TECHNICAL FIELD
[0001] The present disclosure relates to a cold rolling line, a steel sheet production line,
a cold rolling method, and a steel sheet production method.
BACKGROUND
[0002] Steel sheets containing Si, such as electrical steel sheets, have low toughness and
are prone to brittle fracture during rolling. In general, the higher the Si content
in a steel sheet, the lower the ductility brittle transition temperature tends to
be. One method to prevent brittle fracture is to heat a steel sheet above the ductility
brittle transition temperature before rolling.
[0003] In steel sheet rolling lines, tandem mills, and the like, coolant is injected towards
the biting area between the work rolls and the steel sheet to lubricate the steel
sheet during rolling and to prevent thermal deformation of the work rolls. The injected
coolant bounces off the work roll and flows across the steel sheet toward the entry
side. When a steel sheet is heated before rolling, the temperature of the steel sheet
is lowered by the coolant that flows toward the entry side (coolant liquid ride).
[0004] The liquid ride length of the coolant in the longitudinal direction of the steel
sheet is longer at slower line speeds. In addition, a faster line speed yields a stronger
force, by the steel sheet, drawing in the coolant. The liquid ride length thus tends
to be shorter. Therefore, when the line speed is slow, the steel sheet is cooled to
about the temperature of the coolant even if the steel sheet is preheated.
[0005] For example, Patent Literature (PTL) 1 discloses a technique for installing a liquid
drainage device that blows air for liquid drainage on an upper roller to prevent coolant
sprayed on the upper roller of a rolling mill from falling onto the strip and lowering
the strip temperature.
[0006] In order to resolve the lack of lubrication of the steel sheet caused by the liquid
drainage device in PTL 1, a technique for supplying a small amount of emulsion to
the steel sheet at a high concentration has been disclosed, as illustrated in PTL
2, for example.
[0007] On the other hand, in the back-end stand of a multi-stage rolling mill or the like,
the steel sheet temperature rises due to processing heat generated during rolling,
but if the temperature is too high, the heat input to the work rolls increases during
rolling, and a thermal crown is formed on the work rolls. The formation of thermal
crowns deteriorates the rolling shape of the steel sheet.
[0008] In particular, as the rolling speed increases, the heat input per unit time increases,
causing the thermal crowns to grow further and deteriorating the rolling shape of
the steel sheet.
CITATION LIST
Patent Literature
SUMMARY
(Technical Problem)
[0010] Although the liquid drainage device described in PTL 1 is effective for suppressing
sheet temperature drop, this technique tends to cause poor lubrication of the steel
sheets, resulting in sticking.
[0011] In the case of PTL 2, the emulsion is supplied to the steel sheet at the entry side
of the rolling mill. The steel sheet is therefore cooled by the liquid ride of the
emulsion, and the temperature of the steel sheet is lowered.
[0012] Here, if the steel sheet temperature in the downstream stand of a multi-stage rolling
mill or the like is too high due to processing heat generated during rolling, the
steel sheet temperature is lowered by the coolant liquid ride, and the amount of heat
input to the work rolls can be suppressed. However, when the rolling speed is high,
the liquid ride length becomes short, making the cooling effect small.
[0013] The cooling capacity is also improved by increasing the coolant flow rate, and the
cooling capacity is further improved by increasing the liquid ride length. However,
pump augmentation, coolant water supply pipe diameter, and circulation tank size need
to be reconsidered.
[0014] It is an aim of the present disclosure, conceived in light of such issues, to provide
a cold rolling line, a steel sheet production line, a cold rolling method, and a steel
sheet production method that can suppress work roll deformation and brittle cracking
during rolling.
(Solution to Problem)
[0015]
- (1) A cold rolling line according to an embodiment of the present disclosure includes:
one or more cold mills configured to inject coolant towards a work roll and a metal
steel strip and to cold roll the metal steel strip, a plurality of rollers provided
upstream from the one or more cold mills in a conveyance direction of the metal steel
strip and used to convey the metal steel strip, and a control unit configured to control
a height difference of the plurality of rollers, wherein
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a lower position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most upstream mill provided farthest upstream.
- (2) As an embodiment of the present disclosure, in (1), the control unit is configured
to set an inclination angle of the metal steel strip with respect to a biting area
of the one or more cold mills based on at least one of a steel type of the metal steel
strip, a line speed, an injection flow rate of the coolant, a temperature of the metal
steel strip, and a target temperature of the metal steel strip, at an upstream side
of at least a portion of the one or more cold mills including the most upstream mill.
- (3) As an embodiment of the present disclosure, in (2), the control unit is configured
to control the plurality of rollers so that the inclination angle is 2° or more to
10° or less.
