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Flash rust

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Shane Warnick
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Flash rust

Postby Shane Warnick » Fri Mar 07, 2014 12:41 am

I am using muriatic acid to remove dross and mill scale after cutting. I am using it diluted 1:1 with water, I bought the more concentrated acid from the pool store. Anyways, after the acid bath (10-12 hours the dross and millscale is gone) I neutralize the acid by soaking the parts in baking soda and water mix. I usually leave them there for 10 minutes or so, then walk straight to the shop and rinse them so there is no white residue. The shop is only 20 yards away from the acid tubs, and before I can get them rinsed, and blow them dry with an air hose they all have some surface rust on them. Just a real fine orange haze. Won't wipe right off but a suface prep pad on a grinder or rotary air tool and it comes right off. So I am wondering if this is what happens to everyone, and you are just removing the rust and prepping for finishing, or are there some people using another step to prevent it. I was wondering about going from the baking soda solution into something to drive the water off, say mineral spirits or paint thinner, but keeping that stuff from evaporating in the summer here (100-110 degree days) is going to be tricky. So, does everyone have an issue with the light rust immediately after acid, or am I just special? Our humidity is really low almost all the time (in the desert) but I swear I can watch this stuff rust before my eyes.
Thanks in advance for your time on this.

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Re: Flash rust

Postby 1fine79 » Fri Mar 07, 2014 5:30 pm

By any chance are you cutting on a water table plasma setup? I just recently started using the acid soak for dross removal and I'm sure my parts (here in Georgia) don't dry as quickly as yours but after soaking and water rinse I dip my parts back into my plasma water. The sodium nitrite in the water keeps material from rusting for good long time.
Maybe (if you are not cutting over water) you could get some sodium nitrite and mix up some in a tub of water so that you could go from soak to rinse to SN rinse and most likely reduce the flash rust a good bit.
Also, in my opinion, I have had no paint issues with the remaining Sodium Nitrite residue that may be left on the parts after grinding or sanding in prepping for paint. Just my 2 cents...which in this economy is worth about 1/2 a cent...LOL.
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Re: Flash rust

Postby _Ogre » Sat Mar 08, 2014 2:51 pm

set up another dip tank with washing soda mixed in for a final rinse. i use $3 worth of washing soda in my water table and never get rust. even on plates that were splashed with table water and sit on the table over night
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