Zinc Plating
Zinc Plating
(OP)
We have several of our parts Zinc plated. We have been finding that many of them have a powdery coating on them. Screw threads on these parts get packed full of this powder. Is this caused by the Zinc plating process or could this be caused by something else after they are plated. Our plater says that we must be getting the parts wet which is causing the problem. Any input is appreciated.





RE: Zinc Plating
RE: Zinc Plating
Can anyone tell me if there are any chemicals that can be added to the plating process that will help to prevent white rust?
RE: Zinc Plating
Regards,
Cory
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RE: Zinc Plating
RE: Zinc Plating
RE: Zinc Plating
Hexavalent chromium has become a restricted substance for many countries/industries. Because of this, you may want to consider trivalent conversion coatings. There are no yellow versions of this, but the thick film trivalent passivates have shown comparable perform to yellow hex chromate coatings.
Regards,
Cory
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RE: Zinc Plating
See ASTM B633-07, 'Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel,'
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A colorless chromate (Type III) should provide 12 hours resistance to the ASTM B117 salt spray, and a yellow (Type II) should provide 96 hours, before the appearance of white rust.
After this supplemental coating has been depleted, the thickness of the zinc provides the number of years before red rust according to the environment. See Appendix to B633.
I have some doubt as to whether the plater properly reactivated the surface after HE bake-out prior to the colorless chromating. If not, effectively no chromate. And, are you testing for the colorless chromate (indirectly via salt spray or chemical analysis?). Ask for the paperwork (shop travelers initialed at each process step, QC signature verifying drying, lab reports for salt spray testing, solution analysis records, etc.). I.e., a supplier qualification survey.
RE: Zinc Plating
I have some doubts about our plater as well. If I were to send some samples of our plated parts to another plating vendor, would they be able to tell if it was done incorrectly?
Ken
RE: Zinc Plating
Use an independent lab to either
a) test for the presence of colorless (clear) chromate per ASTM B201 (an easy test to do yourself although requires lead acetate solution) or
b) salt spray test per ASTM B117 to see if meets the 12 hours w/o white rust for clear chromated zinc per ASTM B633.
RE: Zinc Plating
RE: Zinc Plating
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