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
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