"Clock Corrosion"

Question:

"I am designing a large display clock geartrain that will run underwater in a courtyard pool constructed of granite. I do not know specifics of the water conditions yet, but I assume that it will be slightly chlorinated. I have tentatively selected 316 SS for the gearing & shafting and am investigating the use of teflon-impregnated electroless nickel coatings for pinions and silver plating for gears to achieve "dry-lubrication" during operation. Being a novice at highly corrosion resistant design, I would appreciate any suggestions of fundamental / major pitfalls to avoid, as well as suggestions on maintenance of water conditions to promote long life of the mechanism."

Answer:

I would avoid 316SS in typical swimming pool water as the 300-series stainless steels have a tendency to pit in hypochlorite solutions. Hypochlorite solutions are difficult to handle without recourse to highly alloyed, expensive materials. Two materials which are suitable include Hastelloy C-276 and titanium. You also may want to consider using teflon or possibly nylon for the gears and pinions. The limited research I conducted also suggests that electroless nickel may not provide a long term solution.

 

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