U.S. patent application number 15/781306 was filed with the patent office on 2018-12-20 for method for coating steel plate with metal and metal-coated steel plate manufactured using same.
The applicant listed for this patent is POSCO. Invention is credited to Chang-Se BYEON, Ki-Cheol KANG, Yeon-Ho KIM, Yon-Kyun SONG.
Application Number | 20180363147 15/781306 |
Document ID | / |
Family ID | 59057208 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180363147 |
Kind Code |
A1 |
KIM; Yeon-Ho ; et
al. |
December 20, 2018 |
METHOD FOR COATING STEEL PLATE WITH METAL AND METAL-COATED STEEL
PLATE MANUFACTURED USING SAME
Abstract
Provided are a method for coating a steel plate with a metal and
a metal-coated steel plate manufactured by the method. The method
includes: heating powder of a first metal at a temperature lower
than a softening temperature; heating a gas to a temperature of
200.degree. C. to 600.degree. C.; vacuum-ejecting the heated first
metal powder together with the heated gas to form a metal coating
layer; and forming a plating layer of a second metal on the metal
coating layer.
Inventors: |
KIM; Yeon-Ho; (Gwangyang-si,
KR) ; KANG; Ki-Cheol; (Gwangyang-si, KR) ;
BYEON; Chang-Se; (Gwangyang-si, KR) ; SONG;
Yon-Kyun; (Gwangyang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO |
Pohang-si |
|
KR |
|
|
Family ID: |
59057208 |
Appl. No.: |
15/781306 |
Filed: |
December 15, 2016 |
PCT Filed: |
December 15, 2016 |
PCT NO: |
PCT/KR2016/014689 |
371 Date: |
June 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 4/06 20130101; C25D
3/12 20130101; C25D 3/22 20130101; C25D 3/00 20130101; C23C 4/08
20130101; C23C 4/12 20130101; C23C 28/02 20130101; C23C 4/137
20160101; C23C 18/16 20130101 |
International
Class: |
C23C 28/02 20060101
C23C028/02; C23C 18/16 20060101 C23C018/16; C23C 4/08 20060101
C23C004/08; C23C 4/137 20060101 C23C004/137; C25D 3/12 20060101
C25D003/12; C25D 3/22 20060101 C25D003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2015 |
KR |
10-2015-0179426 |
Claims
1. A method for coating a steel plate with a metal, the method
comprising: heating a first metal powder to a temperature equal to,
or higher than, room temperature but lower than a softening
temperature; heating a gas to a temperature of 200.degree. C. to
600.degree. C.; vacuum-ejecting the first metal powder, having been
heated, together with the heated gas to form a porous first metal
coating layer; and forming a plating layer of a second metal in
gaps between powder particles of the first metal coating layer.
2. The method of claim 1, wherein the first metal comprises at
least one metal selected from the group consisting of copper (Cu),
aluminum (Al), zinc (Zn), iron (Fe), nickel (Ni), chromium (Cr),
molybdenum (Mo), titanium (Ti), cobalt (Co), manganese (Mn),
tungsten (W), zirconium (Zr), and tin (Sn).
3. The method of claim 1, wherein the first metal powder has an
average particle size of 1 .mu.m to 20 .mu.m.
4. The method of claim 1, wherein the gas comprises at least one
gas having a density equal to, or lower than the density of air
which is selected from the group consisting of nitrogen (N.sub.2),
helium (He), and air.
5. The method of claim 1, wherein the vacuum-ejecting is performed
at a pressure of 0.01 Torr to 20 Torr.
6. The method of claim 1, wherein the vacuum-ejecting is performed
at a temperature of 10.degree. C. to 200.degree. C.
7. The method of claim 1, wherein the second metal comprises at
least one metal selected from the group consisting of zinc (Zn),
nickel (Ni), tin (Sn), copper (Cu), and chromium (Cr).
8. The method of claim 1, wherein the forming of the plating layer
of the second metal is performed by an electroplating method or an
electroless plating method.
9. The method of claim 1, further comprising polishing the plating
layer of the second metal.
10. The method of claim 1, further comprising performing a heat
treatment process at a temperature of 200.degree. C. to
1000.degree. C. after the forming of the plating layer of the
second metal.
11. A metal-coated steel plate manufactured by the method of claim
1.
12. A metal-coated steel plate comprising: a steel plate; a porous
first metal coating layer formed on at least one surface of the
steel plate using a first metal powder; and a plating layer of a
second metal formed in gaps between particles of the first metal
powder of the first metal coating layer.
13. The metal-coated steel plate of claim 12, wherein the second
metal plating layer is formed on a surface region of the first
metal coating layer and in pores of the first metal coating
layer.
14. The metal-coated steel plate of claim 12, wherein an anchoring
layer is formed on an interface between the steel plate and the
first metal coating layer.
15. The metal-coated steel plate of claim 12, wherein the first
metal comprises at least one metal selected from the group
consisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe),
nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt
(Co), manganese (Mn), tungsten (W), zirconium (Zr), and tin
(Sn).
16. The metal-coated steel plate of claim 12, wherein the first
metal powder has an average particle size of 1 .mu.m to 20
.mu.m.
17. The metal-coated steel plate of claim 12, wherein the second
metal comprises at least one metal selected from the group
consisting of zinc (Zn), nickel (Ni), tin (Sn), copper (Cu), and
chromium (Cr).
