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9/1/2014

Flaky Alkaline Zinc Deposits

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Why do steel parts star to flake 12 to 25 hours after zinc plating?

Q. We plate steel parts using an alkaline non-cyanide zinc plating bath. The parts look great when they come out of the plating process and the chemical conversion step, but start to flake 12 to 25 hours after plating. What's going on? –W.K.

A. The first thing to look at is the cleaning process. Assuming the cleaning step is adequate, you should check the temperature of the bath. The bath temperature should always be in the range of 75 to 90° F. Check out the brightener concentration in the bath. You may have too much brightener in the bath, which is known to cause flaking. It's also important that you maintain the proper ratio of zinc to caustic soda. Typically, this number should be approximately 10-to-1.

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