is a schematic
sectional view taken along
a vertical plane passing through the center of a long side of the flat portion
(taken along the line
A-A in FIG. 4(a)).
FIG. 5 is a schematic sectional view taken along the vertical plane passing
through the center
of the short side in FIG. 3 or 4, enlargedly showing a region where the
central protrusion is
provided between the pair of lateral protrusions, wherein a central part of
the central protrusion is
convexed upwardly to form a linear reverse-V or chevron shape, and a central
part of a bottom
protrusion is convexed upwardly to form a linear reverse-V or chevron shape.
FIG. 6 is a schematic top view of an inner bore of the immersion nozzle in
FIG. 5, showing
a relationship between a set of opposed lateral protrusions and a set of
opposed central protrusions.
FIG. 7 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, wherein an
upper end of the central protrusion has a curved surface
FIG. 8 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, wherein the
upper end of the central protrusion has a flat surface
FIG. 9 is a schematic sectional view taken along a vertical plane passing
through the center
of a long side of a flat portion of a modification of the immersion nozzle in
FIG. 3 or 4, wherein
an upper surface of the lateral protrusion or the central protrusion is
configured to extend obliquely
downwardly in a direction toward the center of the inner bore.
FIG. 10 is a schematic top view showing a modification of the immersion nozzle
in FIG. 5,
where the protruding length of the upper surface of each of the lateral
protrusion and the central
protrusion is constant (an inner bore-side edge of each of the lateral
protrusion and the central
protrusion is parallel to an width-directionally extending wall of the flat
portion.
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FIG. 11 is a schematic top view showing a modification of the immersion nozzle
in FIG. 5,
where the protruding length of the upper surface of the central protrusion is
linearly reduced toward
a central region of the width-directionally extending wall.
FIG. 12 is a schematic top view showing a modification of the immersion nozzle
in FIG. 5,
where the protruding length of the upper surface of the central protrusion is
curvilinearly reduced
toward the central region of the width-directionally extending wall.
FIG. 13 is a schematic top view showing a modification of the immersion nozzle
in FIG. 5,
where the protruding length of the upper surfaces of the lateral protrusion
and the central protrusion
is linearly and continuously reduced toward the central region of the width-
directionally extending
wall.
FIG. 14 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, where the
bottom protrusion has a flat upper surface.
FIG. 15 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, where the
bottom protrusion has a curved upper surface.
FIG. 16 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, where the
bottom protrusion is formed such that an upper surface thereof has a convex
part on a central
region thereof, and the diameter thereof gradually increases toward the bottom
of the inner bore.
FIG. 17 is a schematic sectional view taken along a vertical plane passing
through the center
of a short side of a flat portion of a modification of the immersion nozzle in
FIG. 5, where the
bottom protrusion is also provided with a molten steel discharge port.
FIG. 18 is a conceptual diagram showing a mold and the fluctuation of an in-
mold bath
surface (molten steel surface), wherein FIG. 18(a) is a schematic top view of
the vicinity of a bath
surface (inner surface) of a mold, and FIG. 18(b) is a schematic sectional
view (one half in a
longitudinal direction) of the vicinity of the bath surface (inner surface) of
the mold, taken along
a vertical plane passing through the center of a short side of the mold.
FIG. 19 is a graph showing the fluctuation (maximum value, average of right
and left regions)
of the in-mold bath surface (molten steel surface) in Inventive Example 3 in
Table 1.
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DESCRIPTION OF EMBODIMENTS
[0018]
Molten steel flows toward width-directional ends can be formed to a certain
degree by
providing the flow dividing means as disclosed in the aforementioned Patent
Document 3.
However, such fixed and complete flow dividing is likely to generate molten
steel flows separated
in each region, i.e., in each small area, of an inner bore, leading to a
situation where the flow
direction and the flow velocity vary in each position of the inner bore.
Particularly, when the
flow direction or the flow rate changes due to molten steel flow rate control
or the like, significant
turbulence is likely to occur in a discharge flow from the inside of an
immersion nozzle into a
mold, a bath surface, etc.
[0019]
Therefore, in the present invention, for example, as shown in a first
embodiment thereof
illustrated in FIG. 1, a pair of lateral protrusions 1 are first provided on
one of opposed (long-side)
walls extending in a width direction of a flat portion of an immersion nozzle
10, axially
symmetrically with respect to a central axis of the width-directionally
extending wall (see FIG.
