U.S. patent application number 10/287377 was filed with the patent office on 2003-03-20 for method for coating faying surfaces of aluminum-alloy components and faying surfaces coated thereby.
This patent application is currently assigned to The Boeing Company. Invention is credited to Byrd, Norman R., Keener, Steven G..
Application Number | 20030054182 10/287377 |
Document ID | / |
Family ID | 22538328 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030054182 |
Kind Code |
A1 |
Keener, Steven G. ; et
al. |
March 20, 2003 |
Method for coating faying surfaces of aluminum-alloy components and
faying surfaces coated thereby
Abstract
An aluminum-alloy, aircraft structural component having a faying
surface prepared by treating with one or more curable organic
coatings, one or more of which is optionally in an encapsulated
state, and delivering a uniform coating on demand by rupturing and
curing the encapsulated coating.
Inventors: |
Keener, Steven G.; (Trabuco
Canyon, CA) ; Byrd, Norman R.; (Villa Park,
CA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
The Boeing Company
|
Family ID: |
22538328 |
Appl. No.: |
10/287377 |
Filed: |
November 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10287377 |
Nov 4, 2002 |
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09578144 |
May 24, 2000 |
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6475610 |
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09578144 |
May 24, 2000 |
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09151343 |
Sep 11, 1998 |
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Current U.S.
Class: |
428/457 |
Current CPC
Class: |
Y10T 428/31678 20150401;
Y10T 428/31551 20150401; B05D 3/0254 20130101; B05D 2202/25
20130101; C22F 1/053 20130101; B05D 7/14 20130101; Y10T 428/31522
20150401; Y10T 428/2495 20150115; C22F 1/04 20130101 |
Class at
Publication: |
428/457 |
International
Class: |
B32B 015/04 |
Claims
What is claimed is:
1. A method for preparing an aluminum-alloy, aircraft component
comprising the steps of: providing an aluminum-alloy component
precursor curable to a final state; providing a curable organic
coating material having a non-volatile portion that is
predominantly organic and is curable at about a heat-treatment
temperature of the aluminum-alloy component; coating the component
precursor with the organic coating material; and treating the
coated aluminum-alloy component precursor to both treat the
aluminum to the final state and cure the organic coating.
2. The method of claim 1, wherein the curable organic coating
material is encapsulated.
3. The method of claim 1, wherein the step of treating the coated,
aluminum-alloy component comprises heat-treating.
4. The method of claim 3 wherein the step of treating the coated
aluminum-alloy component comprises precipitation heat-treating.
5. The method of claim 1, wherein the step of treating the coated
aluminum-alloy component includes pressure-treating.
6. The method according to claim 1, further comprising the steps of
positioning the coated aluminum-alloy component in an assembly
position contacting a second component; and providing a compressive
force to at least one component.
7. The method of claim 1, wherein the step of providing an
aluminum-alloy precursor includes providing an aircraft component
selected from the group consisting of wing and fuselage skin
panels, stiffeners, frames, and hinges.
8. The method of claim 1, wherein the step of providing an
aluminum-alloy precursor includes the step of providing a wing skin
panel and components thereof.
9. The method of claim 1, wherein the step of providing an
aluminum-alloy component precursor includes the step of providing
an aluminum-alloy component precursor in its fully solution-treated
and annealed state.
10. The method of claim 1, further comprising the step of providing
and applying a second coating to the once coated component.
11. The method of claim 1, further comprising the step of first
anodizing the component provided.
12. The method of claim 10, wherein the second coating is an
encapsulated coating.
13. The method of claim 1, wherein the component precursor is
naturally-aged.
14. The method of claim 1, wherein the component precursor is
artificially-aged.
15. The method of claim 1, wherein the organic coating is cured and
the component precursor is treated to the final state substantially
simultaneously.
16. The method of claim 1, wherein the component precursor has a
faying surface.
17. The method of claim 1, wherein the curable organic coating
material comprises a phenolic resin.
18. The method of claim 1, wherein the encapsulated curable organic
coating material is selected from the group consisting of
phenolics, urethanes, epoxies, and melamines.
19. The method of claim 1, wherein the curable organic coating
material is selected from the group consisting of polyurethanes,
polyvinyl chlorides, silicones, epoxides, acrylates, polyimides and
phenolics.
20. The method of claim 1, wherein the step of treating the
component precursor includes providing a heat-treatment sufficient
to rupture the encapsulated coating to disperse a uniform coating
to the aluminum-alloy component precursor surface.
21. The method of claim 1, further comprising the step of providing
a substantially uniform first coating deposited to a thickness of
from about 0.005 to about 0.010 inch.
22. The method of claim 10, wherein the second coating is selected
from the group consisting of phenolics, epoxies, melamines, and
polyurethanes/polyureas.
23. The method of claim 22, wherein the second coating is deposited
to a thickness of from about 0.0005 to about 0.0015 inch.
24. The method of claim 1, further comprising the steps of
providing a second encapsulated coating material; coating the
heat-treated, aluminum-alloy component with a second, encapsulated
coating material; and rupturing the second, encapsulated coating
material to disburse a uniform coating.
25. The method of claim 24, wherein the step of providing a second,
encapsulated coating material further comprises providing a
catalyst.
26. The method of claim 24, wherein the step of providing a second
coating includes the step of providing a catalyst selected from the
group consisting of Friedel-Crafts acids, Friedel Crafts bases,
peroxides, and azo-bis-nitriles.
27. The method of claim 24, wherein the step of providing a second,
encapsulated coating material includes providing an adhesive as a
substantially uniform layer having a thickness of from about 0.0005
inch to about 0.0015 inch.
28. The method of claim 27, wherein the step of providing a second
coating further comprises providing an adhesive selected from the
group consisting of phenolics, urethanes, epoxies, and
melamines.
29. The method of claim 24, wherein the step of rupturing the
second coating material includes the step of liberating the second
coating material by heat-treating.
30. The method of claim 24, further comprising the step of
liberating the second coating material by exposing the second,
encapsulated coating material to an increased pressure of from
about 1500 to about 2500 psi.
31. The method of claim 24, further comprising the step of
liberating the second coating material by applying pressure to the
surface of the coated component.
32. The method of claim 24, wherein the component precursor has a
faying surface.
33. An aluminum-alloy aircraft component prepared according to the
method of claim 16.
34. A treated, aluminum-alloy aircraft component prepared according
to the method of claim 32.
