One for the chemists

[Ex-SolentBoy]

If you forget to properly protect a stainless steel screw into aluminium you get a buildup of aluminium oxide, I think.

Is there an easy chemical solution to get rid of it? Easy to brush off the screw, but not so easy to get out of the housing, so hence a request for some sort of liquid to pour in.

 

[Mrnotming]

Oxide build up Aluminium

Whilst you are waiting for a chemical reaction, a thought springs to mind.

Groove a Hex headed s/s machine screw of the same thread pattern (with small mini-hacksaw) in an angled fashion.

Introduce this gradually into the tapped hole and withdraw and clean each time as effort becomes difficult to turn?

So you gradually clean out all the gunge?

Chemical solutions may enlarge the hole too much to use the existing threads again?

Good luck with it!

 

[maby]

Aluminium oxide is pretty inert - difficult to remove with any chemical that will not attack the aluminium even faster. You need to remember that aluminium is a very reactive metal - it's only the oxide layer that covers all aluminium surfaces that protects it from rapid reactions with oxygen in the air. If you manage to remove the excess oxide that has resulted from the interaction with the screw, you will also be removing the "good" oxide layer that is stopping the rest of the metal going up in smoke.

 

[johnalison]

I found out too late that Lewmar instructions tell you to remove all stainless screws into aluminium every year, re-grease and replace.

 

[robertj]

try liberally soaking in vinegar as this is acidic and that's what will attack the oxidisation, leave for a while the wash off.
Keep trying till either the screw breaks free or breaks.

Sulphuric or Hydrochloric Acid will do but extremely aggressive!!


bob

 

[Ex-SolentBoy]

Thanks.

I know all about stopping this happen in the first place. We use Tefgel on everything and never have a problem.

This is on a fitting done by someone else. The screw is out and I was looking for one of those urban chemistry solutions that everyone except me seems to know about.

Mr google wants me to use ammonia, but i think we will just use a dental brush.

 

[maby]

Ammonia is a strong alkali and will work, but it will be quite agressive. Suggest you try it on a piece of scrap aluminium (drinks can?) first to gauge how fast it will act.

 

[electrosys]

Oxalic acid should do it: as stewing rhubarb stems (a natural source of oxalic acid) in a dirty old ally pan is a sure-fire way of cleaning it up back to bright metal. It won't stay that bright for long, of course ...

And - if you should ever want to extract large amounts of oxalic acid - rather than stems, use rhubarb leaves, where there is a much higher concentration of the acid.

 

[Oldhairy]

Very strong black tea will soften the oxide, sometimes sufficiently to do the job.