The Department of Defense (DoD) spends millions of dollars each year utilizing solvent-borne organic coatings on weapon systems. Tremendous risk and cost are associated with the use of chromated primers and topcoats containing volatile organic compounds (VOC) and hazardous air pollutants (HAP). Waterborne coatings, although environmentally benign, still require significant drying time and labor to use. Powder coat painting technologies are available that reduce or eliminate environmental risks since they are applied without the use of solvents. In addition, turnaround times for powder coatings are substantially shorter than for liquid-based coatings. However, these coatings still require periods of time in conventional ovens to cure, which limits the size and amount of components that can take advantage of this technology to the capacities of the ovens. Ultraviolet cure powder coatings (UVCPC) offer a shorter processing time, lower energy alternative to conventional powder coating materials. Also, robotics can be used for the cost-effective, efficient, and repeatable curing of parts of all sizes. The objective of this project is to demonstrate, validate, and implement a UVCPC on DoD depot production hardware.
The UVCPC to be demonstrated is a commercial off-the-shelf product that has been in use since 1998 on pre-assembled electric motors and other temperature-sensitive components. This coating is applied directly to the prepared component substrate, eliminating the need for a chromated primer. The powder is preheated by infrared lamps to melt and flow the coating prior to ultraviolet (UV) illumination. The UVCPC is fully curable in 5-10 seconds under UV illumination. In commercial applications, robots are used to cure UV powders because of better performance, lower costs, flexibility, and operating and energy costs. Robots can position UV lamps as close to the surface as needed and move at any rate of speed to produce a perfectly even cure everywhere on the part surface. A single UV lamp on a robot can replace a large bank of lamps and large ovens. Using a preprogrammed profile, robots provide uniform and repeatable cure. For demonstration purposes, the current liquid-based military specification paints will be used as controls.
Powder coatings result in significant reductions in the use of hazardous materials, including HAPs and VOCs. A reduction in the use of hazardous materials results in minimized worker exposure to VOCs, HAPs, and hexavalent chromium. In particular, application of UVCPCs significantly reduces energy use by not requiring ovens and also decreases turnaround times from days to hours. Because no oven is required, large, bulky, and oversized objects can be powder coated and cured. Only the powder needs to be heated to melting; therefore, the substrate is exposed to less heat for shorter periods of time. Lower temperature, shorter heating/curing times reduce both energy costs and return-to-service times associated with this process. Finally, combining reduced process times with the improved transfer efficiency of powder coatings (up to 90% versus 60% for wet coatings) results in less expense, on a square foot basis, to apply powder coatings. (Anticipated Project Completion - 2012)