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Yellow chromate, whats the secret?

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  • bpu699
    started a topic Yellow chromate, whats the secret?

    Yellow chromate, whats the secret?

    I have read about 20-30 posts on here with folks having problems with the yellow chromate. Add me to the list...

    Chromating for 3 seconds or so (what the manual states), does nothing. Chromating for 40 seconds or so, gives a nice color. (PS. I didn't recieve chromate crystals, but a chromate solution)

    As other users have mentioned, touching the chromate while its wet, wipes it right off. When its dry, its much more durable, but a forceful application of my thumbnail wipes it right off. Is it supposed to wipe off when wet?

    I have read tons of posts on here about this, and still have questions:

    1) How durable is the chromate supposed to be

    2) Does the chromate "harden" with time? Will it be more durable after a week or two?

    3) What are the most common reasons for the chromate NOT working? I have seen posts where it was recommended that the acid dip be skipped. Other where it was recommended that one dip for a longer period of time. Some folks recommened more time flushing the newly plated pieces with distilled water. Others have recommended tap water.

    WHAT ARE THE REASONS FOR THE CHROMATE NOT BEING DURABLE?

    More washing time?

    More/less time in the acid dip?

    More drying time?

    Has anyone achieved a VERY durable chromate finish? Whats your secret? The parts look great...but I really don't want to be redoing all of them any time soon...

    Any help appreciated. (PS. I am following the new manual to the letter, when it comes to plating/chromating).

  • jetcat
    replied
    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.

    Leave a comment:


  • JHudgens
    replied
    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

    Leave a comment:


  • zincplater
    replied
    Re: Yellow chromate, whats the secret?

    And speaking of "Yellow chromate, what's the secret?", I have not had a problem with durability since I "got it right" last year. I have read the forums throughly, trying to follow every tip and keep the plating system as tightly controlled as possible and it seems to have paid off. I rarely have sloughing or any issues, so long as everything is done correctly.

    That said, I want my items to have to most durable finish possible. Is the general consensus that the parts should be heated after they've air dried? I haven't been performing this step since I first tried it and the chromate changed to a darker (less favorable) color...I think the temperature might have been too high.

    Since then, I just used compressed air to remove all water, then hang them to "cure" for a day or two.

    Thanks!!!

    Leave a comment:


  • lcaswell
    replied
    Re: Yellow chromate, whats the secret?

    Fixed now.

    Leave a comment:


  • zincplater
    replied
    Re: Yellow chromate, whats the secret?

    Thanks, but attachment no worky.

    Leave a comment:


  • lcaswell
    replied
    Re: Yellow chromate, whats the secret?

    Yellow Chromate.pdf

    Fumes are minimal because the solution is not agitated at all, but when in doubt, you should always use appropriate protection.

    MSDS attached.
    Last edited by lcaswell; 02-14-2010, 12:44 PM.

    Leave a comment:


  • zincplater
    replied
    Re: Yellow chromate, whats the secret?

    Thanks. Not to hijack this thread but should one wear a respirator any time the chromate tank is opened? I try to ventilate my work area (harder when it's 25 degrees out) but spend a lot of time working over the tanks and if I understand it correctly, hexavalent chromate is a lot naster than trivalent. Contact (skin) is practially nil but inhalation of vapors is a concern.

    Leave a comment:


  • lcaswell
    replied
    Re: Yellow chromate, whats the secret?

    Hexavalent

    Leave a comment:


  • zincplater
    replied
    Re: Yellow chromate, whats the secret?

    Wait...is the yellow sold by Caswell hexavalent ortrivalent? EPi produces both. I don't think the Caswell site provides that info and I've seen both mentioned on the forums.

    Leave a comment:


  • NOL4154
    replied
    Re: Yellow chromate, whats the secret?

    First,
    I will recommend to you for future reference is "Product Finishing.com and Metal Finishing.com". I have been in Metal Finishing for 30 years and believe in "Process Control".

    1. Chemistry control: Chrome Concentration & pH. If you control solution in
    it's parameters should not have problems.
    2. Time follow recommendation from Technical Data. Longer time is at times
    the worse option.
    3. Drying time and heat. Chem film also refered to conversion coatings with
    chrome does not do good with high heat. Try to use about 100-125 F air
    circulation oven.
    4. Chromate finish can not be measured!
    5. Also, just because you do not see the rainbow color does not mean that it
    has no chromate film.
    6. How durable is the chromate supposed to be? It's not formualted for
    hardest or a strong for corrision protect. It has it's limits.
    7. Does the chromate "harden" with time? Will it be more durable after a week
    or two? No.
    8. What are the most common reasons for the chromate NOT working?
    Chemistry control! Concentration & pH.
    9. I have seen posts where it was recommended that the acid dip be
    skipped. The chromate process has been set and any changes will lead to
    problems with our finish.
    11. Recommend a predip acid dip before chromating (5-10% Nitric acid).

