Improving aluminum flame spray adhesion on composite?
Improving aluminum flame spray adhesion on composite?
(OP)
Howdy all,
We have had issues with maintaining a good bond between the flame spray aluminum coating used as lightning strike protection on RB211 inlet cowls. The inlet cowl outer panels are carbon fiber and the process is to apply a base coat of an epoxy adhesive, I'm assuming for electrical isolation to prevent galvanic corrosion, then before the adhesive is cured, flame spray the part, then apply a sealing coat of the same epoxy before going to paint. We have had issues where the flame spray just flakes off of the epoxy base coat, showing it has poor adhesion. We don't do the flame spray here so we send it out to be done and I'm trying to learn as much as i can to find and solve the problem.
My questions are:
How much cureing should the epoxy get before begining the flame spray process?
Are there adhesive formulations that work better/worse for this application?
Are there other factors that help/hurt flame spray adhesion?
Thanks for your help.
-Kirby
We have had issues with maintaining a good bond between the flame spray aluminum coating used as lightning strike protection on RB211 inlet cowls. The inlet cowl outer panels are carbon fiber and the process is to apply a base coat of an epoxy adhesive, I'm assuming for electrical isolation to prevent galvanic corrosion, then before the adhesive is cured, flame spray the part, then apply a sealing coat of the same epoxy before going to paint. We have had issues where the flame spray just flakes off of the epoxy base coat, showing it has poor adhesion. We don't do the flame spray here so we send it out to be done and I'm trying to learn as much as i can to find and solve the problem.
My questions are:
How much cureing should the epoxy get before begining the flame spray process?
Are there adhesive formulations that work better/worse for this application?
Are there other factors that help/hurt flame spray adhesion?
Thanks for your help.
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.





RE: Improving aluminum flame spray adhesion on composite?
RE: Improving aluminum flame spray adhesion on composite?
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Improving aluminum flame spray adhesion on composite?
The manual sections that refer to this process are not all unanimous, but one indicates a 6 hour partial cure before flame spraying.
We're trying to follow the process in the RR manual, which is now a Bombardier manual which references the RR materials, processes and other specs. I would think a change of the order you suggest would count as major and need testing to validate how well it protects against lightning. If It was my choice I would go with expanded copper wire mesh adhesively bonded to the CFRP skin. Eliminates galvanic corrosion, provides an excellent conductive path around the periphery of the inlet cowl. But we try and stay as close to the manual as possible.
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.
RE: Improving aluminum flame spray adhesion on composite?
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RE: Improving aluminum flame spray adhesion on composite?
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.
RE: Improving aluminum flame spray adhesion on composite?
Aluminum skins are thick enough that the electrical and thermal conductivity usually results in barely visible surface marks due to lighting strike.
RE: Improving aluminum flame spray adhesion on composite?
Regards
Blakmax
RE: Improving aluminum flame spray adhesion on composite?
There are patents on flame spraying aluminum onto composite substrates here is one, Publication date: 2008-12-18
Patent application number: 20080311374
Check this one out and see if it pertains to the process spec you are using now.
It mentions using glass micro spheres in the resin as an adhesion promoter.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Improving aluminum flame spray adhesion on composite?
I.e., my WAG is that the original process applied the flame spray just after the epoxy reached B-stage, so the molten aluminum was impacting, not on wet runny resin, but on sticky almost-cured resin, such that the first flame sprayed globules penetrated for most of their diameter into sticky resin, and the second pass of flame sprayed globules bonded to those mostly embedded globules.
Maybe you can social-engineer your way to speaking with some of the original crew who figured out how to do it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Improving aluminum flame spray adhesion on composite?
Berkshire, I hadn't thought of doing a patent search, that's a genius idea, I'll check out your suggestion.
MikeHalloran, I think your right about the epoxy being in the b-stage. We've prepared a set of test coupons to see how the cure stage affects adhesion, with and without the peel ply (and I may have them scuff sand and solvent wipe half of the peel play area for a comparison.
Thanks to all for your suggestions.
-Kirby
Kirby Wilkerson
Remember, first define the problem, then solve it.