Note: Descriptions are shown in the official language in which they were submitted.
NSC,ONA--8569
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PROCESS FOR PRODUCING SPRAY-PLATED METAL STRIP
~ACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for
producing a spray-plated metal strip, sheet, or plate by
5 spraying a molten metal on a metal strip.
2. Description of the Related Art
In a spray-plating process , i . e ., a plating of
a metal strip by spraying a molten metal thereon, the
sprayed strip is necess~rily subjected to a smoothing
10 treatment of the sprayed metal layer , to obtain a smooth
surface of a plated metal strip.
Japanese T~n~Y~m~n~l Patent Publication tKokai)
No. 1-201456 published on August 14, 1989 discloses a
process, which comprises cleaning a steel sheet surface,
15 spraying the thus cleaned sheet with a molten metal
atomized by a pressurized gas, and then blowing the
sheet with a pressurized gas by a gas wiping nozzle.
such a gas-wiping conditioning treatment of
the sprayed sheet surface, however, cannot provide a
20 well smoothed surface of a plated strip in comparison
with those obtained by other plating processes such as
electroplating, hot dipping, etc.
SUI~ARY OF THE INVENTION
The object of the present invention is to provide a
25 process for producing a spray-plated metal strip, which
provides a plated strip surface as smooth as a
dip-plated strip surface.
To achieve the above object according to the
present invention, there is provided a process for
30 producing a spray-plated metal strip by spraying molten
metal on a metal strip, which comprises:
spraying, on a metal strip, molten metal particles
having a weight average particle diameter of not more
than 15 times the thickness of a plated layer to be
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formed on the strip.
The term "weight average particle diameter~ as
herein used is defined as follows.
Assuming a non-globular molten metal particle of a
5 volume Vp, a globe of the equivalent volume should have
a diameter, d, which can be calculated from
Vp = (47r/3) x (d/2)3
The diameter "d" is referred to as "equivalent
globe diameter". The weight average particle diameter,
10 dm, is obtained by
d=dm
) d- 0 ( P )
where N: total weigh of particles, in kg,
Vp: volume of a particle having a diameter of d in
terms of the equivalent globe diameter, in m3,
p: specific gravity of a particle, in kg/m3, and
Nd: number of particles having a diameter of d in
terms of the equivalent globe diameter.
Thus, the weight average particle diameter, dm,
ref ers to a particle diameter in terms of the equivalent
globe diameter which satisfies the above equation, i.e.,
a summation of the weight of particles having a diameter
of dm or less amounts to 5096 of the total weight M of
particles having a distribution in diameter.
The term "metal strip ~ as herein ref erred to
includes strips, sheets, and plates of metallic
materials, such as steel, copper, copper alloys,
aluminum, aluminum alloys, etc.
BRIEF DESCRIPTION OF THE DRAwII~1GS
Figure l is a sectional view showing the deposition
of a molten metal particle on a substrate;
Fig. 2 is a graph showing a p~rcentage of
non-plated area as a function of the ratio of the weight
3 average particle diameter of a spray-plating molten
metal particle to the thickness of a plated layer;
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Pig . 3 is a graph showing the deposition ef f iciency
of sprayed molten metal as a function of the molten
metal spraying condition;
Fig. 4 schematically illustrates an arrangement for
5 carrying out a process according to the present
invention;
Fig. 5 is a graph showing the interrelationship
between the weight deposit, the number of effective
nozzle stages, and the speed of metal strip conveying
1 0 line;
Fig . 6 is a graph showing the interrelat ~ ~n.ch i ~
between the heating temperature, the heating time, and
the smoothness of a plated layer; and
Fig. 7 is a graph showing the weight loss by
15 corrosion of a spray-plated steel sheet according to the
present invention in comparison with the conventional
hot-dip plated steel sheet.
DESCRIPTION OF THE PREFERRED EMBODINENTS
The present inventive process uses a spray of
2 molten metal particles having a weight average particle
diameter of not more than 15 times the thickness of a
plated layer to be f ormed on a metal strip . Figure
shows that the molten metal particle of size larger than
the plated layer thickness can be used in the present
25 invention, because the molten metal particle size does
not directly correspond to the plated layer thickness
due to wetting between the molten metal and the
substrate metal strip.
