16 November 2013

Wings: Aileron actuation. Priming and flash rust.

Learned a new term on this round:  "Flash rust".  The aileron pushrods and torque tubes are composed of steel.  Most of it is powder coated from the factory, however the tubes' interiors are not.  So they must be primed.  I dutifully used my Stuart System's primer.  The next morning, I went to check how it was drying and found this (view looking inside one of the tubes):


And this:


In fact, every piece rusted where the primer was applied.  Turns out, this is called "flash rust" and is due to the water-based nature of the primer, even though the primer is specified for steel.  As soon as I saw this, I knew I was in for a good solid several hours of work as part of a remedial effort.   How to do that?  A bag of steel wool and a 12 gauge rod of steel clamped down in the vice was mostly the ticket.  I stuffed the steel wool very tightly into the tubes, then worked it back-and-forth until most of the primer and rust were out.  Then I used the rat-tail file, added some acetone with the steel wool once more and finally used a flap wheel on the drill to effectively sand the insides down. 


Eventually, I worked all the primer and rust out after some 5+ hours.  I reprimed with Napa 7220.  Not a water-based primer.  No flash rusting occurred.

So, that was fun.

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