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Zinc plating salt spray failures

November 3, 2009

Hai,

I am working as a production in charge in a leading zinc electroplater in Chennai, India.
Last month we had a observation that zinc plated parts has crossed salt spray test of 312 hrs no red rust but once baked in 150 deg for an hour and then tested salt spray has failed with in 36 hrs (red rust) instead of 200 hrs.
please suggest your valuable point, to come out of this situation.

regards,

Jayakumar Selvaraj
metal finisher - Chennai, Tamilnadu, India

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Hi, Selvaraj. Don't bake the parts because chromates can only stand 140 °F (60 °C).

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 5, 2009

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Dear Mr.Selvaraj Jayakumar,

Red rust always caused due to low thickness of Zinc Metal. Particularly while baking low thickness areas might develop cracks which leads to Red rust.

Best Regards,

P. Gurumoorthi
electroplating process chemicals - Chennai, Tamilnadu, India
November 13, 2009

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December 2, 2009

Dear Mr.Selva Raj,
Please do the baking or curing before passivation, that is the regular practice.
Means, After zinc plating imm. or within max 4 hours keep the parts in oven, then dip it in 1% HNO3 acid (max 4 minutes), then do the passivation then do the sealant based on need, then this will withstand the salt spray

Kannan Boopathi
- Salem, Tamil Nadu, India