Hello everyone,
How does one distinguish a roller bearing with insufficient lubrication from a vibration spectra? are there any specific frequency ranges etc

vibehigh
I use shock pulse to look for lubrication issues (as well as wear and damage). I use the SPM Leonova Infinity, what this does is gives me two numerical values called dBC (background noise) and dBM (maximum or bearing noise. When you set up the software it asks you for bearing number (or shaft size) and the running speed. It uses this to calculate an acceptable caution and danger zone which on the display is green yellow and red.
Rule of thumb is low levels of both maximum and carpet means a good bearing well lubricated.
A high level of carpet and maximum, where the difference between the two is less than 15dB is an indication that the bearing requires lubrication or there is some other event happening (looseness or misalignment etc). if the equipment has been ok for a while and I see this happen I will send out a work request to grease the bearing.
if there is a difference of more than 15dB, regardless of where the graphs are, this usually indicates a bearing fault.
If you go on to spminstrument.com you will find this explained much better than I have just done

When using vibration spectra I look at the floor of the graph. I'm not sure but i beleive that there is no specific frequency for lubrication. If there is a lot of random noise I look at that as a lubrication issue.

Hope this helps, I'm sure someone will correct me If I am wrong

The insufficient lubrication causes boundary lubrication and development of micro cracks on the races (especially loaded zones). If you take a spectrum in g’s to about 5 kHz you will see a broad cavitation like hump around 2-3 kHz and no distinct bearing frequencies. If these micro cracks develop into spalling you’ll see bearing “ringing” with typical bearing frequencies.
I would look for any higher readings than +/- 2 g’s and look at the spectrum first. I’m not able to attach any typical spectrum as I changed my job and don’t have an access to previous database.

If you are using PeakVue or similar technology the spectrum will show raised floor energy, the twf will show random, high frequency impacting and the auto-correlated twf will show very low correlation factor, in most cases.

Monitoring the twf and listening to the bearing while lubricating will be most enlightening for you if it truly is inadequate lubrication.

Let me add a reminder that lubrication will not repair wear, just damp the vibration. If you have damage like Alex describes, it will either still show in the spectrum at defect frequencies, just at lower amplitudes or it will be damped enough that you don't see it and it will return shortly.

Just to follow on from what Danny was saying, the attached document shows the effect of some grease on a roll bearing. Note that this is peakvue data.

grease.doc (176 Kb, 64 downloads) effect of grease

Ian,

Exactly the conditions I was describing. Thanks.