Metal finishing Q&As since 1989


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Zinc Trivalent - Yellow Dye Co-Deposition vs. Post Passivate Application

We are operating a fairly new and large rack line. We have found that unless we are running very constant work through the line, the yellow dye, when mixed with a clear trivalent passivate, get's consumed from inactivity. This causes the need for large dye-adds, which is very expensive, particularly when not running much work through the line. We have been trying a separate yellow dye application, following passivate, but the consistency of appearance and honestly, the quality of the yellow appearance is not great. Has anyone experienced this problem? Our chemical supplier has been working with us, but lab success and monster-tank success are two different things.

Shannon Kelty
Plating Shop Manager - Cedar Rapids, Iowa
March 31, 2010

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Hi Shannon,

Walk a mile in my shoes buddy. My experience is identical to yours. In full production (800 gal) tank the dye precipitated out about every 2-4 hours. Since the bath was room temp and the dye was liquid, I had to decant and then add make up. Was an expensive nightmare. I can do small scale, batch runs with very good consistency (because the dye all goes away between runs), but I will never go down the full scale road again. Vendors (we use the same ones) say it works fine elsewhere, but pretty much gave up here. Might be the water....who knows. I bought the entire midwest out of dye in 3 weeks. Not stable, inconsistent color, hurts salt spray compared to tri clear...I hope the yellow trivalent urge that a few of our customers favor goes away forever or at least until someone comes up with something worth a darn. I have tried, to date 7 different formulations from 4 different suppliers and can't say one is any better than the other. The more stable ones had a bad color or could not pass ASTM B117.
Good Luck

Trent Kaufman
electroplater - Galva, Illinois
April 9, 2010

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April 9, 2010

Hi, folks. Please join in the crusade to tell the world that trivalent chromate should not be yellow! Not just because it doesn't work right, involves costly extra hassle, and the dye degrades corrosion resistance -- but because that particular shade of yellow is the natural intrinsic color of toxic hexavalent conversion coatings -- items that are poisonous to touch. All this extra effort to disguise a "green" finish to make it look toxic is a terrible shame. All this waste, trying to paint a consistent and pretty skull & crossbones on a hex-free finish that doesn't need or deserve one :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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Trent, I know you feel my pain, neighbor! Thanks for your response, which I respect a great deal, as you represent a reputable shop I am happy to consider friends as well as competitors.

Ted, you said a mouth-full. It is a slow process to convince people that there are many reasons to move away from yellow in the hex-free realm. We have successfully switched a few and they are very happy with the results. Unfortunately, there are many more which either want the yellow appearance, which conforms to a product color scheme or are just reluctant to change. So often, if they could go back to the beginning, they'll find that the only reason their application called for yellow in the first place, was to meet salt spray requirements. We're working hard to make the process work and look good, but is difficult. Thanks to both of you.

Shannon Kelty
- Cedar Rapids, Iowa, US
April 19, 2010