[mikeysp]

How do you remove the rust from steel?

I was given some free steel for my CNC tables; however, as seen in the pics, they have some rust, not heavy, not light. I thought of using a plastic tank and use electrolysis to remove the rust; but, some men say it will make the steel brittle. I know others have used rusted metal for their CNC table. For those who cleaned and painted their tables, how did you remove the rust for painting?

Thanks, -Mike

[109jb]

I have used many methods.

Sandblasting will remove it and gives a finish that is nice for welding and painting.

Angle grinder with wire wheel works good to.

Evaporust is an acid type product that works well.

For just surface rust you can get phosphoric acid, wire brush what you can and then the acid will convert any that remains to iron phosphate which is black and can be painted.

Finally, I have had great success with a product from kbs coatings called rust seal. To use you just wire brush the loose stuff and paint on the rust seal. Once dry it is very tough and is supposed to encapsulate the rust and prevent new rust. I used it on my truck frame and I live in northern Illinois where the roads get salted heavily. I did just as they say and just brushed off the loose and painted. That was several years ago and the truck still looks good. It comes in at least black and gray and in good and satin finish.

Sent from my Z958 using Tapatalk

[mikeysp]

Thank you for the response. I do have this little siphon sand blaster that I bought recently for some small pieces of steel and it worked great. However, I was unsure how it will do on so much steel. I may consider building a larger DIY tank sandblaster; but, first I will test my little one and see how fast it works on the large steel tube. If it works ok, I will build a small catch box, to recycle some of the sand. On a side note, when I purchased that sand blaster less than 3 weeks ago, it was $13 delivered, now it is double.

BTW, anyone know the truth about the elctrolysis technique? If it will not do violence to the integrity of the steel, I would love to use this technique.

Thanks, -Mike

[Jeff0000]

Thank you for the response. I do have this little siphon sand blaster that I bought recently for some small pieces of steel and it worked great. However, I was unsure how it will do on so much steel. I may consider building a larger DIY tank sandblaster; but, first I will test my little one and see how fast it works on the large steel tube. If it works ok, I will build a small catch box, to recycle some of the sand. On a side note, when I purchased that sand blaster less than 3 weeks ago, it was $13 delivered, now it is double.

BTW, anyone know the truth about the elctrolysis technique? If it will not do violence to the integrity of the steel, I would love to use this technique.

Thanks, -Mike

Well electrolysis can introduce hydrogen into the steel, or something like that. So it will weaken the steel. But remember for a cnc router the ultimate strength of the steel isn't what is important, it is the mass, or something like that. And you are talking at most a few % in loss of strength. Just don't leave it in there forever.


Those little sand blasters shoot sand bloody everywhere. But sand blast is awesome and would be my first choice.

[Eldon_Joh]

Well electrolysis can introduce hydrogen into the steel, or something like that. So it will weaken the steel. But remember for a cnc router the ultimate strength of the steel isn't what is important, it is the mass, or something like that. And you are talking at most a few % in loss of strength. Just don't leave it in there forever.

so i have never heard this before, and the sources i've found say that grade 8 hardware (10.8) and below is not susceptible.

furthermore even if you do have steel that is susceptible to hydrogen embrittalment, you must stress it above its embrittlemen threshold. which is probably in the range of above 100,000 psi.

[grg_p]

Try Evapo-Rust from Home Depot.

[JerryBurks]

........Those little sand blasters shoot sand bloody everywhere. But sand blast is awesome and would be my first choice.

I sand blast occasionally and don't have a chamber. So I spread a very large tarp in the middle of the lawn (on a dry day), don a dust mask and gloves and blast away in the middle of the tarp. When I run out of abrasive I fold the tarp to collect the spent abrasive in the middle and strain it back into a bin for re-use. When I am done I need a shower...

Not the most efficient method but I don't do that very often and it works.

[mikeysp]

Thanks for the advice men. JerryBurks, I LOVE the tarp idea and that is what I am planning on doing. All I will need is a tarp. We have used evaporust and it worked for some small parrts, but it would require a lot of it for our steel, and that would drive the free steel cost up; so, I will keep our evapo rust for other projects that I think are more fitted. Again, thank all of you for your advice; however, unless I get a better idea, I really like sandblasting over a large tarp.

[nlancaster]

For an environmentally friendly rust removal, thought it does take quite awhile. Look into using molasses and water to remove the rust. And you can get feed grade molasses cheap from the farm supply stores.