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method for coating a
steel plate with a metal and a metal-coated steel plate
manufactured by the method, and more particularly, to a method of
forming a pore-free coating layer by forming a porous coating layer
through a vacuum ejection coating process and then forming a
plating layer, and a steel plate on which the pore-free coating
layer is formed.
BACKGROUND ART
[0002] A method of coating with particles may be used as a surface
treatment method for coating various materials with various powder
materials, and an ejection velocity is guaranteed by a gas pressure
difference between a powder carrier gas and a coating portion
normally having a boundary at a nozzle. Particle coating refers to
coating with particles, and since particle coating is performed as
particles having a size of several tens to several hundreds of
nanometers (nm) collide with a coating target material, a coating
layer is formed at a much higher rate than in physical vapor
deposition (PVD), chemical vapor deposition (CVD), or the like in
which coating is performed on an atomic or molecular basis. In
addition, the chemical composition of a raw material powder is not
changed during the particle coating.
[0003] Examples of particle coating include a spraying method (such
as a thermal spraying method or a cold spraying method) and a
vacuum ejection method which are generally useful for coating with
solid particles of metals, alloys, cermet, or the like, and in
these methods, temperature and ejection velocity are key
factors.
[0004] In the vacuum ejection method, a coating unit is maintained
in a vacuum state (a low-pressure state) to create a pressure
difference. That is, a coating target member is provided in a
vacuum body, and coating is performed by ejecting powder onto the
coating target member in a state in which the powder is carried by
a carrier gas. This method does not require that the carrier gas
has a high pressure, thereby consuming a smaller amount of gas than
the spraying method and enabling room-temperature coating because
it is not necessary to heat gas to a high pressure.
[0005] The possibility of mass production (coating efficiency) and
economical aspects (the amount of gas consumption) are considered
to apply such particle coating methods to the steel industry, for
example, for steel plate surface treatment. In this regard,
although the vacuum ejection method is economical because of a low
amount of gas consumption, the vacuum ejection method results in
low coating efficiency (stacking amount/total ejection amount) and
is usable for limited coating materials because of a coating
temperature substantially close to room temperature and a lower
powder particle ejection velocity than that of the spraying method
(such as a thermal spraying method or a cold spraying method).
[0006] As disclosed in Korean Patent Application No. 2008-0076019,
the vacuum ejection method is generally used for coating with a
brittle material such as a ceramic material which is pulverized
into powder and recombined during coating and is not suitable for
coating with a ductile material such as a metal requiring a large
amount of energy for plastic deformation.
[0007] In addition, although a particle coating method using the
spraying method (such as a thermal spraying method or a cold
spraying method) has high efficiency in terms of metal powder,
since a body in which a coating target member is provided is
maintained at atmospheric pressure, high-pressure gas having a
pressure of several megapascals (MPa) is used as a powder carrier
gas to create a large pressure difference from atmospheric
pressure, thereby resulting in a large amount of gas consumption.
In addition, expensive low-density gas such as He or N.sub.2 is
commonly used to ensure a particle velocity for high-speed
collisions with a coating target member maintained at atmospheric
pressure. That is, the spraying method is generally used for
coating a small area and requires particles having a size of
several tens of micrometers (.mu.m) for high-speed ejection due to
air resistance at atmospheric pressure. Furthermore, according to
the spraying method, it is necessary to form a thick coating layer
having a thickness within the range of several tens to several
hundreds of micrometers (.mu.m) because of problems such as coating
layer defects and residual stress, and thus it is practically
difficult to form a dense thin coating layer having a thickness of
several micrometers (.mu.m) to several tens of micrometers (.mu.m)
by the spraying method. In general, according to such particle
coating methods for coating with metal powder, pores are formed in
a coating layer, and particularly, in the case of coating with a
thin film having a thickness of several micrometers (.mu.m) to
several tens of micrometers (.mu.m), corrosion factors permeate
through such pores, thereby lowering the corrosion resistance of
steel plates.
[0008] Therefore, if a coating method addressing the
above-described problems with the spraying method and the vacuum
coating method is provided for forming a metal coating layer having
maximized functionality, such as corrosion resistance on a steel
plate surface, the coating method will be widely used in related
fields.
DISCLOSURE
Technical Problem
[0009] An aspect of the present disclosure may provide a method for
coating a steel plate with a metal without pores.
[0010] An aspect of the present disclosure may also provide a
metal-coated steel plate having a pore-free coating layer
manufactured by the metal coating method.
Technical Solution
[0011] According to an aspect of the present disclosure, a method
for coating a steel plate with a metal may include: heating a first
metal powder to a temperature equal to, or higher than, room
temperature but lower than a softening temperature; heating a gas
to a temperature of 200.degree. C. to 600.degree. C.;
vacuum-ejecting the first metal powder, having been heated,
together with the heated gas to form a porous first metal coating
layer; and forming a plating layer of a second metal in gaps
between powder particles of the first metal coating layer.
[0012] The first metal may include at least one metal selected from
the group consisting of copper (Cu), aluminum (Al), zinc (Zn), iron
(Fe), nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti),
cobalt (Co), manganese (Mn), tungsten (W), zirconium (Zr), and tin
(Sn).
[0013] The first metal powder may have an average particle size of
1 .mu.m to 20 .mu.m.
[0014] The gas may include at least one gas having a density equal
to or lower than the density of air which is selected from the
group consisting of nitrogen (N.sub.2), helium (He), and air.
[0015] The vacuum-ejecting may be performed at a pressure of 0.01
Torr to 20 Torr.
