Beginner question on removing mill scale

[racerboy]

I’m new to welding and was planning on doing some work with 1/8” mild steel. I know you are supposed to remove the mill scale to get clean metal. I saw a YouTube video that said to soak it in vinegar. I tried that, and it definitely removed the top layer, but should I also grind it more so it is shiny?
This photo shows the difference after soaking in vinegar overnight (bottom piece).

 

[txvwnut]

I remove mill scale with a flap wheel. Depending the weld process you are going to use any leftover residue from the vinegar soak might cause an issue.

 

[WillyBoy]

I've had good results using a knotted wire wheel in an angle grinder. Easy to run along the area where the bead will go. Just watch where it's going. Trying to remove a shop rag that it sucked up resulted in some bad language. Fortunately it wasn't my shirt.

 

[AldeanFan]

I use a flap wheel

 

[jmdirk]

Never really tried a chemical process. Removing it mechanically is usually faster. Flap wheel, sanding disc, stripping discs, wire wheels all work fairly well.

 

[Jswain]

I’m new to welding and was planning on doing some work with 1/8” mild steel. I know you are supposed to remove the mill scale to get clean metal. I saw a YouTube video that said to soak it in vinegar. I tried that, and it definitely removed the top layer, but should I also grind it more so it is shiny?
This photo shows the difference after soaking in vinegar overnight (bottom piece).

Use either resin fiber discs, flap discs, or grinding wheels to remove the mill scale prior to welding out. Both sides of the material, 1/2" or so around the area you are welding. I mostly find wire wheels just polish it, leaving it on there, unless the metal is slightly rusted as well

 

[bwringer]

Jason at Fireball tool did a video on this testing different methods and consumables not too long ago.

Poke around on YouTube and you'll find it. I'm not in a position to post a link or embed at the moment.

 

[danielbuck]

it's almost always best to get down to bare metal when welding. If the steel isn't shiny looking after whatever method you used to remove the mill scale, a quick hit with a flap or strip disc along the area you'll be welding to right before welding will get any remaining residue off of the metal.

That said, it'll probably weld just fine straight out of the vinegar. I've welded through mill scale before for quick setups (to temporarily brace something while it's being built), it'll weld.

 

[MoonRise]

IMHO, a wire wheel/disk/cup (even a knotted one) is NOT going to reliably and completely remove mill scale.

Red rust, yes.

Black/gray mill scale, nope.

Grinding wheel or flap disk is my usual go-to for mill scale removal. Or media blasting (if the part can fit in the blast cabinet or you are using an 'external' media blaster set up).

Some welding processes can tolerate a certain amount of mill scale or 'crud' and still produce acceptable results. But best welding results are always achieved if you have clean bright shiny metal to start with.

Acid (vinegar is an acid) can remove rust and mill scale on steel, but depending on the specific steel alloy can cause material problems later (corrosion of the steel or hydrogen embrittlement in 'hard' or 'high strength' steels).

 

[garboui]

I have been looking for less grindy ways for this for a while. Vinegar works but often needs a long soak to get through. Other steel in the area will also rust from the open bath vinegar. Muriatic (HCl) is often at concentrations that work fast but are hazardous to handle and creates too many safety tradeoff IMO. This year I started using acidic toilet bowl clear. This stuff is usually ~10% HCl and is on the much safer side of acid concentrations. Being a "gel" it does stick around where you put it or can be brushed back in place. Oh, it smells nice too! Depending on teh thickness of scale, ive had it down to bare metal anywhere from 15min to 1h.

 

[danielbuck]

I have been looking for less grindy ways for this for a while. Vinegar works but often needs a long soak to get through. Other steel in the area will also rust from the open bath vinegar. Muriatic (HCl) is often at concentrations that work fast but are hazardous to handle and creates too many safety tradeoff IMO. This year I started using acidic toilet bowl clear. This stuff is usually ~10% HCl and is on the much safer side of acid concentrations. Being a "gel" it does stick around where you put it or can be brushed back in place. Oh, it smells nice too! Depending on teh thickness of scale, ive had it down to bare metal anywhere from 15min to 1h.

I wonder if citric acid would work? I use citric acid to remove zinc coatings and also rust, it seems to work way faster than Vinegar does. I like it because it's so safe, don't need gloves and can dump down the drain

 

[garfunkle24]

I use stripping discs or Walter flexcut millscale discs or just roloc scotchbrite or flapdisc if not doing much.

 

[scooby074]

For most of the welding we do (ie: non code, simple repairs/fab) grinding off millscale to bare metal really isnt required IMHO. If I do have to, I usually use 3m grinding discs or the Walter wheel made for removing scale. I try to avoid as much grinding as possible.

 

[tarmy]

Flap discs are your friend.

 

[garboui]

I wonder if citric acid would work? I use citric acid to remove zinc coatings and also rust, it seems to work way faster than Vinegar does. I like it because it's so safe, don't need gloves and can dump down the drain

If it removes zinc and rust, seems similar enough to HCL that it would also be effective to remove mill scale. Worth the experiment. For science of course!

 

[Crazyjake8493]

I've always used a flap disc or stripping disc on an angle grinder to remove mill scale. I wouldn't even consider chemicals unless it was a place I couldn't reach with a tool, and if it comes to that I'm probably not good enough to be welding that spot anyway.

