[TheForge] Stainless steel Forging?

[Ries Niemi]

>
>
> Hi Steve;
>
> A dip in nitric acid will do a quite respectable job of passivating
> stainless. You might also recall, because I think you were there, that 
> when Tony
> Robinson was at Gichners, he essentially passivated the dish he made 
> for Bill
> Gichner by heavy duty buffing it. He used a relatively coarse compound 
> and a 2hp
> buffer. At home I believe he uses about a 5hp buffer and 10" wheel. If 
> it is
> simple hardware, that might work well for you.
>
> Regards
> Don Plummer
>

Dipping in nitric acid is passivating, and will work. Nasty stuff to 
use, and not as quick or even as a combo acid/electrical system like 
the commercial electropolishers use. Plus you got to get rid of the 
stuff when you are done. My electropolisher has a 4'x4'x8 heated tank 
of a mix of phosphoric, sulfuric, and other acids, and a 1000 amp power 
supply, and he will polish a whole 8 foot bench for me in 15 minutes. 
And he has all the hazmat permits, and disposes of the stuff legally 
and safely. But for a little piece, that will fit in a slurpee cup, 
doing it yourself with nitric works great. I am currently working on a 
24 foot tall, 2 foot diameter column with a 3 foot globe on top, and 
three 6 foot benches attached to the bottom. No way I wanna buy enough 
nitric acid to dip that thing in. After that, next month, we make 3 
fence panels each 6 foot by 16 foot, all stainless. And my wife wont 
let me fill the hot tub with acid. So I send it all out to a pro.

Buffing is not passivating. It may work, it may not. I would say it is 
fine for indoor applications, but unless you strip the entire surface, 
like in an acid bath, you may have problems in the future. The phone 
call where they say- " I thought this was stainless steel- how come it 
has rust spots on it?"
Cleanliness when working stainless is pretty important- we start all 
new sanding and grinding discs, stainless wire toothbrushes, and label 
them "SS" before we start. We try to keep tables, saws, etc clean, and 
do not even grind mild steel nearby- flying grinder sparks can get 
embedded in the stainless, then cause rust spots later.
Rust will usually show  up pretty quick in stainless outdoors- a month 
or so. So you can go back and spot touch up if you need - like 
sometimes even steel forklift forks will leave a scratch that rusts, or 
chains used to lift something.

ries