[0016] The vacuum-ejecting may be performed at a temperature of
10.degree. C. to 200.degree. C.
[0017] The second metal may include at least one metal selected
from the group consisting of zinc (Zn), nickel (Ni), tin (Sn),
copper (Cu), and chromium (Cr).
[0018] The forming of the plating layer of the second metal may be
performed by an electroplating method or an electroless plating
method.
[0019] The method may further include polishing the plating layer
of the second metal.
[0020] The method may further include performing a heat treatment
process at a temperature of 200.degree. C. to 1000.degree. C. after
the forming of the plating layer of the second metal.
[0021] According to another aspect of the present disclosure, a
metal-coated steel plate may be manufactured by the method of the
aspect of the present disclosure.
[0022] According to another aspect of the present disclosure, a
metal-coated steel plate may include: a steel plate; a porous first
metal coating layer formed on at least one surface of the steel
plate using a first metal powder; and a plating layer of a second
metal formed in gaps between particles of the first metal powder of
the first metal coating layer.
[0023] The second metal plating layer may be formed on a surface
region of the first metal coating layer and in pores of the first
metal coating layer.
[0024] An anchoring layer may be formed on an interface between the
steel plate and the first metal coating layer.
[0025] The first metal may include at least one metal selected from
the group consisting of copper (Cu), aluminum (Al), zinc (Zn), iron
(Fe), nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti),
cobalt (Co), manganese (Mn), tungsten (W), zirconium (Zr), and tin
(Sn).
[0026] The first metal powder may have an average particle size of
1 .mu.m to 20 .mu.m.
[0027] The second metal may include at least one metal selected
from the group consisting of zinc (Zn), nickel (Ni), tin (Sn),
copper (Cu), and chromium (Cr).
Advantageous Effects
[0028] According to the present disclosure, since heated gas is
used, high-pressure gas for ejecting metal powder can be provided
without increasing the amount of gas consumption, and the
efficiency of coating may be increased using plastic deformation of
the metal powder heated to a temperature lower than a softening
point thereof. The metal-coated steel plate of the present
disclosure may have a coating layer not having pores owing to a
plating layer formed between metal powder particles, and thus the
corrosion resistance of the metal-coated steel plate may be
improved while guaranteeing functionality of the coating
powder.
DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a schematic view illustrating an example structure
of a coating layer formed according to the present disclosure.
[0030] FIG. 2 is a schematic view illustrating an example of an
ejection device usable for performing a coating method of the
present disclosure.
[0031] FIG. 3 is a schematic view illustrating another example of
an ejection device usable for performing the coating method of the
present disclosure.
BEST MODE
[0032] Exemplary embodiments of the present disclosure will now be
described in detail with reference to the accompanying drawings.
The disclosure may, however, be exemplified in many different forms
and should not be construed as being limited to the specific
embodiments set forth herein.
[0033] The present disclosure provides a coating technique for
maximizing the functionality of a metal coating layer by forming
the metal coating layer on a steel plate without pores using a
metal plating layer formed in the metal coating layer and/or
between surface metal powder particles of the metal coating layer,
and a steel plate surface-treated using the coating technique.
[0034] Steel plates to which a method for coating a steel plate
with a metal is applicable according to the present disclosure are
not particularly limited. However, the metal coating method of the
present disclosure may be applied to steel plates selected from the
group consisting of hot-rolled steel plates, cold-rolled steel
plates, cold-rolled annealed steel plates, galvanized steel plates,
zinc-based alloy plated steel plates, and aluminum-based plated
steel plates.
[0035] According to the present disclosure, the method for coating
a steel plate with a metal includes: heating a first metal powder
to a temperature equal to higher than room temperature but lower
than a softening point; heating a gas to a temperature of
200.degree. C. to 600.degree. C.; vacuum-ejecting the heated metal
powder together with the heated gas to form a porous first metal
coating layer; and forming a plating layer of a second metal in
gaps between powder particles of the first metal coating layer.
[0036] That is, in the metal coating method of the present
disclosure, a coating structure is formed by mixing a metal powder
and a gas heated to proper temperatures, and ejecting the metal
powder carried by the gas in a low-temperature, low-pressure
atmosphere. According to the present disclosure, since the first
metal powder is vacuum-ejected to the steel plate, an anchoring
layer 8 may be formed on an interface with the steel plate as shown
in FIG. 1.
[0037] Here, room temperature refers to a temperature ranging from
about 15.degree. C. to about 25.degree. C.
[0038] In addition, according to the present disclosure, since the
inside of a vacuum body 100 into which the powder carried by the
gas is ejected is maintained in a low-temperature, low-pressure
state, the gas may be ejected by a high pressure difference between
the carrier gas and a coating portion having a boundary at a nozzle
ejection hole without increasing the consumption of gas.
Furthermore, since the vacuum body 100 is maintained at a low
temperature, even in the case that the gas carrying the powder is
ejected, an increase in the internal pressure of the vacuum body
100 is prevented, and thus the powder may be stably ejected.
[0039] In the process of heating the powder of the first metal to a
temperature equal to or higher than room temperature but lower than
the softening point, the first metal may include at least one metal
selected from the group consisting of copper (Cu), aluminum (Al),
zinc (Zn), iron (Fe), nickel (Ni), chromium (Cr), molybdenum (Mo),
titanium (Ti), cobalt (Co), manganese (Mn), tungsten (W), zirconium
(Zr), and tin (Sn). However, the first metal is not limited
thereto. The first metal may be at least one of the listed metals,
an alloy of at least two of the listed metals, or an alloy
including at least one of the listed metals. For example, powder of
stainless steel may be used. Powder of an Fe-based metal such as
200 series, 300 series, or 400 series stainless steels may be used.
