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7000 series parts dye, but 6000 series won't

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  • #16
    Re: 7000 series parts dye, but 6000 series won't

    Here is an update to this problem...
    I finally found some time to run some experiments.
    I made two ano runs this morning on a set of identical 6061 samples. Both runs were done exactly as previously explained (6amps CD, 70F, with aggitation), only one set was ran for 1.5hrs (.75 mil target), and the other at 2hrs (1 mil taget). All the samples were dyed for exactly 15min @ 140F.
    Here are the variables...
    First run for 1.5 hrs:
    #1 rinsed in baking soda water, then dyed in the old black dye.
    #2 rinsed in distilled water, then dyed in the old black dye.
    #3 rinsed in baking soda water, then dyed in the new black dye.
    #4 rinsed in distilled water, then dyed in the new black dye.
    Second run for 2 hrs:
    #5 rinsed in baking soda water, then dyed in the old black dye.
    #6 rinsed in distilled water, then dyed in the old black dye.
    #7 rinsed in baking soda water, then dyed in the new black dye.
    #8 rinsed in distilled water, then dyed in the new black dye.

    Every sample took the dye a little differently. The finished colors ranged from a silvery dark blue-black to a nice deep true black. Listed from worst to best, here are the results:
    #1
    #3
    #2
    #4
    #5
    #7
    #6
    #8 (the only one that came out really black)

    So, the big surpise is that rinsing in baking soda water inhibits the dye. Thats too bad, because it really works good at eliminating acid carry-over and consequential streaking from holes and crevices.

    Not too surprising is the longer ano times result in a deeper color. This either means that the dye (at least black dye) does penetrate ano layers thicker than .75mil, or that I'm not building an ano layer as thick as I think I am.

    Finally, the Black dye I was using had become old (both PH levels are basically the same in the old and the new, and both were accurately mixed with distilled water).

    So all is well now... new black dye, longer ano times, and eliminating the baking soda rinse has fixed the problem.
    I do things.

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    • #17
      Re: 7000 series parts dye, but 6000 series won't

      Appreciate the info. Since you originally brought up the problem, I have stopped using the neutralizer rinse tank and just use a RO rinse tank only. I had parts dye different tints but could not pin point a problem, just attributed it to a difference in the coating. Now, with your info, I am rethinking the situation.

      One thing on your longer run times. Most likely the dye is not penetrating deeper but the pore size is getting larger and giving a better color.

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      • #18
        Re: 7000 series parts dye, but 6000 series won't

        I believe some black dyes do need a thicker ano layer for proper dying. Might wanna look into that

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        • #19
          Re: 7000 series parts dye, but 6000 series won't

          The dye does get weak with age, we have found. We have tried to strengthen it by adding more new dye to the old and it seems to work to an extent, but it does seem that the dye reaches a point where you have to add about as much new dye as if you were making a completely new batch and it doesn't seem to stay good for long. We haven't done any side by side control experiments, so I wouldn't swear this is true, but it does appear to be true.

          As far as thickness and dye qualities, there may other factors that make it look like a thicker coating dyes better. I know to a degree, a thicker coating is better. Except once a coating gets so thick, it becomes harder to keep growing it. What often happens is the coating gets softer, or more porous (dissolution). You need a certain amount of dissolution to dye the part nicely. As long as it doesn't get too bad, that softer coating dyes faster and darker. It's just a matter of the degree of dissolution, too little is bad for dying, and too much is bad also. There are ways to make a thinner coating more porous so it dyes ok. A higher acid concentration, and/or warmer electrolyte are two ways. A lot of commercial anodizers routinely use a thinner coating that looks good, for them time is money so for the most parts the less time in the tank the more loads they can run. So they have an incentive to get the parts to look acceptable in the least amount of time with as little resources used in the way of electricity and electrolyte degradation. Just something to think about.

          Also, if I remember correctly, at one point I washed dye out of an unsealed part with strong soda water and it worked as well as bleach. I don't have much time to play around with experiments because of time constraints, so I haven't tried it to find out for sure. Some day, if I think of it when it is handy and I have some spare time, I'll do a little experiment unless somebody here tries it first and reports back. Anymore, I don't do much anodizing at all. If I get involved, it is just to help trouble shoot or advise the employees, or when I am doing R&D.

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          • #20
            Re: 7000 series parts dye, but 6000 series won't

            I was going to comment on the soda rinse versus the plain water rinse and acid carry over. This is how we do it, not that it is the best way, but it works for us. We have a rinse tank next to the anodizing tank, and when parts are anodizing we submerge the rack(s) and depend on the parts agitate the racks and/or let them set for a few minutes. Naturally, the acid will build up, and even with a fresh water change you will still have a mildly acidic water left on the parts. We the use a spray rinse (hose) to to try and remove vitually all the acid. The rinse tank gets changed out for new rinse water frequently.

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            • #21
              Re: 7000 series parts dye, but 6000 series won't

              Thanks for the input guys...
              I just did a couple paintball guns, and they are dying a much deeper color now. So far, no acid "carry-over" streaks either!
              My method for rinsing is:
              Spray rinse into the ano tank paying special attention to the small screw holes, etc.
              Dunk in distilled water until ready to dye.
              Spray rinse again coming out of the dunk tank, and going into the dye tank.
              I do things.

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