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Yellow chromate, whats the secret?

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  • #31
    Re: Yellow chromate, whats the secret?

    I have been plating with Copy Cad for over 6 years now and I get excellent results with Yellow Chromate and Blue Chromate and occasionally with Black Chromate.

    I do not use brightener at all since it simply doesn't work for me.

    I polish all of my parts that I am going to chromate with a wire brush immediately after plating.

    I rinse my parts in distilled water using a spray bottle over my plating tank (the idea is to save the plating solution) and then I immediately rinse the part in a tap water bath. I then dry the part with an ordinary cloth towel (clean one) and then I polish the part on a wire brush wheel. I then go immediately into the chromate bath for around 30 seconds or so. I gently agiatate the part by swirling it around in the chromate solution. I then remove the part and rinse it in distilled water over the chromate bath using a spray bottle and then I dip the part in a tap water bath, shake the excess water off and hang the part to dry for 24 hours.

    I have never had a problem with the chromate peeling. The only problem I have had is sometimes a part will not take the chromate or it will have spots and areas that will not take the chromate. After much trial and error, I have come to the conclusion this is always caused by the zinc plate being too thin. In those cases, I strip the chromate off in Pickle #1, rinse in distilled water and re-plate.

    Just a comment; for hydrogen embrittlement, you need to bake your parts at around 400 to 450 degrees F for four hours immediately after plating. It does no good to bake the part after a long time has elasped after plating. I have had only a few failures due to hydrogen embritllement and they were always either springs or bellville washers.

    Again, its very important to have a good thick zinc plate to get good chromate results. I plate for 2 hours, at 120 degrees F (Copy Cad bath temperature) at 25 ma per square inch in my small bath and at around 50 to 75 ma per square inch in my larger bath.

    I have the old Copy Cad bath. I never use a pre-chromate acid dip of any kind.

    Jerry Hudgens

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    • #32
      I know this thread is a bit old but I too had problems with the yellow chromate. I'm new at the overall process so take with a grain of salt but have added the following steps to the chromate process with good results now.
      1. After plating I rinse the part and dip in a 10% sulphuric acid bath for 10 seconds. (seems to brighten part)
      2. Rinse
      3. Dip in chromate for 10 -15 seconds agitating rapidly.
      4. Rinse for a couple of seconds in denatured alcohol bath.
      5. Fan dry.
      The alcohol was the trick. There may be good chemistry reasons not to use it that I'm not aware of but I found using water was too slow to evaporate and could cause flaws to the chromate. The alcohol evaporates very quickly leaving a shinning surface with all the great hues of yellow chromate.

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