In addition, powder of a high-strength alloy may also be used.
Therefore, the softening point may vary according to the first
metal.
[0040] In addition, according to the present disclosure,
preferably, the first metal powder may have an aspect ratio
(long-axis length/short-axis length)) of less than 2.
[0041] For example, the temperature at which the process of heating
the first metal powder is performed may range from room temperature
to 900.degree. C. if the first metal powder is stainless steel
powder.
[0042] If the temperature at which the process of heating the first
metal powder is performed is lower than room temperature, plastic
deformation coating may not smoothly occur. However, this may be
overcome by additionally heating the carrier gas. If the
temperature at which the process of heating the first metal powder
is performed is higher than the softening point, and the first
metal powder has a high melting point, the steel plate may be
damaged, and manufacturing costs may increase.
[0043] The first metal powder may preferably have an average
particle size within the range of 1 .mu.m to 20 .mu.m, and more
preferably within the range of 1 .mu.m to 10 .mu.m. If the average
particle size of the first metal powder is less than 1 .mu.m,
manufacturing costs may increase because of high powdering costs.
Conversely, if the average particle size of the first metal powder
is greater than 20 .mu.m, it is difficult to form a dense powder
coating layer because the size of pores between particles of the
powder coating layer is large, and gas consumption increases
because impact energy necessary for coating the steel plate with
the first metal powder increases and thus it is necessary to use
the gas at a higher pressure.
[0044] In addition, the process of heating the gas is performed
separately from the process of heating the first metal powder, and
more particularly, the gas may preferably heated to a temperature
of 200.degree. C. to 600.degree. C. and more preferably, to a
temperature of 200.degree. to 500.degree. C. If the temperature is
less than 200.degree. C., a sufficient gas pressure is not
guaranteed. Conversely, if the temperature is greater than
600.degree. C., the steel plate may be damaged because the ejection
velocity of the powder may increase, or material bending and high
manufacturing costs may be caused because of a high
temperature.
[0045] Herein, the gas may have a density equal to or lower than
that of air, and the gas may be at least one selected from the
group consisting of nitrogen (N.sub.2), helium (He), and air.
However, the gas is not limited thereto. That is, although a
low-density gas such as nitrogen (N.sub.2) or helium (He) may be
used as the gas, dry air having relatively high density may also be
used as the gas by considering factors such as the consumption
amount or price of the gas.
[0046] A higher powder temperature may be effective in increasing
the efficiency of coating with metal powder by plastic deformation.
However, in the present disclosure, the metal powder is heated to
the above-mentioned temperature, and the metal powder is mixed with
the gas heated to a relative lower temperature and supplied at a
large flow rate. Then, the mixture is ejected, thereby maximizing
the plastic strain of the powder and realizing ejection at an
optimized velocity.
[0047] Thereafter, the porous first metal coating layer is formed
by vacuum-ejecting the heated metal powder together with the heated
gas.
[0048] With reference to FIGS. 2 and 3, the metal coating method of
the present disclosure will now be described in more detail
together with a device that may be used to perform the method.
[0049] For example, the present disclosure may be implemented using
a powder ejection device 1 in which a steel plate being a coating
target member 3 may be provided in the vacuum body 100, and the
powder may be ejected together with the heated high-pressure gas
carrying the powder onto the coating target member 3 using a
heating ejection unit 200 such that the powder may be stacked on
the coating target member 3 while undergoing plastic
deformation.
[0050] The coating target member 3 is mounted on a member transfer
device 3a in the vacuum body 100 so as to be coated. Thereafter,
the gas is provided by a gas supply unit 220 and is heated by a gas
heating unit 230, and the powder is provided by a powder supply
unit 210 and heated by a powder heating unit 240. Then, the powder
and the gas heated to high pressure are provided to a nozzle unit
250 and are ejected at a high velocity into the vacuum body 100
maintained at a vacuum state, and thus the powder may form a
coating layer while being plastically deformed and stacked on the
coating target member 3 provided in the vacuum body 100.
[0051] That is, according to the present disclosure, the gas and
the powder are individually heated before being ejected, and thus
existing vacuum ejection methods in which a high-pressure gas is
provided by increasing the flow rate of the gas and is then ejected
may be improved so as to provide a high-pressure gas for high-speed
ejection of powder without increasing the amount of gas
consumption. In addition, the metal powder used as a coating
material is heated to a particular temperature or higher according
to the kind of the metal powder, so as to increase the plastic
strain of the metal powder and thus to facilitate stacking of the
metal powder when the metal powder collides with the steel
plate.
[0052] For example, the powder heating unit 240 may be provided to
the powder supply unit 210 for heating the powder. The powder is
heated to facilitate plastic deformation of the powder, and the
powder heating unit 240 may be controlled to have an operating
temperature higher than that of the gas heating unit 230 so as to
improve coating efficiency. That is, the powder heating unit 240
may be provided separately from the gas heating unit 230 to
separately heat the gas and the powder and thus to obtain a powder
temperature higher than a gas temperature. In addition, the powder
heating unit 240 may also include a sensor S for temperature
measurement, and the sensor S may be connected to a control unit C
for heating temperature control.
