The Design of Rolling Bearing Mountings

88 Bottom sprocket of a bucket chain dredgerBucket chain dredgers perform dredging work inwaterways. The buckets are carried by a continuouschain from the bottom sprocket to the top sprocketover a large number of support rolls and back.Operating dataLadder length 32 m; number of buckets 44; maximumdredging depth approximately 14 m; radial load onbottom sprocket approximately 250 kN.Bearing selectionRugged operation and unvoidable misalignmentbetween the housings at both ends of the sprocketshaft call for self-aligning bearings. The bearings usedare spherical roller bearings FAG 22240B.MB. Bothbottom sprocket shaft bearings are designed as locatingbearings. However, the bearings are not nipped axially,the housing being mounted with clearance in its ladderyoke seat. For easier bearing dismounting the shaftjournal is provided with oilways and grooves for hydraulicdismounting.Machining tolerancesCircumferential load on the inner ring.Shaft journal to m6; housing to J7.Lubrication, sealingThe grease in the bearing (FAG rolling bearing greaseArcanol L186V) is renewed at intervals of 1 1/2 to 2years coinciding with the general overhaul period ofthe dredger.The bottom sprocket is constantly immersed in water.This requires waterproof sealing. Each bearing locationis, therefore, fitted with two rubbing seals (shaft sealswith bronze garter spring) and, in addition, with twopacking rings (stuffing box). The shaft seals run on abush of seawater-resistant material. The stuffing boxcan be retightened by means of a cover. Grease is regularlypumped into the labyrinth between the shaft sealsand packing rings.88: Bottom sprocket of a bucket chain dredger125 FAG