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Straightness woes after plating and baking

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Q. I am a quality manager for a small fastener distributor. I recently sent some 3/8-24 X 5.00' fully threaded studs after heat treat (RC 36-40) for zinc plate (~~ASTM B655~~ Type ll) and bake. I had a straightness requirement to be within .010 after heat treat and the sample inspection appeared acceptable.

After zinc plate and bake the parts were significantly out of tol for straightness. The heat treater says that the plating house caused this to happen. The plater says otherwise. I thought the temperature for relief was too low to cause this problem.

What do you think?

Jim Campbell
Fastener distributor - Walnut, California, USA
2005

Ed. note: There is a typo in the spec number as that spec has nothing to do with plating.

A. I think the parts warped in heat treat because Rc 36-40 parts are very stiff like spring steel. If the parts are thrown in a basket for heat treating they will distort due to their own weight or the weight of those above.

Russell Richter
- Danbury, Connecticut, USA

A. It would be obvious if the plater bent a 36HRC part. It didn't happen in plating. Either one of two things happened. 1. The parts you tested were OK but you only picked good ones to test, some good and some bad. If they were all bad this couldn't have happened. 2 If they are all bad you should check the method of inspection or the inspector.

Ed Kopaskie
- Covina, California, USA

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