U.S. patent application number 09/728079 was filed with the patent office on 2001-04-26 for method and system for cooling strip material.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Han, Kwang-Hee, Lee, Jae-Young, Lee, Joo-Seung, Matsuda, Naohiko, Nagai, Takanori.
Application Number | 20010000377 09/728079 |
Document ID | / |
Family ID | 18286267 |
Filed Date | 2001-04-26 |
United States Patent
Application |
20010000377 |
Kind Code |
A1 |
Matsuda, Naohiko ; et
al. |
April 26, 2001 |
Method and system for cooling strip material
Abstract
A method and a system for cooling a steel strip are disclosed. A
high water volume mist cooler and a low water volume mist cooler
are disposed along a direction in which the steel strip travels.
The high water volume mist cooler sprays high water volume mists
onto the surfaces of the steel strip to cool the steel strip, and
then the low water volume mist cooler sprays low water volume mists
onto the surfaces of the steel strip to cool the steel strip,
thereby cooling the steel strip while suppressing the influence of
transition boiling, to prevent the steel strip from having a
temperature-nonuniform portion.
Inventors: |
Matsuda, Naohiko;
(Hiroshima, JP) ; Nagai, Takanori; (Hiroshima,
JP) ; Han, Kwang-Hee; (Tokyo, JP) ; Lee,
Jae-Young; (Tokyo, JP) ; Lee, Joo-Seung;
(Kwangyang-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
8110 GATEHOUSE ROAD
SUITE 500 EAST
FALLS CHURCH
VA
22042
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
|
Family ID: |
18286267 |
Appl. No.: |
09/728079 |
Filed: |
December 4, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09728079 |
Dec 4, 2000 |
|
|
|
09205372 |
Dec 4, 1998 |
|
|
|
Current U.S.
Class: |
62/65 ; 266/113;
62/374 |
Current CPC
Class: |
C21D 1/667 20130101;
C21D 1/613 20130101; C21D 1/60 20130101; C21D 9/573 20130101; C23C
2/26 20130101 |
Class at
Publication: |
62/65 ; 118;
62/374; 266/113 |
International
Class: |
F25D 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 1997 |
JP |
9-335235 |
Claims
What is claimed is:
1. A method for cooling a strip material, comprising: passing the
strip material, which is traveling, through a high temperature
cooling zone and a low temperature cooling zone in this order, to
cool the strip material with a high water volume air-water mixture
in the high temperature cooling zone, and then cool the strip
material with a low water volume air-water mixture in the low
temperature cooling zone.
2. A method for cooling a strip material, comprising: passing the
strip material, which is traveling, through a high temperature
cooling zone and a low temperature cooling zone in this order, to
cool the strip material with a high water volume air-water mixture
in the high temperature cooling zone to a temperature in the
vicinity of a temperature at which transition boiling occurs, and
then cool the strip material with a low water volume air-water
mixture in the low temperature cooling zone while suppressing
transition boiling.
3. A system for cooling a strip material, comprising: a high
temperature cooling zone and a low temperature cooling zone
established as cooling zones, in which the strip material is cooled
with a high water volume air-water mixture in the high temperature
cooling zone, and cooled with a low water volume air-water mixture
in the low temperature cooling zone.
4. A system for cooling a traveling strip material, comprising: a
high temperature cooling zone and a low temperature cooling zone
established along a direction in which the strip material travels;
a high water volume air-water mixture cooler installed in the high
temperature cooling zone for cooling the strip material with a high
water volume air-water mixture to a temperature in the vicinity of
a temperature at which transition boiling occurs; and a low water
volume air-water mixture cooler installed in the low temperature
cooling zone for cooling the strip material with a low water volume
air-water mixture while suppressing transition boiling.
5. The system for cooling a strip material according to claim 4,
wherein: the high water volume air-water mixture cooler sprays high
water volume mists onto both sides of the strip material, and the
low water volume air-water mixture cooler sprays low water volume
mists onto both sides of the strip material.
6. The system for cooling a strip material according to claim 4,
wherein: the high water volume air-water mixture cooler includes a
multiplicity of spray pipes arranged vertically, each spray pipe
having a water supply pipe for supplying a high water volume, and
an air supply pipe mounted inside the water supply pipe, said water
supply pipe extending in the direction of the width of the strip
material and having a plurality of nozzle holes drilled facing a
surface of the strip material, and said air supply pipe having a
plurality of nozzle holes drilled in the direction of the width of
the strip material, and the low water volume air-water mixture
cooler includes a multiplicity of spray pipes arranged vertically,
each spray pipe having a water supply pipe for supplying a low
water volume, and an air supply pipe mounted inside the water
supply pipe, said water supply pipe extending in the direction of
the width of the strip material and having a plurality of nozzle
holes drilled facing a surface of the strip material, and said air
supply pipe having a plurality of nozzle holes drilled in the
direction of the width of the strip material.
