This is a 1200 RPM centerhung ID fan with a 4" dia shaft and sleeve bearings. About 8 years ago someone has changed the viscocity of the oil used on these bearings from ISO 68cSt@40degC (recommended by the OEM)to ISO 100cSt@40degC .

This fan is still running all these years but it had 4 occasions of IB bearing failure. Currently, the temperature is 130F on IB (equipped with thrust collars) and 100F on OB. The babbit insert is fabricated in a local shop according to OEM dimensional specs but of unknown material composition. This fan has an automatic damper on inlet operating sometimes at 20% openning which potentially may produce unstable operation in particular in axial direcion but vibration pattern/amplitudes is not affected. No misalignemnt, excessive amplitudes are present. Installation is OK (blueing showed close to 100% contact on the callar faces). The OEM is no longer in business to ask for an advise.

Question:
Is there a prudent accurate method (other then trial and error) to determine the correct oil viscocity for this application? Of course, one can always follow general recommendations, but they are just general...

I'll appreciate your view.

David

This message has been edited. Last edited by: David_G,

Are you really sure that your local shop do a good job? We had a problem like you mention and we found that the babbit sleeve was not well seated and squeeze on the shaft so no oil was able to lubricate. Result: failure. It was the repair shop's fault.
Go to GOOGLE and ask for "BABBIT BEARING" and you will find many shops who specialize with babbit bearing.
On some applications we lubricate with VG150 or VG220 oil for our babbit bearings. I think that the difference between VG68 and VG100 is not the problem.

If you go to the bearing manufacturer and give them the specifics of the application they can often give you a good recommendation of the correct grease or oil for their bearings. We have done this several times. In addition by sampling and analyzing the oil you can tell if it is doing the correct job. Oil with insufficient viscosity will cause different wear than oil with too high of a viscosity.

As abeaudoin suggested VG 68 to VG 100 should not pose any serious prolems.

In my experience ID fans used in Mines usually run on lubes of VG 220 to 460.

Hussam Adeni

The Running temps seem rather low. You have mentioned 100 f. which I am sure is close to the ambient Temp. What is the overall weight of the fan and shaft? The bearing is 4 inches Dia. by at least 8 in. long??? Is the lube fed under pressure. Has the babit had proper oil grouves cut into its face at manufacture What was the original clearance developed at the time of manufacture or installation

These would be the the first questions to be asked in preparation for a lube recomendation.

As a rough guide, the viscosity at operating temperature for a plain bearing running at 1200 rpm is 65-70 cSt.

If you are running at 100 F (38C) then ISO 68 is fine. If you are running at 130F (55°C) then ISO 100 would be more suitable.