Home /
Search 🔍
the Site

Problem? Solution? Chime right in!
(perhaps the world's last 'no registration' site)


"White rust over zinc coated bolts"

September 19, 2018

Q. We have some bolts used in final fitment of automotive bodies, which we can't CED as it will not fit with nut thread after CED. So we are applying Zinc coating. But that zinc coating is also getting white rust after some time. How can I prevent or extend life of zinc coating from white rust?

Subhro Naskar
shop employee - India

September 2018

A. Hi Subhro, Unfortunately, we have insufficient information yet to suggest a course of action. We don't know the plating and chromating specification, and we don't know how many salt spray hours the bolts survive ... so we don't know if your request for longer life from the current specification is reasonable or not.

The generic answer is to compare the salt spray hours you actually obtain to what should be expected from such a specification in order to determine whether the problem is poorly executed plating/chromating or an inadequate specification for the needs. If the actual plating doesn't match reasonable expectations, fix the plating line or find another plater. If the salt spray resistance does meet expectations for that specification, then you must switch to an alloy zinc plating with greater corrosion resistance or at least increase the plating thickness (but time to white rust is primarily dependent on chromating rather than plating thickness). Good luck!


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

September 19, 2018

A. Are you applying a yellow chromate after zinc? If not, then do so. If that's not good enough, you could add a final dip in a water or solvent based rust preventive.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

finishing.com is made possible by ...
this text gets replaced with bannerText
spacer gets replaced with bannerImages

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start 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:

Chemicals &
Consult'g, Train'g
& Software

About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA