PreKote placebo?

[Bill Boyd]

Barkeeper's Friend if you can't find Bon Ami, which for some reason is ridiculously scarce around here...

[CubedRoot]

I thought about using PreKote, but ended up just scotchbrite and acetone.

Now though, I am considering doing something a bit different for all these dang wing ribs. I am going to dip my ribs in a tray of alumaprep bath, then rinse, then dip them in an Alodine bath, rinse and then prime.

This is way less time consuming than trying to scrub all those complex areas and ridges on the ribs.

[scsmith]

All good thoughts from everyone on achieving adhesion of the primer, which was never a worry. (although I think the dishwasher detergent is a bad idea).

What I was worried about was getting a good passivation/corrosion protection under the primer. That is what Alodine does, and what Sol Gel does. These are 'chemical conversion coatings' which create a barrier to corrosion.

Why am I worried about this? Because non-alclad 7075 aluminum is vulnerable to "stress-corrosion cracking" and a good passivation coating is important. Fortunately, our 7075 parts are not exposed to the environment much, and are covered in AKZO. So I think they will last a long time.


By the way, another thought. On Simple Green. I have never seen any evidence that regular (green) Simple Green actually attacks aluminum. All I have seen is the aviation (blue) Simple Green says it does not. But that does not really mean the green stuff does. It may be all marketing. I wonder if this is another folk legend like black sharpie pens on aluminum.

Reminds me of the aerosol dried bug remover sold at the auto parts store, that, on the label says that it removes both male and female bugs equally well. Really?

[rv7charlie]

You can find the MSDS for Simple Green here:
https://simplegreen.com/products/all-purpose-cleaner/
I have no dog in that hunt, but it does seem unlikely that Simple Green could do more damage to aluminum than phosphoric acid, as long as it's rinsed off, as is required with the acid. Perhaps the danger is more from it getting between assembled structure, where it can't be completely rinsed away. (Pure speculation...)

On dish detergent: Perhaps the caution is well advised. But when I started building (probably before VAF existed), conventional wisdom was to use Dawn dish soap to degrease parts prior to any anti-corrosion processing. And I can say that washing my small 2024 & 6061 parts in our dishwasher, using my wife's dishwasher detergent (sorry, don't remember the brand) worked great for me. I got perfect etch/alodine on the parts after the dishwasher treatment.

On alodine/painting of interior structure:

A good friend once conducted a test of corrosion resistance of various processes on 2024 test tabs; bare, etch/alodine, various primers, etc. All were wedged in slots in a 2x4, and periodically dipped in a 5 gal bucket of sea water. They were left outdoors about 30 miles from the FL coast, sitting over the open bucket. The alodined sample survived as well as any of the various epoxy, etc coatings. Someone here later published a European scientific study that basically duplicated his observations. My takeaway was that if I alodined interior parts, there was no need to prime them. Saved both money and weight. :-) YMMV, etc.

Charlie

[scsmith]

Originally Posted by CubedRoot

I thought about using PreKote, but ended up just scotchbrite and acetone.

Now though, I am considering doing something a bit different for all these dang wing ribs. I am going to dip my ribs in a tray of alumaprep bath, then rinse, then dip them in an Alodine bath, rinse and then prime.

This is way less time consuming than trying to scrub all those complex areas and ridges on the ribs.

And how are going to dispose of the used Alodine? NASTY STUFF! PLEASE DO NOT POUR IT DOWN THE DRAIN

[scsmith]

Originally Posted by rv7charlie

You can find the MSDS for Simple Green here:
https://simplegreen.com/products/all-purpose-cleaner/
I have no dog in that hunt, but it does seem unlikely that Simple Green could do more damage to aluminum than phosphoric acid, as long as it's rinsed off, as is required with the acid. Perhaps the danger is more from it getting between assembled structure, where it can't be completely rinsed away. (Pure speculation...)

On dish detergent: Perhaps the caution is well advised. But when I started building (probably before VAF existed), conventional wisdom was to use Dawn dish soap to degrease parts prior to any anti-corrosion processing. And I can say that washing my small 2024 & 6061 parts in our dishwasher, using my wife's dishwasher detergent (sorry, don't remember the brand) worked great for me. I got perfect etch/alodine on the parts after the dishwasher treatment.

On alodine/painting of interior structure:

A good friend once conducted a test of corrosion resistance of various processes on 2024 test tabs; bare, etch/alodine, various primers, etc. All were wedged in slots in a 2x4, and periodically dipped in a 5 gal bucket of sea water. They were left outdoors about 30 miles from the FL coast, sitting over the open bucket. The alodined sample survived as well as any of the various epoxy, etc coatings. Someone here later published a European scientific study that basically duplicated his observations. My takeaway was that if I alodined interior parts, there was no need to prime them. Saved both money and weight. :-) YMMV, etc.

Charlie

Yes, I think if you etch/alodine after dishwasher detergent, it will take off the surfactant film.

Dawn dish soap is great.

Alodine is very good treatment, no question. It is just a very bad chemical, toxic to the environment, and I think a lot of folks dump the used and left-over stuff down the drain. Please don't do that. Its hexavalent chromium. It is not something that just goes away.

[CubedRoot]

Originally Posted by scsmith

And how are going to dispose of the used Alodine? NASTY STUFF! PLEASE DO NOT POUR IT DOWN THE DRAIN

Well considering it has a pretty useful shelf life, if kept out of light, I will probably keep it in my locked chemical cabinet until I need it again.

But, if I need to get rid of it (I have 2 quarts on undiluted solution) I'll take it over to a friends shop. He's an A&P and works with it on the regular. A lunch and some adult beverages and he'll let me add my used Alodine into his disposal tanks.

I've read the MSDS on it, and I do take normal precautions when working with it. I use much of the same PPE as I do when I spray AKZO.

[wirejock]

Originally Posted by scsmith

And how are going to dispose of the used Alodine? NASTY STUFF! PLEASE DO NOT POUR IT DOWN THE DRAIN

Here's how I did it. After a few weeks, the water evaporates and very little is left. I take it to the haz mat disposal. You are correct. Nasty stuff. Use protective gear at all times.
https://drive.google.com/file/d/0B7h...ZmVHpSajQ/view

[longline]

what ph were you striving to attain? I understand using dawn as a surfactant.

woody

[vlittle]

Originally Posted by longline

what ph were you striving to attain? I understand using dawn as a surfactant.

woody

I am targeting a pH of around 8.2.