|Title of Invention||
A COMPRESSOR HAVING A PROTECTIVE COATING
|Abstract||This invention relates to a compressor having a protective coating disposed on an outside surface of the compressor, the protective coating comprising a sprayed metallic layer (12) disposed on the outside surface of a shell housing of the compressor; and an organic based surface layer (12) disposed on the sprayed metallic layer (12).|
|Full Text||BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates generally to compressors and refers more
particularly to a protective coating that reduces corrosion for a compressor.
Discussion of the Related Art:
The outer shell of most compressors is composed of either a low
carbon hot or cold rolled steel stamping or gray cast iron. The steel or cast
iron, without a corrosion protectant coating, would typically corrode at a fast
rate even in a non-marine environment. For conventional compressor
applications, the outer surface of the compressor body is painted to minimize
corrosion. Corrosion mitigation is important not only to extend the useable life
of the compressor, but also to prevent premature failure of the pressurized
shell which may result in personal injury.
The steel compressor"s outer surface is composed of several stamped
steel components that are assembled together primarily by welding. Welding,
in itself, causes the surface of the steel be even more prone to corrosion due
to several metallurgical factors, two of which are hindering paint adhesion and
forming pinholes. The cast iron compressor version is composed of several
iron castings assembled together by fasteners. In the case of gray cast iron,
corrosion is also prone mainly because of the intrinsic presence of graphite
within the cast iron. Graphite encourages corrosion because of the galvanic
difference between iron and graphite, which causes preferential corrosion of
the iron matrix. Therefore, it is obvious to any expert in the corrosion field
that the aforementioned compressor types are highly likely to corrode,
especially in extreme environments.
The painting process mentioned as the prior art, has the following
sequence of events associated with it"s application: Liquid chemical cleaning of
the steel or iron surface to remove organic and inorganic contamination,
phosphatizing the cleaned surface (creating an iron phosphate layer that aids in
the adhesion of the paint), sealing the phosphated coating (sealing controls the
phosphating reaction and prepares the surface for painting), painting the
compressor (either with a powder electrostatic spraying, dipping or liquid
spraying methods), curing the paint either at room temperature or at elevated
Typically, the painted compressor must pass several standard test
methods to be considered acceptable. ASTMB-117 is one such standard test
method. With the paint quality associated with the prior art, it is conceivable
that the compressor would pass the standard test methods and still have
signs of corrosion of the underlying steel or iron (red rust) visible at localized
regions on the painted surface. For most applications, this sporadic red rust
is normal and would not affect the functionality of the compressor for the life
of the compressor.
However, certain compressor applications require very high reliability
and can not succumb to a corrosion failure without great loss. These stringent
applications require no visible red rust corrosion on the surface for an
extended period of time (as mentioned: despite the fact that it passed ASTM
testing). An example of such an application would be climate controlled
marine containers that are transported across the ocean. Marine
environments are especially corrosion causing because of the presence of
salts and other corrosion enhancing constituents found in seawater. The
"containers" may be exposed to marine mist or even periodically come in
contact with seawater due to splashing. Temperature fluctuations and direct
sun light may also be present (which includes the deleterious effect of
ultraviolet rays). These containers need to be refrigerated uninterrupted for
the entire journey to protect the enclosed cargo. These are high reliability
requiring applications, where failure of the compressor would not be easily
repairable and would result in large monetary damages if the climate control
system ceased to function. This represents an extraordinary challenge
considering the especially corrosion inducing marine environment.
