【DESCRIPTION】
【Invention Title】
CONTINUOUS CASTING AND ROLLING APPARATUS AND METHOD
【Technical Field】
The present disclosure relates to a continuous
casting and rolling apparatus and method, and more
particularly, to a technique for preventing wastage of a
strand or steel sheet during switching from a discontinuous
rolling mode to a continuous rolling mode.
【Background Art】
In a minimill process, a strand solidified in a
continuous caster is rolled using the high temperature of
the strand. Since such minimill processes incurs relatively
low equipment costs and operating costs, as compared to
conventional processes, minimill processes are now widely
used.
In addition to such continuous casting and rolling
processes, a discontinuous rolling process may be performed
independently of the continuous casting process. This
technique is disclosed in Korean Patent Application Laidopen
Publication No. 1990-7001437.
That is, as illustrated in FIGS. 1A and 1B, a rolling
process may be continuously performed, together with a
continuous casting process, or a rolling process may be
3
discontinuously performed together with a continuous
casting process in a discontinuous rolling mode.
FIG. 1A illustrates equipment 1' for a continuous
rolling process. Referring to FIG. 1A, a strand 2' having a
constant thickness is produced by a continuous caster 100',
and the strand 2' is primarily rolled by a first rolling
unit 210'. Thereafter, while maintaining the temperature of
the strand 2' using an insulator K, the strand 2' is
transferred to a heater 300' and heated to a final rolling
temperature, and then finally rolled by a second rolling
unit 220' to produce a steel sheet 2a'. After the final
rolling, the steel sheet 2a' is cut by a cutting machine
410' and wound around a rewinder R. In this manner, a
rolled steel sheet 2a' may be produced.
FIG. 1B illustrates equipment 1' for a discontinuous
rolling process. Referring to FIG. 1B, a strand 2' having a
constant thickness is produced by a continuous caster 100',
and the strand 2' is primarily rolled by a first rolling
unit 210'. Thereafter, the strand 2' is cut using a cutting
machine 410' before the strand 2' is transferred to a
second rolling unit 220’. Therefore, a rolling process may
be performed independently of the rate of casting of the
continuous caster 100.
A slab cut from the strand 2' is wound around an
4
intermediate coiler, and then the slab is transferred to a
second rolling unit 220' after being heated to a rolling
temperature by a heater 300'. The second rolling unit 220'
rolls the slab to produce a rolled steel sheet 2a', and a
rewinder R winds the rolled steel sheet 2a'.
Even when a steel sheet 2a', wound around the
intermediate coiler, is unwound and transferred to the
second rolling unit 220' during switching from the
discontinuous rolling process to a continuous rolling
process, the continuous caster 100' continuously produces a
steel sheet 2a'. Thus, a portion of the steel sheet 2a' is
inevitably cut and discarded.
To address this problem, research into continuous
casting and rolling apparatuses and methods is needed.
【Disclosure】
【Technical Problem】
An aspect of the present disclosure may provide a
continuous casting and rolling apparatus and method
allowing for switching between a continuous rolling mode
and a discontinuous rolling mode while preventing wastage
of a strand produced by a continuous caster during
switching from the discontinuous rolling mode to the
continuous rolling mode.
【Technical Solution】
5
According to an aspect of the present disclosure, a
continuous casting and rolling apparatus may include: a
continuous caster configured to produce a strand; a rolling
mill configured to produce a rolled steel sheet by rolling
the strand, the rolling mill including a first rolling unit
connected to the continuous caster and a second rolling
unit spaced apart from an exit side of the first rolling
unit; and a cut withdrawal unit including a cutting machine
configured to cut the strand, the cutting machine being
disposed between the first and second rolling units and
spaced apart from the second rolling unit by a distance at
least equal to a length of the strand required for final
production and discharging the rolled steel sheet.
The cutting machine may be spaced apart from the
second rolling unit by a distance satisfying the following
formula: SL + 6 < D < 2×SL + 12 where SL refers to the
length of the strand, D refers to the distance between the
cutting machine and the second rolling unit, and SL and D
are in meters (m).
