U.S. patent application number 14/237757 was filed with the patent office on 2014-07-10 for continuous casting apparatus for steel.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is Yasuo Maruki, Junji Nakashima, Takehiko Toh, Keiji Tsunenari, Kenji Umetsu, Norimasa Yamasaki. Invention is credited to Yasuo Maruki, Junji Nakashima, Takehiko Toh, Keiji Tsunenari, Kenji Umetsu, Norimasa Yamasaki.
Application Number | 20140190655 14/237757 |
Document ID | / |
Family ID | 48288713 |
Filed Date | 2014-07-10 |
United States Patent
Application |
20140190655 |
Kind Code |
A1 |
Toh; Takehiko ; et
al. |
July 10, 2014 |
CONTINUOUS CASTING APPARATUS FOR STEEL
Abstract
A continuous casting apparatus for steel includes: a casting
mold for casting a molten steel with a pair of long side walls and
a pair of short side walls; a submerged entry nozzle which
discharges the molten steel into the casting mold; and an
electromagnetic stirring device which is disposed along each
external surface of each of the long side walls and stirs an upper
portion of the molten steel within the casting mold. A curved
portion which is convexly curved toward the electromagnetic
stirring device in plan view is formed at least at a position where
the curved portion faces the submerged entry nozzle on each of the
long side walls, and each of the long side walls including the
curved portion has a uniform thickness. The shortest horizontal
distance between a top which is a most depressed position when an
internal surface of the curved portion is seen in plan view and an
outer peripheral surface of the submerged entry nozzle is 30 mm to
80 mm in a range from a lower end portion of the electromagnetic
stirring device to a position higher than an upper end portion
thereof by 50 mm when viewed along a vertical direction.
Inventors: |
Toh; Takehiko; (Tokyo,
JP) ; Nakashima; Junji; (Tokyo, JP) ; Maruki;
Yasuo; (Tokyo, JP) ; Yamasaki; Norimasa;
(Tokyo, JP) ; Tsunenari; Keiji; (Tokyo, JP)
; Umetsu; Kenji; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toh; Takehiko
Nakashima; Junji
Maruki; Yasuo
Yamasaki; Norimasa
Tsunenari; Keiji
Umetsu; Kenji |
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
48288713 |
Appl. No.: |
14/237757 |
Filed: |
November 9, 2011 |
PCT Filed: |
November 9, 2011 |
PCT NO: |
PCT/JP2011/075868 |
371 Date: |
February 7, 2014 |
Current U.S.
Class: |
164/504 |
Current CPC
Class: |
B22D 11/041 20130101;
B22D 11/10 20130101; B22D 11/115 20130101 |
Class at
Publication: |
164/504 |
International
Class: |
B22D 11/115 20060101
B22D011/115 |
Claims
1. A continuous casting apparatus for steel comprising: a casting
mold for casting a molten steel, which includes a pair of long side
walls and a pair of short side walls; a submerged entry nozzle
which discharges the molten steel into the casting mold; and an
electromagnetic stirring device which is disposed along an external
surface of each of the long side walls and stirs an upper part of
the molten steel within the casting mold, wherein a curved portion
which is convexly curved toward the electromagnetic stirring device
in plan view is formed at least at a position where the curved
portion faces the submerged entry nozzle on each of the long side
walls, and each of the long side walls including the curved portion
has a uniform thickness, and a shortest horizontal distance between
a top which is a most depressed position when an internal surface
of the curved portion is seen in plan view and an outer peripheral
surface of the submerged entry nozzle is 30 mm to 80 mm in a range
from a lower end portion of the electromagnetic stirring device to
a position higher than an upper end portion of the electromagnetic
stirring device by 50 mm when viewed along a vertical
direction.
2. The continuous casting apparatus for steel according to claim 1,
further comprising: an electromagnetic brake device disposed below
the electromagnetic stirring device, wherein the electromagnetic
brake device applies a direct current magnetic field having a
magnetic flux density distribution which is uniform in a casting
mold width direction along each of the long side walls in plan
view, in a casting mold thickness direction along each of the short
side walls.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a continuous casting
apparatus for steel, which supplies molten steel into a casting
mold to manufacture a cast piece.
BACKGROUND ART
[0002] In continuous casting for steel, in order to improve surface
properties of a cast piece, hitherto, an electromagnetic stirring
device having an electromagnetic coil provided in the vicinity of
the upper portion of a casting mold is used to electromagnetically
stir molten steel within the casting mold.
[0003] For the electromagnetic stirring, for example, the
electromagnetic stirring devices are disposed along a pair of long
side walls included in the casting mold. In addition, when the
molten steel is discharged from a submerged entry nozzle into the
casting mold, current is supplied to the electromagnetic stirring
devices to apply a thrust to the upper part of the molten steel
within the casting mold. The molten steel is stirred in a
horizontal plane by the thrust such that a swirling flow of the
molten steel is formed. By the swirling flow, trapping of
inclusions, bubbles, and the like in the vicinity of a meniscus at
the upper portion in the casting mold by a solidified shell formed
on the side surfaces of the casting mold is suppressed.
[0004] However, since the submerged entry nozzle is submerged in
the casting mold, regions between the long side walls and the
submerged entry nozzle are narrower than the other regions.
Therefore, in the regions between the long side walls and the
submerged entry nozzle, compared to the other regions, it is
difficult for the molten steel to flow.
[0005] In addition, inclusions and the like are likely to adhere to
and deposit on the periphery of the submerged entry nozzle in the
casting mold. There may be cases where the adhered matter deposited
as such has a thickness of several tens of millimeters. Therefore,
the regions between the long side walls and the submerged entry
nozzle are narrower than the other regions. In this case, the flow
channel for the swirling flow is partially narrowed, and thus it is
difficult for the molten steel to flow in the regions between the
long side walls and the submerged entry nozzle.
[0006] Here, simultaneously with the use of electromagnetic
stirring devices described above, instead of a flat shaped casting
mold having a flat internal surface in a furnace, using a so-called
irregular shaped casting mold in which, as illustrated in FIG. 7,
surfaces 104 and 105 in long side walls 101 and 102, which face a
submerged entry nozzle 103 are convexly curved toward
electromagnetic stirring devices 106 and 107, respectively, is
proposed (Patent Document 1). In addition, in FIG. 7, back plates
108 and 109 made of stainless steel, in which flow channels of
cooling water (not illustrated) used to cool the long side walls
101 and 102 are provided are disposed between the long side walls
101 and 102 and the electromagnetic stirring devices 106 and
107.
[0007] According to the irregular shaped casting mold, since the
surfaces 104 and 105 in the long side walls 101 and 102, which face
the submerged entry nozzle 103 are convexly curved toward the
electromagnetic stirring devices 106 and 107, respectively, the
shortest horizontal distances between the submerged entry nozzle
103 and the long side walls 101 and 102 are longer than those of
the parallel casting mold according to the related art. Therefore,
the flow channels of swirling flows 110 and 111 can be widely
ensured to that extent, and thus the molten steel easily flows.
RELATED ART DOCUMENT
Patent Document
[0008] [Patent Document 1] Japanese Unexamined Patent Application,
First Publication No. 2008-183597
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0009] However, in the above-described technique according to the
related art, in order to convexly curve the surfaces 104 and 105 in
the long side walls 101 and 102, which face the submerged entry
nozzle 103, the center portions of the long side walls 101 and 102
made of copper are cut. Therefore, the thicknesses of the long side
walls 101 and 102 are extremely small in the parts of the curved
surfaces 104 and 105. In general, the electromagnetic field made by
the electromagnetic stirring devices 106 and 107 is an alternate
current magnetic field, and thus the magnetic field is attenuated
in conductors. Therefore, in the parts of the curved surfaces 104
and 105, the magnetic field is less attenuated than the other
linear parts, and thus the electromagnetic force increases.
Accordingly, the flow velocity of the stirring flow in the regions
between the curved surfaces 104 and 105 and the submerged entry
nozzle 103 becomes faster than that in the other regions. As a
result, the flow velocity of stirring flows 110 and 111 becomes
partially non-uniform, a flow disturbance or a stagnant zone is
generated in regions 112 and 113 on the downstream sides of the
stirring flows 110 and 111 in the long side walls 101 and 102, and
there is a problem in that inclusions, bubbles, and the like are
likely to be trapped by a solidified shell. Therefore, enhancement
of steel quality to an expected degree cannot be obtained.
[0010] The inventors had further performed examinations, and found
that trapping of inclusions by the solidified shell of the long
side walls 101 and 102 could not be suppressed by only forming the
curved surfaces 104 and 105 which allow the stirring flows 110 and
111 to easily flow. That is, it was proved that when the horizontal
distance between the curved surfaces 104 and 105 and the submerged
entry nozzle 103 is increased, trapping of bubbles can be
suppressed. However, in the parts of the curved surfaces 104 and
105, the electromagnetic force is also strengthened, and the flow
velocities of the stirring flows that flow in the regions between
the curved surfaces 104 and 105 and the submerged entry nozzle 103
become faster than those of the stirring flows that flow in the
other regions. Therefore, a flow disturbance or a stagnant zone is
generated in the regions 112 and 113 on the downstream sides of the
stirring flows 110 and 111, and thus a problem in which inclusions
are likely to be trapped by the solidified shell is not solved.
[0011] The present invention has been made taking the foregoing
points into consideration, and an object thereof, even in an
irregular shaped casting mold in a continuous casting apparatus for
steel, is to allow the flow velocity of molten steel at the upper
portion in the casting mold to be uniform and to allow a horizontal
distance between a surface concavely curved in the casting mold and
a submerged entry nozzle to be appropriate, thereby enhancing the
quality of a cast piece obtained by casting.
Means for Solving the Problem
[0012] In order to accomplish the object, the present invention
employed the following measures.
[0013] (1) That is, according to an aspect of the present
invention, a continuous casting apparatus for steel includes: a
casting mold for casting a molten steel, which includes a pair of
long side walls and a pair of short side walls; a submerged entry
nozzle which discharges the molten steel into the casting mold; and
an electromagnetic stirring device which is disposed along an
external surface of each of the long side walls and stirs an upper
part of the molten steel within the casting mold. A curved portion
which is convexly curved toward the electromagnetic stirring device
in plan view is formed at least at a position where the curved
portion faces the submerged entry nozzle on each of the long side
walls, and each of the long side walls including the curved portion
has a uniform thickness. The shortest horizontal distance between a
top which is a most depressed position when an internal surface of
the curved portion is seen in plan view and an outer peripheral
surface of the submerged entry nozzle is 30 mm to 80 mm in a range
from a lower end portion of the electromagnetic stirring device to
a position higher than an upper end portion of the electromagnetic
stirring device by 50 mm when viewed along a vertical
direction.
[0014] (2) In the aspect according to the above (1), an
electromagnetic brake device disposed below the electromagnetic
stirring device may be further included, and the electromagnetic
brake device applies a direct current magnetic field having a
magnetic flux density distribution which is uniform in a casting
mold width direction along each of the long side walls in plan
view, in a casting mold thickness direction along each of the short
side walls.
[0015] In addition, in the aspect of the above (1), it is more
preferable that the shortest horizontal distance be 50 mm to 75 mm
in the range from the lower end portion of the electromagnetic
stirring device to a position higher than the upper end portion of
the electromagnetic stirring device by 50 mm when viewed along the
vertical direction.
Effects of the Invention
[0016] According to the aspect described in the above (1), each of
the long side walls has the curved portion which is convexly curved
toward the electromagnetic stirring device at least at a position
that faces the submerged entry nozzle, and each of the long side
walls including the curved portion has a uniform thickness.
Therefore, the electromagnetic force generated by the
electromagnetic stirring device is uniform over the curved portion
and the other parts. As a result, the flow velocity of the stirring
flow becomes uniform. That is, the intensity distribution of the
electromagnetic force when each of the long side walls is seen in
plan view is the same in the curved portion and the parts other
than the curved portion. Therefore, unlike the related art, the
electromagnetic force can be prevented from becoming partially
stronger at a point corresponding to the curved portion.
[0017] Therefore, the generation of a flow disturbance or a
stagnant zone as in the related art can be suppressed, and easy
trapping of bubbles by the solidified shell can be suppressed.
