DESCRIPTION
APPARATUS AND METHOD FOR CONTROLLING HORIZONTAL OSCILLATION OF
AN EDGE DAM OF A TWIN ROLL STRIP CASTER
Technical Field
The present invention relates, in general, to apparatuses
and methods for controlling the horizontal oscillation of edge
dams of twin roll strip casters and, more particularly, to an
apparatus and method for controlling the horizontal
oscillation of an edge dam of a twin roll strip caster which
can prevent a casting roll and the edge dam from being damaged
while oscillating the edge dam to reduce edge skull.
Background Art
Generally, twin roll strip casting is a process including
supplying molten steel to two rolls that are rotating, and
continuously producing a strip having a thickness of several
mms directly from the molten steel.
Fig. 1 is a perspective view of a typical twin roll strip
caster. Fig. 2 is of schematic views showing skull formed in
an edge dam according to a conventional technique.
As shown in Fig 1, in the typical twin roll strip caster,
molten steel is uniformly supplied from a tundish into the
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space between two casting rolls 110 by a nozzle 120, and the
casting rolls 110 rotate. Then, molten steel forms solidified
layers on the surfaces of the casting rolls 110 that are being
cooled, and the solidified layers unite together with each
other at the closest point between the casting rolls 110, thus
continuously forming a strip having a predetermined thickness.
Two edge dam refractories 150 are respectively provided
on opposite ends of the pair of casting rolls 110 to prevent
molten steel from flowing out of the space between the casting
rolls 110. Both high temperature molten steel that has been
supplied between the casting rolls 110 and the casting rolls
110 that are being cooled by water are simultaneously put in
contact with the active surfaces of the edge dam refractories
150 that have been preheated before casting. Hence, of the
surfaces of the edge dam refractories 150, portions that make
contact with the casting rolls 110 cool rapidly, causing heat
loss in the vicinity thereof, thereby forming conditions under
which molten steel can easily solidify.
Therefore, as shown in Fig. 2, molten steel 131 is
solidified on the active surfaces of the edge dam refractories
150, thus forming edge skull 132 and surface skull 134. Such
skull grows on the surfaces of the edge dam refractories 150.
Of the skull, the edge skull 132 undergoes repeated growth and
removal and then becomes mixed with the edges of a casting
strip 140, deteriorating the quality of the casting strip 140.
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In addition, when the skull hardens, it is compressed, forming
lower skull 133 between the casting rolls 110, thus causing
damage to the casting rolls 110, or inducing the strip to
break.
In an effort to overcome the above problems, a technique
of injecting an inert gas into the molten steel through the
lower portion of the edge dam and preventing the molten steel
from solidifying, and a technique of oscillating the edge dam
refractories at a predetermined amplitude and physically
removing the skull were proposed.
The inert gas injection method of the skull removal
techniques is a technique in which a thin metal tube is
installed on the lower portion of each edge dam refractory and
an inert gas is injected into the molten steel through the
metal tube, thus preventing the molten steel from solidifying,
and reducing skull. This technique is comparatively effective
at reducing skull of the lower portion of the edge dam, but
there still remains the problems of the generation and growth
of surface skull on the inner surface of the edge dam and of
edge skull on junction surfaces between the casting rolls and
the active surface of the edge dam.
As shown in Fig. 3, the edge dam oscillation method of
the skull removal techniques is a technique which oscillates
the edge dam refractories at a predetermined amplitude, thus
physically removing skull. In this technique, when an
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oscillation motor (not shown) is operated, an eccentric shaft
330 rotates. Thereby, a slide bushing 320 comes into contact
with a cover 310, thus generating oscillation. The
oscillation is transmitted to an oscillation plate 300, so
that as shown in Fig. 4a, the lower portion of the oscillation
plate oscillates around a bearing 301 provided on the center
of the oscillation plate in the same manner as that of a
pendulum, thus oscillating the edge dam refractory 142,
thereby preventing the skull from fusing with the edge dam.
