U.S. patent application number 10/586346 was filed with the patent office on 2007-07-12 for immersion nozzle for continuous casting and continuous casting method using the immersion nozzle.
Invention is credited to Yuichi Tsukaguchi.
Application Number | 20070158884 10/586346 |
Document ID | / |
Family ID | 34805453 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070158884 |
Kind Code |
A1 |
Tsukaguchi; Yuichi |
July 12, 2007 |
Immersion nozzle for continuous casting and continuous casting
method using the immersion nozzle
Abstract
An immersion nozzle for continuous casting which enables
improvement in quality of a slab surface and increase in the
efficiency of casting by suppressing the self-excited oscillation
of a flow in a mold without using a complicated mechanism such as a
swirl flow generating immersion nozzle is to be provided. A first
immersion nozzle for continuous casting is a nozzle comprising a
cylindrical body and a pair of outlet ports formed to face each
other in a side wall in the vicinity of a bottom part of the
cylindrical body, wherein a ridge-shaped projection extending
parallel with the discharge direction projected on a cross section
of the nozzle is formed on an inner surface of the bottom part,
which is formed in a waterfall basin-like recessed shape having a
maximum depth of 5 mm to 50 mm. A second immersion nozzle for
continuous casting is a nozzle comprising a cylindrical body and a
pair of outlet ports formed to face each other in a side wall in
the vicinity of a bottom part of the cylindrical body, wherein each
sectional area of the outlet ports vertical to a discharge
direction projected on a cross section or longitudinal section of
the nozzle is decreased toward an exit.
Inventors: |
Tsukaguchi; Yuichi; (Osaka,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
34805453 |
Appl. No.: |
10/586346 |
Filed: |
December 22, 2004 |
PCT Filed: |
December 22, 2004 |
PCT NO: |
PCT/JP04/19260 |
371 Date: |
July 14, 2006 |
Current U.S.
Class: |
266/236 |
Current CPC
Class: |
B22D 41/50 20130101 |
Class at
Publication: |
266/236 |
International
Class: |
C21C 5/42 20060101
C21C005/42 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2004 |
JP |
2004-15340 |
Claims
1. An immersion nozzle for continuous casting, which is a nozzle
comprising a cylindrical body and a pair of outlet ports formed to
face each other in a side wall in the vicinity of a bottom part of
the cylindrical body, wherein a ridge-shaped projection extending
parallel with a discharge direction projected on a cross section of
the nozzle is formed on an inner surface at the bottom part, which
is formed in a waterfall basin-like recessed shape having a maximum
depth of 5 mm to 50 mm.
2. An immersion nozzle for continuous casting according to claim 1,
wherein a maximum height of the ridge-shaped projection is as same
as the maximum depth of the waterfall basin-like recess or is in
the range of .+-.10 mm of the maximum depth of the waterfall
basin-like recess, in which the maximum height of the ridge-shaped
projection is 5 mm to 50 mm, and the ridge-shaped projection is in
one form selected from the group consisting of: a ridge-shaped
projection having a peak or a horizontal apex in the central part
or in the vicinity thereof on a cross section of the nozzle, in
which a ridgeline of the ridge-shaped projection extends from the
peak or the horizontal apex to each of two outlet ports by
decreasing a height of the projection so as to reach a position at
a side wall of a waterfall basin-like recessed shape portion lower
than a lower wall of the discharge hall, or in which a ridgeline of
the ridge-shaped projection extends from the peak or the horizontal
apex to each of two outlet ports by decreasing a height of the
projection so as to reach a bottom part and the projection itself
is terminated in the vicinity of an outlet port entrance of the
cross section of the nozzle; and a ridge-shaped projection having a
horizontal apex in the central part or in the vicinity thereof on a
cross section of the nozzle, in which the ridgeline of the
ridge-shaped projection extends from the horizontal apex to each of
two outlet ports by decreasing a height of the projection or by
descending vertically so as to reach the bottom part and the
ridge-shaped projection is only provided in the vicinity of the
central part on the cross section of the nozzle.
3. An immersion nozzle for continuous casting according to claim 1,
wherein the waterfall basin-like recess is in a form of an ellipse
or oval larger than an inner diameter of a nozzle body in the
discharge direction projected on the cross section of the
nozzle.
4. An immersion nozzle for continuous casting according to claim 2,
wherein the waterfall basin-like recess is in a form of an ellipse
or oval larger than an inner diameter of a nozzle body in the
discharge direction projected on the cross section.
5. An immersion nozzle for continuous casting, which is a nozzle
comprising a cylindrical body and a pair of outlet ports formed to
face each other in a side wall in the vicinity of a bottom part of
the cylindrical body, wherein each sectional area of the outlet
ports vertical to a discharge direction projected on a cross
section or longitudinal section of the nozzle is decreased toward
an exit.
6. An immersion nozzle for continuous casting according to claim 5,
wherein an average height of an outlet port exit is 0.5 to 0.9
times of an average width of the outlet port exit.
7. An immersion nozzle for continuous casting according to claim 5,
wherein an upper wall of the outlet port is in a circular form
having a curvature radius "R" of 30 mm to 150 mm and having a cross
section of expanding inner diameter from an inner wall of the body
toward the upper wall of the outlet port, and an angle of a lower
wall of the outlet port is in the range of 15.degree. upward to
45.degree. downward.
8. An immersion nozzle for continuous casting according to claim 6,
wherein an upper wall of an outlet port is in a circular form
having a curvature radius "R" of 30 mm to 150 mm and having a cross
section of expanding inner diameter an inner wall of the body
toward the upper wall of the outlet port, and an angle of a lower
wall of the outlet port is in the range of 15.degree. upward to
45.degree. downward.
9. A continuous casting method using the immersion nozzle for
continuous casting defined by claim 1, wherein an average descend
flow rate of a molten metal "U" of a portion immediately above an
outlet port of a body is 1.0 m/s to 2.5 m/s.
10. A continuous casting method using the immersion nozzle for
continuous casting defined by claim 5, wherein an average descend
flow rate of a molten metal "U" of a portion immediately above an
outlet port of a body is 1.0 m/s to 2.5 m/s.
Description
TECHNICAL FIELD
[0001] The present invention relates to an immersion nozzle for
continuous casting of a molten metal such as molten steel or the
like and a continuous casting method using the same.
