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Yellow Chromate Rubbing Off

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  • Yellow Chromate Rubbing Off

    I'm having an issue of the yellow chromate rubbing off once handling the zinc'd parts. Parts have been hang drying for over 24 hours, several hours with a fan. While removing the part from the copper wire, the chromate is rubbing off exposing the bright zinc'd surface beneath.

    Each part has been dipped for 30 seconds in yellow chromate bath with temperature of about 80 degrees F, rinsed and hanged to dry. The room they are drying in is about 60-65 degrees F.

    Any ideas on what I am doing wrong? Also, to get these parts looking good again can they be rechromated or do they have to be stripped and rezinc'd all over again?
    Last edited by dsylvia; 03-06-2022, 09:00 AM.

  • #2
    Could be a couple things going on here, Have you tried dipping them longer than 30 seconds ? What is your Zinc plating chemical and process ?
    --
    Jason Vanderbroek
    315 946 1213 x116
    www.caswellplating.com

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    • #3
      I am new to the Forum Thank you for letting me post, I too am having an issue with the yellow chromate rubbing off after setting for 24 hours. I just had it yesterday 4/20/22 and I was wondering if I was doing something wrong? I have the cad plating tank heated to 72* and I put the part in the tank for 30 min. after that I double rinse the part in 2 clean rinses (distilled water) them go directly to the yellow chromate tank. I dip the part for about 8-10 seconds to get the color I am trying to achieve and let them dry over a small fan for a few hours and then over night before I touch them. when I look at the other end of the part that was chromated the day before in the same way with moving the part the yellow chromate has been rubbed off. Am I doing something wrong? I know when we put these parts back on the wrenches are going to scrape the chromate off, any suggestions?

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      • #4
        I thought I would post a solution to this problem I found through some experimentation. First, I made several successful runs with my Caswell Zink kit going directly from the Zink rinse tank and spray bottle rinse to the Blue Chromate for 40 seconds. The polished parts are almost like chrome and with no adhesion issues at all. Once I completed my Blue parts run, I went to the Yellow. Going direct from Zink rinse to Yellow Chromate (1 oz./Gal.) just as I had done with the blue. The appearance was good but after 72 hours of dry time not only were there bare Zink areas in the chromate but it was also flaking off. I then added another ounce of chromate to the mix and also started doing a 6 sec dip in 5% Muriatic acid, rinse, then yellow chromate. The result was slightly darker color but still flaking off.

        Now for the solution. I went from the Zink rinse to a 20% by volume Sulfuric dip (1 part battery acid to 4 parts distilled water) for 10 sec. then rinse, then DRY with compressed air, then 45 sec. in the chromate then quickly DRY the part again with compressed air and hang. I believe switching from Muriatic to Sulfuric and drying the part is key both before and after the yellow chromate and that the residual water is weakening the bond. My parts are not only beautiful in color somewhere between iridescent green and golden bronze depending on the angle of the light but the chromate is SOLID! I can remove them from the wires the next morning. No waiting. Give it a try.

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        • #5
          Tomcat11, Well done on finding the solution. I will provide my insights. For the blue (almost chrome) chromate treatment I dip the hardware in nitric acid before chromate dip. For the post chromate dip drying I use a 1970's hair dryer. I made a rig using a vertical four-inch PVC tube with the hair dryer blowing warm air in the bottom and I hang the hardware from the top.
          Good luck and enjoy.
          KRR

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          • #6
            Thanks FASTLIKEJUDY. I never tried to find Nitric, I read of other folks using it too but also heard it's hard to get. That is a very clever idea for drying parts!

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            • #7
              Greetings Tomcat11, I also struggled finding nitric acid but stumbled on finding it at Walmart online (our world keeps getting stranger). I see Walmart still lists various concentrations for sale. I purchased six, one-ounce bottles. Be well and have fun! KRR

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              • #8
                when i first started out with copycad a few years ago i was having the same problem. i went to a 2% post plate nitric dip for desmutting. i could not believe the difference. instantly turns a bright silver and has excellent chromate adhesion. ill never use hydrochloric again. i think they say to use it because its readily available.

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