Vinegar for Mill Scale Removal

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SteveHGraham
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Vinegar for Mill Scale Removal

Post by SteveHGraham » Tue May 23, 2017 5:09 pm

Harold (and possibly others) recommended vinegar to remove mill scale from hot-rolled steel. I decided to give it a shot. Ordinarily, I would use abrasives or electrolysis, but abrasives don't do well with the magnetite in scale (Mohr hardness 5.5+), and electrolysis tends to put magnetite ON things.

Yesterday I took four pieces of steel I had been working on and threw them in a container of washing vinegar (concentrated white vinegar). These pieces had been worked over with abrasives, which polished the scale. They had also been left outside with salt water on them, in order to generate rust which would knock the scale off. The abrasives polished the scale very nicely without removing all of it, and the scale delayed the rusting too much to make the salt water experiment pay off.

Today I took the steel out of the vinegar, and sure enough, it was clean. The scale came off, except for bits here and there, and so did all the rust.

I haven't tried HCl because I don't like keeping it in my shop. When I learned that capped HCl rusts nearby tools, I poured what little I had down the toilet.

Anyway, vinegar did the job.
Every hard-fried egg began life sunny-side up.

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SteveHGraham
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Re: Vinegar for Mill Scale Removal

Post by SteveHGraham » Tue Jun 06, 2017 4:44 pm

I happened to be at the hardware store the other day, so I grabbed some muriatic acid. Today I put around a gallon of water in a bucket, added maybe a pint of acid, and threw in six pieces of steel.

The crud came off the steel much faster than it did with vinegar. In around two hours, the parts of the steel that were completely exposed were free of scale. The undersides had to be rotated up so the acid could get at them.

For around a dollar, I'll have some nice clean steel that only requires a bit of wire wheel work.

A plus to this method is that when you reach into the diluted acid to get your parts, if you have any cuts on your hands, the acid will tell you where they are.
Every hard-fried egg began life sunny-side up.

EOsteam
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Re: Vinegar for Mill Scale Removal

Post by EOsteam » Tue Jun 06, 2017 5:44 pm

I believe Muriatic acid is another name for HCl acid. It caused rust to occur on a cast iron sink when the tightly closed bottle was stored underneath.

HJ

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SteveHGraham
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Re: Vinegar for Mill Scale Removal

Post by SteveHGraham » Tue Jun 06, 2017 6:11 pm

I'm keeping it on the front porch. I already learned my lesson.
Every hard-fried egg began life sunny-side up.

b4autodark
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Re: Vinegar for Mill Scale Removal

Post by b4autodark » Thu Jun 08, 2017 9:07 pm

Google "pickled and oiled pipe". Used to use pickled pipe for hydraulic plant piping on some jobs back in the day. Seems pickled weld fittings were never available so we had to pickle our own. Usually did a TIG root pass and 7018 low hydrogen filler and cap. Weld specs/procedure wanted TIG root because it was cleaner and left less scale inside the pipe. I always enjoyed TIG work weather on Mild steel, stainless, chrome moly or aluminum, though aluminum was my least favorite because it is dirty to work with.

I have been reading some of your posts on your TIG journey Steve, keep on it because you will really find it a rewarding skill in your toolbox and will have it for life.

Pick up some silicon bronze filler rod and try it on some scrap mild steel and cast iron, it flows nice and is very versatile for joining disimilar metals and doing cast iron repair.

Good Luck

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SteveHGraham
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Re: Vinegar for Mill Scale Removal

Post by SteveHGraham » Sat Jun 10, 2017 6:39 pm

Thanks for the help. I will try to remember to do as you suggest.
Every hard-fried egg began life sunny-side up.

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