The Design of Rolling Bearing Mountings

86 Idler garlandGenerally, the service life of a bearing is not terminatedby fatigue but by wear in raceways and on rolling elementsas a result of contamination. Increased cleanlinessduring mounting and efficient sealings increasethe bearing life. The ajdusted rating life calculation isused for comparing different seal designs.New idler bearings feature utmost cleanliness (V =0.3). However, in the course of operation the lubricantgets heavily contaminated by particles (V = 3).As the bearings in belt conveyor systems fail as a resultof wear, the values obtained by the adjusted rating lifecalculation (L hna ) usually are not equivalent to the actuallyattainable lives.In addition to the rigidly troughed belt conveyors thegarland type belt conveyors are being increasinglyused. The idlers of each station are linked to each otherby flexible joints. These joints may consist of a wirerope, a chain link (flat chain, round chain), hinge orsimilar.Idler garlands accommodate impacts elastically; in theevent of problems with a roller the individual garlandis lowered and can be replaced relatively easily if necessary.Machining tolerancesThe two deep groove ball bearings are mounted ontothe idler shaft in a floating bearing arrangement. As theinner rings are subjected to point load the shaft is machinedto h6 or js6. The outer rings are subjected tocircumferential load and are pressed, therefore, into theidler end with an M7 interference fit.Lubrication, sealing and maintenanceThe deep groove ball bearings FAG 6209.2ZR.C3 arepacked, at the manufacturing plant, with a lithiumsoap base grease of penetration class 2 which is sufficientfor the entire bearing service life. Such a grease isalso used for the sealing.With idler bearings, both the attainable life and the lubricantservice life may be considerably reduced bygrease contamination during operation so that the sealingselected is decisive. Figs. 85a...c show various typesof sealing for belt conveyor idlers.Simple seals (figs. 85a and b) are used for clean environments.Fig. 85c shows an idler seal for brown coalopen pit mining.Fig. 86 shows idler garlands connected by chain links.These idlers are part of a conveying installation forrock phosphate. The bearings fitted are deep grooveball bearings FAG 6303.2ZR.C3.Machining tolerancesIdler ends to M7, shaft to h6 or js6.Lubrication, sealing, maintenanceThe deep groove ball bearings (design .2ZR) are sealedby dust shields on both sides and filled with FAG rollingbearing grease, a lithium soap base grease of penetrationclass 2. The grease filling suffices for idler servicelife. A grease chamber with a non-rubbing labyrinthseal is provided at the outboard end. The second,adjacent chamber is closed by a shield pressed into thehub bore. A baffle plate protects the bearing againstcoarse particles.86: Idlers connected by chain link123 FAG