7. The method of claim 1 or 2, wherein an air-to-water ratio of
said high water volume air-water mixture is about 1500, and an
air-to-water ratio of said low water volume air-water mixture is
about 5000.
8. The method of claim 1 or 2, further comprising: cooling the
strip material in the high temperature cooling zone to a
temperature in the vicinity of a temperature at which transition
boiling occurs; and cooling the strip material in the low
temperature cooling zone to a predetermined temperature.
9. The method of claim 1 or 2, wherein said passing step includes
the sub-steps of: cooling the strip material to about 350.degree.
C. in said high temperature cooling zone, and cooling the strip
material from about 350.degree. C. to a predetermined temperature
in said low temperature cooling zone.
10. The system of claim 3, wherein an air-to-water ratio of said
high water volume air-water mixture is about 1500, and an
air-to-water ratio of said low water volume air-water mixture is
about 5000.
11. The system of claim 3, wherein said high temperature cooling
zone cools the strip material to about 350.degree. C., and said low
temperature cooling zone cools the strip material from about
350.degree. C. to a predetermined temperature.
12. A galvanizing system for galvanizing a strip material,
comprising: a hot dip galvanizing tank which galvanizes the strip
material; a heater that heats the galvanized strip material; a
soaking device that soaks the heated strip material; a high
temperature cooling zone which cools the soaked strip material by
spraying a high water volume air-water mixture thereon; and a low
temperature cooling zone which cools the soaked strip material,
after cooling in said high temperature cooling zone, by spraying a
low water volume air-water mixture thereon.
13. The system of claim 12, wherein said hot dip galvanizing tank
contains molten zinc.
Description
FIELD OF THE INVENTION
1. The present invention relates to a method and a system for
cooling a high temperature strip material in two steps.
BACKGROUND OF THE INVENTION
2. As an example of equipment with a system for cooling a high
temperature strip material, a hot dip galvanizing system is shown
in FIG. 3. This system comprises a hot dip galvanizing tank 60, a
heater 71, a soaking device 72, and a mist cooler 80 as a cooling
device.
3. According to the above system, a steel strip 50 is galvanized in
the hot dip galvanizing tank 60, moved vertically upward, and
heated with the heater 71 to alloy the zinc with the steel. The
alloyed steel strip 50 is soaked over its entire width by means of
the soaking device 72. This steel strip 50 traveling in a cooling
zone C is cooled with the mist cooler 80 from 520.degree. C. to
200.degree. C., and carried horizontally by a deflector roll
90.
4. The mist cooler 80 is composed of mist sprayers 81 disposed in
opposing positions at both sides of the ascending steel strip 50.
Each mist sprayer 81 comprises water supply pipes 82 and air supply
pipes 83 arranged vertically in rows such that each air supply pipe
83 is mounted inside each water supply pipe 82 in a double-pipe
configuration. Each water supply pipe 82 has many nozzle holes made
along the width of the steel strip 50, and each air supply pipe 83
has many nozzle holes made along the width of the steel strip 50.
The mist cooler 80 forms mists 86 from water 84 in the water supply
pipes 82 by jetting air 85 through the nozzles of the air supply
pipes 83, and directs the mists 86 toward the surfaces of the steel
strip 50 to cool it.
5. With the foregoing mist cooler 80, mists 86 with a constant
water volume density were sprayed on both sides of the steel strip
50 throughout the cooling zone C to cool the steel strip 50. At a
site in the cooling zone C where the temperature of the steel strip
50 was about 350.degree. C. or lower (i.e., an upper portion of the
cooling zone C), however, the mists 86 adhering to the surfaces of
the steel strip 50 underwent transition boiling, rapidly cooling
the steel strip 50. Transition boiling refers, in terms of water,
to a phenomenon involving transition from a state of cooling with
water vapor to a state of direct cooling with water, or to a state
of cooling with a mixture of water and water vapor. This phenomenon
takes place at about 350.degree. C. Thus, nonuniform temperature
distribution of the steel strip 50 was liable to occur, thereby
deforming the steel strip 50, resulting in its malformation.
