How do I know if a bearing needs regreasing??

[jarimasen]

What is the best method??
I know about the formulas and charts, but I feel they're general and are not based in important parameters like application, grease, dusty environment, unbalanced loads, et cetera.
I have tried listening with an industrial stethoscope, but I couldn't detect much difference and is reasonable to assume I would've detected it only if I already overgreased. I've heard of using vibration monitoring while regreasing, but this is very inefficient in a large plant where there is a constant lubrication program. Any suggestions not involving prayer and/or using a magic eightball??

 

[electricpete]

There are two widely diverging schools of thought.

1 - time based. Go to website of any bearing manufacturer (NTN, FAG, SKF) and download literature which will give rules for amount to add and frequency to add. Will consider factors such as speed, bearing size, sometimes loading etc.

2 - condition-based. Listen for a change in sound when you add grease. When sound decreases you have added enough. I think uesystems and uvlm are two companies pushing this approach. If you have vib equipment you can do roughly similar approach monitoring the demodulated overall.

My personal opinion is #1.



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[Hippo41]

Speak to SKF. They have a vibration sensor called the SEE pen that "listens" to the interface between the rolling elements.

Essentially if it doesn't get a reading it means your lubricant is OK, if it does, and to what degree it does, gives you some idea of whether or not your lubricant film is supporting the load or if the film is breaking down.

As with all these devices, once you get some benchmark data it can make future maintenance far easier.

Lester Milton
Telford, Shropshire, UK

 

[electricpete]

Some reasons why my personal opinion is a time-based approach is better than a condition based approach for routine greasing:

1 - Time-based approach is time-proven and is what your bearing manufacturer and pump/motor manufacture recommend.
2 - Time-based approach takes less time spent lubricating because it is simple and easy.
3 - With time-based approach we can predict exactly how much grease is in the housing and when we may expect the housing to become full.
4 - With condition-based approach I don't think we have any idea how much grease will be added to the housing over a period of time. My fear is that one noisy-bearing machine will cause someone to add grease every time they visit it... quickly resulting in overgreasing.

Sonic guns from the companies I mentioned have been around for awhile with big claims. If they are so good, why haven't any of the bearing manufacturers or equipment oem's gotten on the bandwagon?

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