[0018] In addition, since the shortest horizontal distance between
the top of the curved portion and the submerged entry nozzle is set
to be 30 mm to 80 mm in a range from the position of the lower end
portion of the electromagnetic stirring device to a position higher
than the upper end portion of the electromagnetic stirring device
by 50 mm when viewed in the height direction of the continuous
casting apparatus, a smooth and uniform flow of the molten steel
can be ensured even in the region between the top of the curved
portion and the submerged entry nozzle.
[0019] That is, according to the knowledge newly obtained by the
inventors, when the shortest horizontal distance between the top of
the curved portion and the submerged entry nozzle is smaller than
30 mm, it is difficult for the molten steel to flow in the curved
regions, and bubbles and the like in the molten steel are likely to
be trapped by the solidified shell. In contrast, when the shortest
horizontal distance exceeds 80 mm, it is difficult to ensure a
uniform flow of the molten steel in the curved region, and in a
region where the flow velocity of the molten steel is slow,
inclusions in the molten steel are likely to be trapped by the
solidified shell.
[0020] In the present invention, based on the knowledge, the
shortest horizontal distance between the top of the curved portion
and the submerged entry nozzle is set to 30 mm to 80 mm. Therefore,
in the curved region between the top of the curved portion and the
submerged entry nozzle, a smooth and uniform flow of the stirring
flow of the molten steel is ensured, and bubbles in the molten
steel can be prevented from being trapped by the solidified
shell.
[0021] In addition, the range in the height direction in which the
shortest horizontal distance between the top of the curved portion
and the submerged entry nozzle is set to 30 mm to 80 mm, as such is
a range from the lower end portion of the electromagnetic stirring
device to a position higher than the upper end portion of the
electromagnetic stirring device by 50 mm. This is because although
a part of the molten steel that is directly stirred by the
electromagnetic force generated by the electromagnetic stirring
device is a part from the lower end portion to the upper end
portion of the electromagnetic stirring device, in a practical
operation, the surface of a meniscus is positioned at a position
higher than the upper end portion of the electromagnetic stiffing
device. In addition, typically, in the case where the surface of
the meniscus is positioned at a position higher than the upper end
portion of the electromagnetic stirring device, the height is at a
position higher than the upper end portion of the electromagnetic
stirring device by about 50 mm. Therefore, the range in the height
direction in which the shortest horizontal distance between the top
of the curved portion and the submerged entry nozzle is set to be
30 mm to 80 mm is from the lower end portion of the electromagnetic
stirring device to the position higher than the upper end portion
of the electromagnetic stirring device by 50 mm.
[0022] In addition, a uniform thickness of the long side wall is
referred to as a thickness in which a change in a penetration
degree of an electromagnetic field in the molten steel due to a
change in thickness excluding parts where bolt holes, cooling water
grooves, and the like are formed is less than 10% which is an error
in an acceptable range. This will be described hereinafter. In a
case where a magnetic field having a predetermined magnetic flux
density is applied to the inside of the casting mold from the
outside of the long side wall, the magnetic field intensity induced
inside the casting mold has a loss depending on the value of the
thickness of the long side wall. That is, when the thickness of the
long side wall is changed, the penetration depth of the magnetic
field into the casting mold is changed. When the long side wall is
thick, it is difficult for the magnetic field to penetrate.
Therefore, the magnetic field intensity in the casting mold is
changed with the magnitude of the loss. However, the thickness of
the long side wall is caused to be uniform so that the change is
less than 10% when viewed in the horizontal direction along the
wall surface of the long side wall.
[0023] In addition, the range in the height direction of the
uniform thickness of the long side wall may be a range from the
lower end portion of the electromagnetic stirring device to a
position higher than the upper end portion of the electromagnetic
stirring device by 50 mm as described in the effect of the
electromagnetic stirring device.
[0024] In addition, "the uniform thickness of the long side wall"
will be further supplementarily described. When the long side wall
disposed along the vertical direction is seen in plan view, the
relative relationship between the thickness of the part of the
curved portion and the thickness of the adjacent part excluding the
curved portion is particularly important. That is, "each of the
long side walls including the curved portion has a uniform
thickness" described in the above (1) means that, in a case where
the thickness of the part of the curved portion is t1 and the
thickness of the adjacent part excluding the curved portion is t2,
t1 is within .+-.10% of t2
(0.9.times.t2.ltoreq.t1.ltoreq.1.1.times.t2). In addition, it is
most preferable that t1=t2.
[0025] In addition, as described in the above (2), in the
continuous casting apparatus for steel, the so-called
electromagnetic brake device may also be used together with the
electromagnetic stirring device. That is, an electromagnetic brake
device which is disposed below the electromagnetic stirring device
and which applies the direct current magnetic field having a
magnetic flux density distribution which is uniform in the casting
mold width direction along the long side walls of the casting mold,
in the casting mold thickness direction along the short side walls
of the casting mold may further be included.
[0026] In this case, rising of bubbles and inclusions in the molten
steel discharged from the submerged entry nozzle is accelerated,
and bubbles and inclusions in the molten steel are suspended and
can be impeded from remaining in a cast piece which is casted and
causing a degradation in quality. Therefore, the quality of the
cast piece can be further enhanced.
[0027] In addition, the "uniform magnetic flux density" described
in the above (2) will be supplementarily described. In a case where
the casting mold is seen in plan view and the magnetic flux density
distribution is then seen in the casting mold width direction along
the long side walls, the uniform magnetic flux density means that a
variation in the magnetic flux density in the length dimensions of
the coil parts of the electromagnetic brake devices is within
.+-.30% of the average thereof
[0028] As described above, according to the present invention, the
amount of bubbles and the like included in the cast piece which is
casted can be reduced and thus the quality of the cast piece can be
enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic plan view illustrating a schematic
configuration of a part in the vicinity of a casting mold of a
continuous casting apparatus according to an embodiment of the
present invention.
[0030] FIG. 2 is a longitudinal sectional view when the continuous
casting apparatus is seen in a cross-section taken along the line
A-A in FIG. 1.
[0031] FIG. 3 is a longitudinal sectional view when the continuous
casting apparatus is seen in a cross-section taken along the line
B-B in FIG. 1.
