good comments.

Our procedure on setting the coupling axial gap is roughly the same. Although if at magnetic center forces us too close to mechanical limit of travel, we adjust off of magnetic center to keep at least 1/16" (prefer 1/8") away from the mechanical limit of travel.

Your comment about rotors off magnetic center is also intriguing. Seems to be a controversial subject... different people put different importance on magnetic centering. I would be interested to hear what kinds of problems you have seen.

Using any blade to shape the bearing is not allowed for us. Could be done by a very skilled craftsman, but it carries a lot of risk.

HI Pete,
Actually I meant that we adjust the coupling gap so the rotor is within 1/16“ of the magnetic center which usually give us around ¼” from the brg thrust limit (6” brg). Those motors are direct coupled to a fan mounted on Dodge RTD sleeve oil brg with the thrust brg mounted closer to the coupling. The coupling is Falk grid coupling and need to be mounted with round spacer inside the outer loop of the grid and a rubber sheet between the two coupling, outer wise the magnetic pulse combine with the flexibility of the grid create an axial movement of the shaft that cause some issue with the thrust brg. We are not quite sure of the direct impact on the thrust failure, high temp, loosening thrust collar, balancing issue, high vibration, etc. We have those machines stopped only once a years so we do everything we can to make it last. Brg shaping was an important part of improvement of the reliability of the brg by providing enough support to the film oil on initial started-up. We had few early failures and it always have an economic impact on those large machine especially when it fails on start-up after a 10 days shutdown! A lot of questions asked! Brg shaping has nothing to do with rocket science and given a proper set of Babbitt knife and Prussian blue any skill technician can do the job. Babbitt knife only remove thin slice of material at the time 0.0005” so it takes 1 to 3 hours to do it but it will insure you won’t have an early failure. It is especially important on old shaft that has oil ring runner on the shaft for lubrication, it wear grooves on the shaft that could give ways to oil to escape the load zone. We improve alignment a lot and had to develop a special procedure since there was a lot of shaft’s sag when the machine is not running. Overall it is sometime very hard to pin point the actual cause of failure since sleeve brg failure are often rapid and catastrophic. Given a failed wiped brg, heat, lubricant, alignment, installation, initial shaping, it all look the same! We just give our technician all the support they needed to do the job as best as we can and all those action brought us excellent reliability with those brg.

Best regard,

Back in Dec 2007 RSS_Dave posted the following:

"If I hadn't played around with spike energy and sleeve bearings, I may have believed what I was taught and never found out that it is a VERY GOOD sleeve bearing measurement. You have to have your filters set up properly, but you can certainly see the increase in harmonics as the bearing wears. A normal one usually has three or four harmonics, a worn one may have 8 or 10, a wiped one has high noise floor and harmonics out as far as your F-max."

The last sentence is the most detail I have ever found on analysis of journal bearing using PeakVue or simliar tools.
Does anyone have more info on this subject or places I can go to get information?

On Dodge Sleeve-Oil bearings, the bearing liner actually 'floats' (for lack of a better word) on a pair of beveled "runners" so that the liner is self-aligning. The cooling water lines attach directly to the inner liner and are not attached to the outer bearing housing. I take a reading directly on the cooling water lines (there's usually a pipe nipple that you can get on with a 2-rail magnet). By comparing this reading with the bearing casing reading (spectra and trends) I can tell when the liner is getting loose in the housing. We retorque the liner hold-down bolt, and if the "looseness" indications don't go away, we know we have a worn liner.

Your bearings may be different, but I'd look for something attached to the liner that I could read directly.

Ariel: Thanks for starting this interesting posting!
Duncan Carter (hope you are listening):
I have read the first article you have mentioned in your 27 dec 2007 posting:
file \brnvi97 : 'fluid film bearing diagnostics using envelope spectra'.
My question: Why do you completely ignore the influence of magnetic airgap forces?
Four out of five examples are dealing with electrical machines! Aren't you enveloping magnetic disturbances like stator deflection under (multi) pole attraction, broken bar, excitation asymmetry or other magnetically introduced asymmetries, instead of hydrodynamically induced bearing forces and / or oil pressure / speed pulsations?
What is the basic difference between magnetic origine and hydrodynamic origine appearances in enveloping?
Regards,
Arie Mol

[QUOTE]Originally posted by karun:
Hi
The wiping type of failure results in increased clearance of bearings(purely sleeve bearing not tilting pad) which reflects in 3X vibration. Keep track of 3X and 4X harmonics if you start suspecting bearing deterioration.
===
This 3X and 4X will be due to resulting misalignment or looseness as a result of increase in bearing clearances. If it is so, why 1X and 2X will not be there? Also I will be happy ot know how to use enveloping for journal bearings?
Regards.
Irshad Akhtar

May we give orbital analysis a chance ?