Home /
T.O.C.
FAQs
 
Good
Books
Ref.
Libr.
Advertise
Here
Help
Wanted
Current
Q&A's
Search 🔍
the Site
pub Where the world gathers for
plating, anodizing, & finishing Q&As since 1989





"Yellow passivation film is turning blue"



-----

 

We are electroplating steel drum closures with zinc followed by yellow passivation. The product is centrifugally dried at a temperature of 55 to 60 °C for 6 to 7 minutes. We ensure that the product is completely dried without any traces of water. We pack the product in Polyethylene bags with silica gel pouches. We find that over a period of a month the yellow passivation colour starts turning blue / bluish purple, this is aesthetically not acceptable. What could be the reason for the same and how can it be avoided?

K.V. Phadnis
- Mumbai, Maharashtra, India



 

Did you know that the yellow passivation is a hydroscopic gel? The yellow chromate gel retains water, and requires it to function properly. I wonder if the drying and silica gel dessicant are having a bad effect on the plating system. You should discuss this with your plater, and possibly the plater's chemical supplier.

Hexavalent chromate passivations often get this "rainbow" effect. We see if often on some of our parts. The passivate layer is very thin and has a microscopic thickness. Variations in this thickness can effect the color of the part. This is very hard to control. Normally, we allow color variation in our visual criteria when specifying this type of finish.

You may want to reconsider what is acceptable and not. Very few platers will want to even attempt to guarantee consistent chromate color. Maybe a different, and more expensive, finish would be more appropriate for your needs.

tim neveau
Tim Neveau
Rochester Hills, Michigan



 

Hi Tim,

In my experience, most platers provide remarkably consistent chromate color. For inconsistent results, I would suspect that the platers management system is severely damaged, or that the shape of the part being plated, or manner of plating (say, barrel vs. rack, or the incorrect rack, etc) is the major problem.

tom & pooky   toms signature
Tom Pullizzi
Falls Township, Pennsylvania


none
finishing.com is made possible by ...
this text gets replaced with bannerText
spacer gets replaced with bannerImages



(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact    -    Privacy Policy    -    ©1995-2023 finishing.com, Pine Beach, New Jersey, USA