35. A method for treating an aluminum-alloy, aircraft component
having a faying surface comprising the steps of: providing an
aluminum-alloy component; providing a first coating material;
applying the first coating material to the component; providing a
second coating material to the coated component; applying the
second coating material to the component; and heat-treating the
twice-coated component.
36. The method of claim 35, wherein the second coating material is
an encapsulated coating.
37. The method of claim 35, further comprising the step of
anodizing the component before the first coating is applied.
38. The method of claim 35, wherein the step of providing a first
coating material includes the step of providing coating materials
selected from the group consisting of phenolics, epoxies,
urethanes, silicones, novolaks, acrylates, and melamines.
39. The method of claim 35, wherein the step of providing an
encapsulated coating includes the step of providing a second
coating material selected from the group consisting of phenolics,
epoxies, urethanes, novolaks, melamines, acrylates, and
silicones.
40. The method of claim 35, wherein the step of heat-treating the
component includes the step of heating the component to a
temperature of from about 120 to about 180 degrees F. for a time of
from about 20 minutes to about 1 hour.
41. The method of claim 35, further comprising the step of
providing pressure to the component other than ambient
pressure.
42. The method of claim 35, wherein the component is
naturally-aged.
43. The method of claim 35, wherein the component is
artificially-aged.
44. The method of claim 35, wherein the component has a faying
surface.
45. A treated, aluminum-alloy aircraft component having a faying
surface prepared according to the method of claim 35.
46. An aluminum-alloy aircraft component prepared according to the
method of claim 35.
47. A method for treating an aluminum-alloy, aircraft component
having a faying surface comprising the steps of: providing an
aluminum-alloy, aircraft component; providing a first coating;
providing a second coating; applying the first and second coating
to the component in sequential order; providing a releasable film;
and applying the releasable film to the component to cover the
second coating.
48. The method of claim 47, wherein the second coating comprises
encapsulators.
49. An aluminum-alloy, aircraft component having a faying surface
prepared according to the method of claim 47.
50. A method for treating an aluminum-alloy, aircraft component
having a faying surface comprising the steps of: providing an
aluminum-alloy, aircraft component; providing a first coating;
applying the first coating to the component; heat-treating the
component; providing an encapsulated second coating; applying the
second coating to the coated component; providing a releasable
film; and applying the releasable film to the component to cover
the second coating.
51. The method of claim 50, wherein the second coating comprises
encapsulators.
52. An aluminum alloy-aircraft, component having a faying surface
prepared according to the method of claim 50.
53. A method for treating an aluminum-alloy aircraft, component
having a faying surface comprising the steps of: providing an
aluminum-alloy aircraft component; providing a first coating;
applying the first coating to the component to make a once-coated
component; providing a first heat-treatment to the component;
providing a second coating in an encapsulated state; applying the
second coating to the coated component to make a twice-coated
component; and positioning the component for assembly.
54. The method of claim 53, further comprising the step of
positioning the twice-coated component into a final assembly
position.
55. The method of claim 53, further comprising the step of
providing a force to the twice-coated component sufficient to
liberate the encapsulations of the second coating.
56. The method of claim 53, wherein the step of providing a force
to the component includes providing a pressure in the range of from
about 1500 psi to about 2500 psi.
57. The method of claim 53, wherein the step of providing a force
to the component is a compressive force in the range of from about
1500 psi to about 2500 psi.
58. An aluminum-alloy aircraft component prepared according to the
method of claim 53.
59. An aircraft component having faying surfaces and made from an
aluminum alloy comprising: a uniformly deposited, first
corrosion-resistant, available organic coating material having a
thickness of from about 0.0050 inch to about 0.010 inch; and an
encapsulated second coating comprising a polyurethane/polyuria and
uniformly deposited to a thickness of from about 0.0005 inch to
about 0.0015 inch; wherein the surface of the first coating is tack
free.
60. An aircraft having faying surfaces, said aircraft made from
aluminum-alloy containing components, said components comprising: a
first coating; and a second coating; wherein said coatings and said
component are substantially simultaneously cured in one curing
step.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the preparation of coated,
aluminum-alloy components and their installation and assembly. More
specifically, the present invention relates to pre-treating
surfaces of aluminum-alloy, aircraft structural components.
[0002] It has recently been discovered that the corrosion
protection and ease of processing and assembly of certain, aircraft
structural components can be improved by pre-treating the
components with an organic, corrosion-inhibiting coating material
prior to installation. It had been the conventional practice to
coat such components with wet sealants that are known to require
extensive and expensive special handling, especially with respect
to their disposal. The pretreatment method obviates the use of the
wet sealants, reducing processing time and disposal costs. Such
advances are the subject of commonly owned U.S. Pat. No.
5,614,037.
[0003] As disclosed in U.S. Pat. No. 5,614,037, it has been the
practice to coat some types of fasteners in aircraft assemblies
with organic coating materials to protect the base metal of the
fasteners and surrounding adjacent structure against corrosion
damage. In this usual approach, the fastener is first fabricated
and then heat-treated to its required strength. After
heat-treatment, the fastener is etched with a caustic soda bath or
otherwise cleaned to remove any scale produced in the
heat-treatment. The coating material, dissolved in a volatile
carrier liquid, is applied to the fastener by spraying, dipping, or
the like. The carrier liquid is allowed to evaporate. The coated
fastener is then heated to an elevated temperature for a period of
time to cure the coating; typically one hour at 400.degree. F. The
finished fastener is then ready to be used in the assembly of the
airframe structure.
[0004] This coating methodology works well with fasteners made from
base metals having high melting points, such as fasteners made of
steel or titanium alloys. Such fasteners are heat-treated at
temperatures well above the curing temperature of the coating.
Consequently, the curing process of the coating, conducted after
heat-treatment of the fastener is complete, does not adversely
affect the properties of the already-treated base metal.
[0005] On the other hand, non-ferrous or aluminum alloys have a
much lower melting point, and generally much lower heat-treatment
temperatures, than steel and titanium alloys. It has not been the
practice to coat aluminum-alloy, aircraft structural components
such as wing and fuselage skin panels and fasteners, etc., with
curable coatings, because it is observed that the elevated
temperature required to cure the coatings adversely affects the
resulting strength of the components. The aluminum-alloy, aircraft
structural components must therefore be protected from corrosion
attack by other methods that are extremely labor intensive, such as
the use of wet sealants.
