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topic 9498

Industrial corrosion resistance


I'm searching for a thin metal coating process for small finely threaded electrical fittings used inside high energy boilers. We have tried galvanizing for our products, but find that it causes thread interference. We were initially interested in a zinc dichromate coating, but are open to suggestions and or recommended suppliers.

Mark Mullett
- Halifax, NS, Canada


Try tin plating two tenths of a thousandth of an inch thick. Galvanise is much to thick for most threads.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


A zinc dichromate plating sounds like a reasonable alternative to galvanizing. The zinc plating should be no more than 20 microns thick in the worst case. You can control this down further if you need to.

Your parts are most likely going to be bulk processed using barrels. You will see some thread damage from parts banging against each other. This damage is usually not too bad and often is found to be acceptable. If you need higher quality plating, look for some sort of rack process. There are applicators who do rack processing of fasteners. Racking small parts is much more expensive.

Will these parts see temperatures over 200 degrees Fahrenheit? If so, the dichromate passivation will fail and you will see an early occurance of corrosion.

tim neveau
Tim Neveau
Rochester Hills, Michigan


If it is compatible with your metal, consider silver plated bolts. It is soft enough to "squish" around and still stay in the general vicinity. It is used in many cases for small screws. It certainly would be worth a test bolt or two.

James Watts
- Navarre, Florida

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