Mill scale removal Help

[Avadon]

I have a candlestick base that has a rather complex rose shape made of mild steel. Inside the rose shape is a spire(tower) of wound copper.

I don't have a medial blaster and there is no way I can get the wire wheel inside all those metal rose petals which have intricate and deep folds.

So I guess I need some sort of pickel bath that will strip off that tough scale from forging but also not ruin the copper in the center. I'm guessing I need some sort of pickle bath. I've heard of people using vinegar, but is this strong enough to destroy the bond of steel and scale? and would it eat at the copper? Should I use something like muriatic acid or battery acid instead?

I'd rather do something less castic if possible, but whatever works the best is what I'm going to need to use. I'm going to paint the rose when i'm done.

Thanks

[Frosty]

The problem is going to be electrolysis between the copper and steel in any kind of pickle. The copper will plate the steel.

You might try heating it to a dull red and quenching it in water or perhaps an ultrasonic cleaner.

I'm just guessing though.

Frosty

[Avadon]

Yikes I didn't even think about the elctrolytic factor.

Would vinegar do the same?

[Frosty]

It's an acid isn't it?

I don't think it'd be terribly significant but I'd try some test pieces before committing something I valued.

Frosty

[Awalker]

Put a resist on the copper, wax, grease,etc, then soak in a 50/50 muratic acid and water solution for about 10 minutes.

[irnsrgn]

Automotive paint shop stuff called prepsol, at Automotive parts stores may do the job. its a mild acid. or just plain room temp 7up.

[frogvalley]

I agree with Frosty , I'd do a test in a weak acid, acetic acid 5% would be my choice. Of course I have a 35 gallon tank of it so easier done than said. A vibratory cleaner, with some fine abrasive or shot media might work, you could rig something up with a five gallon bucket or a similar soft container with fine media.

Oh and sometimes, just sometimes, using a very hot torch just playing over the surface of a piece of iron can heat and pop the scale off. Just be sure to heat very quickly and not too long.

I like the idea of a wax resist, though the strength of the muriatic might be a bit much, but I am timid with acid and copper.

Edited January 19, 2009 by frogvalley

[Steve Sells]

Muratic when bought from pool supplies is 30% Hydrochloric acid in a water base. so 50/50 is 15% solution of Hydrochloric. That does seem a bit strong. I prefer the 1/2 vinegar and water solution, slower is safer, and less plating effect from electrolysis.

[Avadon]

Yikes.. hmm.. thank you all for the expert help. This is a candle sculpture piece that i've worked many weeks on. I would put it's lowest value at 1500-2000 (there are two pieces). There is also some leaded areas. I'm not sure if those would react dangerously to muriatic acid? What does lead and muriatic acid do? Anything toxic?

I like the media blastinig but I don't have a hopper. It's a small enough area I could blast it outside. How do you rig up something like that. I have a monster porter cable compressor 175psi so the pressure is no problem. I just don't want to have to buy a sandblaster for 150$ for 5 mins use.

[irnsrgn]

Harbor Freight Tools

$12.99 and $29.99 ones would be ideal

[Avadon]

oooo Most excellent. That is exactly what the doctor ordered! Thank you for the find. I'll give either one of those a shot.

[Ten Hammers]

Abrasive Blasting vs. Soda Blasting For Paint Stripping: tech article

Interesting thread. Had I not read the thread I would not have searched for the link I posted ( which is also an intersting read).

[Avadon]

Cool article Ten Hammers

I made the drive over to harbor freight today and got a handheld 15$ media blaster. All they had was walnut shells of 24grit or the aluminum oxide at 70 grit so I went with the aluminum. But before I try that I tried soaking some steel and some copper in straight distilled vingear. There was no damage to the copper or the steel even after 5 hours so I feel fairly safe dunking the base of the piece. I figure i'll soften up the rust/oxide/scale overnight then tommorow blast it with air/water first and see how that works, anthing left i'll hit with the aluminum media.

As much as I'd love to blow the bank on a media blasting hopper, a computer purchase and then a gas forge purchase are my next big toys. ;D

I'll have pics of these candlesticks up here soon. I think you all will be fairly impressed. Definitely one of the more time consuming and laborious projects i've ever done.

[Avadon]

What is a reasonable soak time to remove soot, rust and millscale in straight distilled vinegar?

(just looking for a benchmark from others)


Can I also add.. how do I remove the left over grey aluminum oxide abrasive residue after i've media blasted the scale off of steel?

I tried Alcohol, Mineral Spirits, Water, and it didn't come off. Is there some other cleaning product that will take it off or do I have to wire wheel it all off? If so that seems kinda silly.. like Ii used the aluminum oxide to get the soot/rust/scale off now do I need another media to get the alumium deposited residue off?

Edited January 20, 2009 by Avadon