Corrosion - Bearing to iron spacer?

[sprintcar]

In our large bearing assemblies we use a cast iron (class 40) ring to locate the preload springs for the thrust bearing. Under load, the ring and bearing surfaces are forced together. At teardown there is discoloration, pitting and even metal transfer between the 2 surfaces. Most drives are electric and correctly grounded, etc. Could this be galvanic, just a mechanical condition or lube related?
Any input is greatly appreciated!
Thanks Keep the wheels on the ground
Bob
showshine@aol.com

 

[piyushjoshi]

I think it is a lube problem, as there are some prevalent conditions exist:
1) The ring is pressed to the springs
2) the tempr. may be high due to lube problem
3) Due to the high tempr. the metal melts and plastic welding phenomena occurs.

You can use high viscosty oil or syntheic oil for lub.
You can also change the material of ring which can sustain high tempr.


Piyush Joshi

 

[Metalguy]

It sounds to me like the ring and thrust bearing (race, I assume) do not rotate against each other. If so, I'd suspect a possible fretting condition (tiny amounts of movement, sometimes caused by vibration).

 

[sprintcar]

Thanks guys
We switched to syn oil for OEM initial fill a few years ago. Its a non-rotating fit, but there could be some fretting as the thrust loads change. Haven't gotten any field feedback yet. Customers tend to randomly change lube brands so there could be some reaction internally with noncompatible oils.

I'm redesigning the preload arrangement to reduce the potential for movement, so if it is fretting this could be the fix. Of course I won't know for certain until 2 or 3 years from now! Keep the wheels on the ground
Bob
showshine@aol.com

 

[Metalguy]

Keep in mind that fretting can involve microscopic movement.

You might also consider using something like Loctite "bearing mount" or equiv. between the faces.

 

[mechanosetboy]

If the system is VVVF driven there is a possibility of flux failure in the bearing housing with the rotor and bearings forming the ground path, This induces a spot welding effect.

 

[RotorEng]

This certainly sound like fretting. You also could try using solid lubrication, MoS2 or other similar lubricant. Since this is a non-rotational surface interface (except for micro-vibration induced fretting) elastohydrodynamic lubrication cannot form and prevent contact between the surface interfaces. A solid lubricant displacer would better serve the job. Another common practice is to increase the hardness of the two contacting surfaces and closely match both hardness and surface finish.