The aerospace industry knows it must meet high specs to create an aircraft that is safe, reliable, and resilient. As aluminum and titanium materials are more often replaced with stronger, lightweight composites, which require adhesive bonds, knowing that bond will stick is pivotal. The strength and success of that adhesive bond depends on properly preparing the composite surface.
BTG Labs boasts a long-term relationship with the aerospace industry. When the need to create reliable adhesive bonds, BTG Labs received an SBIR (Small Business Innovation Research) to collaborate with the USAF. This led to the development of the Surface Analyst™. Using water contact angle measurements--a proven way to predict adhesion in aircrafts--the Surface Analyst is the first hand held surface energy measurement device to accurately and precisely measure surface energy in the aerospace industry. The Surface Analyst also played a major role in the development of the F-35 Joint Strike Fighter. BTG Labs continues to contribute to the aerospace industry as more applications arise. In two seconds, the Surface Analyst determines a surface’s readiness to bond successfully in a fast, easy, accurate, non-destructive, and quantifiable way.
- Surface cleanliness for composite adhesive bonding and repair
- Successful adhesion of aircraft mechanical fasteners
- Bonded repairs of wings, fuselages, helicopter rotor blades
- Metal cleanliness prior to brazing, welding, and heat treating
- Appropriate surface preparation processes
- Parameters for surface treatments
- Surface preparation techniques to train technicians
- Surface preparation processes such as solvent wiping, grit-blasting, pneumatic and hand sanding, and plasma treatment
- Surface energy post surface treatments
- And quantify surface preparation to ensure consistency and repeatability
- Bonding processes
An engineer from a top aircraft manufacturer specializing in major defense applications was teaching mechanics how to use the Surface Analyst to verify clean surfaces during their assembly process. Their surface preparation process included three steps: solvent wipe, hand abrasion, and a different solvent wipe. After these steps, the engineer measured the composite panel surface using the Surface Analyst. The contact angle was embarrassingly high, at 70°. In a typical preparation process situation, the higher the contact angle, the less reactive, or "dirty" the surface is. The lower the contact angle, the more reactive, or "clean" the surface is. These measurements indicate surface preparedness prior to bonding.
Needless to say, this measurement tilted a few heads. Their surface showed a more contaminated after the specified preparation process than before! When and where in the process was this happening?
This is where the Surface Analyst came in to break the process down. The original contact angle taken prior to any surface treatment read 70°. After the first solvent wipe, the contact angle read 50°. After the hand abrasion, 30°. So far, so good. But, after the final step of the solvent wipe, the contact angle hit the roof, reading higher than the original angle of 70°.
This led them to investigate the solvent itself, which was stored in an opaque container. The team poured the solvent into a clear beaker, surprised to find the cleaner was a charcoal color, rather than clear. It was then, that the team explained to the engineer that they first used the solvent to soak other parts. Secondly, they poured it into a container to be reused in the surface bonding preparation process.
The Surface Analyst revealed that the manufacturer was using an extremely contaminated solvent to "clean" their surfaces. While the coloring of this solvent is obvious contamination, a solvent can be quickly contaminated and may lose its integrity well before showing physical proof. But, with in-place verification procedures with the Surface Analyst, the quality of a solvent would never need to be left for guess work.