The Design of Rolling Bearing Mountings

80 Crane run wheelOperating dataWheel load R = 180 kN; operating speedn = 50 min –1 ; wheel diameter d 1 = 630 mm;bearing centres l = 186 mm.0.1 R0.1 RBearing dimensioningThe weight of the crane and the maximum payload areknown. The thrust acting between wheel and rail can,however, only be estimated. The equivalent dynamicload P acting on the bearings is calculated in accordancewith DIN 15 071; this standard specifies thethrust resulting from friction between wheel and rail tobe 10 % of the radial load. The bearing loads P I (bearingI) and P II (bearing II) are:P I = X · [R/2 + 0.1 · R · d 1 / (2 · l)]P II = X · [R/2 – 0.1 · R · d 1 / (2 · l)] + Y · 0.1 · RWith the radial factor X = 1 and e = 0.24 for F a /F r ≤ ethe thrust factor Y = 2.84.Thus P I = 90 + 18 · 630/372 = 120.5 kN = P maxBearing selection0.1 R0.1 RThe bearings fitted in run wheels are often designed ashub mountings. The run wheel rotates, together withthe bearing outer rings, about a stationary shaft.Spherical roller bearings are used because of their veryhigh load carrying capacity.The bearings fitted are two spherical roller bearingsFAG 22220E. The distance between the two bearingsshould not be too small in order to keep the bearingreaction loads resulting from the wheel-rail contactwithin reasonable limits.This bearing arrangement is standardized by DIN15 071. The two spherical roller bearings run on asleeve to allow for rapid replacement of the completerun wheel unit. It is a floating bearing arrangement, theinner rings being displaceable on the sleeve. Dependingon the thrust load direction, either the left-hand orthe right-hand bearing abuts the sleeve collar. Thisarrangement allows optimum bearing loading, sincethe bearing which accommodates the additional thrustloads is relieved of radial load due to the tiltingmoment from the thrust load.P II = 90 – 30.5 + 2.84 · 18 = 110.6 kN = P minAssuming that the bearing loads vary linearly betweenP min and P max ,P = (P min + 2 · P max )/3 = (110.6 + 241)/3 = 117.2 kNWith the dynamic load rating C = 360 kN and thespeed factor f n = 0.885 (n = 50 min –1 ) the index ofdynamic stressingf L = C/P · f n = 360/117.2 · 0.885 = 2.72With the generally recommended value for crane runwheels f L = 2.5...3.5, the bearing mounting is adequatelydimensioned.Machining tolerancesThe bearing outer rings, which carry circumferentialload, are tight fits. The hub is machined to M7, thesleeve to g6, thus providing for a slide fit for the innerrings. This prevents detrimental axial preloading andsimplifies bearing mounting and dismounting.Lubrication, sealingThe bearings are lubricated with a lithium soap basegrease with EP additives (FAG rolling bearing greaseArcanol L186V). The relubrication interval is approximatelyone year.Gap-type seals or simple rubbing seals are in most casessatisfactory.FAG 114