[0006] The inability to pre-apply these protective coatings forces
aluminum-alloy, aircraft structural components such as wing and
fuselage skin panels, etc. to be installed and assembled using
wet-sealant compounds for the primary purposes of corrosion
protection and pressure and fuel sealing. However, the wet-sealant
compounds typically contain toxic, solvent-based compounds and
therefore require multiple precautions for the protection of the
personnel using them as well as their safe disposal to insure
environmental protection. Such wet sealants are also messy and
difficult to work with. In addition, wet sealants require extensive
clean-up of the area around the fastener and adjacent structure.
The clean up is conducted using caustic chemical solutions after
the assembly process has been completed, and therefore represents
an additional and expensive manufacturing step.
[0007] Wet-sealant compounds are also applied to the faying
surfaces between components throughout the aircraft. For the
purpose of this application, it is understood that "faying
surfaces" are the interfaces of abutting or mating components that
become so intimately and permanently fitted in relation to one
another that the point of interface is virtually undetectable after
assembly. The use of wet-sealant compounds on the faying surfaces
of larger aircraft structural components results in additional
waste, excessive application and clean-up time, toxic waste
disposal complications, and increased cost.
[0008] There exists a need for an improved approach for the
protection of the faying surfaces of these aluminum-alloy, aircraft
structural components such as wing and fuselage skin panels,
stiffeners (which include but are not limited to spars, ribs,
stringers, longerons, frames, shear clips, "butterfly" clips,
etc.), hinges, doors, etc., and the mechanical components attached
to these aforementioned components. Furthermore, there exists a
need for improving the delivery methods and systems of such
coatings onto the aluminum-alloy, aircraft structural components,
including relatively large, surface-area components.
SUMMARY OF THE INVENTION
[0009] It has now been discovered that the surfaces of
aluminum-alloy, aircraft structural parts can be pre-treated in
order to enhance processing of the critical faying surfaces while
also improving corrosion protection, reducing or eliminating
cleaning and other processing steps. In addition, the improved
method of applying multiple pre-treatment coatings to
aluminum-alloy, aircraft structural components of the present
invention allows for significant processing advantages in terms of
improved coating thickness tolerances and uniformity, part storage,
general handling, installation, and assembly.
[0010] The present invention provides a method for preparing and
treating the surfaces of aluminum-alloy, aircraft structural
components such as wing and fuselage skin panels, components
collectively referred to as stiffeners, hinges, doors, etc., and
the mechanical components attached to these aforementioned
components. In addition, the present invention is particularly
applicable for the improved processing of the faying surfaces of
these aircraft components. The application of the coating utilizing
this method does not either alter or affect the mechanical or
metallurgical properties or performance of the components and does
not adversely affect the desired, final performance of the
assembled aircraft structure.
[0011] In accordance with one embodiment, the present invention
comprises a method for preparing an aluminum-alloy, aircraft
structural component providing an artificially-aged, aluminum-alloy
precursor following solution heat-treatment that is not in its
final heat-treated state and coating the precursor with a first
organic coating. Optionally, an encapsulated, second coating is
then applied to the first coating. The twice-coated component is
then precipitation heat-treated, and placed into assembly position
and assembled. Encapsulant should be a material that when either
squeezed or crushed is of a chemical structure such that it becomes
an integral part of the adhesive which it is encapsulating.
[0012] In a further embodiment, the present invention comprises
providing a naturally-aged, aluminum-alloy, aircraft structural
component and coating the component with a first coating. The
once-coated component is subjected to an elevated or room
temperature to cure the coating. A second coating is provided in an
encapsulated state and applied onto the first coating. The
twice-coated component is then subjected to an elevated or room
temperature environment to cure the second coating. The component
is then placed into assembly position and contacted to a second
component by applying a temperature or pressure change such as a
compressive assembly force sufficient to liberate the second
coating from its encapsulated state thereby creating a bonded
interface between components.
[0013] In yet another embodiment, the present invention comprises
providing a naturally-aged, aluminum-alloy, aircraft structural
component and coating the component with a first coating.
Optionally, a second coating is provided in an encapsulated state
and applied onto the first coating. The coated component is then
subjected to an elevated temperature environment to cure the
coating. The component is then placed into assembly position and
contacted to a second component by applying rupture conditions such
as a compressive assembly force sufficient to liberate the second
coating from its encapsulated state thereby creating a bonded
interface between component and coating.
[0014] In yet a further embodiment, the present invention comprises
providing either an artificially-aged or a naturally-aged,
aluminum-alloy, aircraft structural component, coating the
component with a first coating, followed optionally by applying an
encapsulated, second coating. A protective release paper is then
provided to the component to cover the encapsulated, coating layer
prior to assembly.
[0015] Still further, the present invention comprises providing an
artificially-aged, aluminum-alloy, aircraft structural component
following solution heat-treatment that is not in its final
heat-treated state. A first organic coating is applied to the
component, followed by precipitation heat-treating the coated
component. The coated component is then coated with an
encapsulated, second coating. The coated component is then
subjected to either an elevated or room temperature environment to
cure the second coating. The twice-coated component is then placed
into assembly position and contacted to a second component with a
compressive assembly force applied sufficient to liberate the
second coating from its encapsulated state thereby creating a
bonded interface between component and coatings.
[0016] In still a further embodiment, the present invention
contemplates providing an artificially-aged, aluminum-alloy,
aircraft structural component in its final heat-treated state. A
first coating is applied to the component optionally followed by
applying an encapsulated, second coating. The component is then
subjected to an elevated temperature environment to cure the two
coatings. A protective release paper designed to protect the
twice-coated component is optionally applied to the surface of the
twice-coated component. The component is then placed into assembly
ready position, the protective release paper is removed exposing
the second coating. The component is then contacted to another
component for final assembly. The coated component is then
compressed against a second structural component in its final
assembly position. The assembly compression force is sufficient to
rupture the adhesive encapsulations contained in the second coating
material. The second coating material reacts between the first
coating and the adjacent, second structural component to enhance
the overall adherence of the surface of the first component with
that of the second component. The second coating material provides
an enhanced bond between the faying surface of the two structural
components.
[0017] In yet another embodiment, an artificially-aged,
aluminum-alloy, aircraft structural component is provided in its
final heat-treated state. A first coating is applied followed by
either a room temperature or elevated temperature exposure to cure
the first coating. A second coating is then applied to the
once-coated component followed by either a room temperature or
elevated temperature exposure to cure the second coating. Release
paper is then optionally applied to the second coating and removed
prior to assembling the component on the airframe.
