The Design of Rolling Bearing Mountings

Internal bearings for the tension/84 take-up pulley of a belt conveyorNon-driven pulleys in belt conveyors are frequently fittedwith internal bearings. The bearings are integratedinto the pulley so that the pulley body revolves aboutthe stationary shaft.Operating dataBelt width 3,000 mm; belt speed 6 m/s; pulley diameter1,000 mm; pulley load 1,650 kN.Bearing selection, dimensioningThese pulleys are supported either in two sphericalroller bearings (fig. a) or in two cylindrical roller bearings(fig. b). The internal design of the cylindrical rollerbearings allows the rolling elements to accommodateload-related shaft deflections without edge running.In a spherical roller bearing arrangement, an FAG23276BK.MB with an adapter sleeve FAGH3276HGJ is used as locating bearing and an FAG23276B.MB is used as floating bearing.In a cylindrical roller bearing arrangement, the floatingbearing is an FAG 547400A and the locating bearingan FAG 544975A. Both cylindrical roller bearingshave the main dimensions 360 x 680 x 240 mm andare interchangeable with spherical roller bearings FAG23276BK.MB with an adapter sleeve FAGH3276HGJ.The bearings must feature the required dynamic loadrating C/the required bore diameter. With an index ofdynamic stressing f L > 4, the bearings are sufficiently dimensionedwith regard to fatigue life.Often, the actual bearing life is considerably shorterthan the nominal rating life determined on the basis ofthe f L value. The cause is wear in raceways and on rollingelements as a result of adverse ambient conditions.Improved cleanliness during mounting and in operationas well as the utilization of a suitable lubricanthave a positive effect on the bearing life. These influencesare taken into account in the adjusted rating lifecalculation and in the modified life calculation in accordancewith DIN ISO 281. It is used for example tocompare the effects of different lubricants. The fatiguelife calculated for pulley bearings with this method inmost cases is not equivalent to the attainable life as theservice life is mainly limited by wear.Machining tolerancesIn view of the circumferential load and the relativelyhigh amount of load the outer rings must be a verytight fit in the pulley bore. Tolerances, see table below.Lubrication, sealingThe bearings are lubricated with a lithium soap basegrease of penetration 2 with EP additives (FAG rollingbearing grease Arcanol L186V).External sealing of the bearings is provided by nonrubbinglabyrinth seals or multi-collar rubbing seals. Inboth cases the labyrinths are filled with the same greaseas the bearings. To supply the bearings with freshgrease and to increase the sealing effect, relubrication iseffected at short intervals (depending on the amountof dirt) via the stationary shaft.Machining tolerancesBearing Seat Diameter tolerance Cylindricity toleranceSpherical roller bearing Shaft h8 IT5/2as locating bearing Pulley bore M7 IT5/2Spherical roller bearing Shaft g6 IT5/2as floating bearing Pulley bore M7 IT5/2Cylindrical roller bearing Shaft g6 IT5/2locating bearing, floating bearing Pulley bore N7 IT5/2FAG 120