The Design of Rolling Bearing Mountings

91 Vibrating road rollerThe vibrations of such road rollers are produced by aneccentric shaft.Operating dataSpeed of eccentric shaft n = 1,800 min –1 ; radial loadF r = 238 kN; number of bearings z = 4; required nominalrating life L h ≥ 2,000 hours.Bearing selection, dimensioningThe centrifugal force from the imbalance weights onboth sides of the roll are accommodated by two bearingseach. The equivalent dynamic load per bearing is:P = 1/z · F r = 1/4 · F r = 59.5 kNFor the above conditions, an index of dynamic stressingf L = 1.52 and a speed factor of f n = 0.302 are obtained.The adverse dynamic stressing is taken into account byintroducing a supplementary factor f z = 1.2. Thus, therequired dynamic load rating of one bearingC = f L /f n · P · f z = 1.52/0.302 · 59.5 · 1.2 = 359.4 kNOn each side of the imbalance weights a cylindricalroller bearing FAG NJ320E.M1A.C4 (dynamic loadrating C = 380 kN) is mounted. Due to the vibratoryloads the bearings are fitted with an outer ring ridingmachined brass cage (M1A). The misalignmentbetween the two bearing locations from housingmachining inaccuracies is less than that permissible forcylindrical roller bearings.Machining tolerancesIn view of the vibrations it is advisable to provide tightfits for both the bearing inner and outer rings. Axialguidance of the eccentric shaft is provided by the lipsof the cylindrical roller bearings.Eccentric shaft to k5, housing bore to M6.Lubrication, sealingThe bearings are lubricated by the oil splashed off fromthe imbalance weights. Additional guide plates improvelubricant supply to the bearings. Mineral oilswith EP additives and anti-corrosion additives haveproved to be suitable.Internal sealing is provided by shaft seals, external sealingby O-ring seals.FAG 128