U.S. patent application number 14/665501 was filed with the patent office on 2015-07-16 for dual powder coating for aluminum heat exchangers.
The applicant listed for this patent is Carrier Corporation. Invention is credited to Mark R. Jaworowski, Michael F. Taras.
Application Number | 20150198389 14/665501 |
Document ID | / |
Family ID | 43796436 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150198389 |
Kind Code |
A1 |
Jaworowski; Mark R. ; et
al. |
July 16, 2015 |
DUAL POWDER COATING FOR ALUMINUM HEAT EXCHANGERS
Abstract
A method includes applying a first powder to an aluminum article
and heating the first powder to form a first layer on the aluminum
article providing mechanical strength, corrosion durability and
bonding potential. The method also includes applying a second
powder to the aluminum article and heating the second powder to
form a second layer on the aluminum article protecting the aluminum
article from ultraviolet radiation. A coated article includes an
aluminum substrate, an epoxy layer and a topcoat layer. The epoxy
layer promotes adhesion, enhances corrosion durability and provides
mechanical strength, and is formed by applying a first powder
containing an epoxy to the aluminum substrate and curing the first
powder. The topcoat layer provides resistance to ultraviolet
radiation and environmental contaminants, and is formed by applying
a second powder to the aluminum substrate and curing the second
powder.
Inventors: |
Jaworowski; Mark R.;
(Glastonbury, CT) ; Taras; Michael F.;
(Fayetteville, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carrier Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
43796436 |
Appl. No.: |
14/665501 |
Filed: |
March 23, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13498175 |
Mar 26, 2012 |
8993070 |
|
|
PCT/US2010/049034 |
Sep 16, 2010 |
|
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14665501 |
|
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61246281 |
Sep 28, 2009 |
|
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Current U.S.
Class: |
165/133 |
Current CPC
Class: |
B05D 2451/00 20130101;
F28F 19/04 20130101; B05D 7/542 20130101; B05D 2451/00 20130101;
B05D 7/546 20130101; B05D 3/102 20130101; Y10T 428/31522 20150401;
Y10T 428/2495 20150115; F28F 21/084 20130101; B05D 2202/25
20130101; B05D 2401/32 20130101; B05D 3/0254 20130101; B05D 2401/32
20130101 |
International
Class: |
F28F 19/04 20060101
F28F019/04 |
Claims
1-15. (canceled)
16. A coated heat exchanger comprising: an aluminum substrate
having first and second layers disposed thereon; wherein the first
layer is an epoxy layer having a thickness between about 15 microns
and about 35 microns for promoting adhesion, enhancing corrosion
durability and providing mechanical strength, formed by applying a
first powder containing an epoxy to the aluminum substrate and
curing the first powder; and the second layer is a topcoat layer
over the first layer, the second layer having thickness between
about 15 microns and about 35 microns for providing resistance to
ultraviolet radiation and environmental contaminants, formed by
applying a second powder to the aluminum substrate and curing the
second powder.
17. The coated heat exchanger of claim 16, wherein the epoxy layer
contains a constituent selected from the group consisting of
epoxies, polyester epoxies, acrylic epoxies and fusion-bond epoxy
powder coatings.
18. The coated heat exchanger of claim 16, wherein the topcoat
layer contains a constituent selected from the group consisting of
acrylics, polyester-based thermoplastic polyurethanes and polyester
triglycidyl isocyanurate.
19. (canceled)
20. The coated heat exchanger of claim 16, further comprising: a
conversion coat layer between the epoxy layer and the aluminum
substrate, formed by applying a conversion coating to the aluminum
substrate before applying the first powder to the aluminum
substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Divisional Application of patent application Ser.
No. 13/498,175, filed on Mar. 26, 2012, which is a national stage
of PCT/US2010/049034 filed Sep. 16, 2010, which claims priority of
U.S. Provisional Application No. 61/246,281, filed Sep. 28, 2009,
the disclosures of which are incorporated herein by reference in
their entireties.
BACKGROUND
[0002] In certain environments, aluminum articles are subjected to
contaminants that cause corrosion or other undesired effects on the
aluminum surface. Unprotected aluminum can become corroded by
acids, salts and other reactive compounds to develop pits or holes
on and through aluminum surfaces. Ultraviolet (UV) radiation can
cause discoloring of aluminum surfaces. Aluminum articles, such as
heat exchangers, are often coated to protect aluminum and aluminum
alloy surfaces. Such coatings provide resistance to corrosion
caused by environmental contaminants or ultraviolet (UV) radiation
or increase mechanical strength. These coatings can be applied to
aluminum surfaces in a number of ways. Coating methods include
electroplating, dip coating, spray coating and electrostatic powder
coating. Protective coatings include conversion coatings and paint
coatings.