BACKGROUND ART
[0002] In a continuous casting, such as a wide slab casting, which
provides a molten metal into a mold with the use of an immersion
nozzle having a pair of outlet ports facing each other, a fluid in
the mold causes fluctuation of a certain period, that is, the
self-excited oscillation, so that a flow velocity fluctuation or
bath level oscillation of the molten metal in the mold is likely to
occur. As a result, a slab surface causes trouble in quality due to
a non-metal inclusion, bubble, mold powder or the like caught in a
solidified shell in the mold. In the case that a flow rate of the
molten metal from the outlet ports is high such as a high speed
casting, these problems are noticeable. Thus, it has been necessary
to decrease a casting speed.
[0003] Conventionally, in order to control the flow in the mold,
for example, a method using an electromagnetic brake or
electromagnetic stirring by electromagnetic force disclosed in
International Publication No. WO99/15,291, a swirl flow generating
immersion nozzle mounting a swirl blade inside of the nozzle
disclosed in Japanese Patent Application Laid-Open (JP-A) No.
2002-239,690, an immersion nozzle having deeper depth of a
waterfall basin-like recess at the bottom disclosed in Japanese
Patent No. 3,027,645 (JP-A No. Hei. 5(1993)-169,212), an immersion
nozzle provided with a bump inside of the nozzle disclosed in
Japanese Patent No. 3,207,793 (JP-A No. Hei. 11(1999)-123,509) and
so on are invented.
[0004] However, since a design cost of the method using the
electromagnetic force is high, a merit which matches the high
investment often cannot be obtained. Also, since it is difficult to
sense a molten metal flow which is an object to be controlled, the
control is performed but the condition of the object to be
controlled often remains unclear. Hence, it is difficult to exhibit
sufficient effect technically. On the other hand, the effectiveness
of the technique of the swirl flow generating immersion nozzle as a
root measure which can stabilize the flow in the mold is confirmed.
However, in the case of casting a molten metal having a low
cleaning level containing a lot of non-metal inclusions, there is a
problem that casting of vast amount of molten metal cannot be
performed continuously since the non-metal inclusion is likely to
be attached to the swirl blade inside of the nozzle. Also, the
nozzle provided with the bump inside of the nozzle or the immersion
nozzle having deeper depth of the waterfall basin-like recess at
the bottom can stabilize the fluid inside of the immersion nozzle,
eventually, in the mold. However, since the effect is small,
further improvement is still required.
[0005] JP-A No. Hei. 6(1994)-218,508 discloses an immersion nozzle
which generates a turbulent flow in a molten steel flow of a molten
pool part by providing a conical projection or a truncated conical
projection on the molten pool part at a bottom part of an in-nozzle
of immersion so as to prevent segregation of a deposit.
[0006] A form of the conical projection or the truncated conical
projection at the molten pool part of the immersion nozzle
disclosed in JP-A No. Hei. 6(1994)-218,508 is central axial
symmetry such as a conical form or polyhedral cone. By such a form,
the segregation of the deposit can be prevented at the molten pool
part. However, there is no particular mention in JP-A No. Hei.
6(1994)-218,508 regarding stabilization of the flow in the
mold.
DISCLOSURE OF INVENTION
[0007] An object of the present invention is to provide an
immersion nozzle for continuous casting which enables improvement
in quality of a slab surface and a long-time and continuous
increase in the efficiency of casting by suppressing the
self-excited oscillation of a flow in a mold without using a
complicated mechanism such as a swirl flow generating immersion
nozzle.
[0008] In order to attain the above object, in a study done by the
inventor of the present invention to control the flow in the mold,
an appropriate form of the vicinity of outlet ports of the
immersion nozzle has been sought. As a result, effective means
thereof is found.
[0009] That is, a first immersion nozzle for continuous casting of
the present invention is a nozzle comprising a cylindrical body and
a pair of outlet ports formed to face each other in a side wall in
the vicinity of a bottom part of the cylindrical body, wherein a
ridge-shaped projection extending parallel with a discharge
direction projected on a cross section of the nozzle is formed on
an inner surface at the bottom part, which is formed in a waterfall
basin-like recessed shape having a maximum depth of 5 mm to 50
mm.
[0010] Also, a second immersion nozzle for continuous casting of
the present invention is an immersion nozzle for continuous
casting, which is a nozzle, wherein each sectional area of the
outlet ports vertical to a discharge direction projected on a cross
section or longitudinal section of the nozzle is decreased toward
an exit.
[0011] A continuous casting method provided by the present
invention is a continuous casting method using the immersion nozzle
for continuous casting of the present invention under the condition
that an average descend flow rate of a molten metal "U" of a
portion immediately above an outlet port of a body is 1.0 m/s to
2.5 m/s.
[0012] According to the immersion nozzle for continuous casting of
the present invention, the molten metal can be stably discharged
from the immersion nozzle without using a complex mechanism such as
the swirl flow generating immersion nozzle. Hence, the self-excited
oscillation of a flow in a mold is suppressed, as a result,
improvement in quality of a slab surface, and increase in the
efficiency of a long-time casting are possible. The immersion
nozzle for continuous casting and the continuous casting method
using the same of the present invention are particularly suitable
for the slab casting. A slab having less surface defect and inner
defect can be produced.
BRIEF DESCRIPTION OF DRAWINGS
[0013] In the accompanying drawings,
[0014] FIG. 1A is a schematic diagram showing two vortexes having
axes of rotation in discharge directions viewed from the front of
an outlet port;
[0015] FIG. 1B is a schematic diagram showing a vortex on the near
side among two vortexes having the axis of rotation in the
discharge direction in a section view of the direction which cuts
outlet ports longitudinally;
[0016] FIG. 2 is an external view (in the state that the outlet
port is shown in either side) from the side of outlet ports of an
immersion nozzle for continuous casting of the present
invention;
[0017] FIG. 3 is an external view showing the immersion nozzle for
continuous casting of the present invention viewed from the front
of an outlet port;
[0018] FIG. 4A is a cross section showing a first immersion nozzle
for continuous casting of the present invention cut at the higher
position than outlet ports;
[0019] FIG. 4B is an A-A section view of FIG. 4A (a section view in
the direction of crossing a ridge-shaped projection);
[0020] FIG. 4C is a B-B section view of FIG. 4A (a section view in
the direction of moving down through the outlet ports);
[0021] FIGS. 5A to 5J are various examples of ridge-shaped
projections provided on an inner surface of a bottom part of an
immersion nozzle for continuous casting of the present invention,
each of which shows a section view of the ridge-shaped projection
and the bottom part of the nozzle in the direction of moving down
through two outlet ports;
[0022] FIG. 6 is a section view showing an example of outlet ports
of the immersion nozzle for continuous casting of the present
invention in the direction of moving down through the outlet
ports;
[0023] FIG. 7 is a section view showing an example of outlet ports
of the immersion nozzle for continuous casting of the present
invention in the direction of moving down through the outlet
ports;
[0024] FIG. 8 is a section view showing an example of outlet ports
of the immersion nozzle for continuous casting of the present
invention in the direction of moving down through the outlet
ports;
[0025] FIG. 9 is a section view showing a constitution of an
immersion nozzle for continuous casting in Example 3;
[0026] FIG. 10 is a section view showing a constitution of an
immersion nozzle for continuous casting in Example 5; and
[0027] FIG. 11 is a section view showing a constitution of an
immersion nozzle for continuous casting in Comparative example
7.