SUMMARY OF THE INVENTION
6. The present invention has been accomplished to solve the
above-described problems.
7. According to a first aspect of the present invention, there is
provided a method for cooling a strip material, comprising:
8. passing the strip material, which is traveling, through a high
temperature cooling zone and a low temperature cooling zone in this
order, to cool the strip material with a high water volume
air-water mixture in the high temperature cooling zone, and then
cool the strip material with a low water volume air-water mixture
in the low temperature cooling zone.
9. According to a second aspect of the present invention, there is
provided a method for cooling a strip material, comprising:
10. passing the strip material, which is traveling, through a high
temperature cooling zone and a low temperature cooling zone in this
order, to cool the strip material with a high water volume
air-water mixture in the high temperature cooling zone to a
temperature in the vicinity of a temperature at which transition
boiling occurs, and then cool the strip material with a low water
volume air-water mixture in the low temperature cooling zone while
suppressing transition boiling.
11. The air-to-water ratio of the high water volume air-water
mixture may be about 1500, and the air-to-water ratio of the low
water volume air-water mixture may be about 5000.
12. The above method may further comprise:
13. cooling the strip material in the high temperature cooling zone
to a temperature in the vicinity of a temperature at which
transition boiling occurs; and
14. cooling the strip material in the low temperature cooling zone
to a predetermined temperature.
15. In the above method, the passing step may include the sub-steps
of:
16. cooling the strip material to about 350.degree. C. in the high
temperature cooling zone, and cooling the strip material from about
350.degree. C. to a predetermined temperature in the low
temperature cooling zone.
17. According to a third aspect of the present invention, there is
provided a system for cooling a strip material, comprising:
18. a high temperature cooling zone and a low temperature cooling
zone established as cooling zones, in which the strip material is
cooled with a high water volume air-water mixture in the high
temperature cooling zone, and cooled with a low water volume
air-water mixture in the low temperature cooling zone.
19. In this system, the air-to-water ratio of the high water volume
air-water mixture may be about 1500, while the air-to-water ratio
or the low water volume air-water mixture may be about 5000.
20. In the above system, the high temperature cooling zone may cool
the strip material to about 350.degree. C., while the low
temperature cooling zone may cool the strip material from about
350.degree. C. to a predetermined temperature.
21. According to a fourth aspect of the present invention, there is
provided a system for cooling a traveling strip material,
comprising:
22. a high temperature cooling zone and a low temperature cooling
zone established along a direction in which the strip material
travels;
23. a high water volume air-water mixture cooler installed in the
high temperature cooling zone for cooling the strip material with a
high water volume air-water mixture to a temperature in the
vicinity of a temperature at which transition boiling occurs;
and
24. a low water volume air-water mixture cooler installed in the
low temperature cooling zone for cooling the strip material with a
low water volume air-water mixture while suppressing transition
boiling.
25. The high water volume air-water mixture cooler may spray high
water volume mists onto both sides of the strip material, and the
low water volume air-water mixture cooler may spray low water
volume mists onto both sides of the strip material.
26. The high water volume air-water mixture cooler may include a
multiplicity of spray pipes arranged vertically, each spray pipe
having a water supply pipe for supplying a high water volume, and
an air supply pipe mounted inside the water supply pipe, the water
supply pipe extending in the direction of the width of the strip
material and having a plurality of nozzle holes drilled facing a
surface of the strip material, and the air supply pipe having a
plurality of nozzle holes drilled in the direction of the width of
the strip material. The low water volume air-water mixture cooler,
on the other hand, may include a multiplicity of spray pipes
arranged vertically, each spray pipe having a water supply pipe for
supplying a low water volume, and an air supply pipe mounted inside
the water supply pipe, the water supply pipe extending in the
direction of the width of the strip material and having a plurality
of nozzle holes drilled facing a surface of the strip material, and
the air supply pipe having a plurality of nozzle holes drilled in
the direction of the width of the strip material.
27. According to a fifth aspect of the present invention, there is
provided a galvanizing system for galvanizing a strip material,
comprising:
28. a hot dip galvanizing tank which galvanizes the strip
material;
29. a heater that heats the galvanized strip material;
30. a soaking device that soaks the heated strip material;
31. a high temperature cooling zone which cools the soaked strip
material by spraying a high water volume air-water mixture thereon;
and
32. a low temperature cooling zone which cools the soaked strip
material, after cooling in the high temperature cooling zone, by
spraying a low water volume air-water mixture thereon.
