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Acid Zinc at casting - lamellar graphite

I have a big problem to acid zinc plating cast pieces.
Some days after the acid zinc plating with CrIII passivation at casting pieces we find black spots at non machined areas.
We tried to improve the shotblasting at the casting supplier considering that is a material problem but we still have the same problem.
Now we believe that we could improve something at our plating line, someone already have the same problem?
Thanks,
Pereira

Guilherme Pereira
internship - Brazil
2007

You have called the parts that you are plating "castings", Guilherme, but you haven't told us whether it's cast iron, or die cast zinc, or pressure cast aluminum, or what. Please clarify what you mean by "castings". Maybe 'lamellar graphite' implies cast iron, but I'm not sure. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

2007

Dear Mr. Mooney.

The parts that we are plating are cast iron (grey iron) produced at a green sand moulding line.

Regards,

Guilherme Pereira
- Brazil

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