[Document Type] SPECIFICATION
[Title of the Invention] METHOD OF SUPPLYING Zn-Al ALLOY TO MOLTEN
ZINC POT, METHOD OF ADJUSTING CONCENTRATION OF Al IN MOLTEN
ZINC BATH, AND APPARATUS FOR SUPPLYING Zn-Al ALLOY TO MOLTEN
ZINC POT
[Technical Field]
[0001] __
The present invention relates to a method of supplying a Zn-Al alloy to a
molten zinc pot in a continupus hot dip galvanizing line for a steel sheet, a method of
adjusting the concentration of Al in a molten zinc bath, and an apparatus for supplying
a Zn-Al alloy to a molten zinc pot.
Priority is claimed on Japanese Patent Application No. 2012-047546, filed on
March 5, 2012, and the content of which is incorporated herein by reference.
[Background Art]
[0002]
The concentration of Al in a molten zinc bath (the weight% of Al to the entire
molten zinc bath) in a molten zinc pot disposed in a continuous hot dip galvanizing
line for a steel sheet affects the quality of a galvanized steel sheet, particularly, the
quality of an alloy layer of base iron and zinc. Therefore, in order to stabilize the
quality of the galvanized steel sheet, it is important to maintain the concentration of Al
in the molten zinc bath at a constant level.
[0003]
Hitherto, for the purpose of compensating the amount of molten zinc taken
out of the molten zinc pot by a steel sheet, a zinc ingot containing Al is injected to the
molten zinc pot from the above the molten zinc pot to maintain the amount of molten
1 -
zinc in the molten zinc bath at a constant level and to roughly adjust the concentration
of Al in the molten zinc (Patent Document 1).
In addition, a method is employed in which the concentration of Al in the
molten zinc bath is measured by ICP analysis performed by drawing up a portion of the
molten zinc in the molten zinc pot or an Al concentration meter installed in the molten
zinc pot. Then, when the concentration of Al in the molten zinc bath is reduced, a Zn-
Al alloy piece (so-called aluminum cake) having a higher concentration of contained
Al than that of a zinc ingot containing Al is injected, controlled by an operator, into the
surface layer of the molten zinc bath from the above the molten zinc pot, thereby finely
adjusting the concentration of Al in the molten zinc. In general, the weight of the zinc
ingot is tens to hundreds of kilograms, and the weight of the Zn-Al alloy piece
(aluminum cake) for fine adjustment is about 5 to 10 kg.
[0004]
Al in the zinc ingot containing Al and the Zn-Al alloy piece has a smaller
specific gravity than zinc. Therefore, in a case where the zinc ingot containing Al or
the Zn-Al alloy piece is injected in the above-described method, the concentration of
Al at the bath surface of the molten zinc bath is increased, and thus, the surrounding of
the bath surface is in a state of having a high Al concentration. On the other hand, the
bottom portion of the molten zinc pot is in a state of having a low Al concentration,
and thus bottom dross is likely to be generated and deposited on the bottom portion.
The bottom dross rises due to stirring flow in the pot and adheres to the steel sheet
when the sheet-threading speed of the continuous hot dip galvanizing line is in high
speed. The bottom dross that adheres to the steel sheet is a cause for pressing flaws
and degrades the product vdue of the galvanized steel sheet. Therefore, in the
present, in order to avoid thts problem, the upper limit of the sheet-threading speed is
- 2 -
restricted, and the bottom dross is pumped out by regularly stopping facilities. The
restriction on the sheet-threading speed and the regular stop of the facilities are the
causes for degradation in productivity.
[0005]
In addition, during the injection by the control of the operator as described
above, the injection pitch is roughened, and an increase in the difference between a
target Al concentration and an actually acquired Al concentration cannot be avoided.
Accordingly, the quality of the alloy layer of the galvanized steel sheet is not
stabilized, and insufficient alloying called half-baking or excessive alloying occurs,
which is the cause for the degradation in product quality.
