[Name of Document] DESCRIPTION
[Title of the Invention] METHOD AND DEVICE FOR REMOVING METAL FUMES
INSIDE SNOUT IN CONTINUOUS HOT-DIP PLATING PLANT
[Technical Field]
5 [0001]
The present invention relates to a method and a device for removing metal fumes
inside a snout which is formed between a continuous annealing furnace outlet and a hot-dip
metal plating bath in a continuous hot-dip plating plant.
[Background Art]
10 [0002]
In a continuous hot-dip plating plant, in which a steel plate is plated by being
continuously immersed in a hot-dip metal plating bath, it is necessary that the steel plate is
immersed in the hot-dip metal plating bath while maintaining the steel plate at a
temperature suitable for plating and keeping the surface thereof in a non-oxidized state.
15 For this reason, equipment having a rectangular cross section, which is referred to as snout,
is formed between a continuous annealing furnace outlet and the hot-dip metal plating
bath.
[0003]
Since a bottom end of the snout reaches a bath surface of the hot-dip metal plating
20 bath, metal vapor of molten metal generated on a molten metal surface is cooled on a
surface of a wall of the snout, and is coagulated and deposited. When this drops, due to
the self-weight, vibration, or the like, on the steel plate and attaches to the steel plate, or on
the bath surface of the hot-dip metal plating bath and then attaches to the steel plate, it may
cause quality defect which is referred to as unplating that a part of the steel plate is not
25 plated. Further, the metal vapor of the molten metal is condensed and formed into a
particle shape (having a size of 1 urn or less in many cases), and after having been
2
deposited on the surface of the wall of the snout as metal fumes, is dropped on and
attached to the steel plate or is directly attached to the steel plate, which causes a similar
quality defect. Those metal vapor and metal fumes further gather together and form
metal dust (having a size of 1 urn or more in many cases), which causes a more serious
5 quality defect.
[0004]
Accordingly, as shown in Patent Document 1, there is suggested technology that
an electric heater is installed around a snout to heat the snout from an outside. When this
method is adopted, the temperature of the inner wall of the snout rises, and hence, the
10 amount of coagulation and deposition of metal fumes is reduced. However, the amount
of coagulation and deposition does not become zero, and metal vapor evaporated from the
molten metal surface is continuously coagulated and deposited on the inner wall of the
snout, which will eventually drop and cause unplating.
[0005]
15 Further, since the heating is performed from an outside using the electric heater,
the temperature of the outer side of the snout becomes higher than the temperature of the
inner side of the snout, and thus, thermal deformation of the snout easily occurs. When
the shell of the snout cracks due to such thermal deformation and the air enters, this also
causes quality defect.
20 [0006]
In addition, Patent Document 2 suggests, as shown in FIG. 1 and FIGS. 2A to 2C,
technology in which an exhaust port 2 is provided to each of the both left and right sides of
a lower part of a snout 1 to exhaust atmospheric gas containing metal vapor evaporated
from a molten metal surface, the metal vapor is condensed and separated using a separator
25 3, and then only the atmospheric gas is sent back to the inside of the snout through an air
inlet port 4 provided to a position on each of the both left and right sides of an upper part.
i
<
I
3
However, in this arrangement, a short path for the atmospheric gas is formed between the
air inlet port 4 and the exhaust port 2, as shown in FIG 2A. Accordingly, it is not
possible to maintain the stream that can shut off the metal vapor in the central part of the
snout 1. Therefore, some of the metal vapor slips through the central part of the snout to
5 the upper part as shown by an arrow 5, and remains inside the snout 1. Further, some of
the metal vapor that has slipped through to the upper part moves toward the continuous
annealing furnace, and coagulates and deposits on the inner wall thereof, which causes
unplating in the same manner.
[Prior Art Document]
10 [Patent Document]
[0007]
[Patent Document 1] JP 2897668B
[Patent Document 2] JP H7-316760A
[Disclosure of the Invention]
15 [Problems to Be Solved by the Invention]
[0008]
An object of the present invention is to solve the above problems, and to provide a
method and a device for removing metal fumes inside a snout, which are capable of
reliably removing metal fumes causing unplating from the snout without heating the outer
20 wall of the snout. Note that, in the description below, metal fumes (in a broad sense) is
used as a term meaning any one of, a combination of two or more of, or a combination of
all of the above-mentioned metal vapor, metal fumes (in a narrow sense), and metal dust.