The molten metal particle must have a weight
30 average particle diameter of not more than 15 times the
plated layer thickness for the following reason.
Figure 2 shows the percentage of a non-plated area
as a function of the ratio of the weight average
particle diameter (d ~m) of a sprayed molten metal to
35 the target thickness (t ~m) of a plated layer. Nhen the
ratio (d/t) is greater than 15, a significant non-plated
area unavoidably remains after the heating of a sprayed
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strip, even if the heating conditions are varied.
A greater particle size also requires a longer time
for the smoothing treatment, a larger heating furnace,
and increased equipment cost.
In a preferred ~mhQ~ir t of the present invention,
the deposition efficiency of the sprayed molten metal on
the strip surface is ensured to be 90% or more by using
the distance "L" from a spraying apparatus to a strip to
be sprayed in the range def ined by the f ollowing
1 0 f ormula:
L < (1.75/~) x (PdV2/c~)~
where L: distance between spraying means and metal
strip to be sprayed in m,
0: flare angle of molten metal spray in rad,
1 5 P: specific gravity of molten metal spray in
kgf /m3,
d: weight average particle diameter of molten
metal spray in m,
v: maximum speed of molten metal spray in m/sec,
2 0 and
~: surface tension of molten metal spray in kgf/m.
It is generally known that the distance (L) between
a spray apparatus and a metal strip to be sprayed is
expressed as:
L = (k/C) x (~dV2/c~)~
Figure 3 shows the deposition efficiency as a
function of the parameter ' k~ . It is seen from Fig. 3
that, to obtain a deposition efficiency of 90% or more,
the k-value should be less than 1.75, i.e., k<l.75, and
in turn, the distance "L" should be in the range as
defined by the above-stated inequality formula.
In a pref erred embodiment of the present invention,
the spraying Qf a molten metal is carried out in
separate spraying steps by directing a metal strip
through separate spraying means. ~his enables the
plated thickness to be controlled in a wide range with
respect to the strip conveying speed while ensuring an
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improved smoothness of a spray-plated strip surface.
The present inventive process preferably further
comprises heating and holding a metal strip, which has
been sprayed with a molten metal, at a temperature of T
5 and for a time of S defined by the following formula, to
provide a smoother surface of a metal strip;
S > 0 . 095 x ( 0 . 5+d/200 ) / ( T/Tm)
where T>Tm,
S: holding time in second,
d: weight average particle diameter in /~m,
T: holding temperature in C, and
Tm: melting point of spraying metal in C.
The heating and holding of a sprayed strip at the
spe~ f ~ e-l temperature and for the specified time
15 promotes wetting between the deposit metal and the
substrate strip and further improves the smoothness of a
spray-plated metal strip product.
When a strip of steel or iron alloy is sprayed
according to the present invention, the strip is
20 preferably electroplated with a precoating metal such as
nickel before belng sprayed, to further improve the
smoothness of a spray-plated metal strip product.
EXANPhE
Figure ~ shows an arrangement in which a steel
25 sheet was plated with zinc by a process according to the
present invention.
A continuous plating arrangement 1 is disposed on
the outlet side of a not-shown continuous ~nn~l in~
furnace. A steel sheet "S', which was being conveyed in
30 the direction denoted by an arrow, was annealed in a
not-shown continuous ~nn~7 ing furnace, had a
temperature of 450C when passing a deflector roll 2,
and was directed through a plating chamber in which
spray nozzles 3 are arranged in two stages along the
35 conveying direction and sprayed a molten metal on the
steel sheet "S ~ being conveyed. The molten metal spray
had a particle size of 25 l~m in tenns o~ the weight
. . , . ~
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average particle diameter. Thls particle size was
obtained by gas-atomizing with a non-~Y~ n~ gas such
as nitrogen, argon, etc. In a heating furnace 4
arranged in continuation with the plating chamber, the
steel sheet "S" was heated by a heater element which can
heat the sheet without being in contact therewith.
Electrical heaters, high frequency heaters, radiant tube
heaters or other non-contact type heaters may be used
for this purpose. The heating atmosphere may be either
1 o oxidizing or non-~Yi ~ i 7 i n~ .
