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Rust on thread holes after EN plating

Hi,

Lately we have detected rust on M1.2 thread hole area in our machined parts after EN plating.

We have tried to change the thread forming, but the outcome is just as bad. The thread is created by a reamer and rolled tapping.

Salma Osanar
metal stamping+machining - Singapore
2005

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What is happening is not terribly uncommon. Traces of the activation acid are getting by the mask (plug) and it becomes quite active in the high temp of the EN tank. After the plating, the threads are not being rinsed out well enough and it is rusting.

One option is to chase the threads and oil them after plate. Another option is to find a better plug. If it is a thru hole, try a larger silicon plug. Another option is to try to reduce the acid by soaking the part in a hot water tank for a couple of cycles prior to starting the plate cycle. This fills up some of the space with water so less chemicals get in. Better final rinsing, followed by the bake cycle, followed by oiling the threads might also help.

James Watts
- Navarre, Florida
2005