[0032] FIG. 4 is a perspective view of a long side wall of the
continuous casting apparatus.
[0033] FIG. 5 is a diagram corresponding to FIG. 3 and is a
longitudinal sectional view for showing sizes in the periphery of
the casting mold of the continuous casting apparatus.
[0034] FIG. 6 is a diagram illustrating a modified example of the
continuous casting apparatus and is a longitudinal sectional view
corresponding to FIG. 2 in a case where a curved portion having a
different shape is included.
[0035] FIG. 7 is a schematic plan view for illustrating a schematic
configuration of parts in the vicinity of a casting mold of a
continuous casting apparatus according to the related art.
EMBODIMENTS OF THE INVENTION
[0036] Hereinafter, an embodiment of the present invention will be
described. FIG. 1 is an explanatory view schematically showing the
configuration of the vicinity of a casting mold of a continuous
casting apparatus 1 for steel according to this embodiment in plan
view, FIG. 2 is an explanatory view schematically showing the
cross-section of the same in front view, and FIG. 3 is an
explanatory view schematically showing a cross-section of the same
in side view.
[0037] The continuous casting apparatus 1 includes a casting mold 2
which is, for example, substantially rectangular in plan view as
illustrated in FIG. 1. The casting mold 2 includes a pair of long
side walls 3a and 3b and a pair of short side walls 4a and 4b. All
of the long side walls 3a and 3b and the short side walls 4a and 4b
are configured of copper sheets, and on the outsides thereof, back
plates 5a, 5b, 6a, and 6b made of austenitic stainless steel, which
are non-magnetic bodies and reinforce the long side walls 3a and 3b
and the short side walls 4a and 4b are disposed. That is, the back
plate 5a is disposed on the outside of the long side wall 3a, the
back plate 5b is disposed on the outside of the long side wall 3b,
the back plate 6a is disposed on the outside of the short side wall
4a, and the back plate 6b is disposed on the outside of the short
side wall 4b.
[0038] In addition, on the outsides of the back plates 5a and 5b,
electromagnetic stirring devices 7a and 7b which respectively
include electromagnetic coils are disposed. In addition,
immediately below the electromagnetic stirring devices 7a and 7b,
electromagnetic brake devices 8a and 8b are disposed. That is, the
electromagnetic stirring device 7a and the electromagnetic brake
device 8a are disposed on the outside of the back plate 5a, and the
electromagnetic brake device 8a is disposed immediately below the
electromagnetic stirring device 7a. In addition, the
electromagnetic stirring device 7b and the electromagnetic brake
device 8b are disposed on the outside of the back plate 5b, and the
electromagnetic brake device 8b is disposed immediately below the
electromagnetic stirring device 7b.
[0039] In this embodiment, the length (casting thickness) when the
short side walls 4a and 4b are seen in plan view is, for example,
about 50 mm to 300 mm. This length is determined depending on a
desired cast piece width, and is about 50 mm to 80 mm in a case of
a thin width cast piece, is about 80 mm to 150 mm in the case of an
intermediate width cast piece, and is about 150 mm to 300 mm in the
case of a typical width cast piece. In addition, a horizontal
direction (the X direction in FIGS. 1 to 3) along the long side
walls 3a and 3b is referred to as a casting mold width direction,
and a horizontal direction (the Y direction in FIGS. 1 and 3) along
the short side walls 4a and 4b is referred to as a casting mold
thickness direction.
[0040] At the center portions of the internal surfaces when the
long side walls 3a and 3b are seen in plan view, curved portions
11a and 11b which are convexly curved toward the electromagnetic
stirring devices 7a and 7b are respectively formed. The curved
portions 11a and 11b are formed at positions facing a submerged
entry nozzle 21 provided in the casting mold 2 which will be
described later. Regarding the thickness distribution of the long
side walls 3a and 3b along the extension direction thereof when the
long side walls 3a and 3b are seen in plan view, the parts
corresponding to the curved portions 11a and 11b are molded so as
not to be different from the straight parts on both adjacent sides
thereof but to have a uniform thickness in the horizontal
direction. Specifically, the curved portions 11a and 11b are formed
in the long side walls 3a and 3b by, for example, press
forming.
[0041] More specifically, the curved portion 11a is formed to
include an internal surface 11a1 which is curved so that the
internal wall surface of the long side wall 3a is separated from
the submerged entry nozzle 21, and an external surface 11a2 which
is curved so that the external wall surface of the long side wall
3a is separated from the submerged entry nozzle 21. Similarly, the
curved portion 11b is formed to include an internal surface 11b1
which is curved so that the internal wall surface of the long side
wall 3b is separated from the submerged entry nozzle 21, and an
external surface 11b2 which is curved so that the external wall
surface of the long side wall 3b is separated from the submerged
entry nozzle 21.
[0042] Since the long side walls 3a and 3b have a uniform thickness
at all the positions including the curved portions 11a and 11b,
each of external surfaces of the long side walls 3a and 3b is
convexly curved toward the electromagnetic stirring devices 7a and
7b in the external surfaces 11a2 and 11b2 included in the curved
portions 11a and 11b.
[0043] In addition, the uniform thickness of the long side walls 3a
and 3b will be supplementarily described. When the long side walls
3a and 3b are seen in plan view, in a case where the thickness at
the curved portions 11a and 11b is t1 and the thickness at both
adjacent parts to the curved portions 11a and 11b is t2, the
uniform thickness means that t1 is within .+-.10% of t2
(0.9.times.t2.ltoreq.t1.ltoreq.1.1.times.t2). In addition, it is
most preferable that t1=t2.
[0044] The back plates 5a and 5b have parts in which the center
internal surfaces thereof have shapes that are convexly curved
toward the electromagnetic stirring devices 7a and 7b so as to fit
the curved shapes of the external surfaces 11a2 and 11b2 of the
curved portions 11a and 11b of the long side walls 3a and 3b.
However, the external surfaces of the back plates 5a and 5b, that
is, the surfaces thereof that face the electromagnetic stirring
devices 7a and 7b are molded to be flat (flat surfaces).
