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Thread: Removing Mill Scale from Hot Rolled Steel?

  1. #1

    Question Removing Mill Scale from Hot Rolled Steel?

    Hey guys (and gals if any should be reading),

    I was wondering what all of you use to remove your mill scale from hot rolled steel. I've been using flap discs and roloc sanders but i was wondering if anyone else had something they used that works better. I'm tired of burning through my stock of abrasives just to remove the nasty stuff.

    I'm always on the look-out for new ideas. Post what you've been using!

    -Spike
    -------------------------------------------
    Spike Customs, Inc.
    Fresno, CA 93727
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  2. #2
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    Quote Originally Posted by Spike View Post
    Hey guys (and gals if any should be reading),

    I was wondering what all of you use to remove your mill scale from hot rolled steel. I've been using flap discs and roloc sanders but i was wondering if anyone else had something they used that works better. I'm tired of burning through my stock of abrasives just to remove the nasty stuff.

    I'm always on the look-out for new ideas. Post what you've been using!

    -Spike

    To remove rust and mill scale from large pieces I use Muriatic Acid. Nasty stuff, but works good. For just cleaning areas to weld, I go with the flap disc for TIG prep, and usually just burn through it for stick or MIG.
    Long arc, short arc, heliarc and in-the-dark!

  3. Default

    Quote Originally Posted by Rambozo View Post
    To remove rust and mill scale from large pieces I use Muriatic Acid. Nasty stuff, but works good. For just cleaning areas to weld, I go with the flap disc for TIG prep, and usually just burn through it for stick or MIG.
    Well said. This is about where you end up, even if you find other answers, this is the way for us commoners. Some have used vinegars, and milder acids, but they lack the industrial effectiveness that we expect in a tool or method.

    I used muriatic acid on 9 sq. feet of plate, and it was nasty, and dangerous. But it did soften the scale enough to come off real well with a flexible 7" wheel. Then final surface treatment with flap wheels. This plate became my flat shop standard for layout, fab, and welding on.

    I've heard of types of surface grinders that can clean large areas perfectly, if perfect is the goal. But that's not the common way. Using a flexible 'hard' wheel cut through the scale fastest, and lasted longest for me. Then I final finish with flap wheels.

    Jim
    Last edited by JimMinKent; 01-08-2013 at 05:12 AM.

  4. #4

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    Quote Originally Posted by Rambozo View Post
    To remove rust and mill scale from large pieces I use Muriatic Acid. Nasty stuff, but works good. For just cleaning areas to weld, I go with the flap disc for TIG prep, and usually just burn through it for stick or MIG.
    ah... muriatic acid... nasty stuff. I had a bad run in once with it once and i try to avoid it as much as possible now. I'm lucky in that if i have a large piece, it usually needs to be cold rolled or chromoly so i don't have to worry about cleaning large pieces. On the rare chance i do have large HRS pieces, i only clean my welded area, and then i let whoever is down the line in the project (a painter, polisher, or chromer) to do the rest. It's like cheating.
    -------------------------------------------
    Spike Customs, Inc.
    Fresno, CA 93727
    ph- 559-549-RIDE(7433)
    -------------------------------------------
    -Follow me on twitter!-

  5. Default

    I know a 2nd common use for Muriatic acid is to etch concrete before staining or epoxy coating, but they also sell citrus based alternative concrete etchers that are much easier on the lungs and skin. Anyone ever try one of the "friendlier" acids built for the same job?
    Poewr I-Mig 205P
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  6. #6

