Military Powder Finishing Efforts

Posted on Tuesday, September 26, 2017

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