finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
Live! From Pine Beach NJ: The world's most popular metal finishing website, and the internet's friendliest corner

topic 55350

Blue or yellow passivation better after Zinc plating?


A discussion started in 2010 but continuing through 2019

July 13, 2010

Q. Dear Sir,

I want to know the comparison between blue and yellow passivation in Zn plating and which is the best one to follow. Explain me with some justification. Do the needful in this regard.

Regards,

Hari Haran
QA/QC Engineer - Riyadh. Kingdom of Saudi Arabia


July 13, 2010

"Zinc Plating"
by Herb Geduld
from Abe Books
or
info on Amazon

A. Hi, Hari. A few years ago the answer would have been that yellow chromate is heavier and contains more hexavalent chromium, and offers about 2-1/2x the corrosion resistance.

But today, what with RoHS standards, most "chromates" are trivalent and basically colorless, and most of the color you see is just dye. Further, the chromates are virtually all proprietary and based on several different technologies: thin film vs. thick film, sealer vs. no sealer, etc. One of the minor pieces of fallout from this generally beneficial change is that the color gives you no indication at all of the corrosion resistance.

Regards,

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


September 19, 2010

A. Welcome all

You can use yellow but if green available you can use it also.

Regards,

Yasser Alshafee, Senior Chemist
steel factory - Cairo, Egypt


Zinc Plating: clear, blue, yellow, green passivation differences (trivalent or hexavalent)

September 9, 2018

Q. I want to know about the processing of zinc plating, different types of passivations (clear, blue, yellow, green), (trivalent or hexavalent), how this is being processed also their advantages and disadvantages.

Himanshu Vashishtha
- Gurgoan, Haryana & India


September 2018
Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.

A. Hi Himanshu. These days you usually must use trivalent chromates because hexavalent chromates are not RoHS compatible. There is usually very little difference in the chromates except for their color, as it is usually just dye, although there are exceptions like proprietary thick-film trivalent chromates.

If you tell us who you are, what you do, why you want to know, and what kind of parts you have in mind we can probably help you arrive at some decisions. But without that it's hard to get started ... books about zinc plating are hundreds of pages long and we have a hard time knowing whether to start with a discussion about rack vs. barrel plating, cyanide vs. acid vs. alkaline zinc plating, pretreatment for plating, chromates & sealers, or what. Thanks.

Regards,

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



What treatment should we give to pregalvanized EMT conduit?

January 20, 2019

Q. The same question for our EMT Conduit Tubes made out of pregalvanized steel sheets. Which passivation should I use to give it anticorrosive properties as well as a clear surface keeping its shine?

Amed Hassan
El Delta El Masreya - Cairo Egypt
  ^- Privately contact this inquirer -^


January 2019

A. Hi Amed. The appropriate chromate quench or clear chromate conversion treatment will have already been applied by the galvanizer. It may be difficult or impractical to apply a chromate a substantial time later because the conduit is no longer clean and active -- and to the best of my knowledge it is not done.

I think you dare not apply an organic clearcoat because you will be defeating the expectation that galvanized conduit is conductive.

If I am misunderstanding, and you are fabricating EMT conduit in house from pre-galvanized material, there will be no zinc left at the weld line, and the whole surface is likely to be dirty and inactive after fabrication; so I think you need to clean, activate, zinc electroplate, and chromate post-treat it after fabrication. As for which chromate, you probably should use a RoHS-compatible proprietary clear chromate. There may be ASTM, ISO, UL and similar standards for EMT tubing that dictate what must be done. Good luck.

Decades ago I worked for a company which manufactured conduit plating machines and I saw them in the field, but I was never personally involved in designing them and I don't know exactly what steps they executed, how thick the plating was, or whether they started with pre-galvanized material. That 'they exist' is about the limit of my knowledge on that subject :-)

Regards,

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



If you have a question in mind which seems off topic, please Search the Site

ADD a Q, A, or Comment on THIS topic START an UNRELATED topicView CURRENT HOT TOPICS

Disclaimer: It's not possible to 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 may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.