Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
MAGNETIC BRAKE APPARATUS FOR CONTINUOUS CASTING MOLD AND
CONTINUOUS CASTING METHOD USING THE SAME
Technical Field
The present invention relates to magnetic or solenoid
brake apparatuses for continuous casting molds and
continuous casting methods using the same. The present
invention particularly relates to a magnetic brake apparatus
for a continuous casting mold which is suitably applied when
a static magnetic field is generated in molten steel in a
mold used in continuous casting to control the flow of the
molten steel, and to a continuous casting method using the
same.
Background Art
~ In general, in continuous casting of slabs, molten
steel reserved in a tundish is introduced into a continuous
casting mold via an sub-entry nozzle connected to the bottom
of the tundish, although no drawing is shown. In this case,
the flow rate of the molten steel discharged from the
discharging opening of the sub-entry nozzle is significantly
higher than the casting rate. Thus, when inclusions or/and
bubbles in the molten steel are deeply penetrated and
captured by solidified shells, these inevitably cause
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defects of the product. When the upward flow is dominant in
the jet stream of the molten steel, the rise of the mold
meniscus promotes fluctuation of the melt surface, resulting
in adverse effects on the slab quality and casting operation
In order to avoid such a problem, for example, Japanese
Patent Laid-Open No. 3-142049 discloses a continuous casting
technology for preventing the occurrence of the above-
mentioned problem, in which a static magnetic field is
applied to the molten steel in the casting mold to brake the
flow of the molten steel in the casting mold.
Fig. 6A iS a cross-sectional view of a main portion of
a casting apparatus disclosed in the above-mentioned patent,
and Fig. 6B is an enlarged longitudinal cross-sectional view
of a part of Fig. 6A. In the drawings, numeral 101
represents a continuous casting mold comprising a pair of
short side walls lOlA and a pair of long side walls lOlB,
its inside being cooled by water. Numeral 102 represents an
sub-çntry nozzle for supplying the molten steel from a
tundish (not shown in the drawing) to the casting mold 101.
Numerals 103A and 103B represent iron core bodies for
forming a magnetic path. Numerals 104A, 104B, 105A and 105B
represent upper and lower magnetic poles (iron cores) which
are connected to the iron core bodies 103A and 103B and
extend along the width direction of the casting mold 101.
Numeral 106 represents a magnetic field controlling means
.. . . . .
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for controlling the intensity of the static magnetic field
generated between the magnetic poles. The magnetic field
controlling means 106 comprises a bracket 107 fixed to a
support, a bracket 108 fixed to the iron core body 103B, a
pivot pin connecting the two brackets 107 and 108, and a
hydraulic cylinder 110 fixed to the support in which the tip
of the rod is engaged with the iron core body. Numeral 102B
in the drawings represents a discharging opening of the sub-
entry nozzle 102.
When the upper magnetic pole 104A at the left or A side
in Fig. 6A is an N pole and the upper magnetic pole 104B at
the B side is an S pole in the continuous casting mold 101,
an A-to-B magnetic field is generated in the upper magnetic
pole whereas a B-to-A magnetic field is generated in the
lower magnetic pole. When molten steel is supplied into
such a magnetic field, the upward flow is decelerated by the
upper magnetic field while the downward flow is decelerated
by the lower magnetic field. When the intensity of the
static magnetic field is modified between the upper magnetic
pole and the lower magnetic pole in the casting mold 101,
the hydraulic cylinder 110 is operated by the magnetic field
controlling means 106 so that the iron core body rotates
around the pivot pin 109 to change the inter-pole distance
of the upper magnetic poles.
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Disclosure of the Invention
In the technology disclosed in the above-mentioned
patent, a position sensor for exactly adjusting the distance,
in addition to the hydraulic cylinder 110 and the pivot pin
109, is required. Thus, a wide space and many devices are
required for a facility for adjusting the intensity of the
static magnetic field. The patent also discloses another
method for adjusting the magnetic field in which a
nonmagnetic material is inserted in a part of the iron core.
This method, however, has disadvantages, that is, the type,
width of the slab and the intensity of the magnetic field in
response to the casting speed cannot be changed without
limitation in the casting process. Since exchange of the
nonmagnetic material requires long periods of time,
operation efficiency is significantly low.
The present invention has been accomplished for solving
these problems, and it is a first object to provide a
technology which can readily change the intensity of the
magnetic field during casting without expensiveness and
limitation.
It is a second object of the present invention to
produce a high-quality cast product by achieving the first
object.
Brief Description of the Drawings
.... . . . .. .
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Fig. 1 is a cross-sectional view of a main portion
which illustrates an outlined configuration of an embodiment
in accordance with the present invention.
Fig. 2 is a schematic view of a combination of poles of
magnetic fields.
Fig. 3 is a line graph illustrating the quality of a
slab prepared in an example.
Fig. 4 is another line graph illustrating the quality
of a slab prepared in an example.
