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  • Mill Scale

    Is mill scale removal required for MIG and\or Flux Core wire feed process on hot roll carbon steel, ASTM A36.

  • #2
    Can you weld over mill scale, sure. Would you want to? Not me.

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    • #3
      For mig, remove the scale for sure. Flux cor will be a little tolerant of the scale.
      7018 stick, weld right over the scale.
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      • #4
        Placed some 18" long , 2" x 2" x 3/16" A36 structural steel in one of those flip top plastic containers from HD for three days in a gallon of muriatic acid , then dropped the steel into a plastic container filled with water and a box of baking soda, seemed to clean off the mill scale, but left rough finish.
        however, 18" is the longest length using this type of container.

        is stick welding better than Mig or flux core when welding A36 structural steel without mill scaled removed?
        considering penetration, fusion, slag inclusions, porosity.

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        • #5
          Originally posted by Almond farmer View Post
          is stick welding better than Mig or flux core when welding A36 structural steel without mill scaled removed?
          considering penetration, fusion, slag inclusions, porosity.
          Code or non code welding? For code welding we were supposed to grind back 1" from either side of the weld. For mig you should grind it off if its real thick. Stick seems to burn thru...Bob
          Bob Wright

          Spool Gun conversion. How To Do It. Below.
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          • #6
            Three days in a pickle bath to remove mill scale? Are you the text book definition of OCD or just like screwing around with stuff? You could've taken a flap disc, scotch bright disc or any number of mechanical means and been done in about two minutes.

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            • #7
              Originally posted by Almond farmer View Post
              ...is stick welding better than Mig or flux core when welding A36 structural steel without mill scaled removed?...
              Flux-bearing processes are by definition better at contaminants. Stick is better than FC. MIG still goes through most mill scale, but now it even more depends on what you are building with it. Does it just need to stick together, or do you need the strength of a full-penetration joint?

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              • #8
                Originally posted by Almond farmer View Post
                Placed some 18" long , 2" x 2" x 3/16" A36 structural steel in one of those flip top plastic containers from HD for three days in a gallon of muriatic acid , then dropped the steel into a plastic container filled with water and a box of baking soda, seemed to clean off the mill scale, but left rough finish.
                Talk about taking the easy way out!

                Here, maybe this will help...have fun! Click image for larger version

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                • #9
                  Roger,
                  First off, Happy 117th Birthday !!!
                  For a Stress Analysis Engineer for a MAJOR mfg like Boeing, you sure do ask some very elementary questions.
                  One thing you seem to struggle with is keeping it simple.
                  People mig weld/mfg every freekin' day on things with mill scale. You should know this. From the level of questions you ask, I sorta doubt it would make much difference what process you choose at this time.
                  I recommend you take a weld class and don't tell ANYONE your background. It would help you immensely.
                  With my 350P on steel I almost never worry much about mill scale before welding on clean steel. Tig is a different story.
                  Critical parts would require critical preparation, again you should already know this.

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                  • #10
                    Still trying to get a straight answer on MIG and mill scale on A36 structural steel from actual experienced welders.

                    Fusionking ,
                    try to find a weldment on aircraft, commercial or military.

                    While in the oil and gas industry everything is welded, mainly stick welded.

                    The community were I now reside in CA has more Trail blazers and Rangers per capita than west texas, pipe pilled sky high in the steel supply yards and racks and racks of structural steel on the main Blvd.
                    however, the bolt supply store has bolts the size of your arm.

                    joined up to this forum to learn about welding machines and there capabilities and not be criticised from asking questions.
                    if no one wants to answer, so be it.
                    I know many of these questions have been ask many times in the past and seem stupid to some.
                    To criticize and make childish fun of the OP is ciber bullying.

                    The topic is not how to remove mill scale from structural steel, even though by last count there is ~ 10 million tons of it produced every year and about 1 million tons of it recycled into new steel.

                    Maybe a MIG arc spray with pulse is the correct procedure for welding through mill scale comprised of many different forms of Fe oxides that are quite hard, really do not know.
                    What affect does constant voltage setting have on melting through mill scale.


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                    • #11
                      Originally posted by Almond farmer View Post
                      try to find a weldment on aircraft, commercial or military.
                      Hmmmm..according to the FAA, welded joints "are quite common in aircraft construction, particularly in tubular structures."

                      I'm more worried about all the steel you ruined through hydrogen embrittlement...aren't you???

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                      • #12
                        Originally posted by Almond farmer View Post
                        Is mill scale removal required for MIG and\or Flux Core wire feed process on hot roll carbon steel, ASTM A36.
                        Wipe down with acetone, then light grinding/heavy sanding of scale to prep the weld area is quicker/cheaper/faster than having to deal with porosity, etc.--after welding. Mill scale comes in a wide variety of types/thickness and contaminants--as you've surmised.
                        Often one can 'get away' with no doing a minute or two of prep....but still occasionally stumble into porosity park and the re-work.
                        Spray welding (with it's large heat input) will readily create lots of porosity if that scale contains any volatiles; ditto for rust.

                        I believe I've submitted a "straight answer on MIG and mill scale on A36 structural steel from actual experienced welders."....for your approval.

                        Weld prep is everything.

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                        • #13
                          Cyber....bullying...???? Wha?????

                          I am checking out on that one amigo. Pull up your big girl panties already.....Cyber bullying?....for cryin out loud....grow a pair would ya?

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                          • #14
                            Posts 2, 3, 5 & 7 were pretty straightforward answers from experienced weldors. My post 7 also included a question for you to be more specific. Maybe I'm on your ignore list or something? Now I feel bullied!
                            Last edited by MAC702; 12-28-2017, 03:33 PM.

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                            • #15
                              Originally posted by Almond farmer View Post
                              Still trying to get a straight answer on MIG and mill scale on A36 structural steel from actual experienced welders.

                              Fusionking ,
                              try to find a weldment on aircraft, commercial or military.

                              While in the oil and gas industry everything is welded, mainly stick welded.

                              The community were I now reside in CA has more Trail blazers and Rangers per capita than west texas, pipe pilled sky high in the steel supply yards and racks and racks of structural steel on the main Blvd.
                              however, the bolt supply store has bolts the size of your arm.

                              joined up to this forum to learn about welding machines and there capabilities and not be criticised from asking questions.
                              if no one wants to answer, so be it.
                              I know many of these questions have been ask many times in the past and seem stupid to some.
                              To criticize and make childish fun of the OP is ciber bullying.

                              The topic is not how to remove mill scale from structural steel, even though by last count there is ~ 10 million tons of it produced every year and about 1 million tons of it recycled into new steel.

                              Maybe a MIG arc spray with pulse is the correct procedure for welding through mill scale comprised of many different forms of Fe oxides that are quite hard, really do not know.
                              What affect does constant voltage setting have on melting through mill scale.

                              Sounds to me like you have all the knowledge and answers.
                              Good luck.

                              Griff

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