[0028] The signs in each figure refer to the following: 1: a nozzle
body; 2: a bottom part of a nozzle; 3: a side wall of a nozzle; 3':
an inside wall of a nozzle; 4a, 4b: outlet ports; 4.sub.in: an
outlet port entrance; 4.sub.out: an outlet port exit; 5: a
ridge-shaped projection; 6a, 6b: upper walls of outlet ports; 7a,
7b: lower walls of outlet ports.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] The inventor of the present invention has repeated a full
scale water model experiment of an immersion nozzle comprising a
cylindrical body and a pair of outlet ports formed to face each
other in a side wall in the vicinity of a bottom part of the
cylindrical body by changing a form in the vicinity of outlet ports
in various way. As a result, it has been found that a flow which
descends inside of the immersion nozzle hits the bottom part of the
nozzle and discharges while forming two vortexes having axes of
rotation in an discharge direction as shown in FIGS. 1A and 1B; the
size of the vortexes formed at the bottom part fluctuates; and
sometimes only one vortex thereof is present depending on the
fluctuation of the size of the vortex formed at the bottom part.
Furthermore, it has been found that the fluctuation of the size of
the vortex formed at the bottom part disturbs a discharge flow from
the immersion nozzle, and eventually, the flow in the mold is
unstably fluctuated.
[0030] As a result of further study, the inventor of the present
invention has found out that by providing a ridge-shaped projection
extending parallel with the discharge direction projected on a
cross section of the nozzle on an inner surface at the bottom part,
stable vortexes heading to two outlet ports facing each other are
formed in two regions separated by the ridge-shaped projection
respectively when a downward flow which reaches the bottom part
changes to vortexes having axes of rotation in the discharge
direction, and thereby a discharge flow stabilizes.
[0031] Also, it has been found that an inner surface of the bottom
part with a waterfall basin-like recessed shape having a maximum
depth of 5 mm to 50 mm is effective in order to suppress the
self-excited oscillation of the flow in the mold. Herein, the
"waterfall basin-like recessed shape" means a recessed shape
surrounded by an inner wall lower than a lower wall of the outlet
port. By forming the bottom part of the immersion nozzle in the
waterfall basin-like recessed shape, a downward flow inside of the
nozzle bounces due to the waterfall basin-like recessed shape when
a downward flow distribution inside of the nozzle is uneven. As a
result, a reversing flow is formed. Since the reversing flow has an
effect to distribute a molten metal on the other side of the
downward flow inside of the nozzle, distribution of the discharge
flow is adjusted resulting in stabilization of the discharge
flow.
[0032] The immersion nozzle disclosed in JP-A No. Hei.
6(1994)-218,508 as aforementioned as a conventional technique has
the conical projection or the truncated conical projection on the
molten pool part at the bottom part of the in-nozzle of immersion.
The conical projection or the truncated conical projection
disclosed in JP-A No. Hei. 6(1994)-218,508 is in a form of central
axial symmetry such as a conical form or a polyhedral cone, that is
to say, in a form having a uniform form in any angle of 360.degree.
around an axis of an immersion nozzle being a center.
[0033] To the contrary, the ridge-shaped projection on the inner
surface of the bottom part of the nozzle of the present invention
present is in a thin form extending substantially parallel with the
discharge direction of the molten steel projected on the cross
section of the nozzle, that is to say, in a thin and long form in
the discharge direction. Therefore, the present invention and the
invention of JP-A No. Hei. 6(1994)-218,508 are basically different
in a projection form.
[0034] Furthermore, the present invention and the invention of JP-A
No. Hei. 6(1994)-218,508 are also different from the viewpoint of
the effect of the projection form. In the invention of JP-A No.
Hei. 6(1994)-218,508, the molten steel is uniformly dispersed in
the vicinity of the projection, and further, the molten steel flow
is stirred in the molten pool part at the bottom part so as to be a
turbulent flow. Thereby, segregation of a deposit can be
suppressed. However, the conical projection or the truncated
conical projection of the invention of JP-A No. Hei.
6(1994)-218,508, does not have the effect of forming a stable
vortex of the molten steel flow in the vicinity of outlet
ports.
[0035] To the contrary, in the present invention, vortexes of the
molten steel flow each of which has an axis of rotation in the
discharge direction are stably formed on both sides of the
ridge-shaped projection viewed from the front of the outlet port.
Thereby, the discharge flow and the molten steel flow in the mold
stabilize.
[0036] A first immersion nozzle for continuous casting of the
present invention is invented based on the above knowledge.
Examples of constitution of the first immersion nozzle for
continuous casting of the present invention are shown in FIGS. 2 to
4. FIG. 2 shows an external view (in the state that the outlet port
is shown in either side) from the side of outlet ports of the
immersion nozzle for continuous casting of the present invention.
FIG. 3 shows an external view showing the immersion nozzle for
continuous casting of the present invention viewed from the front
of an outlet port. Also, FIG. 4A shows a cross section of the first
immersion nozzle for continuous casting of the present invention
cut at higher position than the outlet ports. FIG. 4B shows an A-A
section view of FIG. 4A (a section view in the direction of
crossing a ridge-shaped projection). FIG. 4C shows a B-B section
view of FIG. 4A (a section view in the direction of moving down
through outlet ports).
[0037] Hereinafter, the present invention will be explained in
refer to FIG. 4. The first immersion nozzle of the present
invention comprises a cylindrical body 1 and a pair of outlet ports
4a and 4b formed to face each other in a side wall 3 in the
vicinity of a bottom part 2 of the cylindrical body 1, wherein a
ridge-shaped projection 5 extending parallel with a discharge
direction projected on a cross section of the nozzle is formed on
an inner surface 2 at the bottom part, which is formed in a
waterfall basin-like recessed shape having a maximum depth of 5 mm
to 50 mm.
[0038] The waterfall basin-like recessed shape exhibits its effect
when the maximum depth "H" is set in the range of 5 mm to 50 mm.
