[Type of Document] SPECIFICATION
[Title of the Invention] APPARATUS FOR COOLING HOT-ROLLED STEEL
SHEET
[Technical Field]
[0001]
The present invention relates to an apparatus for cooling a hot-rolled steel
sheet which cools a hot-rolled steel sheet hot-rolled using a finishing mill.
[Background Art]
[0002]
For example, a hot-rolled steel sheet used in cars, industrial machines and the
like is generally manufactured through a rough-rolling process and a finish-rolling
process. FIG 18 is a view schematically illustrating a method for manufacturing a
hot-rolled steel sheet of the related art. In the process for manufacturing a hot-rolled
steel sheet, first, a slab S obtained by continuously casting molten steel having an
adjusted predetermined composition is rolled using a roughing mill 201, and then,
furthermore, hot-rolled using a finishing mill 203 constituted by a plurality of rolling
stands 202a to 202d, thereby forming a hot-rolled steel sheet H having a predetermined
thickness. In addition, the hot-rolled steel sheet H is cooled using cooling water
supplied from a cooling apparatus 211, and then coiled into a coil shape using a coiling
apparatus 212.
[0003]
The cooling apparatus 211 is generally a facility for carrying out so-called
laminar cooling on the hot-rolled steel sheet H transported from the finishing mill 203.
The cooling apparatus 211 sprays the cooling water on the top surface of the hot-rolled
steel sheet H moving on a run-out table from the top in the vertical direction in a water
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4
jet form through a cooling nozzle, and, simultaneously, sprays the cooling water on the
bottom surface of the hot-rolled steel sheet H through a pipe laminar in a water jet
form, thereby cooling the hot-rolled steel sheet H.
[0004]
In addition, for example, Patent Document 1 discloses a technique of the
related art which reduces the difference in surface temperature between the top and
bottom surfaces of a thick steel sheet, thereby preventing the shape of the steel sheet
from becoming defective. According to the technique disclosed in Patent Document
1, the water volume ratio of cooling water supplied to the top surface and the bottom
surface of the steel sheet is adjusted based on the difference in surface temperature
obtained by simultaneously measuring the surface temperatures of the top surface and
the bottom surface of the steel sheet using a thermometer when the steel sheet is cooled
using a cooling apparatus.
[0005]
In addition, for example, Patent Document 2 discloses a technique that cools a
rolled material between two adjacent stands in a finishing mill using a sprayer, thereby
beginning and completing the y-a transformation of the rolled material so as to prevent
sheet-threading performance between the stands from deteriorating.
[0006]
In addition, for example. Patent Document 3 discloses a technique that
measures the steepness at the tip of a steel sheet using a steepness meter installed on
the exit side of a mill, and prevents the steel sheet from being perforated by adjusting
the flow rate of cooling water to be different in the width direction based on the
measured steepness.
[0007]
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4
Furthermore, for example. Patent Document 4 discloses a technique that aims
to solve a wave-shaped sheet thickness distribution in the sheet width direction of a
hot-rolled steel sheet and to make uniform the sheet thickness in the sheet width
direction, and controls the difference between the maximum heat transmissibility and
the minimum heat transmissibility in the sheet width direction of the hot-rolled steel
sheet to be in a range of predetermined values.
[0008]
Here, there are cases in which the hot-rolled steel sheet H manufactured using
the manufacturing method illustrated in FIG. 18 forms a wave shape in the rolling
direction (the arrow direction in FIG. 19) on transportation rolls 220 in the run-out
table (hereinafter sometimes referred to as "ROT") in the cooling apparatus 211 as
illustrated in FIG. 19. In this case, the top surface and the bottom surface of the hotrolled
steel sheet H are not uniformly cooled. That is, there was a problem in that,
due to cooling deviation caused by the wave shape of the hot-rolled steel sheet H, it
became impossible to uniformly cool the steel sheet in the rolling direction.
[0009]
Therefore, for example. Patent Document 5 discloses a technique that, in a
steel sheet formed into a wave shape in the rolling direction, makes uniform the
cooling capabilities of top portion cooling and bottom portion cooling so as to
minimize the influence of the distance between soaked water on the top portion of the
steel sheet and a table roller at the bottom portion in order to uniformly cool the steel
sheet.
[Prior Art Document]
[Patent Document]
[0010]
[Patent Document 1 ] Japanese Unexamined Patent Application, First
Publication No. 2005-74463
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. H05-337505
[Patent Document 3] Japanese Unexamined Patent Application, First
Publication No. 2005-271052
[Patent Document 4] Japanese Unexamined Patent Application, First
Publication No. 2003-48003
[Patent Document 5] Japanese Unexamined Patent Application, First
Publication No. H06-328117
[Summary of the Invention]
[Problem that the Invention is to solve]
[0011]
However, in the cooling method of Patent Document 1, a case of a hot-rolled
steel sheet having a wave shape in the rolling direction is not taken into consideration.
In the hot-rolled steel sheet H having a wave shape described above, there are cases in
which the bottom portion of the wave shape locally comes into contact with the
transportation rolls 220 as illustrated in FIG. 19. In addition, there are cases in which
the hot-rolled steel sheet H locally comes into contact with aprons (not illustrated in
FIG. 19) provided as supports in order to prevent the hot-rolled steel sheet H from
dropping between the transportation rolls 220 at the bottom portion of the wave shape.
In the wave-shaped hot-rolled steel sheet H, the portions that locally come into contact
with the transportation rolls 220 or the aprons become more easily cooled than other
portions due to heat dissipation by contact. Therefore, there was a problem in that the
hot-rolled steel sheet H was ununiformly cooled. That is, in Patent Document 1, the
- 4 -
fact that the wave shape of the hot-rolled steel sheet causes the hot-rolled steel sheet to
locally come into contact with the transportation rolls or the aprons and the contact
portions becomes easily cooled due to heat dissipation by contact is not taken into
consideration. Therefore, there are cases in which it is impossible to uniformly cool a
hot-rolled steel sheet having a wave shape formed as described above.
[0012]
In addition, the technique described in Patent Document 2 is to make (soft)
ultra low carbon steel having a relatively low hardness undergo y-a transformation
between stands in a finishing mill, and does not aim at uniform cooling. In addition,
the invention of Patent Document 2 does not relate to cooling in a case in which a
rolled material has a wave shape in the rolling direction or a rolled material is a steel
material that is so-called high tensile strength steel having a tensile strength (TS) of
800 MPa or more, and therefore there is a concern that uniform cooling may not be
possible in a case in which a rolled material is a hot-rolled steel sheet having a wave
shape or a steel material having a relatively high hardness.
[0013]
In addition, in the cooling method of Patent Document 3, the steepness of the
steel sheet in the width direction is measured, and the flow rate of cooling water is
adjusted in portions having a high steepness. However, when the flow rate of cooling
water in the sheet width direction of the steel sheet is changed, it becomes difficult to
make uniform the temperature of the steel sheet in the sheet width direction.
Furthermore, Patent Document 3 also does not take a hot-rolled steel sheet having a
wave shape in the rolling direction into consideration, and there are cases in which it is
not possible to uniformly cool a hot-rolled steel sheet as described above.
[0014]
»
In addition, the cooling of Patent Document 4 is the cooling of a hot-rolled
steel sheet immediately before roll bites in the finishing mill, and therefore it is not
possible to apply the cooling to a hot-rolled steel sheet which has undergone finishrolling
so as to have a predetermined thickness. Furthermore, Patent Document 4
also does not take a hot-rolled steel sheet having a wave shape in the rolling direction
into consideration, and there are cases in which it is not possible to uniformly cool a
hot-rolled steel sheet in the rolling direction as described above.
[0015]
In addition, in the cooling method of Patent Document 5, the cooling
capability of the top portion cooling includes not only cooling by the cooling water
supplied to the steel sheet from a top portion water supply nozzle but also cooling by
the soaked water in the top portion of the steel sheet. Since the soaked water is
influenced by the steepness of the wave shape formed in the steel sheet or the sheetthreading
speed of the steel sheet, strictly, it is not possible to specify the cooling
capability of the steel sheet due to the soaked water. Thus, it is difficult to accurately
control the cooling capability of the top portion cooling. Therefore, it is also difficult
to make the coohng capabilities of the top portion cooling and the bottom portion
cooling equivalence. Furthermore, the patent document describes an example of a
method for determining the cooling capabilities when the cooling capabilities of the
top portion cooling and the bottom portion cooling are made uniform, but does not
disclose ordinary determination methods. Therefore, in the cooling method of Patent
Document 5, there are cases in which it is not possible to uniformly cool a hot-rolled
steel sheet.
[0016]
The present invention has been made in consideration of the above problems,
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and an object of the present invention is to uniformly cool a hot-rolled steel sheet hotrolled
using a finishing mill.
[Means for Solving the Problems]
[0017]
The present invention employs the following means for solving the problems
and achieving the relevant object.
That is,
(1) According to an aspect of the present invention, an apparatus for cooling a
hot-rolled steel sheet is provided which cools a hot-rolled steel sheet hot-rolled using a
finishing mill in a cooling section provided on a sheet-threading path including a
thermometer that measures the temperature of the hot-rolled steel sheet on a
downstream side of the cooling section; a shape meter that measures a shape of the
hot-rolled steel sheet on the downstream side of the cooling section; a top side cooling
device that cools a top surface of the hot-rolled steel sheet in the cooling section; a
bottom side cooling device that cools a bottom surface of the hot-rolled steel sheet in
the cooling section; and a control device that controls at least one of an amount of heat
dissipated from the top surface by cooling and an amount of heat dissipated from the
bottom surface by cooling of the hot-rolled steel sheet in the cooling section by
controlling the top side cooling device and the bottom side cooling device based on
temperature measurement results of the hot-rolled steel sheet obtained from the
thermometer and the shape measurement results of the hot-rolled steel sheet obtained
from the shape meter, in which the control device includes an average temperature
computation unit that computes a chronological average value of the temperature of the
hot-rolled steel sheet on the downstream side of the cooling section as an average
temperature based on the temperature measurement results; a changing speed
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^ ^
computation unit that computes a changing speed of the hot-rolled steel sheet on the
downstream side of the cooling section based on the shape measurement results; a
control direction-determining unit that, when upward in a vertical direction of the hotrolled
steel sheet is set as positive, in an area with a positive changing speed, in a case
in which the temperature of the hot-rolled steel sheet is lower than an average
temperature of a range of one or more cycles of a wave shape of the hot-rolled steel
sheet, determines at least one of a direction in which the amount of heat dissipated
from the top surface by cooling decreases and a direction in which the amoimt of heat
dissipated from the bottom surface by cooling increases as a control direction, and, in a
case in which the temperature of the hot-rolled steel sheet is higher than the average
temperature, determines at least one of a direction in which the amount of heat
dissipated from the top surface by cooling increases and a direction in which the
amount of heat dissipated from the bottom surface by cooling decreases as the control
direction, in an urea with a negative changing speed, in a case in which the temperature
of the hot-rolled steel sheet is lower than the average temperature, determines at least
one of a direction in which the amount of heat dissipated from the top surface by
cooling increases and a direction in which the amount of heat dissipated from the
bottom surface by cooling decreases as the control direction, and, in a case in which
the temperature of the hot-rolled steel sheet is higher than the average temperature,
determines at least one of a direction in which the amount of heat dissipated from the
top surface by cooling decreases and a direction in which the amount of heat dissipated
from the bottom surface by cooling increases as the control direction; and a total
amount of heat dissipated by cooling-adjusting unit that adjusts a total value of the
amount of heat dissipated from the top surface by cooling and the amount of heat
dissipated from the bottom surface by cooling of the hot-rolled steel sheet in the
8
cooling section based on the control directions determined using the control directiondetermining
unit.
[0018]
(2) In the apparatus for cooling a hot-rolled steel sheet according to the above
(1), a location deviation between a temperature measurement place of the thermometer
and a shape measurement place of the shape meter in the hot-rolled steel sheet is
preferably 50 mm or less.
[0019]
(3) In the apparatus for cooling a hot-rolled steel sheet according to the above
(1) or (2), a sheet-threading speed of the hot-rolled steel sheet in the cooling section is
preferably set in a range of 550 m/min to a mechanical limit speed.
[0020]
(4) In the apparatus for cooling a hot-rolled steel sheet according to the above
(3), a tensile strength of the hot-rolled steel sheet is preferably 800 MPa or more.
[0021]
(5) In the apparatus for cooling a hot-rolled steel sheet according to the above
(3), the finishing mill is preferably constituted by a plurality of rolling stands, and a
supplementary cooling device that carries out supplementary cooling of the hot-rolled
steel sheet is preferably further provided between the adjacent rolling stands.
[Effect of the Invention]
[0022]
According to the above aspect of the present invention, when the phase of the
temperature of a hot-rolled steel sheet is detected, and compared with a wave shape of
the hot-rolled steel sheet, it is possible to adjust the top side cooling capability and the
bottom side cooling capability, and it is possible to adjust the amount of heat dissipated
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1l
from the top surface by cooling and the amount of heat dissipated from the bottom
surface by cooling of the hot-rolled steel sheet. Therefore, afterwards, when the hotrolled
steel sheet is cooled using the adjusted cooling capabilities, it is possible to
uniformly cool the hot-rolled steel sheet.
[Brief Description of the Drawing]
[0023]
FIG. 1 is an explanatory view illustrating a hot rolling facility 1 having an
apparatus for cooling a hot-rolled steel sheet in an embodiment of the present invention.
FIG. 2 is an explanatory view illustrating an outline of a configuration of a
cooling apparatus 14 in the present embodiment.
FIG. 3 is an explanatory view illustrating an outline of a configuration in a
vicinity of the cooling apparatus 14 in the hot rolling facility 1.
FIG. 4 is a graph illustrating a relationship between temperature change and
steepness of the hot-rolled steel sheet H during cooling in a ROT of a typical strip in an
ordinary operation, in which the top graph indicates the temperature change with
respect to a distance from a coil tip or a time at which a coil passes a fixed point, and
the bottom graph indicates the steepness with respect to the distance from the coil tip
or the time at which the coil passes the fixed point.
FIG. 5 is a graph illustrating the relationship between the temperature change
and steepness of the hot-rolled steel sheet H during cooling in a ROT of the typical
strip in the ordinary operation.
FIG. 6 is a graph illustrating the relationship between the temperature change
and steepness of the hot-rolled steel sheet H when an amount of heat dissipated from
the top surface by cooling is decreased and an amount of heat dissipated from the
bottom surface by cooling is increased in a case in which the temperature of the hot-
- 10 -
^
rolled steel sheet H becomes low with respect to an average temperature of the hotrolled
steel sheet H in an area of a positive changing speed of the hot-rolled steel sheet
H and the temperature of the hot-rolled steel sheet H becomes high in an area of a
negative changing speed. Meanwhile, the steepness of a wave shape of the hot-rolled
steel sheet H refers to a value obtained by dividing an amplitude of the wave shape by
a length of a cycle in a rolling direction.
FIG. 7 is a graph illustrating the relationship between the temperature change
and steepness of the hot-rolled steel sheet H when the amount of heat dissipated from
the top surface by cooling is increased and the amount of heat dissipated from the
bottom surface by cooling is decreased in a case in which the temperature of the hotrolled
steel sheet H is low with respect to the average temperature of the hot-rolled
steel sheet H in the area of a positive changing speed of the hot-rolled steel sheet H and
the temperature of the hot-rolled steel sheet H becomes high in the area of a negative
changing speed.
FIG. 8 is an explanatory view illustrating disposition of a thermometer 40 and
a shape meter 41 in the hot rolling facility 1.
FIG. 9 is an explanatory view illustrating a modified example of the cooling
apparatus 14 in the hot rolling facility 1.
FIG. 10 is a graph illustrating a relationship between the steepness and
temperature standard deviation of the hot-rolled steel sheet H.
FIG. 11 is a graph illustrating a relationship between the sheet-threading speed
and temperature standard deviation of the hot-rolled steel sheet H.
FIG. 12 is an explanatory view illustrating a pattern in which a temperature
standard deviation is formed in a sheet width direction of the hot-rolled steel sheet H.
FIG. 13 is an explanatory view illustrating a hot rolling facility 2 for realizing
- 11 -
^
a method for cooling the hot-rolled steel sheet H in another embodiment.
FIG. 14 is an explanatory view illustrating an outline of a configuration of a
cooling apparatus 114 provided in the hot rolling facility 2.
FIG. 15 A is an explanatory view illustrating a shape in which a bottom point
of the hot-rolled steel sheet H comes into contact with a transportation roll 132.
FIG. 15B is an explanatory view illustrating a shape in which the bottom point
of the hot-rolled steel sheet H comes into contact with the transportation roll 132 and
an apron 133.
FIG. 16A is a graph illustrating a change of the temperature of the hot-rolled
steel sheet H over time in a case in which the sheet-threading speed of the hot-rolled
steel sheet H is slow.
FIG. 16B is a graph illustrating a change of the temperature of the hot-rolled
steel sheet H over time in a case in which the sheet-threading speed of the hot-rolled
steel sheet H is high.
FIG. 17 is an explanatory view of a finishing mill 113 that can carry out interstand
cooling.
FIG. 18 is an explanatory view illustrating a method for manufacturing the
hot-rolled steel sheet H of the related art.
FIG. 19 is an explanatory view illustrating a method for cooling the hot-rolled
steel sheet H of the related art.
[Embodiment of the Invention]
[0024]
Hereinafter, as an embodiment of the present invention, an apparatus for
cooling a hot-rolled steel sheet that cools a hot-rolled steel sheet used in, for example,
cars and industrial machines will be described with reference to the accompanying
- 12 -
^
drawings.
[0025]
FIG 1 schematically illustrates an example of a hot rolling facility 1 having
the apparatus for cooling a hot-rolled steel sheet in the present embodiment. The hot
rollmg facility 1 is a facility which aims to sandwich the top and bottom of a heated
slab S using rolls, continuously roll the slab to make the slab as thin as a minimum of 1
mm, and coil the slab.
The hot rolling facility 1 has a heating furnace 11 for heating the slab S, a
width-direction mill 16 that rolls the slab S heated in the heating furnace 11 in a width
direction, a roughing mill 12 that rolls the slab S rolled in the width direction from the
vertical direction so as to produce a rough bar, a finishing mill 13 that further
continuously hot-finishing-rolls the rough bar to a predetermined thickness, a cooling
apparatus 14 that cools the hot-rolled steel sheet H hot-finishing-rolled using the
finishing mill 13 using cooling water, and a coiling apparatus 15 that coils the hotrolled
steel sheet H cooled using the cooling apparatus 14 into a coil shape.
[0026]
The heating furnace 11 is provided with a side burner, an axial burner and a
roof burner that heat the slab S brought from the outside through a charging hole by
blowing flame. The slab S brought into the heating furnace 11 is sequentially heated
in respective heating areas formed in respective zones, and, furthermore, a heatretention
treatment for enabling transportation at an optimal temperature is carried out
by uniformly heating the slab S using the roof burner in a soaking area formed in a
final zone. When a heating treatment in the heating furnace 11 completely ends, the
slab S is transported to the outside of the heating furnace 11, and moved into a rolling
process by the roughing mill 12.
- 13 -
[0027]
The roughing mill 12 passes the transported slab S through gaps between
columnar rotary rolls provided across a plurality of stands. For example, the
roughing mill 12 hot-rolls the slab S only using work rolls 12a provided at the top and
bottom of a first stand so as to form a rough bar. Next, the rough bar which has
passed through the work rolls 12a is fiirther continuously rolled using a plurality of
fourfold mills 12b constituted by a work roll and a back-up roll. As a result, when the
rough rolling process ends, the rough bar is rolled into a thickness of approximately 30
mm to 60 mm, and transported to the finishing mill 13.
[0028]
The finishing mill 13 fmishing-rolls the rough bar transported from the
roughing mill 12 until the thickness becomes approximately several millimeters. The
finishing mill 13 passes the rough bar through gaps between top and bottom finish
rolling rolls 13a linearly arranged across 6 to 7 stands so as to gradually reduce the
rough bar. The hot-rolled steel sheet H finishing-roUed using the finishing mill 13 is
transported to the cooling apparatus 14 using the transportation rolls 32 described
below.
[0029]
The cooling apparatus 14 is a facility for carrying out so-called laminar
cooling on the hot-rolled steel sheet H transported from the finishing mill 13. As
illustrated in FIG. 2, the cooling apparatus 14 has a top side cooling device 14a that
sprays cooling water from cooling holes 31 on the top side to the top surface of the
hot-rolled steel sheet H moving on the transportation rolls 32 in a run-out table, and a
bottom side cooling device 14b that sprays cooling water from cooling holes 31 on the
bottom side to the bottom surface of the hot-rolled steel sheet H. A plurality of the
- 14 -
ID
cooling holes 31 is provided in the top side cooling device 14a and the bottom side
cooling device 14b respectively.
In addition, a cooling header (not illustrated) is connected to the cooling hole
31. The number of the cooling holes 31 determines the cooling capabilities of the top
side cooling device 14a and the bottom side cooling device 14b. Meanwhile, the
cooling apparatus 14 may be constituted by at least one of top and bottom split laminar,
pipe laminar, spray cooling and the like. In addition, a section in which the hot-rolled
steel sheet H is cooled using the cooling apparatus 14 corresponds to a cooling section
in the present invention.
[0030]
In addition, on the downstream side of the cooling section (that is, the cooling
apparatus 14), a thermometer 40 that measures the temperature of a measurement
location set in the rolling direction of the hot-rolled steel sheet H and a shape meter 41
that measures the wave shape of the hot-rolled steel sheet H at the same measurement
location as the thermometer 40 are disposed as illustrated in FIG. 3.
The thermometer 40 and the shape meter 41 are electrically connected to a
control device 50 through cables and the like. In addition, the control device 50 is
electrically connected to the top side cooling device 14a and the bottom side cooling
device 14b through cables and the like.
The thermometer 40 outputs the temperature measurement results of the hotrolled
steel sheet H to the control device 50. The shape meter 41 outputs the shape
measurement results of the hot-rolled steel sheet H to the control device 50.
The control device 50 controls at least one of the amovmt of heat dissipated
from the top surface by cooling and the amount of heat dissipated from the bottom
surface by cooling of the hot-rolled steel sheet H in the cooling section by controlling
- 15 -
the top side cooling device 14a and the bottom side cooling device 14b based on the
temperature measurement results obtained from the thermometer 40 and the shape
measurement results obtained from the shape meter 41.
The control device 50 has an average temperature computation unit 51, a
changing speed computation unit 52, a control direction-determining unit 53 and a total
amount of heat dissipated by cooling-adjusting unit 54 as functions realized by running
of programs. The functions of the respective functional units will be described.
[0031]
The coiling apparatus 15 coils the hot-rolled steel sheet H cooled using the
cooling apparatus 14 at a predetermined coiling temperature as illustrated in FIG. 1.
The hot-rolled steel sheet H coiled into a coil shape using the coiling apparatus 15 is
transported to the outside of the hot rolling facility 1.
Meanwhile, in the hot rolling facility 1 constituted as described above, the top
side cooling device 14a, the bottom side cooling device 14b, the thermometer 40, the
shape meter 41 and the control device 50 constitute the apparatus for cooling a hotrolled
steel sheet in the present embodiment.
[0032]
Next, a method for cooling the hot-rolled steel sheet H, which is realized
using the hot rolling facility 1 constituted as described above, will be described.
Meanwhile, in the following description, a wave shape having a surface
height (wave height) changing in the rolling direction is formed in the hot-rolled steel
sheet H hot-rolled using the finishing mill 13 as illustrated in FIG. 19. In addition, in
the following description, the influence of soaked water remaining on the hot-rolled
steel sheet H will be ignored when cooling the hot-rolled steel sheet H. Actually, as a
result of investigation by the inventors, it has been found that the soaked water
- 16
remaining on the hot-rolled steel sheet H has little influence.
[0033]
First, before cooling the hot-rolled steel sheet H in the cooling apparatus 14,
the cooling capability (top side cooling capability) of the top side cooling device 14a
and the cooling capability (bottom side cooling capability) of the bottom side cooling
device 14b are adjusted respectively in advance. The top side cooling capability and
the bottom side cooling capability are adjusted using the heat transfer coefficient of the
top surface of the hot-rolled steel sheet H, which is cooled using the top side cooling
device 14a, and the heat transfer coefficient of the bottom surface of the hot-rolled
steel sheet H, which is cooled using the bottom side cooling device 14b.
[0034]
Here, a method for computing the heat transfer coefficients of the top surface
and bottom surface of the hot-rolled steel sheet H will be described. The heat transfer
coefficient refers to a value obtained by dividing the amount of heat dissipated from a
unit area by cooling (heat energy) per unit time by the temperature difference between
an article to which heat is transferred and a heat medium (heat transfer
coefficient=amoimt of heat dissipated by cooling/temperature difference). The
temperature difference herein refers to the difference between the temperature of the
hot-rolled steel sheet H, which is measured using a thermometer on an entry side of the
cooling apparatus 14, and the temperature of cooling water used in the cooling
apparatus 14.
In addition, the amount of heat dissipated by cooling refers to a value obtained
by respectively multiplying the temperature difference, specific heat and mass of the
hot-rolled steel sheet H (amount of heat dissipated by cooling=temperature
differencexspecific heatxmass). That is, the amount of heat dissipated by cooling is
- 17 -
ft
an amount of heat dissipated by cooling of the hot-rolled steel sheet H in the cooling
apparatus 14, and a value obtained by multiplying the difference between the
temperatures of the hot-rolled steel sheet H respectively measured using the entry-side
thermometer and an exit-side thermometer in the cooling apparatus 14, the specific
heat of the hot-rolled steel sheet H and the mass of the hot-rolled steel sheet H cooled
using the cooling apparatus 14 respectively.
[0035]
As described above, the computed heat transfer coefficient of the hot-rolled
steel sheet H is classified into the heat transfer coefficient of the top surface and the
heat transfer coefficient of the bottom surface of the hot-rolled steel sheet H. The
heat transfer coefficients of the top surface and the bottom surface are computed using
a ratio that is obtained in advance, for example, in the following maimer.
That is, the heat transfer coefficient of the hot-rolled steel sheet H in a case in
which the hot-rolled steel sheet H is cooled only using the top side cooling device 14a
and the heat transfer coefficient of the hot-rolled steel sheet H in a case in which the
hot-rolled steel sheet H is cooled only using the bottom side cooling device 14b are
measured.
At this time, the amount of cooling water from the top side cooling device 14a
and the amount of cooling water from the bottom side cooling device 14b are set to be
equal. The inverse number of the ratio between the measured heat transfer coefficient
in a case in which the top side cooling device 14a is used and the heat transfer
coefficient in a case in which the bottom side cooling device 14b is used becomes a top
and bottom ratio of the amount of cooling water from the top side cooling device 14a
to the amount of cooling water from the bottom side cooling device 14b in a case in
which a top and bottom heat transfer coefficient ratio is set to " 1 ".
- 18 -
A
In addition, the above-mentioned ratio of the heat transfer coefficients of the
top surface and the bottom surface of the hot-rolled steel sheet H is computed by
multiplying the amount of cooling water from the top side cooling device 14a or the
amount of cooling water from the bottom side cooling device 14b when cooling the
hot-rolled steel sheet H by the top and bottom ratio of the amounts of cooling water
obtained in the above manner.
In addition, in the above description, the heat transfer coefficients of the hotrolled
steel sheet H cooled only using the top side cooling device 14a and only using
the bottom side cooling device 14b are used, but the heat transfer coefficient of the hotrolled
steel sheet H cooled using both the top side cooling device 14a and the bottom
side cooling device 14b may be used. That is, the heat transfer coefficients of the hotrolled
steel sheet H in a case in which the amounts of cooling water of the top side
cooling device 14a and the bottom side cooling device 14b are changed are measured,
and the ratio of the heat transfer coefficients of the top surface and the bottom surface
of the hot-rolled steel sheet H may be computed using the ratio of the heat transfer
coefficients.
[0036]
As described above, the heat transfer coefficients of the hot-rolled steel sheet
H are computed, and the heat transfer coefficients of the top surface and the bottom
surface of the hot-rolled steel sheet H are computed based on the above ratio of the
heat transfer coefficients of the top surface and the bottom surface of~the hot-rolled
steel sheet H (top and bottom heat transfer coefficient ratio).
[0037]
Here, as a result of thorough studies regarding the adjustment of the cooling
capabilities of the top side cooling device 14a and the bottom side cooling device 14b
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#
(control of the amount of heat dissipated from the top surface by cooling and the
amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel
sheet H) in order to uniformly cool the hot-rolled steel sheet H, the inventors further
obtained the following findings.
[0038]
As a result of repeating thorough studies regarding the characteristics of the
temperatiire standard deviation generated by cooling in a state in which a wave shape
of the hot-rolled steel sheet H is generated, the inventors clarified the following fact.
[0039]
The temperature and shape of the hot-rolled steel sheet H in the process of
sheet-threading are measured at measurement locations set in the rolling direction of
the hot-rolled steel sheet H (hereinafter, the measurement locations will be sometimes
referred to as fixed points) using the thermometer 40 and the shape meter 41 at certain
time intervals (sampling intervals), and the chronological data of the temperature
measurement results and the shape measurement results are obtained.
Meanwhile, the temperature measurement area using the thermometer 40
includes all the area of the hot-rolled steel sheet H in the width direction. In addition,
the shape refers to the steepness obtained through the line integration of the heights or
changing components of pitches of the wave using the amount of movement of the hotrolled
steel sheet H in the sheet-threading direction as the amount of change of the hotrolled
steel sheet H in the height direction observed in measurement at the fixed point.
In addition, at the same time, the amount of change per unit time, that is, changing
speed is also obtained. Furthermore, similarly to the temperature measurement area,
the shape measurement area includes all the areas of the hot-rolled steel sheet H in the
width direction. In addition, when the sampling times of the respective measurement
- 20 -
#
results are multiplied by the sheet-threading speed (transportation speed) of the hotrolled
steel sheet H, it is possible to compute the locations of the hot-rolled steel sheet
H in the rolling direction at which the respective measurement results are obtained.
That is, when the times at which the chronological data of the respective measurement
results are sampled are multiplied by the sheet-threading speed, it becomes possible to
link the chronological data of the respective measurement results to the locations in the
rolling direction.
