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-----Plating on cast iron threads
December 26, 2012
Q. I have a customer that is asking about plating on a cast iron part. The part is a retaining fastener that is threaded onto and off of an assembly, and is exposed to water, detergent, acids and bleach in the process. The threads on the mating part are stainless steel, so these conditions do not affect the mating part. The retaining part is removed and reassembled daily, sometimes multiple times per day. Rust on this part or the threads is not acceptable. We are suggesting that the retaining fastener be stainless steel also. The customer is looking into cost saving options. They are asking about zinc nickel plating. My contention is that plating over cast iron on any wear surface is not permanent, and that in daily threading and unthreading the threads will cut and wear the plating. In the caustic environment, this will eventually expose the iron surface and rust is inevitable. Can anyone offer an opinion on this? Thanks in advance.
Sean PriceConsultant - Youngstown, Ohio
A. Hi. Sean. Nothing is 'permanent', although a zinc coating can endure quire well in certain environments. Still, strongly alkaline detergents are tough on zinc, and bleach is even more corrosive.
Stainless might be the best answer, but be watchful of galling if the same grade is used in both halves. Good luck.
Regards,
Ted Mooney, P.E.
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December 26, 2012
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