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Zinc olive passivation

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We have started olive passivation on acid zinc (the old fashioned chrome-VI olive). It gives a beautiful olive colour when we passivate in small buckets or beakers but turns a light grey when we try and passivate in the barrel itself. We have tried slow up and down movement and normal barrel rotation with no improvement. Any idea as to what would be different in the barrel?

Thanks!

Trudy Kastner
Plating shop - Durban, KZN, South Africa

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Miss Kastner

Its the Chloride that affects the chromate. Dragout after rinse is the first aspect.

- Secondly it could be the speed is too high and the formed film is rubbed off since the Greens are the thicker variety of Chromates and V easy to scrub off when wet.

Suggest off the line chromating . Or Chromating on a separate Bucket type line with circulating chromate and stationary parts. Good luck

Asif Nurie Atlanta Global New Delhi, India

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Miss Kastner ,

Further to an earlier mail.

The varying low to lower Current density, and the tendency of organics to co deposit with the zinc selectively at Lo CD's is another factor in barrel plating. You might try cleaning up the organics and running higher CD's in the Acid Zinc Bath too.

Regards,

Asif Nurie Atlanta Global New Delhi, India