Grinding allowance for gas nitriding

[luckymix]

Greetings,

A high tolerance sleeve with a pin that runs in it, the ID is approx 170mm with H7 fit i.e. + 40um, - 0. The sleeve finish is Good/ smooth. Good quality nitridable steel.

Can one go to final size and then gas nitride? Or I imagine ones should leave a grinding/ polishing allowance, but how much per side (or how much on internal diameter)?

Recommendations appreciated.
thx.

 

[unclesyd]

I would get with the people that are going to do the nitriding and do a little consulting. You can get all kinds of numbers on growth and thickness of white layer, if any. Some of the newer low temperature processes give very little growth and essentially no white.

I guess I've answered you question about finishing to size. You tolerances are too close. After you and nitrider run a few parts you can probably work closer to the finish dimensions.

A you gas nitriding for a reason, if not you should look at plasma and liquid nitriding. Their must be a hundred processes out there, so might want to check them out.

 

[TVP]

Just to reinforce what unclesyd wrote, you definitely need to work closely with the heat treater on this type of project. The right machined dimensions will depend on how much white layer is produced, and what type of depth you want to obtain. Also, plasma and liquid nitriding (salt bath nitriding) are excellent processes as well.

 

[Tribman]

The tolerance is very thight, but usally, for liquid nitriding with the proper cooling system, it is possible to not have any movement.

Only the parts with big diameter and very thin wall could move from 0 to 150 µm.

As the other recommended, the best way is to do test with the nitriding compagnies.

A good salt bath process is the Arcor N process.