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  • Smut Bath not etching

    Hi everyone, im new to this and anodized my first part the other day...came out alright . A bit spotty but im sure that was my setup. I attepted my second part yesterday and i dont think it etched. The Smut bath was reacting well but the surface color of the aluminum was not changing. The ends of the part were welded on and they did change but the finned extrusion did not except slighty on the ends where it looks like there was heat from welding.

    I must have sat in the etch a couple hours aa i checked it about every 15 min. Ano bath also didnt seem to work. CC power supply limits to 7 amps and was hovering around 5 volts. The first part was also at 7 amps and voltage started at 25 moved down to 9 and back up to 20 in about 90 min.

    I even set up a battery charger in parallel...15v at unknown amps.

    Could I have an extruded alloy that just wont anodize?

    Thanka

  • #2
    Originally posted by Scott Beatty View Post
    The Smut bath...
    There is no such bath. Your etch tank will create smut on the part which you remove in a deox bath.

    Originally posted by Scott Beatty View Post
    I must have sat in the etch a couple hours...
    Assuming you are using a caustic etch and it was working properly, your part would have been noticeably smaller if not completely dissolved after a couple of hours so I'm assuming this is your problem.

    Originally posted by Scott Beatty View Post
    Could I have an extruded alloy that just wont anodize?
    It's not likely. In fact if it's an aluminum alloy then no, it will anodize if processed correctly. It's more likely that your part was either dirty, not etched properly or something else in your process has gone awry.

    Anodizing welded parts can have some challenges. First being that the weld itself is most likely a different alloy that the part. In general, mixing alloys is not recommended because different alloys anodize at different rates. Second is the fact that welding a part changes the alloy's temper which will also change the anodizing rate. And then there is making sure the 2 parts welded together are the same alloy.

    There really isn't a lot of help I've given you, but if you do need more help, please post your complete process steps. The more we know about what you did, the more we can say what you need to do to fix it.
    GL
    Kevin
    Last edited by KevinB; 04-19-2020, 10:33 AM.
    Process control doesn't give you good quality, it gives you consistent quality.
    Good quality comes from consistently doing the right things.

    Process control systems for Anodizers
    If a post helps you out LIKE the post
    I'm not an Amateur Metal Finisher. I've just been around the industry for a dozen years or so helping and consulting when and where I can.

    Comment


    • #3
      Kevin, thanks for responding. Ill get some pics up this afternoon but heres the process i have been using...i use a separet pair of Nitril glives in each step

      1) Degrease with Scrbbing bubble to get any clear contaminants off.

      2) Rinse in DI water

      3) Clean in an Ultrasonic cleaner for 30 min at 45degC

      4) Rinse in DI water

      5) Etch Bath, 3 table spoons of Lye per gallon...6 gallon bath. This should be 15 min or so but some parts just didnt etch

      6) Rinse in DI water

      7) Ano bath, 50/50 DI water and battery acid 90 min. Bath temp 70 deg. Lead flashing used as cathode. Agilent 200W digital control lab quality power supply

      Rinse in DI water

      9) Rit Dye bath between 140 and 180 F fot 10 to 15 min

      10) Rinse in DI water

      11) Boil 20 min in DI water.

      Comment


      • #4
        Heres a pic if a part in the Lye Bath
        Attached Files

        Comment


        • #5
          Heres the part in the ano bath. Thisis with the power supplies poles reversed...only way to get a rwaction. So ive put it back into the etch bath. Been there about an hour and a half now. Still light in color little to no grey. Could there be a really thick previous anodizing that takes a really long time to etch off?
          Attached Files

          Comment


          • #6
            So latest attempt. The ano bath looks like its working backwards. Bubbles and reaction are moving from the lead cathode. Everything I have read and seen seems opposite.

            Comment


            • #7
              Originally posted by Scott Beatty View Post
              So latest attempt. The ano bath looks like its working backwards. Bubbles and reaction are moving from the lead cathode. Everything I have read and seen seems opposite.
              You should see bubbles forming on the cathodes. This is hydrogen ions (given off by the anodizing reaction) combining to make Hydrogen gas.
              Process control doesn't give you good quality, it gives you consistent quality.
              Good quality comes from consistently doing the right things.

              Process control systems for Anodizers
              If a post helps you out LIKE the post
              I'm not an Amateur Metal Finisher. I've just been around the industry for a dozen years or so helping and consulting when and where I can.

              Comment


              • #8
                I think its most likely i screwed up the chemistry in the etch bath. The first test part took dye really well but subsequent parts formed a coating of what looks like Aluminum Oxide.

                I used a piece of Aluminum TIG rod as a hanging wire which dissolved. Im assuming that threw the chemistry out of wack and now it doesnt etch properly and effects every step down the line.

                Comment


                • #9
                  Originally posted by Scott Beatty View Post
                  subsequent parts formed a coating of what looks like Aluminum Oxide.
                  That's the goal, however, for many alloys with a 0.5 mill you can't really see the coating unless you know what to look for.

                  What did your coating looking like? Was it a white power?

                  From your previous comments, yes your etch bath is no good.

                  Process control doesn't give you good quality, it gives you consistent quality.
                  Good quality comes from consistently doing the right things.

                  Process control systems for Anodizers
                  If a post helps you out LIKE the post
                  I'm not an Amateur Metal Finisher. I've just been around the industry for a dozen years or so helping and consulting when and where I can.

                  Comment

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