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Splotchy anodize or dye result

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  • #16
    Based on my testing it doesn't do that well for de-oxidizing, but if the parts are left in for hours it will eventually. There are other chemicals used as well as stripper or sodium hydroxide, but we use the sodium hydroxide on parts that we feel need to de-oxidized. Various alloys act differently, but ones like 2011 and 6061 will quickly have a smut layer form from the sodium hydroxide action. We leave them in until a light layer is formed, the time will depend much on concentration and temperature. It seems like a fairly strong solution with a short (30-120 seconds) imersion time works best overall for us, as compared to a weak solution and longer time.


    Curiously, some alloys like 6063 (and 1000 series if I remember correctly) are much slower to form a smut layer and resists the normal dulling from the lye. We de-oxidize 6063 in the sodium hydroxide bath according to the 6061 times. The finished results and consistency are much better on parts that are totally de-oxidized.

    We did get 5 gallons of Caswell's de-smutting concentrate, and do use it for that purpose and it works very well for that.

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    • #17
      so say I strip the ano off some parts.....let them dry, then polish. Say the parts then sit a couple days, or even weeks before ano. Your saying they can oxidize and the desmut/deoxidizer that caswells carries simply wont remove it?

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      • #18
        We have anodized fully machined parts that are several weeks old (even a few months, actually), and they come out perfect without a seperate de-oxidizing step. So, unless there is something about the buffing process that causes parts to oxidize quicker than normal, I would guess the parts should anodize ok even after a fews weeks time goes by.

        On the other hand we have parts that are vibratory tumbled, and they need to be de-oxidized because of that. Even if the parts are freshly machined, de-oxidized in sodium hydroxide, and tumbled for 10 minutes, they still need to go through the de-oxidizing step again before tumbling.

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        • #19
          Gentlemen:

          I began this thread under the login “sccc”, but that was a temporary login because my regular one wasn’t working, and I couldn’t get it reset due to ISP problems. That’s fixed now, so all my future posts will be from “seanc”.

          I’ve run 2 more anodize tests, and now know the source of my original problem (I think), and can now get great results! See:



          neilfj, you had my problem properly identified first time. Keeping the part wetted at all times!

          In my 3rd test, everything was going well until the after the part was sealed. In my haste to get it out of the hot sealant into the rinse tub, I dropped the part. By the time I could grab it back up, it had mostly dried. Doesn’t take long when the part is at 210º or so! If I’d have been thinking right, I should have put it back in the hot sealant, but I didn’t. I rinsed it, and the finish is horrible, as the photo shows. This might be salvaged by polishing, but I haven’t tried yet. Just wanted to get the photos first.

          So on my 4th test, I did 2 things differently. 1) reduced dye temp to 120º (a recommendation I saw elsewhere), and 2) left the part in the sealant, and cooled the sealant by dropping the tank into a larger bucket of cold water. When the sealant was down to 90-95º, I pulled and rinsed it. It came out great! I plan to cool the sealant this way from now on.

          So I think I’ve got this figured out, and my next run will be on the real parts.

          Thanks everyone!
          Seans Zinc Plating page

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          • #20
            Glad to help.

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