However, this technique pertains to a mechanical
oscillating method using an oscillation cam 302, which is
fixed in amplitude. Thus, when it is necessary to change the
amplitude, it is required to replace the eccentric shaft 330,
an eccentric ring or others with new ones before casting, and
depending on a worker, the amplitude may be different. Hence,
even if edge skull forms during the casting, it is impossible
to control the amplitude, forcing the casting operation to be
interrupted. Moreover, because the edge dam refractory
oscillates in the same manner as that of a pendulum, the upper
and lower portions of the edge dam reliably oscillate, but as
it becomes closer to the center of the edge dam, the amplitude
reduces, and a dead zone 200 that does not oscillate is
eventually formed at the center of the edge dam. In the dead
zone, skull is still formed and grown, causing the problem of
mixing with a casting strip. Meanwhile, although it is
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possible to increase the amplitude to prevent the occurrence
of the dead zone, this may damage the edge dam, and fragments
of the damaged edge dam may mix with a casting strip.
Disclosure
Technical Problem
Accordingly, the present invention has been made keeping
in mind the above problems occurring in the prior art, and an
object of the present invention is to provide an apparatus and
method for controlling the horizontal oscillation of an edge
dam of a twin roll strip caster which can rapidly remove edge
skull that is formed by stagnation and solidification of
molten steel, and can effectively suppress the generation and
growth of skull, thus preventing a component such as a casting
roll or an edge dam from being damaged, thereby ensuring the
stability of casting, and improving the quality of a casting
strip.
Technical Solution
In order to accomplish the above object, in an aspect,
the present invention provides an apparatus for controlling
horizontal oscillation of an edge dam of a twin roll strip
caster, the apparatus including an oscillation unit
horizontally oscillating an oscillation plate in accordance
with an oscillation waveform so that an edge dam refractory
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coupled to the oscillation plate horizontally oscillates, a
servo valve outputting the oscillation waveform to the
oscillation unit to perform the horizontal oscillation, and a
control unit applying the oscillation waveform to the servo
valve, thus controlling the horizontal oscillation of the
oscillation unit.
The oscillation unit may include a main body installed
with a hydraulic line, a hydraulic cylinder fastened to the
main body, a cylinder rod placed through the hydraulic
cylinder so as to be movable to opposite sides of the
hydraulic cylinder, and a support connecting opposite ends of
the cylinder rod to opposite ends of the oscillation plate.
The apparatus for controlling the horizontal oscillation
of the edge dam of the twin roll strip caster may further
include an oscillation-unit-displacement measuring device
transmitting information about a real time position of the
oscillation unit to the control unit.
The control unit may include an oscillation information
collector collecting from an HMI (Human Machine Interface)
information about an ON/OFF status of the oscillation, and an
amplitude, a frequency and a waveform of the oscillation, an
oscillation waveform generator generating, using the
information received from the oscillation information
collector, a reference of the oscillation waveform having an
amplitude and a frequency that are required to control the
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horizontal oscillation, and a horizontal oscillation
controller controlling the servo valve both using the
information about the oscillation waveform received from the
oscillation waveform generator and using information about a
position of the oscillation unit that is received from the
oscillation-unit-displacement measuring device, thus
controlling the horizontal oscillation of the oscillation
unit.
The control unit may further include a ramping unit
varying at constant rates the amplitude and the frequency of
the reference of the oscillation waveform generated from the
oscillation waveform generator.
The control unit may further include an oscillation-unitcenter
measuring device transmitting information about a
center position of the oscillation unit to the horizontal
oscillation controller.
The oscillation waveform may comprise a sine wave, a
rectangular wave or a triangular wave.
The amplitude of the oscillation waveform may range from
10 μm to 1,500 μm, and the frequency may range from 0.1 Hz to
20 Hz.
In another aspect, the present invention provides a
method for controlling horizontal oscillation of an edge dam
of a twin roll strip caster, the method including horizontally
oscillating an oscillation plate using a servo valve and a
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cylinder in accordance with an oscillation waveform so that an
edge dam refractory coupled to the oscillation plate
horizontally oscillates, thus eliminating a zone which does
not oscillate, and reducing edge skull.