[0018] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1a shows a wing panel sub-structure.
[0020] FIGS. 1b-1f show enlarged partial views of component aspects
of the wing panel where faying surfaces occur:
[0021] FIG. 1g shows a section of fuselage skin attached to a frame
section.
[0022] FIG. 2 is a process flow diagram for a method of the
invention using an artificially-aged alloy and curing of both
coatings with precipitation heat-treatments.
[0023] FIG. 3 is a process flow diagram for one form of a method of
the invention comprising a naturally-aged alloy and curing each
coating individually at either room or elevated temperature.
[0024] FIG. 4 is a process flow diagram for a method of the
invention where the multiple coatings are cured together at either
room or elevated temperature.
[0025] FIG. 5 is a process flow diagram for a method of the
invention wherein either naturally or artificially-aged alloy
components have both coatings cured at room temperature.
[0026] FIG. 6 is a process flow diagram for a method of the
invention wherein artificially-aged alloy components have the
primary coating cured by precipitation heat-treatment with a second
coating applied followed by either a room or elevated temperature
cure.
[0027] FIG. 7 is a process flow diagram for a method of the present
invention using an artificially-aged alloy component in its final
state where either one or both of the coatings are cured
simultaneously at elevated temperature.
[0028] FIG. 8 is a process flow diagram for a method of the present
invention using an artificially-aged alloy component in its final
state where each coating is subjected to a separate elevated
temperature cure.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The invention of the present invention relates to any
aircraft structural components such as wing and fuselage skin
panels stiffeners, stringers, spars, clips, frames, etc., where
faying surfaces exist. FIG. 1a shows an aircraft wing panel
assembly 1 prior to affixing the aluminum skins. The panel assembly
1 comprises hardware shown in enlarged FIGS. 1b-1f. FIG. 1b shows a
stringer 2 attached to wing panel skin 7. FIG. 1c depicts a spar
cap 3 attached to wing panel skin 7. FIG. 1d shows an angled shear
clip 4 in position between stringers 2. FIG. 1e shows a butterfly
clip 5 in position adjoining a stringer 2 and a shear clip 4. FIG.
1f shows a center spar clip 6 affixed to a section of wing panel
skin 7. Finally, FIG. 1g depicts a section of fuselage structure
showing framing 8 affixed to fuselage skin 7. These components
preferably have their faying surfaces "pre-coated" following the
completion of their normal fabrication cycle, but prior to final
assembly. Large sections of aluminum also could be coated during or
after final assembly.
[0030] FIG. 2 shows one preferred method of the present invention.
In this embodiment, an artificially-aged (and optionally anodized
11), aluminum-alloy component 10 and the first coating material 12
are provided with the coating applied thereto 14. The component 10
is not in its final heat-treated state. A second coating 16
optionally is provided and applied 18 thereto. If a second coating
is applied, the twice-coated component is precipitation
heat-treated 20. Release paper is then optionally applied and
adhered 22 to the twice-coated component. The paper is removed
prior to assembling the component. The component is then positioned
and assembled 24. In a preferred embodiment, either one or both of
the first and second coatings are encapsulated. The encapsulant
material preferably is activated when surface pressure is
applied.
[0031] FIG. 3 shows an alternate method of the present invention
wherein a first coating material 32 is provided and applied 34 to
the component 30 followed by either a room or elevated temperature
cure step 36. As in the process of FIG. 2, the component may be
optionally anodized 31 prior to first coating 34. A second coating
material 38 is provided and applied 40 to the component 30. A
second cure step occurs 42 at either room or elevated temperature
before the now twice-coated and twice-cured component is positioned
for assembly 44. As with the method of FIG. 2, it is particularly
preferred that either one or both of the first and second coatings
comprise encapsulations.
[0032] FIG. 4 shows another method of the present invention. A
naturally-aged, aluminum-alloy component 50 is optionally anodized
51 and immediately coated with a first coating material 54 that has
been provided 52. Optionally, a second coating material is provided
56 and applied 58 to the component. The twice-coated component is
then subjected to either room or elevated temperatures 60 for
curing. Release paper is then optionally applied 62 to the
component until the component is to be used. The paper is then
removed from the component and the component used in assembly 64.
It is understood that the release paper is itself a protective
film, or comprises a protective film.
[0033] In FIG. 5, the component 61 is either an artificially or a
naturally-aged alloy in its final heat-treated state. The component
is optionally anodized 62 and then coated with a first coating 63,
followed by an optional second coating 65. The component 61 is then
cured at room or elevated temperature 66. As with FIGS. 2-4, it is
understood that a releasable film 68 is optionally applied to the
component after the second coating is applied. The film is then
removed from the component without disturbing the coatings, prior
to positioning and assembling the part 69. As with FIGS. 2-4, it is
particularly preferred that either one or both of the first and
second coatings be encapsulated.
[0034] In FIG. 6, the artificially-aged component 70 is optionally
anodized 71 and has a first coating 72 that is applied 74 and
followed by precipitation heat-treatment 76. An encapsulated second
coating 78 is applied 80 onto the first coating. The component can
be subjected to either a room or elevated temperature cure process
82. A release paper or film 83 is then optionally applied to the
cured second coating, and subsequently removed upon assembly. The
twice-coated component is then positioned for assembly 84.
[0035] FIG. 7 depicts a block flow diagram representing a variation
of the embodiment shown in FIG. 5. In FIG. 7, an artificially-aged,
aluminum-alloy component 86 is provided in its final heat-treated
state. The component is optionally anodized 86a and is coated
respectively 88, 90 with a first 87 and optionally a second coating
89, then heat cured 91 at an elevated temperature. Release paper is
optionally applied to the second coating 92 and removed prior to
assembling the component 94.
[0036] In FIG. 8 an artificially-aged, aluminum-alloy component 100
is provided in its final or finished, heat-treated state. A first
coating is provided 102 and applied 104. The coated component is
then cured at an elevated temperature 105. The second coating is
provided 106 and applied 108 and subjected to a second, elevated
heat environment 110 to cure the second coating. Release paper is
again optionally applied 112, and the component is positioned and
assembled 114. As with FIGS. 2-7, the component is then exposed to
an assembly compressive force sufficient to overcome the structural
integrity of the adhesive encapsulations, and adhere the component
in place.
