From Machinery Lubrication,The pitfalls of using oil rings as a lube-delivery:
Oil bath or oil sump lubrication is one of the oldest and simplest methods of oil lubrication; only grease lubrication is older than oil bath lube. The bearing rolling elements pass, or “plough”, through a portion of this oil sump as the shaft revolves (Figure 1). Oil bath lubrication is feasible unless and until too much frictional heat is generated by the plowing action of rolling elements at excessively high speeds. Because heat reduces oil film strength and accelerates the rate at which oil oxidizes, the oil bath lube method is avoided on process pumps whenever DN (the inches of shaft diameter [D] multiplied by shaft revolutions per minute [N]) exceeds 6,000.
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