33. The hot dip galvanizing tank may contain molten zinc.
34. The present invention described above is carried out, for
example, as a cooling system in hot dip galvanizing equipment. That
is, this invention is applied in cooling a steel strip that has
passed through a heater and a soaking device after undergoing hot
dip galvanization. When the invention is applied as a cooling
system in hot dip galvanizing equipment, the steel strip after hot
dip galvanization is cooled with a high water volume air-water
mixture (high water volume mists) in the high temperature cooling
zone, and then cooled with a low water volume air-water mixture
(low water volume mists) in the low temperature cooling zone. As a
result of this two-step cooling, the temperature at which
transition boiling occurs is lowered. Since the steel strip is not
rapidly cooled, its temperature distribution becomes uniform. Thus,
malformation of the steel strip due to thermal deformation does not
occur.
BRIEF DESCRIPTION OF THE DRAWINGS
35. The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
36. FIG. 1 is a schematic side view of a hot dip galvanizing
apparatus with a strip material cooling system according to an
embodiment of the present invention;
37. FIG. 2 is a diagram showing a steel strip cooling rate versus
the temperature of a steel strip and the amount of water supply for
mists; and
38. FIG. 3 is a schematic side view of a conventional hot dip
galvanizing apparatus.
PREFERRED EMBODIMENTS OF THE INVENTION
39. FIG. 1 is a schematic side view of a cooling system according
to an embodiment of the present invention, in which the invention
is applied to the cooling of a hot dip galvanized steel strip.
40. In FIG. 1, the reference numeral 60 denotes a hot dip
galvanizing tank containing molten zinc 61. In the hot dip
galvanizing tank 60, a deflector roll 62, over which a steel strip
50 is passed, is disposed. Above the hot dip galvanizing tank 60, a
heater 71 is disposed. Above the heater 71, a soaking device 72 is
disposed. Above the soaking device 72, a cooling zone is
established. This cooling zone comprises a high temperature cooling
zone A, and a low temperature cooling zone B located downstream of
(or above) the high temperature cooling zone A. In the high
temperature cooling zone A, a high water volume mist cooler 10 is
installed as a high water volume air-water mixture cooler. In the
low temperature cooling zone B, a low water volume mist cooler 20
is installed as a low water volume air-water mixture cooler.
41. The high water volume mist cooler 10 comprises high water
volume mist sprayers 11 disposed on both sides of a path for the
movement of the steel strip 50. Inside the high water volume mist
sprayer 11, many water supply pipes 12 perforated with many nozzle
holes in the direction of the width of the steel strip 50 are
provided vertically in a row. Inside each water supply pipe 12, an
air supply pipe 13 perforated with many nozzle holes in the
direction of the width of the steel strip 50 is mounted in a
double-pipe configuration. The water supply pipes 12 are connected
to a water supply source (not shown) . The air supply pipes 13 are
connected to an air supply source (not shown).
42. The low water volume mist cooler 20 comprises low water volume
mist sprayers 21 disposed on both sides of the path for the
movement of the steel strip 50. Inside the low water volume mist
sprayer 21, many water supply pipes 22 perforated with many nozzle
holes in the direction of the width of the steel strip 50 are
provided vertically in a row. Inside each water supply pipe 22, an
air supply pipe 23 perforated with many nozzle holes in the
direction of the width of the steel strip 50 is mounted in a
double-pipe configuration. The water supply pipes 22 are connected
to a water supply source (not shown). The air supply pipes 23 are
connected to an air supply source (not shown).
43. On the exit side of (or above) the low water volume mist cooler
20, a deflector roll 90 for guiding the steel strip 50 is
disposed.
44. The steel strip 50 is passed through the molten zinc in the hot
dip galvanizing tank 60, whereby it is hot dip galvanized. The hot
dip galvanized steel strip 50 is moved vertically upward, and
passed through the heater 71. Upon heating the steel strip 50 in
the heater 71, zinc and steel are alloyed. Then, the alloyed steel
strip 50 is guided into the soaking device 72, whereby it is soaked
over its entire width.
