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"Can Type II Chromate be done on Mechanical Galvanizing?"



October 14, 2016

I have a client who wants bolts to be mechanically galvanized to ASTM B695-85 Class 50 Thickness (minimum), with Type II Chromate Treatment.

Can you do chromate treatment on galvanized surface?

Thanks

Atanu Bose
- New York, New York
^


October 17, 2016

A. First of all, the answer is yes. Now for the editorial comment. Most mechanically galvanized articles are not chromated because that is the practice for hot dip. But chromating offers fantastic 'bang for the buck.' And the post application of a silicated 'sealer' can get a mechanically galvanized/chromated/passivated article well over 1000 hours of salt spray. Of course, yellow or olive drab chromates are not ROHS-compliant. There are ROHS-compliant alternatives.

tom_rochester
Tom Rochester Plating Systems & Technologies, Inc.  


supporting advertiser
CTO - Jackson, Michigan, USA

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December 21, 2016

Q. I must assume that any surface that has been zinc plated and pure zinc metal can also be coated with a chromate coating correct?

Marvin Sevilla
- Managua, Nicaragua
^


December 23, 2016

A. That is correct. Mechanical galvanizing is a deposit that is approximately 95% zinc and 5% tin, and all conventional chromates work on it.

tom_rochester
Tom Rochester Plating Systems & Technologies, Inc.  


supporting advertiser
CTO - Jackson, Michigan, USA

plating systems & technologies banner ad
^


What metals can be electrolytically chromated?

December 25, 2016

Q. Thanks for responding back, I wonder if one could chromate other metals by applying a low current and stainless steel anode.

Marvin Sevilla
- Managua Nicaragua
^


"Electrolytic and Chemical Conversion Coatings"
by Biestek & Weber
from Abe Books
or

affil. link

December 2016

Hi Marvin. Chromating of other metals probably has ever decreasing utility because of RoHS and similar requirements which limit the presence of hexavalent chromate on components. Further, the chromate coating may not function quite the same way on other metals as it does on zinc. But yes, chromating of copper and silver is not even uncommon; I designed a tin-zinc plating line that incorporated electrolytic chromating; and according to Biestek & Weber =>
it is even possible to electrolytically chromate nickel, chromium, steel, stainless steel, titanium, and zirconium.

Regards,

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

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