[0040]
First, the total value of the amount of heat dissipated from the top surface by
cooling and the amount of heat dissipated from the bottom surface by cooling of the
hot-rolled steel sheet H is adjusted using the chronological data. Specifically, the
total value of the amount of heat dissipated from the top surface by cooling and the
amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel
sheet H is adjusted so that the chronological average value of the temperatures
measured using the thermometer 40 matches a predetermined target value.
In addition, when adjusting the total value of the amount of heat dissipated
from the top surface by cooling and the amount of heat dissipated from the bottom
surface by cooling, the on-oflf control of cooling headers connected to the cooling
apparatus 14 may be carried out on a theoretical value obtained in advance using an
experimental theoretical formula represented by, for example, Mitsuzuka's formula
based on a learned value set to correct the error with an actual operation achievement.
Alternatively, the on-off of the cooling headers may be feedback-controlled or
feedforward-controlled based on the temperature actually measured using the
thermometer 40.
[0041]
- 21
Next, the cooling control of the ROT of the related art will be described using
data obtained from the above-described thermometer 40 and a shape meter 41. FIG. 4
illustrates the relationship between the temperature change and steepness of the hotrolled
steel sheet H during cooling in the ROT of a typical strip in an ordinary
operation. The top and bottom heat transfer coefficient ratio of the hot-rolled steel
sheet H in FIG. 4 is 1.2:1, and the top side cooling capability is superior to the bottom
side cooling capability. The top graph in FIG. 4 indicates the temperature change
with respect to the distance from a coil tip or a time at which a coil passes the fixed
point, and the bottom graph in FIG. 4 indicates the steepness with respect to the
distance from the coil tip or the time at which the coil passes the fixed point.
The area A in FIG. 4 is an area before the strip tip portion illustrated in FIG. 3
is bit in a coiler of the coiling apparatus 15 (since there is no tension, the shape is
defective in this area). The area B in FIG. 4 is an area after the strip tip portion is bit
in the coiler (the area in which the wave shape is changed to be flat by the influence of
unit tension). There is a demand for improving a large temperature change (that is,
the temperature standard deviation) occurring in the area in which the shape of the hotrolled
steel sheet H is not flat.
[0042]
Therefore, the inventors carried out thorough tests for the purpose of
controlling the increase in the temperature standard deviation in ROT, and,
consequently, obtained the following findings.
[0043]
Similarly to FIG. 4, FIG. 5 illustrates the temperature-changing component
with respect to the steepness of the same shape during cooling in the ROT of the
typical strip in the ordinary operation. The temperature-change component is a
- 22 -
^
residual error obtained by subtracting the chronological average of the temperature
from the actual steel sheet temperature (hereinafter sometimes referred to as "average
temperature"). For example, the average temperature may be the average of the
temperature of a range that is a cycle or more of the wave shape of the hot-rolled steel
sheet H.
Meanwhile, the average temperature is, in principle, the average of the
temperature range of the unit cycle. In addition, it is confirmed from operation data
that there is no large difference between the average temperature of a range of a cycle
and the average temperature of a range of two or more cycles.
Therefore, the average temperature simply needs to be computed from a range
of at least a cycle of the wave shape. The upper limit of the range of the wave shape
of the hot-rolled steel sheet H is not particularly limited; however, a sufficiently
accurate average temperature can be obtained when the range is preferably set to 5
cycles. In addition, even when the average temperature is computed not from a range
of the unit cycle but from a range of 2 to 5 cycles, a permissible average temperature
can be obtained.
[0044]
Here, when upward in the vertical direction (the direction that is perpendicular
to the top and bottom surfaces of the hot-rolled steel sheet H) of the hot-rolled steel
sheet H is set as positive, in an area with a positive changing speed measured at the
fixed point, in a case in which the temperature (the temperature measured at the fixed
point) of the hot-rolled steel sheet H is lower than the average temperature of a range
of one or more cycles of the wave shape of the hot-rolled steel sheet H, at least one of a
direction in which the amount of heat dissipated from the top surface by cooling
decreases and a direction in which the amount of heat dissipated from the bottom
- 23 -
^
surface by cooling increases is determined as a control direction, and, in a case in
which the temperature of the hot-rolled steel sheet H is higher than the average
temperature, at least one of a direction in which the amount of heat dissipated from the
top surface by cooling increases and a direction in which the amount of heat dissipated
from the bottom surface by cooling decreases is determined as the control direction.
In addition, in an area with a negative changing speed measured at the fixed
point, in a case in which the temperature of the hot-rolled steel sheet H is lower than
the average temperature, at least one of a direction in which the amount of heat
dissipated from the top surface by cooling increases and a direction in which the
amount of heat dissipated from the bottom surface by cooling decreases is determined
as the control direction; and, in a case in which the temperature of the hot-rolled steel
sheet H is higher than the average temperature, at least one of a direction in which the
amount of heat dissipated from the top surface by cooling decreases and a direction in
which the amount of heat dissipated from the bottom surface by cooling increases is
determined as the control direction.
In addition, it was found that, when at least one of the amount of heat
dissipated from the top surface by cooling and the amount of heat dissipated from the
bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is
adjusted based on the control direction determined as described above, as illustrated in
FIG. 6, the temperature change occurring in the area A in which the shape of the hotrolled
steel sheet H is not flat can be reduced compared with FIG. 5.
[0045]
A case in which an opposite operation to the above case is carried out will be
described below. In an area with a positive changing speed measured at the fixed
point, in a case in which the temperature of the hot-rolled steel sheet H is lower than
- 24 -
the average temperature of the hot-rolled steel sheet H, at least one of a direction in
which the amount of heat dissipated from the top surface by cooling increases and a
direction in which the amount of heat dissipated from the bottom surface by cooling
decreases is determined as the control direction, and, in a case in which the
temperature of the hot-rolled steel sheet H is higher than the average temperature, at
least one of a direction in which the amount of heat dissipated from the top surface by
cooling decreases and a direction in which the amount of heat dissipated from the
bottom surface by cooling increases is determined as the control direction.
In addition, in an area with a negative changing speed measured at the fixed
point, in a case in which the temperature of the hot-rolled steel sheet H is lower than
the average temperature, at least one of a direction in which the amount of heat
dissipated from the top surface by cooling decreases and a direction in which the
amount of heat dissipated from the bottom surface by cooling increases is determined
as the control direction, and, in a case in which the temperature of the hot-rolled steel
sheet H is higher than the average temperature, at least one of a direction in which the
amount of heat dissipated from the top surface by cooling increases and a direction in
which the amount of heat dissipated from the bottom surface by cooling decreases is
determined as the control direction.
In addition, it was found that, when at least one of the amount of heat
dissipated from the top surface by cooling and the amount of heat dissipated from the
bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is
adjusted based on the control direction determined as described above, as illustrated in
FIG. 7, the temperature change occurring in the area A in which the shape of the hotrolled
steel sheet H is not flat enlarges compared with FIG. 5. Meanwhile, in the
examples described herein, an assumption does not apply in which the cooling end
- 25 -
temperature may be changed.
[0046]
Use of the above relationship clarifies which cooling capability of the top side
cooling device 14a and the bottom side cooling device 14b in the cooling apparatus 14
needs to be adjusted in order to reduce the temperature change, that is, the temperature
standard deviation. Meanwhile, the above relationship is summarized in Table 1.
26
ims^imi^im^^m^^iii^ii^^s^ mmmmmmm
[0047]
[Table 1]
Changing speed
Temperature
Amount of heat
dissipated by cooHng
Top surface side
Bottom surface side
Positive
Low
Decrease
Increase
High
Increase
Decrease
Negative
Low
Increase
Decrease
High
Decrease
Increase
- 27 -
mmmm'^mmisrmtm
fe
[0048]
The apparatus for cooling a hot-rolled steel sheet of the present embodiment is
to realize the above-described cooling method. That is, the average temperature
computation unit 51 in the control device 50 computes the chronological average value
of the temperature measurement results obtained from the thermometer 40 in
chronological order as the average temperature. In addition, the changing speed
computation unit 52 computes the changing speed of the hot-rolled steel sheet H as an
average temperature based on the shape measurement results obtained from the shape
meter 41 in chronological order.
When upward in the vertical direction of the hot-rolled steel sheet H is set as
positive, in an area with a positive changing speed measured at the fixed point, in a
case in which the temperature (the temperature measured at the fixed point) of the hotrolled
steel sheet H is lower than the average temperature of a range of one or more
cycles of the wave shape of the hot-rolled steel sheet H, the control directiondetermining
unit 53 determines at least one of a direction in which the amount of heat
dissipated from the top surface by cooling decreases and a direction in which the
amount of heat dissipated firom the bottom surface by cooling increases as a control
direction, and, in a case in which the temperature of the hot-rolled steel sheet H is
higher than the average temperature, the control direction-determining unit 53
determines at least one of a direction in which the amount of heat dissipated firom the
top surface by cooling increases and a direction in which the amount of heat dissipated
from the bottom surface by cooling decreases as the control direction.
In addition, in an area with a negative changing speed measured at the fixed
point, in a case in which the temperature of the hot-rolled steel sheet H is lower than
the average temperature, the control direction-determining unit 53 determines at least
- 28 -
Is
one of the direction in which the amount of heat dissipated from the top surface by
cooling increases and the direction in which the amoimt of heat dissipated from the
bottom surface by cooling decreases as the control direction; and, in a case in which
the temperature of the hot-rolled steel sheet H is higher than the average temperature,
the control direction-determining unit 53 determines at least one of the direction in
which the amount of heat dissipated from the top surface by cooling decreases and the
direction in which the amount of heat dissipated from the bottom surface by cooling
increases as the control direction.
In addition, the total amount of heat dissipated by cooling-adjusting unit 54
adjusts the total value of the amount of heat dissipated from the top surface by cooling
and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled
steel sheet H in the cooling section based on the control directions determined as
described above.
[0049]
Meanwhile, when adjusting the cooling capability of the top side cooling
device 14a and the cooling capability of the bottom side cooling device 14b, for
example, the cooling headers connected to cooling holes 31 in the top side cooling
device 14a and the cooling headers connected to cooling holes 31 in the bottom side
cooling device 14b may be on-off controlled respectively. Alternatively, the cooling
capabilities of the respective cooling headers in the top side cooling device 14a and the
bottom side cooling device 14b may be controlled. That is, at least one of the sprayed
water density, pressure and water temperature of cooling water sprayed from the
respective cooling holes 31 may be adjusted.
In addition, the flow rate or pressure of cooling water sprayed from the top
side cooling device 14a and the bottom side cooling device 14b may be adjusted by
- 29 -
^
thinning out the cooling headers (cooling holes 31) of the top side cooling device 14a
and the bottom side cooling device 14b. For example, in a case in which the cooling
capability of the top side cooling device 14a before thinning out the cooling headers is
superior to the cooling capability of the bottom side cooling device 14b, the cooling
headers that constitute the top side cooling device 14a are preferably thinned out.
[0050]
The hot-rolled steel sheet H is uniformly cooled by spraying cooling water
onto the top surface of the hot-rolled steel sheet H from the top side cooling device 14a
and spraying cooling water onto the bottom surface of the hot-rolled steel sheet H from
the bottom side cooling device 14b using the cooling capabilities adjusted as described
above.
[0051]
After that, the temperature and shape of the hot-rolled steel sheet H cooled
using the cooling apparatus 14 are measured at the same point of the fixed point
respectively using the thermometer 40 and the shape meter 41, and the temperature and
the shape are measured as chronological data. Meanwhile, the temperature
measurement area includes all the area of the hot-rolled steel sheet H in the width
direction. In addition, the shape indicates the amount of change of the hot-rolled steel
sheet H in the height direction observed in a measurement at the fixed point.
Furthermore, similarly to the temperature measurement area, the shape measurement
area includes all the area of the hot-rolled steel sheet H in the width direction. When
the sampling times are multiplied by the sheet-threading speed, it becomes possible to
link the chronological data of the measurement results of the temperature, the changing
speed and the like to the locations in the rolling direction.
[0052]
30
§
As described using FIGS. 4, 5, 6 and 7, in an area with a positive changing
speed at the fixed point in the hot-rolled steel sheet H, in a case in which the
temperature of the hot-rolled steel sheet H at the fixed point is lower than the average
temperature at the fixed point, it is possible to reduce the temperature standard
deviation by decreasing the top side cooling capability (the amount of heat dissipated
from the top surface by cooling). Similarly, it is possible to reduce the temperature
standard deviation by increasing the bottom side cooling capability (the amount of heat
dissipated from the bottom surface by cooling). Use of the above relationship
clarifies which cooling capability of the top side cooling device 14a and the bottom
side cooling device 14b in the cooling apparatus 14 needs to be adjusted in order to
reduce the temperature standard deviation.
[0053]
That is, understanding of the change of temperature with respect to location
linked to the wave shape of the hot-rolled steel sheet H enables clarifying which of the
top side cooling and the bottom side cooling causes the currently occurring
temperature standard deviation. Therefore, the increase and decrease directions
(control directions) of the top side cooling capability (amount of heat dissipated from
the top surface by cooling) and the bottom side cooling capability (amount of heat
dissipated from the bottom surface by cooling) for decreasing the temperature standard
deviation are determined, and it is possible to adjust the top and bottom heat transfer
coefficient ratio.
In addition, it is possible to determine the top and bottom heat transfer
coefficient ratio based on the degree of the temperature standard deviation so that the
temperature standard deviation falls into a permissible range, for example, a range of
the minimum value to the minimum value+10°C. Meanwhile, when the temperature
- 31 -
standard deviation falls into a range of the minimum value to the minimum
value+10°C, the variations in yield stress, tensile strength and the like are suppressed
within the manufacturing permissible ranges, and the hot-rolled steel sheet H can be
uniformly cooled. In addition, although there are large variations, the temperature
standard deviation falls into a range of the minimum value to the minimum
value+10°C as long as a sprayed cooling water density ratio is ±5% or less with respect
to the sprayed cooling water density ratio at which the temperature standard deviation
becomes the minimum value. That is, in a case in which the sprayed cooling water
density is used, the top and bottom ratio of the sprayed cooling water density (sprayed
cooling water density ratio) is desirably set to ±5% or less with respect to the sprayed
cooling water density ratio at which the temperature standard deviation becomes the
minimum value. However, the permissible range does not always include the top and
bottom sprayed water density.
[0054]
According to the above embodiment, the hot-rolled steel sheet H is cooled by
adjusting the cooling capabilities of the top side cooling device 14a and the bottom
side cooling device 14b, and then the cooling capability of the top side cooling device
14a and the cooling capability of the bottom side cooling device 14b are fiirther
adjusted based on the measurement results of the temperature and wave shape of the
cooled hot-rolled steel sheet H. Since the cooling capabilities of the top side cooling
device 14a and the bottom side cooling device 14b can be adjusted to be qualitatively
and quantitatively appropriate cooling capabilities through feedback control in the
above manner, it is possible to further improve the uniformity of the hot-rolled steel
sheet H which will be cooled afterwards.
[0055]
- 32
§
As described above, according to the present embodiment, it is possible to
uniformly cool the hot-rolled steel sheet H by minimizing the temperature standard
deviation of the hot-rolled steel sheet H.
[0056]
In the above embodiment, the temperature and shape of the hot-rolled steel
sheet H are measured at the fixed point at the same measurement location using the
thermometer 40 and the shape meter 41; however, as a result of investigation by the
inventors, it was found that the measurement locations of the thermometer 40 and the
shape meter 41 may not be strictly the same. It was found that, specifically, when the
location deviation (distance) L between the temperature measurement place PI of the
thermometer 40 and the shape measurement place P2 of the shape meter 41 on the hotrolled
steel sheet H is 50 mm or less and preferably 30 mm or less as illustrated in FIG.
8, it is possible to appropriately understand the temperature and shape of the hot-rolled
steel sheet H.
The direction of the location deviation L between the measurement places of
the thermometer 40 and the shape meter 41 may be the sheet-threading direction of the
hot-rolled steel sheet H as illustrated in FIG. 8, may be the sheet thickness direction of
the hot-rolled steel sheet H, and may be an arbitrary direction. Meanwhile, in the
example of FIG. 8, the thermometer 40 is disposed on the upstream side of the shape
meter 41, conversely, the shape meter 41 may be disposed on the upstream side of the
thermometer 40.
[0057]
Here, the reason for the location deviation L between the measurement places
of the thermometer 40 and the shape meter 41 being preferably set to 50 mm or less
will be described. Table 2 describes the relationship between the temperature
- 33 -
#
standard deviation of the hot-rolled steel sheet H and the differences (the differences of
the standard deviations from the minimum value) between the respective temperature
standard deviations and the minimum value (the minimum value=10.0 in Table 2) in a
case in which the location deviation L between the measurement places of the
thermometer 40 and the shape meter 41 is changed in a range of-200 mm to +200 mm
in the rolling direction under the same conditions of the top and bottom heat transfer
coefficient ratio, the steepness and the sheet-threading speed when the invention is
applied to an actual apparatus.
Meanwhile, in Table 2, the temperature measurement place PI of the
thermometer 40 is used as a criterion, a location deviation L is indicated using a
positive value in a case in which the shape measurement place P2 of the shape meter
41 is set on the downstream side of the temperature measurement place, and a location
deviation L is indicated using a negative value in a case in which the shape
measurement place P2 of the shape meter 41 is set on the upstream side of the
temperature measurement place. In addition, in a case in which the temperature
measurement place PI of the thermometer 40 and the shape measurement place P2 of
the shape meter 41 are set to the same location, the location deviation L becomes zero.
As illustrated in Table 2, it was found that, when the location deviation L
between the measurement places of the thermometer 40 and the shape meter 41 was 50
mm or less regardless of whether the value was positive or negative, the difference of
the standard deviation fi-om the minimum value can be reduced to +10°C or less.
- 34
A
[0058]
[Table 2]
Location deviation L between thermometer and shape meter
(mm)
-200.0
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
200.0
Temperature standard deviation Y
41.8
32.3
21.1
15.2
10.0
16.2
28.5
35.1
40.5
Difference of standard deviation from minimum
value
(°C)
31.8
22.3
11.1
5.2
0.0
6.2
18.5
25.1
30.5
35
wimmmmmimt
9
[0059]
Therefore, when the location deviation L between the measurement places of
the thermometer 40 and the shape meter 41 is 50 mm or less, similarly to the above
embodiment, it is possible to determine the increase and decrease directions (control
directions) of the top side cooling capability and the bottom side cooling capability for
decreasing the temperature standard deviation, and it is possible to feedback-control
the cooling capabilities of the top side cooling device 14a and the bottom side cooling
device 14b.
[0060]
In the above embodiment, the cooling section in which the hot-rolled steel
sheet H is cooled may be divided into a plurality of sections, for example, two divided
cooling sections Zl and Z2 in the rolling direction as illustrated in FIG. 9. Each of
the divided cooling sections Zl and Z2 is provided with the cooling apparatus 14. In
addition, the thermometer 40 and the shape meter 41 are provided respectively at the
border between the respective divided cooling sections Zl and Z2, that is, on the
downstream side of the divided cooling sections Zl and Z2. Meanwhile, in the
embodiment, the cooling section is divided into two divided cooling sections, but the
number of divisions is not limited thereto, and can be arbitrarily set. For example, the
cooling section may be divided into 1 to 5 divided cooling sections.
[0061]
In this case, the temperature and wave shape of the hot-rolled steel sheet H on
the downstream side of the divided cooling sections Zl and Z2 are respectively
measured using the respective thermometers 40 and the respective shape meters 41.
In addition, the cooling capabilities of the top side cooling device 14a and the bottom
side cooling device 14b at the respective divided cooling sections Zl and Z2 are
- J 6 -
*
controlled based on the measurement results. At this time, the cooling capabilities are
controlled so that the temperature standard deviation of the hot-rolled steel sheet H
falls into the permissible range, for example, a range of the minimum value to the
minimum value+10°C as described above. Thereby, at least one of the amount of
heat dissipated from the top surface by cooling and the amount of heat dissipated from
the bottom surface by cooling of the hot-rolled steel sheet H at the respective divided
cooling sections Zl and Z2 is adjusted.
[0062]
For example, in the divided cooling section Zl, the cooling capabilities of the
top side cooling device 14a and the bottom side cooling device 14b are feedbackcontrolled
based on the measurement results of the thermometer 40 and the shape
meter 41 on the downstream side, thereby at least one of the amount of heat dissipated
from the top surface by cooling and the amount of heat dissipated from the bottom
surface by cooling is adjusted.
In addition, in the divided cooling section Z2, the cooling capabilities of the
top side cooling device 14a and the bottom side cooling device 14b may be
feedforward-controlled or feedback-controlled based on the measurement results of the
thermometer 40 and the shape meter 41 on the downstream side. In any cases, in the
divided cooling section Z2, at least one of the amount of heat dissipated from the top
surface by cooling and the amount of heat dissipated from the bottom surface by
cooling is adjusted.
[0063]
Since the method for controlling the cooling capabilities of the top side
cooling device 14a and the bottom side cooling device 14b based on the measurement
results of the thermometer 40 and the shape meter 41 is the same as in the above
- 37 -
p
embodiment described using FIGS. 4 to 7, the method will not be described in detail.
[0064]
In this case, since at least one of the amount of heat dissipated from the top
surface by cooling and the amount of heat dissipated from the bottom surface by
cooling of the hot-rolled steel sheet H is adjusted in the respective divided cooling
sections Zl and Z2, finer control becomes possible. Therefore, it is possible to more
uniformly cool the hot-rolled steel sheet H.
[0065]
In the above embodiment, in the respective divided cooling sections Zl and
Z2, when adjusting at least one of the amount of heat dissipated from the top surface
by cooling and the amount of heat dissipated from the bottom surface by cooling of the
hot-rolled steel sheet H, at least one of the steepness of the wave shape of the hotrolled
steel sheet H and the sheet-threading speed of the hot-rolled steel sheet H may
be used in addition to the measurement results of the thermometer 40 and the shape
meter 41. For example, since there are cases in which the steepness or sheetthreading
speed of the hot-rolled steel sheet H is different for each coil, the steepness
or the sheet-threading speed is also taken into consideration.
[0066]
According to the investigation by the inventors, for example, when the
steepness of the wave shape of the hot-rolled steel sheet H becomes large as illustrated
in FIG. 10, the temperature standard deviation of the hot-rolled steel sheet H becomes
large. In addition, for example, when the sheet-threading speed of the hot-rolled steel
sheet H becomes a fast speed as illustrated in FIG. 11, the temperature standard
deviation of the hot-rolled steel sheet H becomes large.
[0067]
- 38 -
In a case in which the steepness or sheet-threading speed of the hot-rolled
steel sheet H is not constant as described above, the change of the temperature standard
deviation with respect to the top and bottom heat transfer coefficient ratio can be
qualitatively evaluated, but cannot be accurately quantitatively evaluated. Therefore,
the temperature standard deviation is corrected by, for example, obtaining a
temperature standard deviation in accordance with the steepness or sheet-threading
speed of the hot-rolled steel sheet H in advance and measuring at least the steepness or
sheet-threading speed of the hot-rolled steel sheet H. In addition, the amount of heat
dissipated from the top surface by cooling and the amount of heat dissipated from the
bottom surface by cooling of the hot-rolled steel sheet H in the respective divided
cooling sections Zl and Z2 are corrected based on the corrected temperature standard
deviation. Thereby, it is possible to more uniformly cool the hot-rolled steel sheet H.
[0068]
In addition, according to the present embodiment, it becomes possible to
finish the hot-rolled steel sheet so that a uniform shape or material is formed in the
sheet width direction of the hot-rolled steel sheet H as well. FIG 12 illustrates an
example of a wave shape having an amplitude changing in the sheet width direction
due to elongation at the center. As such, even in a case in which a temperature
standard deviation is caused by the wave shape having an amplitude changing in the
sheet width direction, according to the above-described embodiment, it becomes
possible to reduce the temperature standard deviation in the sheet width direction.
[0069]
Here, as a result of thorough studies, the inventors found that, when the sheetthreading
speed of the hot-rolled steel sheet H is set in a range of 550 m/min to the
mechanical limit speed, it is possible to more uniformly cool the hot-rolled steel sheet
39
9
H.
[0070]
It was found that, when the sheet-threading speed of the hot-rolled steel sheet
H is set to 550 m/min or more, the influence of soaked water on the hot-rolled steel
sheet H becomes significantly small even when cooling water is sprayed onto the hotrolled
steel sheet H. Therefore, it is possible to prevent the ununiform cooling of the
hot-rolled steel sheet H due to soaked water.
[0071]
FIG. 13 schematically illustrates an example of a hot rolling facility 2 in
another embodiment. The hot rolling facility 2 is a facility aimed to sandwich the top
and bottom of a heated slab S using rolls, continuously roll the slab to make the slab as
thin as a minimum of 1.2 mm, and coil the slab.
The hot rolling facility 2 has a heating furnace 111 for heating the slab S, a
width-direction mill 116 that rolls the slab S heated in the heating fiimace 111 in a
width direction, a roughing mill 112 that rolls the slab S rolled in the width direction
from the vertical direction so as to produce a rough bar, a finishing mill 113 that further
continuously hot-finishing-rolls the rough bar to a predetermined thickness, a cooling
apparatus 114 that cools the hot-rolled steel sheet H hot-finishing-rolled using the
finishing mill 113 using cooling water, and a coiling apparatus 115 that coils the hotrolled
steel sheet H cooled using the cooling apparatus 114 into a coil shape.
[0072]
The heating furnace 111 is provided with a side burner, an axial burner and a
roof burner that heat the slab S brought from the outside through a charging hole by
blowing flame. The slab S brought into the heating furnace 111 is sequentially heated
in respective heating areas formed in respective zones, and, furthermore, a heat-
- 40 -
retention treatment for enabling transportation at an optimal temperature is carried out
by uniformly heating the slab S using the roof burner in a soaking area formed in a
final zone. When a heating treatment in the heating furnace 111 completely ends, the
slab S is transported to the outside of the heating furnace 111, and moved into a rolling
process by the roughing mill 112.
[0073]
In the roughing mill 112, the slab S transported from the heating furnace 111
is passed through gaps between columnar rotary rolls provided across a plurality of
stands. For example, the roughing mill 112 hot-rolls the slab S only using work rolls
112a provided at the top and bottom of a first stand so as to form a rough bar.
Next, the rough bar which has passed through the work rolls 112a is further
continuously rolled using a plurality of fourfold mills 112b constituted by a work roll
and a back-up roll. As a result, when the rough rolling process ends, the rough bar is
rolled into a thickness of approximately 30 mm to 60 mm, and transported to the
finishing mill 113. Meanwhile, the configuration of the roughing mill 112 is not
limited to what has been described in the embodiment, and the number of rolls and the
like can be arbitrarily set.
[0074]
The finishing mill 113 finishing-rolls the rough bar transported from the
roughing mill 112 until the thickness becomes approximately several millimeters.
The finishing mill 113 passes the rough bar through gaps between top and bottom
finish rolling rolls 113a linearly arranged across 6 to 7 stands so as to gradually reduce
the rough bar. The hot-rolled steel sheet H finishing-rolled using the finishing mill
113 is transported to the cooling apparatus 114 using transportation rolls 132 (refer to
FIG. 14). Meanwhile, a mill having the above-described pair of finish rolling rolls
- 41 -
113a linearly arrayed vertically is also referred to as a so-called rolling stand.
[0075]
In addition, cooling apparatuses 142 (supplementary cooling apparatus) that
carry out inter-stand cooling (supplementary cooling) during finish rolling are disposed
between the respective rolling rolls 113a arrayed across 6 to 7 stands (that is, between
the rolling stands). The details of the apparatus configuration and the like of the
cooling apparatus 142 will be described below with reference to FIG. 17. Meanwhile,
FIG. 13 illustrates a case in which the cooling apparatuses 142 are disposed at two
places in the finishing mill 113, but the cooling apparatuses 142 may be provided
between all the rolling rolls 113a, or may be provided between some of the rolling rolls.
[0076]
The cooling apparatus 114 is a facility for carrying out nozzle cooling on the
hot-rolled steel sheet H transported from the finishing mill 113 through laminating or
spraying. As illustrated in FIG. 14, the cooling apparatus 114 has a top side cooling
device 114a that sprays cooling water from cooling holes 131 on the top side to the top
surface of the hot-rolled steel sheet H moving on the transportation rolls 132 in a runout
table, and a bottom side cooling device 114b that sprays cooling water from
cooling holes 131 on the bottom side to the bottom surface of the hot-rolled steel sheet
H.
A plurality of the cooling holes 131 is provided in the top side cooling device
114a and the bottom side cooling device 114b respectively. In addition, a cooling
header (not illustrated) is connected to the cooling holes 131. The number of the
cooling holes 131 determines the cooling capabilities of the top side cooling device
114a and the bottom side cooling device 114b. Meanwhile, the cooling apparatus 114
may be constituted by at least one of top and bottom split laminar, pipe laminar, spray
- 42 -
^
cooling and the like.
[0077]
In the cooling apparatus 114, when adjusting the cooling capability of the top
side cooling device 114a and the cooling capability of the bottom side cooling device
114b, for example, the cooling headers connected to cooling holes 131 in the top side
cooling device 114a and the cooling headers connected to cooling holes 131 in the
bottom side cooling device 114b may be on-off controlled respectively.
Alternatively, the operation parameters of the respective cooling headers in
the top side cooling device 114a and the bottom side cooling device 114b may be
controlled. That is, at least one of the sprayed water density, pressure and water
temperature of cooling water sprayed from the respective cooling holes 131 may be
adjusted.
In addition, the flow rate or pressure of cooling water sprayed from the top
side cooling device 114a and the bottom side cooling device 114b may be adjusted by
thinning out the cooling headers (cooling holes 131) of the top side cooling device
114a and the bottom side cooling device 114b. For example, in a case in which the
cooling capability of the top side cooling device 114a before thinning out the cooling
headers is superior to the cooling capability of the bottom side cooling device 114b, the
cooling headers that constitute the top side cooling device 114a are preferably thinned
out.
[0078]
The coiling apparatus 115 coils the hot-rolled steel sheet H cooled using the
cooling apparatus 114 at a predetermined coiling temperature as illustrated in FIG. 13.
The hot-rolled steel sheet H coiled into a coil shape using the coiling apparatus 115 is
transported to the outside of the hot rolling facility 2.