[109jb]

https://www.youtube.com/watch?v=3foqAjUZeK4

[mikeysp]

109jb, I had read about so many different options, but this video of Muriatic Acid (Hydrocloric Acid) cut with 50% water is AMAZING!I will price the acid and if it is reasonable, I am switching from sand blasting to Acid. The guy sprayed the metal lightly with the acid, then resprayed it. Let it sit a little and rinsed it off with water from a pressure washer. He didn't turn on the pressure washer, just the little jet stream that comes out from water pressure.

UPDATE: Priced a gallon of Muriatic Acid at Lowes for $7.88.

Looks like this will be cheaper than a tarp and sand for my sandblaster, cheaper than evapo rust. Easier than building a electrolysis tank. Will be easier, cheaper, and faster than all the other techniques. Obviously, one needs to be careful when working with acid.

I may not do it for several weeks as I am knee deep in much work right now; however, I will tell of my results and post some before and after photos on this thread when I do remove the rust.

Here is a before and after picture I captured from the video:

[Jeff0000]

so i have never heard this before, and the sources i've found say that grade 8 hardware (10.8) and below is not susceptible.

furthermore even if you do have steel that is susceptible to hydrogen embrittalment, you must stress it above its embrittlemen threshold. which is probably in the range of above 100,000 psi.

I really couldn't remember, very old information from my memory.

[1Jumper10]

Cool technique! Its probably a good idea to rinse it with some Arm & Hammer baking soda (soduim bi-carbonate) and water to neutralize any remaining acid.

[mikeysp]

1Jumper10, good point. We don't want any acid to keep working. I had used vinegar to remove some surface rust before and the folks who recommended it, said the same thing, use baking soda to neutralize the acid.

[pippin88]

Hydrochloric (muriatic) acid will keep on eating (corroding) good steel.

Phosphoric acid will convert the rust to an inert form and won't attack the good steel.

[mikeysp]

pippin88 brings up a good point. I read many folks saying it would start an unstoppable eating of the steel, because of the porosity of the steel. Here was an interesting thread I found on a car enthusiast forum discussing it. Some folks believe the process is stoppable with a baking soda and water solution. Others say it is like salt in the north on metal, once the rust starts, it doesn't stop. I may be back to sand blasting; but, I will do more reading. I have used phoso before, and it turned the rust to a black paintable surface. This would be bad since it would make a less perfect surface; however, after watching a few videos, you can work it with a brush and it won't cake. However, at that point, I think sandblasting on a tarp might be easier. I may consider the electrolysis route also. I could frame a a long box, like a raised garden bed, and line it with some plastic, and use some rebar to draw the rust to. Sandblasting on the tarp sounds simple and eliminates any concerns I have, except, the inside of the square tubing won't be reachable; however, is that even important? I can just weld on some endcaps, and the rust surface inside the tube will serve as the protective coating on the inside of the tube and paint will serve as the outside coating.

[ger21]

I'd just sand it with an angle grinder.

[109jb]

Personally, for what you will be using this steel for, I would just wire brush it and paint with KBS coatings Rust Seal.

https://www.kbs-coatings.com/stop-rust-paints.html

[mikeysp]

Ger21, I do a lot of angle grinding and if I was only prepping the weld edge or a small part, I would go this route; however, I am making two tables - 5x10 Mechmate router style and 5x10 plasma with this steel (probably close to 200 ft of steel, so I would be concerned about missing some of it, ruswt coming through the paint, and taking away too much steel, effecting the surface. If I knew I was going to epoxy the rail mounting surface, I would more likely consider this. However, I think it would be easier and give better results using the tarp and sandblaster.

109jb, those coatings look nice; but are a bit spendy. I am sweating to save money. Rustoleam paint is $27 a gallon, no shipping, vs KBS $135 plus shipping.

Sand blasting, all I need is a tarp, and a bag of sand.
Electrolysis, all I need is some plastic. I already have the washing soda for conductivity, the wood for a tank structure, and a dc power supply.
Muriatic acid is cheap at $8 a gallon and I have a sprayer.
Phosphoric acid is $15.40 qallon and I have a sprayer.

They all come with concerns for me, except sandblasting. Perhaps the concerns are overrated on some of the techniques. I would love to see some real world testing side-by-side; but, alas, the sand blasting looks to be the safest route for me. I would love an "experienced" metallurgist's take on the "reality" of the concerns.

I am tempted to take several pieces and do some testing, just to help clarify reality vs paper. However, I fear it would be ridiculed for not taking into account certain variables, or not being conducted intelligently. Who knows, maybe we will get some other good ideas on this thread.

[109jb]

How big a table are you building that needs a gallon of paint. I did an entire full size truck frame with 1 quart and a brush. Keep in mind with the KBS paint, all you need is a hand held wire brush to remove loose rust. You don't have to remove it all.