Herein, the maximum depth "H" means a distance between a position
where a lower wall of the outlet port and an inner wall of the
nozzle body cross and the deepest position of the waterfall
basin-like recess. If the maximum depth "H" is below 5 mm, the
effect by forming the waterfall basin-like recessed shape cannot be
obtained. On the other hand, if the maximum depth "H" exceeds 50
mm, a non-metal inclusion is attached and deposited to the
waterfall basin-like recess, and additionally, the immersion nozzle
becomes too long. Thus, handling may be deteriorated. It is more
preferable that the maximum depth "H" of the waterfall basin-like
recessed shape is 10 mm to 30 mm. As the form of the waterfall
basin-like recess, a portion not having the ridge-shaped projection
5 formed may be horizontal, inclined, or concave on a spherical
surface.
[0039] A form of the ridge-shaped projection 5 may not be
particularly limited if the ridge-shaped projection 5 is provided
on the inner surface of the bottom part of the nozzle parallel with
the discharge direction projected on the cross section and can form
a stable vortex formed at the bottom part. Examples of constitution
of the ridge-shaped projection 5 are shown in FIGS. 5A to 5J
(section views in the direction of moving down through two outlet
ports). For example, a height in the section view cut in the
direction of moving down through outlet ports (hereafter, it may be
solely referred as height), that is, a ridgeline may be or may not
be constant as shown in FIG. 5A. As examples of cases not having
constant height, specifically, there may be FIGS. 5B and 5C having
a peak in the central part of the cross section of the nozzle and
having ridgelines from the peak lowering toward two outlet ports,
FIGS. 5D in a trapezium, that is, having a horizontal apex in the
vicinity of the central part of the cross section of the nozzle and
having ridgelines from the apex lowering toward two outlet ports or
the like. In this case, the ridgeline may be a continuous incline
such as linear, radial or the like, or may be a non-continuous
incline such as trapezium or stepwise.
[0040] The ridgeline may reach a position lower than the lower wall
of the outlet port of the side wall of the waterfall basin-like
recessed shape portion (for example, FIGS. 5A to 5D), may reach the
bottom part in the vicinity of outlet ports of the cross section of
the nozzle so that the ridge-shaped projection 5 itself is
terminated (for example, FIGS. 5A to 5G), or may reach the bottom
part in the vicinity of the central part of the nozzle so that the
ridge-shaped projection 5 is provided only in the vicinity of the
central part of the cross section of the nozzle (for example, FIGS.
5H to 5J). In the case that the ridge-shaped projection 5
terminates in the vicinity of outlet ports of the cross section of
the nozzle or provided only in the vicinity of the central part of
the cross section of the nozzle, the ridgeline which descends
vertically from a horizontal apex or in the course of lowering
toward outlet ports and reaches the bottom part of the nozzle is
included (for example, FIGS. 5G and 5J). Herein, in the case of a
general immersion nozzle having an inner diameter of about 80 to 90
mm, "in the vicinity of outlet ports of the cross section of the
nozzle" means a range about 15 mm from an outlet port entrance of
the cross section of the nozzle. "In the vicinity of the central
part of the cross section of the nozzle" means a range from a
center to a radius of about 20 mm of the cross section of the
nozzle.
[0041] As a result of further study with the water model
experiment, the inventor of the present invention has found that if
the size of the ridge-shaped projection 5 is too large, there is a
flow condition similar to the case that the depth of the waterfall
basin-like recess is shallow so that the effect of forming the
waterfall basin-like recessed shape cannot be fully exhibited.
Then, further study has been done by the inventor of the present
invention. As a result, it has been found that the ridge-shaped
projection 5 preferably has the following form in order to exhibit
the effect of the waterfall basin-like recessed shape and the
ridge-shaped projection 5 sufficiently and in good balance.
[0042] That is, the preferable form of the ridge-shaped projection
5 is a form wherein the height in the central part or in the
vicinity thereof of the cross section of the nozzle is highest and
the height in the vicinity of an outlet port entrance of the cross
section of the nozzle is low. Since a flow rate of a downward flow
inside of the nozzle in the central part and in the vicinity
thereof of the cross section of the nozzle is high, by providing
the ridge-shaped projection having highest height in the central
part or in the vicinity thereof of the cross section of the nozzle
as mentioned above, a vortex formed at the bottom formed when the
downward flow inside of the nozzle hits the bottom part of the
nozzle can be formed more effectively and stably. Also, in the case
of a ridge-shaped projection having low height in the vicinity of
the outlet port entrance, a vortex formed at the bottom part is
likely to enter the bottom part of the waterfall basin-like recess.
Hence, the effect of bouncing the downward flow by the waterfall
basin-like recessed shape inside of the nozzle can be further
increased.
[0043] In the above-mentioned preferable form of the ridge-shaped
projection 5, the highest portion of the central part or in the
vicinity thereof of the cross section of the nozzle may be a peak
or a horizontal apex. Also, "low height in the vicinity of the
outlet port entrance" includes a case that the ridgeline of the
ridge-shaped projection 5 lowers from the peak of the ridge-shaped
projection 5 or from the peak of the ridge-shaped projection 5
toward two outlet ports and reaches the position lower than the
lower wall of the outlet port of the side wall of the waterfall
basin-like recessed shape portion, a case that the ridge-shaped
projection 5 itself is terminated in the vicinity of the outlet
port entrance of the cross section of the nozzle, a case that the
ridge-shaped projection 5 is solely provided in the vicinity of the
central part of the cross section of the nozzle or the like.
[0044] Specifically, as the preferable form of the ridge-shaped
projection 5, there may be, firstly, a case having a peak or a
horizontal apex in the central part or in the vicinity thereof of
the cross section of the nozzle, wherein the ridgeline reaches a
position lower than the lower wall of the outlet port of the side
wall of the waterfall basin-like recessed shape portion while
lowering toward two outlet ports from the peak or the horizontal
apex. Specifically, there may be cases shown in FIGS. 5B, 5C and
5D. Also, there may be a case having a peak or a horizontal apex in
the central part or in the vicinity thereof of the cross section of
the nozzle, wherein the ridgeline reaches the bottom part in the
vicinity of the outlet port entrance of the cross section of the
nozzle while lowering toward two outlet ports from the peak or the
horizontal apex so that the projection itself is terminated.
Specifically, there may be cases shown in FIGS. 5E, 5F and 5G.
Furthermore, there may be a case having a horizontal apex in the
central part or in the vicinity thereof of the cross section of the
nozzle, wherein the ridgeline reaches the bottom part by lowering
toward two outlet ports from the horizontal apex or descending
vertically so that the ridge-shaped projection is only provided in
the central part or in the vicinity thereof of the cross section of
the nozzle. Specifically, there may be cases shown in FIGS. 5H and
5J.
[0045] It is preferable that the ridge-shaped projection 5 has the
above-mentioned preferable form, and at the same time, the maximum
height of the ridge-shaped projection is as same as the maximum
depth of the waterfall basin-like recess "H" or in the range of
.+-.10 mm of the maximum depth of the waterfall basin-like recess
"H", and the maximum height of the ridge-shaped projection is 5 mm
to 50 mm. If the maximum height of the ridge-shaped projection is
less than 5 mm, the effect of the ridge-shaped projection cannot be
sufficiently obtained. On the other hand, if the maximum height of
the ridge-shaped projection exceeds 50 mm, it is difficult to
maintain the strength due to a structural problem and produce the
nozzle.
[0046] As for a thickness of the ridge-shaped projection 5 (the
cross section of the ridge-shaped projection 5), it is preferable
that an upper part of the projection may be about 5 mm to 15 mm
since if a thickness of the upper part of the projection is too
thin, durability of the projection may be insufficient. If the
thickness of the upper part of the projection is too thick, it has
an adverse effect to formation of vortexes. A lower part of the
projection may have the same thickness as the upper part of the
projection or may be in a form which increases thickness from the
upper part toward the lower position so as to broaden toward the
end.
[0047] The ridge-shaped projection 5 is generally disposed in the
central part on the inner surface of the bottom part of the nozzle
so as to divide the inner surface of the bottom part of the nozzle
equally, that is, a position symmetric with respect to a central
axis of the nozzle body. However, it is not necessary that the
ridge-shaped projection 5 is disposed in the central part of the
inner surface of the bottom part of the nozzle. In the case that
the downward flow inside of the nozzle is to descend unevenly due
to a sliding gate or the like disposed at an upper part of the
nozzle, the ridge-shaped projection 5 may be disposed with a shift
from the central part on the inner surface of the bottom part of
the nozzle according to the unevenness of the downward flow inside
of the nozzle.
[0048] By providing the ridge-shaped projection, the flow becomes
similar to the condition that the height of the waterfall
basin-like recess is shallow. Thus, there may be a case that the
effect of the waterfall basin-like recess cannot be sufficiently
obtained. The inventor of the present invention has found out that
if the waterfall basin-like recessed shape at the bottom part is
expanded to the discharge direction projected on the cross section
and is in a form of an ellipse or oval having larger size than the
inner diameter of the nozzle body in the first immersion nozzle for
continuous casting of the present invention, the above problem can
be solved and the effect of the waterfall basin-like recessed shape
can be increased. The stable vortexes formed at the bottom part by
the ridge-shaped projection are strong vortexes with axes of
rotation in the discharge direction and are progressive flows in
the discharge direction. Such a flow is in the similar state as a
flow having high viscosity and is not likely to enter the bottom of
a small concave. Hence, in order that the flow can enter the
waterfall basin-like recess and be bounced, it is necessary to
enlarge a sectional area of the waterfall basin-like recess so that
the flow easily enters the bottom of the waterfall basin-like
recess. Therefore, in the immersion nozzle of the present
invention, in which stable and strong vortexes can be formed by the
ridge-shaped projection, it is assumed that the effect of the
waterfall basin-like recess can be further improved by the
waterfall basin-like recess in a form of the ellipse or oval having
larger size than the inner diameter of the nozzle body as mentioned
above. Also, such an effect of the waterfall basin-like recess can
be obtained when the inner diameter of the nozzle body itself is in
a form of the ellipse or oval expanded in the discharge
direction.
[0049] Furthermore, the inventor of the present invention has found
out that it is important that the discharge flow is discharged
without being detached (separated) from a side wall or an upper and
lower wall of the outlet port in order to stabilize the discharge
flow, other than the effect by the ridge-shaped projection and the
waterfall basin-like recess. This is because fluctuation itself of
the discharge flow running distantly and along the wall makes the
flow unstable, and additionally, because the phenomenon, wherein
the amount of the non-metal inclusion contained in the molten metal
which attaches to the outlet port increases in the immersion nozzle
for continuous casting due to such a disturbance of the flow, and
the form of the outlet port changes in accordance with proceeding
of casting so as to destabilize the discharge flow, is caused.
[0050] A second immersion nozzle for continuous casting of the
present invention has been invented based on the above knowledge.
The second immersion nozzle for continuous casting of the present
invention is a nozzle comprising a cylindrical body and a pair of
outlet ports formed to face each other in a side wall in the
vicinity of a bottom part of the cylindrical body, wherein each
sectional area of the outlet ports vertical to a discharge
direction projected on a cross section or longitudinal section of
the nozzle is decreased from an entrance toward an exit.
[0051] Examples of constitution of the first immersion nozzle for
continuous casting of the present invention are shown in FIGS. 6 to
8. FIGS. 6 to 8 are section views in the direction of moving down
through the outlet ports of the second immersion nozzle for
continuous casting of the present invention.
[0052] Hereinafter, the present invention will be explained in
refer to FIG. 6. The second immersion nozzle of the present
invention comprises a cylindrical body 1 and a pair of outlet ports
4a and 4b formed to face each other in a side wall 3 in the
vicinity of a bottom part 2 of the cylindrical body 1, wherein each
sectional area of the outlet ports vertical to a discharge
direction projected on a cross section or longitudinal section of
the nozzle is decreased from an outlet port entrance 4 in toward an
exit 4.sub.out.
[0053] By decreasing each sectional area of the outlet ports
vertical to the discharge direction projected on the cross section
or longitudinal section of the nozzle from the outlet port entrance
4.sub.in toward the outlet port exit 4.sub.out, separation of the
discharge flow from an outlet port wall can be prevented, and there
by the discharge flow can be stabilized. Furthermore, since
stagnation of the discharge flow in the vicinity of the outlet
ports is less likely to occur, attaching of the non-metal inclusion
contained in the molten metal or the like to the outlet ports can
be suppressed and generation of blockage of the outlet ports and
defect of a slab due to peeling of the deposit can be prevented.
Thus, stable operation and quality of slab can be secured even by
casing for a long time.
[0054] The sectional area of the outlet port may be gradually
narrowed or steeply narrowed in the vicinity of the exit. However,
it is not preferable if the degree of narrowing is too steep from
the viewpoint of stably discharging the discharge flow and
preventing attachment of the non-metal inclusion. Also, the
sectional area of the outlet port may be decreased in the direction
of height or width, or in both directions of height and width.
