The finishing needs of the defense market continue to
advance and change. This includes the evolution of powder
coatings, which must address the following requirements:
- Survivability of the warfighter
- Outstanding durability
- Excellent corrosion resistance
- Exceptional performance
- Green initiatives that focus on lowering VOCs and
HAPs, plus the ability to reuse overspray
The first point is the most important: securing the safety and
welfare of U.S. military personnel worldwide by keeping military
assets ready and available. But the potential loss of critical assets
and sophisticated pieces of military equipment also carries a
substantial monetary cost.
A July 11, 2017, report from Bloomberg Government
entitled “Rust Never Sleeps” notes that corrosion costs the U.S.
Department of Defense (DoD) approximately $20 billion per
year, or about 20 percent of the dollars spent on maintenance
of equipment, weapon systems and facilities through the DoD’s
Office of Corrosion Control. The report notes that the House
of Representatives has, through its latest version of the fiscal
2018 National Defense Authorization Act, stepped up its efforts
to reduce corrosion and in turn save DoD dollars. The effort
would end the DoD’s Office of Corrosion Control’s statutory role
and designate civilian program managers as service Corrosion
Control and Prevention Executives (CCPEs). The CCPEs would
have broad roles that include annual budgeting justifications
regarding corrosion, and the prevention and mitigation thereof.
In addition to meeting the remaining criteria extremely
well, powder coatings offer durability and corrosion resistance
through higher film builds.
Powder Coating’s Role in Fighting
Military Corrosion
The use of powder coatings as the finish of choice across a
multitude of industries continues to trend upward. It only makes
sense that the technology’s role in military applications will
continue to expand significantly.
Key advantages over liquid coatings include providing one
of the most durable and economic finishes attainable today. The
use of powder coatings offers a solvent-free finishing technique
that can help reduce overall line costs and ease cleanup. Powder
coatings also help finishers achieve their sustainability efforts,
as they have very low to virtually zero VOCs and contain no
heavy metals. More than 95 percent of overspray may be reused,
reducing the amount of waste that goes into landfills. Product
waste that must be discarded can generally be disposed of in
conventional landfills (applicable regulations should be checked
for proper disposal methods). Powders coatings provide a defi-
nite advantage in coating difficult-to-coat components with odd
shapes or sharp edges. Proper application techniques can help
with the Faraday cage effect, allowing better powder penetration
into internal corners or nooks.
Potential cost advantages for powder coatings vs. liquid
coatings include the fact that a finisher may realize lower
insurance premiums, as powder coatings contain no flammable
solvents. Cubic feet per minute costs are potentially lower for
both ovens and air make-up, and booth air is fully exhaustible
to the plant, thus eliminating the need for external exhaust
systems.
While there are advantages to powder coatings, there are
also issues that must be understood and addressed to successfully
utilize powder coatings.
A finisher considering entering the realm of military powder
coatings will be best served by a supplier with a proven track
record that exhibits prior experience and know-how.
Proper spray techniques, line maintenance, pretreatment
and powder storage are among the keys to ensuring the effi-
ciency and efficacy of any powder coating process. Falling into
bad habits can occur all too easily and often goes unnoticed but
can result in efficiency losses and quality issues. Every powder
coating is manufactured to a particular particle size range,
which needs to be maintained to deliver a proper coating thickness,
finish quality and transfer efficiency.
Powder coatings are still evolving as a technology, but have
progressed to the point where the DoD has developed specifications
for its use on military equipment.
Defense and Powder Coatings
Although the defense market has seen intermittent use of
powder coatings since the late 1980s, these technologies have
been secondary to liquid coatings. However, with the issuance
and upgrades of military specifications by both the Army
Research Laboratory (ARL) and Naval Sea Systems Command
(NavSea), powder coatings applications have increased exponentially.
NavSea issued the first military specification focused on
powder in 1989. The first MIL powder spec, MIL-PRF-24712A,
was created for the use of powder coatings on naval assets,
but carried no qualification. The spec was revised in 2014
(MIL-PRF-24712B), and covers thermosetting powder coatings
in non-immersion service for both interior and exterior environments.
The revision provides an opportunity for finishers, who
choose not to install an E-Coat line, to use powder coatings as
an alternative for corrosion protection.
Examples of powder coated naval assets include shipboard
metallic equipment and furniture, electrical enclosures and
miscellaneous metal parts.
The current Naval spec includes four types of
powder coatings:
- Type I: Epoxy resin, without zinc
- Type II: Epoxy resin, zinc-rich
- Type III: Triglycidyl isocyanurate (TGIC) polyester
- Type IV: Hybrid of these resin systems
- Class 1: Exterior, first coat of a two-coat system
- Class 2: Exterior, topcoat of a two-coat system
- Class 3: Exterior, single-coat system
- Class 4: Interior, single-coat system
Today, virtually every Naval shipyard is equipped for powder
coating application. The Norfolk Naval Shipyard’s Regional
Repair Center—closed in the 1990s but recently reopened after
a significant investment—is now equipped to perform maintenance
powder coating. And, the newest naval vessel—the USS
Gerald Ford, the world’s most advanced aircraft carrier—carries
more powder coated parts than any other ship in the fleet.
For the Army and Marine Corps, the MIL-PRF-32348 specification
(part of the overall Chemical Agent Resistant Coating,
or CARC, spec MIL-DTL-53072) was released in 2010. Several
years in development, the spec provided formal approval for the
use of powder coatings on military tactical equipment. Maintained
by the ARL, this MIL spec includes four types:
- Type I: For use as a primer with CARC finish coatings
- Type II: For use as a primer with no finish coating (interior
use only)
- Type III: For use as a camouflage, CARC finish coating
- Type IV: For use as an ammunition container, CARC
finish coating
- Class 1: No maximum temperature of substrate
during cure
- Class 2: Maximum temperature 350 degrees F of
substrate during cure
The MIL-PRF-32348 specification carries stringent
requirements for military equipment for corrosion resistance,
flexibility and weathering. The Type III coating has strictly
defined mandates in that the technology must possess the
CARC characteristics for ease of decontamination upon
exposure to chemical warfare agents (CWA). It also must
provide superior camouflage properties for possession of
a defined infrared (IR) signature, derived from specific
pigments, thus reducing visibility of coated equipment to
enemy forces.
Since an initiative funded through the Strategic Environmental
Research and Development Program (SERDP) was funded
in 2012, CARC powder topcoat systems have been successfully
developed, have gone through field trials, and are approved
and commercially available for use on a wide variety of military
equipment and vehicles. There are currently three approved
manufacturers producing CARC powder coatings that meet the
Type III criteria.
The newest military specification, one designed to work
in conjunction with the CARC system, as well as others, is
MIL-PRF-32550. This specification provides guidelines for metalrich
powder coating primers for corrosion protection of abrasive-blasted
steel substrates in conjunction with CARC powder
coating finish coats (see Type III below). Metal-rich zinc epoxy
primer technologies have been in use for several years, but the
specification was not formalized until August 2016. It includes:
- Type I: Organic metal-rich primer; may be formulated as
a two component epoxy or single component moisture
cured polyurethane.
- Class S: Maximum VOC 3.5
- Class L: Maximum VOC 2.8
- Class U: Maximum VOC 2.1
- Type II: Inorganic metal-rich primer
- Type III: Metal-rich powder primer
- Form A: Zinc-rich pigment based
- Form B: Aluminum-rich pigment based
- Form C: Mixed metal-rich pigment based
where the primary pigment is something
other than zinc or aluminum
There are currently two coatings manufacturers that have
been approved to produce metal-rich powder primers under this
specification.
Challenges Exist, but So Do Opportunities
Successful military powder coating finishers understand
that several challenges exist. There is a cost of entry in terms of
knowledge, finishing techniques, equipment and acceptance of
the fact that these are emerging technologies; specifications may
change over time, and the finisher must remain vigilant in keeping
up with these changes.
Becoming familiar with MIL-DTL-53072 is the first step.
The specification and qualified suppliers can be found at this
website: http://quicksearch.dla.mil. Historical versions of the
spec are also located there to provide full background.
Tier 1 and Tier 2 fabricators should include an in-house
finishing and processing system, along with a thorough understanding
of how any system specification addresses powder
requirements. The OEM may require process approval before
awarding a contract. Once a contract is awarded, a fabricator
should expect the potential for audits on a regular basis.
Non-fabricators that have fabricator customers producing
parts for the defense business also have an opportunity, but again,
it is important to be familiar with the MIL-DTL-53072 specifi-
cation. For example, specific information on key areas such as
pretreatment requirements and cleaning/preparation go above
and beyond what may be considered “normal.” The spec is very
clear in its definition.
Opportunities are regularly publicized at fbo.gov (Federal
Business Opportunities, or FedBizOpps)—a single point of entry
for federal government procurement regarding projects in excess
of $25,000.
Finally, working with a coatings manufacturer that is both
familiar with and currently manufacturing products to meet these
MIL specifications across the board is a major advantage in delivering
finished goods to protect our most important asset—the
men and women of the U.S. military who protect us every day.
Dr. Beth Ann Pearson is global product manager—general industrial
at Sherwin-Williams. She can be reached via email at
beth.a.pearson@sherwin.com