Bearing destruction due to lack of lubrication 2

[cedeng]

Hi
I would like to know the typical destruction scenario of a bearing (ball, approx 2 in., no trust) having lack of lubrication (almost no lubrication at all). For example, inner ring is rotating (fit on the shaft), outer race is fit in the casing, no rotation. RPM = 3600

1- How much time it can roll without lubrication before catastrophic failure ?
2- What are temperatures it could reach on inner ring ?
3- Is outer race damaged or not ? (the one we are investigating is almost in perfect shape)

4- If you have typical visual references for this type of bearing failure, it would be good for comparison.

We are investigating bearing failure, we try to justify first hypothesis which is lack of lubrication.

Thanks
Ced

 

[MikeHalloran]

In the wake of many hurricanes, we read testimonials about how so-and-so's outboard motor ran for many hours on straight gasoline because no lube oil was available, and at the end of that ordeal, the engine either:
- finally seized, or
- was undamaged, or
- was rebuildable, or
- was replaced with a new one by the mfgr.
Regardless of the variant, the story always has a happy ending, because outboards are built with ball, needle and roller bearings, all of which can survive operation with just a whisper of lube oil.

I suggest that you ask the manufacturer of your specific failed bearings for help. They have the resources, and some incentive to figure out what caused the failure, or at least what didn't.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Is this an academic exercise or a real basket case?

 

[JJPellin]

Research lube oil mist. A ball bearing can survive on drops of oil per day. And there are documented cases of entire units with many machines running for hours with no lube oil mist delivered with no failures. In an outboard motor, the bearings are still lubricated by gasoline. Gasoline is not a great lubricant, but it does provide some lubrication. When I get back to work, I have some better information on the results of a failure from lack of lube.

Johnny Pellin

 

[JJPellin]

The last bearing failure that I saw that I believe was a result of a complete lack of lubrication happened just a few days ago. I believe that the oil ring came out of the groove in the adapter and stopped spinning. The failure appears to have started with the cage. This makes some sense. The contact between the balls and races is rolling contact. The contact with the cage is always sliding contact. This was a double row bearing acting as a radial bearing in a between-bearings pump. The stamped steel cage failed and one section was pulled between a ball and race. That cage broke up into individual sections. The other cage popped out, almost intact. The balls then slumped to one side without the cage to support them. The inner race eventually popped off to the side opposite the balls resulting in an extreme misalignment. The inner race was almost melted down on one side. The balls had been ground into the inner race. One ball actually broke in half. The outer race was almost perfect. With the shaft making this outrageous orbit, the forces transmitted across to the steam turbine driver caused it to fail. The radial bearing in the turbine was wiped out with the worse damage on the top. The vibration on the turbine was so extreme that all six hold-down bolts came loose and the shims came out from under the feet. At first, we were not sure if the turbine failed first and took out the pump or the other way around. But, when we examined the failed parts, it became clear that the pump was the start of the failure.

This failure demonstrates why we don't like stamped steel cages. Our preferred thrust bearing is a pair of back-to-back single row bearings with machined bronze cages. Our preferred radial bearing is a deep groove, single row bearing with a riveted steel cage. The double row bearing is a bad idea since it cannot be made with anything but a stamped steel cage (unless it has a split inner race). We converted the pump to a single row bearing of the same size and modified the adapter to accommodate the narrower bearing. The modern version of the same model pump is built with the single row bearing, so we had good confidence that it could take the imposed load. We also redesigned the oil ring to make it more stable with a higher or lower oil level. We considered extending the flange on the end of the adapter to make it harder for the oil ring to jump out of the groove. But, in the end, we stayed with the same adapter.

I have seen this same sort of failure before. The damage has tended to be worse on the inner race. Even with a back-to-back pair of bearings, the inner race can become almost molten, rolling up over the lock-washer and nut.


Johnny Pellin

 

[caoimhin1]

One other point. As someone mentioned, bearings can run on very little lubrication. There have been cases of people forgetting to grease bearings or forgetting to open the oil valve, and the bearing runs happily away for a few weeks solely lubricated by the rust inhibitor applied at manufacture. But all depends on the loads and speeds applied.

The tempering colour is a good indication of the temperature the bearing has reached. Search on the web, there should be some colour charts available.

 

[Fugeguy]

See the attached showing bearing discoloration due to temperature.

 

[cedeng]

JJ Pellin, I'm glad to hear your story because it looks like our case.

Thanks a lot. Indeed, the inner race was melted and balls were indented on its surface. Outer race was good. So, your story fits with our case and confirm that lack of lube is a real mess at high speed and high load.

Have a nice day

 

[unclesyd]

One problem is that you have a bearing in a basket and from your description of the failure it will be virtually impossible to ascertain if lubrication or lack thereof is the root cause unless you have a smoking gun.
It has been my experience with bearings that have the same or similar mode of failure as yours is to install the same bearing using all the tools available to you to get the very best installation possible. I would change the lubrication either grease or oil to the highest grade available, the ones I use are from LE. By doing this you can get a little time on the bearing where you can do a better analysis while it's running under load. I started this process when the best available analytical tool was a stethoscope and the hand.

I don't have the numbers but a least 80% of the bearings that were checked in this manner remained in service for their expected life.

 

[electricpete]

Bearing in a basket - I like that. I'm with unclesyd... lack of lub would be one of many scenario's that culminates in bearing in a basket.

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