Removal of coatings around thin-walled ligaments or potentially defective structures require a precision tool that does not impact the structure leading to failure. The removal of any metal or damage to the surface must be avoided in these scenarios, which disqualifies highly abrasive removal methods such as blast cleaning and water-jetting. Atmospheric plasma coating removal (APCR) is a precision tool that can remove the layers of the original coating and modify the surface properties of the bare metal surface to promote chemical adhesion by increasing surface energy. Presented in this work will be our results on the removal efficiency of the original coating, change in water contact angle (adhesion promotion) before and after plasma treatment, and the increased adhesion strength shown by standard adhesion tests. Multiple metal surfaces and adhesives will be presented that represent the commonly used materials for naval and infrastructure industries.
This paper details a precision process for removal of coatings and preparation of the metal surface underneath for optimal chemical adhesion without damaging the metal surface or the surface profile. A precision process is required for removal of coatings around corroded surfaces, potentially defective structures, or thin-walled ligaments where abrasive removal procedures will damage the substrate. In these cases, removing metal will worsen or cause a defect where replacement is expensive. A precision tool that can safely remove the coating, allow for inspection, and enhance adhesion for recoating is needed. This type of tool would enhance existing repair technologies and eliminate the immediate need for replacement.
The atmospheric coating removal technology was developed from surface modification plasma technology typically used at vacuum pressures. The atmospheric air plasma is generated using a compressed air source (70-100 psi, 80-100 slm flow rate) and electricity (208-240 volt). Inside the plasma applicator, a pulsed electric field is applied over a small gap distance with high velocity air flowing through it. The plasma is generated in this gap distance and directed through the applicator to a nozzle that concentrates the plasma flow into a beam. This creates a highly reactive environment that is delivered to the substrate for coating removal. Once the plasma is in contact with the coating, the organic components are oxidized, and a significant portion is converted into water vapor and carbon dioxide. This process then blows these molecules away via the compressed air flow and leave behind mostly inorganic pigments and fillers that are able to be collected by a HEPA vacuum. This process can be done both handheld and integrated with robotic platforms for automated coating removal. Shown in Figure 1 below are the APCR system's plasma generator with the handheld applicator and the robotic stage with a mounted plasma applicator.