[0045] Typically, in this type of back plate, a cooling water flow
channel used to cool the long side wall made of copper is formed
therein. However, in order to form the flow channels in the back
plates 5a and 5b, for example, groove-like flow channels are formed
on the surfaces (the internal surfaces) of the back plates 5a and
5b on the sides that come into contact with the long side walls 3a
and 3b, thereby easily forming the cooling water flow channel. That
is, by assembling the back plates 5a and 5b having the groove-like
flow channels formed on the internal surfaces so that the internal
surfaces come into close contact with and overlap the external
surfaces of the long side walls 3a and 3b, the groove-like flow
channels can be easily formed.
[0046] The curved portions 11a and 11b are formed to face the
submerged entry nozzle 21 from the upper end positions of the long
side walls 3a and 3b in a downward direction as illustrated in
FIGS. 2 and 3. Each of the lower end positions of the curved
portions 11a and 11b may be formed to be at the same height as the
lower end position of the submerged entry nozzle 21 or to be lower
than the lower end position of the submerged entry nozzle 21. In
spaces (gaps) between the curved portions 11a and 11b and the
submerged entry nozzle 21, curved regions 9a and 9b are
respectively formed as illustrated in FIG. 1.
[0047] The curved portions 11a and 11b have shapes in which the
curved parts gradually disappear toward their lower ends (that is,
depressions that form the curved portions 11a and 11b gradually
become shallow and disappear). In this embodiment, as illustrated
in FIG. 4, for example, in the internal surface of the long side
wall 3a, the boundary line between the curved portion 11a and the
other flat part is a straight line (a straight line SL horizontal
along the X direction in FIG. 4) parallel to the length direction
of the long side wall 3a at the lower end part of the curved
portion 11a and is a straight line (a straight line VL in the
extension direction along the Z direction in FIG. 4) parallel to
the height direction of the long side wall 3a at both side edge
parts of the curved portion 11a.
[0048] As illustrated in FIG. 5, in a case where the curved
portions 11a and 11b are seen in a cross-section along the sheet
thickness direction thereof, the shortest horizontal distances L
between the tops of the curves (the most depressed points) and the
peripheral surfaces of the submerged entry nozzle 21 have tapered
shapes in which the depressions gradually become shallow and
disappear toward the lower ends of the curved portions 11a and 11b,
and thus the lengths thereof in the height direction vary. In this
embodiment, in a range from the position of the lower end portion
of each of the electromagnetic stirring devices 7a and 7b to a
position higher than the upper end portion of each of the
electromagnetic stirring devices 7a and 7b by 50 mm, the shortest
horizontal distance L is set to be 30 mm to 80 mm. In addition, the
shortest horizontal distance L is preferably 30 mm to 80 mm as
specified here, but is more preferably 50 mm to 75 mm.
[0049] That is, this will be described with reference to FIG. 5.
The shortest horizontal distances L between the tops of the curves
of the curved portions 11a and 11b and the peripheral surfaces of
the submerged entry nozzle 21 are set to be 30 mm to 80 mm in a
range H from the positions of the lower end portions of the
electromagnetic stirring devices 7a and 7b to heights higher than
the upper end portions of the electromagnetic stirring devices 7a
and 7b by 50 mm. The length of h in FIG. 5 is 50 mm.
[0050] Depths D of the depressions that form the curved portions
11a and 11b for ensuring 30 mm to 80 mm as the shortest horizontal
distances L between the tops of the curves of the curved portions
11a and 11b and the peripheral surfaces of the submerged entry
nozzle 21 depend on the thicknesses of the long side walls 3a and
3b. However, in consideration of the strengths of the back plates
5a and 5b and reducing the total thickness due to the
electromagnetic force which is weakened as the electromagnetic
stirring devices 7a and 7b become distant in position from the
molten steel, the depths D of the depressions may be appropriately
set. As the upper limit of the depth D of the depression, 50 mm or
less, and preferably 40 mm or less, are exemplary examples. As the
lower limit of the depth D of the depression, 5 mm or greater and
preferably 10 mm or greater are exemplary examples. That is, the
depth D is preferably 5 mm to 50 mm, and more preferably 10 mm to
40 mm.
[0051] Regarding the above-mentioned submerged entry nozzle 21, as
illustrated in FIG. 3, during casting, the lower portion thereof is
submerged in the molten steel M within the casting mold 2. In
addition, in FIG. 3, in order to clearly show the structure inside
the continuous casting apparatus 1, hatching of the molten steel M
is omitted. In the vicinity of the lower end of the side surface of
the submerged entry nozzle 21, discharge holes 22 that discharge
the molten steel obliquely downward in the casting mold 2 are
formed at two points. The discharge holes 22 are formed at
positions that respectively face the short side walls 4a and 4b of
the casting mold 2. A discharge flow 23 discharged from each of the
discharge holes 22 includes Ar gas bubbles blown to clean nozzles,
alumina or slag-based inclusions, and the like. The bubbles and
inclusions rise to the vicinity of a meniscus 24. In addition, on
the meniscus 24, a molten powder 25 having molten oxides is
supplied by a supply mechanism (not illustrated).
[0052] On the internal surface of the casting mold 2, as
illustrated in FIG. 3, a solidified shell 26 in which the molten
steel M cools and solidifies is formed.
[0053] Each of the electromagnetic stirring devices 7a and 7b has
the electromagnetic coil, and receives an alternate current power
supplied from a power supply (not illustrated) and generates an
electromagnetic force, thereby applying a thrust to the molten
steel M at the upper portion of the casting mold 2. In addition,
the molten steel M to which the thrust is applied horizontally
swirls around the submerged entry nozzle 21 in the casting mold 2
and generates a stirring flow that stirs the molten steel M. By the
stirring flow, the inclusions, the bubbles, and the like in the
vicinity of the meniscus 24 at the upper portion of the casting
mold 2 are prevented from being trapped by the solidified shell 26
formed on the side surfaces of the casting mold 2.