The cut withdrawal unit may further include a
withdrawing machine disposed between the cutting machine
and the second rolling unit to remove a cut portion of the
steel sheet.
The rolling mill may further include a third rolling
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unit disposed at an exit side of the second rolling unit,
and the continuous casting and rolling apparatus may
further include a heater disposed at an entrance side of
the second rolling unit and a heater disposed between the
second rolling unit and the third rolling unit.
According to another aspect of the present disclosure,
a continuous casting and rolling method allowing for
switching between a continuous rolling mode and a
discontinuous rolling mode may include: producing a strand
by continuous casting; after producing the strand by
continuous casting, rolling the strand using a rolling mill
to produce a rolled steel sheet; and cutting the strand in
the discontinuous rolling mode before finishing the rolling
of the strand, wherein the cutting of the steel sheet is
performed using a cutting machine spaced apart from a
second rolling unit by a distance at least equal to a cut
length of the strand in the discontinuous rolling mode.
The rolling of the strand may include: after the
producing of the strand by continuous casting, primarily
rolling the strand to produce a first rolled steel sheet,
the primary rolling being performed in the continuous
rolling mode; and receiving and secondarily rolling the
strand or the first rolled steel sheet to produce a second
rolled steel sheet, the secondary rolling being performed
7
in the continuous rolling mode and the discontinuous
rolling mode.
The primary rolling may also be performed in the
discontinuous rolling mode to obtain a final rolled steel
sheet thickness of 1.5 mm to 4 mm.
【Advantageous Effects】
According to the continuous casting and rolling
apparatus and method of the present disclosure, a strand or
steel sheet is not partially discarded during switching
from a discontinuous rolling mode to a continuous rolling
mode
Therefore, the yield of a continuous casting and
rolling process may be improved.
【Description of Drawings】
FIGS. 1A and 1B are views illustrating continuous
casting and rolling apparatuses of the related art.
FIG. 2 is a process view of a continuous casting and
rolling apparatus according to an exemplary embodiment of
the present disclosure.
FIGS. 3 and 4 are flowcharts illustrating a
continuous casting and rolling method according to an
exemplary embodiment of the present disclosure.
【Best Mode】
Exemplary embodiments of the present disclosure will
8
now be described in detail with reference to the
accompanying drawings. The disclosure may, however, be
exemplified in many different forms and should not be
construed as being limited to the specific embodiments set
forth herein. Rather, these embodiments are provided so
that the disclosure will be thorough and complete, and will
fully convey the scope of the present invention to those
skilled in the art.
In the drawings, the shapes and dimensions of
elements may be exaggerated for clarity, and the same
reference numerals will be used throughout to designate the
same or like elements.
The present disclosure relates a continuous casting
and rolling apparatus and method designed to secure a space
having at least a length SL corresponding to a length of a
strand 2 required for producing a final rolled steel sheet
2a and thus to prevent the loss of the strand 2 or the
rolled steel sheet 2a during switching from a discontinuous
rolling mode to a continuous rolling mode
That is, according to the continuous casting and
rolling apparatus and method of the present disclosure, a
second rolling unit 220 and a cut withdrawal unit 400 may
be spaced apart from each other by at least a length SL
corresponding to a length of a strand 2 required for
9
producing and discharging a final rolled steel sheet 2a,
and thus, during switching from a discontinuous rolling
mode to a continuous rolling mode, some of the strand 2 or
the rolled steel sheet 2a may not be discarded. Therefore,
the productivity of a continuous rolling process may be
improved.
In detail, FIG. 2 is a process view of a continuous
casting and rolling apparatus 1 according to an exemplary
embodiment of the present disclosure. Referring to FIG. 2,
the continuous casting and rolling apparatus 1 of the
exemplary embodiment may include: a continuous caster 100
configured to produce a strand 2; a rolling mill 200
including a first rolling unit 210 associated with the
continuous caster 100 and a second rolling unit 220 spaced
apart from an exit side of the first rolling unit 210, the
rolling mill 200 being configured to produce a rolled steel
sheet 2a by rolling the strand 2; and a cut withdrawal unit
400 including a cutting machine 410 configured to cut the
strand 2, the cutting machine 410 being disposed between
the first rolling unit 210 and the second rolling unit 220
and spaced apart from the second rolling unit 220 by at
least a length SL corresponding to a length of the strand 2
required for final production and discharging the rolled
steel sheet 2a.