Fig. 5 is a cross-sectional view of a main portion
which illustrates an outlined configuration of another
embodiment in accordance with the present invention.
Fig. 6 is an outlined cross-sectional view of a
conventional casting mold.
Fig. 7 is a cross-sectional view of a main portion
which illustrates an outlined configuration of another
embodiment in accordance with the present invention.
Fig. 8 is a schematic view of another combination of
poles of magnetic fields.
Fig. 9 is a schematic view of another combination of
poles of magnetic fields.
<Reference Numerals>
continuous casting mold
12 sub-entry nozzle
14A upper iron core at the free side
"
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14B upper iron core at the fixed side
16A upper coil at the free side
16B upper coil at the fixed side
17A first upper electromagnet
17B second upper electromagnet
18A lower iron core at the free side
18B lower iron core at the fixed side
20A- lower coil at the free side
20B lower coil at the fixed side
21A first lower electromagnet
21B second lower electromagnet
22A connecting iron core
22B connecting iron core
24A current controlling unit
24B current controlling unit
24C current controlling unit
~ 24D current controlling unit
Sm molten steel
Best Mode for Carrying Out the Invention
The embodiments of the present invention will now be
described in detail with reference to the drawings.
Figs. 1 and 7 are cross-sectional views of a main
portion illustrating outlined configurations of embodiments
in accordance with the present invention. The magnetic
.. .. . . .. ..
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brake apparatus in these embodiments in accordance with the
present invention is applied to a continuous casting mold
shown by reference numeral 10 in the drawings. The
continuous casting mold 10 is substantially the same as that
shown in Fig. 6. Cooling water circulates through the
interior of the side wall, and molten steel Sm is supplied
to the continuous casting mold 10 through a discharging
opening (not shown in the drawings) of an sub-entry nozzle
12. The magnetic brake apparatus in these embodiments has a
first upper electromagnet 17A comprising an upper iron core
14A which is placed near the rear face of the side wall of
the continuous casting mold 10 at the free side (the left
side in the drawings) and lies slightly above the
discharging opening of the sub-entry nozzle 12, and an upper
magnetic coil 16A wound around the electromagnet; and a
second upper electromagnet 17B at the fixed side (the right
side in the drawings) in the position of the same height
comprising an upper iron core 14B and an upper magnetic coil
16B. The first and second upper electromagnets 17A and 17B
are oppositely placed with the continuous casting mold 10
intervening therebetween.
In Fig. 1, a first lower electromagnet 21A at the free
side comprising a lower iron core 18A and a lower magnetic
coil 20A, and a second lower electromagnet 21B at the fixed
side comprising a lower iron core 18B and a lower magnetic
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coil20B are provided below the upper electromagnet. These
two electromagnets 21A and 21B are also oppositely placed.
The upper iron cores 14A and 14B and the lower iron cores
18A and 18B are integrally formed with connecting iron cores
22A and 22B provided therebetween, and are magnetically
connected to each other. In this embodiment, a current is
supplied to these two upper magnetic coils 16A and 16B being
constituents of the first and second upper electromagnets
through an upper current controlling unit 24A, and
independently, a current is supplied to these two lower
magnetic coils 20A and 20B being constituents of the first
and second lower electromagnets through a lower current
controlling unit 24B. These currents are independently
controllable.
That is, a current of a given ampere is applied to the
two upper magnetic coils 16A and 16B, whereas a current of
another ampere is applied to the two lower magnetic coils
20A and 20B. The intensities of the static magnetic fields
between the upper electromagnets 1 7A and 1 7B and between the
lower electromagnets 21A and 21B are independently
adjustable.
In Fig. 7, a first lower electromagnet 21A at the free
side comprising a lower iron core 18A and a lower magnetic
coil20A and a second lower electromagnet 21B at the fixed
side comprising a lower iron core 18B and a lower magnetic
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coil 20B are provided below the upper electromagnets. These
two electromagnets are also oppositely placed. The upper
iron cores 14A and 14B and the lower iron cores 18A and 18B
are integrally formed with connecting iron cores 22A and 22B
provided therebetween and are magnetically connected to each
other. Different currents are independently supplied to the
four magnetic coils 16A, 16B, 20A and 20B through current
controlling units 24A to 24D.
The operation of the embodiments will now be described.
In Fig. 1, when normal static magnetic fields are
generated at the upper and lower portions, two current
controlling units 24A and 24B independently control the
currents for the upper electromagnets 17A and 17B and the
lower electromagnets 21A and 21B. Thus, as shown in the
relationship of the magnetic poles of the upper and lower
electromagnets in Fig. 2, when the upper magnetic pole at
the free side is an S pole, the opposing upper magnetic pole
at the fixed side is an N pole, the lower magnetic pole at
the free side is an N pole, and the lower magnetic pole at
the fixed side is an S pole. That is, poles opposing each
other across the molten steel and the upper and lower poles
on the same side are different from each other. In this
embodiment, in order to prevent capture of mold powder at
the meniscus section of the molten steel, the upper magnetic
field may be enhanced to moderate the fluctuation of the
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molten surface. In order to prevent penetration of
nonmetallic inclusions into the deep interior of the molten
steel, the lower magnetic field may be lowered to suppress
the downward flow of the molten steel in the casting mold.
