Pit & Quarry, October 2018
Adding circulating oil can significantly reduce bearing wear there is no wear of the shaft or bearing and the bearing is generally safe from contaminants smaller than the oil film Still if insufficient lubrication is provided then the bearing will run in boundary or mixed film regimes and risk accelerated wear OIL RING LUBRICATION Hydrodynamic journal bearings in lowspeed up to about 150 ft per minute to medium speed up to about 4000 ft per minute applications are often lubricated by one or more oil rings that ride on the shaft and dip into the oil sump below As the shaft turns friction between the shaft and the oil rings causes them to turn as well bringing oil from the sump to the shaft and lubricating the bearing Key benefits to oil ring lubrication are that it is cost effective allows the bearing to be fully self contained and if sized properly to the application can provide sufficient lubrication to the bearing at the required operating speeds But there are situations where oil ring lubrication alone is not ideal At startup there is no oil available to separate the shaft and bearing This results in metal to metal contact and bearing wear Oil ring lubrication is also not ideal during slow speed operation When the shaft speed is low the oil film between the shaft and bearing will be much thinner than during normal operation and the A hydrodynamic fan bearing configured for circulating oil bearing may operate in the mixed film or boundary lubrication regimes and risk accelerated wear Likewise at high speeds about 4000 ft per minute or greater oil rings struggle to deliver enough oil to fully lubricate the bearing A large difference in shaft and oil ring rotation speed prevents the oil rings from delivering adequate oil to the bearing resulting in mixed film or boundary lubrication This can cause the bearing to fail at high speeds due to temperature Oil rings can also begin to oscillate Bearing and shaft surfaces during boundary lubrication a mixed film lubrication b and full film lubrication regimes c SIZE www kpijci com pitandquarry com October 2018 PIT QUARRY 21
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