[0003] Powder coating provides a less expensive way to coat
aluminum articles. Powder coatings do not require special baths or
large quantities of chemicals other than the powder coatings
themselves. Powder coatings do not require solvents which can
adversely impact air and water quality or can permanently damage
aluminum articles. Traditional powder coatings have drawbacks,
however. Prior to the present invention, powder coating
formulations were generally optimized for one function (i.e.
strength/bonding or UV resistance), but not both. Additionally, the
traditional application of powder coatings did not provide the
amount of control and uniformity that other coating processes
possessed. Uniform levels of powder coatings are difficult to
apply. In some cases, bare metal was left exposed following powder
coating. This bare metal did not possess any of the protective
characteristics that the powder coating provided. On the other
hand, in some locations, the powder coating was excessively thick,
which was detrimental for surface characteristics such as thermal
and hydraulic properties.
SUMMARY
[0004] A method according to the present invention includes
applying a first powder to an aluminum article and heating the
first powder to form a first layer on the aluminum article
providing mechanical strength, corrosion durability and bonding
potential. The method also includes applying a second powder to the
aluminum article and heating the second powder to form a second
layer on the aluminum article protecting the aluminum article from
ultraviolet radiation.
[0005] The present invention also provides a coated article having
an aluminum substrate, an epoxy layer and a topcoat layer. The
epoxy layer promotes adhesion, enhances corrosion durability and
provides mechanical strength, and is formed by applying a first
powder containing an epoxy to the aluminum substrate and curing the
first powder. The topcoat layer provides resistance to ultraviolet
radiation and environmental contaminants, and is formed by applying
a second powder to the aluminum substrate and curing the second
powder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a side sectional view of a powder coating system
for use on an aluminum article.
[0007] FIG. 2 is a side sectional view of a powder coating system
for use on an aluminum article having a conversion coating.
[0008] FIG. 3 is a flow chart illustrating a method for coating an
aluminum article.
[0009] FIG. 4 is a flow chart illustrating another method for
coating an aluminum article.
DETAILED DESCRIPTION
[0010] The present invention describes a dual powder coating system
which can provide improved bonding capabilities and improved
environmental protection for aluminum articles such as heat
exchangers. The dual powder coating system allows for the
application of two powder-based coatings to an aluminum article:
one to primarily enhance the mechanical strength, corrosion
durability and/or adhesive bonding characteristics of the aluminum
article and another one to primarily provide additional resistance
to UV radiation. The dual powder coating system can work with any
type of aluminum article and is particularly useful for aluminum
heat exchangers, especially aluminum microchannel heat exchangers.
While specific embodiments are described with reference to aluminum
heat exchangers, the invention can also provide benefits to other
aluminum articles. "Aluminum articles" refers to articles
containing aluminum, aluminum alloys or a combination of the
two.
[0011] Heat exchangers are used in a variety of environments,
including marine, industrial and urban environments. Often, heat
exchanger surfaces are aluminum and subject to the corrosion and
discoloring described above. Heat exchangers can contain inlet and
outlet manifolds; heat exchange tubes, coils or channels; fins and
other structures that are made of aluminum or aluminum alloys. All
of these surfaces need to be protected in order to prevent or
reduce corrosion and other undesired effects.
[0012] Multiple coatings can be applied to the surfaces of a heat
exchanger. Various coatings can be applied to an aluminum heat
exchanger by spraying, dipping, painting or brushing, anodization,
electroplating and other methods. In order for multiple coatings to
effectively adhere to the surface of a heat exchanger, the surface
chemistry of the heat exchanger must sometimes be changed. The
surface chemistry is modified to provide improved bonding potential
between the surface of the heat exchanger and subsequent coating
layers. An adhesion promoting coating can be used to modify the
heat exchanger surface so that later applied coatings bond to the
surface strongly. Epoxy-based coatings are one type of coating that
improves bonding and adhesion between an aluminum surface and later
applied coatings. Epoxy-based coatings also provide additional
mechanical strength and improved corrosion durability of the
aluminum surface.
[0013] Epoxy-based coatings can deteriorate when exposed to UV
radiation. As such, a second coating can be applied to surfaces of
a heat exchanger to provide UV protection. Acrylics,
polyester-based thermoplastic polyurethanes and polyester
triglycidyl isocyanurate (TGIC) are types of coatings that provide
resistance to UV radiation. The second coating also adds a
mechanical barrier to protect any areas of the heat exchanger that
were missed when the first coating was applied.
[0014] Some heat exchangers (i.e. aluminum microchannel heat
exchangers) often have complex geometries with sharp corners and
edges and small spaces that make coating the heat exchanger
surfaces difficult. Powder coatings typically do not provide as
much control and self-leveling as some of the other coating
technologies might (e.g., electrophoretic painting). Nonetheless,
powder coatings make up for some of these deficiencies with other
advantages (no toxic solvents, easier to apply, no need for rinsing
and drying operations, etc.). A single application of a powder
coating can leave areas of the heat exchanger uncoated where bare
aluminum is exposed. Applying a second powder coating over a first
powder coating minimizes the impact of uncoated and exposed
aluminum. The second coating is able to infiltrate gaps left by the
first coating so that the aluminum receives some level of
additional protection. While the second coating primarily provides
protection from UV radiation, the second coating also provides at
least some increase in mechanical strength and corrosion
protection.