[Prior Art Document]
[Patent Document]
[0006]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2005-240155
[Disclosure of the Invention]
[Problem that the Invention is to solve]
[0007]
An object of the present invention is to solve the above-described problems.
That is, an object of the present invention is to provide a method of supplying a Zn-Al
alloy to a molten zinc pot in which the concentration of Al in a molten zinc bath in the
molten zinc pot in a continuous hot dip galvanizing line for a steel sheet is always
maintained at a constant level and pressing flaws, insufficient alloying, excessive
alloying, and the like do not occur even when the sheet is passed at a higher speed than
that according to the related'Srt, a method of adjusting the concentration of Al in a
- 3
c--
molten zinc bath, and an apparatus for supplying a Zn-Al alloy to a molten zinc pot.
[Means for Solving the Problems]
[0008]
The present invention is contrived on the basis of the above knowledge, and
the gist thereof is as follows.
(1) That is, according to an aspect of the present invention, a method of
supplying a Zn-Al aUoy to a molten zinc pot which accommodates a molten zinc baith
in a hot dip galvanizing line, includes: supplying the Zn-Al alloy from a supply portion
provided at a lower portion pf an insertion guide having a pipe shape, in which the
supply portion is immersed between an inner wall of the molten zinc pot on a
downstream side in a travelling direction of a steel sheet and a front support roll
installed in the molten zinc bath at a depth within ±400 mm from a lower end of the
front support roll, and an inside of the insertion guide is pressurized by inert gas to
prevent the molten zinc bath from advancing to the inside of the insertion guide.
[0009]
(2) In the method of supplying a Zn-Al alloy to a molten zinc pot according to
(1), the Zn-Al alloy may have a form of any one of a wire, a chip, and powder.
[0010]
(3) In the method of supplying a Zn-Al alloy to a molten zinc pot according to
(1), the supply portion of the insertion guide may be installed in a discharge flow
which is generated between the front support roll in the molten zinc bath and the steel
sheet which travels.
[0011]
(4) According to another aspect of the present invention, a method of
adjusting a concentration of Al in a molten zinc bath includes: controlling an amount of
- 4 -
the Zn-Al alloy supplied according to the method of supplying a Zn-Al alloy to a
molten zinc pot according to any one of (1) to (3) depending on the concentration of Al
measured by an Al concentration meter installed in the molten zinc pot.
[0012]
(5) According to another aspect of the present invention, an apparatus for
supplying a Zn-Al alloy to a molten zinc pot which accommodates a molten zinc bath
in which a front support roll is immersed in a hot dip galvanizing line, includes: an
insertion guide having a pipe shape, which has a supply portion at a lower portion and
is installed between an inner, wall of the molten zinc pot on a downstream side in a
travelling direction of a steel sheet and the front support roll installed in the mohen
zinc bath; and a gas supply device which supplies inert gas into the insertion guide, in
which an installation position of the supply portion is in the molten zinc bath and at a
depth within +400 mm from a lower end of the front support roll, and the Zn-Al alloy
is supplied to the molten zinc bath from the supply portion of the insertion guide.
[Effect of the Invention]
[0013]
According to the aspects of the present invention, by supplying the Zn-Al
alloy into the molten zinc pot from the supply portion provided at the lower portion of
the insertion guide having a pipe shape, which is installed between the inner wall of the
molten zinc pot on the downstream side in the travelling direction of the steel sheet and
the front support roll installed in the molten zinc bath at a depth within ±400 mm from
the lower end of the front support roll in the molten zinc bath, Al can be uniformly
difiused in the molten zinc bath. As a result, the generation of bottom dross due to
the non-uniformity of the concentration of Al in the molten zinc bath in the molten zinc
pot is suppressed, and thus pffessing flaws caused by rising of the bottom dross are
reduced even when the sheet-threading speed is increased. Therefore, it is possible to
achieve the enhancement in productivity.
