Improvements In Bearing Life Using New Sealing Technology

Abstract

As many as 91 percent of all rolling element bearings fail to achieve their calculated theoretical lifetimes. One of the primary reasons for this failure is contamination of the lubricants. Past practice for protecting bearings from contamination includes the use of lip seals and labyrinth isolators, but both of these solutions suffer from certain shortcomings that lead to premature bearing failures. Using modern mechanical seal technology, it is now possible to hermetically seal pump bearing housings, gearboxes, and other rotating equipment, so as to completely contain the lubricant and totally exclude contaminants. With this hermetic seal in place, it is easier to cost-justify the use of superior (but more costly) synthetic lubricants, and lower the total cost of operating the equipment significantly. THEORETICAL BEARING LIFE CALCULATION The value of excluding lubrication oil contamination is best explained by first considering bearing life under ideal conditions. The L10 life of a rolling bearing is defined as the number of revolutions (or operating hours) that the bearing is capable of enduring before the first sign of fatigue (flaking, spalling) occurs (SKF, 1999). The L10 life is the lifetime that 90 percent of a large group of identical bearings would be expected to achieve/exceed. The median life is five times the L10 life (i.e., 50 percent of the bearings would be expected to achieve/exceed a life that is 53 longer than L10). The L10 life for a rolling element bearing is expressed as: