ESTCP Principal Investigators replace current coating removal methods that use methylene chloride, a hazardous and potentially carcinogenic chemical, with safe and environmentally friendly alternatives.
By Tracy G. Mallard, Ed.D.
Wheel before de-painting
An ESTCP technology that could eliminate worker exposure to potentially cancerous chemicals and divert nearly 32,000 pounds of hazardous waste disposal per year started with a series of “what ifs.”
In 2018, Michael Froning, Technical Director for Product Support Engineering at the Air Force Life Cycle Management Center, and his colleagues at IBC Materials and Technologies (IBC) and the University of Dayton Research Institute (UDRI) started investigating new technologies to remove protective paint coatings from wheels and other aircraft components without the use of hazardous chemicals or plastic media blasting (PMB). They wondered, “what if we used electricity instead of chemicals and PMB to remove coatings?” This initial curiosity kicked off the innovation process for replacing current methods. The team first tried to immerse aircraft wheels in an electrolytic water bath where high energy electrical impulses were applied. The results showed the surface coating was removed without affecting the underlying material and without the use of harsh chemicals. However, this process was energy and time intensive to complete.
Dissatisfied with initial results at the de-painting process, Froning and his team then asked, “what if we soaked the wheel in hot water before the electrolytic bath to shorten the time it takes to remove the coating?” The pre-soak aided removal, but still did not adequately reduce the time to complete.
Wheel after ultrasonication de-paint
Finally, the team asked, “what if we added vibration and an environmentally friendly chemical additive to the presoak?" They discovered the pretreatment followed by a high pressure water rinse completely removed the coating. This environmentally friendly process, now named the ultrasonically activated de-paint system (UADP), eliminated the need to use hazardous chemicals and large amounts of plastic media.
Coating removal is a common process across the Air Force during repair and maintenance processes, often helping to reveal any damage caused to aircraft parts. It is one process among many that ensures airworthiness (an aircraft’s fitness for a safe flight), which governs aviation safety standards. Expanding beyond each aircraft tested, Froning connects every wheel and component inspected to the Air Force’s Total Force vision where all Airmen work to support all aspects of airpower, including airworthiness.
“Airworthiness is a big deal. We have to understand we aren’t going to endanger a pilot or endanger an aircraft or have something catastrophic happen unexpectedly,” said Froning. “Understanding and being able to predict the life of a part and knowing that any process you do to it isn’t going to end up with an unforeseen failure is huge.” Thus, Froning and his team constantly test and iterate to perfect their processes, inspired by the greater mission to defend the country.
Protective coatings are used to protect aircraft parts, like wheels, from wear and corrosion. However, the inspection and maintenance of most components require de-painting. As a part of routine inspection, aircraft wheels are evaluated at pre-determined intervals. The protective coatings on the wheels are removed to reveal cracking or other damage to the parts. Once the wheel passes inspection, it is then repainted. This process is largely conducted at the Air Force’s depot maintenance installations, and wheel de-painting occurs mostly at Hill Air Force Base in Utah.
Fully de-painted wheel
The current process for de-painting involves dipping the wheel in a large paint stripper bath made of methylene chloride. Methylene chloride is considered hazardous, and likely carcinogenic by multiple chemical regulatory bodies. This chemical bath starts the de-painting process by loosening the coating. The wheel must then be blasted with plastic pellets to remove all coatings. The plastic media mixes in with the discarded paint, causing the pellets to also become hazardous waste. About 25 wheels are de-painted and inspected each day at Hill Air Force Base, resulting in the generation of roughly 36,000 pounds of hazardous waste each year at this site alone.
The Air Force, Army, and Navy have expedited their search for safe, effective, and efficient ways to remove coatings from aircraft and other military parts during maintenance and inspection. They have eliminated most uses of methylene chloride; however, the remaining uses are mission critical, and have no other substitutes available. Because of safety concerns, workers who currently use methylene chloride must be outfitted in personal protective equipment (PPE), including gloves, safety glasses, and respirators. The Air Force uses the largest amount of methylene chloride out of all the services, primarily for paint stripping during aircraft inspection.
Project Team (starting at top right, counterclockwise around table: Michael Froning, AFLCMC, PI; Solomon Berman, IBC; David Frederick, AFMC; Paul Jarosz, IBC; Gajanan Kulkarni, IBC). The table shows an assortment of parts that have had coatings successfully removed, including various wheel types and other small complex parts.
Froning and his team have successfully demonstrated that UADP works as effectively to remove protecting coatings from aircraft wheels as the current paint stripping bath that uses methylene chloride. At time of writing, UADP has only been tested at the vendor, IBC in Lebanon, Indiana, but a pilot line was recently commissioned at the Air Force Life Cycle Management Center Advanced Technology and Training Center, located adjacent to Robins Air Force Base. This replacement is estimated to reduce the amount of hazardous waste related to wheel de-painting entering the environment by up to 90%.
In the future, the team intends to continue testing their process at other Air Force bases and on other military components, with hopes of scaling across the DoD. If the project successfully scales to the potential imagined by its creators, 32,000 pounds of waste diverted will be a vast underestimate of its environmental impact. Not to mention, UADP eliminates worker exposure to harsh chemicals, nearly eliminates the need for PPE, and decreases both time and cost to complete the process.
The project team was recognized at the 2022 SERDP and ESTCP Symposium for their dedication to the Air Force mission, while also protecting the people who are committed to achieving airworthiness and protecting the environment. UADP provides a safe substitute to paint stripping using methylene chloride and could radically change the aviation standards in the coating removal process.
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About SERDP & ESTCP
The Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP) harness the latest science and technology to improve the Department of Defense’s environmental performance, reduce costs, and enhance and sustain mission capabilities. The programs respond to energy and environmental technology requirements across the military services. SERDP and ESTCP are independent DoD programs managed jointly to coordinate the full spectrum of research and development efforts, from the laboratory to field demonstration and validation. For more information, visit https://www.serdp-estcp.org. Follow us on Twitter, Facebook, and LinkedIn.