[0014]
In addition, according to the aspects of the present invention, by controlling
the amount of the Zn-Al alloy supplied depending on the concentration of Al in the
molten zinc bath measured by the Al concentration meter, the concentration of Al in
the molten zinc bath including the surface of the steel sheet on which an alloying
reaction between base iron and zinc occurs can be always maintained at a constant
level. Therefore, the quality of the alloy layer is stabilized, and thus the occurrence of
insufficient alloying called half-baking or excessive alloying can be prevented.
[Brief Description of the Drawing]
[0015]
FIG 1 is an explanatory view of a method of supplying a Zn-AI alloy to a
molten zinc pot according to an embodiment of the present invention.
FIG 2 is a cross-sectional view of the main part of FIG 1.
FIG 3 is a side view illustrating the flows of a molten zinc bath in the molten
zinc pot.
FIG 4A is an explanatory view showing the respective positions of particle
counters in a test using a water model, and is a side view.
FIG 4B is an explanatory view showing the respective positions of the
particle counters in the test using the water model, and is a plan view.
FIG 5 is a graph showing the relationship between a distance from the lower
end of a front support roll to a position at which acrylic tracers are added and a tracer
detection ratio s, which are converted into values of the real facility, in the test using
the water model. ''
J
FIG 6 is an explanatory view of a steel sheet width ratio.
FIG 7 is a graph showing the relationship between the steel sheet width ratio,
a tracer detection ratio ri, and a tracer detection ratio \x.
FIG 8A is a side view illustrating the positions of Al concentration meters in
Example.
FIG 8B is a side view illustrating the positions of the Al concentration meters
in Example.
FIG 9 is a graph showing the concentration of Al at a position X of FIGS. 8A
and SB.
FIG 10 is a graph showing the ratio of the concentration of Al at a position Y
of FIGS. 8A and 8B to the concentration of Al at the position X of FIGS. 8A and 8B.
FIG 11 is a graph showing the ratio of the concentration of Al at a position Z
of FIGS. 8A and 8B to the concentration of Al at the position X of FIGS. 8A and 8B.
FIG 12 is a graph showing a dross rising rate.
[Embodiment of the Invention]
[0016]
Hereinafter, exemplary embodiments of the present invention will be
described.
In FIG. 1, reference numeral 1 denotes a molten zinc pot in a hot dip
galvanizing line for a steel sheet, and reference numeral 2 denotes a molten zinc bath
accommodated therein. In the molten zinc pot 1, a sink roll 3, a front support roll 4,
and a back support roll 5 are installed in a state of being immersed in the molten zinc
bath 2. A steel sheet S is introduced into the molten zinc bath 2 in an inclined
direction as illustrated in FIG 1, is turned by the sink roll 3, and is then pulled up in the
vertical direction between the front support roll 4 and the back support roll 5 in the
- 7 -
molten zinc bath. In this embodiment, the rightward direction in FIG. 1 is referred to
as an upstream side in the travelling direction of the steel sheet, and the leftward
direction in FIG. 1 is referred to as a downstream side in the travelling direction of the
steel sheet.
[0017]
Above the liquid surface of the molten zinc pot 1, an adding apparatus 6 for a
Zn-Al alloy (an apparatus for supplying a Zn-Al alloy) is provided. The details
thereof are as illustrated in FIG 2. A wire 7 of the Zn-Al alloy is wound around a
drum 8, and the wire 7 of the Zn-Al alloy is drawn out in the downward direction via
guide rolls 10 and 10 by rotating the drum 8 using a motor 9 to be supplied into the
molten zinc bath 2 from a supply portion provided at the lower portion of an insertion
guide 11 having a pipe shape. Considering the safety of an operation of replacing the
Zn-Al alloy wire, it is preferable that the drum 8 be not disposed above the bath
surface of the molten zinc but be disposed above an operation floor 19. The Zn-Al
alloy wire 7 is preferably continuously supplied but may also be intermittently supplied
at a short interval. The insertion guide 11 is made of a ceramic having heat
resistance, such as alumina, and is installed between an irmer wall 20 on the
downstream side in the travelling direction of the steel sheet in the molten zinc pot and
the front support roll installed in the molten zinc bath, that is, in a hot dip galvanizmg
bath on the left of the figure from the front support roll. Moreover, the abovementioned
supply portion is set to have a depth within ±400 mm from the lower end of
the front support roll 4 in the molten zinc bath.