[0053] To form a vacuum, the vacuum body 100 may include a chamber
unit 110 in which the steel plate 3 is provided, and a vacuum unit
130 provided at the chamber unit 110.
[0054] Here, the chamber unit 110 may be hermetically sealed to
maintain a vacuum formed by the vacuum unit 130. The transfer
device 3a on which the steel plate 3 is provided may also be
provided in the chamber unit 110.
[0055] Furthermore, in the present disclosure, the vacuum ejection
may preferably be performed at a pressure of 0.01 Torr to 20 Torr,
and more preferably at a pressure of 0.1 Torr to 15 Torr.
[0056] If the vacuum ejection is performed at a pressure less than
0.01 Torr, manufacturing costs increase to form a high-degree
vacuum, and if the vacuum ejection is performed at a pressure
greater than 20 Torr, a sufficient powder ejection velocity may not
be obtained because of an increase in the pressure of a vacuum
chamber.
[0057] For example, as illustrated in FIGS. 2 and 3, the vacuum
unit 130 may have a function of forming a vacuum in the chamber
unit 110, and to this end, the vacuum unit 130 may include a vacuum
pump 131, a powder filter 132, and a cooler 133. That is, the
vacuum unit 130 may have a function of maintaining the inside of
the chamber unit 110 in a low-degree vacuum state ranging from 0.01
Torr to 20 Torr.
[0058] The vacuum body 100 may further include a cooling unit 120
to enable high-speed ejection by increasing a temperature
difference between the vacuum body 100 and the heating ejection
unit 200 to create a higher pressure difference.
[0059] That is, preferably, the vacuum ejection may be performed at
a temperature of 10.degree. C. to 200.degree. C., and more
preferably at a temperature of 25.degree. C. to 100.degree. C. If
the vacuum ejection is performed at a temperature less than
10.degree. C., costs for maintaining the temperature increases, and
if the vacuum ejection is performed at a temperature greater than
200.degree. C., a sufficient pressure difference may not be
obtained because of an increase in the pressure of the vacuum
chamber.
[0060] That is, the cooling unit 120 may maintain the entire
internal area of the chamber unit 110 at a low temperature, thereby
increasing the pressure difference between the inside of the
chamber unit 110 and supplied gas for powder ejection at a higher
velocity, and maintaining stable powder ejection by preventing an
increase in the internal pressure of the chamber unit 110 even when
the heating ejection unit 200 (described later)) ejects the gas and
powder.
[0061] Therefore, according to the present disclosure, the vacuum
body 100 of the powder ejection device 1 may include the chamber
unit 110 and the cooling unit 120 provided on the chamber unit 110
to maintain the inside of the chamber unit 110 at a low
temperature. The cooling unit 120 may surround outer surfaces of
the chamber unit 110 in a dual structure as shown in the powder
ejection device 1 shown in FIG. 2 to cool the entire surface of the
chamber unit 110, or may be provided as a cooling coil or cooling
fins as shown in an ejection device 1, shown in FIG. 3.
[0062] As the gas and the first metal powder are heated and ejected
into the vacuum body 100 at a higher velocity, the steel plate 3
being a coating target member provided inside the vacuum body 100
may be coated with the first metal powder undergoing plastic
deformation. To this end, the heating ejection unit 200 may include
the powder supply unit 210, the gas supply unit 220, the gas
heating unit 230, the powder heating unit 240, the nozzle unit 250,
etc.
[0063] The powder supply unit 210 supplies the powder to be ejected
for coating the steel plate 3, and the powder may be heated by the
powder heating unit 240 and then may be supplied. In addition, the
powder supply unit 210 may adjust the supply amount of the powder
and may receive some gas from a connection tube 223a connected to a
gas distributor 223 of the gas supply unit 220 such that powder
stored in the powder supply unit 210 may float in the gas and may
receive driving force from the gas while the floating powder being
transferred.
[0064] In addition, the gas supply unit 220 supplies high-pressure
gas for ejecting the powder at a high velocity. That is, since the
powder is ejected into the vacuum body 100 in a state in which the
powder is carried by the high-pressure gas ejected into the vacuum
body 100, if the high-pressure gas is ejected at a high velocity,
the powder may also be ejected at a high velocity. In addition, for
high-speed ejection of the gas, the gas supply unit 220 may be
maintained in a high-pressure state, and in addition to this, the
gas may be provided in a high-temperature, high-pressure state
owing to heating by the gas heating unit 230. To this end, the gas
supply unit 220 may include a gas storage chamber 221, a gas
transfer tube 222, the gas distributor 223, a dehumidifier 224,
etc., and a sensor S for measuring temperature may be provided in
connection with the control unit C so as to control the temperature
of heating by the gas heating unit 230.
[0065] The temperatures and velocities of gas and powder are key
factors determining the velocity of ejection and may be properly
set according to the material of the metal powder. If the
temperature or velocity of the gas is excessively low, when the
metal powder collides with the steel plate, sufficient impact
energy for coating may not be obtained. Conversely, if the
temperature or velocity of the gas is excessively high, etching
rather than coating may occur, or the powder may not be stacked but
may bounce off the steel plate after collision with the steel
plate.
[0066] That is, proper impact energy is necessary for coating the
steel plate with the metal powder, and to this end, the temperature
and velocity conditions of the gas and the powder are key factors.
