The Design of Rolling Bearing Mountings

114 Blanket cylinder of a sheet-fed offset pressTo date it was common practice to integrate cylindricalroller bearings, needle roller bearings or other designsin a sliding bearing supported sleeve and to accuratelyfit this complete unit into an opening in the sidewallof the machine frame; this required an elaborate technologyand was costly. Both the considerable cost andthe risk of the sleeve getting jammed during the "impressionon" and "impression off" movements of theblanket cylinder are eliminated by using a new tripleringeccentric bearing unit. It offers the benefit of absolutezero clearance which is not possible with theconventional unit as the sleeve always requires someclearance. Another significant advantage is the adjustablepreload which allows its radial rigidity to be considerablyincreased compared to bearings with clearance.Lubrication, sealingThe eccentric units can be lubricated both with greaseand with oil. Thanks to the favourable ambient conditions,the lubricant is only very slightly stressed so thatlong grease relubrication intervals and thus a longservice life are possible. A non-rubbing gap-type sealprevents grease escape.With oil lubrication, the oil flows to the bearing rollersthrough feed ducts. Via collecting grooves and returnholes the oil returns to the oil circuit.Bearing arrangementThe FAG triple-ring eccentric bearing units (floatingbearings) are available both with a cylindrical and witha tapered bore. The ready-to-mount unit is based onan NN cylindrical roller bearing design which is usedas a low-friction precision bearing in machine tools, anda double-row needle roller bearing which guides theeccentric ring. Axial guidance of the cylinder is providedby angular contact ball bearings (FAG 7207B) in Xarrangement, or by a thrust ball bearing.Operating dataRoll weight; press-on force; nominal speedBearing dimensioningAn index of dynamic stressing f L of 4...4.5 would beideal. This corresponds to a nominal life L h of 50,000 –80,000 hours. Under the given conditions the bearingsare adequately dimensioned so that an adjusted ratinglife calculation is not required.Machining tolerancesThe inner rings are subjected to circumferential load. