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Risk of replacing hot dip zinc by sealed electrolytic zinc

June 27, 2008

Hi to everyone,

I have a customer that failed in a screw and nut design that were supposed to be hot dip zinc plated. The customer failed to make bigger the internal diameter of the screw and now he is trying to get the screws electrolytic zinc plated. I am aware the durability of the hot dip process surpass that of the electrolytic process, so does my customer. He is proposing to add a sealant to the screw in order to improve the durability if we change to electrolytic plating; my concern is that the inner diameter of the nut is not zinc plated, because the original practice is to leave unplated that section and the zinc in the screw would do the catodic protection. Nevertheless, I wonder if that catodic protection is lost if we use a sealant over the zinc in the screw.

I will appreciate any coment. Thanks again to every one.

Guillermo Castorena G.
Plating Jobshop - San Luis Potosi, Mexico

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Hi, Guillermo. It probably depends on how many you are making, how critical the corrosion would be, and how good the sealant is. However, my belief is that it will be okay. These sealants are very good at sealing everything (including moisture) away from the thread. If they were not, pipe joints would leak :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 30, 2008

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Thanks a lot Ted,

Mil gracias!

Guillermo Castorena
Plating jobshop - San Luis Potosi, Mexico
July 2, 2008