The Design of Rolling Bearing Mountings

83 Head pulley of a belt conveyorOne head pulley is not sufficient for very long belts,steeply inclined belts or heavily loaded belts. In suchcases several head pulleys are mounted in tandem. Inthis application, two head pulleys are arranged at thedrive station. Three identical driving motors are used:the first pulley is driven from both ends, the secondone from one end only.With an index of dynamic stressing f L ≈ 4 the bearingsare adequately dimensioned compared to field-provenbearing arrangements. Often the bearing life is limitedby wear on rolling elements and raceways and is generallyshorter than the nominal rating life (approx.50,000 h), calculated with the index of dynamic stressingf L . Improved cleanliness during mounting and operation,and a suitable lubricant, reduce wear, thus increasingthe bearing life. These influences are takeninto account in the adjusted rating life calculation bythe factor a 23 .Machining tolerancesOperating dataPower consumption 3 x 430 kW; belt width2,300 mm; belt speed 5.2 m/s; conveying capacity7,500 m 3 /h; pulley diameter 1,730 mm.Bearing selection, dimensioningThe shaft of the head pulley is supported on plummerblocks. The shaft diameter is dictated by strength considerations,thus determining the bearing bore andhousing size. Spherical roller bearings FAG23264K.MB are mounted. The one-piece plummerblock housings FAG BND3264K are made of caststeel GS-45. One of the plummer blocks acts as thelocating bearing, the other one as the floating bearing.To simplify mounting and dismounting hydraulicsleeves are used.The bearing inner rings carry circumferential load.They are fitted on the shaft with adapter sleeves FAGH3264HG.Shaft to h8 and cylindricity tolerance (DIN ISO1101) IT5/2; housing bore to H7.Lubrication, sealingGrease lubrication with a lithium soap base grease ofpenetration class 2 with EP additives (FAG rolling bearinggrease Arcanol L135V or L186V).The housing covers and rings on the shaft form nonrubbinglabyrinth seals. These multiple labyrinths arefilled with the same grease as the bearings and preventpenetration of foreign matter. In very dusty environmentsrelubrication at short intervals is required.Grease is injected into the bearing until some of thespent grease escapes from the labyrinths.FAG 118