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Chromatization on zinc diecast parts

Please anyone tell the process of chromatization on (hot chamber) zinc Diecast parts. This is not like electroplating process. No metal deposit on the original surface. Something like washing the surface.

Anantha kumar
automotive parts designer - Bangalore, Karnataka, India
2003

Sorry, Anantha, I am not familiar with the term 'chromatization' . . . but I believe you are referring to what I would call 'chromate conversion coating'. Zinc plated parts are almost always chromate conversion coated to retard rust, and it is possible to apply the same process directly onto zinc diecast parts.

After pretreatment the parts are immersed in an ambient temperature or nearly ambient temperature proprietary mixture of somewhere around 1-2 percent chromic acid together with sulfuric and/or nitric and/or hydrofluoric acid to cause the buildup of the chromate conversion coating.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

I am also interested to know about this process. I have some parts which have chromating. Recently we are facing problem that the chromating appearance gets washed after vacuum impregnation. I don't know what is the standard/ correct process flow: 'chromating-vacuum impregnation' or 'vacuum impregnation-chromating'

Ravindra Mahajan
- Pune, India
2007

July 6, 2010

Hi, Ravindra. The coating produced by chromating is a hydrated gel with poor temperature resistance (over 140 deg F is problematic) and low abrasion resistance. It is typical to try to do chromating after all other operations when practical.

Regards,

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

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