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Black spot after zinc plating of SG iron

January 7, 2011

Dear sir,

In SG iron grade: FCD450 after plating (trivalent Zinc plating) we are getting black spots over the surface of the castings & gone through several trials to simulate the same, but we are still stuck with the same issue, can you help by any means how to avoid such black spots over the casting surface or what could be the proper root cause.

Thanks

Palani Deenadayalan
plating shop employee - Chennai, Tamil Nadu, INDIA

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January 14, 2011

dear Sir,
such a problem occurs due to porosity of cast iron,due to which loosing out of solution is happened it is practice to give shot blast before plating
regards
Rahul

Rahul Potphode
- Pune, Maharashtra, India

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February 8, 2011

Dear Palani,

We were doing Zinc Plating on SG Cast Iron on braking parts.

Rahul has rightly said that porosity is the main root cause,
1. Pertreatment chemicals enter the pores.
2. If the parts are not dried at elevated temperature, you will face such Black spots.
3. Drying temperature should be between 80- 100 deg for Trivalent passivated parts with top coat.

Thanks & Regards,

Parashar S R

Sanjeev Raman Parashar
- PUNE, Maharashtra, India

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Sand blasting is recommended however heating to that temperature will result in Failure in Corrosion Test I would suggest centrifugal drying at higher RPM
good luck

MAHENDRA GARGATTI
ELECTROPLATERS - BELGAUM KARNATAKA INDIA
February 17, 2011