#
[0079]
In a case in which the hot-rolled steel sheet H having a wave shape with a
surface height (wave height) changing in the rolling direction is cooled in the cooling
apparatus 114 of the hot rolling facility 2 constituted as described above, as described
above, it is possible to uniformly cool the hot-rolled steel sheet H by appropriately
adjusting the water quantity densities, pressures, water temperatures and the like of
cooling water sprayed from the top side cooling device 114a and cooling water sprayed
from the bottom side cooling device 114b. However, particularly, in a case in which
the sheet-threading speed of the hot-rolled steel sheet H is slow, a period of time during
which the hot-rolled steel sheet H and the transportation rolls 132 or aprons 133 locally
come into contact with each other becomes long, and the contact portions of the hotrolled
steel sheet H with the transportation rolls 132 or the aprons 133 become easily
coolable due to heat dissipation by contact, and therefore cooling becomes ununiform.
The causes of the ununiformity of the cooling will be described below with reference
to the accompanying drawings.
[0080]
As illustrated in FIG. 15 A, in a case in which the hot-rolled steel sheet H has a
wave shape in the rolling direction, there is a possibility of the bottom portion of the
wave shape of the hot-rolled steel sheet H locally coming into contact with the
transportation rolls 132. In addition, there are cases in which the apron 133 is
provided between the adjacent transportation rolls 132 in the rolling direction as a
support for preventing the hot-rolled steel sheet H from dropping as illustrated in FIG.
15B. In this case, there is a possibility of the bottom portion of the wave shape of the
hot-rolled steel sheet H locally coming into contact with the transportation rolls 132
and the aprons 133. As such, in the hot-rolled steel sheet H, portions that locally
- 44 -
#
come into contact with the transportation rolls 132 or the aprons 133 become more
easily coolable than other portions due to heat dissipation by contact. Therefore, the
hot-rolled steel sheet H is unimiformly cooled.
[0081]
Particularly, in a case in which the sheet-threading speed of the hot-rolled
steel sheet H is slow, a period of time during which the hot-rolled steel sheet H locally
comes into contact with the transportation rolls 132 or the aprons 133 becomes long.
As a result, portions at which the hot-rolled steel sheet H locally comes into contact
with the transportation rolls 132 or the aprons 133 (portions surrounded by the dotted
line in FIG. 16A) become more easily coolable than other portions as illustrated in FIG.
16A, and the hot-rolled steel sheet H is ununiformly cooled.
On the other hand, when the sheet-threading speed of the hot-rolled steel sheet
H is set to a fast speed, the contact period of time becomes short. Furthermore, when
the sheet-threading speed is increased, the hot-rolled steel sheet H in the process of
sheet-threading becomes floated from the transportation rolls 132 or the aprons 133
due to repulsion by the contact between the hot-rolled steel sheet H and the
transportation rolls 132 or the aprons 133.
In addition, when the sheet-threading speed is increased, the hot-rolled steel
sheet H does not only become floated from the transportation rolls 132 or the aprons
133 due to repulsion by the contact, but the contact period of time or number of
contacts between the hot-rolled steel sheet H and the transportation rolls 132 or the
aprons 133 also decreases, and therefore the temperature decrease by the contact
becomes negligible.
Therefore, the heat dissipation by contact can be suppressed by increasing the
sheet-threading speed, and the hot-rolled steel sheet H can be more uniformly cooled
- 45
#
as illustrated in FIG. 16B. In addition, the inventors found that the hot-rolled steel
sheet H can be sufficiently uniformly cooled by setting the sheet-threading speed to
550 m/min or more in addition to the above-described control of the amounts of heat
dissipated from the top and bottom surfaces.
Meanwhile, the above finding is about the cooling of the hot-rolled steel sheet
H having a wave shape; however, regardless of the height of the wave shape, the
lowermost point of the hot-rolled steel sheet H comes into contact v^th the
transportation rolls 132 or the aprons 133, and therefore, regardless of the height of the
wave shape, an increase in the sheet-threading speed is effective for uniform cooling.
[0082]
In addition, when the sheet-threading speed of the hot-rolled steel sheet H is
set to 550 m/min or more, since the hot-rolled steel sheet H becomes floated from the
transportation rolls 132 or the aprons 133, there is no soaked water on the hot-rolled
steel sheet H as in the related art even when cooling water is sprayed onto the hotrolled
steel sheet H in the above state. Therefore, it is possible to prevent the hotrolled
steel sheet H fi-om being ununiformly cooled due to soaked water.
[0083]
As described above, when the sheet-threading speed of the hot-rolled steel
sheet H in the cooling section is set to 550 m/min or more, it is possible to more
imiformly cool the hot-rolled steel sheet H having a wave shape with a height
periodically changing in the rolling direction.
Meanwhile, the sheet-threading speed of the hot-rolled steel sheet H is
preferably a faster speed, but it is impossible to exceed the mechanical limit speed (for
example, 1550 m/min). Therefore, practically, the sheet-threading speed of the hotrolled
steel sheet H in the cooling section is set in a range of 550 m/min to the
- 46 -
tfe
mechanical limit speed. In addition, in a case in which the upper limit value of the
sheet-threading speed in an actual operation (operation upper limit speed) is set in
advance, the sheet-threading speed of the hot-rolled steel sheet H is preferably set in a
range of 550 m/min to the operation upper limit speed (for example, 1200 m/min).
Naturally, the control of the amount of heat dissipated from the top surface by
cooling and the amount of heat dissipated from the bottom surface by cooling of the
hot-rolled steel sheet H and the setting of the sheet-threading speed to a fast speed (set
in a range from 550 m/min to the mechanical limit speed) may be combined by
applying the apparatus for cooling a hot-rolled steel sheet described using FIG. 3 to the
hot rolling facility 2.
[0084]
In addition, in general, in the case of the hot-rolled steel sheet H having a
large tensile strength (particularly, a steel sheet called so-called high tensile strength
steel having a tensile strength (TS) of 800 MPa or more and an experimental upper
limit of 1400 MPa), it is known that heat generation by working occurring in the hot
rolling facility 2 during rolling is increased due to a high hardness of the hot-rolled
steel sheet H. Therefore, in the related art, the hot-rolled steel sheet H was
sufficiently cooled by suppressing the sheet-threading speed of the hot-rolled steel
sheet H in the cooling apparatus 114 (that is, the cooling section) to be low.
[0085]
However, when the sheet-threading speed of the hot-rolled steel sheet H in the
cooling apparatus 114 is suppressed to be low, in a case in which a wave shape is
formed in the hot-rolled steel sheet H, the local contacts between the hot-rolled steel
sheet H and the transportation rolls 132 or the aprons 133 make the contact portions
more easily coolable due to heat dissipation by contact as described above, and the hot-
- 47 -
w
rolled steel sheet H is ununiformly cooled.
[0086]
Therefore, the inventors found that, when cooling is carried out between a pair
of finish rolling rolls 113a (that is, rolling stands) provided across, for example, 6 to 7
stands in the finishing mill 113 of the hot rolling facility 2 (so-called inter-stand
cooling), the heat dissipation by working can be suppressed, and the sheet-threading
speed of the hot-rolled steel sheet H in the cooling apparatus 114 can be set to 550
m/min or more. Hereinafter, the inter-stand cooling will be described with reference
to FIG. 17.
[0087]
FIG. 17 is an explanatory view of the finishing mill 113 that can carry out the
inter-stand cooling, in which a part of the finishing mill 113 is enlarged for the
description and three rolling stands are illustrated. Meanwhile, in FIG. 17, the same
components as in the above embodiment will be given the same reference numeral.
As illustrated in FIG. 17, a plurality (three in FIG. 17) of rolling stands 140 having a
pair of vertically linearly arrayed finish rolling rolls 113a and the like is provided in the
finishing mill 113. The cooling apparatuses 142 which are facilities that carry out
nozzle cooling through lamination or spraying are provided between the respective
rolling stands 140, which make it possible to carry out the inter-stand cooling on the
hot-rolled steel sheet H between the rolling stands 140.
[0088]
The cooling apparatus 142 has a top side cooling device 142a that sprays
cooling water from the top side through cooling holes 146 onto the hot-rolled steel
sheet H transported in the finishing mill 113 and a bottom side cooling device 142b
that sprays cooling water from the bottom side onto the hot-rolled steel sheet H as
- 48 -
^
illustrated in FIG. 17. A plurality of the cooling holes 146 is provided respectively in
the top side cooling device 142a and the bottom side cooling device 142b. In addition,
a cooling header (not illustrated) is connected to the cooling hole 146. Meanwhile,
the cooling apparatus 142 may be constituted by at least one of top and bottom split
laminar, pipe laminar, spray cooling and the like.
[0089]
In the finishing mill 113 having the configuration illustrated in FIG. 17,
particularly, in a case in which the tensile strength (TS) of the hot-rolled steel sheet H
is 800 MPa or more, the heat dissipation by working in the hot-rolled steel sheet H is
suppressed by carrying out the inter-stand cooling. Thereby, it becomes possible to
maintain the sheet-threading speed of the hot-rolled steel sheet H in the cooling
apparatus 114 at 550 m/min or more. Therefore, the problem of the related art caused
in a case in which cooling was carried out at a slow sheet-threading speed, which was
the local contacts between the hot-rolled steel sheet H and the transportation rolls 132
or the aprons 133 and the contact portions becoming more easily coolable due to heat
dissipation by contact is solved, and the hot-rolled steel sheet H can be sufficiently
uniformly cooled.
[0090]
In the above embodiment, the cooling of the hot-rolled steel sheet H using the
cooling apparatus 114 is preferably carried out in a temperature range of the exit-side
temperature of the finishing mill to the hot-rolled steel sheet H of 600°C. The
temperature range in which the temperature of the hot-rolled steel sheet is 600°C or
higher is a so-called film boiling range. That is, in this case, it is possible to avoid the
so-called transition boiling area and to water-cool the hot-rolled steel sheet H in the
film boiling area. In the transition boiling area, when cooling water is sprayed onto
- 49
#
the surface of the hot-rolled steel sheet H, portions covered with a vapor film and
portions in which the cooling water is directly sprayed onto the hot-rolled steel sheet H
are present in a mixed state on the surface of the hot-rolled steel sheet H. Therefore,
it is not possible to uniformly cool the hot-rolled steel sheet H.
On the other hand, in the film boiling area, since the hot-rolled steel sheet H is
cooled in a state in which the entire surface of the hot-rolled steel sheet H is covered
with a vapor film, it is possible to uniformly cool the hot-rolled steel sheet H.