[0055] The downward flow inside of the nozzle changes direction at
the bottom part of the nozzle so as to have a rate vector in the
horizontal direction, and enters the outlet port obliquely
downward. Due to the characteristic of the flow in the vicinity of
the outlet port, the discharge flow is to be discharged along the
lower wall of the outlet port. Therefore, if the height of the
outlet port is too high, the discharge flow separates from the
upper wall of the outlet port. As measures to prevent separation of
the discharge flow, it is preferable that the second immersion
nozzle for continuous casting of the present invention has outlet
ports having horizontally long width longer than the height of the
outlet ports. As the horizontally long form, specifically, it is
preferable that an average height of the outlet port exit is 0.5 to
0.9 times of an average width of the outlet port exit. It is not
preferable if the average height of the outlet port exit is less
than 0.5 times of the average width of the outlet port exit, since
the area of the outlet port is not enough. If the average height of
the outlet port exit exceeds 0.9 times of the average width of the
outlet port exit, the effect of the horizontally long outlet port
cannot be obtained. The form of the outlet port may not be
particularly limited if it is in a horizontally long form as
mentioned above, for instance, a polygon other than a quadrangle,
an ellipse, an approximate quadrangle having "R" at the corners or
the like.
[0056] Furthermore, as shown in FIGS. 7 and 8, it is preferable
that each upper wall of the outlet ports 6a or 6b of the second
immersion nozzle for continuous casting of the present invention is
in a circular form having a curvature radius of R 30 mm to R 150 mm
and has a cross section of expanding inner diameter from the inner
wall of the nozzle body 3' toward the upper wall of the outlet
port, and an angle of each lower wall of the outlet ports 7a or 7b
may be in the range of 15.degree. upward to 45.degree. downward,
within the range for the purpose of decreasing the sectional area
of the outlet port toward the exit thereof. FIG. 7 shows a case
that the angles of the lower walls of the outlet ports 7a and 7b
are 15.degree. upward. FIG. 8 shows a case that the angles of the
lower walls of the outlet ports 7a and 7b are 450.degree. downward.
By forming the upper wall of the outlet port in such a form, the
flow obliquely downward in the vicinity of the outlet port
discharges along the upper wall of the outlet port. Thus,
separation of the discharge flow from the upper wall of the outlet
port can be effectively prevented.
[0057] If the curvature radius "R" of the upper wall of the outlet
port is smaller than 30 mm, separation of the discharge flow is
more likely to occur since decrease of the sectional area of the
outlet port is not sufficient and the discharge flow cannot be
discharged along the upper wall due to a steep curvature. Also, if
the curvature radius "R" of the upper wall of the outlet port is
larger than 150 mm, the thickness of the nozzle at the upper wall
of the outlet port may decrease so as to decline strength. On the
other hand, if the angle of the lower wall of the outlet port is
larger upward than 15.degree. upward, the flow which goes up from
the outlet port becomes strong so as to cause fluctuations of the
bath level in the mold. Furthermore, if the angle of the lower wall
of the outlet port is larger downward than 45.degree. downward, the
discharge flow deeply penetrates to the mold so that the supply of
the molten metal to the bath level of the mold may become
insufficient. Thereby, the supply of heat to the bath level may be
insufficient so as to decrease temperature of the bath level, thus,
a problem that removing of the non-metal inclusion and bubble by
floatation is inhibited may be raised. Furthermore, since it
becomes difficult to decrease the sectional area of the outlet port
toward the exit, an original purpose, which is to prevent
separation of the discharge flow from the outlet port wall, cannot
be attained.
[0058] In the case of an immersion nozzle for continuous casting of
the present invention using each means employed for the first
immersion nozzle for continuous casting and the second immersion
nozzle for continuous casting of the present invention in
combination, the flow of the discharge flow further stabilizes and
the self-excited oscillation of the flow in the mold can be
effectively suppressed due to the multiplier effect.
[0059] As aforementioned, by using the immersion nozzle for
continuous casting provided by the present invention, the discharge
flow from the immersion nozzle for continuous casting can be
stabilized. Thus, the self-excited oscillation of the flow in the
mold can be suppressed. As a result, a non-metal inclusion, bubble,
mold powder or the like caught in a solidified shell can be
prevented. Therefore, improvement in quality of a slab surface can
be attained. Also, due to the effect of stabilized discharge flow,
increase in the efficiency of casting can be attained.
Specifically, a stable flow in a mold can be formed for a long time
even in the case of a high through put in which a discharge flow
amount from the immersion nozzle is about 4.5 to 7.0 t/min.
[0060] Casting using the immersion nozzle for continuous casting of
the present invention can form a stable discharge flow in the
above-mentioned increase in the efficiency of casting. However, if
further improvement in quality of slab is required, it is
preferable that an average descend flow rate "U" of the molten
metal inside of the nozzle of a portion immediately above the
outlet port of the body is in the range of 1.0 m/s to 2.5 m/s.
Herein, "the portion immediately above the outlet port" means a
portion where the upper wall 6 of the outlet port and the inner
wall 3' of the nozzle body cross. By having the average descend
flow rate "U" of the molten metal inside of the nozzle within the
above range, a particularly high effect of stabilization of the
discharge flow, that is, an effect of stabilization of the flow in
the mold can be obtained. If the average descend flow rate "U" of
the molten metal inside of the nozzle of the portion immediately
above the outlet port is below 1.0 m/s, the molten metal flow
amount becomes small with respect to the inner diameter of the
nozzle, thus, the descend flow inside of the nozzle becomes
unstable. Due to the effect thereof, the discharge flow also
becomes unstable. Therefore, under the casting condition of small
amount of the molten metal flow amount, it is necessary to secure
the average descend flow rate "U" of the molten metal inside of the
nozzle of 1.0 m/s or more by having a smaller inner diameter of the
nozzle If the average descend flow rate "U" of the molten metal
inside of the nozzle of the portion immediately above the outlet
port exceeds 2.5 m/s, the descend flow rate inside of the nozzle
becomes too high, and eventually, the discharge flow rate becomes
too high. Thereby, problems such as fluctuation of bath level and
remelting of a solidified shell in the mold may be raised.
[0061] The average descend flow rate "U" of the molten metal inside
of the nozzle can be calculated by "(an average descend flow amount
of a molten metal inside of a nozzle)/(a sectional area of a nozzle
body)". Herein, "the average descend flow amount of the molten
metal inside of the nozzle" is a value calculated by "(a casting
speed of a slab).times.(a sectional area of a slab).times.(gravity
of a slab)/(gravity of a molten steel)".
[0062] An inner diameter of the portion immediately above the
outlet port is used for calculating the average descend flow rate
"U" of the molten metal inside of the nozzle if the inner diameter
of the nozzle body is diverse between an upper part of the nozzle
and the portion immediately above the outlet port.
EXAMPLES
[0063] Hereinafter, the effect of the present invention will be
explained with comparison between Examples and Comparative examples
of the present invention.
