The Design of Rolling Bearing Mountings

28 Marine reduction gearThe hardened and ground gearings of marine gearstransmit great torques.Operating dataInput power P = 5,475 kW; input speed 750 min –1 ;output speed 209 min –1 ; operating temperature ca.50 °C.Bearing selectionCoupling shaftThe coupling shaft (upper right) is supported at thedrive end by a spherical roller bearing 23248B.MB(locating bearing) and at the opposite end by a cylindricalroller bearing NU1056M (floating bearing). Theshaft transmits only the torque. The bearings have toaccommodate only the slight deadweights and minorgearwheel forces from a power take-off system. Thebearing dimensions are determined by the design; as aresult larger bearings are used than needed to accommodatethe loads. Consequently, a life calculation isnot required.Input shaftAt the input shaft the radial loads from the gearing areaccommodated by two spherical roller bearings23248B.MB. The thrust loads in the main sense of rotationduring headway operation are separately accommodatedby a spherical roller thrust bearing 29434E.The bearing 23248B.MB on the left side also accommodatesthe smaller axial loads in the opposite direction.It is adjusted against the spherical roller thrustbearing with a slight clearance and preloaded bysprings. The preload ensures that the thrust bearingrollers do not lift off the raceways when the loadchanges but keep rolling without slippage. The housingwasher of the spherical roller thrust bearing is notradially supported in the housing to ensure that thisbearing can transmit no radial loads.Output shaftAt the output shaft, radial and axial loads are accommodatedseparately. The radial loads are accommodatedby two spherical roller bearings 23068MB. In thelocating bearing position at the output end a sphericalroller thrust bearing 29464E accommodates the differencefrom the propeller thrust during headway operationand the axial tooth loads. The smaller axial loadsduring sternway operation are taken up by the smallerspherical roller thrust bearing 29364E. These twothrust bearings are also adjusted against each otherwith a slight axial clearance, preloaded by springs andnot radially supported in the housing.Bearing dimensioningBased on the operating data, the following nominalfatigue lives are obtained for the different bearings. Theminimum value of L h = 40,000 hours required for classificationwas not only reached but far exceeded.Shaft Bearing Rolling bearing Equivalent Index of Nominal Viscosity Factor Attainablelocation dynamic dynamic fatigue ratio life atload stressing life = a 23 = utmostP f L L h / 1 a 23II · s cleanliness[kN] [h] L hna [h]Coupling shaftLocating bearing 1 23248B.MB only slightly loaded by deadweightFloating bearing 2 NU1056M only slightly loaded by deadweightInput shaftRadial bearings 3 23248B.MB 242 3.98 49,900 6.3 >114 »200,0003 new 23048B.MB 242 1.88 4,100 5.8 >114 »200,0004 23248B.MB 186 5.18 120,000 6.3 >114 »200,000Thrust bearings 5 29434E 80 >6.03 >200,000 5.2 >114 »200,0005 new 29334E 80 4.91 102,000 5.0 >114 »200,000Output shaftRadial bearings 6 23068MB 158 >6.03 >200,000 2.4 >84 »200,0007 23068MB 293 4.64 83,500 2.4 >84 »200,0007 new 23968MB 293 2.70 13,600 2.3 39 »200,000Thrust bearings 8 29364E only briefly loaded during sternway operation9 29464E 650 3.81 43,300 2.5 > 87 »200,0009 new 29364E 650 2.35 8,600 2.3 > 84 »200,000FAG 42