- (4) As an embodiment of the present disclosure, in any one of (1) to (3), the one
or more cold mills includes a plurality of cold mills, and
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
- (5) A cold rolling line according to an embodiment of the present disclosure includes
one or more cold mills configured to inject coolant towards a work roll and a metal
steel strip and to cold roll the metal steel strip, a plurality of rollers provided
upstream from the one or more cold mills in a conveyance direction of the metal steel
strip and used to convey the metal steel strip, and a control unit configured to control
a height difference of the plurality of rollers, wherein
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
- (6) As an embodiment of the present disclosure, in (5), the control unit is configured
to set an inclination angle of the metal steel strip with respect to a biting area
of the one or more cold mills based on at least one of a steel type of the metal steel
strip, a line speed, an injection flow rate of the coolant, a temperature of the metal
steel strip, and a target temperature of the metal steel strip, at an upstream side
of at least a portion of the one or more cold mills including the most downstream
mill.
- (7) As an embodiment of the present disclosure, in (6), the control unit is configured
to control the plurality of rollers so that the inclination angle is -10° or more
to -2° or less.
- (8) A steel sheet production line according to an embodiment of the present disclosure
includes the cold rolling line according to any one of (1) to (7), and a line for
cutting the metal steel strip.
- (9) A cold rolling method according to an embodiment of the present disclosure is
a cold rolling method to be performed on a cold rolling line including one or more
cold mills configured to inject coolant towards a work roll and a metal steel strip
and to cold roll the metal steel strip, a plurality of rollers provided upstream from
the one or more cold mills in a conveyance direction of the metal steel strip and
used to convey the metal steel strip, and a control unit configured to control a height
difference of the plurality of rollers, the cold rolling method including:
controlling, by the control unit, the plurality of rollers so that the metal steel
strip is at a lower position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most upstream mill provided farthest upstream.
- (10) A cold rolling method according to an embodiment of the present disclosure is
a cold rolling method to be performed on a cold rolling line including one or more
cold mills configured to inject coolant towards a work roll and a metal steel strip
and to cold roll the metal steel strip, a plurality of rollers provided upstream from
the one or more cold mills in a conveyance direction of the metal steel strip and
used to convey the metal steel strip, and a control unit configured to control a height
difference of the plurality of rollers, the cold rolling method including:
controlling, by the control unit, the plurality of rollers so that the metal steel
strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
- (11) A steel sheet production method according to an embodiment of the present disclosure
includes performing the cold rolling method according to (9) or (10), and cutting
the metal steel strip.
(Advantageous Effect)
[0016] According to the present disclosure, a cold rolling line, a steel sheet production
line, a cold rolling method, and a steel sheet production method that can suppress
work roll deformation and brittle cracking during rolling can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the accompanying drawings:
FIG. 1 is a diagram illustrating an example configuration of cold mill provided in
a cold rolling line according to an embodiment of the present disclosure;
FIG. 2 is a diagram illustrating an example configuration of cold mill provided in
a cold rolling line according to an embodiment of the present disclosure; and
FIG. 3 is a diagram illustrating the change in temperature of a metal steel strip
in the cold rolling line.
DETAILED DESCRIPTION
[0018] A cold rolling line, a steel sheet production line, a cold rolling method, and a
steel sheet production method according to an embodiment of the present disclosure
will be described below with reference to the drawings.
[0019] First, with reference to FIG. 3, an example of the temperature change of a metal
steel strip in a cold rolling line is explained. In the example in FIG. 3, the cold
rolling line is equipped with a heating device, a plurality of rollers, and first
through fourth cold mills. The first through fourth cold mills perform cold rolling
of a metal steel strip that is heated by the heating device and conveyed by the plurality
of rollers. The cold rolling line includes the heating device, the first cold mill,
the second cold mill, the third cold mill, and the fourth cold mill in this order
from the upstream side to the downstream side in the conveyance direction of the metal
steel strip. The cold rolling line may form part of a steel sheet production line.
The steel sheet production line may be further equipped with a line for cutting the
metal steel strip, for example located downstream from the fourth cold mill, to cut
out steel sheets of the desired size.
[0020] Each of the first through fourth cold mills is equipped with a coolant header (see
FIG. 1) that injects coolant towards the work rolls and the metal steel strip. The
coolant is a liquid mixture of rolling oil and water, for example, and is injected
to ensure lubrication and to cool the work rolls.
[0021] When a metal steel strip enters a cold mill, brittle fracture may occur if the metal
steel strip is not at a certain temperature. Steel sheets produced by production lines
equipped with cold rolling lines include, for example, electrical steel sheets. Since
an electrical steel sheet usually has a ductility brittle transition temperature of
70 °C to 80 °C, the electrical steel sheet is heated to a temperature above the ductility
brittle transition temperature (such as 200 °C to 500 °C) before being inserted into
the rolling line and rolled. However, if the temperature of the steel sheet is lowered
by rolling oil provided during rolling or the like, and the temperature of the metal
steel strip at the time of biting in the cold mill (hereinafter also referred to as
"sheet temperature") falls below the ductility brittle transition temperature, fracture
is likely to occur. In the cold rolling line, the sheet temperature could be lower
than expected, depending on the liquid ride of the rolling oil.