[0018]
The entirety of the adding apparatus 6 is accommodated in a hermetic seal
box 12 as illusfrated in FIG 2, and to the inside thereof, inert gas such as nifrogen gas
- 8
^
or Ar gas is supplied from a gas supply device (not illustrated) through a valve 13.
Reference numeral 14 denotes a pressure meter that detects the internal pressure of the
hermetic seal box 12. The pressure meter controls the internal pressure of the
insertion guide 11 by controlling the amount of inert gas supplied from the gas supply
device through the valve 13. The supplied inert gas presses the molten zinc that
attempts to advance into the insertion guide 11 down to, for example, the surrounding
of the lower end of the insertion guide 11. Accordingly, the wire 7 of the Zn-Al alloy
is lowered to the lower end of the insertion guide 11 without coming into contact with
the molten zinc and at the moment of coming out of the lower end portion, comes into
contact with the molten zinc and starts dissolving, that is, the supply of the Zn-Al alloy
into the mohen zinc bath is started. The position at which the supply of the Zn-Al
alloy to the molten zinc bath is started corresponds to the supply portion of the
insertion guide. In addition, when air (atmosphere) is used instead of the inert gas,
there is a concern that the molten zinc and the Zn-Al alloy may be oxidized, which is
not preferable.
[0019]
As illustrated in FIG 1, an appropriate number of Al concentration meters 15
are installed in the molten zinc pot 1. In this embodiment, the amount of the Zn-Al
alloy supplied is controlled depending on the Al concentration measured by the Al
concentration meters 15. Accordingly, the concentration of Al in the molten zinc bath
2 can be maintained at a constant level. In addition, the amount of the Zn-Al alloy
supplied can be controlled by, for example, changing the transport speed of the wire 7.
When the transport speed of the wire is increased, there may be cases where the wire is
not immediately dissolved even when coming into contact with the molten zinc.
However, in this case, the wire may be pre-heated.
- 9 -
C
m
[0020]
Next, the reason that the supply portion of the insertion guide 11 is set to have
a depth within ±400 mm from the lower end of the front support roll 4 in the molten
zinc bath 2 will be described.
FIG 3 is a diagram illustrating the flows of the molten zinc bath generated in
the molten zinc pot 1. In the molten zinc bath 2, a roll rotation flow B caused by the
front support roll 4 and an accompanying flow A in the vicinity of the steel sheet S
collide with each other and thus a strong discharge flow C which is directed toward the
downstream side (to the left jn the figure) in the traveling direction of the steel sheet is
generated. The discharge flow C collides with the wall surface and is separated into
upper and lower flows to be circulated in the entire molten zinc pot 1. In this
embodiment, the position at which the Zn-Al alloy is supplied from the insertion guide
11 is set to be in the discharge flow C such that the Zn-Al alloy is efficiently and
uniformly diffused on the strong discharge flow C.
[0021]
As described above, the discharge flow C is directed toward the downstream
side in the travelling direction of the steel sheet of the front support roll. Therefore,
the inventors thought that it is effect to install the insertion guide so that the supply
portion of the insertion guide is on the downstream side in the travelling direction of
the steel sheet with respect to the front support roll. Moreover, for more detailed
examination on the installation position of the insertion guide, the inventors conducted
a test using a 1/5 scale water model which simulated the real equipment and the Froude
number a plurality of numbers of times for flow analysis. In the flow analysis, acrylic
tracers having a particle diameter of 50 (xm were used, and the acrylic tracers were
added from various depths t0*count the number of tracers detected by particle counters
- 10
c-^--'
16, 17, and 18 on the bath surface side and the bath bottom side. The positions of the
particle counters 16, 17, and 18 are illustrated in FIGS. 4A and 4B. In addition, (the
number of fracers detected on the bath surface side/ the number of tracers detected on
the bath bottom side) is referred to as a tracer detection ratio s, and the relationship
between the distance from the lower end of the front support roll 4 to the position at
which the acrylic tracers are added and the tracer detection ratio 8 is arranged in the
graph of FIG 5. In addition, the distance from the front support roll of FIG 5 is a
value converted into the distance in the real facility from the ratio between the water
model and the real facility. ,
Here, the number of tracers detected on the bath surface side used to obtain s
is the resuh measured by the particle counter 16 of FIG. 4A, and the number of tracers
detected on the bath bottom side is the result measured by the particle counter 18 of
FIG 4A.