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    Quote Originally Posted by Rambozo View Post
    To remove rust and mill scale from large pieces I use Muriatic Acid. Nasty stuff, but works good. For just cleaning areas to weld, I go with the flap disc for TIG prep, and usually just burn through it for stick or MIG.
    I'm with you as far as flap discs for tig and just burning through with mig (I love mig) I've always avoided using acids as much as possible. I had a can of paint stripper that I think was probably Muriatic acid that was left sitting half full in the shop for a couple years (maybe three) it wound up eating through the bottom of the can I cought it in time but that could have been a real desaster. Nasty stuff could be cnsidered an understatement LOL.
    Powertig 200DX
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  7. #7
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    Quote Originally Posted by agent4573 View Post
    I know a 2nd common use for Muriatic acid is to etch concrete before staining or epoxy coating, but they also sell citrus based alternative concrete etchers that are much easier on the lungs and skin. Anyone ever try one of the "friendlier" acids built for the same job?
    It's used for soldering in the HVAC trade and I can't think of anything that is much worse than inhaling that smoke while soldering galvanized sheet metal flashings! For soldering stainless, copper, lead, and other misc. materials, Blitz is used instead of Muriatic acid. I have never used Blitz outside of soldering sheet metal for watertight seams, so I'm not aware of any other purposes it may have. It's certainly not strong and potent like Muriatic acid is, but it's still acid.

    Another vote for flap discs here. I used the Rolocs at work quite often, but I always seemed to burn through them quickly. They are great for getting into tight spaces though when attached to a small right angle grinder!
    Andy
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  8. #8

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    i've also heard that vinegar will get the stuff off if you submerge it for 48 hours. Has anyone tried it?
    -------------------------------------------
    Spike Customs, Inc.
    Fresno, CA 93727
    ph- 559-549-RIDE(7433)
    -------------------------------------------
    -Follow me on twitter!-

  9. #9

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    Quote Originally Posted by Spike View Post
    i've also heard that vinegar will get the stuff off if you submerge it for 48 hours. Has anyone tried it?
    48 hours. Wow. I use Roloc and 2-3" cutoff wheel for tight spots.
    Mike R.
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  10. #10

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    Quote Originally Posted by Spike View Post
    i've also heard that vinegar will get the stuff off if you submerge it for 48 hours. Has anyone tried it?
    Looks like I'll have to give that a try ... white vinegar I would imagine.
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  11. #11

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    Quote Originally Posted by Winky View Post
    Looks like I'll have to give that a try ... white vinegar I would imagine.
    Yep, the cheapest grocery store kind.
    -------------------------------------------
    Spike Customs, Inc.
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    ph- 559-549-RIDE(7433)
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  12. #12

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    Quote Originally Posted by Spike View Post
    Yep, the cheapest grocery store kind.
    Now that's what I like to hear lol
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  13. #13

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    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.
    IMig 200

  14. #14

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    Quote Originally Posted by Kendall View Post
    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.
    Powertig 200DX
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  15. Default

    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.
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  16. #16
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    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.
    Andy
    New Everlast PowerTig 250EX that is begging for me to come up with a few welding projects so it can stretch it's legs. Did someone say aluminum???

    MISC. TOOLS:
    Atlas 618 lathe
    Milwaukee Porta Band with custom made stand
    Dewalt 4-1/2" angle grinder
    Dewalt 14" chop saw

    Strong Hand Nomad portable table
    Juki sewing machine I've had for years (yes I know sewing is for girls)

  17. Default

    Quote Originally Posted by youngnstudly View Post
    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.
    It all depends on what your doing obviously, but it's not time consuming at all if your setup for it. I have a blasting cabinet too but for large flat pieces of sheet metal the acid is the quickest way to go. I do a lot of cnc plasma cutting, some of the pieces are 50" across. I have a hose right in my driveway off the garage and an air hose right of the garage, it takes me 5 minutes to get it done on a large piece.


    Sent from my SPH-L710 using Tapatalk 2
    Soon to be 2013 250EX tig machine
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    South Bend 9 lathe WW2 vintage
    Devilbiss 6.5hp 80gal 175psi 2 stage compressor
    HF blast Cabinet modified for foot pedal operation better gun.
    Oxy/A torches
    Delta 4x6 band saw
    Hand and power tools up the wazoo.

    The name's "Marcel" in case I forget to sign.

  18. #18
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    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
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    Quote Originally Posted by DVA View Post
    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.
    Long arc, short arc, heliarc and in-the-dark!

  20. #20
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    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.
    Last edited by jakeru; 02-19-2013 at 03:25 AM.
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