U.S. patent application number 17/424301 was filed with the patent office on 2022-05-05 for immersion nozzle.
This patent application is currently assigned to KROSAKIHARIMA CORPORATION. The applicant listed for this patent is KROSAKIHARIMA CORPORATION. Invention is credited to Shinichi FUKUNAGA, Hiroki FURUKAWA, Kazuhisa KATSUKI, Junya YANO.
Application Number | 20220134420 17/424301 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220134420 |
Kind Code |
A1 |
FUKUNAGA; Shinichi ; et
al. |
May 5, 2022 |
IMMERSION NOZZLE
Abstract
It is intended to provide a flat immersion nozzle capable of
stabilizing a molten steel discharge flow to stabilize an in-mold
bath surface, i.e., reduce the fluctuation of the in-mold bath
surface. Provided is an immersion nozzle having a flat portion
whose inner bore has a thickness and a width greater than the
thickness, wherein two lateral protrusions each protruding in a
thickness direction are provided on each of opposed walls of the
flat portion extending in a width direction. The lateral
protrusions are arranged at axial symmetrical positions with
respect to a longitudinal central axis of the width-directionally
extending walls, in pairs, such that each of them extends obliquely
downwardly in the width direction, wherein two pairs of the lateral
protrusions are arranged, respectively, on the opposed
width-directionally extending walls, in opposed relation.
Inventors: |
FUKUNAGA; Shinichi;
(Fukuoka, JP) ; KATSUKI; Kazuhisa; (Fukuoka,
JP) ; YANO; Junya; (Fukuoka, JP) ; FURUKAWA;
Hiroki; (Fukuoka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KROSAKIHARIMA CORPORATION |
Fukuoka |
|
JP |
|
|
Assignee: |
KROSAKIHARIMA CORPORATION
Fukuoka
JP
|
Appl. No.: |
17/424301 |
Filed: |
January 15, 2020 |
PCT Filed: |
January 15, 2020 |
PCT NO: |
PCT/JP2020/001078 |
371 Date: |
July 20, 2021 |
International
Class: |
B22D 41/50 20060101
B22D041/50 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2019 |
JP |
2019-007948 |
Claims
1. An immersion nozzle having a flat portion whose inner bore has a
thickness Tn and a width 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
comprising 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, each of the portions extending 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 claimed in claim 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 claimed in claim 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 claimed in claim 1, 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 claimed in claim 1, wherein one or each
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 claimed in claim 1, 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 claimed in claim 1, which comprises a
protrusion provided around a center of a bottom of the inner bore
to protrude upwardly.
8. The immersion nozzle as claimed in claim 1, which is used for
continuous casting carried out under conditions including a molten
steel flow rate of 0.04 (t/(mincm.sup.2)) 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.
Description
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 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] 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 [0010] Patent Document 2:
JP-A H11-047897 [0011] Patent Document 3: JP-A 2001-501132 [0012]
Patent Document 4: WO-A 2017/081934
SUMMARY OF INVENTION
Technical Problem
[0013] 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/(mincm.sup.2)) 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.
[0014] 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
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 1. An immersion nozzle having a flat portion whose inner
bore has a thickness Tn and a width 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 5. The immersion nozzle as described in any one of the
sections 1 to 4, wherein one or each 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.
[0026] 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.
[0027] 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.
[0028] 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/(mincm.sup.2)) 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.
[0029] 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
[0030] 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/(mincm.sup.2)) 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 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.
[0031] 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
[0032] 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)).
[0033] 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)).
[0034] 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 line A-A in FIG.
3(a)).
[0035] 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)).
[0036] 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.
[0037] 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.
[0038] 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
[0039] 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
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
DESCRIPTION OF EMBODIMENTS
[0051] 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.
[0052] 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"),
[0053] 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.
[0054] 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 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.
[0055] 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.
[0056] 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.
[0057] 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 1a in FIG. 2; each of the lateral protrusions 1a
will hereinafter be referred to as "lower lateral protrusion"), two
pairs of lateral protrusions (assigned with the reference code 1b
in FIG. 2; each of the lateral protrusions 1b will hereinafter be
referred to as "upper lateral protrusion") are provided,
respectively, above the two pairs of lower lateral protrusions.
[0058] 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 embodiment illustrated
FIG. 4, the central protrusion 1p is provided between the axial
symmetrical lower lateral protrusions 1 illustrated in FIG. 2.
[0059] 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/(mincm.sup.2)) 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.
[0060] 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.
[0061] 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.ltoreq.0.40.
[0062] 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
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.
[0063] 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.
[0064] 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.
[0065] 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 1a, one or more sets of axial
symmetrical and plain-symmetrical protrusions (upper protrusions)
1b may be provided thereabove. The axial symmetrical and
plain-symmetrical upper protrusions 1b may be formed in a similar
optimizing configuration to that of the axial symmetrical and
plain-symmetrical lower protrusions 1a.
[0066] The axial symmetrical and plain-symmetrical upper
protrusions 1b have a function of 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.
[0067] A central protrusion may be provided between the axial
symmetrical protrusions 1b in a similar manner to the central
protrusion between the axial symmetrical protrusions 1a.
[0068] 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.
[0069] Next, the present invention will be described with reference
to examples.