[0015] FIG. 1 illustrates a side sectional view of dual powder
coating system 10 and aluminum article 12. Dual powder coating
system 10 includes first layer 14 and second layer 16. First layer
14 is formed on surface 18 of aluminum article 12 using a first
powder. First layer 14 improves the mechanical strength, corrosion
durability and bonding capabilities of surface 18. Second layer 16
is formed over first layer 14 on surface 18 using a second powder.
Second layer 16 improves the UV resistance of surface 18.
[0016] The first powder and the second powder are applied to
surface 18 in different steps. The first powder can be applied
following cleaning of surface 18. Where surface 18 was previously
contacted with brazing flux material and brazed, any residual flux
may need to be removed so that first layer 14 can bond strongly
with surface 18. A method for removing residual flux is provided in
International Application No. PCT/US09/42552, filed May 1, 2009,
which is incorporated by reference.
[0017] First layer 14 is formed by applying the first powder to
surface 18. The first powder is selected to provide additional
mechanical strength and improve corrosion durability of surface 18
and/or promote adhesion and bonding between surface 18 and later
applied coatings. Suitable first powders include epoxy-based powder
coatings such as epoxies, polyester epoxies, acrylic epoxies,
fusion-bond epoxy powder coatings and combinations thereof.
Specific examples of suitable first powders include epoxy powder
coatings based on Bisphenol A or Bisphenol F resins.
[0018] First layer 14 is formed by applying the first powder to
surface 18 and heating the first powder. The first powder can be
applied to surface 18 by spraying, dipping, fluidized bed spraying,
electrostatic deposition, electrostatic magnetic brush coating and
combinations thereof. The first powder can be applied to surface 18
and then heated, applied to an already heated surface 18 or a
combination of the two. Heat can be applied to surface 18 and/or
the first powder by induction heating, oven heating, infra-red
heating and combinations thereof.
[0019] One method of applying the first powder to surface 18 and
forming first layer 14 includes spraying the first powder onto
surface 18 and then heating the first powder. A wide variety of
spray guns or nozzles can be used, depending on the consistency of
the first powder. The first powder is sprayed evenly across surface
18. The first powder is then heated (cured) either directly or by
heating surface 18. Once the first powder melts, it forms a uniform
film on surface 18. The first powder and surface 18 are cooled to
form first layer 14.
[0020] Application methods can also be combined to increase their
effectiveness. For example, during fluidized bed spraying, the
first powder is fluidized, suspended in a stream of air (or other
gas). Often, the fluidized first powder is sprayed onto heated
surface 18 using suitable spray guns or nozzles. Once the fluidized
first powder contacts heated surface 18, first powder melts into a
liquid. The liquid is cooled, forming first layer 14. Fluidized bed
spraying can be combined with electrostatic deposition. The
fluidized first powder is applied using an electrostatic spray gun.
The electrostatic spray gun ionizes the first powder, imparting its
particles with a positive electric charge. Heated surface 18 is
grounded or imparted with a negative charge. The positively charged
fluidized first powder uniformly deposits on heated surface 18 due
to the powder's positive electrical charge and melts into a liquid
form. The liquid is cooled, forming first layer 14. In one
exemplary embodiment, the first powder is electrostatically sprayed
onto surface 18 and then heated to provide a uniform first layer
14.
[0021] Second layer 16 is formed by applying the second powder to
surface 18. The second powder is selected to provide additional UV
resistance to first layer 14 and surface 18. Epoxies can
deteriorate following exposure to UV radiation. Where first layer
14 is epoxy-based, first layer 14 can deteriorate unless it is
protected from UV radiation. Suitable second powders include
thermoset powder coatings such as acrylics, polyester-based
thermoplastic polyurethanes, polyester triglycidyl isocyanurate
(TGIC) and combinations thereof. Specific examples of suitable
second powders include acrylic clearcoats such as PCC10106
(available from PPG industries).
[0022] Second layer 16 is formed in similar fashion to first layer
14. Second layer 16 is formed by applying the second powder to
surface 18 (already covered with first layer 14) and heating the
second powder. The second powder can be applied to surface 18 by
spraying, dipping, fluidized bed spraying, electrostatic
deposition, electrostatic magnetic brush coating and combinations
thereof. The second powder can be applied and then heated, applied
to an already heated surface 18 or a combination of the two. Heat
can be applied to surface 18 and/or the second powder by induction
heating, oven heating, infra-red heating and combinations thereof.
