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Zn Plating Process/Thickness required to withstand 50 hrs CASS test

2007

Dear Sir/Madam,
I am facing problem on surface finish supplied by our vendor which is Zn Plated & blue passivation on Zinc pressure die cast component.

They provide us the components with a thickness of 10-12 micron.

As per my customer the part has to be withstand a 50 hour CASS test consist of two cycles of 24h and 1h drain period which the part does not meet.

Composition of Salt Solution:
1. Distilled water by weight : 95 parts
2. Sodium Chloride LR grade by weight : 5parts
3. Specific gravity : 1.0268 - 1.0413
4. pH (35±1 °C) : 6.5 to 7.2

Please suggest me what will be the proper proper thickness and process, so that I can validate my vendor and also satisfy my customer.

Thanking you,

Somnath Patra
Product Designer - Kolkata,West Bengal, India

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Dear Mr. Somanth,

Composition of salt solution given corresponds to Neutral Salt Spray (NSS) testing and not for a CASS Test.
CASS test is most corrosive one and is recommended for Nickel Chromium plated steel components.

50 Hrs of neutral salt spray life for 12 microns zinc plated and chromated steel is very much possible by employing proper type of chromate and if required, a water based organic sealent.

Thanks !

D.T. Thakur
- Mumbai, Maharashtra State, INDIA
2007

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