finishing.com -- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing

HomeFAQsBooksHelpWantedAdvertiseForum
topic 718

Question about olive drab chromating


(1998)

I am evaluating OD chromates on zinc (from zinc sulfate bath), and am finding a generally low chromate bath tolerance for dissolved zinc, and am at a general loss as to what to attempt to control (pH, chromate %, dissolved zinc) in my tube/wire application. Immersion times are ~15 seconds.

By low tolerance, I mean that we see a fairly quick loss of color on the plated product, with marginal SST affects. The chromate coating also serves as an adhesion barrier for paint, so the marginal reduction in SST to white rust in minimized.

How long are OD chromate baths 'good' for, in general, and what should I attempt to control to extend bath life, while maintaining a good conversion coating?

Thanks!

Robert Church



(1998)

Robert,
Every company uses a slightly different formulation, so there will be some difference between the critical elements of each bath.
I worked with a chromate that was used for both chloride Zn and Cd. One metal was a poison to the other and the zinc required a less aggressive chromate than the Cad did. Your vendor should have a separate set of operating conditions for Zn. There was a terrible tendancy to add excessive brightener to maintain a 100% bright range which made chromating on a panel nearly impossible. Are you using a very dilute acid rinse prior to the chromate. Might help. 15 seconds seems to be a rather short immersion time. If the chromate is slowed down some, it might be less sensitive. Try some different combinations in the lab. The lab folks at your vendor should be able to help if your salesman has not been much help. If push comes to shove, consider using a different vendor. I have had good luck with two vendors and not so good with another.
Good Luck, Jim

James Watts
- Navarre, Florida


(1998)

If you are using a proprietary product, I would say the most important factor in chromate life is dragin of other processing solutions. Do you drag in a lot in your tubes?

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 



This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Q or A to THIS thread START a NEW THREADView This Week's 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


©1995-2017 finishing.com     -    Privacy Policy
How Google uses data when you visit this site.