The Design of Rolling Bearing Mountings

Crane pillar mounting with a spherical roller thrust bearing78 and a spherical roller bearingOperating dataThrust load (crane superstructure and payload) F a =1,700 kN; radial load (reaction forces resulting fromtilting moment and wind pressure) F r = 1,070 kN;speed n = 1 min –1 .Bearing selection, dimensioningIn this case F r /F a > 0.55. The radial load is relativelyhigh. Therefore, it is accommodated by an additionalradial bearing, a spherical roller bearing. The two bearingsare mounted so that their pivoting centres coincide.Thus angular alignability is ensured. A thrustwasher inserted between the two bearings prevents excessiveradial loading on the thrust bearing. The sphericalroller bearing size depends on that of the sphericalroller thrust bearing. The outside diameter of theradial bearing must be larger than the housing washerof the thrust bearing. To ensure close guidance of thecrane superstructure, the reduced radial clearance C2 isprovided for the radial bearing.Crane pillar mountings with one spherical roller bearingand one spherical roller thrust bearing providecompact designs. They require, however, a widermounting space than mountings with one singlespherical roller thrust bearing.The mounting features a spherical roller thrust bearingFAG 29440E with the static load rating C 0 = 8,500 kNand a spherical roller bearing FAG 23056B.MB.C2with the static load rating C 0 = 3,000 kN.For calculating the equivalent static load for the sphericalroller thrust bearing it is assumed that the frictionat the thrust washer, acting as a radial load, is 150 kN.Thus F r /F a < 0.55 for the spherical roller thrust bearing.Equivalent static load:P 0 = F a + X 0 · F r = F a + 2.7 · F r for F r ≤ 0.55 F a= 1,700 + 2.7 · 150 = 2,100 kNFor the spherical roller bearing:P 0 = F r = 1,070 kNHence the indices of static stressing f s = C 0 / P 0 are:Spherical roller thrust bearing = 8,500 / 2,100 = 4.05Spherical roller bearing = 3,000 / 1,070 = 2.8These values show that the bearings are safely dimensioned.The shaft washer and housing washer of spherical rollerthrust bearings with f s values of ≥ 4...≤ 6 must befully supported axially; good radial support of thehousing washer is also required.Machining tolerancesSpherical roller thrust bearing:Shaft washer to j6,housing washer to K7Spherical roller bearing:shaft to j6; housing to J7Lubrication, sealingThe bearing housing is filled with oil beyond the upperedge of the spherical roller bearing, i.e. the bearingsrun in an oil bath. Thus they are well protected againstcondensation water and corrosion.Outer sealing is provided by labyrinths. In view of theadverse ambient conditions an additional, rubbing sealwith elastic lip is provided. Inner sealing is effected bythe tube communicating with the housing, and a labyrinth.Thrust washer78: Crane pillar mounting with a spherical roller thrust bearing and a spherical roller bearing111 FAG