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Zinc black plating SST requirement

2003

Dear Sir,

We are in sheet metal business and vendors of Mahindra & Mahindra, Nasik. My question is regarding Zinc black plating.I need this information for one component(spring) of vehicle SCORPIO which requires black plating and is also exposed directly to atmosphere. Queries: 1)What SST hours shall black zinc plating sustain? 2)Can we improve SST hrs with extra methods? 3)What exactly the process of hydrogen de-embrittlement is,and how we can check whether the component is undergone that treatment? We will be extremely thankful to get answers of these questions.

Thank you for your kind service.

Umesh Kulkarni
- Nasik, Maharashtra, India

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2003

Dear Mr UK,

1. 12 to 34 hours to white rust.

2. A topcoat of a water based lacquer will improve the initial onset of white rust by another 6 to 8 hours in a SST.

3. Nothing can be done with black passivation. Costs a lot and gives the poorest SST resistance. Zinc - Iron plating with black passivation costs as much but is the only way to meet the Spec.

4. You need to have a test Kit containing known hardness of spring washers and a conical mandrel. Each washer should accompany a batch as a witness piece. The washer will break when elongated beyond a point that is your nogo.

An easier way is to learn the difference in colour of the black passivation for De-embrittled parts and non de-embrittled parts which will be lighter on account of the zinc turning mostly passive in between baking and passivation.

You may also have a cyclic test SPM, and define the cycles per hour. The best way is prevention of Embrittlement by a non embrittling plating process.

Regards,

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India