AGMA 11FTM21 PDF

The service life of a gearbox is determined by many factors. The bearings in the gearbox play a major role since they themselves deliver an important function, and in addition interact with the shafts, the casing and the oil. Without a doubt, the sizing of the bearings is of great importance for the gearbox reliability. Since more than 50 years the bearing dynamic carrying capacity has been used to determine a suitable size needed to deliver a sufficient fatigue life - but despite the advanced calculation methods developed, the methods do not fully predict service life. Producers of high quality bearings have introduced high performance class bearings and, lacking better ways to express the improved performance, this is only represented by increased dynamic carrying capacity. The availability of high-strength shaft materials in combination with bearings with high carrying capacity allows slimmer shafts to be used. The modulus of elasticity remains the same, so seat design for bearings and gears must be given close attention. This paper covers the following: sizing of bearings based on dynamic carrying capacity and how this relates to service life; how the design of the interface between bearing and shafts should be adapted to modern shaft materials; how the design of the interface between bearing and gearbox casing influences service life of the gearbox; and influence of modern electric motor speed controls in bearing type selection.