How To Remove Mill Scale and Rust [FAST]
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- เผยแพร่เมื่อ 10 ก.ย. 2024
- shoptoolreview...
We show you How To Remove Mill Scale and Rust, the easy way.
Mill scale and rust are major contaminants when it comes to welding or finishing metal, especially when it comes to tig welding or painting. The typical approach is to reach for your grinder and start grinding away at it. You've probably been there before, and it seems to work pretty well in the beginning. However, the longer you work, the more the flap disc or grinding wheel fills up and clogs up the wheel.
We turn to a solution that takes away the elbow grease and long labor hours, however, it does require additional safety. Be sure that your area is well ventilated, and preferably outside in the open. White vinegar will work at removing the mill scale and rust; however, you probably want to leave it several hours or overnight. We've found the best and fastest way on how to remove mill scale and rust is to use Muriatic Acid. You can get this at your big-box stores as well as a local pool supply store. It's only a few bucks a gallon. Again, be extra careful in transport and use. DON'T BREATHE IT!!
Depending on your parts and pieces, you may have to fabricate your own vat or container. We're doing a project where we will have ten or more pieces that are ~3-feet long. We used some cardboard, hot glue, and tape to build a trough, and it wasn't pretty. Then, we lined the trough with Visqueen to contain the Muriatic Acid. It's not so hard and it's quick to build. Just make sure you have a plan on recovering the fluid into a proper container.
Once you soak the pieces in the Muriatic Acid for 10 or 15-minutes, they should be ready for a good rinse with lots of water. The steel should be clean and ready. Be sure you do something with it fast, or get some rust inhibitor on it. It will start to rust immediately. Now, you know how to remove mill scale and rust from your metal, but remember to use proper PPE and stay safe.
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I use this all the time and here are a few tips:
Wear goggles and do this outside.
Do not leave open containers in your shop because the fumes will rust your tools.
Wear a respirator or at least stay upwind to avoid breathing fumes.
This works great on odd shaped steel or pitted steel.
This will strip mill scale, rust and zinc. (galvanized)
Real Muriatic Acid is actually 32% hydrochloric acid. The big box stores will cheat you by selling a lower concentration. In my area, Atwoods sells the real 32% stuff at a good price.
I dilute mine with water to 10-15% HCl for safety and to get more volume.
Towel dry instead of air dry to help prevent instant rust.
If the steel is oily, you may need to wash it with some dish soap to make this process work better.
Oil will help prevent instant rust but doesn't work for welding. I prefer a coat of phosphoric acid which creates a thin layer of iron phosphate that acts as a rust barrier. It also makes paint stick well. I sometimes weld through the iron phosphate layer but it will also grind off easily with a flapper disc for welding. The iron phosphate layer also lets me store the steel for a long time with almost no rusting.
PVC pipe works well for long pieces.
HCl will dissolve nylon. If you need to use a rope to hang items, or a piece of carpet to prevent puncturing containers, use poly.
Prior to disposing the acid it should be neutralized and what you get is salt water. Baking soda works very fast. Calcium also works. A cheap method is to place a good sized limestone rock in the liquid and let it set for a couple of weeks. Limestone has lots of calcium.
I experimented with acid and with standard strength white vinegar. I used 6 inch x 2" x 5/32" mild steel pieces in a tupperware box, they were heavily scaled and rusted. I left the vinegar for 12 hours and I'd give it 4/10, not worth the effort IMO. The acid took 15 minutes to get 90% clean, and a light scrub with scotch rite got all the crap off. Dipped them in a bucket of baking soda and water then rinsed in tap water and dried with a paper towel. For welding all I need to do is a light pass with a wire wheel or flapper disk to get them shiny. My acid was 19%, I initially covered the steel in fresh water then slowly added muriatic, total depth maybe 1 inch then I got a reaction happening. Excellent method, very easy in practice and far faster and cheaper than simply grinding, mill scale quickly clogs up grinder disks. Thanks for the video.
Just one thing: water won’t neutralize acid, but it will dilute it.
Folks, please wear goggles when working with muriatic acid, or any acid for that matter. A little on your fingers isn't a huge deal, but on the mucous membrane of your eye it's an entirely different story. I'm very surprised that this issue wasn't addressed in this video.
Opening muriatic acid in your garage will cause all the metal in your shop to rust. Usually takes a little bit to happen but it will happen if the container of acid is left open over a period of time. I learned this the hard way.
Safety glasses as well when handling acid!
Very good point. Thanks for watching.
we use an old air mattress with the top cut off to soak big stuff
Thank you for sharing.
