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Ideal Sequence for Alkaline Zinc Plating

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February 6, 2022

Q. For New Alkaline Zinc the below process Sequence can be done in Auto Line:

Water Rinse - 2 Stations
Acid Pickling
Water rinse - 2 Stations
Zinc Plating (5 Station)
Water Rinse - 3 Stations
Nitric Dip
Water Rinse - 2 Stations
Water Rinse- 3 Stations
Top Coat

The Pre Treatment is enough for Zinc Plating or we need to add second stage of Anodic and Second stage of Acid Dip?

Srinivasan Krishnan
- Chennai Tamil Nadu, India

February 2022

A. Hi Srinivasan. Although I have seen double cleaning - double acid cycles, it is rather unusual and I'd guess that less than one shop in a dozen uses such. Your treatment cycle sounds quite robust and fine to me. In fact, rinsing after the nitric dip is probably not necessary. Whether 5 zinc plating stations is enough depends on your production rate and desired plating thickness; it might be enough but sounds light to me.

To be fully economically viable, the number of treatment steps, the number of programmed hoists, and the production rate need to be carefully balanced. With this many treatment steps you'll probably want 2 hoists. And with two hoists you may want more than 5 plating stations especially if the production rate is optimized with "put & take" in the plating tank (meaning one cell is always empty).

Luck & Regards,

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

April 30, 2022

A. What is the "Activation" step before the plating tank in your line? Normally here I have an anodic cleaner tank filled with sodium hydroxide to push the smut out of the parts left over from the acid pickling.

Also in regards to rinsing after Nitric, in my view, the necessity of this depends on to what scale the drag-in of nitric has an effect to the chromate tank.

As an example, many chromate solutions are nitric based in the sense they have nitric acid in the formula, so drag in of nitric wouldn't be an issue. However some Hexavalent black solutions are not nitric based, and the TDS mentions nitrates are a contaminmant and can lead to discoloration. As such I have a rinse tank after my Nitric for this reason.

Boris Siljanoski
- Perth, Australia

May 2022

thumbs up sign Hi Boris. Thanks for advising that not all chromates are nitric-acid based; I hadn't realized that.

Luck & Regards,

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

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