Under optimized conditions, high impact energy may induce metallic
bonding between interfaces of the steel plate and the metal coating
layer; an intermetallic layer may be formed of components of the
steel plate and the coating powder material; initial collision
particles may dig into the steel plate and form an anchoring layer
owing to high impact energy; or at least two or all of these
structures may be formed. In more detail, if impact energy is low,
the formation of an anchoring layer and stacking may occur even in
the case that metallic bonding or the formation of an intermetallic
layer does not occur. As impact energy increases, metallic bonding
occurs together with the formation of an anchoring layer, and an
intermetallic layer may be formed if the steel plate and the powder
have different components. In addition, if impact energy is low,
adhesion may be somewhat low. However, a heat treatment process
(described later) may be performed to induce metallic bonding which
guarantees adhesion.
[0067] As described above, owing to the metallic bonding, the
intermetallic layer, and the anchoring layer between the steel
plate and the first metal coating layer, strong adhesion may be
obtained between the steel plate and the first metal coating layer.
In addition, metallic bonding or an intermetallic layer involving
plastic deformation may be present even between particles of the
coating layer.
[0068] Through these processes, the metal powder may be ejected to
the steel plate to form the metal coating layer with high coating
efficiency. Although coating efficiency is high in this case, most
powder particles may participate in coating the steel plate while
colliding with the steel plate in a state in which the powder
particles maintain their shapes with slight deformation, and due to
this, pores may be formed in the coating layer, thereby causing
problems such as low corrosion resistance.
[0069] According to the present disclosure, preferably, the first
metal powder may have an aspect ratio (long-axis length/short-axis
length)) of less than 2.
[0070] Therefore, according to the present disclosure, the process
of forming the second metal plating layer is performed.
[0071] That is, according to the present disclosure, an additional
metal layer is formed between the metal powder particles by plating
a surface region, an inner region, or both regions of the metal
coating layer to provide a final pore-free coating layer, thereby
preventing permeation of corrosion factors and maximizing the
functionality of the coating material.
[0072] In this case, the second metal may include at least one
selected from the group consisting of zinc (Zn), nickel (Ni), tin
(Sn), copper (Cu), and chromium (Cr). However, the second metal is
not limited thereto. For example, the second metal may be one of
the listed metals, an alloy of at least two of the listed metals,
or an alloy including at least one of the listed metals.
[0073] In addition, the process of forming the plating layer may be
performed by an electroplating method or an electroless plating
method.
[0074] The is, the steel plate on which the metal coating layer is
formed may be plated with an additional plating layer by an
electroplating method or an electroless plating method to fill
pores between powder particles of the metal coating layer, thereby
removing pores of the metal coating layer.
[0075] FIG. 1 is a schematic view illustrating a structure in which
an additional metal layer is formed by plating gaps between metal
powder particles of a metal coating layer and a surface region of
the metal coating layer. In another example, a plating layer may be
formed mainly on pores between metal powder particles inside the
coating layer while suppressing the surface region of the coating
layer from being plated. In the latter case, an inhibitor may be
included in a plating solution, and the metal layer may
additionally only be formed in the pores of the metal coating
layer.
[0076] In this case, the inhibitor is not particularly limited. An
inhibitor generally used in an electroplating method or an
electroless plating method may be used as long as the inhibitor
optimizes characteristics of the metal coating layer determined by
the kind of metal and the size of powder of the metal coating layer
of the present disclosure. For example, a surfactant such as a
polyol-based or amine-based organic compound surfactant may be
used.
[0077] In addition, according to the present disclosure, a process
of polishing the second metal plating layer may be additionally
included.
[0078] If the polishing process is performed, pores in a surface
region may be minimized, and hair lines or metallic texture may be
imparted to the surface of the metal coating layer to improve
appearance. Owing to friction during the polishing process, surface
pores may be closed, and owing to metal texture such as hair lines
formed through the polishing process, the value of products may
also be improved.
[0079] In addition, in the coating method of the present
disclosure, a heat treatment process may be additionally performed
at a temperature of 200.degree. C. to 1000.degree. C., and it may
be more preferable that the heat treatment temperature be within
the range of 300.degree. C. to 850.degree. C.
[0080] The temperature of the additional heat treatment process may
be lower than the melting point of the metal or alloy of the metal
coating layer, and if the steel plate is a plated steel plate, the
heat treatment process may be performed at a low temperature for a
long period of time by considering the melting point of a plating
layer and the alloying temperature of the plating layer.
[0081] In addition, a heat treatment method such as a laser or
plasma heating method may be used to have heat treatment effects
only on the coating layer while minimizing the influence of heat on
the steel plate.
[0082] As described above, owing to the additional heat treatment
process, pores in the metal coating layer may be further minimized,
and adhesion may be secured between the steel plate and the metal
coating layer, between powder particles of the metal coating layer,
and between metal powder particles and the plating layer, thereby
improving workability together with corrosion resistance.
[0083] The reason for this is that sintering occurs at interfaces
during the additional heat treatment. In addition, although
dislocations occur in crystal grains due to plastic deformation of
powder particles during the coating process, the heat treatment
removes the dislocations, and crystal grains of the powder
particles recrystallize to a size less than the original average
size D50 of the powder particles. Thus, workability improves
compared to the case in which the metal coating layer is not heat
treated.
[0084] In this case, different metals may form intermetallic layers
at an interface between the metal power particles and at an
interface between the base steel plate and the metal coating
layer.
[0085] The additional heat treatment process may be performed
before or after the polishing process. That is, the order of the
processes is not limited.
[0086] The present disclosure provides a metal-coated steel plate
manufactured by the above-described method for coating a steel
plate of the present disclosure.
[0087] In more detail, the metal-coated steel plate of the present
disclosure includes: a steel plate; a porous first metal coating
layer formed on at least one surface of the steel plate using a
first metal powder; and a plating layer of a second metal formed in
gaps between metal powder particles of the first metal coating
layer.
[0088] Referring to FIG. 1, a metal-coated steel plate 2 includes:
a first metal coating layer 4 formed on a steel plate or a plated
steel plate 3 by ejecting a first metal powder onto the steel plate
3; and a second metal plating layer 6 formed in gaps between metal
powder particles 5 of the first metal coating layer 4. That is, the
metal-coated steel plate 2 has a pore-free coating layer 4a.
[0089] In this case, the second metal plating layer may be formed
in pores of the first metal coating layer and/or on a surface
region of the first metal coating layer. Therefore, a coating layer
free of pores is finally provided, thereby guaranteeing corrosion
resistance because corrosion factors are prevented from reaching
the steel plate, and maximizing the functionality of the metal of
the coating layer.
[0090] In addition, according to the present disclosure, the porous
first metal coating layer is formed through a vacuum ejection
process, and thus the size of crystal grains of the first metal
powder is less than the average size D50 of original powder
particles.
[0091] In addition, an intermetallic layer is present at interface
between the first metal powder particles and the second metal
plating layer formed between the first metal powder particles, and
metallic bonding, an anchoring layer 8, and an intermetallic layer
may be formed on an interface between the steel plate and the first
metal coating layer.
[0092] The first metal may include at least one metal selected from
the group consisting of copper (Cu), aluminum (Al), zinc (Zn), iron
(Fe), nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti),
cobalt (Co), manganese (Mn), tungsten (W), zirconium (Zr), and tin
(Sn). However, the first metal is not limited thereto. The first
metal may be at least one of the listed metals, an alloy of at
least two of the listed metals, or an alloy including at least one
of the listed metals. For example, powder of stainless steel may be
used. Powder of an Fe-based metal such as 200 series, 300 series,
or 400 series stainless steels may be used. In addition, powder of
a high-strength alloy may also be used. Therefore, the softening
point may vary according to the first metal.
[0093] The first metal powder may be powder of a single metal
having an average particle size preferably within the range of 1
.mu.m to 20 .mu.m, more preferably within the range of 3 .mu.m to
10 .mu.m, and even more preferably within the range of 5 .mu.m to
10 .mu.m. If the average particle size of the first metal powder is
less than 1 .mu.m, manufacturing costs may increase because of high
powdering costs. Conversely, if the average particle size of the
first metal powder is greater than 20 .mu.m, it is difficult to
form a dense powder coating layer because the size of pores between
particles of the powder coating layer is large, and gas consumption
increases because impact energy necessary for coating the steel
plate with the first metal powder increases and thus it is
necessary to use gas at a higher pressure.
[0094] In this case, the second metal may include at least one
selected from the group consisting of zinc (Zn), nickel (Ni), tin
(Sn), copper (Cu), and chromium (Cr). However, the second metal is
not limited thereto. For example, the second metal may be one of
the listed metals, an alloy of at least two of the listed metals,
or an alloy including at least one of the listed metals.
[0095] Hereinafter, the present disclosure will be described more
specifically through examples. The following examples are for
illustrative purposes only and are not intended to limit the scope
of the present invention.
MODE FOR INVENTION
Examples
[0096] 1. Experiment for Checking Temperature-Dependent Variations
in Coating Layer During Coating Process
[0097] A cold-rolled steel plate was used as a coating target
object to be coated, and stainless steel powder was used as a
coating material. The average particle size D50 of the powder was 5
.mu.m, and the particle size of the powder followed a normal
distribution within the range of 1 .mu.m to 10 .mu.m.
[0098] A coating experiment was performed using the coating device
shown in FIG. 2 by filling the powder supply unit 210 with the
powder and setting coating conditions as follows: an initial
pressure of the vacuum body 100 was set to 5.times.0.01 Torr, and a
gas pressure before ejection through a nozzle was set to 800 Torr.
At that time, dry air was used as gas, and the flow rate was set to
be 30 L/min at a powder transfer tube 211 and 200 L/min at the gas
transfer tube 222. In addition, a cylinder nozzle having a throat
size of 0.8 mm.times.100 mm was used as the nozzle unit 250 in such
a manner that the nozzle unit 250 was fixed at a distance of 10 mm
away from the coating target material, and coating was performed
while moving the coating target material left and right twice at a
velocity of 10 mm/sec.
[0099] The powder heating unit 240 and the gas heating unit 230
were operated to adjust the temperatures of the powder transfer
tube 211 and the gas transfer tube 222 to values shown in Table 1
below during the coating experiment.
[0100] The thickness of a coating layer of the cold-rolled steel
plate being a coating target member was measured by cross-sectional
element analysis of chromium (Cr) using a scanning electron
microscope (SEM), and average values of the measured values are
shown in Table 1 below according to coating conditions.