The painting procedure described as the prior art does not have a high
enough corrosion preventative property associated with it. The prior art,
although acceptable for most applications, does not fulfill the requirements of
preventing "no visible red rust" during the life of the compressor. The prior art
has a weakness in that when nicks or dings occur due to, for example,
accidental impact or scratching damage during compressor handling or
preventative maintenance, the paint cracks and exposes bare steel which
then corrodes at an accelerated rate. The prior art paint process serves only
to provide a weak barrier coating. Once this coating is penetrated to the
underlying steel, corrosion immediately occurs. Bare metal exposed in this
manner will corrode quickly because there is no strong "cathodic protection"
provided by the prior art"s paint. This is a weakness of the prior art especially
because of the long hours the compressors are exposed to corrosive
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a
compressor system is provided which is coated with an environmental
protective coating. The coating is comprised of two or three layers, the first
being a sprayed porous metallic layer disposed on the compressor. The
second layer being a organic based surface layer disposed on the sprayed
metallic layer for sealing the metallic layer pores and the optional third layer
being an organic based topcoat finish used for cosmetic reasons as well as to
further enhance corrosion resistance.
The sprayed metallic layer is formed by powder flame spraying, wire flame
spraying, or electric arc spraying. The metallic layer thickness should be between 0.010
to 0.015 inches. The sprayed metallic layer should have a tensile bond adhesion level
of at least 1,000 psi.
Also disclosed is a method of having the steps of treating the surface
of the compressor with an abrasive grit to a suitable finish. After the surface
of the compressor is treated, a metallic coating is thermally sprayed onto the
treated surface of the compressor. A organic-based sealer and an optional
top coat finish are then applied to the metallic coating to seal the pores within
the thermally sprayed layer.
BRIEF DESCRIPTION OF THE/DRAWINGS
Still other advantages of the present invention will become apparent to
those skilled in the art after reading the following specification and by
reference to the drawings in which: Figures 1-3 show parts of the compressor
main body in various stages of the processing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figures 1-3 show the parts of the compressor main body 10 in the
various stages of processing. As can be seen, the spray head 11 from the
thermal sprayer apparatus is shown applying the metallic coating layer 12
onto the surface of the compressor.
The coating system of the present invention provides a strong "barrier"
property because of the sprayed metallic layer 12. The form and composition
of the sprayed metallic layer 12 described herein is ductile and very adherent
to the underlying steel. Therefore, if accidental impact occurs, such as with a
wrench, the aluminum will just dent and smear and still remain basically in
tact and still cover or protect the steel. The sprayed metallic layer 12, of
course, must be thick enough to supply this property.
Moreover, the electrochemical galvanic potential relationship between
the sprayed metallic layer 12 and steel are such that the steel or iron
compressor housing 10 becomes protected even when bare steel or iron
regions are locally exposed to the corrodant. The sprayed metallic, which is
preferably an aluminum coating, is sacrificial to the steel and therefore
protects the steel from corroding. The approximate relationship describing
this is as follows: Service Life in Years=(0.64 x Aluminum Coating Thickness
(micrometers))/Percent Surface Area As Bare Steel.
The first step in the present invention is to clean the outer surfaces of
the compressor body 10 to be coated of all grease, oil or other organic
contamination. An aqueous alkaline cleaning system will suffice. In the case of
gray cast iron an additional step may be needed depending upon condition of
the cast iron surface. Graphite present on the surface of the cast iron may
inhibit adhesion of the metallic coating. A special chemical treatment may be
necessary to remove some or most of the exposed surface graphite. One such
method is known in the industry as Kolene Electrolytic Salt process. It is
understood that there may be other methods that are more economical in the
industry that will serve the same purpose. In certain cases, this graphite
removal step may not be necessary depending upon the quality of the casting
surface and the effectiveness of the grit blasting.
It is preferable that the compressor"s outer surface is first thoroughly
treated by abrasive grit blasting. The blasting must be sufficient enough to
satisfy the surface finish requirements of SSPC SP 5 or NACE #1 "White
Metal". Proper surface preparation by blasting is critical to produce a well
adhering thermally sprayed metallic coating. This roughened surface texture
not only removes surface contamination by exposing fresh steel or iron, but
also serves to mechanically anchor the aluminum coating firmly to the
substrate. Angular hard steel grit of mesh size of about 25-40 can be used, but
the preferred grit media is aluminum oxide with a mesh size of about 16-30. It
is preferred that the indentation that the shot makes on the surface of the steel
ambient air temperature shall be about 5 degrees Fahrenheit minimum above
the dew point.