45. The steel strip 50 that has passed through the soaking device
72 enters the high water volume mist cooler 10 in the high
temperature cooling zone A. In this zone, high water volume mists
16 are sprayed on the surfaces of the steel strip 50 by the high
water volume mist sprayers 11. In detail, water 24 in a high water
volume is fed to the water supply pipes 12, while compressed air 25
is fed to the air supply pipes 13. Air is jetted through the nozzle
holes of the air supply pipes 13, whereby water 24 in the water
supply pipes 12 is turned into the high water volume mists 16 and
sprayed onto the surfaces of the steel strip 50 through the nozzle
holes of the water supply pipes 12. By the action of the high water
volume mists 16, the steel strip 50 is cooled from 520.degree. C.
to about 350.degree. C. In the high temperature cooling zone A, as
noted from this, the steel strip 50 is cooled, at a high cooling
rate using a low air/water ratio, i.e., high water volume mists, to
a temperature in the vicinity of the temperature of transition
boiling. In the present embodiment, about 350.degree. C. is cited
as such a temperature to which the steel strip is cooled to.
Needless to say, however, the steel strip may be cooled to a
temperature close to about 350.degree. C.
46. The steel strip 50 that has left the high water volume mist
cooler 10 enters the low water volume mist cooler 20 provided in
the low temperature cooling zone B. In this zone, low water volume
mists 26 are sprayed on the surfaces of the steel strip 50 by the
low water volume mist sprayers 21. In detail, water 24 in a low
water volume is fed to the water supply pipes 22, while compressed
air 25 is fed to the air supply pipes 23. Air 25 is jetted through
the nozzle holes of the air supply pipes 23, whereby water 24 in
the water supply pipes 22 is turned into the low water volume mists
26 and sprayed onto the surfaces of the steel strip 50 through the
nozzle holes of the water supply pipes 22. By the action of the low
water volume mists 26, the steel strip 50 is cooled from abut
350.degree. C. to a temperature required before a subsequent step
is performed, for instance, 200.degree. C. As noted from this, the
steel strip 50 is cooled in the low temperature cooling zone B,
with the transition boiling phenomenon being suppressed.
47. The steel strip 50 that has left the low water volume mist
cooler 20 is carried in a horizontal direction by a deflector roll
90.
48. FIG. 2 shows the results of experiments on the cooling rate of
the steel strip 50 according to changes in the temperature of the
steel strip 50 and the amount of water fed. The amount of air fed
per nozzle of the water supply pipe was set at a constant value of
0.3 Nm.sup.3/min, and the air/water ratio was set at varying values
of 1500, 3000, 3600, 4200 and 5000. Under these conditions, the
cooling rate of the steel strip 50 at varying temperatures was
measured. In FIG. 2, it appears that .circle-solid. and .DELTA.
represent the transition boiling phenomenon, while .quadrature.,
.gradient. and .largecircle. represent the absence of this
phenomenon. This is because high air/water ratios corresponding to
these symbols result in a low frequency of direct contact between
water and the steel strip, thereby suppressing the transition
boiling phenomenon.
49. Even when the amount of air fed and the amount of water fed are
increased, the same tendency as shown in FIG. 2 is exhibited at the
same air/water ratio. That is, when the amount of water fed is
increased, the cooling rate for .quadrature. (air/water ratio:
3,600), .gradient. (air/water ratio: 4,200) or .largecircle.
(air/water ratio: 5,000) is raised. However, there is no surge at a
temperature of about 350.degree. C.
50. Based on these results of experiments, the optimum amount of
water to be fed was determined such that the air/water ratio would
be 1500 in the high temperature cooling zone A, and 5000 in the low
temperature cooling zone B. By setting the air/water ratio at 1500
for the high temperature cooling zone A, the steel strip 50 can be
cooled at a high rate.
1TABLE 1 Appropriate water volumes in high temperature cooling
Amount of air Air/water Steel strip portion fed (Nm.sup.3/min)
ratio temperature (.degree. C.) High temperature 0.3 1500 520
.fwdarw. 350 cooling zone (A portion) Low temperature 5000 350
.fwdarw. 200 cooling zone (B portion)
51. As the air-water mixture in the present embodiment, a fog with
a small water particle size may be used in place of the high water
volume mist 16 and the low water volume mist 26. That is, "mist"
also means a fog with a small water particle size.
52. According to the present embodiment, the steel strip 50
traveling in the high temperature cooling zone A is cooled from
520.degree. C. to 300.degree. C. with the high water volume mist 16
as an air-water mixture, whereafter the steel strip 50 traveling in
the low temperature cooling zone B is cooled from 300.degree. C. to
200.degree. C. with the low water volume mist 26. Thus, the steel
strip temperature at which water in the mist 26 sprayed on the
steel strip 50 traveling in the low temperature cooling zone
undergoes transition boiling on the surface of the steel strip 50
can be lowered to 200.degree. C. hence, the temperature
distribution of the steel strip 50 can be made uniform, and
malformation of the steel strip can be prevented.
