Best way to Remove Mill Scale?

Discussion in 'Tools and Fabrication' started by D'Animal, Dec 23, 2012.

  1. D'Animal

    D'Animal Rescuer of Beagle and Landcruisers Moderator

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    What have you found is the best way to remove mill scale on raw metal before welding?

    I have been using the cupped 40 grit and 80 grit layered sander disc on my 4" Grinder. They seam to plug up and not be very effective. I have tried various brands and one does not stand up any better than another.

    I have tried using actual grinder discs. Using a course stone leaves little grooves on the metal. This brings the suckage when doing body work on 16g metal. I do not want to skim coat the area with body filler and the grooves are a little too deep to use a filler type primer. When I use finer grit grinding stone, it just plugs up.

    So, what have you found is the best way to remove mill scale on raw metal before welding or in the initial stages of prepping for paint?


    Thanks
  2. spressomon

    spressomon glutton

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    Won't work for large pieces but straight vinegar soak for 24-48 hours did an amazing job of reducing mill scale on some plate pieces. Then there's muriatic acid...just be careful with it because, as you probably know, its nasty stuff.
  3. HenryAZ

    HenryAZ

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    I use the muriatic acid when the pieces will fit into a glass baking pan. It cleans them up nicely for welding and later painting. I like the method because there is little work involved, other than remembering to take them out.
  4. scrapdaddy

    scrapdaddy Standing on the corner SILVER Star

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    So with this Muriatic Acid, you can't use it as a wipe down? The metal has to soak also. No good if you're in a mood to work. I use a flap disc, also.
    Last edited: Dec 23, 2012
  5. Wile E Coyote

    Wile E Coyote Dave's not here! SILVER Star

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    As stated, Muriatic acid or (what I use) Phosphoric acid is nasty stuff if not treated with respect. Wear a respirator and cover all exposed skin if you plan to put it in a spray bottle. The acid wash trick works most of the time, but I've had to break out the flap disc more than once to help it along.
  6. Joe_E

    Joe_E

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    What about flap discs Dan? I use these alot. They don't tend to clog, just wear off and expose newer grit.

    [​IMG]
  7. D'Animal

    D'Animal Rescuer of Beagle and Landcruisers Moderator

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    That is what I have been using. They work Great for about the 1st minute and then begin literally polishing the mill scale.
  8. Joe_E

    Joe_E

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    Lol
    Now i realized you called it a layered cup disc.
  9. i dont buy much hot rolled anymore for just this reason, but sometimes i get some at a great price or free so i usually just hit the area i'll be welding with a good old fashion grinding disc, a belt sander works pretty well too. if appearance will be an issue sand blast it with a real coarse grit.
  10. Rwhat

    Rwhat

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    Muratic acid works good. I bought it at lowes. It's used for cleaning concrete and etching. Make sure to pour the acid into water. I usually keep bucket of baking soda/water on hand to neutralize the acid. if your doing anything structural I would be carful since it can cause hydrogen inbrittlement. Also use the stuff outside and make sure to store the bottle outside or sealed up good. If the fumes leak out it will cause stuff to rust.
  11. smtyblt

    smtyblt

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    D a knotted heavy wire wheel will also do the trick most of the time.

    Cam

  12. Pin_Head

    Pin_Head

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    Use flux core or stick welding and you won't have to worry about removing the mill scale.
  13. D'Animal

    D'Animal Rescuer of Beagle and Landcruisers Moderator

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    I'm not good enough to use my stick welder on body panels. LOL


    :D
  14. You have mill scale on body panels? :confused:
  15. Pin_Head

    Pin_Head

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    I think that is called rust.
  16. D'Animal

    D'Animal Rescuer of Beagle and Landcruisers Moderator

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    The New 16 gauge steel that is replacing the rust has Mill Scale. :doh:
  17. Gusb

    Gusb

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    16 GA hot roll or cold roll steel? What about the Metal Prep/ready stuff (from the POR15 people) or something like it? Before you do too much extra work you might be better off buying good cold roll.
  18. SM Racing

    SM Racing

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    Don't use hot rolled for body panels, you will hate life. Go get some cold rolled sheet and cut the pieces you need. You could sand blast or bead blast the pieces to get the mill scale off, plus it leaves a great finish for paint/primer.
  19. scottm

    scottm

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    x2 on sandblast, especially if you are talking small parts. I haven't seen sheet steel with mill scale, I order everything HRPO (hot rolled pickled and oiled). The pickling takes off the mill scale, then a protective oil is applied.
  20. titanpat57

    titanpat57 SILVER Star

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    The Depot has some blue "fiber strand" wheels that fit on the grinder...they seem to do a better job than the flapdisk.

    The one thing I would do is wear safety glasses..seems these fibers fly everywhere.

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