The Design of Rolling Bearing Mountings

Attainable lifeThe actually attainable life L hna is considerably longerthan the nominal life L h .L hna = a 1 · a 23 · L h is calculated with the following data:Nominal viscosity of the oil: 40 = 100 mm 2 /sOperating temperature: t = 50 °COperating viscosity: = 58 mm 2 /sSpherical roller bearing 23248B (no. 3):C = 2,450 kN; C 0 = 4,250 kN; n = 750 min –1 ;d m = (440 + 240)/2 = 340 mmRated viscosity: 1 = 9.2 mm 2 /sViscosity ratio: / 1 = 6.3Spherical roller thrust bearing 29464E (no. 9):C = 4,300 kN; C 0 = 15,600 kN; n = 209 min –1 ;d m = (580 + 320)/2 = 450 mmRated viscosity: 1 = 23 mm 2 /sViscosity ratio: = / 1 = 2.5A stress index f s* = C 0 /P 0* > 14 is obtained for bothbearings; consequently, K 1 = 1 and K 2 = 1; therefore,K = 1 + 1 = 2.From the viscosity ratio and the factor K the followingbasic factors are obtained:– for the radial spherical roller bearing a 23II = 3.8– for the spherical roller thrust bearing a 23II = 2.9Factor a 23 is obtained from a 23 = a 23II · s.The cleanliness factor s is determined on the basis of thecontamination factor V. Both bearings operate underutmost cleanliness conditions (V = 0.3). Cleanliness isutmost if the particle sizes and filtration ratios of contaminationfactor V = 0.3 are not exceeded.Taking into account the viscosity ratio and the stressindex f s* , a cleanliness factor of s > 30 and consequentlyan a 23 factor = a 23II · s > 114 and > 87, respectively, isobtained for the bearings under consideration. Theattainable life is in the endurance strength range.This means that smaller bearings could be provided forbearing locations 3, 5, 7 and 9 to accommodate thesame shaft diameter (see table: 3 new, 5 new, 7 new, 9new) and would, in spite of the now higher bearingloads, still be in the endurance strength range.Machining tolerancesAs all bearing inner rings in this application are subjectedto circumferential load they are fitted tightlyonto the shaft seats:– Radial bearings to n6– Thrust bearings to k6.If the radial bearing outer rings are subjected to pointload, the bearing seats in the housings are machined toH7.As the spherical roller thrust bearings are to accommodateexclusively thrust loads they are fitted with clearance,i.e. radially relieved, into the housing seats whichare machined to E8.Lubrication, sealingTo meet the high requirements on safety and reliability,adequate lubrication and cleanliness conditions areprovided for marine gears. The circulating oil ISO VG100, which is used to lubricate both gear wheels androlling bearings, is cooled and directly fed to the bearings.By-pass filters with filter condition indicators andwith an adequate filtration ratio ensure an oil conditionwhere no particles bigger than 75 µm are foundand where, consequently, cleanliness is usually utmost(contamination factor V = 0.3).For this reason, the oil cleanliness class should be14/11 or 15/12 (ISO 4406).Radial shaft seals protect the transmission from contamination.FAG 44