Letter 26040

Is plating or blackodizing better on spring washers  

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Our company manufactures electrical switches, wherin we use spring washers. I want to know which plating process must be done on these washers to prevent hydrogen embrittlement. We have tried zinc plating and cadmium plating but washer cracks after few hours of application of torque. Can you give us any information whether blackodizing these washers is a better option than plating.

Zankar Desai
trainee engineer - Vadodara, Gujarat, India

Baking for hydrogen embrittlement relief is necessary regardless of which process you use unless--which is unlikely for a low cost product like this--you prepare the surfaces by blasting instead of pickling; then it might be possible to do black oxide without embrittlement relief. Zinc plating is a far more corrosion resistant finish than black oxide, and would be my preference.

I suspect you are doing no baking, or late and inadequate baking, and that must be corrected.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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