Pit & Quarry, October 2018
POWER TRANSMISSION COMPONENTS How to increase uptime in ring lubricated hydrodynamic bearings BY STEVE PASTERNAK ydrodynamic journal bearings also known as oil film bearings are frequently used in critical applications such as fans pumps motors crushers conveyors and high speed gearboxes where they are required to run for long periods of time Advantages of hydrodynamic bearings include long service life minimal maintenance requirements and damping that can significantly reduce vibration Several methods of lubricating these bearings can be found in various applications They include oil slinger discs gas lubrication oil rings or forced feed circulating oil The benefits of circulating oil in ring lubricated hydrodynamic bearings are plentiful BACKGROUND In hydrodynamic journal bearings the shaft rides on a thin film of oil which separates the shaft from the Babbitt bearing surface The clearance between the shaft and the bearing bore the bearing load and the shaft speed determine the thickness of this film When the shaft first begins to turn at slow speeds there is very little lubricant between the shaft and bearing This is known as the boundary lubrication regime During this period the asperities or microscopic imperfections on the shaft surface come into contact Nearly all of the wear that occurs in journal bearings happens during boundary lubrication In this condition the bearing is vulnerable to damage from contaminants such as dirt or ash that may be larger than the oil film As the shaft speed increases the oil film forms between the two surfaces At first the film is thin enough that the asperities still come into contact which is known as the mixed film lubrication regime Once the film is thick enough to fully separate the surfaces it is known as the full film lubrication regime During this regime H Oil ring lubricated journal bearing 20 PIT QUARRY October 2018 pitandquarry com ALL IMAGES ABB MOTORS MECHANICAL INC THE BENEFITS OF CIRCULATING OIL IN HYDRODYNAMIC BEARINGS Journal bearing during operation Oil ring oscillation axially a conically b and in a pendulum motion c
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