10
In the continuous casting and rolling apparatus 1 of
the exemplary embodiment, the cutting machine 410 may be
spaced apart from the second rolling unit 220 by a distance
D satisfying the formula: SL + 6 < D < 2SL + 12. In the
formula, SL refers to a length corresponding to a length of
a strand 2 required for producing and discharging a final
rolled steel sheet 2a, D refers to the distance between the
cutting machine 410 and the second rolling unit 220, and SL
and D are in meters (m).
Furthermore, according to the exemplary embodiment,
the cut withdrawal unit 400 of the continuous casting and
rolling apparatus 1 may further include a withdrawing
machine 420 disposed between the cutting machine 410 and
the second rolling unit 220 to remove a cut steel sheet 2a.
Furthermore, according to the exemplary embodiment,
the rolling mill 200 of the continuous casting and rolling
apparatus 1 may further include a third rolling unit 230
disposed at an exit side of the second rolling unit 220,
and the continuous casting and rolling apparatus 1 may
further include a heater 300 disposed at an entrance side
of the second rolling unit 220 and a heater 300 disposed
between the second rolling unit 220 and the third rolling
unit 230.
The continuous caster 100 may produce a strand 2
11
through a casting process. That is, in the continuous
caster 100, molten steel may be supplied from a tundish to
a mold in which the molten steel may be cooled and formed
into a strand 2, and the strand 2 may be guided by guide
rolls to the rolling mill 200 (described later).
Since the continuous caster 100 produces a strand 2
depending on the solidification rate of molten steel, it is
difficult to adjust the production rate of the strand 2.
Therefore, if the strand 2 produced by the continuous
caster 100 is continuously fed into the rolling mill 200 to
produce a rolled steel sheet 2a by rolling the strand 2,
the production rate of the rolled steel sheet 2a may be
limited.
On the other hand, if the strand 2 produced by the
continuous caster 100 is discontinuously fed into the
rolling mill 200 for producing a rolled steel sheet 2a, the
rolling mill 200 may perform a rolling process at a high
production rate to produce a rolled steel sheet 2a
independently of the production rate of the continuous
caster 100.
That is, a rolling process for producing a rolled
steel sheet 2a using the rolling mill 200 from a strand 2
produced by the continuous caster 100 may be performed in a
continuous rolling mode or a discontinuous rolling mode.
12
For example, the rolling process may be performed while
switching between such rolling modes.
The rolling mill 200 may receive a strand 2 produced
by the continuous caster 100 and may produce a rolled steel
sheet 2a by rolling the strand 2. To this end, the rolling
mill 200 may roll the strand 2 or the steel sheet 2a while
passing the strand 2 or the steel sheet 2a between a pair
of rolling rolls. For example, the rolling mill 200 may
include a plurality of rolling roll pairs.
In addition, the rolling mill 200 may include the
first rolling unit 210 and the second rolling unit 220
disposed at different positions.
The first rolling unit 210 of the rolling mill 200
may be connected to a rear end (exit side) of the
continuous caster 100 and may produce a rolled steel sheet
2a in cooperation with the second rolling unit 220 in the
continuous rolling mode. The first rolling unit 210 may
include a stand having a pair of rolling rolls.
That is, in the continuous rolling mode, since a
strand 2 is rolled in a state in which the strand 2 is
connected to the continuous caster 100, the continuous
caster 100 may be negatively affected if rolling starts
suddenly. Thus, the first rolling unit 210 may produce a
first rolled steel sheet 2a having a certain thickness, and
13
then the second rolling unit 220 may finally produce a
second rolled steel sheet 2a.
Therefore, the first rolling unit 210 may only be
used in the continuous rolling mode, and in the
discontinuous rolling mode, the second rolling unit 220 may
only be used to produce a rolled steel sheet 2a by rolling
a strand 2.
