ABSTRACT
Bearing problems are more common in gear boxes than are gear failures. A basic choice when designing a unit is which type of bearing to use. There are two general classes, one being journal-type bearings, the other being rolling-element-type bearings. Journal bearings are characterized by operating with a relatively thick oil film between the rotating and stationary elements, the oil film being sheared by relative sliding. Rolling element bearings include ball, roller, and needle bearings with many design variations in each of these classes. Gearbox shaft seals are usually either elastomeric lip seals or noncontacting labyrinth seals. Elastomeric lip seals are generally found in low-speed applications in conjunction with rolling element bearings. On occasion, carbon face seals are incorporated in gear applications where speeds are high and a more positive seal than a labyrinth is desired. Labyrinth and lip seals will allow oil leakage if the gearbox internal pressure is higher than the external ambient pressure.
