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I have a question about the alodine process. This was my first attempt at doing this and was wondering if the finish is typically uniform, or it is only uniform if you don't look to closely. From a distance of several feet back (at least with my eyes), or in all the pictures except the close up, the alodined parts seem to have a uniform coating. In the close-up, it is quite obvious the coating varies, is this normal, or should I be figuring out a better procedure ?

Procedure I used:
The first task was to clean the parts in soap and water, I spent about 10 minutes total per rib scrubbing with scotchbrite and then drying.

What I did next was use four tanks, the first of which had the 25% solution of Alumiprep, about an inch deep, enough completely cover any parts. I put the parts in there a few at a time for a total of three minutes while I gently sloshed the fluid back and forth. Half way through I turned the parts over. When the three minutes was up, I moved the parts to a near full tank of clean water and rinsed them each for 15 to 20 seconds before leaving them in the rinse water until all ten ribs were finished with this process.

Once all ten ribs were in the rinse water, I took them to a water supply and thoroughly rinsed the parts under running water returning them to a fresh clean tank of water.

The ribs were then placed a few at a time in the 33% solution of Alodine for another three minutes using the same procedure as with the Alumiprep. Once the three minutes was up, the parts were moved to a fourth tank containing clean water after being dunked in and out of the clean water several times.

Again, once all parts were in the rinse water, it was taken to a water supply and each part rinsed under running water. The parts were than dryed with compressed air.

My guess, if indeed improvement is needed, is that parts need to be cleaned even better, perhaps by scrubbing with the Alumiprep and not just sloshing in the solution, something I was trying to avoid this first time.
The parts all have at least some level of gold/tan finish on them, it just all isn't the same.


Setup as described ready for use


Left to right: Wash tank after alodine, alodine, wash tank after alumiprep


Set of ten ribs after drying with an untreated rib on the right


Close-up of finish on one of the alodined parts

They look a little on the light side as far as coloration goes. I've only got other pictures to compare to because I've never alodyned anything. I'm very interested in were this goes though because I'm going to alodyne my parts too.

svanarts wrote:They look a little on the light side as far as coloration goes.

Thanks, that's the kind of comments I need to help figure this out. The close-up is really washed out from the flash, the one with all the ribs, or even the one with the parts still in the water (left most tank) is more representative of the color. I find it hard to take a picture and put it on a computer screen that represents true color.

I think that the pic of the treated parts next to the untreated looks great. Looks like enough treatment to me ... mine weren't any darker.
Much darker and you start getting problems with overdoing it...

Thomas

What are you going to do for the longer pieces like the spar channels?

svanarts wrote:What are you going to do for the longer pieces like the spar channels?

Either use one of the ideas from another thread http://www.rivetbangers.com/cgi-php/for ... php?t=1006
or build a frame and line it with plastic. I am going to try to stay away from the brush on idea if at all possible. The inside of the skins I'm still undecided, may have to resort to brushing it on as I want to keep the outside surface away from the chemicals. There is also the idea of doing nothing to the skins or just using self etching primer on some or all of the surface. I like to try various things and see what works best for me, then pick something that doesn't go overboard on the time involved, imo of course.

Quite a number of builders around here don't believe in priming much of anything beyond the minimum. I hope to be doing a lot of flying in humid and coastal areas and therefore am going the full priming route with alodine followed by two part epoxy. This whole priming thing is definitely one of those very personal choices that there are as many opinions on as there are builders. There is no right or wrong, just different choices.

Thanks for the reminder! I'd completely forgotten about that. My wife is going to love you guys. I just bought her a FoodSaver from Costco.

Too bad all the bags are already gone and it isn't even out of the box!

I used this method extensively for the spars in the tail. My only recommendation is to be careful with what you are doing, it can be a bit tough to manage at times. I definately lost some alodine using the bags carelessly. A second set of hands can really help out here.

- Spike

I alodined most of the small parts and even the "J" channels under the body skins. I did not alodine any parts that were riveted together because, I'm told, you cannot tell for sure if the protected surfaces have been neutralized in between the assembled parts. Before you get carried away with trying to alodine the inside and outside of the skins, remember that these are mostly 2024-T3 alclad and have a thin protective layer of almost pure aluminum on the surfaces. This in itself acts as a corrosion protection by corroding first and creating a barrier from further corrosion.
I read somwhere that more than 30000 C-172's don't have skin protection other than exterior paint.
Good luck!

acwrench

acwrench wrote:2024-T3 alclad and have a thin protective layer of almost pure aluminum on the surfaces. This in itself acts as a corrosion protection by corroding first and creating a barrier from further corrosion.

Actually, Alclad is a thin layer of pure aluminum, and pure aluminum is highly corrosion resistant. The clad is the corrosion protection. Aluminum alloys are not as corrosion resistant as pure aluminum. Now, if you had another type of metal contacting the clad aluminum such as steel bolts and washers, the aluminum acts as an anode and will corrode faster because you have set yourself up for dissimalar metal corrosion. I chase a lot of corrosion on aircraft at work and am very familar with corrosion on aluminum surfaces.

After a bit of experimentation I settled on the setup pictured to etch and alodine the longer pieces. The chemical bath is nothing more than a wooden frame with a couple of layers of thin plastic draped into the cavity and held from slipping with tape. The wash water tank is a 3x6 foot table turned over (it has a 3 inch lip) and again lined with plastic. Yes it was way after dark and the mosquitos were out for blood, but I was determined to get the rest of my HS pieces alodined.



Yesterday I tried the 2 part expoxy primer spraying thing, I need to work on my spray paint setup and technique, way too think in some places, but 'good enough' for a first attempt. Now maybe I will get to put a few rivets into this project.