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Understanding chromate passivations


I have questions regarding Chromate passivations. I am a Technical Service representative with a Powder coatings company. We have a customer in China that coats SECC steel for computer housings. The process is as follows. The SECC parts are dipped in a waterborne degreaser and then put through the chromate passivation. The problem that we have encountered is the adhesion of the powder coating after the part has gone through the passivation process. When the treated parts are cleaned with MEK / methyl ethyl ketone the adhesion properties of the powder is enhanced. Could you shed some light or give me a contact to establish an understanding of the chromate passivation process and what it might effect if the process is not calibrated for the lack of better terms.

Thank you,

Michael Weirich
- Grand Haven, Michigan


Either I am greatly misunderstanding you or you are greatly misunderstanding chromate passivation. It is used on aluminum and it is used on zinc plated/galvanized surfaces, but it is not used on steel.

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


Chromate treatment has been used on steel to produce a material called "blackplate". This is basically a mild steel with improved corrosion resistance. Any further corrosion resistance should be imparted by using lacquers or paints.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


Apologies, I didn't check my original reply! I meant to say that chromate treatment is used on blackplate to give it better corrosion resistance. This product is known as ECCS (Electrolytically Chromate Coated Steel). It will withstand more severe conditions that conventional blackplate,which is oiled low carbon steel, but for best protection, it needs painting or lacquering. Sorry for any misleading - I must learn to read what I think I am submitting sometime!

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


Adhesion of any top coat will suffer if the substrate surface is oily or greasy. Likely the MEK removes the oily or greasy layer allowing adhesive powder coat. Pl check if this is the case. If it is so any organic solvent will do the trick. May be I have oversimplified the problem!
good luck!

indivudual - Bangalore, Karnataka

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