    12. Other where it was recommended that one dip for a longer period
    of time. Follow your technical data.
    13. Some folks recommened more time flushing the newly plated
    pieces with distilled water. Recommend but expense!
    14. Others have recommended tap water. Could effect finish later in time
    with corrision (Cl or Fl ions in tap water).
    15. WHAT ARE THE REASONS FOR THE CHROMATE NOT BEING DURABLE? Not
    formulated for hardeness. Finish is for corrision protection and for under
    coat for paint.
    16. More washing time? ?? Do you mean clean base material before
    chromating?
    17. More/less time in the acid dip? 6-8 seconds.

    18. More drying time? Dry for 30 mins or less in air circulating oven.

    I my experince with chromate finish has been excellent in the Hardware, auto and aerospace industry. The secret is process control for consist and repeatable finish.

    Nol4154

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Re: Yellow chromate, whats the secret?

    For the chromating process. The solution should be mixed at 1/2 to 2% by volume and used at 65 to 90 degrees F.Once the parts have been plated and rinsed with distilled water, you should dip in the yellow chromate for 5 to 30 seconds, do a cold water rinse followed by a hot water rinse @150 F, both for about 10 seconds. After these steps you should hot air dry at no more than 170 degrees F. You can use a 1% sulfuric acid etch after plating to neutralize any residual plating solution. before chromating. If you dip the parts into the chromate for a longer period than recommended it will start to eat itself off.

    Leave a comment:


  • red911
    replied
    Re: Yellow chromate, whats the secret?

    Hi,

    The best thing I can add after only having done one batch is to use Blue Chromate for 45 seconds and then heat to 200 degrees for three hours.

    Good luck, Tom

    Leave a comment:


  • kxkraze
    replied
    Re: Yellow chromate, whats the secret?

    Tom,

    Congrats on your success and thanks for the write up!!

    FYI -- I referbished a very high end golf course greens mower last year with the Caswell zinc system -- double chromate (blue then yellow) on everything. Some of the parts are carb. parts and the machine has been used all year. The zinc and chromate job has held up great!!! There are only a few parts that will need to be replated this Winter and that is because they were in high wear areas and I expected they would need replating. Even in those high wear areas, the chomate conversion coatings were removed by abrasion, but the zinc plating held up and did not expose the raw steel -- which is the ultimate goal of electroplating anyway.

    Anyway, congrats on your success again.

    Leave a comment:


  • red911
    replied
    Re: Yellow chromate, whats the secret?

    Update with new setup:

    Yippee!! It works!!

    My issue with Yellow Chromate soughing off is solved. I took the forums advice of using Blue Chromate as an intermediate step between the Copy Cad and Yellow Chomate and it works great, Plus the Blue Chromate is a wonderful product in its own right.

    Here is my process with a 5 gallon Copy Cad pail system with at 25 amp recifier:

    o I prepare the parts by using a 6 inch bench grinder with a fine wire wheel, or for rougher parts, I use the blasting cabinet.
    o I wire the parts with brass picture frame wire to increase the conductivity of the wire. Additionally, I use a small spring for small bolts and a larger spring for bigger bolts. Also, I have bent a few wires to carry washers and bolts. Looks like a continuous "z" with about 10 or 12 places for washers and nuts.
    o I use the Caswell, SP Degreaser heated to 180 degrees F in a three (3) quart crock pot. I rinse the parts on the wires for 20 seconds to get rid of the fingerprints and remaining oil.
    o Then, I rinse in a 5 gallon pail with tap water for 5 seconds.
    o Then, I place the parts in Muratic Acid for only 5 seconds if the parts are rust free, to etch the metal. If I cannot wire wheel very small washers or other small parts, then I will only soak those parts for a max of 20 seconds, as I have found that the Muratic Acid will turn the nice, shiny wire wheeled parts a dark color and all I want to do is etch the parts.
    o Then I rinse the parts coming out of the Muriatic Acid for 20 seconds in the plain tap water pail and then follow that rinse up with a spray bottle filled with distilled water (NEW STEP).
    o Heat the Copy Cad to 90 degrees F and put bandages from Caswell on the anodes (NEW STEP). Personally, I plate for six minutes per side at a very small rate with small bubbles from the nuts and bolts to be plated. I am not smart enough to measure the square inches of the parts to plate. I use the Caswell Copy Cad Brightner too. A tablespoon every four cycles of plating.
    o After the 12 minutes of plating, I spray the parts with the spray bottle of distilled water (NEW STEP).
    o Then I place the parts in Blue Chromate from Caswell for 20 seconds at room temperature and I get the most wonderful, deep, shiny parts from the Blue Chromate (NEW STEP).
    o Then I spray the parts with distilled water (NEW STEP), and place them in Yellow Cromate for 45 seconds. The Yellow Chromate is heated to 80 degrees F.
    o Then, I spray the parts with distilled water (NEW STEP).
    o I hang the parts for 48 hours.
    o I have not baked the parts yet, but I will do that in the next day or two.

    This is my process, and I can tell you that the process has totally eliminated the sloughing issue of the Yellow Chromate and the parts (carb parts in this case) present in the yellow, red and green flowing colors that we all want!!

    This is the process that will not fail you.

    Good luck, Tom

    Leave a comment:

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