The horizontally oscillating may comprise horizontally
oscillating the oscillation plate such that at an initial
stage of casting, an amplitude of the oscillation is
maintained within a range from 500 μm to 1,200 μm, and after
the initial stage has passed, the amplitude is maintained
within a range from 200 μm to 600 μm, and at a final stage of
the casting, the amplitude is maintained within a range from
400 μm to 700 μm.
The method for controlling the horizontal oscillation of
the edge dam of the twin roll strip caster may include
reducing the frequency of the oscillation waveform or changing
the oscillation waveform from a sine wave into a rectangular
or triangular wave, thus minutely controlling the amplitude of
the oscillation waveform.
The method for controlling the horizontal oscillation of
the edge dam of the twin roll strip caster may include an
operation of selecting information about an ON/OFF status of
the oscillation, and an amplitude, a frequency and a waveform
of the oscillation using an HMI (Human Machine Interface)
monitor, a slow loop operation of collecting the information
selected using the HMI monitor and transmitting the
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information to a medium loop, a medium loop operation of
generating, using the information received from the slow loop,
a reference of the oscillation waveform having an amplitude
and a frequency that are required to control the horizontal
oscillation, and transmitting the reference to a fast loop,
and a fast loop operation of controlling the servo valve both
using the information about the reference of the oscillation
waveform received from the medium loop and using information
about a position of an oscillation unit received from an
oscillation-unit-displacement measuring device, thus
controlling horizontal oscillation of the oscillation unit.
The medium loop operation may include varying the
amplitude and frequency of the reference of the oscillation
waveform at constant rates, and transmitting the information
about the reference of the oscillation waveform to the fast
loop.
The fast loop operation may include controlling the
horizontal oscillation of the oscillation unit in a period of
0.001 or less.
Advantageous Effects
The present invention variably controls the amplitude,
frequency and waveform of the oscillation depending on casting
conditions, and horizontally oscillates an edge dam using a
servo valve and a hydraulic cylinder. Therefore, the present
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invention can rapidly remove edge skull and suppress
generation and growth of skull, thus preventing a casting roll
or the edge dam from being damaged, thereby ensuring the
stability of casting, and improving the quality of a casting
strip.
Description of Drawings
Fig. 1 is a perspective view of a typical twin roll strip
caster.
Fig. 2 is of schematic views showing skull formed in an
edge dam according to a conventional technique.
Fig. 3(a) is a front view of a conventional edge dam
oscillating device, and Fig. 3(b) is an enlarged view of a
critical portion.
Fig. 4(a) is a schematic view showing an oscillation form
of the conventional edge dam oscillating device, and Fig. 4(b)
is a schematic view showing an oscillation form of an edge dam
oscillating device according to the present invention.
Fig. 5 is of graphs illustrating the extent of mixture of
the skull as functions of the oscillation ON/OFF of the edge
dam and the oscillation method, wherein (a) illustrates when
it does not oscillate, (b) illustrates the conventional
method, and (c) illustrates the method according to the
present invention.
Fig. 6 is views showing the construction of an
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oscillation unit of an apparatus for controlling the
horizontal oscillation of an edge dam, according to the
present invention, wherein (a) is a plan view, (b) is a front
view, (c) is a plan view, (d) is a view showing the operation
when oil is drawn into a first inlet line, and (e) is a view
showing the operation when oil is drawn into a second inlet
line.
Fig. 7 is a conceptual view illustrating a method for
controlling horizontal oscillation of an edge dam according to
the present invention.
Fig. 8 is a block diagram showing the apparatus and
method for controlling horizontal oscillation of the edge dam
according to the present invention.
Fig. 9 is a graph showing the amplitude of oscillation at
an initial stage of casting and the frequency of mixture of
skull.
Fig. 10 is of graphs showing the amplitude of
oscillation, wherein (a) is a graph showing the amplitude of
oscillation as a function of oscillation frequency, and (b) is
a graph showing the amplitude of oscillation as a function of
a change in the waveform of the oscillations.
*Description of the Reference Numerals in the Drawings*
110. casting roll 120. nozzle
130. molten steel pool 131. molten steel
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132. edge skull 133. lower skull
134. surface skull 140. casting strip
150. edge dam refractory 200. dead zone
300. oscillation plate 301. center bearing
302. oscillation cam 310. cover
320. slide bushing 330. eccentric shaft
400. oscillation unit 410. oscillation plate
420. hydraulic cylinder 425. cylinder rod
430. first inlet line 440. second inlet line
450. main body
460. oscillation-unit-displacement measuring device
470. support 480. bolt assembly part
501. control unit 503. fast loop
504. ramping unit
505. medium loop 506. slow loop
507. oscillation-unit-center measuring device
508. horizontal oscillation controller
509. servo valve
510. HMI (Human Machine Interface)
511. oscillation information collector
512. oscillation waveform generator
Best Mode
Hereinafter, an apparatus for controlling horizontal
oscillation of an edge dam of a twin roll strip caster
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according to the present invention will be described in detail
with reference to the attached drawings.
Fig. 6 is views showing the construction of an
oscillation unit of the oscillation control apparatus
according to the present invention, wherein (a) is a plan
view, (b) is a front view, (c) is a plan view, (d) is a view
showing the operation when oil is drawn into a first inlet
line, and (e) is a view showing the operation when oil is
drawn into a second inlet line. Fig. 7 is a conceptual view
illustrating a method for controlling horizontal oscillation
of the edge dam according to the present invention. Fig. 8 is
a block diagram showing the apparatus and method for
controlling horizontal oscillation of the edge dam according
to the present invention.
As shown in Fig. 6, the oscillation control apparatus
according to the present invention is configured such that an
oscillation unit 400 horizontally oscillates an oscillation
plate 410, which is coupled to a rear surface of an edge dam
refractory 150 that is an inactive surface, in accordance with
an oscillation waveform output from a servo valve 509, thus
horizontally oscillating the edge dam refractory 150 coupled
to the oscillation plate 410, thereby reducing edge skull.
As shown in Fig. 8, the servo valve 509 is controlled by
a horizontal oscillation controller 508 of a fast loop 503 of
a control unit 501. The servo valve 509 receives a waveform
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having a predetermined amplitude and oscillation frequency
from the horizontal oscillation controller 508 and moves a
cylinder rod 425 of a hydraulic cylinder 420 of the
oscillation unit 400 to the left and right, thus controlling
the horizontal oscillation of the edge dam refractory.
As shown in Fig. 6(c), the oscillation unit 400 includes
a main body 450 in which the first inlet line 430 and the
second inlet line 440 are formed at opposite sides. The
hydraulic cylinder 420 is fastened to the main body 450. The
cylinder rod 425 is placed through the hydraulic cylinder 420
and is able to be moved in both directions by the hydraulic
pressure of the hydraulic cylinder 420. Further, opposite
ends of the cylinder rod 425 are respectively fastened to
opposite ends of the oscillation plate 400 by supports 470.
Each end of the cylinder rod 425 is connected to the
corresponding support 470 by a bolt passing through a bolt
assembly part 480.
The oscillation control apparatus according to the
present invention includes the control unit 501 which applies
an oscillation waveform having a predetermined amplitude and
oscillation frequency to the servo valve 509, thus controlling
horizontal oscillation of the oscillation unit 400.
As shown in Fig. 8, the control unit 501 includes an
oscillation information collector 511 which receives
information about the ON/OFF status of the oscillating
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operation, and an amplitude, frequency and waveform of
oscillation that are input by an operator using an HMI (Human
Machine Interface) and transmits the information to a medium
loop 505, or transmits a variety of feedback information from
the medium loop 505 to the HMI and displays the feedback
information on an HMI monitor.
Further, an oscillation waveform generator 512 of the
control unit generates an oscillation waveform having an
amplitude and oscillation frequency that are required to
control horizontal oscillation, in response to the information
received from the oscillation information collector 511. The
generated oscillation waveform information is transmitted to
the horizontal oscillation controller 508 of the fast loop
503.