 

[danielbuck]

I've always used a flap disc or stripping disc on an angle grinder to remove mill scale. I wouldn't even consider chemicals unless it was a place I couldn't reach with a tool, and if it comes to that I'm probably not good enough to be welding that spot anyway.

if you had a large plate, chemical would probably be alot easier and way less effort. Small pieces, grinder is way quicker.

 

[BigMike782]

My experience has been it depends.....
I have used hard grinding wheels, flap discs, wire wheels and a needle scaler.
When I built my welding table the scale was so heavy and thick that the only thing that would take it off was a needle scaler.

 

[Graham08]

These are my go-to for mill scale: https://www.mcmaster.com/8236A13/

Fortunately, my local steel supplier has most everything I use in either cold rolled or pickled and oiled finish so I don't have to deal with scale very much.

 

[csp]

A stripping disc is far superior to a flap disc and doesn't remove the underlying steel either.

 

[b-dog]

A stripping disc is far superior to a flap disc and doesn't remove the underlying steel either.

Yep. This.

These are my go-to for mill scale. Contrary to what you might think, they're quicker than a flap disc too.

 

[Jswain]

Yep. This.

These are my go-to for mill scale. Contrary to what you might think, they're quicker than a flap disc too.

I just assumed he was talking about the purple or black stripping discs, I didn't know those worked good for mill scale. Good to know

I like the thought of using them as they probably wouldn't gum up like a flap disc or resin fibre

 

[Slednut]

Mill scale, rust, paint this does it quick, and does not remove the steel itself.

 

[All]

Good Grinder Almighty!

That is quite the collection of already chucked up grinders at the ready.

There is some experience evident in that photo.

 

[Avadon]

Mill scale, rust, paint this does it quick, and does not remove the steel itself.

For real, these are wayyyy better than flap wheels. They don't remove material unless you really go to down. They're great for paint, mill scale, rust. I stopped using flap wheels, too expensive and don't do a great job at hard mill scale. You can even get these paint stripping wheels in packs off of amazon for cheap.

 

[Monza Harry]

@b-dog & @slednut can you share a link or two of those? I've never seen any like yours b-dog, and I've only seen close to yours slednut, but not exactly. TIA Harry

 

[Sumboodie]

Weld it. It'll be fine.

 

[LopezBart]

I find that 7018 leaves a much nicer finish if I remove the scale first. 6010/11 doesn't leave a nice finish anyway

 

[Slednut]

@b-dog & @slednut can you share a link or two of those? I've never seen any like yours b-dog, and I've only seen close to yours slednut, but not exactly. TIA Harry

Simply search strip disc on Amazon

 

[larry4406]

Mill scale, rust, paint this does it quick, and does not remove the steel itself.

Nice fab table. Homemade? Looks to be at least 3/8-1/2" thick. Nice shot of the ground connection as well.

 

[b-dog]

@b-dog & @slednut can you share a link or two of those? I've never seen any like yours b-dog, and I've only seen close to yours slednut, but not exactly. TIA Harry

Sure thing, I use the 36 grit 4 1/2" disc

https://www.3m.com/3M/en_US/p/dc/v000587556/

But, there's a whole mess of different options:

https://www.3m.com/3M/en_US/p/c/abrasives/brushes/bristle-discs/

 

[Slednut]

Nice fab table. Homemade? Looks to be at least 3/8-1/2" thick. Nice shot of the ground connection as well.

Yeah home made, ground goes to a clamp for stuff that won’t get a good ground to the table. 1/2 inch top with 5/8” holes. Also has six 32” deep drawers. Still haven’t painted it

 

[larry4406]

Yeah home made, ground goes to a clamp for stuff that won’t get a good ground to the table. 1/2 inch top with 5/8” holes. Also has six 32” deep drawers. Still haven’t painted it

That’s a beast!

 

[Slednut]

That’s a beast!

Yeah, it also has a landing gear caster system.

 

[larry4406]

Yeah, it also has a landing gear caster system.

We need to see this!

 

[Slednut]

We need to see this!

Here it is

 

[jhn9840]

Very nice welding table!

jhn9840
John

 

[SM Racing]

I tend to use a combination of techniques. Grind it, either with a flap wheel, rock, or small 90 die grinder. Heavy scale tends to clog those. If I am working with plate or short segments of tube, I have an acid tank outside that uses muriatic acid mixed 7:1. I can drop the parts in the tank and go deal with something else.
Option 3 is sand blasting in my cabinet and that's usually my go to. It leaves a nice finish to piant, cleans up all mill scale, rust corrosion, etc.

 

[BD1]

I like the Eastwood CST contour tool. It does a great job and they have 1'' wide wheels plus a variety of the 4'' ones. It is great for cleaning the welding table top too. Amazon has them and so does Harbor Freight.

Eastwood CONTOUR SCT® - Surface Conditioning Tool

Multiple Tools In One! Removes Rust, Paint, Body Fillers Conditions Metal so it is Ready to Paint Buff Metal to a Mirror Finish Professional Grade Backed by a 3 Year Warranty US Patent #D814,261

www.eastwood.com

 

[Wamsutta]

Walter flexcut millscale discs

Are those good? I've been wanting to try some.