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anodized coating coming off???

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  • anodized coating coming off???

    Hi everyone,

    I’m starting to get into anodizing and initially had good results with different parts and colors I tried. I just did a batch of 24 parts with a somewhat fresh batch of black dye. The first couple parts I dyed came out fine, but this batch is having issues. When the parts were finished there were patches on all sides where it was a different shade of black, almost like a stain or a patchy area. It was still black though and wasn’t coming off when wiping the parts down (even after with acetone) so I was going to move on anyways. As I was wrapping up the parts I got some tape on one of them and when I pulled it off, one of the “patches” came off with it, leaving a somewhat bare silver/grey area. I tried sticking tape on the other parts and every single one is the same way. What would cause this I’m running 10% sulfuric acid at 72 degrees, 720 calculations at 6 amps per sf with the surface area being pulled directly from CAD files. Parts are cleaned with a heavy duty cleaner and pass water break test, rinsed, desmut for 2-3 minutes at around 70 degrees, rinse, anodize tank, rinse, dye at 140 for 20-30 minutes, rinse, nickel acetate sealer. I’m not using distilled water, but as I said before, I had great results for a few months before this came up... Hoping someone here might have an answer.

  • #2
    Whats your starting and ending voltage during anodize? Although I suspect this to be ok.

    I would try making sure the parts and or the solution is circulating for the dye process. I have seen dye settle on parts causing thicker areas. I would also try lowering the temp a bit to around 120F as this is what I get the best results with. In my opinion 30min. is a long time for a part to be sitting stagnant in dye. Personally if I'm doing a long dye session, every 3-5min. I swish the part around to maintain a clean and consistently exposed part to the dye because it can slough, build up, and can cause issues. I think black is the most susceptible to this and of course because its black you can't see this happening. What you're pulling off with tape isn't the anodic coating, its dye. This excess should leach out during seal but in this case it may not be.
    Last edited by xNocturnalx; 08-01-2019, 05:29 AM.


    • #3
      It sounds like its an adhesion issue, especially now that its coming off with tape.

      I see that you have heavy duty cleaners but do you have an etch process prior to anodizing your parts?

      If the surface is not etched properly you might be dealing with a thin aluminum oxide layer in between the part and the anodizing layer.
      Jason Panarra, MBA CEF
      Coatings Chemist – Coatings