Muriatic acid is hydrochloric acid, what's in your stomach. It doesn't attack organic matter like your fingers as fast as other things like rust or mill scale (oxide coating formed when white-hot steel is exposed to air). I always use it to remove galvanizing before welding. It will remove the thick, hot-dip zinc coating from galvanized iron pipe in just a few minutes. Great stuff, but don't spill it. For rust removal on more sensitive items such as a motorcycle gas tank, muriatic will work but can be too strong. I've had terrific results using an organic chelation rust removal product like Metal Rescue. It's quite benign to the parent metal.
Good video, helped a coworker make suggestions to our employer about reducing mill scale grinding labor (we grind that scale off)
Thanks for sharing! Just beware of the fumes. Thanks for watching
Hydrochloric acid (muriatic acid) is produced by passing hydrogen chloride gas into water. The reaction is reversible and hydrogen chloride gas rises all the time from an open container of hydrochloric acid. It severely irritates the respiratory tract and rusts everything in the same room. Always do this outside.
Once you have removed the Mill scale, it must be neutralized immediately. Water does not help, it only dilutes the acid, but does not remove it. A base is needed. Professionals use sodium hydroxide=NaOH=lye, the end result is table salt and water. Lye can be found e.g. in drain cleaners. Another option is washing soda, baking soda works too.
If you go with flap discs go for the silicon carbide. If you want to go the acid route use phosphoric acid. Stronger than vinegar but weaker and not as dangerous as muriatic acid. Note: muriatic acid fumes will damage any metal in your shop if the container is not sealed shut.
Lol. You are exactly right. The fumes rolled out of this plastic bowl and onto the stainless surface, and just the fumes/fog stained the surface. Thanks for watching.
How much phosphoric acid per gallon? And what ph?
@@TheTank8 I just use the klean-strip Concrete Etch, Metal Prep and Rust Inhibitor from homedepot.
I like it...... “Go out and do something nice for someone.” 👍
Thank you very much, and thank you for watching.
Home Depot sells vinegar that is 6 times as concentrated as household vinegar
One very big question that you didn’t cove is “the best procedure to cleaning the metal to PAINT", because most metal will be painted as an end result. If Muriatic Acid (or household Vinegar) is used, should one have to follow with a Soda Solution to naturalize the residual acid left behind, to maybe not affect the paint adhesion?
I may try car wax as it would stick longer than oil after. Antique gun collectors use auto wax on their rifle barrels to prevent rust. Gravity will cause oil to slowly creep away. I have not tried this. Just heard about it.
Another option for cleaning is Naval Jelly. It's acid that's been made into a gel so that it sticks to the metal and doesn't run off like the liquid acid. But use a respirator!
We'll have to try that method. Thanks for watching.
Does naval jelly work good for mill scale or only rust?
I used muriatic acid in my garage one time and it literally destroyed everything bare steel and continued to do so for about a year, everything just kept rusting, couldn't see or smell the fumes but they were lingering somehow
Ya I don't know why people do test with all kinds of acids for rust removal that cost much more and is weaker if you need more or want it to be kinda safer juat dilute it with water distilled would be best but tap is probably fine but keep it all outside because everything in your shop will start to use
If you find yourself facing a grease fire, remember that water or gasoline will neutralize the fire.
Will it be safe to cook on after the mill scale is removed this way. I had a rocket stove made and the welder said it had mil scale on it.
There are aluminum balcony bars and static paint on it, so I want to take this paint off by immersion, what I can use, an acid that won't fly if possible
Is your welding table stainless? Cause three hours with Naval Jelly, that mill scale laughed at me. I need a sand blaster.
For those that don’t know, mill scale is very hard. It’s actually very rough on carbide cutters when you’re milling HRS.
What if I want to use it on a fence. Can I use a brush and "paint" the acid over the fence to strip the scale and rust?
Use Naval Jelly
Flap discs are overrated. High quality resin fiber discs work far better on flat surfaces. 24 grit for mill scale at slower speeds to avoid heating the scale. Then, an 80 grit cleanup pass on the clean metal to smooth the scratches.
You have a point. Some of these new ceramic discs are doing a much better job with removing mill scale. You're right, you have to keep the mill scale cool. Still, acid works pretty well also. Thanks for watching.
I totally agree that flap discs are over-rated. Wire brush attachment is just as good in most cases, and if I really want sandpaper I use the replaceable paper discs with a rubber backing. Much cheaper than flap wheels.
@@Shoptoolreviews Just tried some silicone carbide fiber discs on mill scale and it rocks! It sucks on metal but destroys mill scale.
In the length it took for you to finish the video, you must have stained all that metal around you, damn shame! YOU DONT EVER USE MURIATIC ACID INSIDE A METAL SHOP! lol
I want to use this on my welding table 40"x96". I'm thinking about putting it in a spray bottle:
That "slippery" feeling is you skin dissolving in the acid.
Not exactly, but it's definitely not good for your skin. Thanks for watching.