Given information about a real-time position of the
oscillation unit 400 that has been received from an
oscillation-unit-displacement measuring device 460 which is
coupled to the upper end of the oscillation plate 410, the
horizontal oscillation controller 508 applies the oscillation
waveform information from the oscillation waveform generator
512 to the servo valve 509 and controls the hydraulic pressure
in the hydraulic cylinder 420 based on a positional value of a
center of the oscillation unit 400 that is transmitted from an
oscillation-unit-center measuring device 507, so that such
control makes the edge dam refractory 150 horizontally
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oscillate to the left and right at high speed
Here, the oscillation-unit-displacement measuring device
460 checks in real time the positional information of the
oscillation unit 400 and transmits it to the control unit 501.
The oscillation-unit-center measuring device 507 transmits the
positional value of the center of the oscillation unit 400 to
the horizontal oscillation controller of the fast loop 503 so
that the oscillation unit 400 can horizontally oscillate to
the left and right based on the center between both casting
rolls 110.
The control unit 501 further includes a ramping unit 504
which smoothly varies at constantly increasing rates the
amplitude and oscillation frequency of a reference of an
oscillation waveform generated from the oscillation waveform
generator 512 so as to prevent the apparatus from being
exposed to the impacts which may be generated by drastically
changing the amplitude and oscillation frequency of the
reference of the oscillation waveform. In other words, the
ramping unit 504 controls the reference values of the
amplitude and oscillation frequency of the oscillation
waveform transmitted from the oscillation waveform generator
512 such that the reference values slowly varies at a constant
rate, before transmitting the reference values to the
horizontal oscillation controller 508.
In the oscillation control apparatus of the present
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invention, the oscillation waveform is a sine wave, a
rectangular wave or a triangular wave. As shown in Fig. 10,
in the case of the sine wave, the amplitude can be reliably
controlled, while as the oscillation frequency increases, the
amplitude reduces, deteriorating the performance of control.
On the other hand, unlike the sine wave, the rectangular wave
and the triangular wave do not reduce the amplitude even if
the oscillation frequency increases, but the control
performance deteriorates if the oscillation frequency is low.
Therefore, depending on casting conditions, an appropriate
oscillation waveform must be selected.
Furthermore, the amplitude of the oscillation waveform
used in the oscillation control apparatus of the present
invention ranges from 10 μm to 1,500 μm, and the oscillation
frequency ranges from 0.1 Hz to 20 Hz. The oscillation
control apparatus is designed such that depending on casing
conditions and the kind of a mixed skull, the amplitude and
the oscillation frequency are controlled to within the above
ranges.
Hereinafter, the method for controlling horizontal
oscillation of the edge dam of the twin roll strip caster
according to the present invention will be described in detail
with reference to the attached drawings.
The method for controlling the horizontal oscillation of
the edge dam of the twin roll strip caster according to the
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present invention includes a real time feedback control.
Under the control of the control unit 501 which successively
conducts the steps of a slow loop 506, the medium loop 505 and
the fast loop 503, the servo valve 509 and the hydraulic
cylinder 420 horizontally oscillate the oscillation plate 410
in accordance with an oscillation waveform having a
predetermined amplitude and oscillation frequency that is
applied from the control unit 501. Thereby, the refractory
150 of the edge dam that is coupled to the oscillation plate
410 is horizontally oscillated, thus eliminating a dead zone
200 that is a portion which is not affected by the
oscillation, and reducing edge skull.
The steps of controlling the horizontal oscillation of
the edge dam will be explained in detail. As shown in Figs. 7
and 8, at step S1, information about the ON/OFF status of the
oscillating operation, and the amplitude, frequency and
waveform of oscillation is selected using the HMI monitor 510.
Here, the HMI 510 exchanges information about the casting and
the horizontal oscillation of the edge dam with the slow loop
506 of the control unit 501 once per second.
At step S2 (the step of the slow loop 506), the
information about the oscillation of the edge dam that has
been selected by the HMI monitor is received and transmitted
to the medium loop 505.
