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black die looks grey

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  • black die looks grey

    Hello all this is my first post. I'm trying to anodize some 6061 and my black is coming out grey looking. Ph is 5.2 at 140 degrees. Should I check it cold or hot? Could I be anodizing it to long?

  • #2
    Could be a poor connection and the film isn't growing enough or simply not leaving it in the dye long enough. How long is it in the dye? I run my dye temps a little cooler 130 to 135 and it seems to absorb better. If it gets too warm it will start sealing the pores and could lock out before full absorption.

    I haven't run into dissolution problems myself yet so I can't say if you are anodizing too long. What is the part SA and amp specs that you are using?

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    • #3
      It's not my connection because all my other colors come out great. I was thinking I was anodizing to long and film was to big maybe. The last price I done was 150 square inches at .7 thickness set at 6.25 amps and 15 volts. Does that seem correct

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      • #4
        Running 150sqin at 6.25 amps yields just about 6ASF (amps/sqft). At that current density you should have run for about just under 1.5 hours to get 0.7 mil. Is that how long you ran for?
        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 spread the love and LIKE the post
        _____________________________________________
        Last edited by kevinB: Now. Reason: superfluous typo's

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        • #5
          At that amperage you'd need a full 2 hours in the ano tank to have enough depth in the pores for a full black dye uptake.

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          • #6
            Gardinhackle is correct. Running to .7 mils is likely the issue. Most black dye requires a thicker film (.9 - 1 mil) to hold enough dye in the pores to block all light and give you a good black. There are some other black dyes available that claim to achieve "jet black" at a much lower film thickness. I've used them with great success at .7 mils (and even slightly thinner).

            One other possible cause is a low bath temp. Pore size decreases with lower temperature, and temps lower than about 65F can result in pores that are too small to accept the "fat" black dye molecules.

            The parts in the below photo were run at 72F, to a film thickness of .7 mils.

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            • #7
              Awesome finish on that part Halfape! I can't get over the shine you have achieved.

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              • #8
                Thanks gardinhackle! I've done a lot of experimenting to try and achieve high gloss, and I think I've got it figured out (for the most part). Lots of time on the buffing wheel, very careful degreasing, building as thin a film as you can get away with, and a few other little minor things. Below is a video of the entire gun to give you a better idea of how it came out.


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                • #9
                  Well done Halfape!

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