The upper and lower electromagnets can appropriately control
the intensities of the magnetic fields to adequately control
the flow of the molten steel depending on the purposes.
Thus, the quality of the cast slab is improved by
casting while adequately controlling the intensities of the
static magnetic fields by the upper and lower electromagnets
in response to the width and type of the slab and the
casting speed using the magnetic brake apparatus of this
embodiment.
In Fig. 7, when normal static magnetic fields are
generated at the upper and lower portions, the four current
controlling units 24A to 24D independently control the
currents for the corresponding electromagnets. Thus, as
shown in the relationship of the magnetic poles of the upper
and lower electromagnets in Fig. 2, poles opposing each
other across the molten steel and the upper and lower poles
on the same side are different from each other. In this
case, the most effective results are achieved when the
currents of the magnetic coils for the opposing poles are
the same. In order to prevent capture of mold powder at the
meniscus section of the molten steel, the upper magnetic
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field may be enhanced to moderate the fluctuation of the
molten surface. In order to prevent penetration of
nonmetallic inclusions into the deep interior of the molten
steel, the lower magnetic field may be lowered to suppress
the downward flow of the molten steel in the casting mold.
In conventional apparatuses, it is impossible to make
the intensity of the upper or lower magnetic field zero even
when the current to the magnetic coil is zero, because the
upper and lower iron cores are magnetically connected to
each other through the connecting iron core. In contrast,
in this embodiment, the direction of the current of one
magnetic coil between the two opposing electrodes is
inverted by the current controlling units 24A to 24D so that
the opposing magnetic poles are the same as shown in Figs. 8
and 9. The intensity of the magnetic field thereby becomes
zero.
~ Thus, in order to prevent inclusion of non-metallic
impurities into the solid shell at the meniscus section for
the purpose of securing the quality below the skin rather
than capture of powder by the fluctuation of the molten
surface, or in order to prevent capture of bubbles of argon
gas blown into the steel so that the discharging opening of
the sub-entry nozzle is not clogged, a magnetic field of
zero between the upper electromagnets is effective when the
flow of the molten steel is required at the meniscus section.
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This embodiment can readily perform such a control.
<EXAMPLE>
An example of the embodiment will now be described.
Continuous casting was performed under the following
conditions using a mold having a magnetic brake apparatus in
accordance with the embodiment shown in Fig. 1 or 7 to
produce a cast slab of low-carbon aluminum-killed steel.
Its surface and internal quality was examined. Fig. 3 shows
the results when the intensity of the lower magnetic field
was fixed to 2,400 gauss while the intensity of the upper
magnetic field was varied. On the other hand, Fig. 4 shows
the results when the intensity of the upper magnetic field
was fixed to 2,500 gauss.
[Casting Conditions]
Casting speed: 2.5 m/min
Width of slab: 1,400 mm
~ Thickness of slab 220 mm
Intensity of lower magnetic field: 2,000 to 3,000 gauss
Intensity of upper magnetic field: 2,000 to 3,000 gauss
The results shown in Figs. 3 and 4 illustrate that
adjustment of the intensity of the magnetic field in
response to the operational conditions is significantly
effective.
As described above, since the flow of the molten steel
can be appropriately controlled in the casting mold in this
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embodiment, inclusion of non-metallic impurities into the
molten steel pool by the jet stream of the molten steel and
capture of mold powder into the molten steel by the
fluctuation of the molten surface at the meniscus section
are prevented. Accordingly, a high-quality slab can be
produced with high efficiency.
Another embodiment in accordance with the present
invention will now be described.
Fig. 5 is a cross-sectional view, which corresponds to
Fig. 1, of an outlined configuration of a magnetic brake
apparatus in accordance with the present invention. The
magnetic brake apparatus in this embodiment has no
connecting iron cores 22A and 22B, shown in Fig. 1, for
magnetically connecting the upper and lower iron cores at
the free and fixed sides, and thus upper and lower iron
cores 14A, 14B, 18A and 18B are magnetically independent of
each other. Other configurations are substantially the same
as those in the first embodiment.
Since the upper and lower iron cores at the same side
are not magnetically connected to each other in this
embodiment, the input current generates a magnetic field
with a lower intensity than that in the above-mentioned
embodiment. Similar control can, however, be performed and
the static magnetic field of either the upper or lower
electromagnet can be set to be near zero.
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Although the present invention has been described in
detail, the present invention is not limited to the above-
mentioned embodiments and includes various modifications
within a scope without departing from the gist of the
present invention.
14
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, .
Industrial Applicability
According to the present invention as described above,
the intensity of the magnetic field between the magnetic
poles of the upper and lower electromagnets can be readily
and inexpensively varied during casting without restriction.