[0037] As with the above-described methods, it is particularly
preferred that either one or both of the first and second coatings
be encapsulated. In this instance, the assembly compressive force
supplied to the twice-coated component is sufficient to liberate
the coatings from their encapsulated state. A protective releasable
film is preferably applied to the twice-coated component to protect
the coatings during storage, delivery, handling, installation or
final positioning, and then may be removed prior to contacting the
component to another mating structural component in its final
orientation. The component is then compressed in the assembled
state to activate the encapsulated, adherent composition in either
one or both of the coatings.
[0038] Many variations of the above-stated methods are contemplated
by the present invention. For example, in one variation (not
shown), a releasable film may be coated with one or more coatings.
The coated, releasable film may then be applied to the component to
be treated. Before or after curing as desired, the film may be
released, leaving a component coated and ready for handling and
placement into its final assembly position. The film may be a
paper, polyethylene, plastic or laminate, or any suitable material
as would be understood by one skilled in the films and coatings
field.
[0039] It is further understood that the elevated temperature
curing steps may be conducted in conjunction with adjustments in
the cold-working levels of the components achieved during
fabrication so as to achieve the desired results on the aluminum
alloy and the coating or coatings thereon. In certain embodiments,
component and coating thermal treatments may be effected at either
room temperature, or at temperatures and associated times lower
than normal heat-treating times and temperatures for example, from
about 150 to about 375 degrees F. for periods of about 10 minutes
to about 1 hour, if certain additional levels of cold-work in the
material are present.
[0040] The aluminum-alloy precursor component, and the finished
component, preferably may be made of an aluminum alloy having a
temper achieved by artificial-aging to its final state. This
precursor component preferably is provided in a
solution-treated/annealed condition suitable for the subsequent
utilization of a strengthening, precipitation heat-treatment, but
is not as yet in its final, heat-treated state. Optionally, the
precursor is anodized, preferably in a chromic-acid solution, to
improve the chemical and mechanical adhesion of the subsequently
applied coating to the precursor, and also preferably without
sealing the anodized surface of the precursor.
[0041] The organic coating material, in a liquid, encapsulated
state, is applied to the anodized, unsealed surface of the
precursor which is not in its final heat-treated state. In this
embodiment, the heat-treatment of the precursor component is
thereafter completed to bring the finished component to its full
strength by heating to an elevated temperature in a precipitation
heat-treatment. The coating is simultaneously cured while achieving
the component's required metallurgical properties during the
precipitation heat-treatment/aging according to the combination of
temperature(s), time(s), and environment(s) specified for the
particular aluminum-alloy base metal of the aircraft component.
Thus, no separate curing procedure is required for the coating
after the coated component has been heat-treated.
[0042] In another preferred embodiment, the components include
those made of an aluminum alloy having a temper that is achieved by
natural-aging. The distinction between artificial and natural-aging
is that during precipitation heat-treatment, artificial-aging
involves heating the component to an elevated temperature for a
prolonged period. Natural-aging is accomplished at room temperature
over an extended period. In the present invention, the component
may be plastically deformed by cold-working the component during
the fabrication process prior to coating with the organic coating
material and subsequent to natural-aging. The component is then
coated and subsequently treated with a modified thermal treatment
to cure the coating and simultaneously provide some stress relief
or annealing. The additional deformation or cold-working provided
to the component during fabrication, and prior to curing of the
coating, enables the component's material properties to fall within
the acceptable limits when the component is subjected to the
elevated temperature conditions needed to cure the coating.
[0043] The component of the present invention may not be
heat-treated, but instead may be in a final deformation state that
has had significant levels of cold work applied to its
metallurgical structure, either before or during fabrication. In
this embodiment, the precursor preferably is 1) over-deformed to a
deformation state greater than that required in the final
component; 2) optionally anodized in chromic-acid solution and
unsealed; 3) coated with the organic coating material; and then 4)
heated to cure the coating and partially anneal the precursor to
the required deformation state.
[0044] It is further understood that additional, encapsulated
coating layers may be provided to the first coating layer.
Preferably, the second coating is an accelerator or adhesive
coating, preferably containing encapsulated particles of adhesive
held in suspension. As with the first encapsulated layer, a
temperature or pressure change is imposed on the coated component.
The preferred encapsulant preferably has a chemical structure such
that it becomes an integral part of the adhesive which it is
encapsulating. Preferred encapsulant material include
polyurethanes, polyvinylchlorides, silicones, epoxies, acrylates,
polyimides, and phenolics, with acrylates being particularly
preferred.
[0045] The present invention also contemplates the manufacture of
any aluminum-alloy, aircraft structural components compatible with
a selected corrosion-inhibiting coating formulation and requiring
an aging/curing period. The aging/curing period can be conducted at
either an elevated or room temperature environment for a length of
time to facilitate curing. Once cured, it is preferred that the
coating be tack-free to enable handling.
[0046] The coating thickness achievable by the present invention
may vary according to the preferred end-result characteristics of
the coated component and the coating itself. Preferably, the first
coating thickness ranges from about 0.005 inch to about 0.010 inch.
The second coating thickness preferably ranges from about 0.0005
inch to about 0.0015 inch.
[0047] The preferred corrosion-inhibiting coatings are those
capable of minimizing the passage of water, acids, or bases from
the ambient, environmental surroundings to the aluminum substrate.
Thus, such coatings are either hydrophobic materials and/or
sacrificial substances, e.g, SrCr.sub.2O.sub.4 or other chromates,
etc. Such useful coatings include hydrophobic coatings such as,
polyethylene, polyethylene/tetrafluoroethyl- ene copolymers,
phenolics, epoxies, polyimides, polyurethanes, polyvinylchlorides,
silicones and novolaks, with and/or without chromate fillers, with
polyurethanes/polyureas being the most preferred.
[0048] Novolaks are phenol/formaldehyde polymers that are formed by
reacting phenol with less than an equivalent amount of formaldehyde
(i.e., approximately 1:0.8 mole ratio) in an acid catalyzed
reaction. This results in a more flexible polymer than the standard
phenol formaldehyde which allows for ease of handling and
application prior to it being further crosslinked at a later stage.
Thus, novolaks can be applied to a substrate and later crosslinked
by the addition of, for example, hexamethylene tetramine.
[0049] The second coating applied to the first protective coating
preferably comprises an adhesive or primer, and is similar to those
coatings used for the bonding of aircraft structural panels.
Preferred coatings are those capable of minimizing the passage of
water, acids, or bases from the ambient environment to the aluminum
substrate, and are also capable of bonding to the substrates as
well as being a sealant. Additionally, the second coating is
capable of adsorbing encapsulated coatings for use in further
bonding and sealant needs. Such coatings include phenolics,
epoxies, melamines, and polyurethanes, with polyurethane/polyurea
being most preferred.
[0050] In accordance with the present invention, it is most
preferred if the second coating alone, or both the first and second
coating are encapsulated. The coatings are encapsulated according
to known encapsulation techniques. Encapsulation is a process
whereby one substance, A, is dispersed in a medium in which this
first substance is not soluble. As a high-speed stirring and
shearing action is applied to disperse the substance A into a fine,
colloidal particle, a second substance, B, is added which may be in
a monomeric form. This second substance B is then polymerized,
while still undergoing the high-speed stirring. This allows
substance A to be encapsulated with the second substance, polymer
B. Alternatively, substance A may be obtained in a fine particulate
form and added to a solution of substance B, which coats the
particulates of substance A. The resultant mixture is blown into an
evacuated chamber. The solvent used in preparing the solution
containing substance B is then removed under vacuum causing the
encapsulated particles to precipitate and collect on the bottom of
the chamber.
[0051] The encapsulated coatings may be delivered to the component
surface by any acceptable method known in the field of spray
coatings. An encapsulated coating, when dispersed in an aqueous or
non-aqueous medium, can be sprayed onto the substrate. When the
non-solvent carrier evaporates away or dries out, the encapsulated
particles are left behind. Alternatively, the encapsulated
particles can be electrostatically sprayed onto the substrate
surface. It is further contemplated that the second coating
preferably use microsuspension bead-technology similar to the known
technology in the laser jet ink field. In this way, the second
coating applied to the once-coated component preferably bursts upon
impact to deliver a relatively uniform, final coating of from about
0.0005 inch to about 0.0015 inch.
[0052] It is contemplated that this microsphere or bead-like
delivery system can be used to deliver various types of useful
initiators or catalysts to an aircraft structural component. Such
initiators may be in any state and may be Friedel-Crafts ionic
catalysts such as, but not limited to metal halides, acids, amines,
boron trifluoride, boron trifluoride-etherate, etc. The catalyst
chosen is preferably matched to the aging/curing requirements of
each particular application.
[0053] For handling purposes, it is preferred that the coated
component surface be tack-free. This requires that the coating be
cured via either a room or elevated temperature treatment, pressure
treating, or irradiation, etc. Preferably a coating is allowed to
rest at room temperature on the component surface and become
tack-free after a suitable time, e.g. from about 2 to about 4
hours. Still further, it is contemplated that the second,
encapsulated coating is delivered to the once-coated component and
cured after a short time; from about 10 to about 30 minutes.
[0054] In addition, to assist in handling the coated component, a
releasable paper or film may be placed over the coating for
protection. The film preferably is designed to release from the
coating's surface without disturbing the coating or its surface.
However, it is contemplated that the release paper could activate
the coating it covers upon its removal therefrom. It is further
contemplated that the releasable film itself could be coated with
one or more coatings that are then transferred to the component
surface being treated, followed by an optional curing protocol. The
releasable film is then removed from the component, leaving the
cured film adhered and cured to the component surface. Preferred
films or release papers include glassine paper, fluorinated
ethylene/propylene copolymer (FEP) film, kraft paper, Armalon film
(fluorinated release film), IVEX Corp. release papers such as
CP-96A (a glossy coating on a 112# basis weight class paper) and
IVEX LC-19 papers with CP-96A or IVEX LC-19 papers being
particularly preferred.
[0055] The preferred selected temperature curing regimen for the
present invention is governed by the availability of the active
catalyst/initiator and the reactivity of the catalyst/initiator
with the monomer or organic compound comprising the first coating.
For example, benzoyl peroxide preferably heated to about 80.degree.
C. is a suitable polymerization initiator in a free radical
polymerization of some vinyl monomers, such as styrene. However,
benzoyl peroxide can also be used at lower temperature if higher
pressures are provided. In addition, the selected catalyst for the
second coating may be an active catalyst; i.e. decomposable at room
temperature, such as, e.g., liquid peroxide in the presence of a
tertiary amine. However, it is often necessary to allow such
reactive monomers or others such as adhesives (low molecular weight
polymers) to be mixed and applied to a substrate in position before
it is subjected to a further reaction, such as polymerization,
curing, bonding, etc. to another adhesive surface. It is therefore
preferred to mix all components in a carrier medium to achieve a
relatively homogeneous state prior to placement on a substrate.
This applies to monomers with catalysts and also adhesive films
applied for subsequent bonding. In this way the coatings are
applied such that no chemical action occurs until desired through
applying, for example, a temperature or pressure change. In other
words, the active materials to be reacted are "protected" from
reacting prematurely. Therefore, in one particularly preferred
embodiment of the present invention all "active" species are
provided in an inert medium, but available for use on demand, even
at room temperature.
[0056] As mentioned, one preferred method is to encapsulate such
"active" materials in a protective, colloidal, sphere-like pellet
or ball which, upon being subjected to a specified temperature or
pressure, breaks or ruptures in a predictable way, thus coating the
aluminum component precursor surface substantially uniformly. This
described encapsulation coating technique of the present invention,
also can be used for any catalyst or initiator for any reaction
such as polymerization, crosslinking polymer adhesives, bonding
adhesives to substrates, curing elastomers, or any other reaction
where a room temperature catalyst may be needed, but only on
demand. This above-described technique is versatile enough to be
used with solid, liquid or gaseous materials, including metal salts
or inorganic compounds such as BF.sub.3. In addition, encapsulated
adhesives may be used latently to achieve release, by applying the
encapsulations to the substrate, then later applying the required
pressure or temperature changes needed to liberate the encapsulated
coating contents.
[0057] It is understood then, that the encapsulations or pellets,
applied to either the component substrate or a coating can be
ruptured in any desired fashion, including simply compressing two
components together during or after assembly. Once such pellet
layers "burst" due to compressive or other forces, a desirable,
adhesively-bonded interface is achieved between the components.
Such a bonding process greatly enhances the integrity of the
primary or base coating to the faying surface interfaces of the
structural components, resulting in enhanced corrosion protection
and improved pressure sealing characteristics.