Particularly, when a rolling process switches from
the discontinuous rolling mode to the continuous rolling
mode, the first rolling unit 210 performs gradual rolling.
That is, in the discontinuous rolling mode, a strand 2 is
cut and supplied to the second rolling unit 220, and the
cut strand 2 is rolled by the second rolling unit 220.
However, in the continuous rolling mode, a strand 2 is not
cut but is continuously supplied to the second rolling unit
220 in a state in which the strand 2 is engaged with the
first rolling unit 210, and as the second rolling unit 220
engages with the strand 2, rolling is started and continued.
When the rolling process switches from the
discontinuous rolling mode to the continuous rolling mode,
the thickness of a steel sheet 2a passing through the first
rolling unit 210 may be varied. That is, in the
discontinuous rolling mode, the thickness of a steel sheet
2a passing through the first rolling unit 210 may be equal
14
to the thickness of a strand 2 or smaller than the
thickness of the strand 2 due to rolling by the first
rolling unit 210.
After the strand 2 is finally cut in the
discontinuous rolling mode, the strand 2 may have a
transitional thickness region due to rolling by the first
rolling unit 210. In general, the transitional thickness
region of the strand 2 is cut into predetermined lengths
and withdrawn by the cut withdrawal unit 400. Then, if the
thickness of the strand 2 reaches a value proper for the
continuous rolling mode, the strand 2 is not cut and is
supplied to the second rolling unit 220.
At the moment when the strand 2 or steel sheet 2a is
engaged with the second rolling unit 220, the first rolling
unit 210 holds the strand 2 or steel sheet 2a, and thus the
strand 2 or steel sheet 2a may not be moved back to the
continuous caster 100 and may be stably rolled in the
continuous rolling mode.
The second rolling unit 220 may directly receive a
first rolled steel sheet 2a from the first rolling unit 210
or a strand 2 from the continuous caster 100 and may
finally produce a second rolled steel sheet 2a. The second
rolling unit 220 rolls a strand 2 using rolling rolls to
produce a rolled steel sheet 2a, and the rolled steel sheet
15
2a is discharged after being coiled by a rewinder R. The
second rolling unit 220 may include at least one stand
having a pair of rolling rolls.
To this end, the second rolling unit 220 may be
connected to a rear end (exit side) of the first rolling
unit 210, and the cut withdrawal unit 400 may be disposed
between the second rolling unit 220 and the first rolling
unit 210.
Particularly, the second rolling unit 220 may be
spaced apart from the cutting machine 410 of the cut
withdrawal unit 400 by at least a length SL corresponding
to a length of a strand 2 required for producing a rolled
steel sheet 2a to be coiled and discharged as a coil. In
this manner, a space for placing a finally rolled steel
sheet 2a may be provided, and the second rolling unit 220
may be operated independently of the first rolling unit 210.
In addition to the cutting machine 410, the heater
300 (described later) may be disposed between the first
rolling unit 210 and the second rolling unit 220, and the
length SL between the cutting machine 410 and the second
rolling unit 220 may be adjusted by considering an
installation length of the cutting machine 410 and the
heater 300.
That is, the distance D between the cutting machine
16
410 and the second rolling unit 220 may be set by
considering a length SL of a strand 2 required for
producing a final rolled steel sheet 2a to be coiled and
discharged as a coil and an installation length for the
cutting machine 410 and the heater 300.
In general, the installation length for the cutting
machine 410 and the heater 300 may be 6 m.
In addition, the distance D between the cutting
machine 410 and the second rolling unit 220 may be set to
be as short as possible so as to prevent thermal loss in a
strand 2. Thus, only the upper limit of the distance D may
be set.
For example, since an auxiliary space is necessary
for other operations and repairing operations, the upper
limit of the distance D between the cutting machine 410 and
the second rolling unit 220 may be set to be twice the
length SL required for producing a final rolled steel sheet
2a. In addition to this, an auxiliary space for installing
the first rolling unit 210 and the heater 300 may be
considered.
