Cryogenic tempering (perhaps not the universally accepted terminology) has
been recommended to me as an alternative to induction hardening and/or case
carburizing in a pin used in a large thrust bearing (about 3' in diameter).
The pins serve as "axles" to hold an array of 40 radially arranged tapered
rollers in their assigned places within a cage assy.
The pins are currently 4140 QT (120ksi yield) induction hardened or 8620
case carburized x .55" diameter x 4.5 long. They have acceptable wear life
and fatigue life but are expensive to make mainly because they need to be
ground after hardening. The 4140 parts have a surface hardness of about 55RC
the carburized parts can be a little higher. The parts are press fit into
the cage with a substantial interference fit. We hold the diameters to
+/-.0002" by grinding after hardening. If the parts would remain
dimensionally stable after cryogenic tempering we have the ability to
machine them to that tolerance without grinding in their unhardened state.
If I adopt the cryogenic process I will no longer have a surface hardened
part but that may be OK.
I have three questions:
1--Is this method suitable for producing a wear resistant surface when
subjected to rotary sliding contact in my "axle" application?
2--Is the pin likely to be significantly more brittle?
3--Are the parts likely to be dimensionally stable enough that we can
eliminate the grinding after hardening?
I have the opinion of engineers from another division of our company that
use the process in an application where the workpiece is subjected to heavy
impact (it's inside a rock crusher) that feel that it has extended the life
of their parts, but their application is different. I am looking for some
opinions from persons using this method in applications more similar to my
own.
Jon Juhlin
snipped-for-privacy@jcieug.com
- posted 11 years ago