At step S3 (the step of the medium loop 505), based on
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the information about the oscillation of the edge dam that has
been received from the slow loop 506, reference values of the
oscillation waveform having a predetermined amplitude and
oscillation frequency that are required to control the
horizontal oscillation of the edge dam are created in a period
of 0.01 second. The reference values of the oscillation
waveform are transmitted to the fast loop 503. At the step of
the medium loop, to mitigate the impact that is caused by
drastic changes in the amplitude and oscillation frequency of
the reference generated in the oscillation waveform generator
512, oscillation waveform, the amplitude and oscillation
frequency of the reference of the oscillation waveform are
smoothly varied at constant rates, and then information about
the reference of the oscillation waveform is transmitted to
the fast loop 503.
At step S4 (the step of the fast loop 503), using both
the information about the reference of the oscillation
waveform that has been transmitted from the medium loop 505
and the information about the real-time position of the
oscillation unit 400 that has been received from the
oscillation-unit-displacement measuring device 460, an
oscillation waveform having a predetermined amplitude and
oscillation frequency that are required for the horizontal
oscillation is applied to the servo valve 509 in a period of
0.001 second or less, thus controlling the hydraulic pressure
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in the hydraulic cylinder 420 of the oscillation unit 400.
Thereby, the horizontal oscillation of the edge dam refractory
is controlled based on the center as determined by the
oscillation-unit-center measuring device 507 of the medium
loop 505. Therefore, feedback control is conducted 1000 times
or more per second, thus enhancing the precision of the
oscillation control.
The operation of the oscillation unit of the oscillation
control apparatus of the present invention will be described
in detail. As shown in Fig. 6d, when oil is supplied into the
hydraulic cylinder 420 through the first inlet line 430 of the
main body 450, the cylinder rod 425 is moved to the right by
the hydraulic pressure. Thereby, the oscillation plate 410
connected to the cylinder rod 425 by the supports 470 is also
moved to the right, so that the edge dam refractory 150
coupled to the oscillation plate 410 is also moved to the
right. In a related fashion, moving the edge dam refractory
150 to the left can be realized by supplying oil into the
hydraulic cylinder 420 through the second inlet line 440 and
moving the cylinder rod 425 to the left. Here, if the
hydraulic cylinder 420 is controlled by the servo valve 509,
the cylinder rod 425 is moved by the flow rate of oil supplied
into the hydraulic cylinder 420, so that the amplitude, etc.
can be controlled depending on casting conditions.
Meanwhile, as shown in Fig. 5, in a twin roll type strip
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casting process, at the initial stage of casting when the
casting is not yet stabilized, heat loss of the molten steel
through the edge dam refractory causes a lot of skull. To
remove such skull, it is required to impart the amplitude of
the oscillation waveform with a large value. Fig. 9 is a
graph showing the frequency of mixture of skull as a function
of the amplitude of oscillation at the initial stage of
casting. It can be appreciated that at the initial stage of
casting, as the amplitude of oscillation increases, the
frequency of mixture of skull is reduced. Therefore, in the
oscillation control method according to the present invention,
at the initial stage when the casting is not yet stabilized,
the amplitude of oscillation is controlled such that it is
maintained to be comparatively large, in detail, to be within
the range of from 500 μm to 1,200 μm. The reason for this is
because if the amplitude of oscillation is less than 500 μm at
the initial stage of the casting, formed skull is continuously
mixed with a casting strip for a fairly long time after the
casting has begun, rather than being rapidly removed, thus
deteriorating the quality of the casting strip, and if the
amplitude of oscillation is greater than 1,200 μm, the
stability of the edge dam refractory may not be ensured, or
the edge dam refractory may be worn, reducing its lifetime.
After the initial stage of the casting has passed, and
the stage is one in which the casting has stabilized, it is
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required to suppress the generation and growth of skull. If
the amplitude of oscillation is kept large so as to achieve
the above purpose, there is the likelihood of the edge dam
being damaged by excessive oscillation during the casting.
Further, if the amplitude of oscillation is large for a
comparatively long time, abnormal wear of the edge dam is
caused, thus deteriorating the quality of the edges of the
casting strip, or reducing the lifetime of the edge dam
refractory. Hence, after the initial stage of the casting has
passed, at the stage in which most of skull that had been at
the initial stage of the casting has been removed, the
amplitude of oscillation must be maintained to be as small as
possible within a range that can prevent damage or abnormal
wear of the edge dam and mitigate the generation and growth of
skull. To achieve this, after the initial stage of casting,
the amplitude of oscillation must be maintained within a range
from 200 μm to 600 μm because if the amplitude of oscillation
is less than 200 μm, the generation and growth of skull cannot
be effectively suppressed, and if the amplitude of oscillation
is greater than 600 μm, there may be abnormal wear of the edge
dam.