In other words, the distance D between the cutting
machine 410 and the second rolling unit 220 may be at least
equal to or greater than the sum of the length SL of a
strand 2 required for producing a final rolled steel sheet
17
2a and the installation length for the cutting machine 410
and the heater 300. For example, the distance D may be
equal to or shorter than twice the sum of the length SL and
the installation length.
This may be expressed by the formula: SL + 6 < D <
2SL + 12. In the formula, SL refers to a length
corresponding to a length of a strand 2 necessary for
producing and discharging a final rolled steel sheet 2a, D
refers to the distance between the cutting machine 410 and
the second rolling unit 220, and SL and D are in meters (m).
The distance D may be varied according to the length
of a strand 2 produced by the continuous caster 100. That
is, if the thickness of a strand 2 increases, a relatively
short length of a strand 2 is necessary for producing a
final coil 2a, and thus an absolute length required to
accommodate a piece of the strand 2 is varied.
Owing to such a space, during switching from the
discontinuous rolling mode to the continuous rolling mode,
a strand 2 or rolled steel sheet 2a may not be discarded
except for a length of the strand 2 or rolled steel sheet
2a necessary for thickness adjustment.
That is, owing to a space corresponding to the
distance D, during switching from the discontinuous rolling
mode to the continuous rolling mode, a raw material may not
18
be discharged except for a length of the raw material
necessary for thickness adjustment.
In addition, since a length of a strand 2
corresponding to a final coil is placed in a space having a
length corresponding to the length SL of the strand 2 in
the discontinuous rolling mode, the second rolling unit 220
may roll the strand 2 or rolled steel sheet 2a
independently of the first rolling unit 210.
That is, according to the related art, in the
discontinuous rolling mode, an intermediate coiler disposed
next to the first rolling unit 210 receives a first rolled
steel sheet 2a and provides the first rolled steel sheet 2a
to the second rolling unit 220 for second rolling.
In this case, when the process begins to switch from
the discontinuous rolling mode to the continuous rolling
mode, the second rolling unit 220 secondarily rolls a steel
sheet 2a unwound from the intermediate coiler while the
continuous caster 100 continuously produces a strand 2.
Thus, a part of the strand 2 produced during this period
can not be transferred to the intermediate coiler or the
second rolling unit 220, and thus the part of the strand 2
is cut and discarded.
However, according to the exemplary embodiment of the
present disclosure, instead of using an intermediate coiler,
19
a space corresponding to a length SL of a strand 2 produced
in the discontinuous rolling mode is provided between the
cutting machine 410 and the second rolling unit 220, and
thus, during switching from the discontinuous rolling mode
to the continuous rolling mode, some of a steel sheet 2a
may not be discarded, thereby preventing waste.
In addition, since the heater 300 (described later)
is disposed at the entrance side of the second rolling unit
220, a strand 2 or steel sheet 2a may be heated before
rolling.
Furthermore, the rolling mill 200 may further include
the third rolling unit 230 at the exit side of the second
rolling unit 220, and thus a steel sheet 2a rolled by the
second rolling unit 220 may be further rolled to a thinner
thickness by using the third rolling unit 230. The third
rolling unit 230 may include at least two stands, each
including a pair of rolling rolls.
If the period during which a steel sheet 2a is rolled
by the second rolling unit 220 is long, the steel sheet 2a
may be cooled to a temperature not suitable for rolling.
For this case, another heater 300 may be disposed between
the second rolling unit 220 and the third rolling unit 230.
Furthermore, in the continuous rolling mode or the
discontinuous rolling mode, if the thickness of a steel
20
sheet 2a rolled by the second rolling unit 220 is
insufficient, the steel sheet 2a may be further rolled
using the third rolling unit 230.
As described above, the continuous casting and
rolling apparatus 1 of the exemplary embodiment includes
the heater 300 between the first rolling unit 210 and the
second rolling unit 220, and if the temperature of a steel
sheet 2a is insufficiently high when the first rolling unit
210 or the second rolling unit 220 is operated, the steel
sheet 2a may be heated using the heater 300.
