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How to do trivalent conversion coating

WE ARE SCREW MANUFACTURERS AND AFTER ZN PLATING, HOW TO DO TRIVALENT PLATING, AND WHAT ARE THE SALTS, THEIR AVAILABILITY

H.S. BHATIA
- Gurgaon, India
April 3, 2009

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Hi, H.S. Until rather recently trivalent chromate conversion coating was generally not done because it was not a robust and corrosion resistant finish. With RoHS concerns about toxicity of hexavalent, the major manufacturers invested substantial R&D to develop good trivalent coatings. You buy them from the suppliers and apply them per their tech data sheets (there are different technologies such as thin film and thick film, topcoat and no topcoat, and the operating instructions consequently vary).

To the best of my knowledge there are no generic formulations for workable trivalent conversion coating. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 3, 2009

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Hello

You must first know the customer requirements of salt spray resistance.There are 2 different types of TCP.1.Trivalent yellow (thick) passivation and Trivalent transparent (blue) passivation with top coats. The first type will pass 96 hrs Salt spray test as per ASTM B117 to white corrosion and the second one passes 48 hrs salt spray. Barrel plating generally calls for 72 hrs only for Trivalent thick passivation whereas vat plating calls for 96 hrs.

Subramanian Ramajayam
consultant - Bangalore, India
April 23, 2009