In addition, FIG 4 A is a side view of a water tank used for the water model
test. FIG. 4B is a plan view of the water tank. As can be seen from FIGS. 4A and
4B, the particle counters 16, 17, and 18 are installed at different positions in the depth
direction and the width direction of the steel sheet.
[0022]
As shovra in the graph of FIG 5, it was confirmed that when the position at
which the acrylic tracers are added was in a range of about ±400 mm from the lower
end of the front support roll 4 (within 400 mm on the bath surface side and within 400
mm on the bath bottom side), the tracer detection ratio 8 had approached 1, that is, the
acrylic tracers were uniformly dispersed on the bath surface side and the bath bottom
side. Therefore, in the present invention, the Zn-Al alloy was supplied from the
supply portion of the inserticTn guide 11 immersed at a depth within ±400 mm from the
11 -
lower end of the front support roll 4. For more uniform distribution, a depth within
±300 mm from the lower end of the front support roll 4 is preferable, and a depth
within ±200 mm therefrom is more preferable.
[0023]
Similarly, as illustrated in FIG 6, the position at which the acrylic tracers were
added was changed in the width direction of the steel sheet S and the numbers of
tracers detected by the particle counters on the bath surface side and the bath bottom
side at the same position in the width direction were counted. In addition, (the
number of tracers detected on the bath surface side+the number of tracers detected on
the bath bottom side)/the number of tracers injected was defined as a tracer detection
ratio r| and was arranged in the graph of FIG. 7. Here, the number of tracers detected
on the bath surface side used to obtain r\ is the result measured by the particle counter
16 of FIG 4 A, and the number of tracers detected on the bath bottom side is the result
measured by the particle counter 18 of FIG. 4A.
The steel sheet width ratio of the horizontal axis of the graph represents a
value (L/W) obtained by dividing a distance L from the edge of the steel sheet to the
position at which the acrylic tracers are added by the sheet width W of the steel sheet
as illustrated in FIG 6. FIG 7 also shows the tracer detection ratio \x obtained by
dividing the number of tracers detected by the particle counter installed on the outside
(steel sheet width ratio=l 10%) of the sheet width of the steel sheet by the number of
tracers injected. In addition, the particle counter used to obtain [i is the particle
counter 17 of FIG. 4A.
[0024]
As can be seen from FIG. 7, it was confirmed that in a case where the acrylic
tracers were added from thcouter side than the edge of the steel sheet S, the number of
12 -
tracers detected in the steel sheet width was reduced and the number of tracers detected
in the surrounding of the edge of the steel sheet S was increased. This proves that the
added Al is concentrated on the surrounding of the edge of the steel sheet S and causes
alloying failure in the surrounding of the edge of the steel sheet S. In contrast, in a
case where the acrylic tracers were added from the surrounding of the center of the
steel sheet width, the tracer detection ratio r\ is high and Al is relatively efficiently
dispersed. Therefote, the steel sheet width ratio (L/W) is preferably 0 to 100%, more
preferably 20 to 80%, and most preferably 40 to 60%.
[Examples]
[0025]
The content of the present invention described above was checked by the real
equipment. The molten zinc pot had dimensions of 3.1 mx3.9 mx2.6 m (depth), and
the Zn-Al alloy was supplied from the supply portion of the insertion guide by setting
the supply portion of the insertion guide at the same height (depth) as the lower end of
the front support roll.