[0064] Immersion nozzles for continuous casting comprising a
cylindrical body and a pair of outlet ports formed to face each
other in a side wall in the vicinity of a bottom part of the
cylindrical body used in Examples 1 to 6 and Comparative examples 7
to 9 are shown in Table 1. TABLE-US-00001 TABLE 1 Example 1 2 3 4 5
Inner surface form at bottam part of nozzle Waterfall Flat form
Waterfall Waterfall Waterfall basin- basin- basin- basin- like form
like form like form like form Maximum depth of waterfall basin-like
15 0 15 15 15 recess (mm) Plain form of waterfall basin-like recess
Ellipse -- Round Ellipse Ellipse 80 .times. 90 .phi.80 (mm) 90
.times. 110 (mm) 90 .times. 110 (mm) (mm) Maximum height of
ridge-shaped projection 15 0 (No 18 8 15 at bottom part (mm)
projection) Side form of ridge-shaped projection at Base: 90 mm --
Base: 50 mm Base: 110 mm Base: 110 mm bottam part Isosceles Upper
base: Height: 8 mm Isosceles triangle 20 mm Rectangle triangle
Trapezium Thickness of ridge-shaped projection at 10 -- 10 Base: 12
10 bottom part (mm) Upper end: 7 Average height of outlet port exit
(mm) 78 64 67 64 64 Average width of outlet port exit (mm) 78 89 79
89 89 Form of upper wall of outlet port 25.degree. R60 mm R120 mm
R60 mm R60 mm downward Form of lower wall of outlet port 25.degree.
15.degree. 5.degree. 15.degree. 25.degree. downward downward upward
downward downward Outer diameter of nozzle body (mm) .phi.155
.phi.160 .phi.155 .phi.155 .phi.155 Inner diameter of nozzle body
(mm) .phi.80 .phi.90 .phi.80 .phi.90 .phi.90 Descend flow amount
inside of nozzle (m.sup.3/s) 0.00885 0.00974 0.01062 0.01036
0.01166 Descend flow rate inside of nozzle (m/s) 1.76 1.53 2.11
1.63 1.83 Campatible claims 1, 2, 3, 7 4, 5, 6, 7 1, 2, 4, 5, 6, 7
1, 3, 4, 5, 6, 7 1, 2, 3, 4, 5, 6, 7 Flow stability index of mold B
B A A A+ Example Comparative example 6 7 8 9 Inner surface form at
bottam part of nozzle Waterfall Flat form Waterfall Waterfall
basin- basin- basin- like form like form like form Maximum depth of
waterfall basin-like 35 0 15 30 recess (mm) Plain form of waterfall
basin-like recess Ellipse -- Round Round 80 .times. 90 (mm) .phi.90
(mm) .phi.90 (mm) Maximum height of ridge-shaped projection 30 0
(No 0 (No 0 (No at bottom part (mm) projection) projection)
projection) Side form of ridge-shaped projection at Base: 60 mm --
-- -- bottam part Isosceles triangle Thickness of ridge-shaped
projection at Base: 15 -- -- -- bottom part (mm) Upper end: 8
Average height of outlet port exit (mm) 43 79 60 88 Average width
of outlet port exit (mm) 70 86 72 58 Form of upper wall of outlet
port R90 mm 15.degree. R40 mm 10.degree. downward upward Form of
lower wall of outlet port 10.degree. 15.degree. 45.degree.
10.degree. downward downward downward upward Outer diameter of
nozzle body (mm) .phi.150 .phi.155 .phi.160 .phi.160 Inner diameter
of nozzle body (mm) .phi.80 .phi.80 .phi.90 .phi.90 Descend flow
amount inside of nozzle (m.sup.3/s) 0.00731 0.01151 0.01152 0.00540
Descend flow rate inside of nozzle (m/s) 1.45 2.60 1.81 0.85
Campatible claims 1, 2, 3, 4, 5, 6, 7 -- -- -- Flow stability index
of mold A+ F C F
[0065] An average height and average width of an outlet port exit
when a corner of an outlet port exit is in an "R" form can be
obtained as follows. That is, a tetragonum not having an "R" form
at a corner and having the same area as an outlet port, a corner of
which is in an "R" form, is obtained by reducing both height and
width of the outlet port. The height and the width of thus obtained
tetragonum are referred as an average height and a width of an
outlet port exit. For example, in FIG. 9 showing Example 3, a form
of an outlet port exit is an approximate tetragonum having a height
of 68 mm and a width of 80 mm and having "R" in a corner. If R 10
mm form of the corner is taken into account, the average height of
the outlet port exit and the average width of the outlet port exit
are respectively reduced by about 1 mm with respect to the height
of the outlet port exit and the width of the outlet port exit. That
is, the average height of the outlet port exit is 67 mm (decimal
places are rounded off) and the average width of the outlet port
exit is 79 mm (decimal places are rounded off). Similar methods of
estimation of the average height of the outlet port exit and the
average width of the outlet port exit are used for other Examples
and Comparative examples.
(Evaluation method)
[0066] In Examples and Comparative examples shown in Table 1, a
flow stability in a mold was evaluated using a full scale water
model experiment, which is a simulative slab continuous casting
device having a mold thickness of 235 to 270 mm, a mold width of
1,500 to 2300 mm, by changing a size and a form of a bottom part
and outlet ports of an immersion nozzle for continuous casting and
a molten metal descend flow rate "U" inside of the nozzle. A
constitution of an immersion nozzle for continuous casting used for
each Example or Comparative example is shown in Table 1 as well as
FIGS. 9 to 11 accordingly.
[0067] Herein, "the flow stability in a mold" is an evaluation of a
value sorted by level, wherein the value was obtained by a standard
deviation of measured data divided by an average value, which are
flow rates in a direction of a mold width at 1/2 thickness and 1/4
width inside of the mold and 50 mm under water surface measured at
two places at each side of the direction of the mold width for 15
minutes each in the full scale water model experiment. In the
measurement, a propeller flow meter was used and the flow rate was
measured by a pitch of 0.5 second. Since an instantaneous value
data measured by a pitch of 0.5 seconds may significantly fluctuate
due to the effect of a minute swirl, an average value for every 2.5
minutes of the data was used for the calculation of the standard
deviation as a minimum unit.
