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Mill scale removal ?

cuslog

cuslog

Super User
Premium Member
Any one got a pet method of mill scale removal ?
I've got a welding / fab table I made up, the top is a circle of 1" thick AR 400 steel about 36" dia. Really hard stuff - I've drilled a couple holes in it and they were a real struggle ! Of course there's the mill scale too - getting a good ground is kind of hit or miss ! Tried grinding some but that's not easy either and you've got to use a wheel that's so aggressive that it gouges up the surface - was hoping to keep a nice smooth surface (and did I say I hate grinding dust ?).
I've heard of soaking with a vinegar / salt solution, also heard of molasses. I've tried the vinegar / salt - it does work but slow and messy (small pieces in a pan). Evaporust ?
 
cuslog said:
Any one got a pet method of mill scale removal ?
I've got a welding / fab table I made up, the top is a circle of 1" thick AR 400 steel about 36" dia. Really hard stuff - I've drilled a couple holes in it and they were a real struggle ! Of course there's the mill scale too - getting a good ground is kind of hit or miss ! Tried grinding some but that's not easy either and you've got to use a wheel that's so aggressive that it gouges up the surface - was hoping to keep a nice smooth surface (and did I say I hate grinding dust ?).
I've heard of soaking with a vinegar / salt solution, also heard of molasses. I've tried the vinegar / salt - it does work but slow and messy (small pieces in a pan). Evaporust ?
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I think the chemical approach can yield reasonable results on A36. For the harder stuff, I agree, you just gorge it. My solution is to sandblast. In Calgary there is a drive in DIY place for large items. Or you can have it done.
 
You could go with the Evaporust and it will take a while but would do it. Any mild acid type solution "should" do the job but you have to watch out for fumes - only do that stuff in an open environment and wearing PPE.

Edit: @CalgaryPT 's sand blast might be the better/safer solution.
 
For rust removal I have used muriatic acid and vinegar, they both are fast and effective, but I find the rust tends to come back later on with a vengence. I have used Coke, which is phosphoric acid, which chemically converts rust to a benign magnetite coating, but it is slow. It was fairly effective and the rust has not returned. Molasses, which I have never used, works on the same principle. I have used Evaporust, and it seems to work the best, seems to be long lasting and is relatively fast. The stuff is a bit expensive though. In your case, if you are doing a table top, I might try a grinder with a sanding disc, my experience has been that it seems to polish without gouging, although maybe this won't work on that grade of steel.
 
I've read online the fumes from strong acids will rust everything in your shop. I found the mill scale wore out sand paper really fast. I'd try vinegar. It's cheap and with some patience pretty effective. Make a temporary tray out of some plastic film sheeting and some lumber. Put the weld table top in it and let it soak overnight or more.
 
"I've read online the fumes from strong acids will rust everything in your shop."
Yes, I've seen it first hand - wicked stuff - friend of mine had a 1930's vintage car body stored in his heated shop. Body had been stripped to bare metal. A few feet away was a 1 gallon jug of Muriatic acid. I forget how long it took but at least 1 year I believe, the side of the car body facing the jug of acid was completely red with rust, side facing away, nothing - and I believe the top was screwed on the jug of acid.
 
Try a belt sander with one of the ceramic belts (quick and cheap). If it doesn't work, then move to "plan B" above. Let us know what works.

Muriatic acid is basically hydrochloric acid - the fumes created is chlorine. I used it at full strength to clean up some concrete (out doors, on a windy day, I stayed up wind and work a respirator with organic cartridges - I got a little break through and coughed for an hour). The muriatic acid did a great job on the concrete clean up, but I won't be trying it again anytime soon.
 
I have used cleaning vinegar (10% versus the regular 5%) on small parts in a tub and it worked well when left over night. I saw a video on a welding table recently where the guy in the video used a few different chemicals on a large plate steel piece. He coated paper towel or cloth with the stuff and covered it all with a tarp/plastic to keep it from drying out to much while it worked on the metal. Seemed to do an ok job.
 
Hruul said:
He coated paper towel or cloth with the stuff and covered it all with a tarp/plastic to keep it from drying out to much while it worked on the metal. Seemed to do an ok job.
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Thanks for that ! - I have used Vinegar / salt mix before on small parts in a pan and it worked OK, but this table must be 300 lbs and I couldn't imagine how I could get the top of it into a pan to soak, hadn't thought of soaking paper towels / cloths and covering them - good idea !
 
I cut the top off a plastic “tote” and i know have a 4x4’ by 8” high basin to clean/soak parks in.

Others use kiddy pools from Walmart


Sent from my iPhone using Tapatalk
 
kevin.decelles said:
I cut the top off a plastic “tote” and i know have a 4x4’ by 8” high basin to clean/soak parks in.

Others use kiddy pools from Walmart


Sent from my iPhone using Tapatalk
Click to expand...
I dug a Walmart clothes bin out of a dumpster and cut it down with a Skil saw to make an oil drain pan. Easily holds 16 gallons of used oil

I didn’t do any math the first oil change I did I was hoping it didn’t overflow :D
 
I needed to remove some rust and mill scale from a piece of 1/2 steel that I got for cheap that I want to use for a portion of a welding table top. I hit it with a wire brush and that did very little. So I soaked a cloth with cleaning vinegar (10% strength) and covered it with a plastic bag and some weight. I re-soaked the cloth after a few hours. Around 24 hours later I took the cloth off and this is how it turned out. Going to have to proceed with the rest of the top and then the bottom. The last picture is a comparison of the cloth after and what it used to look like. o_O
 

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Try citric acid or oxalic acid. they 'kelate" the rust away rather than oxidizing it. Neither will harm metal, nor will they promote rust as much as vinegar does. I just bought 1/2 kg of citric acid for deliming my coffeemaker, and remove some scale.
 
Mill scale reacts the same as rust, it is primarily oxides and carbides. Once the oxides react, there is no bonding to the parent metal for the carbides.
 
As a chemist, i will say that citric acid is awesome to se for rust and mill scale removal. Rust is removed faster than mill scale but both can be effectively removed with citric acid. I was clean g up the rust on my Emco lathe handles with it and was very pleased with the results. Citric acid can be purchased inexpensively on Amazon. Using hot water can significantly speed up reaction.Oh and the is chelate but it is pronounced “key late”. If you want to get really fancy you can use EDTA but it is kind of expensive and overkill for the home shop. I suspect that is what is in Evap-rust.
 
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