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Is there an EASY way to remove the black scale from the surface of hot rolled steel?

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  • Is there an EASY way to remove the black scale from the surface of hot rolled steel?

    The title says it all! I've tried a wire brush and a powered wire brush. All this seems to do is make the scale appear shiny. There must be a better way. PLEASE tell me.


  • #2
    Pickled. You soak in Acid. I would use sulfuric, probably 10%....but at least knowing what it is called will get you started googling for ideas. I think with commercial ops its a blended concoction. I doubt after getting all the ingredients and containers and futzing about with it it qualifies as easy, but that's how its done.

    PS....wondering why you want to? bar stock or sheet? you can just machine through it (yeah its slightly messy, but the hobby isn't stamp collecting), it takes paint well and is a great protector from rust. I fabrication, we only want HR because P&O (pickled and oiled) rusts so quickly and can't be painted (well, not unless you want wash all the oil off).
    Last edited by Mcgyver; 09-24-2016, 10:50 AM.


    • #3
      I don't mean to be flippant, but where possible, one can pay more and get bright cold rolled instead.

      Of course, if CR is what you've got, then chemical pickling or mechanical removal (sanding, grinding, sand/bead/nutshell/olive-pit blasting) are your options for getting the scale off.


      • #4
        Most metal retailers sell cold rolled BUT be sure it is what you want. When you cut/mill/turn CRS you release all the stress put into it when it is formed and it warps/twists, some times badly.
        The shortest distance between two points is a circle of infinite diameter.

        Bluewater Model Engineering Society at


        • #5
          I have some sizable chunks of hot rolled plate already in the shop. I try to use that if I can rather than buying more steel.


          • #6
            Angle grinder fitted w/ flap disks.

            3M has a black NON-woven product that works well and which is sold in a variety of formats: brushes, disks, flap wheels & ect. The name doesn't jump to mind at the moment - if you express interest, I will go check in the shop.

            Edit: NON-woven. Initially wrote woven.

            These products are from 3M's Scotch-Brite division. I suspect they are essentially the same silicon carbide media packaged in different formats.

            Here is a velcro-backed version for use with a matching pad mounted on an arbour: Coating Removal Disk

            Here is another variation fitted directly with an arbour: Clean and Strip Disk D2

            Use either of those styles for smaller surfaces, edges or confined areas. Otherwise, look for the grinding disk versions and go to town.

            Goes without saying that a respirator ought to be worn to keep this media out of the lungs

            Last edited by EddyCurr; 09-24-2016, 11:31 AM.


            • #7
              I find sandblasting to be the most effective. Causes the scale to flake right off, gives you a clean surface that will take either oil or paint with gleeful abandon, and avoids any gouges or other apprentice marks that may go along with manually grinding.

              Flap disk is probably the fastest, but I always find it frustrating with hot rolled because the flap wheel wants to 'skate' over the low points.


              • #8
                Plain white vinegar works but takes a loooong time. I immersed some hot rolled in vinegar on a Friday afternoon, Saturday is wasn't yet removed, Sunday it may have been complete but I couldn't get to it. Monday after a rinse and a scrub it was nice and clean.

                If you're in any type of hurry I'd go with the above suggestions.


                • #9
                  Originally posted by planeman View Post
                  I have some sizable chunks of hot rolled plate already in the shop. I try to use that if I can rather than buying more steel.
                  If the material is edge to edge decarb the acid is best bet.
                  If it is discrete islands (already seasoned, light rust), an angle grinder with a 9" pipeline style wheel is effective.
                  Such a disc is 1/8" thick and designed to cut on the edge, similar to a cut-off, but quite flexible. (not invulnerable)
                  Keep the grinder moving, light pressure and work the scale edges. Usually portions will flake off, so it's not like you're grinding the whole plate.
                  A cup stone in the grinder works pretty well too but heavier to handle.
                  "Easy" is a relative term.


                  • #10
                    Head over to the belt sander and it will be gone with some coarse abrasive in a hurry.

                    Yes, it may start out by polishing a bit, but then you get through it.

                    Wire brushes are worthless, unless you get the coarse "knotted" type, which work pretty well.

                    Keep eye on ball.
                    Hashim Khan


                    • #11
                      I vote flap disc on electric grinder


                      • #12
                        Blast cabinet shooting slag is the most efficient,no acid to mess with and no pile of abrasive particles floating in the air landing on your machine ways,going down your lungs etc.

                        Best part is if you intend to paint later nothing latches onto paint better than a white blasted surface.
                        I just need one more tool,just one!


                        • #13
                          I used muriatic acid to de-rust some parts one time. It worked well but what I found was that if I didn't fully remove or otherwise remove the acid that the parts rusted pretty much while they were drying. This required copious rinsing or rinsing in a pretty strong solution of baking soda.

                          Vinegar might be slower but I suspect it will leave the metal much more tolerant during drying off the metal.


                          • #14
                            Originally posted by BCRider View Post
                            I used muriatic acid to de-rust some parts one time.
                            Countless folks have observed that merely having that bottle of acid in the shop or the garage will corrode items - even all the way across the room. Doesn't matter how tight the cap is. And then there is the issue of residual on the material, as you observed. And hydrogen embrittlement.

                            A blast cabinet seems to be the cleanest and easiest way to clean metal. The dust from a rotary wire brush or disc can be pretty hard on the lungs. I suppose a wood or cardboard box with a window might be a good way to isolate a hand grinder and avoid the hassles of the protective gear and spread of dust in the shop. It also wouldn't need the venting of a blast cabinet.


                            • #15
                              Short answer---No. It will require either mechanical abrasion of some kind or else chemicals that you really don't want in your shop nor in your lungs.
                              Brian Rupnow