At a final stage of the casting, the temperature of the
molten steel decreases, thus increasing the possibility of
skull generation and growth. Therefore, it is required to
increase the amplitude of oscillation to suppress the
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generation and growth of skull. Given this, at the final
stage of the casting, it is preferable for the amplitude of
oscillation to be maintained within a range from 400 μm to 700
μm. The reason for this is because if the amplitude of
oscillation is less than 400 μm, it is difficult to suppress
the generation of skull which may be caused by a decrease in
the temperature of the molten steel, and if the amplitude of
oscillation is greater than 700 μm, a lower portion of the
edge dam is worn, causing damage, such as a deep nick, to the
edge.
As stated above, if the amplitude of oscillation is
increased, there is a likelihood of the edge dam being
damaged. Given this, as shown in Fig. 10, reducing the
oscillation frequency of the waveform or changing the waveform
from a sine wave into a rectangular or triangular wave is
needed so that the amplitude of oscillation can be minutely
controlled, thus minimizing the possibility of the edge dam
being damaged while increasing the amplitude of oscillation.
Actually, in the results of the most general three kinds
of tests on the extent of mixture of skull as functions of the
ON/OFF status of the oscillation of the edge dam and the
oscillation method, as shown Fig. 5(a), it can be appreciated
that if the edge dam does not oscillate, the mixture of skull
is continuously induced, which renders casting impossible
after a predetermined time has passed. As shown in Fig. 5(b),
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in the case where the edge dam was mechanically oscillated
using the conventional oscillation cam, the mixture of skull
was reduced compared to the case of Fig. 5(a), but because of
the presence of a dead zone, when the temperature of molten
steel is reduced, for example, at the time of replacement of a
ladle or at the final stage of the casting, the mixing of
skull was observed. As shown in Fig. 5(c), when the
horizontal oscillation method of the present invention was
used, all sides of the edge dam refractory uniformly
oscillated, so that not only skull that formed at the initial
stage of the casting could be continuously removed, but also
there was no dead zone. Thus, the mixing of skull was not
observed even at the time of replacement of the ladle or in
the final stage of the casting.
Eventually, in the method of controlling the horizontal
oscillation of the edge dam according to the present
invention, the servo valve and the hydraulic cylinder
horizontally oscillate the edge dam refractory in accordance
with an oscillation waveform having a predetermined amplitude
and oscillation frequency that is applied thereto from the
control unit, thus eliminating the dead zone 200 which is a
portion that does not oscillate. Further, depending on
casting conditions, the amplitude, oscillation frequency and
the oscillation waveform are variably controlled. Therefore,
skull that has been formed at the initial stage of the casting
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can be rapidly removed, the generation and growth of skull can
be suppressed, and damage to the casting roll or edge dam can
be prevented, so that the stability of casting can be ensured
and the quality of a produced casting strip can be improved.
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We claim:-
1. An apparatus for controlling horizontal oscillation of
an edge dam of a twin roll strip caster, the apparatus
comprising:
an oscillation unit horizontally oscillating an
oscillation plate in accordance with an oscillation waveform
so that an edge dam refractory coupled to the oscillation
plate horizontally oscillates;
a servo valve outputting the oscillation waveform to the
oscillation unit to perform the horizontal oscillation; and
a control unit applying the oscillation waveform to the
servo valve, thus controlling the horizontal oscillation of
the oscillation unit.
2. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to claim 1, wherein the oscillation unit comprises:
a main body installed with a hydraulic line;
a hydraulic cylinder fastened to the main body;
a cylinder rod placed through the hydraulic cylinder so
as to be movable to opposite sides of the hydraulic cylinder;
and
a support connecting opposite ends of the cylinder rod to
opposite ends of the oscillation plate.