[0022] On the other hand, a high sheet temperature at the time of biting can prevent fracture,
but due to heat such as processing heat generated during rolling, the sheet temperature
can become even higher in the downstream rolling passes. If sheet temperature is higher
than expected, the thermal crown of the work rolls may grow and cause shape defects
in the post-rolling metal steel strip.
[0023] The lower graph in FIG. 3 illustrates the change in temperature of the metal steel
strip. The vertical axis indicates the temperature of the metal steel strip, and the
horizontal axis indicates the position in the production process corresponding to
the cold rolling line illustrated in the upper portion of the diagram. Coolant injected
in the first through fourth cold mills bounces off the work rolls and flows over the
metal steel strip toward the entry side (upstream), yielding a coolant liquid ride.
The length, in the longitudinal direction (conveyance direction) of the metal steel
strip, of the coolant liquid ride becomes longer at slower line speeds, but becomes
shorter at higher line speeds because the coolant is drawn in more strongly by the
steel sheet. In a cold rolling line, the metal steel strip is rolled and stretched
in the longitudinal direction by the rolling mill. The line speed therefore increases
from the cold mills on the upstream side towards the cold mills on the downstream
side. In the example in FIG. 3, the coolant liquid ride length becomes longer at the
first cold mill and the second cold mill, where the line speed is relatively slow,
and the temperature of the metal steel strip falls below the optimal temperature (below
the ductility brittle transition temperature). The coolant liquid ride length is short
at the fourth cold mill, where the line speed is relatively high, and heat such as
processing heat generated during rolling accumulates, raising the temperature of the
work rolls to or above the shape defect occurrence temperature, at which shape defects
occur in the metal steel strip.
[0024] As explained below, the cold rolling line according to the present embodiment can
adjust the length of the coolant liquid ride by setting the inclination angle of the
metal steel strip with respect to the biting area of the cold mill upstream from each
cold mill, based on the results of measuring sheet temperature and the like as illustrated
in FIG. 3 below, for example. By the length of the coolant liquid ride being adjusted,
the temperature of the metal steel strip remains within the optimal temperature range,
thereby suppressing deformation of the work rolls and suppressing brittle cracking
during rolling.
[0025] FIG. 1 is a diagram illustrating an example configuration of a cold mill provided
in a cold rolling line according to the present embodiment. The cold rolling line
includes one or more cold mills configured to inject coolant towards a work roll and
a metal steel strip and to cold roll the metal steel strip, a plurality of rollers
provided upstream from the cold mills in the conveyance direction of the metal steel
strip and used to convey the metal steel strip, and a control unit that controls the
height difference of the plurality of rollers. The number of cold mills included in
the cold rolling line is not particularly limited but is described as being four in
the present embodiment, as illustrated in FIG. 3. FIG. 1 illustrates an enlarged view
of one cold mill in the plurality of cold mills included in the cold rolling line.
[0026] As illustrated in FIG. 1, each of the rollers on the entry side of the cold mill
can be adjusted in height by a lifting and lowering device. The lifting and lowering
device is, for example, a screw jack but is not limited to any particular device.
The control unit controls the height difference of the plurality of rollers by causing
the lifting and lowering device to lift and lower the rollers via a control signal.
In the example illustrated in FIG. 1, the control unit controls the plurality of rollers
so that the metal steel strip is at a lower position towards the downstream side in
the conveyance direction. The angle of the entering metal steel strip with respect
to the horizontal direction at the biting area of the cold mill is the inclination
angle, and in the example in FIG. 1, the control unit controls the inclination angle
to be positive. When the inclination angle is positive, the coolant that bounces off
the work roll and flows over the metal steel strip toward the entry side (upstream
side) returns to the biting area of the cold mill due to the inclination. The length
of the coolant liquid ride can thus be shortened. Therefore, the control unit can
increase the temperature of the metal steel strip by controlling the metal steel strip
to be at a lower position towards the downstream side in the conveyance direction
at the entry side of the cold mill, where the temperature of the metal steel strip
has dropped below the optimal temperature. The coolant liquid ride length is generally
longer at the entry side of the most upstream mill provided farthest upstream, and
the temperature of the metal steel strip falls below the optimal temperature. The
control unit may therefore control the metal steel strip to be at a lower position
lower towards the downstream side in the conveyance direction at the upstream side
of one or more cold mills including the most upstream mill. In the example in FIG.
3, the control unit raises and lowers the rollers at the entry side so that the inclination
angle becomes positive for the first cold mill (the most upstream mill) and the second
cold mill, thereby shortening the coolant liquid ride length and increasing the temperature
of the metal steel strip to be within the optimal temperature range.
[0027] Here, the control unit may set the inclination angle in the first cold mill to the
same inclination angle as the second cold mill, or to a different angle. The control
unit may set the inclination angle based on at least one of the steel type of the
metal steel strip, the line speed, the injection flow rate of the coolant, the temperature
of the metal steel strip, and a target temperature of the metal steel strip, at the
upstream side of the one or more cold mills including the most upstream mill. The
control unit may set the inclination angle of the first cold mill (the most upstream
mill) based, for example, on the temperature of the metal steel strip and the target
temperature of the metal steel strip. The control unit may also set the inclination
angle of the second cold mill to be smaller than the inclination angle of the first
cold mill, based on differences in line speed, for example.
[0028] The control unit preferably controls the plurality of rollers so that the inclination
angle is 2° or more. The control unit preferably controls the plurality of rollers
so that the inclination angle is 10° or less. As illustrated in the experimental examples
described below, when the inclination angle is less than 2°, the degree of shortening
of the coolant liquid ride length is small, and the effect of temperature increase
is small. When the inclination angle is greater than 10°, smooth conveyance of the
metal steel strip may be hindered. In a case in which the inclination angle is 5°
or more, it may be possible to shorten the length of the coolant liquid ride by 50
% or more. The control unit may therefore control the plurality of rollers so that
the inclination angle is 5° or more to 10° or less.
[0029] Here, the inclined portion should have a certain length, because if it is too short,
the coolant liquid ride may surpass the inclined portion. The length of the inclined
portion is preferably 1 m or more as an example. In addition, an upper limit may be
set on the length of the inclined portion due to equipment constraints. The length
of the inclined portion is preferably 3 m or less as an example.
[0030] FIG. 2 is a diagram illustrating another example configuration of a cold mill provided
in a cold rolling line according to the present embodiment. The cold rolling line
includes one or more cold mills, a plurality of rollers, and a control unit, as in
FIG. 1. FIG. 2 is described as illustrating an enlarged view of one cold mill in the
plurality of cold mills included in the same cold rolling line as FIG 1.
[0031] Each of the rollers on the entry side of the cold mill can be adjusted in height
by a lifting and lowering device, as in FIG. 1. In the example illustrated in FIG.
2, the control unit controls the plurality of rollers so that the metal steel strip
is at a higher position towards the downstream side in the conveyance direction. In
other words, in the example in FIG. 2, the control unit controls the inclination angle
to be negative. When the inclination angle is negative, the coolant that bounces off
the work roll and flows over the metal steel strip toward the entry side (upstream
side) extends further upstream due to the inclination. The length of the coolant liquid
ride can thus be increased. Therefore, the control unit can decrease the temperature
of the metal steel strip by controlling the metal steel strip to be at a higher position
towards the downstream side in the conveyance direction at the entry side of the cold
mill, where the temperature of the metal steel strip has risen to or above the shape
defect occurrence temperature. The coolant liquid ride length is generally shorter
at the entry side of the most downstream mill provided farthest downstream, and the
temperature of the metal steel strip rises to or above the shape defect occurrence
temperature due to the accumulation of heat such as processing heat during rolling.
The control unit may therefore control the metal steel strip to be at a higher position
lower towards the downstream side in the conveyance direction at the upstream side
of one or more cold mills including the most downstream mill. In the example in FIG.
3, the control unit raises and lowers the rollers at the entry side so that the inclination
angle becomes negative for the fourth cold mill (the most downstream mill), thereby
increasing the coolant liquid ride length and decreasing the temperature of the metal
steel strip to be within the optimal temperature range.
[0032] Here, the control unit may set the inclination angle based on at least one of the
steel type of the metal steel strip, the line speed, the injection flow rate of the
coolant, the temperature of the metal steel strip, and a target temperature of the
metal steel strip, at the upstream side of the one or more cold mills including the
most downstream mill. The control unit may set the inclination angle of the fourth
cold mill (the most downstream mill) based, for example, on the temperature of the
metal steel strip and the target temperature of the metal steel strip. The control
unit may calculate the optimal coolant ride length based, for example, on the type
of the metal steel strip, the line speed, and the injection flow rate of the coolant,
and set the inclination angle of the fourth cold mill so that the coolant ride length
matches the calculated value.
[0033] The control unit preferably controls the plurality of rollers so that the inclination
angle is -10° or more. The control unit preferably controls the plurality of rollers
so that the inclination angle is -2° or less. As illustrated in the experimental examples
described below, when the inclination angle is -2° or more, the degree of increase
in the coolant liquid ride length is small, and the effect of temperature decrease
is small. When the inclination angle is less than -10°, smooth conveyance of the metal
steel strip may be hindered. In a case in which the inclination angle is -3° or less,
it may be possible to extend the length of the coolant liquid ride by a factor of
three or more. The control unit may therefore control the plurality of rollers so
that the inclination angle is -10° or more to -3° or less.
[0034] Here, the type of cold mill included in the cold rolling line is not limited. The
cold mill may, for example, be a multi-stage rolling mill or a reverse rolling mill.
Different types of cold mills may also be included. Even if the cold mill is a reverse
rolling mill, it suffices to set the inclination angle to adjust the length of the
coolant liquid ride so that the temperature of the metal steel strip is in the optimal
range.
[0035] The cold rolling line may have a limiting mechanism to prevent the inclination angle
from exceeding a predetermined angle range (for example, -10° to 10°). The limiting
mechanism may, for example, be a mechanical stopper or a device that limits the range
of motion of the lifting and lowering device based on a signal from a proximity switch
or other detection device.
[0036] The cold rolling line according to the present embodiment is used as part of a steel
sheet production line, as described above. The control unit of the cold rolling line
can perform a cold rolling method that includes controlling the plurality of rollers
so that the metal steel strip is at a lower position towards a downstream side in
the conveyance direction at an upstream side of one or more cold mills including the
most upstream mill. The control unit of the cold rolling line can perform a cold rolling
method that includes controlling the plurality of rollers so that the metal steel
strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of one or more cold mills including the most downstream mill.
The steel sheet production line can perform a steel sheet production method including
performing the cold rolling method and furthermore cutting the metal steel strip.
[0037] As described above, through the aforementioned configuration or processes (steps),
the cold rolling line, steel sheet production line, cold rolling method, and steel
sheet production method according to the present embodiment adjust the length of coolant
liquid ride to bring the temperature of the metal steel strip within the optimal temperature
range. Therefore, deformation of the work rolls can be controlled, and brittle cracking
during rolling can be suppressed.
[0038] While embodiments of the present disclosure have been described with reference to
the drawings, it should be noted that various modifications and amendments may easily
be implemented by those skilled in the art based on the present disclosure. For example,
functions or the like included in each component or the like can be rearranged without
logical inconsistency, and a plurality of components or the like can be combined into
one or divided. Embodiments according to the present disclosure can also be realized
as a program executed by a processor included in an apparatus or as a storage medium
having the program recorded thereon. Such embodiments are also to be understood as
included in the scope of the present disclosure.
[0039] A cold rolling line including four cold mills has been described in the above embodiment
with reference to FIG. 3, but the number of cold mills that the cold rolling line
includes is not limited. For example, a cold rolling line may include only one cold
mill, and the control unit may be configured to perform only one of control of the
plurality of rollers so that the metal steel strip is at a lower position towards
a downstream side in the conveyance direction and control of the plurality of rollers
so that the metal steel strip is at a higher position towards a downstream side in
the conveyance direction. In a case in which the cold rolling line includes a plurality
of cold mills, each of the intermediate cold mills, excluding the most upstream mill
and the most downstream mill, may be adjusted by the control unit to have a positive
inclination angle or a negative inclination angle, or adjustment of the inclination
angle may be omitted.
[0040] The effects of the present disclosure will be described in detail below based on
examples (experimental examples), but the subject matter of the present disclosure
is not limited to the examples.
EXAMPLES
[0041] Rolling experiments were conducted using the cold rolling line described in the above
embodiment to determine whether sticking and sheet fracture occur after rolling. The
cold rolling line was equipped with four cold mills, as illustrated in FIG. 3. The
components (mass%) of the targeted steel sample IDs A-C are illustrated in Table 1.
In Table 1, "Bal." indicates that the balance is Fe.
[Table 1]
[0042]
(Table 1)
|
Si (mass%) |
Mn (mass%) |
Al (mass%) |
Fe (mass%) |
Steel sample ID A |
2 |
1 |
0.5 |
Bal |
Steel sample ID B |
3.5 |
1 |
0.5 |
Bal |
Steel sample ID C |
5 |
1 |
0.5 |
Bal |
[0043] A rolling experiment (first experiment) was conducted by changing the inclination
angle from 0° to 10°. In the first experiment, the inclination angle of the first
cold mill (No. 1 std.), which is the most upstream mill, was changed. The coolant
flow rate was 100 L/min to 300 L/min. The initial temperature of the steel sheet (metal
steel strip) for sheet passing was 200 °C. The steel sheet (metal steel strip) size
was set for a width of 1000 mm and an initial thickness of 2.0 mm. The line speed
was 15 mpm or 100 mpm. The plate thickness was set to be from 2.0 mm to 1.2 mm by
rolling in the first cold mill. The coolant used was 5 % rolling oil plus 95 % pure
water. The coolant temperature was 60 °C.
[0044] Table 2 illustrates the results of the first experiment. Under a set of conditions
including No. 1, the liquid ride length was 100 mm or less, but sticking occurred.
