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Black spots on Trivalent Chromium plated screws

2005

Lately I encounter some trivalent chormium plated fasteners having black spots appear on the screw head, and some have rusty appearance on the screw head.

1) How is the black spot formed on the trivalent surface?
2) Will the black spot turn to rust after some time, let say 2~4 weeks, of storage?
3) How to prevent or minimize black spot appearance on trivalent chormium plated surface?

Thanks

Chung Chong Choy
Fasteners supplier & traders - Singapore

Are you using stainless steel baskets when passivating? if you are try using poly baskets.

Steve Jennings
- Australia
2005

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