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Clear Chromate on zinc plating is turning yellow

Hi. I have a zinc product, plated with a clear chromate conversion coating. My problem is that after we ship to the customer about 50% are turning yellow after a few days. The problem only occurs after they are put in their final packaging which is a Bio Bag? Any ideas what might be causing it?

Darragh Murphy
engineer - Cork, Ireland
October 20, 2011

October 24, 2011

This is a known problem which is mainly observed on big parts.

Try to reduce the conversion coating's thickness by reducing dipping time, pH and concentration.

Sara Michaeli
Tel-Aviv-Yafo, Israel

November 27, 2011

Yes, I agree with Miss Sarah,
This type of yellow shades are more found on the bigger surface area parts...even if you control your pH, concentration etc. with huge volume now a days it is much more difficult to control and get a pure clear white finish on bigger parts especially on zinc trivalent white passivation.

Jayakumar Selvaraj
metal finisher - Chennai, Tamilnadu, India

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