The spray nozzles 3 had a maximum spray amount of
160 g/sec/m(width) and a controllable range of from 160
to 80 g/sec/m(width).
An annealed steel sheet having a temperature of
450C was sprayed with zinc-0.2wt~ aluminum in the plating
chamber provided with two stages of spray nozzles 3
having a spray amount of 160 g/sec/m(width) per stage.
The temperature of the molten zinc spray was 460C. The
thus sprayed steel sheet was heated at 450C for 0.5 sec
by being held in an atmosphere of 10096 nitrogen gas held
at 450C.
To obtain a deposition efficiency of 9096 or more,
the spraying distance ~'L~ or the distance between the
spray nozzles 3 and the steel sheet "S" was det~rminpd
with respect to the particle size, the lnitial speed,
and the flare angle of the molten metal spray, as
expressed by the following relationship:
L ~ ~1.75/5) x (PdV2/~)~
where the symbols have the same meanings as herein
previously defined.
A spray-plating test of a steel sheet was carried
out by using an arrangement provided with seven stages
of spray nozzles.
Figure 5 shows the interrelationship between the
number of nozzle stages actually used, thc weight
deposit on the sheet surface per unit area of one sheet
side, and the speed of a steel sheet conveying line.
.. .. . , . _, ,, . , ,,, , . , , . _ _ _ _ _ . . _ _ _ _ . .
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The abscissa represents the line speed in m/min, the
lef t ordinate the weight deposit, and the right ordinate
the total spray amount from the spray nozzles. It is
seen from Fig. 5 that the more the nozzle stages used,
the wider the controllable ranges of both the weight
deposit and the line speed. When the spray amount per
stage is Lncreased, the total number of no2zle stages
can be reduced, but the uncontrollable range denoted by
"A" becomes wider. When the spray amount per stage is
too small, the number of nozzle stages should be
increased and the equipment cost is raised. It is,
then, important that the number of nozzle stages be
reasonably determined in accordance with the line speed
and the maximum weight deposit for specific cases.
Figure 6 shows the interrelationship between the
residence time "S" in the heating furnace 4, a parameter
"X ' as defined below, and the surface smoothness of a
spray-plated metal strip product.
X = ( 0 . 5 + d/200 ) / (T/Tm)
where T~Tm,
d: weight average particle diameter in ~m,
T: holding temperature in C, and
Tm: melting point of spray metal in C.
In Fig. 6, the blank circles, the solid circles,
and the ~X"-marks mean that the surface of a
spray-plated steel sheet product is perfectly smooth,
has few defects, and is significantly defective,
respectively. The perfect smoothness region of "A" can
be defined by a line S=0 . 095X and the residence time 5 -
required ior obtaininq a good smoothness should be in
the range specif Led as:
S~ 0.095 x (0.5 + d/200)/(T/Tm)
A spray-plated steel sheet was produced by using
two stages of spray nozzles at a weight deposit zinc of
80 g/mZ per one sheet side, under the same condition as
mentioned above. The product sheet was subjected to a
salt water spray test to estimate the corrosion
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resistance of the steel ~heet.
For, , ~r~ ~on, ~ conventional hot-dip plated steel
sheet was also tested under the same testing condLtion.
~he hot-dipping was carried out under the condition of a
zinc plating bath temperature of 450C, a pre-dip steel
sheet temperature of 453C, a zinc plating bath
composition of 99.8wt~ zinc and 0.2wt% aluminum.
Figure 7 shows the plots of the thus obtained
results in terms of the weight loss by corrosion as a
function of the duration of salt water spray. The
result proves that the present inventive spray-plated
steel sheet has a good corrosion resistance comparable
with that of the conventional hot-dlp plated steel
sheet .
To sun~narize the advantages of the present
Lnventive process:
( l ) It produces a spray-plated metal strip having
a good surface smoothness comparable with that obtained
by the conventional hot-dip process;
(2) It makes it possible to accelerate the
spray-plating process;
( 3 ) Either both sides or one side of a metal strip
can be plated; and
(4) Different metals can be plated on either sides
of a metal strip.