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3. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to claim 1, wherein the control unit comprises:
an oscillation information collector collecting from an
HMI (Human Machine Interface) information about an ON/OFF
status of the oscillation, and an amplitude, a frequency and a
waveform of the oscillation;
an oscillation waveform generator generating, using the
information received from the oscillation information
collector, a reference of the oscillation waveform having an
amplitude and a frequency that are required to control the
horizontal oscillation; and
a horizontal oscillation controller controlling the servo
valve both using the information about the oscillation
waveform received from the oscillation waveform generator and
using information about a position of the oscillation unit
that is received from the oscillation-unit-displacement
measuring device, thus controlling the horizontal oscillation
of the oscillation unit.
4. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to claim 3, wherein the control unit further
comprises
a ramping unit varying at constant rates the amplitude
and the frequency of the reference of the oscillation waveform
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generated from the oscillation waveform generator.
5. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to claim 3, wherein the control unit further
comprises
an oscillation-unit-center measuring device transmitting
information about a center position of the oscillation unit to
the horizontal oscillation controller.
6. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to claim 1, further comprising
an oscillation-unit-displacement measuring device
transmitting information about a real time position of the
oscillation unit to the control unit.
7. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to any one of claims 1 through 6, wherein the
oscillation waveform comprises a sine wave, a rectangular wave
or a triangular wave.
8. The apparatus for controlling the horizontal
oscillation of the edge dam of the twin roll strip caster
according to any one of claims 1 through 6, wherein the
amplitude of the oscillation waveform ranges from 10 μm to
1,500 μm, and the frequency ranges from 0.1 Hz to 20 Hz.
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9. A method for controlling horizontal oscillation of an
edge dam of a twin roll strip caster, the method comprising
horizontally oscillating an oscillation plate using a
servo valve and a cylinder in accordance with an oscillation
waveform so that an edge dam refractory coupled to the
oscillation plate horizontally oscillates, thus eliminating a
zone which does not oscillate, and reducing edge skull.
10. The method for controlling the horizontal oscillation
of the edge dam of the twin roll strip caster according to
claim 9, wherein the horizontally oscillating comprises
horizontally oscillating the oscillation plate such that at an
initial stage of casting, an amplitude of the oscillation is
maintained within a range from 500 μm to 1,200 μm, and after
the initial stage has passed, the amplitude is maintained
within a range from 200 μm to 600 μm, and at a final stage of
the casting, the amplitude is maintained within a range from
400 μm to 700 μm.
11. The method for controlling the horizontal oscillation
of the edge dam of the twin roll strip caster according to
claim 9 or 10, comprising reducing the frequency of the
oscillation waveform or changing the oscillation waveform from
a sine wave into a rectangular or triangular wave, thus
minutely controlling the amplitude of the oscillation
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waveform.
12. The method for controlling the horizontal oscillation
of the edge dam of the twin roll strip caster according to
claim 9, comprising:
an operation of selecting information about an ON/OFF
status of the oscillation, and an amplitude, a frequency and a
waveform of the oscillation using an HMI (Human Machine
Interface) monitor;
a slow loop operation of collecting the information
selected using the HMI monitor and transmitting the
information to a medium loop;
a medium loop operation of generating, using the
information received from the slow loop, a reference of the
oscillation waveform having an amplitude and a frequency that
are required to control the horizontal oscillation, and
transmitting the reference to a fast loop; and
a fast loop operation of controlling the servo valve both
using the information about the reference of the oscillation
waveform received from the medium loop and using information
about a position of an oscillation unit received from an
oscillation-unit-displacement measuring device, thus
controlling horizontal oscillation of the oscillation unit.
13. The method for controlling the horizontal oscillation
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of the edge dam of the twin roll strip caster according to
claim 12, wherein the medium loop operation comprises varying
the amplitude and frequency of the reference of the
oscillation waveform at constant rates, and transmitting the
information about the reference of the oscillation waveform to
the fast loop.
14. The method for controlling the horizontal oscillation
of the edge dam of the twin roll strip caster according to
claim 12, wherein the fast loop operation comprises
controlling the horizontal oscillation of the oscillation unit
in a period of 0.001 or less.