TABLE-US-00001 TABLE 1 Temperature of Temperature of Thickness of
powder transfer gas transfer coating layer No tube (.degree. C.)
tube (.degree. C.) (.mu.m) Comparative Room temperature Room
temperature less than 0.2 Example 1 coating Comparative Room
temperature 150 2.5 Example 2 Example 1 Room temperature 200 10
Example 2 Room temperature 600 29 Example 3 300 600 34 Example 4
600 600 53 Example 5 800 600 86
[0101] As shown in Table 1 above, coating scarcely occurred in
Comparative Example 1 performed under room temperature conditions,
and the thickness of a coating layer increased as the temperature
of the gas increased as shown in Comparative Example 2 (the size of
particles followed a normal distribution within the range of 1
.mu.m to 10 .mu.m), Example 1, and Example 2. However, in
Comparative Example 2, a structure not having pores was obtained
with low coating efficiency, and thus Comparative Example 2 is not
useful. In Examples 1 to 5, pores were formed.
[0102] The reason for these results is that the pressure of the gas
increases as the temperature of the gas increases, and the ejection
velocity of powder increases as the pressure difference between the
high-pressure gas and the inside of the vacuum body 100
increases.
[0103] In addition, it could be understood that the thickness of
the coating layer increased owing to heating of the powder.
Therefore, the plastic strain of the metal powder could be
maximized by heating the metal powder, and thus the efficiency of
coating could be markedly increased when compared to Comparative
Example 1.
[0104] 2. Experiment for Checking Properties of Coating Layer
According to Coating Processes
[0105] The same base steel plate and coating conditions as those
used in Experiment 1 were used. In detail, the same temperature
conditions as those in Example 4 shown in Table were used, but
samples were prepared by setting the average particle size of
powder to be 5 .mu.m and the coating thickness to be about 25
.mu.m.
[0106] The samples prepared in this manner were additionally
subjected to processes such as an electroplating process, a heat
treatment process, or a polishing process as shown in Table 2
below, and when a plurality of subsequent processes were performed,
the processes were performed in the order of an electroplating
process, a heat treatment process, and a polishing process.
[0107] The electroplating process was performed to plate a metal
powder coating layer with nickel (Ni) using a plating solution to
which an inhibitor was added in a very small amount under the
conditions of a current density of 20 A/dm.sup.2, a plating
solution temperature of 50.degree. C., and a plating weight of 2
g/m.sup.2.
[0108] The heat treatment process was performed at 850.degree. C.
for 5 minutes under a reducing atmosphere, and the polishing
process was performed using general sand paper until a surface
region was removed by about 2 .mu.m to 5 .mu.m.
[0109] The corrosion resistance and workability of the samples
prepared as described above were measured, and results thereof are
shown in Table 2 below.
[0110] Corrosion resistance was measured through a salt spray test
by measuring the time taken until an area of red rust reached 5% of
the total area, 75 mm.times.150 mm, of each sample.
[0111] Workability was measured through a bending test by checking
the formation of cracks in a portion bent to 90.degree. C. with a
radius of curvature of 3 mm by using an optical microscope. In
Table 2 below, "X" denotes that cracking occurred, and "O" denotes
that cracking did not occur.
TABLE-US-00002 TABLE 2 Salt spray test (red rust 5% Electro- Heat
occurrence Bending No plating treatment Polishing time) test
Comparative not not not less than 24 x Example 3 performed
performed performed hours Comparative not performed not 24 to 48
.smallcircle. Example 4 performed performed hours Comparative not
not performed 96 to 120 x Example 5 performed performed hours
Comparative not performed performed 96 to 120 .smallcircle. Example
6 performed hours Example 6 performed not not 120 to 168 x
performed performed hours Example 7 performed performed not 240
hours or .smallcircle. performed longer Example 8 performed not
performed 240 hours or x performed longer Example 9 performed
performed performed 240 hours or .smallcircle. longer
[0112] In the case of Comparative Examples 3 to 6 having pores in
metal coating layers, corrosion resistance could be increased to
some degree through the heat treatment process or polishing process
even in the case that the metal coating layers did not include a
metal in addition to the metal powder. However, the corrosion
resistance and functionality of the STS powder coating layer were
not sufficient.
[0113] In addition, as shown in Example 6, the functionality of the
coating layer was more effectively shown when an additional metal
is included between coating powder particles, and as shown in
Examples 7 to 9, the characteristics of the coating layer could be
further improved by additionally performing heat treatment and
polishing.
[0114] While exemplary embodiments have been shown and described
above, the scope of the present disclosure is not limited thereto,
and it will be apparent to those skilled in the art that
modifications and variations could be made without departing from
the scope of the present invention as defined by the appended
claims.
TABLE-US-00003 [Reference numerals] 1: POWDER EJECTION DEVICE 2:
METAL-COATED STEEL PLATE 3: COATING TARGET MATERIAL (SUPPLY PIPE OR
PLATED STEEL PLATE) 4: METAL COATING LAYER 4A: PORE-FREE COATING
LAYER 5: FIRST METAL POWDER PARTICLES 6: SECOND METAL 7: PORES 8:
ANCHORING LAYER 100: VACUUM BODY 110: CHAMBER UNIT 120: COOLING
UNIT 130: VACUUM UNIT 131: VACUUM PUMP 132: POWDER FILTER 133:
COOLER 200: HEATING EJECTION UNIT 210: POWDER SUPPLY UNIT 211:
POWDER TRANSFER TUBE 220: GAS SUPPLY UNIT 221: GAS STORAGE CHAMBER
222: GAS TRANSFER TUBE 223: GAS DISTRIBUTOR 223A: CONNECTION TUBE
224: DEHUMIDIFIER 230: GAS HEATING UNIT 240: POWDER HEATING UNIT
250: NOZZLE UNIT
* * * * *