Removing Mill Scale from Hot Rolled Steel?

[Kendall]

I've been using flap disks with success except for some plate that I bought the other day. It was some older steel drops that had been stored outside but under cover. There was some rust present that came off easy, but a 40 grit flap disk wouldn't touch it? I'm not sure what the problem was but decided that if it was that hard to remove that it wasn't going anywhere so I welded through it and painted right over it.

[Winky]

I've been using flap disks with success except for some plate that I bought the other day. It was some older steel drops that had been stored outside but under cover. There was some rust present that came off easy, but a 40 grit flap disk wouldn't touch it? I'm not sure what the problem was but decided that if it was that hard to remove that it wasn't going anywhere so I welded through it and painted right over it.

Sometimes that's just the easiest thing to do ... mig or stick you can get away with it but if you tig it the scale should be off of it ... I've had some success with heating stubborn stock in my forge and then after it cools enough hit it with my flap disc ... but usually I just leave it on and weld it with mig or flux core.

[xalky]

The muriatic acid treatment leaves a nice clean surface. I normally spray it on with a spray bottle. It's best done outdoors. Keep a water hose and an air nozzle nearby so you can rinse it off and neutralize the acid and dry it off. You can also spray it with a baking soda solution to further neatralize the acid after your done and rinse it off. Then blow it dry with an air nozzle immediately to stop the rust. It might be a little toxic but it's the quickest easiest way to getter done. It's so quick and easy that if you've never done it before, you'll wonder why you wasted so much time grinding and sanding in the past.

Also works great for removing surface rust in a hurry.

[youngnstudly]

I could see using the acid on a heavy piece of steel that was an odd shape or something, but for most of the material that just has light rust or scale on it, the acid approach is simply too messy and time consuming. I do agree that baking soda and water works wonders for neutralizing acid afterwards though.

The main problem for me is that by the time you drag everything out to chemically strip the metal (the air hose, the garden hose, rags, baking soda, a stand to set your dirty material on, gloves, goggles, etc.), the work piece has been handled 4 or 5 times during that process alone. Plus I can't work with toxic chemicals as they make me sick.

The local junior college welding programs method proved to be another effective option for removing mill scale. We (the students) used a bead blasting cabinet for removing the scale from our test plates and backup strips, then we would follow that up with a few (light) passes on the belt sander. It was a quick method of stripping the garbage off of our metal prior to welding (it only took a few minutes to strip a few sets of test plates per student). Obviously you have to have access to a media blasting cabinet though.

[DVA]

I have used this stuff, but it does not take all of the mill scale off and the fumes are horrible. I never looked at the ingredients and just may be muriatic acid. Whatever the case, I was mainly using it to remove rust and noticed that some mill scale came off as well:

http://www.industrialmetalsupply.com...0Degreaser.pdf

[Rambozo]

I have used this stuff, but it does not take all of the mill scale off and the fumes are horrible. I never looked at the ingredients and just may be muriatic acid. Whatever the case, I was mainly using it to remove rust and noticed that some mill scale came off as well:

http://www.industrialmetalsupply.com...0Degreaser.pdf

Probably not as muriatic acid will not cut grease at all. You need to have all the oil and grease off before using it. My guess would be some kind of caustic soda product, but that's just a guess.

[jakeru]

An angle grinder with a grinding disc should do the trick for mill scale removal a lot more quickly than with a flap wheel, (and without the hazards of using an acid to pickle it away.)

For larger scale production, shot blasting (using steel shot) may be desirable, in that it not only effectively removes the mill scale, but also leaves behind desirable compressive stresses into the surfaces (a peening effect.)

Some steel suppliers can also provide "pickled and oiled" steel, which costs a little extra than the usual (mill scale-laden) hot rolled product, may generally still be cheaper than cold rolled. Like cold rolled, just wipe it with a rag and some solvent, and it's ready to weld.

[Rambozo]

There are some new options as well, like SCS. Looks nice, but only available in a few places.

http://www.scsprocess.com/index.html