airguy

airguy

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I took my first crack at alodining this evening, I wanted to throw a photo on here and see what the general consensus is - I think it appears very similar to other alodined pieces I've seen on other builders site, but since I haven't done this before I really don't know what to look for either. These are the angle attach brackets for the HS and the rudder control horn, those are the only non-alclad parts on the 9A empennage. All parts will get AKZO before assembly, but I wanted to alodine the non-alclad parts before AKZO.

My prep was maroon scotchbrite, soap and water, wipe down with laquer thinner, then immersion in 5:1 dilution alumiprep 33, rinse/dry, immersion in 3:1 alodine solutions, rinse/dry. The parts were still damp when I shot the photo so you can see a little water shine on them.

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Looks ok but I think you could cut your time down by quite a bit by just using the scotchbrite with the etch then rinsing and then putting the pieces into full strength alodine.(and of course rinsing after the conversion) This is how I have been taught (by guys who have worked on airplanes longer than I am alive) and how I have done it with good results.
 
Looks good

Looks good to me. Watch out that the color doesn't get too dark. That indicates too long in the Alodine and results in a chalky surface that you'll have to scotch-brite before priming. Based on the color in your photo, you might be getting close to that point on the angle attach brackets.

Also, I would suggest hanging the alodined parts by a wire through a rivet hole to dry. The freshly-alodined surface must dry completely before touching it or else the alodined finish gets partially rubbed off.

In response to previous post, the method of scotchbriting with the acid etch does save some time, but makes a mess and wastes the acid etch. If you scotchbrite and then clean before dipping in acid, the acid etch solution can be re-used for a very long time.

Bill Swatling
RV-7 Fuselage
Acid etching and dipping in Alodine with three 55-gallon tanks
 
Greg
Well done. Your parts look good. The others who have responded have all given good advice. I do not believe that any of your parts are "to dark". When the parts are brown, they are to dark.
It is possible to leave the parts in both the etch or the Alodine for to long. (Ask me how I know this!) Parts left in the etch to long will turn gray. On the Alclad parts, this happens on the raw edges and holes. As mentioned above, the Alodined (or Iridited) parts are brown. It is possible to fix these problems immediately, without starting over. The trick is to submerge the affected part in your rinse water tank before allowing it to dry. With latex or nitrile gloves on your hands, simply rub the gray or brown off of the part as needed, and continue.
As mentioned earlier by another lister, do not wait to dry the parts coming out of the etch solution. Rinse them immediately. Once out of the rinse tank, place them into the Alodine tank before allowing them to dry. This will prevent problems and reduces your work load.
6061-T6 parts take from 2 to 4 times as long to turn gold, when compared to Alclad 2024-T3 parts. I've always used the Alodine full strength. Diluting it increases the submergion time required. However, if your Alodine quantities are limited, dilution is permisible.
Please store your Alodine in a cool, dark area. I store my Alodine in 5 gallon paint buckets with sealed tops. I place these buckets under my work bench at the rear of my shop (away from the doors and sun light)
If you do your Alodining outside in the sunlight, you will have ruined the Alodine, as it is photochemically reactive. That's a fancy way to say that the sun light ruins it. Do your Alodining in the garage, with the overhead door open to allow good ventilation.
Good luck with your project.
Charlie Kuss
 
Thanks for the practical use and storage tips. I bought a gallon each of the Alumiprep and Alodine, I have no problems running them full strength, I was simply following the printed directions I had received from some unknown source way back in the cobwebs. I currently have my (clear plastic) gallon jugs sitting in my workshop away from sunlight but in full view of my UV-producing flourescent shop lights, so I'll have to move them to a darker location.

When running full-strength alodine, how long do you keep your parts in? I left these in the diluted solution (about 3:1) for about 3 minutes, I'm thinking straight alodine would probably be good at a minute to a minute and a half. I thought about suspending them in the solution with a wire or string, but wasn't sure about whether I would get a good coating on the portion where the wire contacted the part, so I just dumped them into the solution and stirred the parts around a bit with a scrap piece.
 
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Seems to me that Scotchbrite and acid etch are just a duplication of effort. The Scotchbrite mechanically etches the parts while the acid does it chemically. In other words, skip one or the other.

My IA, who does museum work and has produced some impressive award winners, says on interior parts, just use an etch (he uses Scotchbrite), clean with acetone or lacquer thinner and prime. And since the value of priming interior parts is debatable (see 10,000+ posts on the topic), it doesn't seem like you are giving up much to save some time and effort and skip the alodine. Of course if you are going to fly off saltwater, these comments should be ignored.
 
Etch alone will not give great results. The alodine will be a little spotty. A little rubbing with scotchbrite and etch will makes things more even.
 
I have often wondered about all this. I assume etching chemically produces very tiny pits, whereas scotchbriting produces much deeper and wider scratches. When the alodine gets in the pits it produces one type of visual effect, while alodine in scratches produces a more visible effect. Are there any knowledgeable chemists here who could tell me if any of this is really a good indicator of how well the alodine has been applied?
 
Alodine thingys

First wear vinyl gloves, clean the parts with Acetone or lacquer thinner then wash the parts thoroughly with soap and water (I use tide), if you touch them with your bare hand you will more than likely get blotches. Rinse them, then submerse them in etch at 3/1, for a minute, Rinse them with water, let them dry completely. Then submerse them in 100% alodine for 45 sec to 1min, max, I try not to touch any surface when removing them from the alodine, I use a hook through a hole (ie). Rinse with water, and don?t touch until dry.

Let me know how it works for you.

Randy
 
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