In addition, when the third rolling unit 230 is
further provided, another heater 300 may be disposed
between the second rolling unit 220 and the third rolling
unit 230.
In addition, the heaters 300 may include insulators
for maintaining the temperature of a steel sheet 2a for a
longer time. For example, the insulators may surround at
least one side of a strand 2 or steel sheet 2a so as to
maintain the temperature of the strand 2 or steel sheet 2a.
The insulators may be arranged entirely around a
strand 2 or steel sheet 2a for efficient insulation, and
insulation gas may be supplied to the insulators for more
efficient insulation.
The insulators may be formed of refractory bricks
21
including a ceramic material. The insulators may be
provided in the form of holding furnaces.
The cut withdrawal unit 400 may cut a strand 2 or
steel sheet 2a or withdraw the strand 2 or steel sheet 2a.
To this end, the cut withdrawal unit 400 may include the
cutting machine 410 and the withdrawing machine 420.
A plurality of cutting machines 410 may be provided
in a region between the first rolling unit 210 and the
second rolling unit 220 and a region beside the exit side
of the second rolling unit 220.
Particularly, the cutting machine 410 may be spaced
apart from the second rolling unit 220 by a distance equal
to at least a length SL of a strand 2 required for
producing and discharging a final rolled steel sheet 2a. In
this case, a strand 2 produced by the continuous caster 100
may not be wasted as described above.
The withdrawing machine 420 may discharge a defective
strand 2 or steel sheet 2a. That is, the withdrawing
machine 420 disposed between the first rolling unit 210 and
the second rolling unit 220 may remove defective steel
sheets from first steel sheets 2a produced by the first
rolling unit 210.
In other words, the withdrawing machine 420 may
remove a defective strand 2 produced by the continuous
22
caster 100 at an early stage of continuous casting or a
defective steel sheet 2a having an uneven thickness
produced when the first rolling unit 210 performs gradual
rolling during switching from the discontinuous rolling
mode to the continuous rolling mode.
In addition, the cut withdrawal unit 400 may include
another cutting machine 410 at the exit side of the second
rolling unit 220 so as to cut a steel sheet 2a to be coiled
in the continuous rolling mode.
FIGS. 3 and 4 are flowcharts illustrating a
continuous casting and rolling method according to an
exemplary embodiment of the present disclosure. FIG. 4 is a
flowchart illustrating the continuous casting and rolling
method in a continuous rolling mode, and FIG. 5 is a
flowchart illustrating how the first rolling unit 210 and
the cut withdrawal unit 400 are operated in the continuous
rolling mode and a discontinuous rolling mode. Switching
between the discontinuous rolling mode and the continuous
rolling mode is possible by varying operations of the first
rolling unit 210 and the cut withdrawal unit 400.
Referring to FIGS. 3 and 4, according to the
exemplary embodiment of the present disclosure, the
continuous casting and rolling method may be performed
while switching between the continuous rolling mode and the
23
discontinuous rolling mode. The continuous casting and
rolling method may include: a continuous casting process to
produce a strand 2; a process of rolling the strand 2 using
the rolling mill 200 after the continuous casting process,
so as to produce a rolled steel sheet 2a; and a process of
cutting the strand 2 in the discontinuous rolling mode
before the rolling process is finished, the cutting process
being performed using the cutting machine 410 spaced apart
from the second rolling unit 220 by at least a length SL
corresponding to a cut length of the strand 2.
According to the exemplary embodiment, after the
continuous casting process, the rolling process of the
continuous casting and rolling method may include a primary
rolling process to produce a first rolled steel sheet 2a by
rolling the strand 2 in the continuous rolling mode; and a
secondary rolling process to produce a second rolled steel
sheet 2a from the strand 2 or the first rolled steel sheet
2a in the continuous rolling mode and the discontinuous
rolling mode.
In the continuous casting and rolling method of the
exemplary embodiment, the primary rolling process may be
also performed in the discontinuous rolling mode to obtain
a final rolled steel sheet 2a having a thickness of 1.5 mm
to 4 mm.