[0054] The electromagnetic brake devices 8a and 8b which are
respectively disposed below the electromagnetic stirring devices 7a
and 7b and include electromagnets and the like may apply a direct
current magnetic field having a substantially uniform magnetic flux
density distribution in the casting mold width direction (the X
direction in FIGS. 1 and 2) along the long side walls 3a and 3b of
the casting mold 2 to the discharge flows 23 of the molten steel M
immediately after being respectively discharged from the discharge
holes 22 in the casting mold thickness direction (the Y direction
in FIGS. 1 and 2) along the short side walls 4a and 4b of the
casting mold 2. By the direct current magnetic field and the
discharge flows 23 of the molten steel M respectively discharged
from the discharge holes 22, an induced current is generated in the
casting mold width direction (the X direction in FIGS. 1 and 2),
and by the induced current and the direct current magnetic field,
counter flows that flow in the opposite directions to the discharge
flows 23 are formed in the vicinity of the discharge flows 23. By
the counter flows, deep infiltration of the bubbles and included
portions into the molten steel M in the discharge flows 23 are
suppressed, and rising of the bubbles and included portions is
accelerated, thereby suppressing trapping of the bubbles and
included portions by the solidified shell 26.
[0055] In addition, the "uniform magnetic flux density" will be
supplementarily described. In a case where the casting mold 2 is
seen in plan view and the magnetic flux density distribution is
then seen in the casting mold width direction along the long side
walls 3a and 3b, the uniform magnetic flux density means that a
variation in the magnetic flux density in the length dimensions of
the coil parts of the electromagnetic brake devices 8a and 8b is
within .+-.30% from the average thereof
[0056] The continuous casting apparatus 1 according to this
embodiment is configured as described above. Next, a continuous
casting method of the molten steel M using the continuous casting
apparatus 1 will be described.
[0057] First, while Ar gas is blown into the submerged entry nozzle
21, the molten steel M is discharged into the casting mold 2 from
each of the discharge holes 22 of the submerged entry nozzle 21.
The molten steel M is discharged obliquely downward such that the
discharge flows 23 directed from the discharge holes 22 toward the
short side walls 4a and 4b of the casting mold 2 are formed. The
discharge flows 23 include the Ar gas bubbles and the other
inclusions, and they are suspended in the molten steel M within the
casting mold 2 and rise by the buoyancy due to a difference in the
specific gravity between the bubbles and inclusions, and the molten
steel M.
[0058] In addition, the electromagnetic brake devices 8a and 8b may
be operated at the same time as when the molten steel M is
discharged from the submerged entry nozzle 21. In the case of using
the electromagnetic brake devices 8a and 8b, counter flows in the
opposite direction to the flows of the discharge flows 23 are
formed in the molten steel M. As a result, as described above, deep
infiltration of the bubbles and the other inclusions into the
molten steel M in the discharge flows 23 is suppressed and
diffusing towards the periphery of the submerged entry nozzle 21 is
suppressed. In addition, the bubbles and the other inclusions in
the discharge flows 23 rise to the vicinity of the meniscus 24 from
the vicinity of the submerged entry nozzle 21 by the counter
flows.
[0059] In addition, at the same time during the operation of the
electromagnetic brake devices 8a and 8b, the electromagnetic
stirring devices 7a and 7b are operated. Therefore, as described
above, the stirring flow is formed in the molten steel M in the
vicinity of the meniscus 24 within the casting mold 2 due to the
electromagnetic stirring by the electromagnetic force. In addition,
the Ar gas bubbles and the like that rise to the vicinity of the
meniscus 24 by riding on the counter flows described above are
swirled by the stirring flow and are incorporated into, for
example, the molten powder 25 having the molten oxides without
being trapped by the solidified shell 26 of the casting mold 2 so
as to be removed.
[0060] Since the curved portions 11a and 11b are respectively
formed at the center positions of the upper portions of the long
side walls 3a and 3b of the casting mold 2, the curved regions 9a
and 9b are formed between the curved portions 11a and 11b and the
submerged entry nozzle 21. At this time, since the long side walls
3a and 3b also include the curved portions 11a and 11b and have the
uniform thickness, the magnetic flux density of the electromagnetic
force applied to the molten steel M by the electromagnetic stirring
devices 7a and 7b is at the same degree in both (1) the molten
steel M that flows in the curved regions 9a and 9b and (2) the
molten steel M that linearly flows at positions other than the
curved regions 9a and 9b. Therefore, the stirring flow having a
uniform flow velocity can be formed along the flow direction of the
molten steel M. Accordingly, a flow disturbance or a stagnant zone
is prevented from occurring in regions (the regions 112 and 113 in
the related art described with reference to FIG. 7) on the
downstream sides of the stirring flow in the long side walls 3a and
3b. Therefore, it is possible to suppress trapping of bubbles and
the like by the solidified shell due to the occurrence of the
stagnant zone.
[0061] In addition, although the long side walls 3a and 3b
including the curved portions 11a and 11b have a uniform thickness
at each position, the thicknesses of the back plates 5a and 5b at
the parts corresponding to the curved portions 11a and 11b are
thin, and thus the magnetic flux density becomes non-uniform to
that extent. However, since the electromagnetic field during the
electromagnetic stirring is generally an alternate current magnetic
field, the electromagnetic field is attenuated in conductors, and
the attenuation particularly becomes intensive as the electrical
conductivity is increased. In addition, since this type of the back
plates 5a and 5b is made of non-magnetic austenitic stainless
steel, the electrical conductivity thereof is much smaller than
that of the long side walls 3a and 3b made of copper. Therefore,
even though the thicknesses of the back plates 5a and 5b are
partially thin, the effect thereof is rarely present, and the
uniform magnetic flux density can be obtained even in the molten
steel M that flows in the curved regions 9a and 9b.
[0062] The inventors had actually measured and examined the
magnetic flux density using a gaussmeter and found the following.
That is, in a case where the continuous casting apparatus 1 was
viewed along the height direction, the magnetic flux density at the
center position of the height of the electromagnetic stirring
device 7a and at a point of 10 mm toward the submerged entry nozzle
21 from the top of the curve of the curved portion 11a of which the
depression depth D was 30 mm was measured using the gaussmeter, and
it was confirmed that the magnetic flux density varied by 10% or
less even when compared to the magnetic flux density of the linear
parts other than the curved portion 11a of the long side wall 3a.
