Coatings Technology

The Coatings Technology Branch of the Mercer Engineering Research Center (MERC) has researched, developed, and tested several systems for applying and removing coatings.

This combination was chosen after a study of the requirements that a coating would have to have to meet to enhance the life of the blade and the process requirements demanded by the customer. The driving process requirements were: maximum process temperature of 190° F, not affect the base material's mechanical properties (fatigue, tensile, etc.), and the process should already be industrialized. The coating system needed to be harder than silca, since it was determined that the main cause of erosion was from sand impact during landing operations on rough field conditions.

The hard anodize outer layer has Rc 65, which is harder than silica. Unfortunately, hard anodize has a detrimental affect on the substrate to which it is plated. MERC engineers then proposed an intermediate coating of pure aluminum to act as a buffer between the hard top coat of anodize and the 7076T6 substrate material.

Robotic Paint Application
MERC designed a paint proportioning system to be used in conjunction with the F-15 Safari robot. The system was designed to be adaptable for use with the robot or used manually for breakdown or touch up work. The system included a paint kitchen, piping, a paint proportioning system, a flow control computer, and a delivery system. The system handled epoxy primer and three colors of urethane top coat.

Stripping/Cleaning With C02 Pellets
MERC has acquired a vast wealth of experience on cleaning parts and /or stripping paint using CO2.

MERC conducted a study on the feasibility of using the CO2 cleaning system operated by the AF to clean parts from a large carrier airplane. The AF uses solid CO2 pellets as an abrasive media, propelled by compressed air to mechanically remove material coatings. After striking the surface of the part to be cleaned, the CO2 pellets sublimate, leaving only the coating residue. Because of this advantage over other cleaning mediums, CO2 blasting offers an environmentally benign alternative for cleaning both C-130 propellers and pump housing.

MERC also evaluated and enhanced the AF's current CO2 pellet blasting delivery process to provide a uniform pellet distribution to the paint surface. An evaluation was performed on the blasting pellet from formation through delivery. This information was used to improve the delivery process to ensure a uniform and consistent pellets were available to the nozzle. Computer simulations and analysis of various nozzle designs were performed to achieve the necessary flow parameters. With this information, the nozzle was enhanced to allow the acceleration of the pellets to blasting speeds while maintaining the desired pellet consistency and uniform distribution.

Finally, MERC was tasked to integrate and implement the technological operation and capability of the SwRI robots and CO2 paint stripping system at WR-ALC in the F-15 paint booth. Included were enhancements to the CO2 paint removal system, such as increasing stripping speeds and eliminating material damage, modifications to the control room and completion of material testing on F-15 skins. Additional enhancements included optimized pellet delivery to the aircraft surface. Also, the Xenon flashlamp (FlashJet) was integrated into the CO2 paint removal system to allow removal of paint from composite and thin skin surfaces.