As shown in Figures 1-3, the incident angle of the metallic spray should
be as close to 90 degrees as possible. The angle should not be less than 45
degrees. It has been shown that coating porosity increases as the incident
angle is reduced below 90 degrees. Distance of the spray gun to compressor
body 10 shall not farther than 8 inches for similar reasoning.
The most preferred composition is pure aluminum (99.9 % minimum purity). The
metal system deposited on the steel may be an aluminum alloy, having less than about
10% magnesium. An alloyed aluminum metal system preferably has less than about 5%
magnesium, which has good corrosion resistance. Aluminum/Zinc alloys should be
avoided in marine corrosion conditions, because they have less corrosion resistance
because of its solubility in salt water. The thickness of the aluminum shall be such that
there is no interconnected porosity from the atmosphere to the base steel or iron
substrate. This condition helps to prevent corrosion of the substrate. To help avoid this
porosity problem, the thickness of aluminum must be about .010 to .015 inch in thickness.
The aluminum coating thickness should be measured with an eddy current, ultrasonic or
magnetic induction type instruments. The tensile bond adhesion strength of the
aluminized coating must be 1000 PSI minimum as checked with the Elcometer Model 106
adhesion tester in accordance with ASTM D 4514. The wire diameter of the aluminum
shall be about .0625 inch. The nozzle gas pressure during aluminizing shall be about 55
The metallic coating can be Powder Flame Sprayed or Wire Flame
Sprayed, but the preferred method is by Electric Arc Wire Spraying. Electric
Arc Wire Spraying exhibits a higher quality coating and is more economical
than flame spraying for this application. Electric Wire Arc Spraying is
performed by contacting two aluminum wires which are at a potential to each
other and generating a melt inducing arc. This arc is in proximity to a forced
gas or air jet. The gas may be an inert gas, but for economic reasons, dry and
cleaned compressed air may be used.
The aluminum wire becomes molten in the vicinity of the arc and the gas
jet atomizes the aluminum and forces the droplets to impinge upon the steel or
iron substrate. The droplets of aluminum impinge upon the steel and build up
layer-by-layer until the desired thickness is achieved. The droplets start to cool
and partially solidify prior to impingement. The kinetic energy of the droplets
cause deformation and flattening of the aluminum particles as they hit the steel
forming a uniform layer of aluminum on the steel or iron surfaces. Because of
the nature of this deposition process, a small amount of porosity forms between
the particles of aluminum. To maximize corrosion resistance, interconnected
porosity (porosity that connects the marine atmosphere with the underlying
ferrous substrate), must not exist. To prevent this, a sufficient amount of
aluminum must be deposited and an adequate sealer must be employed to
block the pores. The coating must be applied in multiple, thin even coatings
and not heavily applied in one spray. It has been found advantageous, for
completeness of coating, to perform spray strokes at 90 degrees from each
other and to allow some overlap for each subsequent spray stroke. The
practical application of this process dictates that it be automated and applied by
a robot or similar technology. This will assure consistency and completeness of
the coating. The grit blasting, described above, shall also be automated for the
same reasons. The complex shape of a compressor makes it difficult to
consistently coat or blast manually. Automation assures that all areas of the
compressor are adequately treated.
After thermal spraying the compressor, a seal coating is applied. The
purpose of a sealing step is to fill any porosity present in the thermally sprayed
metal coating and to further enhance corrosion resistance. If a sealer is used
without a top coat finish, it shall exhibit ultraviolet radiation stability from
exposure to the sun. This step enhances the corrosion resistance of the
metallized coating and increases the useable life of the aluminized compressor.
When only a sealer is used, the sealer also serves to produce a cosmetically
acceptable aluminized compressor. The aluminized compressor must not
exhibit dark blotches, which occur if improperly sealed or if an inadequate
sealer is used.
Several properties of the sealer must be unique to this compressor
application. Therefore a special custom formulated sealer has been invented.
The viscosity of the seal must be low enough so that the coating wicks into the
pores and does not agglomerate on the surface. The thickness of the seal coat
should not be greater than about .002 inch dry film thickness over the top of the
aluminized coating. No moisture should be present on the surface of the
metallized compressor prior to sealing unless the sealer is a water-based type.
If moisture is present, the compressor shall be heated to 250° F to remove
moisture prior to the application of the sealant. Application of the seal coat
should take place within about 24 hours of metallizing for optimal results.
Ultraviolet protection properties should also be incorporated into the seal coat if
no topcoat is used.
In addition, the chosen seal coat type must be such that it will withstand
a constant compressor operating temperature of 300° F. Only certain regions
of the compressor"s surface may reach this magnitude of temperature,
therefore the sealer must not discolor in the heated region and remain
uncolored in the non-heated region so as to produce a two-tone appearance.
After long term exposure to 300 F, the sealant must not degrade it"s corrosion
preventing sealing properties. Moreover, the sealer must retain it"s all of the
stated properties after exposure to normal compressor oils such as; polyol
ester, mineral oils, etc.. Accidental spillage of these oils may occur that exposes
the aluminized and sealed surface to such oils.
The application of the sealant may be by brushing, spraying or dipping
into the sealant. For the same reasons as above, the sealer shall be applied in
a consistent manner that preferably utilizes automation. The curing process for
the sealant should not exceed 300 F as to not damage the internal components
of the compressor due to excessive thermal degradation. The sealant should
coat the compressor uniformly without agglomeration, which exceeds the
required sealer thickness.
There are several chemical families that will meet the aforementioned
requirements. Generally, the customized sealant described herein will have a carrier, an
organic component, and an inorganic component. The first sealer consists of a silicon
resin acrylic sealant containing: parachlorobenzotriflouride, phenyl propyl silicone, mineral
spirits, high solids silicone, acrylic resin and cobalt compounds. Additionally, particulates
such as aluminum and/or silica can be incorporated. The silicon resin coating has good
U.V. stability and is stable at 300°F. Applying two coats of about .001 inch dry film
thickness each has been found to achieve better results than one coat at about .002 inch
Another possible sealant coating is an epoxy polyamide with n-butyl
alcohol, C8.C10 aromatic hydrocarbons, zinc phosphate compounds and
The final coating considered acceptable for this application is a cross-
linked epoxy phenolic with an alkaline curing agent. The adherence and
performance of this sealant shall be enhanced by first applying an aluminum
conversion coating on top of the thermally sprayed aluminum. Two such
conversion coatings known in the industry are Alodine or Iridite. The epoxy
phenolic is then applied over the conversion coating.
Top coat finishes shall be of higher viscosity and similar in nature to
paints. The maximum topcoat thickness shall be about .004 inch. The topcoat
is applied over the sealer. The topcoat shall not be too thick as to negate the
cathodic protective properties of the underlying thermally sprayed coating. For
cosmetic reasons, it is preferable that dark coloring agents such as carbon
black be added to the sealant or top coat to achieve a black or gray color.
Moreover, the topcoat must be compatible with the sealer to maintain good
adhesion. Top coat finishes should not be applied over an un-sealed
The following are topcoat finishes that comply with the cosmetic and
functional requirements setforth herein: The first topcoat finish is a polyurethane
polymer with curing agents containing ethyl acetate, hexamethylene
diisocyanate, homopolymer of HDI, n-butyl acetate and fine aluminum particles.
This sealant also complies with the requirements of this application. The color
of this top coat is gray-black.
Yet another top coat coating is a neutral urethane base acrylic with ethyl benzene,
methyl ketone, xylene, aromatic naphtha, barium sulfate, and 1,2,4 trimethyl benzene and
a polyisocyanate curing agent. The color of this product is black. The final top coat finish
considered is an epoxy polyamide which contains magnesium silicate, titanium dioxide,
black iron oxide, butyl alcohol and naptha. The color of this product is haze gray.
A wide variety of features can be utilized in the various materials
disclosed and described above. The foregoing discussion discloses and
describes a preferred embodiment of the present invention. One skilled in the
art will readily recognize from such discussion, and from the accompanying
drawings that various changes, modifications, and variations can be made
therein without departing from the true spirit and fair scope of the invention.
1. A compressor having a protective coating disposed on an outside surface
of the compressor, the protective coating comprising:
a sprayed metallic layer (12) disposed on the outside surface of a shell
housing of the compressor; and
an organic based surface layer (12) disposed on the sprayed metallic layer
2. The compressor as claimed in claim 1 wherein the sprayed metalic layer
(12) is a flame sprayed layer (12).
3. The compressor as claimed in claim 2 wherein the flame sprayed layer
(12) is a powder flame sprayed layer (12).
4. The compressor as claimed in claim 2 wherein the flame sprayed layer
(12) is a wire flame sprayed layer (12).
5. The compressor as claimed in claim 1 wherein the sprayed metalic layer
(12) is formed by electric arc wire spraying.
6. The compressor as claimed in claim 1 wherein the sprayed metalic layer
(12) comprises aluminum.
7. The compressor as claimed in claim 6 wherein the sprayed metalic layer
(12) additionally comprises magnesium.
8. The compressor as claimed in claim 7 comprising less than 10 percent
9. The compressor as claimed in claim 7 wherein the metallic layer (12)
comprises less than about 5 percent magnesium.
10. The compressor as claimed in claim 6 wherein the metallic layer (12)
comprises more than about 99 percent aluminum.
11. The compressor as claimed in claim 1 wherein the sprayed metaiic layer
(12) has a thickness of between 0.010 to 0.015 micrometers.
12. The compressor as claimed in claim 1 wherein the sprayed metaiic layer
(12) has a tension bond adhesion strength between the compressor and
the sprayed metallic layer (12) of at least 1,000 psf.
13. The compressor as claimed in claim 1 wherein the sprayed metaiic layer
(12) comprises flattened droplets of metal.
14. The compressor as claimed in claim 1 wherein the sprayed metallic layer
(12) is a porous coating.
15. A compressor having a housing vessel win an exterior surface and a
protective coating disposed on the exterior surface, the protective coating
a sprayed aluminum layer (12) disposed on the exterior surface of the
housing vessel; and
an organic surface layer (12) disposed on the sprayed aluminum layer
16. The compressor as claimed in claim 15 wherein the organic surface layer
(12) comprises an epoxy-based carrier, and an organic compound.
17. The compressor as claimed in claim 16 wherein the organic surface layer
(12) additionally comprises inorganic particulate.
18. The compressor as claimed in claim 17 wherein the inorganic particulate
19. The compressor as claimed in claim 15 wherein the organic surface layer
(12) comprises an ultraviolet stabilizer.
20. The compressor as claimed in claim 15 wherein the organic surface layer
(12) can withstand greater than 300.degree. F. exposure wihout
21. The compressor as claimed in claim 15 wherein the organic based surface
layer (12) has a thickness of less than 0.002 inch.
This Invention relates a compressor having a protective coating disposed on
an outside surface of the compressor, the protective coating comprising a
sprayed metallic layer (12) disposed on the outside surface of a shell housing of
the compressor; and an organic based surface layer (12) disposed on the
sprayed metallic layer (12).
|Indian Patent Application Number||706/CAL/2001|
|PG Journal Number||06/2007|
|Date of Filing||21-Dec-2001|
|Name of Patentee||COPELAND CORPORATION|
|Applicant Address||Delaware, United States of America, 1675 W. Campbell Road, Sidney, Ohio 45365-0669.|
|PCT International Classification Number||B23B 15/04,15/16|
|PCT International Application Number||N/A|
|PCT International Filing date|