Example A
[0070] 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 1a 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 1a, 1b wherein the central protrusion 1p is not
provided between each of the two pairs of lower lateral protrusions
1a, 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 protrusions 1a, 1b are
provided, wherein the central protrusion 1p is not provided between
each of the two pairs of lower lateral protrusions 1a.
[0071] Specifications of the immersion nozzles are as follows.
[0072] Overall length: 1165 mm [0073] Molten steel inlet: .phi.86
mm [0074] Width of inner bore (Wn) at upper edge of discharge port:
255 mm [0075] Thickness of inner bore (Tn) at upper edge of
discharge port: 34 mm [0076] Height of upper edge of discharge port
from nozzle lower edge face: 146.5 mm [0077] Height of central
protrusion (from nozzle lower edge face): 155 mm: [0078] Thickness
of wall of immersion nozzle: about 25 mm [0079] Thickness of
(central top of) bottom of immersion nozzle: height 100 mm [0080]
Upper lateral protrusion (1b): Length in width direction of
immersion nozzle=25 mm (In each of right and left upper lateral
protrusions) [0081] Ratio Ts/Tn=0.74 [0082] Inclination angle
toward discharge port=45 degrees [0083] Posture of upper end
surface in width direction and thickness direction of immersion
nozzle=horizontal [0084] Distance between right and left upper
lateral protrusions=100 mm [0085] No center protrusion [0086] Lower
lateral protrusion (1a): Length in width direction of immersion
nozzle=40 mm (In each of right and left lower lateral protrusions)
[0087] Ratio Ts/Tn=0.1 to 1.0 (no space) [0088] Inclination angle
toward discharge port=45 degrees [0089] Posture of upper end
surface in width direction and thickness direction of immersion
nozzle=horizontal [0090] Distance between right and left left
lateral protrusions=60 mm [0091] Ratio Tp/Tn of central
protrusions=0 (no central protrusions) to 0.7
[0092] Conditions of a mold and a fluid are as follows. [0093]
Width of mold: 1650 mm [0094] Thickness of mold: 65 mm [0095]
(Central top: 185 mm) [0096] Immersion depth (from upper edge of
discharge port to water level): 83 mm [0097] Fluid supply speed:
0.065 t (mincm.sup.2) [0098] * Value converted to molten steel
[0099] 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.ltoreq.in-mold uneven
flow index.ltoreq.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.
[0100] 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.
[0101] A result of evaluation is shown in Table 1.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative
Inventive Comparative Comparative Example Example Example Example
Example Example 1 2 3 1 4 5 Ts/Tn 0.1 0.18 Tp/Tn 0 0.25 0.4 0 0.25
0.4 Magnitude relationship Tp < Ts Tp > Ts Tp > Ts Tp <
Ts Tp > Ts Tp > Ts between Tp and Ts Maximum bath surface 18
24 32 12 18 22 fluctuation value Sw (mm) Evaluation* x x x
.smallcircle. x x Inventive Inventive Inventive Comparative
Inventive Inventive Inventive Comparative Example Example Example
Example Example Example Example Example 2 3 4 6 5 6 7 7 Ts/Tn 0.5
0.9 Tp/Tn 0 0.25 0.4 0.7 0 0.25 0.4 0.7 Magnitude relationship Tp
< Ts Tp < Ts Tp < Ts Tp > Ts Tp < Ts Tp < T s Tp
< Ts Tp < Ts between Tp and Ts Maximum bath surface 5 4 9 17
12 10 14 23 fluctuation value Sw (mm) Evaluation* .smallcircle.
.smallcircle. .smallcircle. x .smallcircle. .smallcircle.
.smallcircle. x Comparative Comparative Comparative Comparative
Example Example Example Example 8 9 10 11 Ts/Tn 0.95 1 Tp/Tn 0 0.4
0 0.4 Magnitude relationship Tp < Ts TP < Ts Tp < Ts Tp
< Ts between Tp and Ts Maximum bath surface 28 36 >>15
>>15 fluctuation value Sw (mm) Evaluation* x x x x
*.smallcircle.: Satisfying criterion (Good), x: Failing to satisfy
criterion (NG)
[0102] 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.
[0103] 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.
Example B
[0104] 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 1a 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.
[0105] 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 (.theta. 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.
[0106] 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.
[0107] 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.
LIST OF REFERENCE SIGNS
[0108] 10: immersion nozzle [0109] 1: lateral protrusion [0110] 1a:
lower lateral protrusion [0111] 1b: upper lateral protrusion [0112]
1p: central protrusion [0113] 2: molten steel inlet [0114] 3: inner
bore (molten steel flow passage) [0115] 4: discharge port (short
side wall) [0116] 5: bottom [0117] 6: discharge port (bottom)
[0118] 7: bath surface [0119] 20: mold [0120] Wn: width of inner
bore of immersion nozzle (length in long-side direction) [0121] Wp:
width between opposite ends of lateral protrusion [0122] Wc: width
of central protrusion [0123] Tn: thickness of inner fore of
immersion nozzle (length in short-side direction) [0124] Ts:
protruding length of opposed lateral protrusions toward space
(total protruding length of opposed ones) [0125] Tp: protruding
length of opposed central protrusions toward space (total
protruding length of opposed ones) [0126] ML: width of mold (long
side) [0127] Ms: thickness of mold (short side, lateral end) [0128]
Mc: thickness of mold (short side, central region) [0129] Sw:
fluctuation range of in-mold bath surface (size between top and
bottom)
* * * * *