Although no burning occurred under a set of conditions including No. 5, the coolant
ride length was a long value of 600 mm, and the plate temperature at the entry side
was 60 °C, which was 140 °C lower than the initial temperature, causing sheet fracture.
No. 3 and No. 4 are the results of inclining the pass line, and no sticking occurred
in either case. In No. 3 and No. 4, the plate temperature on the entry side was also
80 °C or more, which is equal to or greater than the ductility brittle transition
temperature, and no sheet fracture occurred.
[0045] Other results are illustrated in Table 2. For the Comparative Examples, the inclination
angle was 0°, and sheet fracture occurred at a high rate. As can be seen from the
Examples in Table 2, in a case in which the initial temperature of the steel sheet
(metal steel strip) is 200 °C, the prevention effect is further enhanced if the inclination
angle of the most upstream rolling mill is 5° or more in order to incline the pass
line and prevent sheet fracture. This result is considered to be similar for the intermediate
cold mills, where the temperature of the steel sheet (metal steel strip) on the entry
side is below the ductility brittle transition temperature.
[Table 2]
[0046]
(Table 2)
No. |
Steel sample ID |
Sheet temperature at No. 1 std entry side |
Target temperature at No. 1 std biting area |
Line speed (No. 1 std entry side) |
Coolant flow rate (steel sheet upper side) |
No. 1 std inclination angle (+: entry side > biting area, -: entry side < biting area) |
Estimated ΔT (error temperature) |
Fracture rate (per 100 coils) |
Notes |
1 |
A |
150 °C |
100°C |
15 mpm |
100 L/min |
0° |
-37 °C |
0.5 % |
Reference Example |
2 |
A |
150 °C |
100 °C |
15 mpm |
100 L/min |
2° |
-24 °C |
0.2 % |
Example |
3 |
A |
150 °C |
100°C |
15 mpm |
100 L/min |
5° |
-2 °C |
0.1 % |
Example |
4 |
A |
150 °C |
100°C |
15 mpm |
100 L/mm |
10° |
+1 °C |
0.1 % |
Example |
5 |
A |
200 °C |
100°C |
15 mpm |
100 L/min |
0° |
-35 °C |
0.5 % |
Reference Example |
6 |
A |
150 °C |
60°C |
15 mpm |
100 L/min |
0° |
-3 °C |
0.4 % |
Reference Example |
7 |
A |
150 °C |
100 °C |
100 mpm |
100 L/min |
0° |
-5 °C |
0.4 % |
Reference Example |
8 |
A |
150 °C |
100°C |
15 mpm |
300 L/mm |
0° |
-55 °C |
0.4 % |
Reference Example |
9 |
B |
150 °C |
100°C |
15 mpm |
100 L/min |
0° |
-38 °C |
3.3 % |
Comparative Example |
10 |
B |
150 °C |
100°C |
15 mpm |
100 L/min |
2° |
-21 °C |
0.4 % |
Example |
11 |
B |
150 °C |
100°C |
15 mpm |
100 L/min |
5° |
-5 °C |
0.2% |
Example |
12 |
B |
150 °C |
100 °C |
15 mpm |
100 L/min |
10° |
+2 °C |
0.2 % |
Example |
13 |
B |
200 °C |
100°C |
15 mpm |
100 L/min |
0° |
-34 °C |
3.3 % |
Reference Example |
14 |
B |
150 °C |
60°C |
15 mpm |
100 L/mm |
0° |
+1 °C |
3.5 % |
Reference Example |
15 |
B |
150 °C |
100°C |
100 mpm |
100 L/min |
0° |
-22°C |
1.0 % |
Reference Example |
16 |
B |
150 °C |
100°C |
15 mpm |
300 L/mm |
0° |
-55 °C |
3.4 % |
Reference Example |
17 |
C |
150 °C |
100 °C |
15 mpm |
100 L/mm |
0° |
-35 °C |
4.0% |
Comparative Example |
18 |
C |
150 °C |
100°C |
15 mpm |
100 L/min |
2° |
-25°C |
0.5 % |
Example |
19 |
C |
150 °C |
100°C |
15 mpm |
100 L/min |
5° |
-10 °C |
0.2% |
Example |
20 |
C |
150 °C |
100°C |
15 mpm |
100 L/min |
10° |
-2 °C |
0.7 % |
Example |
21 |
C |
200 °C |
100°C |
15 mpm |
100 L/min |
0° |
-36 °C |
4.7 % |
Reference Example |
22 |
C |
150 °C |
60°C |
15 mpm |
100 L/min |
0° |
-3 °C |
4.4 % |
Reference Example |
23 |
C |
150 °C |
100 °C |
100 mpm |
100 L/min |
0° |
-20°C |
3.3 % |
Reference Example |
24 |
C |
150 °C |
100°C |
15 mpm |
300 L/mm |
0° |
-55 °C |
4.9 % |
Reference Example |
[0047] Rolling experiments were also conducted using the cold rolling line described in
the above embodiment to determine whether shape defects occur after rolling. The cold
rolling line was equipped with four cold mills, as illustrated in FIG. 3. The components
(mass%) of the targeted steel sample IDs A-C are illustrated in Table 1.