Therefore, it is possible to more uniformly cool the hot-rolled steel sheet H in a range
in which the temperature of the hot-rolled steel sheet H is 600°C or higher as in the
embodiment.
[0091]
Thus far, the preferable embodiment of the present invention has been
described with reference to the accompanying drawings, but the present invention is
not limited to the above embodiment. It is evident that a person skilled in the art can
imagine a variety of modified examples and revised examples within the scope of ideas
described in the claims, and it is needless to say that the examples belong to the
technical scope of the present invention.
[Examples]
[0092]
The inventors carried out cooling tests on a hot-rolled steel sheet as examples
in order to verify that the hot-rolled steel sheet could be uniformly cooled by setting
the sheet-threading speed of the hot-rolled steel sheet to 550 m/min or more.
[0093]
(Example 1)
Hot-rolled steel sheets with an intermediate wave having a sheet thickness of
- 50 -
#
2.5 mm, a width of 1200 mm, a tensile strength of 400 MPa and a steepness of 2%
were cooled with varying sheet-threading speeds in a cooling apparatus. Specifically,
the sheet-threading speeds were 400 m/min, 450 m/min, 500 m/min, 550 m/min, 600
m/min and 650 m/min, and the hot-rolled steel sheets were cooled at the respective
sheet-threading speeds 20 times.
In addition, the temperatures of the hot-rolled steel sheets during coiling were
measured, and an average value (amount of CT temperature change) of the standard
deviations of temperature changes was computed using the temperature measurement
results. The evaluation results of the computed CT temperature change amount are
described in Table 3 below. Meanwhile, in terms of the evaluation criteria, a case in
which the CT temperature change amount was larger than 25°C was evaluated as
ununiform cooling, and a case in which the CT temperature change amount was 25°C
or less was evaluated as uniform cooling.
51 -
'25°C B: 25>CT>10 A: 10>CT
52
WPIUMMIMKWWW
^
[0095]
As described in Table 3, in a case in which the sheet-threading speed is 500
m/min or less, the amount of CT temperature change is not sufficiently reduced (higher
than 25°C), and the hot-rolled steel sheet is not sufficiently uniformly cooled. On the
other hand, in a case in which the sheet-threading speed is 550 m/min or more, it was
found that the CT temperature change amount is suppressed to 25°C or less, and the
hot-rolled steel sheet is uniformly cooled. Meanwhile, in a case in which the sheetthreading
speed is 600 m/min or more, it was found that, since the CT temperature was
suppressed to lower than 10°C (8°C and 6°C), the above condition is more preferable
for the uniform cooling of the hot-rolled steel sheet.
[0096]
(Example 2)
The inter-stand cooling was carried out on hot-rolled steel sheets with an
intermediate wave having S: sheet thickness of 2.5 mm, a width of 1200 mm, a tensile
strength of 800 MPa and a steepness of 2% so that the exit-side temperature of finish
rolling became 880°C, and cooling was carried out with varying sheet-threading
speeds in a cooling apparatus. Specifically, the sheet-threading speeds were 400
m/min, 450 m/min, 500 m/min, 550 m/min, 600 m/min and 650 m/min, and the hotrolled
steel sheets were cooled at the respective sheet-threading speeds 20 times.
In addition, the temperatures of the hot-rolled steel sheets during coiling were
measured, and an average value (amoiont of CT temperature change) of the standard
deviations of temperature changes was computed using the temperature measurement
results. The evaluation results of the computed CT temperature change amount are
described in Table 4 below. Meanwhile, the same evaluation criteria as in Example 1
were used, and the inter-stand cooling was not carried out only in a case in which the
- 53 -
#
sheet-threading speed was 400 m/min.
54
%
[0097]
[Table 4]
Sheet-threading speed [m/min]
Inter-stand cooling
CT temperature change amount [°C]
Evaluation
400
No
62
C
450
Yes
43
C
500
Yes
28
C
550
Yes
10
B
600
Yes
6
A
650
Yes
6
A
An inter-stand cooling was appropriately carried out so that the exit-side temperature after finishing rolling became 880°C.
Evaluation C: CT>25°C B: 25>CT>10 A: 10>CT
- 55 -
mmmsmmmmi
IP
[0098]
As described in Table 4, in a case in which the sheet-threading speed was 500
m/min or less, even when the inter-stand cooling was carried out, the amount of CT
temperature change was not sufficiently reduced (higher than 25°C), and the hot-rolled
steel sheet was not sufficiently uniformly cooled. On the other hand, in a case in
which the sheet-threading speed was 550 m/min or more, it was found that the CT
temperature change amount was suppressed to 25°C or less, and the hot-rolled steel
sheet was uniformly cooled.
[0099]
In addition, in cases in which the inter-stand cooling was carried out (that is,
the cases described in Table 4), the amount of CT temperature change was suppressed
even in the hot-rolled steel sheets having a relatively high hardness (tensile strength
800 MPa). That is, it was found that it became possible to uniformly cool all steel
materials, particularly, steel materials having a high hardness by setting the sheetthreading
speed during the cooling of the hot-rolled steel sheet to 550 m/min or more,
and, additionally, carrying out the inter-stand rolling in a finishing mill.
[Industrial Applicability]
[0100]
The present invention is useful when cooling a hot-rolled steel sheet which
has been hot-rolled using a finishing mill so as to have a wave shape having a surface
height changing in the rolling direction.
[Description of Reference Numerals and Signs]
[0101]
1,2: HOT ROLLING FACILITY
11,111: HEATING FURNACE
- 56
12, 112: ROUGHING MILL
12a, 112a: WORK ROLL
12b, 112b: FOURFOLD MILL
13, 113: FINISHING MILL
13a, 113a: FINISH ROLLING ROLL
14,114: COOLING APPARATUS
14a, 114a: TOP SIDE COOLING DEVICE
14b, 114b: BOTTOM SIDE COOLING DEVICE
15, 115: COILING APPARATUS
16, 116: WIDTH-DIRECTION MILL
31, 131: COOLING HOLE
32, 132: TRANSPORTATION ROLL
40: THERMOMETER
41: SHAPE METER
50: CONTROL DEVICE
51: AVERAGE TEMPERATURE COMPUTATION UNIT
52: CHANGING SPEED COMPUTATION UNIT
53: CONTROL DIRECTION-DETERMINING UNIT
54: TOTAL AMOUNT OF HEAT DISSIPATED BY COOLINGADJUSTING
UNIT
H: HOT-ROLLED STEEL SHEET
S: SLAB
Zl, Z2: DIVIDED COOLING SECTION
- 57

[Type of Document] CLAIMS
[Claim 1]
An apparatus for cooling a hot-rolled steel sheet which cools a hot-rolled steel
sheet hot-rolled using a finishing mill in a cooling section provided on a sheetthreading
path, the apparatus comprising:
a thermometer that measures a temperature of the hot-rolled steel sheet on a
downstream side of the cooling section;
a shape meter that measures a shape of the hot-rolled steel sheet on the
downstream side of the cooling section;
a top side cooling device that cools a top surface of the hot-rolled steel sheet
in the cooling section;
a bottom side cooling device that cools a bottom surface of the hot-rolled steel
sheet in the cooling section; and
a control device that controls at least one of an amount of heat dissipated from
the top surface by cooling and an amount of heat dissipated from the bottom surface by
cooling of the hot-rolled steel sheet in the cooling section by controlling the top side
cooling device and the bottom side cooling device based on temperature measurement
results of the hot-rolled steel sheet obtained from the thermometer and the shape
measurement results of the hot-rolled steel sheet obtained from the shape meter,
wherein the control device includes:
an average temperature computation unit that computes a chronological
average value of the temperature of the hot-rolled steel sheet on the downstream side
of the cooling section as an average temperature based on the temperature
measurement results;
a changing speed computation unit that computes a changing speed of the hot-
- 58 -
i^^m
rolled steel sheet on the downstream side of the cooling section based on the shape
measurement results;
a control direction-determining unit that, when upward in a vertical direction
of the hot-rolled steel sheet is set as positive, in an area with a positive changing speed,
in a case in which the temperature of the hot-rolled steel sheet is lower than an average
temperature of a range of one or more cycles of a wave shape of the hot-rolled steel
sheet, determines at least one of a direction in which the amount of heat dissipated
from the top surface by cooling decreases and a direction in which the amount of heat
dissipated from the bottom surface by cooling increases as a control direction, and, in a
case in which the temperature of the hot-rolled steel sheet is higher than the average
temperature, determines at least one of a direction in which the amount of heat
dissipated from the top surface by cooling increases and a direction in which the
amount of heat dissipated from the bottom surface by cooling decreases as the control
direction,
in an area with a negative changing speed, in a case in which the temperature
of the hot-rolled steel sheet is lower than the average temperature, determines at least
one of a direction in which the amount of heat dissipated from the top surface by
cooling increases and a direction in which the amount of heat dissipated from the
bottom surface by cooling decreases as the control direction, and,^ in a case in which
the temperature of the hot-rolled steel sheet is higher than the average temperature,
determines at least one of a direction in which the amount of heat dissipated from the
top surface by cooling decreases and a direction in which the amount of heat dissipated
from the bottom surface by cooling increases as the control direction; and
a total amount of heat dissipated by cooling-adjusting unit that adjusts a total
value of the amount of heat dissipated from the top surface by cooling and the amount
- 59 -
of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet in
the cooling section based on the control directions determined using the control
direction-determining imit.
[Claim 2]
The apparatus for cooling a hot-rolled steel sheet according to Claim 1,
wherein a location deviation between a temperature measurement place of the
thermometer and a shape measurement place of the shape meter on the hot-rolled steel
sheet is 50 mm or less.
[Claim 3]
The apparatus for cooling a hot-rolled steel sheet according to Claim 1 or 2,
wherein a sheet-threading speed of the hot-rolled steel sheet in the cooling
section is set in a range of 550 m/min to a mechanical limit speed.
[Claim 4]
The apparatus for cooling a hot-rolled steel sheeft according to Claim 3,
wherein a tensile strength of the hot-rolled steel sheet is 800 MPa or more.
[Claim 5]
The apparatus for cooling a hot-rolled steel sheet according to Claim 3,
wherein the finishing mill is constituted by a plurality of rolling stands, and
a supplementary cooling device that carries out supplementary cooling of the
hot-rolled steel sheet is further provided between the adjacent rolling stands.