[0058] In addition, according to the present invention, by
obviating the use of a wet-sealant at faying surfaces during
aircraft component assembly and instead "pre-coating" the
components with protective, tack-free coatings, improved tack-free
surfaces are produced. Such surfaces enable the components to be
handled during processing and assembled in an automated manner thus
greatly reducing production cost and cycle time.
[0059] The preferred embodiments of the present invention relate to
the preparation of aluminum-alloy, aircraft structural components
and the following discussion will emphasize such articles. The use
of the invention is not limited to components such as aircraft wing
and fuselage skin panels, hinges, doors, etc., and instead is more
broadly applicable. However, its use in aircraft structural
components offers particular advantages. The procedures of the
present invention in no way inhibit the optimum performance of the
alloy components. To the contrary, the present methods allow the
components to maintain their optimum mechanical and metallurgical
properties while providing equivalent and or improved levels of
corrosion protection and pressurizations without the disadvantages
associated with the wet-sealant approach.
[0060] As used herein, "aluminum-alloy" or "aluminum-base" means
that the alloy has more than 50 percent by weight aluminum but less
than 100 percent by weight of aluminum. Typically, the
aluminum-base alloy has from about 85 to about 98-percent by weight
of aluminum, with the balance being alloying elements, and a minor
amount of impurity. Alloying elements are added in precisely
controlled amounts to predictably modify the properties of the
aluminum alloy. Alloying elements that are added to aluminum in
combination to modify its properties include, for example,
magnesium, copper, and zinc, as well as other elements.
[0061] In one case of interest, the aluminum alloy is
heat-treatable. For aircraft structural components having faying
surfaces such as wing and fuselage skin panels, stiffeners, frames,
doors, hinges, etc., it is preferred that such components would
have their faying surfaces "pre-coated" following the completion of
their normal fabrication cycle but prior to final assembly,
although coating of large sections of aluminum also could be coated
during or after final assembly. The component such as a wing skin
panel or wing skin panel stiffener such as a stringer is first
fabricated to a desired shape. The alloying elements are selected
such that the fabricated shape may be processed to have a
relatively soft state, preferably by heating it to an elevated
temperature for a period of time and thereafter quenching it to a
lower temperature. This process is termed "solution heat-treating"
or "annealing." In the solution heat-treating/annealing process,
solute elements are dissolved into the alloy matrix (i.e.,
solution-treating) and retained in solution by the rapid quenching,
and the matrix itself is simultaneously annealed.
[0062] After the component is solution-treated/annealed, it may be
further processed to increase its strength several fold to have
desired high-strength properties. Such further processing,
typically by a precipitation-hardening/aging process, may be
accomplished either by heating to an elevated temperature for a
period of time (termed artificial-aging) or by holding at room
temperature for a longer period of time (termed natural-aging). In
conventional, Aluminum Association terminology, different
artificial-aging, precipitation heat-treatments (some in
combination with intermediate deformation or cold working), produce
the basic T6, T7, T8, or T9 temper conditions. A natural-aging
precipitation treatment produces the basic T3 or T4 temper
conditions. Aluminum Association terminology for heat-treatments,
alloy types, and the like are understood by those skilled in the
metallurgical field, and will be used herein. Some alloys require
artificial-aging and other alloys may be aged in either fashion.
The treated structural components of the present invention are
commonly made of both types of materials.
[0063] In both types of aging, strengthening occurs as a result of
the formation of second-phase particles, typically termed
precipitates, in the aluminum-alloy matrix. Collectively, all of
the processing steps leading to their strengthening are generally
termed "heat-treating", wherein the component is subjected to one
or more periods of exposure to an elevated temperature for a
duration of time. Heating and cooling rates are selected to aid in
producing the desired final properties. The temperatures, times,
and other parameters required to achieve particular properties are
known to those skilled in the field of aluminum-base alloys and
metallurgy.
[0064] The 7150 alloy is a specific, artificially-aged,
aluminum-base alloy of particular interest for aircraft structural
applications. The 7150 alloy has a composition of about 2.2 percent
by weight copper, about 2.3 percent by weight magnesium, 6.4
percent by weight zinc, about 0.12 percent by weight zirconium and
balance of aluminum plus minor impurities. Other suitable alloys
include, but are not limited to, 2000, 4000, 6000, and 7000 series
heat-treatable aluminum alloys. The 7150 alloy is available
commercially from several aluminum companies, including ALCOA,
Reynolds, and Kaiser.
[0065] After the component is fabricated to the desired shape, the
7150 alloy is fully solution-treated/annealed to have an ultimate
tensile strength of about 42,000 pounds per square inch (psi) and
yield strength of about 24,000 psi with an ultimate elongation of
about 12% or as otherwise required. This state is usually obtained
following the component's fabrication processing including
machining, forging, or otherwise forming the component into the
desired shape. This condition is termed the "untreated state"
herein, as it precedes the final aging/precipitation heat-treatment
cycle required to optimize the strength and other properties of the
material. The component may be subjected to multiple forming
operations and is periodically re-annealed as needed, prior to the
strengthening, precipitation heat-treatment process. After forming
(and optionally re-annealing), the 7150 alloy may be heat-treated
at a temperature of about 250.degree. F. for about 24 hours.
[0066] An alternative two-stage heat treatment may be used. This
treatment is comprised of first heat-treating the component at a
temperature of about 225.degree. F. from about 6 hours to about 8
hours. The temperature is thereafter increased from about
250.degree. F. to about 350.degree. F. for a period from about 6
hours to about 10 hours, followed by an ambient air cool. This
final state of heat-treatment, termed T77511 condition, produces a
strength of from about 82,000 psi to about 89,000 psi in the 7150
alloy, which is suitable for aircraft structural component
applications.
[0067] It is understood that additional, optional steps may be
inserted into the above-described preferred methods. In one
particularly preferred optional step, the component is initially
optionally chemically-etched, grit-blasted or otherwise processed
to roughen its surface, and thereafter anodized in chromic-acid
solution. Chromic-acid solution is available commercially or
prepared by dissolving chromium trioxide in water. The chromic-acid
solution is preferably of a concentration of about 4 percent
chromate in water, and at a temperature of from about 90.degree. F.
to about 100.degree. F. The article or component to be anodized
becomes the anode in the mildly agitated chromic-acid solution at
an applied DC voltage of from about 18 volts to about 22 volts.
