Anodizing Aluminum at Home DIYS

[jibes138]

A quick search

This is the exact same problem I had, the shotpeen pounds iron dust into the surface of the aluminum. Looks like a 50% concentration of Nitric Acid will do the trick for 15 minutes. I'll still check tomorrow but this should work if you need it quick. Be careful working with these chemicals. You need proper ventilation and disposal of waste is also an issue.


January 17, 2008
Hello,

I'm working in a aeronautic company, in the quality department. For some time we have a problem when we have to remove residual iron left on the surface of the aluminum piece after we made shot peening process. Our sequence decontamination of shot peening is to introduce the pieces in a bath of HNO3 50% with agitation for 15 minuts. This sequence, in principle, should be sufficient to eliminate the iron but is not the case. We don't know which may be the causes, contaminatio shot, concentration of inadequate decontamination bath, whether we should have some intermediate step ... In addition we are unable to make any treatment as in the case of aeronautic many restrictions. What are the solutions for our problem ? And where it may be our fault? PLEASE

THANK YOU VERY MUCH

(EXCUSE MY ENGLISH)
SHEILA C.
QUALITY ENGINEER - ITALY





January 28, 2008

Sheila,

50% Nitric acid should be sufficient to decontaminate parts after shot peening. If 15 minutes is not sufficient time then simply extend the immersion time if it is practical to do so.

You may need to look at the analysis of the solution. If the solution is low in nitric acid that will explain why the process has slowed. You may also want to check the level of dissolved iron in the bath. If the bath is too heavily loaded this will prevent further iron from being dissoved. If this is the case the solution is to dump the tank and make up a fresh one.

Finally, check with your shot peeners about what sort of shot they are using and whether nitric acid is a suitable material to use for decontamination.
Brian Terry
Aerospace - Yeovil, Somerset, UK

 

[Timo42]

Have you seen the Caswell site? I have used some of their other stuff. They have the stripper you are looking for. You can get the acid at NAPA, be careful with the waste chemicals though.

 

[jibes138]

Cleaning is the key

I took a look at the process and it seems cleaning is the key. Aluminum has, in addition to the embedded iron, an oxide layer that may make it not susceptible to the process. The process we use to prepare the surface is a pretty aggressive set of steps:
1. Aqueous degreasing
2. Alkaline cleaner with Formost 35ES
3. Aluminum etch with Formost 10-A
4. Cold water rinse
5. Aluminum de-smut with Isopropyl alcohol
6. Final water rinse.
7. Set up by racking to apply the current
8. Run for 1 to 1.5 hours ( I need to get you the solution)
9. Salt seal
This sounds like it is too much to set up at home for a single part. I STRONGLY RECOMMEND YOU USE ALODINE INSTEAD! You will still need to prepare the surface, having good bare aluminum to react is half the battle,

 

[Hermit Scott]

Have you seen the Caswell site? I have used some of their other stuff. They have the stripper you are looking for. You can get the acid at NAPA, be careful with the waste chemicals though.

Tim-I don't know if I told you or not but I finally go that solonoid you gave me installed about a month ago. Starting the engine from the cockpit instead of haveing to go below and open up the engine compartment is quite an improvement. Thanks again.

jibes-one thing all the home diyselfers on the internet had in common is they had a lye solution to clean the al before anodizing. I have some kind of acid solution that foams up immediately, smells like hell and brightens the al immediately. I thought I would be ok with that.
As far as it being more trouble than it's worth, a lot of things I do aren't cost efficient. But I love being able to add a skill to my toolbox. It' worth it to me. Thank you for checking out these things and helping me out.

 

[jibes138]

Chemical Milling of Aluminum

Very strong basic solutions will remove aluminum. We used to chemically mill aluminum using this process, then we switched to machining all over with the advent of high speed machining on 5 axis machines and the increasing intolerance for chemical waste.
I have some other info to share as follows: For type II anodize per Mil A-8625
Immediately after etching and rinsing per previous instructions
1. immerse in 12 - 20% by weight sulphuric acid in water.
2. Apply a potential of 10 to 15 volts to produce an anode current density of 10-15 amps/sq. ft.
3. Treat parts for 20 - 35 minutes.
4. Solution should be 60 - 75 degs. F
5. Agitate the solution during processing
6. Maximum of 12 grams aluminum per liter of solution is allowed.
7. Immediately rinse in clean chloride free cold water and seal by rinsing in 5% solution of potassium dichromate with PH of 5 to 6.0 at a temp of 208 to 212 degs. F for 15 minutes.
8. Dry parts

Like I said this is an extensive set of steps with several different chemicals. I applaud your efforts. I hope these instructions help. I'm sure others have their own recipes, we no longer anodize as it has all been outsourced, so these are old instructions but should work if you can figure out how to do the set up. Chemical processing can be quite lucrative. A guy on my street where I used to live owned a plating plant and once a year a couple more cars would show up, another addition on the house, an iron fence, new swimming pool, etc, etc.