Alodining Question

So I Alumipreped and Alodined in preperation for priming all the horizontal stab parts this evening for the first time. Some of the parts are a pretty dark brown color while some of the others are golden. When I tried to dry off the dark brown parts, lots of the brown stuff wiped off. What do I need to do to these to make them ready for primer? Thanks!

Jay

Don't leave them in the alodine so long. If the're brown, you over-did it. I'd re-scrub them and try again.

PJ
RV-10 #40032

Dangit, I was afraid of that! Oh well, live and learn. Would you recommend scrubbing them with Alumniprep and a scotchbrite pad?

Jay

I'd probably just take some MEK and clean off any residue that is there and then prime. You won't remove the conversion coating made by alodine.
You will notice as you use the alodine that the time to achieve the light brown color gets longer the more you use it - it does get "used up." Early on it takes very little time to adequately treat parts.

T.

DarinFred said:

So I Alumipreped and Alodined in preperation for priming all the horizontal stab parts this evening for the first time. Some of the parts are a pretty dark brown color while some of the others are golden. When I tried to dry off the dark brown parts, lots of the brown stuff wiped off. What do I need to do to these to make them ready for primer? Thanks!

Jay

Click to expand...

I did the same thing with the rear spars on my HS. You definitely left the parts in the solution to long. Remove the excess, clean any contaminates off with a solvent like lacquer thinner or MEK, then prime. If you can't clean the excess off, or you remove all of the Alodine, simply submerge the parts in your AlumiPrep (or similar) and start over.
I found that the best way to remove excess Alodine build up is during the rinse stage after the part is removed from the Alodine tank. By immersing the part in a tank (Coleman coolers, gardening planter boxes or garbage cans work well) of fresh water, you can rub the affected areas with your hand. Make sure you are wearing Latex or Nitrile gloves while doing this. Rub only while the part is submerged in the water. This will safely remove the excess buildup. Several times in the past, I have left parts in the AlumiPrep tank to long. This is evidenced by a grayish or black oxide coating on the non alclad areas of 2024 T-3 parts. The same method described above works well for removing this coating. This is important because the oxide coating will prevent proper bonding of the Alodine to these areas.
I have done this and it has worked fine for me. Hope this helps.

I think there is some bad info. here.

I was trained in chem-filming about 10 years ago by a pretty big aerospace supplier per the old Douglas Spec. (DPS). I'm sure its the exact same as any mil or ANSI spec used today so here goes:

1.) You should not alumiprep for more than 3 minutes, it weakens the metal, so if you already 33'd it don't do it again. I know of a case when someone left the parts in the acid bath for 10 minutes and proceded to the alodine, the parts were sent out for a salt spray test and they failed. You really only need alumi-prep for badly oxidized pcs., if they are already "clean" wash them with bule dawn and call it good.

2.) The dark gold is ok. It sounds like you dipped in full strength alodine which is not recommended but if you limit your dips to 1 minute it should be ok. To prevent wiping away your new coating DO NOT TOUCH THE PART WITH ANYTHING exept the rinse water (rinse well). Then hang to dry for a few hours preferably 24 hours. You don't need to rinse them twice but you can if you want. If you plan to prime and you touched the part and rubbed a little off don't worry about it, just try not to touch the parts.