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  • #16
    Originally posted by lugnut View Post

    What the hell would you do if you lived in a area where the humidity averages over 90%, like it is where I live?
    Nothing different. After mill scale removal, I soak the part in a solution of baking soda, then rinse with water. Both of those actions are fairly high humidity events.

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    • #17
      Originally posted by Doozer View Post
      Why so concerned about mill scale ???
      When I turn or mill something, the mill scale comes off,
      so ? ? ? ?
      If it is not being machined, and I am going to paint something,
      I just use a wire wheel on a grinder to clean any rust off
      then paint it.
      I have never in my life wanted to remove mill scale before I
      began machining something or really, paint something.
      unless it was also rusty.
      So please explain to me why you want to get rid of it ?

      -Doozer
      for (tig)-welding and proper painting. e.g., if you want to use a zink primer it has to go on bare metal.

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      • #18
        Grinding an edge bevel for Tig welding takes care of mill scale.
        Zinc primer prep makes sense.
        But I have never used zinc primer.

        -D

        DZER

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        • #19
          Originally posted by dian View Post

          for (tig)-welding and proper painting. l.
          All "proper" painting means is you follow the spec. temp, humidity, thickness, surface prep etc. We do a fair bit of sand blasting, to whatever profile the spec calls for, however I can tell you >95+ of large fabrications, cranes and equipment are painted direct to the mill scale. You would see more blasting on structural shapes than plate and sheet, where the mill scale is hard smooth and durable
          in Toronto Ontario - where are you?

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          • #20
            I agree. For a customer, sandblast or similar prep for sure.
            I used to be in the bridge expansion joint business. The state had a
            spec on that for sure. We would usually send stuff out for blasting
            and then sometimes galvanizing.
            But for stuff around my shop, I have had really good luck with just
            wire brushing structural steel, and spraying on phosphoric acid,
            and when it is dry, brush painting with Rustoleum oil paint, no primer.
            I don't think the phosphoric acid just sprayed on removes any mill scale,
            it just passivates the surface.

            -Doozer

            BTW- Our bridge joint shop was an old Westinghouse building, with
            a 20 ton crane. Riveted construction, don't know the name.
            It was 3 phase motors with fluid coupling drive. No brakes or they
            did not work. To stop it, you had to reverse the motor. Thankfully
            the hoist had a brake. --D
            DZER

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            • #21
              Originally posted by nickel-city-fab View Post

              LOL you're 80 yrs old ??? j/k
              Hahaa. Sure feel like it sometimes. No, Im young, well relative to all the old farts here JR

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              • #22
                Originally posted by Doozer View Post
                I don't think the phosphoric acid just sprayed on removes any mill scale,
                it just passivates the surface.

                -Doozer
                --D
                100% correct, the phosphates are used extensively to blacken guns in order to protect the machined surfaces. It's just porous enough to retain oil. Manganese Phosphate or Zinc Phosphate. There's actually a mil-spec for the process (fairly simple). The same process is often used to blacken and protect tools -- such as hex keys, impact sockets, etc.

                BTW a large fab sop was hiring all last year for a expansion joint welder. It's prolly your old employer now owned by BASF. I have zero interest in welding 2" plate with flux core unless their bennies package is huge. (defined pension, 100% medical)

                I regular see their ads online in the local area.
                25 miles north of Buffalo NY, USA

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                • #23
                  Nope, not Watson-Bowman-Acme. It was my father's own business, Superior Contractors.
                  We had a shop in Tommy Price Trucking's building on Mystic St, off Hopkins, near SouthPark
                  and Tift streets. We operated it for 7 years, but NYS was always late on the budget and it
                  was difficult to have payroll for the men when no payments were coming in. We had a stud
                  welder that was 1800 amps. Would weld a 1" stud down in 1/2 a second. Later after we
                  moved out of Price's building, a CNC outfit moved in there. Just last year, I saw Cash Cunningham
                  auctioning all the machines off. Nice stuff to. Even a HBM or 2 as I recall.

                  --Doozer
                  DZER

                  Comment


                  • #24
                    Originally posted by Doozer View Post
                    Nope, not Watson-Bowman-Acme. It was my father's own business, Superior Contractors.
                    We had a shop in Tommy Price Trucking's building on Mystic St, off Hopkins, near SouthPark
                    and Tift streets. We operated it for 7 years, but NYS was always late on the budget and it
                    was difficult to have payroll for the men when no payments were coming in. We had a stud
                    welder that was 1800 amps. Would weld a 1" stud down in 1/2 a second. Later after we
                    moved out of Price's building, a CNC outfit moved in there. Just last year, I saw Cash Cunningham
                    auctioning all the machines off. Nice stuff to. Even a HBM or 2 as I recall.

                    --Doozer
                    Cool that's some good info. FWIW there is another bridge shop in Sanborn that hires sporadically http://www.nbrfab.com/
                    pretty sure they used to be Great Lakes Metal. Core Welding is still out that way, and Buffalo Gear but I don't see much activity around their shops in the last ~20 yrs. I'm curious to find out what kind of gear machines they have.
                    25 miles north of Buffalo NY, USA

                    Comment


                    • #25
                      Originally posted by Mcgyver View Post

                      All "proper" painting means is you follow the spec. temp, humidity, thickness, surface prep etc. We do a fair bit of sand blasting, to whatever profile the spec calls for, however I can tell you >95+ of large fabrications, cranes and equipment are painted direct to the mill scale. You would see more blasting on structural shapes than plate and sheet, where the mill scale is hard smooth and durable
                      no idea about cranes, but i would guess that a different primer must be used on mill scale.

                      also, from my experience, phosphoric creates a phosphate layer on steel but does nothing to mill scale. how would iron oxide get "passivated".

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                      • #26
                        Mill scale is an oxide, a ceramic. It is just along for the ride.
                        But you knew that. And you knew that I knew that.
                        You know the passivation was for the base metal.
                        Do you think I just walked out from behind the barn
                        with shlt on my boots ? ? ? Play with someone else.
                        Maybe Jerry needs a playmate.

                        -D
                        DZER

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                        • #27
                          Doesn't matter if there is scale on the material, phosphatizing will still work:

                          "Ferrous materials, including steel, may be somewhat protected by promoting oxidation ("rust") and then converting the oxidation to a metalophosphate by using phosphoric acid and further protected by surface coating. As the uncoated surface is water-soluble, a preferred method is to form manganese or zinc compounds by a process commonly known as parkerizing or phosphate conversion."

                          from Wiki:https://en.wikipedia.org/wiki/Passivation_(chemistry)

                          On a somewhat related note, rust bluing is an old, old technique: allow the part to rust under controlled conditions, then boil it in hot water. Repeat this a few dozen times. You get a nice velvet black coating which retains oil. The boiling converts red rust (FeO2) to black iron oxide (FeO3) The technique is commonly used in protecting shotgun barrels (a subject I have been researching lately)
                          25 miles north of Buffalo NY, USA

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                          • #28
                            so phosphoric will get under the scale and produce a phophate coat on the metal there?

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                            • #29
                              If water will rust steel that has mill scale on it
                              then phosphoric acid will passivate steel with mill scale on it.
                              Or is there something I am not taking into account ? ? ?

                              -D
                              DZER

                              Comment


                              • #30
                                Originally posted by dian View Post
                                so phosphoric will get under the scale and produce a phophate coat on the metal there?
                                It doesn't need to get under it. It is possible to have more than one oxygen atom bound to iron, and that is what is happening with the phosphates, and with the old-time slow rust blueing.
                                25 miles north of Buffalo NY, USA

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