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How is a zinc dichromate tested?

How is the quality of a zinc dichromate tested? If salt spray or humidity, what is the expected # of hours expected? How does a customer know if the zinc dichromate is of expected quality?

Ed K [last name deleted for privacy by Editor]
- Madison Heights, Michigan, USA
2001

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2001

Zinc platings should be tested using the salt spray test according to ASTM B117. Exact pass-fail criteria is on a case-by-case basis, depending on your application. White corrosion specs go by what type of dichromate you are using, generally from 24 to 200 hours. Red rust specifications could be anywhere from 96 to 500 hours.

The plater should be monitoring their process closely to make sure variables such as temperature, pH, and concentration of each bath are under control. The plater should also make periodic measurements of plating thickness in mils or microns. Platers usually also have their chemical suppliers come in and do their own testing. Ask to see the plater's lab, meet the person running the lab, and see what kind of system they have to detect and correct process problems.

Tim Neveau
Rochester Hills, Michigan