53. The embodiment described above shows the present invention as
being applied to the cooling of a steel strip after hot dip
galvanization. However, the present invention is not limited
thereto, and can be applied generally to the cooling of a high
temperature strip material.
54. According to the method for cooling a strip material as the
first aspect of the present invention, the strip material, which is
traveling, is passed through a high temperature cooling zone and a
low temperature cooling zone, in this order, to cool the strip
material with a high water volume air-water mixture in the high
temperature cooling zone, and then cool the strip material with a
low water volume air-water mixture in the low temperature cooling
zone. Thus, the strip material can be cooled with the influence of
transition boiling being suppressed, and malformation of the strip
material can be prevented.
55. According to the method for cooling a strip material as the
second aspect of the present invention, the strip material, which
is traveling, is passed through a high temperature cooling zone and
a low temperature cooling zone, in this order, to cool the strip
material with a high water volume air-water mixture in the high
temperature cooling zone to a temperature in the vicinity of a
temperature at which transition boiling occurs, and then cool the
strip material with a low water volume air-water mixture in the low
temperature cooling zone while suppressing transition boiling.
Thus, malformation of the strip material can be prevented.
56. According to the system for cooling a strip material as the
third aspect of the invention, a high temperature cooling zone and
a low temperature cooling zone are established as cooling zones, in
which the strip material is cooled with a high water volume
air-water mixture in the high temperature cooling zone, and cooled
with a low water volume air-water mixture in the low temperature
cooling zone. Since the strip material is thus cooled in two steps,
it can be cooled with the influence of transition boiling being
suppressed. Hence, the temperature distribution of the strip
material can be made uniform, and malformation of the strip
material can be prevented.
57. According to the system for cooling a traveling strip material
as the fourth aspect of the invention, a high temperature cooling
zone and a low temperature cooling zone are established along a
direction in which the strip material travels; a high water volume
air-water mixture cooler is installed in the high temperature
cooling zone; and a low water volume air-water mixture cooler is
installed in the low temperature cooling zone, whereby the strip
material is cooled in two steps. Thus, the strip material can be
cooled with the influence of transition boiling being suppressed.
Thus, the temperature distribution of the strip material can be
made uniform, and malformation of the strip material can be
prevented.
58. In the system for cooling a strip material as the fourth aspect
of the invention, the high water volume air-water mixture cooler
sprays high water volume mists onto both sides of the strip
material, and the low water volume air-water mixture cooler sprays
low water volume mists onto both sides of the strip material.
Because of this constitution, the strip material can be cooled
efficiently with transition boiling being suppressed. Thus, the
temperature distribution of the strip material can be made uniform,
and malformation of the strip material can be prevented.
59. In the system for cooling a strip material as the fourth aspect
of the invention, the high water volume air-water mixture cooler
includes a multiplicity of spray pipes arranged vertically, each
spray pipe having a water supply pipe for supplying a high water
volume, and an air supply pipe mounted inside the water supply
pipe, the water supply pipe extending in the direction of the width
of the strip material and having a plurality of nozzle holes
drilled facing a surface of the strip material, and the air supply
pipe having a plurality of nozzle holes drilled in the direction of
the width of the strip material; and the low water volume air-water
mixture cooler includes a multiplicity of spray pipes arranged
vertically, each spray pipe having a water supply pipe for
supplying a low water volume, and an air supply pipe mounted inside
the water supply pipe, the water supply pipe extending in the
direction of the width of the strip material and having a plurality
of nozzle holes drilled facing a surface of the strip material, and
the air supply pipe having a plurality of nozzle holes drilled in
the direction of the width of the strip material. Because of this
constitution that cools the strip material in two steps, the strip
material can be cooled with transition boiling being suppressed.
Thus, the temperature distribution of the strip material can be
made uniform, and malformation of the strip material can be
prevented.
60. According to the galvanizing system as the fifth aspect of the
invention, a galvanized strip material is cooled with a high water
volume air-water mixture (high water volume mists) in a high
temperature cooling zone to a temperature in the vicinity of a
temperature at which transition boiling occurs, and the strip
material is then cooled with a low water volume air-water mixture
(low water volume mists) in a low temperature cooling zone, with
transition boiling being suppressed. Because of these different
modes of cooling, the strip material can be cooled with the
influence of transition boiling being suppressed. Consequently, any
nonuniform portion is not formed in the temperature distribution of
the steel strip after galvanization. Thus, deformation of the steel
strip due to a nonuniform temperature distribution is
prevented.
61. The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *