【Technical Field】
The present disclosure relates to a continuous
casting machine including a mold and segments guiding a
strand, and more particularly, to a continuous casting
machine in which the number and distance of rolls of outer
frames are set to be different from those of rolls of inner
frames for producing slabs having improved quality.
【Background Art】
Generally, in a continuous casting process, molten
steel is continuously supplied to a mold having a
predetermined shape, and a slab semi-solidified in the mold
is continuously drawn from a lower side of the mold.
FIG. 1 is a schematic view illustrating the structure
and segments of a general continuous casting machine.
The continuous casting machine includes: ladles 10 in
which molten steel refined through a steel making process
is poured; a turndish 20 temporarily storing the molten
steel supplied from the ladles 10 through a nozzle; a mold
30 receiving the molten steel from the turndish 20 for
primarily solidifying the molten steel to have a
predetermined shape; and a strand guide 40 including a
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plurality of segments 50 arranged below the mold 30 to
guide and cool a slab not fully solidified.
The segments 50 are arranged in such a manner that a
plurality of rolls 52 and 54 face each other. Each of the
segments 50 includes: upper and lower frames 51 and 53
spaced apart from each other in a vertical direction; a
plurality of tie rods (not shown) vertically connecting the
upper and lower frames 51 and 53; and a plurality of
hydraulic cylinders (not shown) using the tie rods as
pistons to control gaps between the upper and lower frames
51 and 53 for applying depressive force to a slab 1.
In the continuous casting machine, molten metal
contained in the mold 30 has to be maintained at a constant
level during a casting process. However, if the rate of
casting is increased, the level of molten metal contained
in the mold 30 may be markedly varied. In this case, the
rate of casting may not be further increased. Furthermore,
a slab having a high temperature may periodically swell
between the rolls 52 and 54 of the segments 50 due to
pressure, and thus mold level hunting may occur.
【Disclosure】
【Technical Problem】
An aspect of the present disclosure may provide a
continuous casting machine configured to reduce mold level
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hunting caused by periodic pressure-induced swelling of a
high-temperature slab passing between rolls during a highspeed
casting process.
An aspect of the present disclosure may also provide
a continuous casting machine for producing slabs having
improved quality by reducing mold level hunting caused by
periodic swelling of the slabs.
【Technical Solution】
The present disclosure provides segments and a
continuous casting machine as described below.
According to an aspect of the present disclosure, a
continuous casting machine may include: a mold providing a
slab; and a plurality of segments configured to guide the
slab through a strand guide and cool the slab, wherein each
of the segments may include an inner frame, an outer frame
spaced apart from the inner frame, and a plurality of rolls
disposed on the inner and outer frames through roll
supports, and the number Nfixed of the rolls disposed on the
outer frame may be set to be different from the number
Nloosed of the rolls disposed the inner frame so as to reduce
mold level hunting caused by a slab shape.
The outer frame may have an average roll pitch
Pavg,fixed different from an average roll pitch Pavg,loosed of
the inner frame.
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The inner frame and the outer frame may have the same
segment length so as to be disposed in a horizontal or
vertical zone of the strand guide.
The outer frame may have a segment length greater
than that of the inner frame, and the outer and inner
frames may be disposed in a bow zone of the strand guide,
wherein the average roll pitch Pavg,fixed of the outer frame
and the average roll pitch Pavg,loosed of the inner frame may
satisfy the following formula:
where tslab refers to a slab thickness, and r refers a
curvature of radius of the strand guide.
The number Nloosed of the rolls disposed the inner
frame may be greater than the number Nfixed of the rolls
disposed on the outer frame (NfixedPavg,fixed).
As described above, since the Pavg,loosed of the loosed
frame 151 is different from the Pavg,fixed of the fixed frame
154, gaps between the rolls 152 and 155 are different.
Therefore, a distance that a slab travels from one roll to
the next roll of the rolls 152 and 155 of the loosed and
fixed frames 151 and 154 is different from the next
distance that the slab travels, thereby preventing mold
level hunting that occurs when a slab makes contact with
rolls constantly and repeatedly as in the case of the
related art.
The pinch rolls 153 and 156 of the rolls 152 and 155
used to draw a slab passing through the segment 150 may not
be aligned at centers thereof. The reason for this is as
follows: in a high-speed casting process, the influence of
shearing caused by misaligned centers of the pinch rolls
153 and 156 is low, but mold level hunting is severe if the
pinch rolls 153 and 155 are aligned to periodically
correspond to each other. Herein, high-speed casting
refers to casting having a rate of 400 mm•m/min or greater
(for example, a slab weighing 80 metric tons is produced at
a rate of 5 m/min or greater).
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FIG. 4 illustrates a segment 160 configured to be
used in a bow zone of a strand guide 140.
Referring to FIG. 4, the segment 160 includes: a
loosed frame 161 loosely and movably disposed to face the
center of the vow zone; and a fixed frame 164 disposed at a
side opposite to the loosed frame 161. A plurality of
rolls 162 and 164 are arranged on the loosed frame 161 and
the fixed frame 164, and the rolls 162 and 164 include a
pair of pinch rolls 163 and 166.
Like in the embodiment shown in FIG. 3, in the
segment 160 shown in FIG. 4, the rolls 161 are arranged at
regular intervals on the overall segment length lseg,loosed of
the loosed frame 161, and the number of the rolls 162 is
Nloosed. The rolls 152 are arranged on the loosed frame 151
with a constant pitch Ploosed. Although the pinch roll 163
has a diameter slightly larger than that of the rolls 162,
gaps lloosed between the rolls 152 are substantially equal.
The rolls 165 are arranged at regular intervals on
the overall segment length lseg,fixed of the fixed frame 164,
and the number of the rolls 165 is Nfixed. The rolls 165 are
arranged on the loosed frame 161 with a constant pitch
Pfixed. Although the pinch roll 166 has a diameter slightly
larger than that of the rolls 165, gaps lfixed between the
rolls 165 are substantially equal.
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The segment 160 of the embodiment shown in FIG. 4 is
used in a bow zone. In a continuous casting machine 100
(refer to FIG. 5), the bow zone of the strand guide 140
(refer to FIG. 5) is curved with a curvature of radius (r),
and the segment length lseg,loosed of the loosed frame 161 is
different from the segment length lseg,fixed of the fixed
frame 164 disposed at a side opposite to the loosed frame
161.
In detail, the segment length lseg,loosed of the loosed
frame 161 and the segment length lseg,fixed of the fixed frame
164 are set to satisfy lseg,loosed : lseg,fixed = r : r-tslab,
where tslab refers to the thickness of a slab. Since the
thickness of the slab has a positive value, the segment
length lseg,loosed of the loosed frame 161 is shorter than the
segment length lseg,fixed of the fixed frame 164.
Like in the previous embodiment shown in FIG. 3, in
the current embodiment, the numbers Nloosed and Nfixed of the
rolls 162 and 165 of the loosed and fixed frame 161 and 164
are different. Thus, average pitches Pavg satisfy Formula 2
below.
... Formula 2
As the difference between the average pitch of the
rolls 162 of the loosed frame 161 and the average pitch of
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the rolls 165 of the fixed frame 164 is increased, mold
level hunting may be suppressed. Particularly, in the
embodiment shown in FIG. 4, the segment length lseg,loosed of
the loosed frame 161 is shorter than the segment length
lseg,fixed of the fixed frame 164. Therefore, if the number
Nfixed of the rolls 165 of the fixed frame 164 is greater
than the number Nfixed of the rolls 162 of the loosed frame
161, the difference between the average pitches may be
increased, and thus mold level hunting caused by the shape
of a slab may be effectively prevented.
FIG. 5 illustrates the continuous casting machine 100
including a plurality the segments 150 and 160 according to
an embodiment of the present disclosure. The continuous
casting machine 100 includes: ladles 110 in which molten
steel refined through a steel making process is poured; a
turndish 120 temporarily storing the molten steel supplied
from the ladles 110 through a nozzle; a mold 130 receiving
the molten steel from the turndish 20 for primarily
solidifying the molten steel to have a predetermined shape;
and the cooling line 140 including the segments 150 and 160
arranged below the mold 30 to perform a series of forming
processes on a slab not fully solidified while cooling the
slab.
In the segments 150 and 160 included in the strand
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guide 140 of the continuous casting machine 100, the number
Nloosed of the rolls 152 and 162 of the loosed frames 151 and
161 is greater than the number Nfixed of the rolls 155 and
165 of the fixed frames 154 and 164 (Nloosed > Nfixed), and
thus the average pitch of the rolls 155 and 165 of the
fixed frames 154 and 164 is greater than the average pitch
of the rolls 152 and 162 of the loosed frames 151 and 161
(Pavg,loosed Nfixed) in both bow
and horizontal zones 141 and 142 of the strand guide 140.
However, the segments 150 and 160 arranged in the bow zone
of the strand guide 140 may be configured such that the
number Nloosed of the rolls 152 and 162 of the loosed frames
151 and 161 is greater than the number Nfixed of the rolls
155 and 165 of the fixed frames 154 and 164 (Nloosed > Nfixed),
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and the segments 150 and 160 arranged in the horizontal
zone of the strand guide 140 may be configured such that
the number Nloosed of the rolls 152 and 162 of the loosed
frames 151 and 161 is smaller than the number Nfixed of the
rolls 155 and 165 of the fixed frames 154 and 164 (Nloosed <
Nfixed).
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We Claim:
【Claim 1】
A continuous casting machine comprising:
a mold providing a slab; and
a plurality of segments configured to guide the slab
through a strand guide and cool the slab,
wherein each of the segments comprises an inner frame,
an outer frame spaced apart from the inner frame, and a
plurality of rolls disposed on the inner and outer frames
through roll supports, and
the number Nfixed of the rolls disposed on the outer
frame is set to be different from the number Nloosed of the
rolls disposed the inner frame so as to reduce mold level
hunting caused by a slab shape.
【Claim 2】
The continuous casting machine of claim 1, wherein
the outer frame has an average roll pitch Pavg,fixed different
from an average roll pitch Pavg,loosed of the inner frame.
【Claim 3】
The continuous casting machine of claim 2, wherein
the inner frame and the outer frame have the same segment
length so as to be disposed in a horizontal or vertical
zone of the strand guide.
【Claim 4】
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The continuous casting machine of claim 2, wherein
the outer frame has a segment length greater than that of
the inner frame, and the outer and inner frames are
disposed in a bow zone of the strand guide,
wherein the average roll pitch Pavg,fixed of the outer
frame and the average roll pitch Pavg,loosed of the inner
frame satisfy the following formula:
where tslab refers to a slab thickness, and r refers a
curvature of radius of the strand guide.
【Claim 5】
The continuous casting machine of claim 4, wherein
the number N loosed of the rolls disposed the inner frame is
greater than the number Nfixed of the rolls disposed on the
outer frame (Nfixed