That is, the magnetic flux density at the same height of the
continuous casting apparatus 1 was measured at a plurality of
points, and the values were compared to each other. It was
confirmed that the measurement value at the point corresponding to
the curved portion 11a and the measurement values at the flat parts
on both sides of the curved portion 11a had a difference of only
about 10%.
[0063] For reference, in a case where the curved portion having a
depression depth D of 30 mm was formed by cutting only a curved
concave surface from the long side wall as in the related art and
the thickness of the curved portion was thinned, it was confirmed
that the magnetic flux density thereof was increased by about 40%
from the magnetic flux density of the linear part of the long side
wall. That is, similarly to the structure of the related art
illustrated in FIG. 7, the curved concave surface similar to that
of the above-described example was formed only on the internal
surface while the external surface of the long side wall was flat,
and the magnetic flux density was measured to perform the same
evaluation. As a result, it was confirmed that the measurement
value at the point corresponding to the curved portion was higher
than the measurement values at the flat parts on both sides of the
curved portion by about 40%. Therefore, the effect of this
embodiment could be confirmed by the foregoing point.
[0064] This will be described with reference to FIG. 5. In this
embodiment, the shortest horizontal distances L between the tops of
the curves of the curved portions 11a and 11 and the submerged
entry nozzle 21 are set to 30 mm to 80 mm in the range H from the
lower end portions of the electromagnetic stirring devices 7a and
7b to the positions higher than the upper end portions of the
electromagnetic stirring devices 7a and 7b by 50 mm. In this
configuration, the flow velocity of the stirring flow that flows in
the curved regions 9a and 9b is uniform, and a smooth and steady
flow of the molten steel M can be ensured. Therefore, it is
possible to sufficiently stir the molten steel M in the casting
mold 2, and trapping of the bubbles and the like by the solidified
shell 26 can be suppressed by the foregoing point.
[0065] Moreover, in this embodiment, since the electromagnetic
brake devices 8a and 8b are also used, the rising of the inclusions
such as bubbles in the molten steel M is accelerated and the
diffusion to the periphery thereof is suppressed. Therefore,
trapping of the bubbles and the like by the solidified shell 26 can
be further suppressed.
[0066] In addition, in this embodiment, as illustrated in FIGS. 2
and 4, the shapes of the curved portions 11a and 11b are shapes in
which the boundary between the curved portion 11a and the flat part
of the periphery thereof is a straight line (the straight line SL
along the X direction in FIGS. 2 and 4) parallel to the length
direction of the long side wall 3a at the lower end part of the
curved portion 11a and is a straight line (the straight line VL
along the Z direction in FIGS. 2 and 4) parallel to the height
direction of the long side wall 3a at both side parts of the curved
portion 11a. However, other shapes may also be employed as the
shapes of the curved portions 11a and 11b. For example, as
illustrated in FIG. 6, curved portion 11c having a so-called
inverted bell shape in which the boundary line between the curved
portion and the other flat parts is converged on a single point at
the lowermost end as it goes to the lower end and disappears may be
employed. That is, as illustrated in FIG. 6, the curved portion 11c
having a boundary line in a semi-elliptical shape that tapers to
the lower portion in an opposed view of the long side wall 3a may
be employed.
EXAMPLE 1
[0067] Hereinafter, an effect of removing Ar gas bubbles and
inclusions included in molten steel in a case where a continuous
casting apparatus for steel according to Examples of the present
invention is used will be described. When the Examples were
performed, the continuous casting apparatus 1 illustrated in FIGS.
1 to 3 was used as a continuous casting apparatus for steel.
[0068] At the formation position of the meniscus 24 in the casting
mold 2 having a width of 1200 mm, a height of 900 mm, and a
thickness of 250 mm, the electromagnetic stirring devices 7a and 7b
having a height of 200 mm and a thrust of 100 mmFe were set so that
the upper end positions thereof had the same height as the position
of the meniscus, and the electromagnetic brake devices 8a and 8b
which were disposed to apply the maximum magnetic flux density at a
position having a depth of 500 mm down from the meniscus 24 were
used. In addition, the submerged entry nozzle 21 having a maximum
outside diameter of 190 mm and an inside diameter of 100 mm was
inserted into a molten steel submerged portion at a position having
a depth of 400 mm down from the meniscus 24 along the vertical
direction to perform casting.
[0069] The continuous casting machine 1 of this example included
vertical portions having bend radiuses of 7.5 m and 2.5 m. By using
the continuous casting machine 1, a low carbon aluminium-killed
steel was casted at a casting rate of 2 m/min. The discharge holes
22 of the submerged entry nozzle 21 faced the internal surfaces of
the short side walls 4a and 4b in the space of the casting mold 2
and had a discharge angle .theta. (see FIG. 2) of 30 degrees in the
downward direction, and a two-hole nozzle having a hole diameter of
70 mm was used as the submerged entry nozzle 21.
[0070] The thicknesses of the long side walls 3a and 3b were
constant at 30 mm, and a typical casting mold having parallel long
side copper sheets and the center parts of the long side copper
sheets were subjected to press forming, and the back plates 5a and
5b were cut to have depression depths D of 0, 5, 10, 20, 30, 40,
50, and 55 mm at the position of the meniscus 24. That is, when the
long side walls 3a and 3b were produced, rectangular copper sheets
having a uniform thickness of 30 mm were prepared, press forming
was performed on the center portions of the upper ends of the
copper sheets, and accordingly, seven types of long side walls 3a
and 3b having depression depths D of 0, 5, 10, 20, 30, 40, 50, and
55 mm at the height position of the meniscus 24 were produced. In
addition, a depression depth D of 0 mm means a casting mold having
a long side wall without depressions.
[0071] On the other hand, seven types of back plates 5a and 5b in
which the shapes of the curved concave portions (the depths of the
curves) were different were produced so as to fit the shapes (the
depths of the curves) of the curved portions 11a and 11b of the
seven types of long side walls 3a and 3b. In addition, the
thickness of each of the back plates 5a and 5b was 80 mm, but the
part where the curved concave portion was formed was thinner.