24
In the continuous casting process, the strand 2 is
produced by the continuous caster 100. That is, the
continuous caster 100 continuously receives molten steel
and produces the strand 2. At an early stage of the
continuous casting process, the strand 2 is produced in a
state not satisfying required conditions, and thus an early
length of the strand 2 may be cut and discarded using the
cut withdrawal unit 400 connected to an exit side of the
continuous caster 100.
In the rolling process, the strand 2 produced in the
continuous casting process is received and rolled to
produce a rolled steel sheet 2a.
The rolling process may be performed in the
continuous rolling mode so as to produce a rolled steel
sheet 2a by continuously receiving the strand 2 produced in
the continuous casting process. In the continuous rolling
mode, the rolling process may be performed through the
primary rolling process and the secondary rolling process.
In this case, the continuous caster 100 may be less
affected by the rolling process.
That is, the primary rolling process may be performed
to obtain a primarily rolled steel sheet 2a having a
certain thickness before a final thickness, and the
secondary rolling process may be performed after the
25
primary rolling process so as to finally obtain a
secondarily rolled steel sheet 2a by rolling the primarily
rolled steel sheet 2a.
The primary rolling process may not be performed in
the discontinuous rolling mode. That is, the primary
rolling process may only be performed in the continuous
rolling mode.
However, this is a non-limiting example. For example,
in the discontinuous rolling mode, if the thickness of a
rolled steel sheet 2a finally produced through the
secondary rolling process is insufficiently, the primary
rolling process may be performed as a preliminary rolling
process.
In detail, even in the discontinuous rolling mode, if
it is required to produce a rolled steel sheet 2a having a
final thickness of 1.5 mm to 4 mm, the primary rolling
process may be performed to preliminarily roll a strand 2
produced by the continuous caster 100.
The primary rolling process may be performed after
the continuous casting process, and the secondary rolling
process may be performed after the primary rolling process.
In addition, so as to produce a rolled steel sheet 2a
having improved qualities, a heating process may be
performed between the continuous casting process and the
26
primary rolling process, and another heating process may be
performed between the primary rolling process and the
secondary rolling process.
Because the heating process between the primary
rolling process and the secondary rolling process provides
additional heating, the heating process may be referred to
as an additional heating process.
If a defective strand 2 not satisfying required
conditions is produced at an early stage of the continuous
casting process, a first cutting/withdrawing process may be
performed to remove the defective strand 2. The first
cutting/withdrawing process may be performed after
determining whether the continuous casting process is at
its early stage or not.
In the first cutting/withdrawing process, the cutting
machine 410 disposed at the exit side of the first rolling
unit 210 may be operated to cut out a defective leading end
part of the strand 2 produced by the continuous caster 100,
and the defective leading end part of the strand 2 may be
discharged to the outside by the withdrawing machine 420.
As described above, the continuous casting and
rolling method of the exemplary embodiment may further
include a heating process so as to produce a steel sheet 2a
having improved qualities by heating a strand 2 and then
27
transferring the strand 2 to the rolling mill 200.
If the heating process is performed before the
rolling process, a rolled steel sheet 2a produced by
rolling a strand 2 may have improved qualities. That is, if
the heating process is performed between the primary
rolling process, the secondary rolling process, and a
gradual rolling process (described later) of the rolling
process, a rolled steel sheet 2a having improved qualities
may be produced.
According to the exemplary embodiment, the continuous
casting and rolling method may be performed while switching
between the continuous rolling mode and the discontinuous
rolling mode. In this case, although the continuous caster
100 is not affected during switching from the continuous
rolling mode to the discontinuous rolling mode, the
continuous caster 100 may be affected during switching from
the discontinuous rolling mode to the continuous rolling
mode. Thus, a particular process may be performed.
In detail, while a strand 2 is continuously produced
by the continuous caster 100, if the strand 2 is suddenly
rolled by the rolling mill 200, the moving speed of the
strand 2 at the continuous caster 100 may be suddenly
decreased, or the strand 2 may be moved backwards because
of a reduction of the thickness of the strand 2 in the
28
rolling mill 200. In this case, the surface of molten steel
may suddenly rise.