[0068] Criteria of evaluation of the flow stability in a mold were
"A+" (particularly excellent) for a value calculated by "standard
deviation/average value" of less than 0.4; "A" (excellent) for a
value calculated by "standard deviation/average value" of 0.4 or
more and less than 0.5; "B" (good) for a value calculated by
"standard deviation/average value" of 0.5 or more and less than
0.6; "C" (passable) for a value calculated by "standard
deviation/average value" of 0.6 or more and less than 0.7; and "F"
(failed) for a value calculated by "standard deviation/average
value" of 0.7 or more. From the experience of the inventor of the
present invention, if the flow stability in the mold is "A+", "A"
or "B", the flow in the mold is stable, oscillation of bath level
and fluctuation of level are small and surface quality of a slab
becomes excellent when the immersion nozzle is mounted in an actual
device. Also, if the flow stability in the mold is "C" or "F", the
flow in the mold is more likely to be unstable in the actual
device, the oscillation of bath level in the mold and the level
fluctuation tend to become large and surface quality of the slab
tends to deteriorate.
(Evaluation result)
[0069] Example 1 is an immersion nozzle having characteristics of
the first immersion nozzle for continuous casting of the present
invention, wherein both waterfall basin-like recessed shape and
ridge-shaped projection are formed in preferable shapes. That is,
the waterfall basin-like recess formed on an inner surface of a
bottom part of the nozzle is in a large ellipse form in a discharge
direction projected on a cross section. A sectional view (side
surface form) in a direction moving down through outlet ports of
the ridge-shaped projection is in an isosceles triangle form having
a base of the same length as a major axis of the ellipse and a
maximum height of the same length as a depth of the waterfall
basin-like recess. The ridgeline reaches a bottom part of the
nozzle at a position where the bottom part of the nozzle and the
side wall of the nozzle cross. Therefore, swirls having axes of
rotation in the discharge direction were stably formed at the
bottom part of the nozzle. Furthermore, an excellent flow stability
in the mold was obtained since the immersion nozzle was used under
a preferable condition of the descend flow rate inside of the
nozzle.
[0070] Example 2 is an immersion nozzle having characteristics of
the second immersion nozzle for continuous casting of the present
invention. In the immersion nozzle, sectional areas of the outlet
ports vertical to the discharge direction projected on a cross
section or longitudinal section of the nozzle are gradually
decreased according to the relationship between an "R" form of an
upper wall of an outlet port and an angle of a lower wall. Also,
since the outlet ports were in a horizontally long form, a
discharge flow was less likely to be separated from the upper wall
of the outlet port. Furthermore, since the upper walls of the
outlet ports were in a circular form and the angles of the lower
walls was within a preferable range, a discharge flow outflowed
without stagnation and separation of the discharge flow from the
upper wall of the outlet port was effectively prevented. Further,
since the immersion nozzle was used under a preferable descend flow
rate inside of the nozzle, excellent flow stability in the mold was
obtained.
[0071] Example 3 is an immersion nozzle having both characteristics
of the first and the second immersion nozzles for continuous
casting of the present invention. Even though a flow stabilization
effect at a bottom part of the nozzle by a waterfall basin-like
recessed shape was weak since the waterfall basin-like recessed
shape was not extended to a discharge direction projected on a
cross section as shown in FIG. 9, a ridge-shaped projection and
outlet ports are in preferable forms and the nozzle was used under
a preferable condition of descend flow rate inside of the nozzle.
Thereby, a stable discharge flow was formed. Particularly, due to a
multiplier effect of having characteristics of the first and the
second immersion nozzles at the same time, flow stability in the
mold superior to that of Examples 1 and 2 was obtained.
[0072] Example 4 is an immersion nozzle having both characteristics
of the first and the second immersion nozzles for continuous
casting of the present invention. Since a ridge-shaped projection
having the same height was provided from the central part on a
cross section of the nozzle to a side wall of a waterfall
basin-like recessed shape portion, a vortex having an axis of
rotation in a discharge direction generated by the ridge-shaped
projection was less likely to enter the waterfall basin-like bottom
part, and a flow stabilization effect by the waterfall basin-like
recess tended to decrease slightly. However, since forms of the
ridge-shaped projection, the waterfall basin-like recess and outlet
ports were in preferable shapes and the nozzle was used under a
preferable condition of a descend flow rate inside of the nozzle, a
stable discharge flow was formed. Particularly, due to a multiplier
effect of having characteristics of the first and the second
immersion nozzles at the same time, flow stability in the mold
superior to that of Examples 1 and 2 was obtained.
[0073] Examples 5 and 6 are immersion nozzles having both
characteristics of the first and the second immersion nozzles for
continuous casting of the present invention. Since a ridge-shaped
projection, a waterfall basin-like recess and outlet ports were in
preferable shapes and the nozzle was used under a preferable
condition of a descend flow rate inside of the nozzle, a
particularly stable discharge flow was formed. Hence, due to each
technical element of the ridge-shaped projection, the waterfall
basin-like recess and the outlet ports, particularly, due to a
multiplier effect of having characteristics of the first and the
second immersion nozzles at the same time, flow stability in the
mold was the best of all. The immersion nozzle of Example 10 is
shown in FIG. 10.
[0074] On the other hand, Comparative examples 7 to 9 are not
compatible with the present invention.
[0075] As shown in FIG. 11, both waterfall basin-like recess and
ridge-shaped projection were not provided on an inner surface at a
bottom part of the nozzle in Comparative example 7. Furthermore,
sectional areas of outlet ports vertical to a discharge direction
projected on a cross section or longitudinal section of the nozzle
were constant. Hence, a discharge flow was not stabilized.
Additionally, since a descend flow rate inside of the nozzle was
high, a flow stability in a mold was "F".
[0076] An inner surface of a bottom part of an immersion nozzle of
Comparative example 8 was formed in a waterfall basin-like recessed
shape. However, since a ridge-shaped projection was not provided, a
sufficiently stable vortex was not formed at the bottom part. Also,
upper walls of outlet ports were in a circular form of R 40 mm, a
wall inside of a body to the upper walls of the outlet ports was in
a tube expansion form on a cross section, and angles of lower walls
of the outlet ports were in a form downward to 45.degree.. However,
the combination of the form of the upper wall of R 40 mm and the
form of the lower wall downward to 45.degree. does not decrease the
sectional areas of the outlet ports toward the exits, but rather
the sectional areas in the vicinity of the exits were enlarged.
Thus, a discharge flow was not stabilized and flow stability in the
mold was "C".
[0077] An inner surface at a bottom part of a nozzle of Comparative
example 9 was formed in a waterfall basin-like recessed shape.
However, a ridge-shaped projection was not disposed. Hence, a
sufficiently stable vortex was not formed at the bottom. Also,
sectional areas of the outlet ports were constant, thus, a
discharge flow was not stabilized. Furthermore, since a descend
flow rate inside of the nozzle was low, a discharge flow was
unstable. Thus, flow stability in the mold was "F".
* * * * *