[0072] The curved portions 11a and 11b in the long side walls 3a
and 3b were formed to have a length of 400 mm from the center of
the casting mold width in the casting width direction to each of
both sides, and as illustrated in FIG. 2, the boundary between the
curved portion 11a (11b) and the other flat part was, as the curved
portion 11a (11b) goes to the lower end, a straight line parallel
to the length direction (the X direction in FIG. 2) of the long
side wall 3a at the lower end part of the curved portion 11a (11b)
and was a straight line parallel to the height direction (the Z
direction in FIG. 2) of the long side wall 3a at both side parts of
the curved portion 11a, thereby forming a rectangular shape. The
long side walls 3a and 3b having the curved portions 11a and 11b
were used as a part of the casting mold.
[0073] Bubbles and inclusion defects of a cast piece were evaluated
by observing a part having a depth of 50 mm from the cast piece
surface layer of the cast piece and counting the number of bubbles
and inclusions having a diameter of 100 .mu.m or greater as
indexes. The index of the number of Ar gas bubbles in Table 1
represents the ratio of the number of Ar gas bubbles in each
condition with respect to the number of Ar gas bubbles which was
set to 1 in a case where the distances L (see FIG. 5) between the
curved portions 11a and 11b and the submerged entry nozzle 21 were
25 mm and the depression depth D was 0 mm, that is, the curved
portions 11a and 11b were not formed on the long side walls 3a and
3b.
[0074] In addition, similarly, the index of the number of
inclusions represents the ratio of the number of inclusions in each
condition with respect to the number of inclusions which was set to
1 in a case where the distances L between the curved portions 11a
and 11b and the submerged entry nozzle 21 were 25 mm and the
depression depth D was 0 mm, that is, the curved portions 11a and
11b were not formed on the long side walls 3a and 3b. In addition,
the distances L between the curved portions and the submerged entry
nozzle in Table 1 show dimensions at the lower end positions of the
electromagnetic stirring devices 7a and 7b. In addition, the
depression depth D shows dimensions at the height position where
the meniscus 24 is present.
[0075] In addition, in order to check the effects of the Examples
of the present invention, first, a result of operating only the
electromagnetic stirring devices 7a and 7b without operating the
electromagnetic brake devices 8a and 8b is shown in Table 1.
TABLE-US-00001 TABLE 1 Distance between Index of curved portion
Depression number of and submerged depth of Index of inclusions of
entry nozzle curved portion number of casting mold L (mm) D (mm) Ar
gas bubbles parallel portion 25 0 1 1 25 5 1 1 30 5 0.6 1 40 10 0.4
1 50 20 0.2 1 60 30 0.2 1.1 70 40 0.2 1.2 80 50 0.2 1.3 85 55 0.2
2.0
[0076] According to the result shown in Table 1, in a case where
the distance L was 25 mm, even when the curved portions 11a and 11b
having a depression depth D of 5 mm were formed, similarly to the
case where the depression depth D was 0 mm, both the index of the
number of Ar gas bubbles and the index of the number of inclusions
were 1, and it was found that the number of Ar gas bubbles and
inclusions could not be reduced.
[0077] However, at a distance L of 30 mm, even though the
depression depth D was 5 mm and small, the index of the number of
Ar gas bubbles was reduced to 0.6.
[0078] In addition, at a distance L of 80 mm, the index of the
number of Ar gas bubbles was 0.2 which is a low level. Moreover,
the index of the number of inclusions was 1.3 which is also a low
level. However, it was seen that at a distance L of 85 mm, the
index of the number of inclusions was rapidly increased to 2.0.
EXAMPLE 2
[0079] Next, under the same conditions as those of Example 1, the
electromagnetic stirring devices 7a and 7b were also used while
operating the electromagnetic brake devices 8a and 8b, and the
result is shown in Table 2.
TABLE-US-00002 TABLE 2 Distance between Index of curved portion
Depression number of and submerged depth of Index of inclusions of
entry nozzle curved portion number of casting mold L (mm) D (mm) Ar
gas bubbles parallel portion 25 0 1 1 25 5 1 1 30 5 0.5 1 40 10 0.3
1 50 20 0.1 1 60 30 0.1 1 70 40 0.1 1.1 80 50 0.1 1.2 85 55 0.1
1.8
[0080] According to the result shown in Table 2, the same tendency
as in the case where the electromagnetic brakes 8a and 8b were not
operated was shown. That is, in a case where the distance L was 25
mm, even when the curved portions 11a and 11b having a depression
depth D of 5 mm were formed, both the index of the number of Ar gas
bubbles and the index of the number of inclusions were 1, and there
was no change from the case where the depression depth D was 0 mm.
Therefore, the number of Ar gas bubbles and inclusions could not be
reduced.
[0081] On the other hand, at a distance L of 30 mm, even when the
depression depth D was 5 mm, the index of the number of Ar gas
bubbles was halved to 0.5.
[0082] In addition, at a distance L of 80 mm, the index of the
number of Ar gas bubbles was 0.1 and was further reduced compared
to 0.2 shown in Table 1. Therefore, it could be confirmed that in
the case where the electromagnetic brake devices 8a and 8b were
also used, there was an effect in removing Ar gas bubbles. However,
at a distance L of 85 mm, it was seen that the effect of removing
Ar gas bubbles was still high, and the index of the number of
inclusions was rapidly increased to 1.8.
INDUSTRIAL APPLICABILITY
[0083] The present invention is effective in supplying molten steel
into a casting mold and producing a cast piece.
BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS
[0084] 1: CONTINUOUS CASTING APPARATUS
[0085] 2: CASTING MOLD
[0086] 3a, 3b: LONG SIDE WALL
[0087] 4a, 4b: SHORT SIDE WALL
[0088] 5a, 5b, 6a, 6b: BACK PLATE
[0089] 7a, 7b: ELECTROMAGNETIC STIRRING DEVICE
[0090] 8a, 8b: ELECTROMAGNETIC BRAKE DEVICE
[0091] 9a, 9b: CURVED REGION
[0092] 11a, 11b, 11c: CURVED PORTION
[0093] 21: SUBMERGED ENTRY NOZZLE
[0094] 22: DISCHARGE HOLE
[0095] 23: DISCHARGE FLOW
[0096] 24: MENISCUS
[0097] 25: MOLTEN POWDER
[0098] 26: SOLIDIFIED SHELL
[0099] M: MOLTEN STEEL
* * * * *