Summary for zinc olive passivation Discussion
Zinc olive passivation is the issue here: Trudy Kastner reports that an old-style chrome-VI olive finish looks beautiful in small buckets or beakers, but turns light grey when done in the barrel. Asif Nurie replies that chloride is the key factor affecting the chromate, and says dragout after rinse is the first thing to check. He also notes that the barrel speed may be too high, causing the freshly formed olive/green chromate film to be rubbed off while still wet, since these thicker chromates are easy to scrub away. His practical recommendation is to try chromating off the line or on a separate bucket-type line with circulating chromate and stationary parts. The thread suggests the barrel process is mechanically harsher and more prone to contamination or film damage than the beaker test.
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
2004
A. Miss Kastner
It’s 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 [deceased]
– New Delhi, India
With deep sadness we acknowledge the passing of Asif on Jan 24, 2016
A. 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 [deceased]
– New Delhi, India
With deep sadness we acknowledge the passing of Asif on Jan 24, 2016