Removing Pitting with Acid

[Oshie]

I was sitting around the other day and wondering if there was an easier way to get out pitting and rust other then hand sanding.

Has anyone tried Hydrochloric acid.
I don't know how easy it would be to find some, and if it would work. Does anyone have any experience with acid ?


Oshie

[Neil Miller]

I have used it - mainly mixed with nitric acid to form aqua regia to dissolve gold. It is not something to trifle with - the concentrated form can give of a mist that will attack human tissue such as lungs and skin. The mist is not as noticable as that of fuming nitric acid, but is a hazard nevertheless.

I have also used it in a less concentrated form for pickling metal - it removes scale and oxides, but never for removing pitting.

I'm not sure that it would remove pitting, particularly if it attacks the metal in equal proportions - in other words it may eat away metal at the same rate as it deepens the pits. Not what you want.

I'm not too sure how it would react with a steel alloy either - it might have a differential effect on different parts of the alloy and make it porous - again not what you want!

While I don't know definitively whether it would work or not I wouldn't risk it if I was you!

Regards,
Neil

[Mike Blue]

Hydrochloric acid will etch the blade further. You won't see it with the naked eye but you will further pit the blade microscopically. It will lift away any of the loose rust by dissolving the oxides and it makes for a mostly clean surface but it will not removd pitting.

I suggest you also investigate "electrolytic rust removal". There are hundreds of sites on the net devoted to very simple and non toxic electro-chemical rust removal. These processes should not harm the surface by removing metal and they will not do anything about the pitting, but the rust will be gone gone gone. You will still need to apply some sort of rust preventer afterward, but it will look a lot cleaner.

[IanS]

You want a chemical that distinguishes shapes of macroscopic elements. You aren't going to find it. Good old fashioned abrasion is the only way I'm aware of to remove pitting.

[onimaru55]

HCL can cause steel to rust & create a nice antique look. Phosphoric acid will convert red rust to a black color. Neither is a solution to pitting... As above, ya gotta sand like the rest of us

[PhatMan]

Oshie,

I wouldn't recommend using hydrochloric or nitric acids ro remove rust in pitting on straights.

Phosphoric acid based products (Naval jelly etc) have been used as rust 'neutralisers' on steel/iron, as the phosphate passivates the metal surface. I would not recommend these either for straights.

As has been said, abrasion to the bare metal is the way to go

Best of luck !

Have fun !

Best regards

Russ

[gstep51]

Obviously you must be very careful when using acids. The oxidizer that was used in the missile system I worked on in the AF was nitrogen tetroxide or red fuming nitric acid. Concentrations as little as 5 ppm were capable of causing damage to the lungs.

[Oshie]

I would like to thank everyone for all the info.
After hearing your comments, I think I'll stick to sand paper.
It takes some time but it sound like it's really the only option that works.


Oshie

[mackie]

I think the main problem is that the acid would get in the pits and make them deeper.