The methods and examples described above with respect to the first
powder can also be used for the second powder.
[0023] First layer 14 and second layer 16 can have varying
thicknesses depending on various needs such as the heat exchanger's
operating environment. Typically, first layer 14 and second layer
16 each have a thickness between about 15 microns and about 35
microns. This range of thickness is appropriate for most heat
exchange applications. In an exemplary embodiment, first layer 14
and second layer 16 each have a thickness of about 25 microns.
[0024] The time and temperature required for curing the first and
second powders depends on the design of surface 18 (e.g.,
convoluted surfaces, flat surface, etc.), the chemistry of surface
18 (e.g., aluminum, aluminum alloy, etc.), the characteristics of
the first and second powders selected, the thicknesses of first
layer 14 and second layer 16 and the curing oven characteristics.
For most surfaces 18 and first and second powders described herein,
a curing temperature between about 190.degree. C. (375.degree. F.)
and about 200.degree. C. (390.degree. F.) is typical. At these
temperatures, curing times between about 10 minutes and about 15
minutes are appropriate.
[0025] First layer 14 and second layer 16 can also contain
additional corrosion-inhibiting compounds. These compounds can be
incorporated into the first powder and/or the second powder so that
they are incorporated into first layer 14, second layer 16 or both
layers 14 and 16. Suitable additional corrosion-inhibiting
compounds include corrosion inhibitive pigments, galvanically
sacrificial metals (e.g., zinc, zinc alloys, magnesium),
lanthanoids, molybdates, vanadates and tungstates.
[0026] In one exemplary embodiment of the present invention, the
first powder is applied to bare surface 18 of aluminum article 12
to form first layer 14 as described above and illustrated in FIG.
1. In another exemplary embodiment, a conversion coating is applied
to surface 18 of aluminum article 12 before the first powder is
applied. Conversion coatings typically offer adhesion promoting
and/or corrosion inhibiting characteristics to surface 18.
[0027] FIG. 2 illustrates a side sectional view of dual powder
coating system 10a and aluminum article 12 with conversion coating
20. Conversion coating 20 is applied to surface 18 before the first
powder is applied and before first layer 14 is formed. Conversion
coating 20 can be applied by spraying, dipping, fluidized bed
spraying, electrostatic deposition, electrostatic magnetic brush
coating or any other suitable coating method. Examples of suitable
conversion coatings include chromate and phosphate conversion
coatings, coatings containing trivalent chromium, zinc phosphate,
iron phosphate, or manganese phosphate and combinations
thereof.
[0028] Dual powder coating system 10a includes first layer 14 and
second layer 16 as described above. First layer 14 is formed on
aluminum article 12 over conversion coating 20 using a first
powder. First layer 14 improves the mechanical strength, corrosion
durability and bonding capabilities of aluminum article 12. Second
layer 16 is formed over first layer 14 on aluminum article 12 using
a second powder. Second layer 16 improves the UV resistance of
aluminum article 12.
[0029] Dual powder coating systems 10 and 10a provide a method for
coating an aluminum article. FIG. 3 is a flow chart illustrating a
method of coating an aluminum article according to the present
invention. Method 22 includes applying a first powder to an
aluminum article (step 24), and heating the first powder to form a
first layer on the aluminum article (step 26). The first layer
provides increased mechanical strength, enhanced corrosion
protection and improved bonding potential for the aluminum article.
Method 22 also includes applying a second powder to the aluminum
article (step 28), and heating the second powder to form a second
layer on the aluminum article (step 30). The second layer protects
the aluminum article from ultraviolet radiation. Application of
each powder to the aluminum article and heating the powder can
occur successively or contemporaneously. According to method 22,
the first powder is heated before the second powder is applied to
the aluminum article. According to method 22, the first powder can
be applied directly to surface 18 of aluminum article 12 or to an
aluminum article 12 having a conversion coating 20.
[0030] FIG. 4 is a flow chart illustrating another method of
coating an aluminum article. Method 32 includes applying a first
powder to an aluminum article (step 34), applying a second powder
to the aluminum article (step 36) and heating the first and second
powders to form first and second layers on the aluminum article
(step 38). According to method 32, the second powder is applied to
the aluminum article before the first powder is heated to form the
first layer. The first and second layers are formed
contemporaneously. According to method 32, the first powder can be
applied directly to surface 18 of aluminum article 12 or to an
aluminum article 12 having a conversion coating 20.
[0031] The dual powder coating system and method of the present
invention provide an aluminum article with enhanced mechanical
strength, improved bonding capability, enhanced corrosion
durability and improved resistance to UV radiation. Aluminum
articles can possess improved features in all of these areas rather
than having to pick and choose from among them.
[0032] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiments disclosed, but that the invention will
include all embodiments falling within the scope of the appended
claims.
* * * * *