Anodizing is preferably continued for from about 30 minutes to
about 40 minutes, but shorter times were also found to be
sufficient. The anodizing operation produces a strongly adherent
oxide surface layer from about 0.0001 inches to about 0.0003 inches
thick on the aluminum-alloy article, which surface layer promotes
the adherence of the subsequently applied first organic
coating.
[0068] The optional anodizing process, preferably in chromic acid,
conducted prior to application of the coating serves to promote
strong chemical and mechanical bonding of the organic coating to
the aluminum-alloy article substrate. The bonding is apparently
promoted both by physical, mechanical interlocking and
chromate-activated, chemical bonding effects. To enhance the
physical, mechanical interlocking effect, the anodized surface is
not chemically-sealed against further water intrusion after the
anodizing process. The subsequently applied and cured organic
coating serves to seal the anodized surface.
[0069] The first coating material described above is preferably
provided in about 100% low-viscosity solid solution or "neat"
material so that it may be readily and evenly applied. The usual
function of the coating material is to protect the base metal to
which it is applied from corrosion, including, for example,
conventional electrolytic corrosion, galvanic corrosion, and stress
corrosion. The first coating material is a formulation primarily
comprising an organic composition, but also may contain additives
to improve the properties of the final coating. The coating may
also be desirably dissolved initially in a carrier liquid and
encapsulated. After application, the coating material is subjected
to an environmental change of temperature and/or pressure to
rupture the encapsulation. The coating is thus released to the
component's substrate surface where it is subsequently cured to
effect structural changes within the organic coating, typically
crosslinking organic molecules to improve the adhesion and cohesion
of the coating.
[0070] A number of curable, organic coating materials are available
and may be used in the present process. A preferred coating
material of this type comprises resin mixed with one or more
plasticizers, other organic components such as
polytetrafluororoethylene, and inorganic additives such as aluminum
powder and/or chromates, such as strontium chromate, barium
chromate, zinc chromate, and the like. One such preferred first
curable organic coating is Hi-Kote F/S1.TM. produced by the
Hi-Shear Corp. (Torrance, Calif.). Alternatively, non-chromated
coatings may be used. These coating materials are preferably
dispersed in a suitable solvent present in an amount to produce a
desired consistency depending upon the application selected. The
solvent may be an ethanol mixture but preferably is an aqueous
medium. Phenolics, urethanes (polyurethanes and ureas), epoxies,
melamines, acrylates, and silicones are representative examples of
the preferred encapsulated adhesives in the second coating. A
preferred second coating is the polyurethane/urea-based HI-Kote
F/S2.TM. produced by the Hi-Shear Corp. (Torrance, Calif.).
[0071] In the preferred embodiments, the base metal of the aircraft
structural component and the applied coating are together heated to
a suitable elevated temperature, to achieve two results
simultaneously. In this single step, the aluminum alloy is
precipitation heat-treated by artificial-aging to its final desired
strength state, and the coating is cured to its desired, final
bonded state. Preferably, the temperature and time for this thermal
treatment is selected to be that required to achieve the desired
properties of the aluminum-alloy, base metal, as provided in the
industry-accepted and proven process standards for that particular
aluminum-base alloy.
[0072] As disclosed herein, the curing of the coating can sustain
larger variations in time and temperature with acceptable results
compared with the heat-treatment of the metal. In accordance with
the present invention, the cured coatings exhibit acceptable
material properties as well as satisfactory adhesion to the
aluminum-alloy substrate and other related properties during
service.
[0073] In the case of the preferred 7150 aluminum-base alloy and
`Hi-Kote F/S` coating representative of those coatings discussed
above, the preferred heat-treatment is the T77511 precipitation
heat-treatment aging process of 7150 alloy 68 hours at 225.degree.
F., followed by a ramping up of from 225.degree. F. to 350.degree.
F., followed by maintaining the temperature at 350.degree. F. for
6-10 hours, with an ambient air cool to room temperature.
[0074] Thus, the precipitation heat-treatment procedure of the
artificially-aged, aluminum-alloy component involves significantly
longer times at different temperatures than is recommended by the
manufacturer for the organic coating. There was initially a concern
that the higher temperatures and longer times, beyond those
required for the standard curing procedure of the coating, would
degrade the coating and its properties during service. However, it
was discovered that the first coating strongly adhered to the base
metal aluminum alloy and was also strongly internally coherent. The
first coating is preferably from about 0.005 to about 0.010 inch
thick after heat-treating.
[0075] The second encapsulated coating, i.e. phenolic, urethane,
melamine, etc., preferably is dispersed in an aqueous medium and
coated onto the substrate. The solvent, preferably water, is
allowed to evaporate leaving behind the particles of encapsulated
coating. The final coating thickness is from about 0.0005 inch to
about 0.0015 inch. The coated component is then ready for assembly
appropriate to its type. In the case of the wing panel, it is
assembled to the various stringers, ribs, spars, etc.
[0076] The installation step reflects one of the advantages of the
present invention. If the coatings were not applied to the
component before assembly, it would be necessary to place a
viscous, wet-sealant material onto the faying surfaces to coat the
contacting surfaces as the mating components are either assembled
or installed. The wet-sealant material is potentially toxic to
workers, messy and difficult to work with, and necessitates
extensive cleanup (of both tools and the exposed surfaces of the
resulting aircraft section) with caustic chemical solutions after
component installation. Moreover, it has been observed that the
presence of residual, wet-sealant inhibits the adhesion of
later-applied paint or other top coats onto the assembled
components. The present coating approach overcomes these problems.
As a result of the present invention, wet-sealant is not needed or
used during installation and consequent assembly.
[0077] Further, it is highly advantageous to apply the protective
fay-surface coating of the present invention to aluminum-alloy,
aircraft structural components to facilitate automated part
assembly and inspection. Since the parts are precoated, there can
be no chance of human error as to the proper treatment of a faying
surface. The present invention further enhances the integrity,
consistency and performance of aircraft faying surfaces, as well as
improving existing part storage, general handling, installation,
and assembly systems. In short, the present invention allows for
the coated components to retain all mechanical and metallurgical
properties, and the required degree of corrosion protection,
without any of the disadvantages of the conventional wet sealant
corrosion treatments.
[0078] Many other modifications and variations of the present
invention are possible to the skilled practitioner in the field in
light of the teachings herein. It is therefore understood that,
within the scope of the claims, the present invention can be
practiced other than as herein specifically described.
* * * * *