Summary for type ii chromate on mechanical galvanizing Discussion
Type II chromate on mechanical galvanizing is possible, according to Tom Rochester, who answered the original question directly: yes, mechanically galvanized bolts meeting ASTM B695 Class 50 can be chromate treated. He added an editorial note that most mechanically galvanized parts are not chromated because that practice is more common with hot-dip galvanizing, but he said chromating gives excellent value and that a post-applied silicated sealer can help a mechanically galvanized/chromated/passivated part exceed 1000 hours of salt spray. He also cautioned that yellow and olive drab chromates are not RoHS-compliant, though RoHS-compliant alternatives exist. In a later exchange, another contributor noted that chromating other metals is increasingly limited by RoHS and may not behave the same as on zinc, though electrolytic chromating of several metals is described in Biestek & Weber.
October 14, 2016
I have a client who wants bolts to be mechanically galvanized to ASTM B695 Class 50 Thickness (minimum), with Type II Chromate Treatment.
Can you do chromate treatment on galvanized surface?
Thanks
Atanu Bose
– New York, New York
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
CTO – Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
October 17, 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 21, 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
CTO – Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
December 23, 2016
What metals can be electrolytically chromated?
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
December 25, 2016
“Electrolytic and Chemical Conversion Coatings”
by Biestek & Weber
( Rarely avail. for purchase, but see library holdings on Worldcat.org)
on Amazon
or
or
(affil link)
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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
December 2016