[0048] A rolling experiment (second experiment) was conducted by changing the inclination
angle from 0° to -10°. In the second experiment, the inclination angle of the fourth
cold mill (No. 4 std.), which is the most downstream mill, was changed. The coolant
flow rate was 2000 L/min to 3000 L/min. The initial temperature of the steel sheet
(metal steel strip) for sheet passing was 300 °C. The steel sheet (metal steel strip)
size was set for a width of 1000 mm and an initial thickness of 2.0 mm. The line speed
was set to 1000 mpm to 1500 mpm. The plate thickness was set to be from 0.4 mm to
0.3 mm by rolling in the fourth cold mill. The coolant used was 5 % rolling oil plus
95 % pure water. The coolant temperature was 60 °C.
[0049] Table 3 illustrates the results of the second experiment. Setting the inclination
angle to 0° and the sheet temperature at the entry side to 250 °C yielded a coolant
liquid ride length of 400 mm, and quarter elongation (shape defect) occurred. Setting
the inclination angle to -2° and the sheet temperature at the entry side to 250 °C
yielded a coolant liquid ride length of 1500 mm, and quarter elongation did not occur.
[0050] Other results are illustrated in Table 3. For the Comparative Examples, the inclination
angle was 0°, and shape defects occurred at a high rate. As can be seen from the Examples
in Table 3, in a case in which the initial temperature of the steel sheet (metal steel
strip) is 300 °C, the prevention effect is enhanced if the inclination angle of the
most downstream rolling mill is -2° or less in order to incline the pass line and
prevent shape defects. This result is considered to be similar for the intermediate
cold mills, where the temperature of the steel sheet (metal steel strip) on the entry
side is at or above the shape defect occurrence temperature.
[Table 3]
[0051]
(Table 3)
No. |
Steel sample ID |
Sheet temperature at No. 4 std entry side |
Target temperature at No. 4 std biting area |
Line speed (No. 4 std entry side) |
Coolant flow rate (steel sheet upper side) |
No. 4 std inclination angle (+: entry side > biting area, -: entry side < biting area) |
Estimated ΔT (error temperature) |
Fracture rate (per 100 coils) |
Notes |
1 |
A |
250 °C |
150°C |
1000 mpm |
3000 L/min |
0° |
+62 °C |
1.5 % |
Comparative Example |
2 |
A |
250 °C |
150 °C |
1000 mpm |
3000 L/min |
-2° |
+12 °C |
0.4 % |
Example |
3 |
A |
250 °C |
150°C |
1000 mpm |
3000 L/min |
-5° |
±0 °C |
0.3 % |
Example |
4 |
A |
250 °C |
150 °C |
1000 mpm |
3000 L/mm |
-10° |
-5 °C |
0.2 % |
Example |
5 |
A |
300 °C |
150 °C |
1000 mpm |
3000 L/min |
0° |
+50 °C |
2.0 % |
Reference Example |
6 |
A |
250 °C |
200 °C |
1000 mpm |
3000 L/min |
0° |
+12 °C |
1.5 % |
Reference Example |
7 |
A |
250 °C |
150 °C |
1500 mpm |
3000 L/mm |
0° |
+70 °C |
2.5 % |
Reference Example |
8 |
A |
250 °C |
150 °C |
1000 mpm |
2000 L/min |
0° |
+54 °C |
2.2 % |
Reference Example |
9 |
B |
250 °C |
150°C |
1000 mpm |
3000 L/mm |
0° |
+60 °C |
1.3 % |
Comparative Example |
10 |
B |
250 °C |
150 °C |
1000 mpm |
3000 L/mm |
-2° |
+13 °C |
0.3 % |
Example |
11 |
B |
250 °C |
150 °C |
1000 mpm |
3000 L/mm |
-5° |
+1 °C |
0.3 % |
Example |
12 |
B |
250 °C |
150°C |
1000 mpm |
3000 L/min |
-10° |
-2 °C |
0.1 % |
Example |
13 |
B |
300 °C |
150 °C |
1000 mpm |
3000 L/min |
0° |
+51 °C |
2.1 % |
Reference Example |
14 |
B |
250 °C |
200 °C |
1000 mpm |
3000 L/min |
0° |
+10 °C |
1.7 % |
Reference Example |
15 |
B |
250 °C |
150°C |
1500 mpm |
3000 L/min |
0° |
+74 °C |
2.4 % |
Reference Example |
16 |
B |
250 °C |
150 °C |
1000 mpm |
2000 L/min |
0° |
+52 °C |
2.3 % |
Reference Example |
17 |
C |
250 °C |
150°C |
1000 mpm |
3000 L/min |
0° |
+61 °C |
1.6 % |
Comparative Example |
18 |
C |
250 °C |
150°C |
1000 mpm |
3000 L/mm |
-20 |
+13 °C |
0.5 % |
Example |
19 |
C |
250 °C |
150 °C |
1000 mpm |
3000 L/min |
-5° |
+2 °C |
0.4 % |
Example |
20 |
C |
250 °C |
150°C |
1000 mpm |
3000 L/min |
-10° |
-4 °C |
0.5 % |
Example |
21 |
C |
300 °C |
150 °C |
1000 mpm |
3000 L/mm |
0° |
+55 °C |
2.0 % |
Reference Example |
22 |
C |
250 °C |
200 °C |
1000 mpm |
3000 L/min |
0° |
+13 °C |
1.9 % |
Reference Example |
23 |
C |
250 °C |
150°C |
1500 mpm |
3000 L/mm |
0° |
+78 °C |
2.1 % |
Reference Example |
24 |
C |
250 °C |
150 °C |
1000 mpm |
2000 L/mm |
0° |
+55 °C |
2.2 % |
Reference Example |
1. A cold rolling line comprising one or more cold mills configured to inject coolant
towards a work roll and a metal steel strip and to cold roll the metal steel strip,
a plurality of rollers provided upstream from the one or more cold mills in a conveyance
direction of the metal steel strip and used to convey the metal steel strip, and a
control unit configured to control a height difference of the plurality of rollers,
wherein
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a lower position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most upstream mill provided farthest upstream.
2. The cold rolling line according to claim 1, wherein the control unit is configured
to set an inclination angle of the metal steel strip with respect to a biting area
of the one or more cold mills based on at least one of a steel type of the metal steel
strip, a line speed, an injection flow rate of the coolant, a temperature of the metal
steel strip, and a target temperature of the metal steel strip, at an upstream side
of at least a portion of the one or more cold mills including the most upstream mill.
3. The cold rolling line according to claim 2, wherein the control unit is configured
to control the plurality of rollers so that the inclination angle is 2° or more and
is 10° or less.
4. The cold rolling line according to any one of claims 1 to 3, wherein the one or more
cold mills comprises a plurality of cold mills, and
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
5. A cold rolling line comprising one or more cold mills configured to inject coolant
towards a work roll and a metal steel strip and to cold roll the metal steel strip,
a plurality of rollers provided upstream from the one or more cold mills in a conveyance
direction of the metal steel strip and used to convey the metal steel strip, and a
control unit configured to control a height difference of the plurality of rollers,
wherein
the control unit is configured to control the plurality of rollers so that the metal
steel strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
6. The cold rolling line according to claim 5, wherein the control unit is configured
to set an inclination angle of the metal steel strip with respect to a biting area
of the one or more cold mills based on at least one of a steel type of the metal steel
strip, a line speed, an injection flow rate of the coolant, a temperature of the metal
steel strip, and a target temperature of the metal steel strip, at an upstream side
of at least a portion of the one or more cold mills including the most downstream
mill.
7. The cold rolling line according to claim 6, wherein the control unit is configured
to control the plurality of rollers so that the inclination angle is -10° or more
and is -2° or less.
8. A steel sheet production line comprising the cold rolling line according to any one
of claims 1 to 7, and a line for cutting the metal steel strip.
9. A cold rolling method to be performed on a cold rolling line comprising one or more
cold mills configured to inject coolant towards a work roll and a metal steel strip
and to cold roll the metal steel strip, a plurality of rollers provided upstream from
the one or more cold mills in a conveyance direction of the metal steel strip and
used to convey the metal steel strip, and a control unit configured to control a height
difference of the plurality of rollers, the cold rolling method comprising:
controlling, by the control unit, the plurality of rollers so that the metal steel
strip is at a lower position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most upstream mill provided farthest upstream.
10. A cold rolling method to be performed on a cold rolling line comprising one or more
cold mills configured to inject coolant towards a work roll and a metal steel strip
and to cold roll the metal steel strip, a plurality of rollers provided upstream from
the one or more cold mills in a conveyance direction of the metal steel strip and
used to convey the metal steel strip, and a control unit configured to control a height
difference of the plurality of rollers, the cold rolling method comprising:
controlling, by the control unit, the plurality of rollers so that the metal steel
strip is at a higher position towards a downstream side in the conveyance direction
at an upstream side of at least a portion of the one or more cold mills including
a most downstream mill provided farthest downstream.
11. A steel sheet production method comprising performing the cold rolling method according
to claim 9 or 10, and cutting the metal steel strip.