In order to measure the concentration of Al, the Al concentration meters were
installed at positions X, Y, and Z in the molten zinc bath shovm in FIG. 8. X is a
position below 200 mm from the liquid surface (bath surface) in the vicinity of the
inner wall surface on the upstream side in the travelling direction of the steel sheet, and
Y is a position below 2000 mm from the liquid surface similarly in the vicinity of the
inner wall surface on the upstream side in the travelling direction of the steel sheet. Z
has the same depth as X on the outside in the width direction of the front support roll.
[0026]
FIG 9 shows a change in the concentration of Al at the position X. The
vertical axis represents a first*Al concentration index shown as the concentration of Al
13 -
in the related art/the concentration of Al in the method of the present invention. It
was confirmed that contrary to the method of the present invention, in the related art (a
method of injecting aluminum cakes), the concentration of Al was significantly
changed due to the injection of the aluminum cakes.
[0027]
FIG 10 shows a change in the ratio (a second Al concentration index) of the
concentration of Al at the position X to the concentration of Al at the position Y in the
related art and in the method of the present invention. It appears that in the related
art, the value is always smaller than 1 and Al is insufficiently supplied to the bath
bottom portion. On the other hand, according to the present invention, the value was
mostly stabilized to 1, and it was confirmed that the difference in the concentration of
Al between the bath surface and the bath bottom of the molten zinc bath could be
solved.
[0028]
FIG 11 shows a change in the ratio (a third Al concentration index) of the
concentration of Al at the position X to the concentration of Al at the position Z. In
the related art, the concentration of Al is significantly increased due to the injection of
the aluminum cakes and the concentration of Al is significantly changed with time.
That is, it appears that it takes much time to stabilize the concentration of Al. On the
other hand, according to the method of the present invention, the value of the third Al
concentration index is always stabilized and thus the concentration of Al can be
stabilized in the entire molten zinc pot.
[0029]
FIG 12 shows how the sheet-threading speed of the steel sheet (line speed:
LS) changes a dross rising rate. The dross rising rate is a value which indexes the
- 14 -
^
number of pieces of dross suspended at 110 m/min, which is the sheet-threading speed
of the related art, as 100 regarding the number of pieces of dross suspended. A
reduction in the ratio of pieces of dross suspended indicates a reduction in the amount
of dross deposited. According to the present invention, even when the sheetthreading
speed was increased to 140 m/min, the dross rising rate could be suppressed
to 100%, and a sheet-threading regulation speed could be increased by 30 m/min from
that of the related art. Accordingly, productivity could be enhanced, and a reduction
in an alloying failure rate during an actual operation to 1/2 of that of the related art had
succeeded.
[0030]
In addition, the present invention is not limited to the embodiments described
above, and various design changes can be made without departing from the gist
thereof. For example, in the above-described embodiment, the Zn-Al alloy is added
in the form of a wire. However, the form of the Zn-Al alloy is not necessarily limited
to the wire, and forms of chips, powder, and the like can be employed instead of the
wire form. In the case of the chip or powder form, a quantitative delivery device such
as a granular material may be used to supply it from the supply portion of the insertion
guide having the pipe shape.
[0031]
In addition, although the Zn-Al alloy is added in the above-described
embodiment, other alloys such as a Zn-Al-Mg alloy can be applied as long as they are
dissolved in the molten zinc bath.
[0032]
In addition, although the Zn-Al alloy is supplied from the supply portion
provided at the lower portion^naf the insertion guide in the above-described
15
C--
- ^
embodiment, the position of the supply portion is not limited to the lower portion of
the insertion guide. For example, the dissolving start position of the Zn-Al alloy may
be set to the surrounding of the center portion of the insertion guide by controlling the
pressure of the inert gas, and a hole may be pierced in the side surface of the
surrounding of the center portion of the insertion guide to supply the Zn-Al alloy from
the hole into the molten zinc bath. In this case, the position (hole) at which the Zn-Al
alloy is injected may be at a position within ±400 mm from the lower end of the front
support roll.
[0033]
In addition, although the insertion guide having a linear pipe shape is used in
the above-described embodiment, the insertion guide may have a shape other than the
linear shape, for example, a shape with a curvature as long as the supply position
thereof can be set to a predetermined position.
[0034]
As described above, according to the present invention, Al can be uniformly
dispersed in the molten zinc bath. Therefore, even when the sheet is passed at a
higher speed than that of the related art, pressing flaws due to the rising of the bottom
dross are not generated, and insufficient alloying, excessive alloying, and the like due
to the non-uniformity of the concentration of Al do not occur.
[Industrial Applicability]
[0035]
According to the present invention, Al can be uniformly diffused in the molten
zinc bath. Therefore, the generation of bottom dross due to the non-uniformity of the
concentration of Al in the molten zinc pot is suppressed, and thus pressing flaws
caused by rising of the bottom dross are reduced even when the sheet-threading speed
- 16 -
- ^
is increased. Therefore, it is possible to achieve the enhancement in productivity.
[Description of Reference Numerals and Signs]
[0036]
1: MOLTEN ZINC POT
2: MOLTEN ZINC BATH
3: SINK ROLL
4: FRONT SUPPORT ROLL
5: BACK SUPPORT ROLL
6: ADDING APPARATUS (APPARATUS FOR SUPPLYING Zn-Al
ALLOY)
. 7: WIRE OF Zn-Al ALLOY
8: DRUM
9: MOTOR
10: GUIDE ROLLER
11: INSERTION GUIDE
12: HERMETIC SEAL BOX
13: VALVE
14: PRESSURE METER
15: Al CONCENTRATION METER
16, 17, 18: PARTICLE COUNTER
19: OPERATION FLOOR
20: INNER WALL
21: SUPPLY PORTION
C--
17

[Document Type] CLAIMS
1. A method of supplying a Zn-Al alloy to a molten zinc pot which
accommodates a molten zinc bath in a hot dip galvanizing line, the method comprising:
supplying the Zn-Al alloy from a supply portion provided at a lower portion
of an insertion guide having a pipe shape,
wherein the supply portion is immersed between an inner wall of the molten
zinc pot on a downstream side in a fravelling direction of a steel sheet and a front
support roll installed in the molten zinc bath at a depth within ±400 mm from a lower
end of the front support roll, and
an inside of the insertion guide is pressurized by inert gas to prevent the
molten zinc bath from advancing to the inside of the insertion guide.
2. The method of supplying a Zn-Al alloy to a molten zinc pot according to
claim 1,
wherein the Zn-Al alloy has a form of any one of a wire, a chip, and powder.
3. The method of supplying a Zn-Al alloy to a molten zinc pot according to
claim 1,
wherein the supply portion of the insertion guide is installed in a discharge
flow which is generated between the front support roll in the mohen zinc bath and the
steel sheet which travels.
4. A method of adjusting a concentration of Al in a molten zinc bath, the method
comprising:
controlling an amount of the Zn-Al alloy supplied according to the method of
- 18 -
c
supplying a Zn-Al alloy to a molten zinc pot according to any one of claims 1 to 3
dependmg on the concentration of Al measured by an Al concentration meter installed
in the molten zinc pot.
5. An apparatus for supplying a Zn-Al alloy to a molten zinc pot which
accommodates a molten zinc bath in which a front support roll is immersed in a hot dip
galvanizing line, the apparatus comprising:
an insertion guide having a pipe shape, which has a supply portion at a lower
portion and is installed between an inner wall of the molten zinc pot on a downstream
side in a travelling direction of a steel sheet and the front support roll installed in the
molten zinc bath; and
a gas supply device which supplies inert gas into the insertion guide,
wherein an installation position of the supply portion is in the molten zinc
bath and at a depth within ±400 mm from a lower end of the front support roll, and
the Zn-Al alloy is supplied to the molten zinc bath from the supply portion of
the insertion guide.