To prevent such a sudden rise of the surface of
molten steel, the rolling process may include a gradual
rolling process. That is, rolling may be performed while
gradually reducing a gap between the rolling rolls of the
first rolling unit 210, so as to prevent the continuous
caster 100 from being impacted.
However, due to the gradual rolling process, a steel
sheet 2a having a thickness transition region in which the
thickness of the rolled steel sheet 2a is gradually reduced
may be produced. Since the thickness transition region of
the steel sheet 2a may cause a decrease in the quality of
the steel sheet 2a when the steel sheet 2a is rolled by the
second rolling unit 220. The thickness transition region
may be cut and removed from the steel sheet 2a.
To this end, a second cutting/withdrawing process may
be performed after the gradual rolling process. In the
second cutting/withdrawing process, a defective region of a
steel sheet 2a produced by the first rolling unit 210 may
be cut out using the cutting machine 410, and the cut
defective region may be discharged to the outside using the
withdrawing machine 420. Thus, the quality of the steel
sheet 2a may be improved.
29
In addition, since a rolled steel sheet 2a not having
a defective region is produced as described above, after
the rolled steel sheet 2a is wound into a coil, the whole
coil may not be discarded because of a partial defective
region of the rolled steel sheet 2a.
30
【WE CLAIM:】
【Claim 1】
A continuous casting and rolling apparatus comprising:
a continuous caster configured to produce a strand;
a rolling mill configured to produce a rolled steel
sheet by rolling the strand, the rolling mill comprising a
first rolling unit connected to the continuous caster and a
second rolling unit spaced apart from an exit side of the
first rolling unit; and
a cut withdrawal unit comprising a cutting machine
configured to cut the strand, the cutting machine being
disposed between the first and second rolling units and
spaced apart from the second rolling unit by a distance at
least equal to a length of the strand required for final
production and discharging the rolled steel sheet.
【Claim 2】
The continuous casting and rolling apparatus of claim
1, wherein the cutting machine is spaced apart from the
second rolling unit by a distance satisfying the following
formula:
SL + 6 < D < 2×SL + 12
where SL refers to the length of the strand, D refers
to the distance between the cutting machine and the second
rolling unit, and SL and D are in meters (m).
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【Claim 3】
The continuous casting and rolling apparatus of claim
1, wherein the cut withdrawal unit further comprises a
withdrawing machine disposed between the cutting machine
and the second rolling unit to remove a cut portion of the
steel sheet.
【Claim 4】
The continuous casting and rolling apparatus of claim
1, wherein the rolling mill further comprises a third
rolling unit disposed at an exit side of the second rolling
unit, and
the continuous casting and rolling apparatus further
comprises heaters disposed at an entrance side of the
second rolling unit, and the third rolling unit.
【Claim 5】
A continuous casting and rolling method allowing for
switching between a continuous rolling mode and a
discontinuous rolling mode, the continuous casting and
rolling method comprising:
producing a strand by continuous casting;
after producing the strand by continuous casting,
rolling the strand using a rolling mill to produce a rolled
steel sheet; and
cutting the strand in the discontinuous rolling mode
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before finishing the rolling of the strand, wherein the
cutting of the steel sheet is performed using a cutting
machine spaced apart from a second rolling unit by a
distance at least equal to a cut length of the strand in
the discontinuous rolling mode.
【Claim 6】
The continuous casting and rolling method of claim 5,
wherein the rolling of the strand comprises:
after the producing of the strand by continuous
casting, primarily rolling the strand to produce a first
rolled steel sheet, the primary rolling being performed in
the continuous rolling mode; and
receiving and secondarily rolling the strand or the
first rolled steel sheet to produce a second rolled steel
sheet, the secondary rolling being performed in the
continuous rolling mode and the discontinuous rolling mode.
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【Claim 7】
The continuous casting and rolling method of claim 5,
wherein the primary rolling is also performed in the
discontinuous rolling mode to obtain a final rolled steel
sheet thickness of 1.5 mm to 4 mm.