[Means for Solving the Problems]
[0009]
25 In order to solve the above object, according to one aspect of the present invention,
there is provided a method for removing metal fumes inside a snout in a continuous hot-dip
4
plating plant, including supplying heated inert gas to an inside of a snout which is formed
between a continuous annealing furnace outlet and a hot-dip metal plating bath, and
exhausting gas having a flow rate greater than a flow rate of the supplied gas while
maintaining an atmospheric temperature of the inside of the snout and a temperature of an
5 inner wall of the snout at a temperature that does not cause coagulation of metal fumes.
[0010]
In the method for removing metal fumes inside a snout in a continuous hot-dip
plating, a steel plate may be passed through inside the snout. It is preferred that a stream
of the heated inert gas be formed, the stream flowing from an air inlet port formed on one
10 side surface of the snout to an exhaust port formed on another side surface that is a surface
opposite to the one side surface on which the air inlet port is formed and that is at a
downstream of the air inlet port in a steel plate passing direction. Further, the air inlet
port may be a front side air inlet port capable of supplying air to a front side of the steel
plate through a first side surface of the snout, and there may further be provided a back
15 side air inlet port capable of supplying air to a back side of the steel plate through a second
side surface of the snout. The exhaust port may be a front side exhaust port capable of
exhausting air from the front side of the steel plate through the second side surface, and
there may further be provided a back side exhaust port capable of exhausting air from the
back side of the steel plate through the first side surface. The heated inert gas may be
20 supplied from the front side air inlet port and exhausted from the front side exhaust port
and the heated inert gas may also be supplied from the back side air inlet port and
exhausted from the back side exhaust port. Therefore, a gas stream of the heated inert gas
is separated into a first gas stream flowing along the front side of the steel plate and a
second gas stream flowing along the back side of the steel plate. The first gas stream and
25 the second gas stream also cross each other in a separated manner at front and back of the
steel plate.
5
[0011]
Further, according to another aspect of the present invention, there is provided a
device for removing metal fumes inside a snout in a continuous hot-dip plating plant,
including a unit configured to supply heated inert gas to an inside of a snout which is
5 formed between a continuous annealing furnace outlet and a hot-dip metal plating bath,
and a unit configured to exhaust gas having a flow rate greater than a flow rate of the
supplied gas while maintaining an atmospheric temperature of the inside of the snout and a
temperature of an inner wall of the snout at a temperature that does not cause coagulation
of metal fumes.
10 [0012]
In the device for removing metal fumes, a steel plate may be passed through
inside the snout. It is preferred that the device include an air inlet port formed on one side
surface of the snout and an exhaust port formed on another side surface that is a surface
opposite to the one side surface on which the air inlet port is formed and that is at a
15 downstream of the air inlet port in a steel plate passing direction, and that a stream of the
heated inert gas be formed which flows from the air inlet port to the exhaust port. Further,
the air inlet port may be a front side air inlet port capable of supplying air to a front side of
the steel plate through a first side surface of the snout, and there may further be provided a
back side air inlet port capable of supplying air to a back side of the steel plate through a
20 second side surface of the snout. The exhaust port may be a front side exhaust port
capable of exhausting air from the front side of the steel plate through the second side
surface, and there may further be provided a back side exhaust port capable of exhausting
air from the back side of the steel plate through the first side surface. The heated inert gas
may be supplied from the front side air inlet port and exhausted from the front side exhaust
25 port and the heated inert gas may also be supplied from the back side air inlet port and
exhausted from the back side exhaust port. Therefore, a gas stream of the heated inert gas
6
is separated into a first gas stream flowing along the front side of the steel plate and a
second gas stream flowing along the back side of the steel plate. The first gas stream and
the second gas stream also cross each other in a separated manner at front and back of the
steel plate.
5 [Effect of the Invention]
[0013]
According to the present invention, the heated inert gas is supplied to the inside of
the snout to maintain the atmospheric temperature of the inside of the snout and the
temperature of the inner wall of the snout at a temperature that does not cause the
10 coagulation of the metal fumes, the exhausted gas having a flow rate greater than the flow
rate of the supplied gas. Accordingly, since the metal fumes evaporated from the molten
metal surface join the gas stream and are exhausted from the inside of the snout, the
coagulation and deposition do not occur on the surface of a wall of the snout. In addition,
the pressure of the inside of the snout is kept negative, and hence, a stream is formed
15 which flows from the continuous annealing furnace outlet to the exhaust port of the snout,
and the metal fumes do not enter the continuous annealing furnace. As the result thereof,
the rate of occurrence of unplating can be significantly reduced. Further, there is no risk
of thermally deforming the snout as in the case of heating the outer side of the snout of the
prior art.
20 [0014]
Further, when air inlet ports and exhaust ports corresponding thereto, respectively,
are disposed separately in the front and back side of a steel plate that is passed through
inside the snout, the inert gas streams flowing from the air inlet ports to the exhaust ports
are caused to cross each other in a separated manner at the front and the back side of the
25 steel plate. Accordingly, collision of the gas streams and passing of the gas streams along
short paths can be prevented. Therefore, it can be reliably prevented that the metal fumes
7
evaporated from the molten metal surface slip through to the upper part, and a more
desirable result can be obtained.
[Brief Description of the Drawings]
[0015]
5 [FIG. 1] FIG. 1 is a side cross-sectional view showing a snout according to prior
art.
[FIG. 2A] FIG. 2A is an elevational view showing the snout according to prior art.
[FIG. 2B] FIG. 2B is a cross-sectional view along the line A-A of FIG. 2A.
[FIG. 2C] FIG. 2C is a cross-sectional view along the line B-B of FIG. 2A.
10 [FIG. 3] FIG. 3 is a side cross-sectional view showing a snout according to an
embodiment of the present invention.
[FIG. 4A] FIG. 4A is an elevational view showing the snout according to an
embodiment of the present invention.
[FIG. 4B] FIG. 4B is a cross-sectional view along the line C-C of FIG. 4A.
15 [FIG. 4C] FIG. 4C is a cross-sectional view along the line D-D of FIG. 4A.
[FIG. 5] FIG. 5 is a graph showing a relationship between an exhaust rate and a
metal fume index.
[FIG. 6A] FIG. 6A is a diagram schematically showing an air stream inside the
snout under a state in which the exhaust rate is less than 100%.
20 [FIG. 6B] FIG. 6B is a diagram schematically showing an air stream inside the
snout under a state in which the exhaust rate is 100%.
[FIG. 6C] FIG. 6C is a diagram schematically showing an air stream inside the
snout under a state in which the exhaust rate exceeds 100%.
[FIG. 7A] FIG. 7A is a graph showing a result obtained by studying a desirable
25 positional relationship between an air inlet port and an exhaust port.
[FIG. 7B] FIG. 7B is a diagram illustrating the result shown in FIG. 7A.
8
[FIG. 8A] FIG. 8A is a diagram explaining a specific reason that the positional
relationship shown in FIG. 7A is desirable, and shows a case where W/L is less than 0.75.
[FIG. 8B] FIG. 8B is a diagram explaining a specific reason that the positional
relationship shown in FIG. 7A is desirable, and shows a case where W/L exceeds 1.75.
5 [FIG. 8C] FIG. 8C is a diagram explaining a specific reason that the positional
relationship shown in FIG 7A is desirable, and shows a case where 0 exceeds A+5°.
[FIG. 8D] FIG. 8D is a diagram explaining a specific reason that the positional
relationship shown in FIG. 7A is desirable, and shows a case where 0 is less than A-5°.
[Mode for Carrying out the Invention]
10 [0016]
Hereinafter, referring to the appended drawings, preferred embodiments of the
present invention will be described in detail. It should be noted that, in this specification
and the appended drawings, structural elements that have substantially the same function
and structure are denoted with the same reference numerals, and repeated explanation
• 15 thereof is omitted.
[0017]
FIG. 3 and FIGS. 4A to 4C are each a diagram showing an embodiment of the
present invention. A snout 10 is formed between a continuous annealing furnace outlet 11
and a hot-dip metal plating bath 12. In general, although in most of the cases the snout 10
20 has a rectangular cross section, the shape of the cross section is not necessarily limited to a
rectangle, and may be any shape as long as it is approximately a rectangle. The exhaust
port 13 is formed at a lower side of the snout 10, which is near to the hot-dip metal plating
bath 12, on each of the both side surfaces of the snout 10. The air inlet port 14 is formed
at a position higher than the exhaust port 13, that is, at an upper side of the snout 10, which
25 is near to the continuous annealing furnace, on each of the both side surfaces of the snout
10. Inside the snout 10, a steel plate 15 that has come out from the continuous annealing
9
furnace runs continuously toward the hot-dip metal plating bath 12. In the hot-dip metal
plating bath 12, the steel plate 15 is subjected to hot-dip galvanizing, for example.
[0018]
As shown in FIG. 4A, in the present embodiment, air inlet ports 14a and 14b
5 formed on side surfaces of the snout 10 are formed obliquely downward toward exhaust
ports 13a and 13b formed on the respective opposite side surfaces of the snout 10. From
r
those air inlet ports 14a and 14b, inert gas heated by a heater 16 is blown inside the snout
10. That is, the heated inert gas is blown in an oblique direction with respect to the
extending direction of the snout 10 (direction from the continuous annealing furnace to the
10 hot-dip metal plating bath 12). As the inert gas, nitrogen gas is used, for example. With
the heated inert gas being blown in in this manner, the atmospheric temperature of the
inside of the snout 10 and the temperature of the inner wall of the snout are maintained at
high temperature and approximately uniform, and thus, coagulation and deposition of the
metal fumes on the inner wall of the snout 10 are suppressed. Further, thermal
15 deformation of the snout 10 can also be prevented.
[0019]
As shown in FIG. 4A, the inert gas blown in from the air inlet port 14a and the
inert gas blown in from the air inlet port 14b, the air inlet ports 14a and 14b being provided
at right and left side surfaces, cross each other in a separated manner in the inside of the
20 snout 10, and are exhausted from the exhaust ports 13a and 13b. In more detail, from the
air inlet port 14a formed on the right side surface of the snout 10, the inert gas is blown in
toward the exhaust port 13a formed on the left side surface. From the air inlet port 14b
formed on the left side surface of the snout 10, the inert gas is blown in toward the exhaust
port 13b formed on the right side surface. In order to cause gas streams of the blown-in
25 inert gas to cross each other in a separated manner in the inside of the snout 10, the air inlet
ports 14a and 14b, and the exhaust ports 13a and 13b are disposed separately at the front
10
and back of a steel plate 15 that is passed through inside the snout 10. That is, as shown
in FIG. 4B and FIG. 4C which are the cross-sectional view along the line C-C of FIG. 4A
and the cross-sectional view along the line D-D of FIG. 4A, respectively, the air inlet port
14a is disposed at the front side of the steel plate 15, and the air inlet port 14b is disposed
5 at the back side of the steel plate 15. On the other hand, the exhaust port 13a is disposed
at the front side of the steel plate 15, and the exhaust port 13b is disposed at the back side
of the steel plate 15. In this way, the gas stream from the air inlet port 14a to the exhaust
port 13a at the front side of the steel plate 15 and the gas stream from the air inlet port 14b
to the exhaust port 13b at the back side of the steel plate 15 cross each other in a separated
10 manner with the steel plate 15 being provided therebetween. With the generation of such
gas stream in the inside of the snout 10, it can be prevented that the metal fumes rising
from the side of the hot-dip metal plating bath 12 slip through the gas stream and flow to
the side of the continuous annealing furnace. Note that, although it is preferred that the
air inlet ports 14a and 14b and the exhaust ports 13a and 13b be provided completely
15 separately on the front side and on the back side of the steel plate 15 as shown in FIGS. 4A
to C, it is also allowed to have one air inlet port or one exhaust port that occupies over the
front and back of the steel plate 15 as shown in FIGS. 6Ato C to be described later, since
the presence of the steel plate 15 itself separates the gas stream.
[0020]
20 In addition, in the present invention, the gas exhausted from the exhaust port 13
has a flow rate greater than the supplied gas. Accordingly, the pressure of the inside of
the snout 10 becomes slightly negative, and, as shown by an arrow 17 in FIG. 3, a gas
stream is formed from the continuous annealing furnace to the snout 10. Therefore, metal
fumes generated from the hot-dip metal plating bath 12 are reliably exhausted from the
25 exhaust port 13. Further, it can be also prevented that the metal fumes enter inside the
continuous annealing furnace.
#
11
[0021]
In this way, according to the present invention, since the metal fumes inside the
snout can be removed rapidly, generation of unplating can be significantly reduced.
Hereinafter, specific data thereof will be described.
5 [0022]
FIG. 5 is a graph showing a relationship between an exhaust rate and an amount of
metal fumes inside the snout or an amount of metal fumes inside the continuous annealing
furnace. Here, the exhaust rate on the horizontal axis is determined by dividing the
exhaust flow rate by the air supply flow rate and is represented in percentage. The metal
10 fume index inside the snout or inside the continuous annealing furnace on the vertical axis
is a value determined by representing in an index a mass of metal fumes (in a broad sense)
present inside the snout or inside the continuous annealing furnace, where the total value of
the mass of metal fumes inside the snout and the mass of metal fumes inside the
continuous annealing furnace is 100 when the exhaust rate is zero.
15 [0023]
; With reference to the graph, the metal fume index inside the snout represented by
a black dot drastically decreases when the exhaust rate exceeds 100%. However, when
the exhaust rate becomes 150% or more, the rate of decline of metal fume index per
exhaust rate becomes low, and even if the exhaust rate is increased further, the metal fume
20 index does not change much. From this result, it is found that in order to obtain a notable
effect in reduction of metal fumes inside the snout, it is preferred to set the exhaust rate to
a value exceeding 100%. Further, it is also found that it is sufficient when the exhaust
rate is set to 150% or more. Meanwhile, in the same manner, the metal fume index inside
the continuous annealing furnace represented by a rhombus drastically decreases when the
25 exhaust rate exceeds 100%, and does not change much when the exhaust rate becomes
150%o or more. Accordingly, it may also be said that in order to obtain a notable effect in
reduction of metal fumes inside the continuous annealing furnace, it is preferred to set the
exhaust rate to a value exceeding 100%, and it is sufficient when the exhaust rate is set to
150% or more.
[0024]
5 FIGS. 6A to 6C are each a diagram schematically showing an air stream inside the
snout based on difference in the exhaust rate, and FIG. 6A represents a state in which the
exhaust rate is less than 100%, FIG. 6B represents a state in which the exhaust rate is 100%,
and FIG. 6C represents a state in which the exhaust rate exceeds 100%. Under the sate
shown in FIG 6A, since the gas stream is formed from the snout to the continuous
10 annealing furnace, fumes coagulates and deposits on the entire inner wall of the snout and
the entire furnace wall of the continuous annealing furnace, which causes quality defect.
On the contrary, under the state shown in FIG. 6C, since the gas stream is formed from the
continuous annealing furnace to a molten metal surface, coagulation and deposition of the
metal fumes on the inner wall of the snout and the furnace wall of the continuous annealing
15 furnace are suppressed. FIG. 6B shows the state in which the both streams are balanced,
but since there is also a gas stream that flows toward the continuous annealing furnace, it is
unable to obtain sufficient metal fume-suppression effect.
[0025]
FIG 7A, FIG. 7B, and FIGS. 8A to 8D are each a diagram showing a.result
20 obtained by studying a positional relationship between an air inlet port and an exhaust port.
In this study, as shown in FIG. 7B, the width of the snout is represented by W, the
difference between the heights of the air inlet port and the exhaust port is represented by L,
and in addition, the angle between the line connecting the air inlet port and the exhaust port
and the extending direction of the snout is represented by 0. Note that, in the present
25 embodiment, since the air inlet port is provided in a manner that it faces the direction of the
exhaust port, the angle of the air inlet port with respect to the side surface of the snout is
i
13
equal to the angle 9.
[0026]
The results of the study are shown in the graph of FIG. 7A. A desired positional
relationship between the air inlet port and the exhaust port is defined with W/L and the
5 angle 9. To be more specific, a region satisfying the following is desirable,
0.75