The Design of Rolling Bearing Mountings

42 Axle box roller bearings of an Intercity train carriageThe type of axle box roller bearings presented here isused for Intercity traffic in Europe.The bogie frame is supported on the bearing housingby a central coil spring, arranged above the bearings.The wheelsets are guided by plate-type guiding armswhich are bolted on one side.Operating dataDeadweight of the carriage plus maximum payload:64,000 kg; two bogies, each with two wheelsets, implies4 wheelsets per car.Resulting axle weight per wheelset: A = 64,000/4 =16,000 kg; weight of wheelset G R = 1,260 kg;acceleration due to gravity g = 9.81 m/s 2 ;supplementary factor for dynamic loads occurring duringoperation f z = 1.3;thrust factor for cylindrical roller bearings f a = 1;number of bearings per wheelset i R = 4.Thus the equivalent dynamic load per bearing is:P = (A – G R )/i R · g · f z · f aP = (16,000 – 1,260)/4 · 9.81 · 1.3 · 1 = 46,990 NP = 46.99 kNWheel diameter D R = 890 mm;maximum speed v max = 200 km/h (possible speed250 km/h).Bearing selectionCylindrical roller bearings installed as axle box rollerbearings offer important advantages:Mounting is simple and they are easy to check andmaintain in main inspections.Axial clearance is irrelevant for radial clearance. Cylindricalroller bearings are pure radial bearings, but thelips allow the safe accommodation of all thrust loads(guiding forces) occurring in operation.Of all the roller bearing types cylindrical roller bearingshave the lowest friction. Their speed suitability istherefore greater than in the case of other roller bearings.Cylindrical roller bearings do not, however, compensatefor misalignment between axle and bogie frame.Therefore misalignment must be corrected by angularfreedom of the housing.The same cylindrical roller bearings are used for passengercars and freight cars. This simplifies stockkeeping.Each axle box accommodates two cylindrical rollerbearings, one FAG WJ130x240TVP and one FAGWJP130x240P.TVP.The bearing dimensions (d x D x B) are 130 x 240 x80 mm; the dynamic load rating C of one bearing is540 kN.The nominal rating life (L h10 ) is checked in kilometreswhen dimensioning the axle box bearings:L h10km = (C/P) 3.33 · D · π = (540/46.99) 3.33 · 890 · π =3,397 · 2,497.6 ≈ 9.5 million kilometres.Under these conditions the bearings are sufficiently dimensioned.5 million kilometres (lower limit) appliestoday as a basis for dimensioning axle box bearings forpassenger train carriages.Machining tolerancesBearing inner rings carry circumferential load; thereforethey are press-fitted: axle journal p6, housing H7.Bearing clearanceThe tight fit expands the bearing inner rings which reducesradial clearance. The air stream cools the outerrings to a greater extent than the inner rings duringtravel which leads to a further reduction in radial clearance.Therefore the bearings have a radial clearance of120 to 160 microns.Lubrication, sealingThe bearings are lubricated with a lithium soap basegrease. Lamellar rings at the wheel side provide for effectivenon-rubbing sealing. A baffle plate at the coverend keeps the grease close to the bearing. Despite thesmall amount of grease (≈ 600 g) high running efficiency(800,000 km and more) can be reached due tothe polyamide cages without changing the lubricant.FAG 62