1(a), etc.; the pair of lateral protrusions will hereinafter be also referred
to simply as "axial
symmetrical lateral protrusions"),
Each of the pair of lateral protrusions 1 is configured such that an upper
surface thereof is
extends from a center-side end of the lateral protrusions 1 obliquely
downwardly in the width
direction of the flat portion, i.e., obliquely downwardly toward a respective
one of a pair of
discharge ports 4. Such an inclined surface makes it possible to gently change
the flow velocity
and flow pattern of molten steel from the inside of an inner bore 3 or the
discharge port 4, while
suppressing the occurrence of a vortex flow or the like, thereby optimizing
the flow velocity and
flow pattern of the molten steel.
[0020]
The pair of axial symmetrical lateral protrusions are also provided on the
other width-
directionally extending wall across the inner bore, in plane-symmetrical
relation with respect to a
thickness direction of the flat portion (see FIG. 1(b); each of two sets of
the lateral protrusions
arranged in plane-symmetrical relation will hereinafter be also referred to
simply as "plane-
symmetrical lateral protrusions"). In the present invention, for example, as
shown in FIG. 6, the
total length Ts in the thickness direction of the plane-symmetrical lateral
protrusions is set in the
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range of 0.18 to 0.90, when expressed as an index on the basis of 1 indicative
of the thickness Tn
of the inner bore at a position where the plane-symmetrical lateral
protrusions are provided. That
is, there is a space allowing molten steel to pass therethrough, between the
plane-symmetrical
lateral protrusions.
By providing the space having such a spacing, the flow direction and flow
velocity of molten
steel passing therethrough is gently controlled without fixedly and completely
separating a molten
steel flow in the inner bore. This makes it possible to mitigate a situation
where molten steel
flows toward the discharge ports with a clear boundary.
[0021]
Further, by adjusting the position, length, direction, etc., of each lateral
protrusion, it becomes
possible to avoid a molten steel flow concentrating on around the center or
lateral sides, and
diverge the molten steel flow into two directions toward width-directional
ends, i.e., the discharge
ports, and a direction toward the central region, while giving adequate
balance to the diverged
flows. In addition, differently from simple divergence, since respective
regions around the lateral
protrusions are spatially communicated with each other, the molten steel flow
will be diverged,
while forming a moderate boundary therebetween, and uniforming flow under
gentle mixing,
instead of a completely divided state.
[0022]
The position, length, direction, etc., of each lateral protrusion can be
appropriately adjusted,
as mentioned above. For example, in a second embodiment illustrated in FIG. 2,
in addition to
the two pairs of lateral protrusions (assigned with the reference code la in
FIG. 2; each of the
lateral protrusions la will hereinafter be referred to as "lower lateral
protrusion"), two pairs of
lateral protrusions (assigned with the reference code lb in FIG. 2; each of
the lateral protrusions
lb will hereinafter be referred to as "upper lateral protrusion") are
provided, respectively, above
the two pairs of lower lateral protrusions.
[0023]
Further, in the present invention, a protrusion (central protrusion) having a
protruding length
less than that of each of the axial symmetrical lateral protrusions may be
provided between the
axial symmetrical lateral protrusions, as in third and fourth embodiments
illustrated FIGS. 3 and
4. More specifically, in the third embodiment illustrated FIG. 3, the central
protrusion 1p is
provided between the axial symmetrical lateral protrusions 1 illustrated in
FIG. 1, and, in the fourth
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embodiment illustrated FIG. 4, the central protrusion 1p is provided between
the axial symmetrical
lower lateral protrusions 1 illustrated in FIG. 2.
[0024]
This structure brings out an effect opposite to that of a structure in which a
protrusion
(protrusion portion) having a protruding length greater than that of each of
the axial symmetrical
lateral protrusions is provided in the Patent Document 4 to allow the flow
rate of a molten steel
flow toward the lateral ends to become greater than that of a molten steel
flow toward between the
axial symmetrical lateral protrusions, i.e., an effect of increasing the ratio
of the flow rate of the
molten steel flow toward between the axial symmetrical lateral protrusions
(central region) / the
flow rate of the molten steel flow toward the lateral ends. In continuous
casting having a
relatively large molten steel flow rate (about 0.04 (t / (min=cm2)) or more),
it is effective to increase
the ratio of the flow rate of the molten steel flow toward between the axial
symmetrical lateral
protrusions (central region) / the flow rate of the molten steel flow toward
the lateral ends.
[0025]
The balance of the molten steel flows to the central region and the lateral
ends can be
optimized by adjusting the magnitude of the molten steel flow velocity (molten
steel flow rate per
unit tine or per unit sectional area), a drawing speed, the size and shape of
a mold, an immersion
depth, a nozzle structure such as the area of the discharge port, etc.
Specifically, it is possible to
employ a method of adjusting the width-directional or downward angle, width-
directional length,
protruding length, etc., of each lateral protrusion, a method of selecting the
presence or absence of
the central protrusion between the axial symmetric lateral protrusion, a
method of adjusting the
protruding length (height) of the central protrusion, a method of adjusting
the shape of an upper
end surface of the central protrusion, etc.
For example, with regard to the protruding length of the central protrusion,
as exemplified in
FIG. 6, the protruding length Tp/2 thereof is set to be less than the
protruding length Ts/2 of the
lateral protrusion 1, wherein a total protruding length Tp expressed as an
index on the basis of 1
indicative of the thickness of the inner bore at the position where the plane-
symmetrical or opposed
lateral protrusions are provided. In other words, Tp < Ts, wherein Tp/Tn <
0.40.
[0026]
Further, the upper end surface of the central protrusion may be formed in a
shape extending
horizontally in the width direction, as shown in FIG. 8, or a curved shape
having a top at a midpoint
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thereof, as shown in FIG. 5, or an upwardly protruding shape including a
bending point, as shown
in FIG. 7. These shapes make it possible to further change the flow velocity
and flow pattern of
molten steel, thereby optimizing the flow velocity and flow pattern.
[0027]
Further, an upper end surface of the lateral protrusion or the central
protrusion may be formed
in a shape extending from a top thereof at a boundary with the width-
directionally extending (long-
side) wall of the flat portion of the immersion nozzle, obliquely downwardly
in a direction toward
a thickness-directional center of the flat portion of the immersion nozzle,
i.e., a direction toward
the center of the inner bore (toward a space). This inclination makes it
possible to further change
the flow velocity and flow pattern of molten steel, thereby optimizing the
flow velocity and flow
pattern.
[0028]
Further, the protruding length of the upper end of the lateral protrusion or
the central
protrusion may be formed to be constant, as shown in FIG. 10, or may be formed
to become shorter
in a direction toward the center of the width-directionally extending (long-
side) wall of the flat
portion of the immersion nozzle, as shown in FIGS. 11 to 13. These
inclinations make it possible
to further change the flow velocity and flow pattern of molten steel, thereby
optimizing the flow
velocity and flow pattern.
[0029]
In the flat immersion nozzle, the discharge port in each of the short-side
lateral walls is
configured to have an opening which is long in the longitudinal direction.
Thus, the discharge
flow velocity is likely to be reduced in an upper region of the discharge
port, and, particularly in
the vicinity of an upper edge of the discharge port, a backflow phenomenon
that molten steel is
sucked into the immersion nozzle is often observed. Therefore, in the present
invention, for
example, as shown in FIGS. 2 and 4, in addition to the aforementioned axial
symmetrical and
plain-symmetrical lower protrusions la, one or more sets of axial symmetrical
and plain-
symmetrical protrusions (upper protrusions) lb may be provided thereabove. The
axial
symmetrical and plain-symmetrical upper protrusions lb may be formed in a
similar optimizing
configuration to that of the axial symmetrical and plain-symmetrical lower
protrusions la.
[0030]
The axial symmetrical and plain-symmetrical upper protrusions lb have a
function of
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CA 03121954 2021-06-02
suppressing, particularly, decrease of the flow velocity in the upper region
of the discharge port,
or turbulence of a molten steel flow such as the backflow in the vicinity of
the upper edge of the
discharge port, to complement a function of uniforming the distribution of
flow velocity in
respective longitudinal positions of the discharge port, and a function of
adjusting flow rate balance
toward an upper limit.
A central protrusion may be provided between the axial symmetrical protrusions
lb in a
similar manner to the central protrusion between the axial symmetrical
protrusions la.
[0031]
A bottom 5 of the immersion nozzle may be formed as a wall serving simply as a
partition
wall with respect to a mold without forming any discharge port around the
center thereof, as shown
in FIG. 14, or may be formed in a configuration comprising a protrusion
provided around the
center thereof to protrude upwardly, as shown in FIGS. 1 to 5, 7, 8, 15 and
16. Further, a
discharge port 6 may be additionally in the bottom 5, as shown in FIG. 17.
Such a protrusion of
the bottom is useful in changing the flow direction/pattern, flow velocity,
etc., when changing a
molten steel flow directed toward the ventral region to directions toward the
discharge ports.
[0032]
Next, the present invention will be described with reference to examples.
[0033]
[Example Al
Example A is a result of water model experiments, showing a relationship
between the ratio
Ts/Tn or Tp/Tn of the protrusion length Ts of the opposed lower lateral
protrusions la toward a
space of the inner bore of the immersion nozzle or the protrusion length Tp of
the opposed central
protrusions 1p toward the space of the space of the inner bore (the total
length of the plane-
symmetrical protrusions) to the thickness (length in the short-side direction)
Tn of the inner bore
of the immersion nozzle, and a degree of fluctuation of the in-mold bath
surface (in-mold uneven
flow index, in-mold bath surface fluctuation height), with respect to each
immersion nozzle
according to the second embodiment of the present invention illustrated in
FIG. 2, which is
provided with the two-stage axial symmetrical and plane-symmetrical lateral
protrusions la, lb
wherein the central protrusion 1p is not provided between each of the two
pairs of lower lateral
protrusions la, and according to the fourth embodiment of the present
invention illustrated in FIG.
4, which is provided with the two-stage axial symmetrical and plane-
symmetrical lateral
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CA 03121954 2021-06-02
protrusions la, lb are provided, wherein the central protrusion 1p is not
provided between each of
the two pairs of lower lateral protrusions la.
[0034]
Specifications of the immersion nozzles are as follows.
= Overall length : 1165
mm
= Molten steel inlet :(p,
86 mm
= Width of inner bore (Wn)
at upper edge of discharge port : 255 mm
= Thickness of inner
bore (Tn) at upper edge of discharge port : 34 mm
= Height of upper edge of discharge port from nozzle lower edge face :
146.5 mm
= Height of central
protrusion (from nozzle lower edge face ) : 155 mm:
= Thickness of wall of
immersion nozzle : about 25 mm
= Thickness of (central
top of) bottom of immersion nozzle : height 100 mm
= Upper lateral protrusion (lb) : Length in width direction of immersion
nozzle = 25 mm
(In each of right and left upper lateral protrusions)
Ratio Ts/Tn = 0.74
Inclination angle toward discharge port = 45 degrees
Posture of upper end surface in width direction and thickness
direction of immersion nozzle = horizontal
Distance between right and left upper lateral protrusions
= 100 mm
No center protrusion
= Lower lateral protrusion (la) : Length in width direction of immersion
nozzle = 40 mm
(In each of right and left lower lateral protrusions)
Ratio Ts/Tn = 0.1 to 1.0 (no space)
Inclination angle toward discharge port = 45 degrees
Posture of upper end surface in width direction and thickness
direction of immersion nozzle = horizontal
Distance between right and left left lateral protrusions
=60 mm
Ratio Tp/Tn of central protrusions =0 (no central protrusions)
to 0.7
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CA 03121954 2021-06-02
[0035]
Conditions of a mold and a fluid are as follows.
= Width of mold : 1650 mm
= Thickness of mold : 65
mm
(Central top: 185 mm)
= Immersion depth (from upper edge of discharge port to water level): 83 mm
= Fluid supply speed : 0.065 t (min=cm2)
* Value converted to molten steel
[0036]
Here, when an in-mold uneven flow index expressed on the basis of 1 indicative
of a state in
which there is no uneven flow satisfies the following relationship: 0.8 < in-
mold uneven flow index
< 1.2, and an in-mold bath surface fluctuation height (mm) is equal to or less
than 15 mm, an effect
capable of solving the problem addressed by the present invention was deemed
to be obtained.
This was used as evaluation criterion.
The in-mold uneven flow index means a result obtained by measuring a flow
velocity at a set
bath surface (at an under-water position of 30 mm from a set upper surface of
water) around each
of the right and left discharge ports of the immersion nozzle in a mold, in
the water model
experiment, and expressing the right and left flow velocities as a ratio
(absolute value), i.e., an
absolute value of the left flow velocity / the right flow velocity (or the
right flow velocity / the left
flow velocity), and the in-mold bath surface fluctuation height means a
maximum value of Sw in
FIG. 18.
[0037]
A result of evaluation is shown in Table 1.
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Date Recue/Date Received 2021-06-02
Comp Comp Comp Inve Comp Comp Inve Inve Inve Comp Inve Inve Inve Comp Comp
Comp Comp Comp
arative arative arative ntive arative arative ntive ntive ntive arative ntive
ntive ntive arative arative arative arative arative
Examp Examp Examp Exa Examp Examp Exa Exa Exa Examp Exa Exa Exa Examp Examp
Examp Examp Examp
le le le mple le le mple mple mple
le mple mple mple le le le le le
1 2 3 1 4 5 2 3 4 6 5 6 7
7 8 9 10 11
Ts/Tn 0.1 0.18 0.5 0.9
0.95 1
Tp/Tn 0 0.25 0.4 0 0.25 0.4 0 0.25 0.4 0.7 0 0.25 0.4 0.7
0 0.4 0 0.4
P
Magnitude
2
,
r.,
,
relationship Tp < Tp > Tp > Tp Tp > Tp > Tp Tp Tp Tp > Tp Tp Tp Tp < Tp < TP<
Tp < Tp < u,
N)
between Tp Ts Ts Ts < Ts Ts Ts < Ts < Ts < Ts Ts < Ts < Ts < Ts
Ts Ts Ts Ts Ts
,
,
,
and Ts
o
r.,
Maximum
bath surface
fluctuation 18 24 32 12 18 22 5 4 9 17 12 10 14 23 28 36 >>15 >>15
value Sw
(mm)
Evaluation* x x x o x x c o o x o c o
x x x x x
* o: Satisfying criterion (Good), x:
Failing to satisfy criterion (NG)
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CA 03121954 2021-06-02
[0038]
As seen in Table 1, when the ratio of Ts to Tn (Ts/Tn) regarding the lateral
protrusions is in
the range of 0.18 to 0.90, the in-mold uneven flow index and the in-mold bath
surface fluctuation
height can satisfy the criterion.
Further, in the case of the center protrusions are provided, when the
protruding length thereof
is less than that of the lateral protrusions, and the ratio of Tp to Tn
(Tp/Tn) is 0.4 or less, the in-
mold uneven flow index and the in-mold bath surface fluctuation height can
satisfy the criterion.
[0039]
[Example B]
Example B is a result of water model experiments, showing a degree of in-mole
bath surface
fluctuation when the upper end surface of each of the lower lateral protrusion
la and the central
protrusion 1p is formed in a planar shape extending obliquely downwardly
toward the center of
the inner bore, as shown in FIG. 9, in the forth embodiment of the present
invention illustrated in
FIG. 4.
[0040]
Here, the ratio Ts/Tn regarding the lower lateral protrusions and the ratio
Tp/Tn regarding the
central protrusions were set, respectively, to 0.74 and 0.18, and two cases
where the inclination
angle (0 in FIG. 9) of each of the lower lateral protrusion and the central
protrusion toward the
center of the inner bore was set to 0 degree (horizontal) and 45 degrees were
compared with each
other. The remaining conditions are the same as those of Example A.
[0041]
A result is shown in FIG. 19. The vertical axis of FIG. 19 represents an
average value of
maximum bath surface fluctuation values Sw (mm) around the right and left
discharge ports, in
both the cases where the inclination angle is 0 degree and 45 degrees.
[0042]
FIG. 19 shows that, in both the cases where the inclination angle is 0 degree
and 45 degrees,
the in-mold bath surface fluctuation height is significantly smaller than 15
mm as the criterion,
and, in the case where the inclination angle is 45 degrees, the in-mold bath
surface fluctuation
height is reduced to 2.0 (mm), which is about 1/2 of 3.75 (mm) in the case
where the inclination
angle is 0 degree.
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CA 03121954 2021-06-02
LIST OF REFERENCE SIGNS
[0043]
10: immersion nozzle
1: lateral protrusion
la: lower lateral protrusion
lb: upper lateral protrusion
1p: central protrusion
2: molten steel inlet
3: inner bore (molten steel flow passage)
4: discharge port (short side wall)
5: bottom
6: discharge port (bottom)
7: bath surface
20: mold
Wn: width of inner bore of immersion nozzle (length in long-side direction)
Wp: width between opposite ends of lateral protrusion
Wc: width of central protrusion
Tn: thickness of inner fore of immersion nozzle (length in short-side
direction)
Ts: protruding length of opposed lateral protrusions toward space (total
protruding length of
opposed ones)
Tp: protruding length of opposed central protrusions toward space (total
protruding length of
opposed ones)
ML: width of mold (long side)
Ms: thickness of mold (short side, lateral end)
Mc: thickness of mold (short side, central region)
Sw: fluctuation range of in-mold bath surface (size between top and bottom)
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Date Recue/Date Received 2021-06-02
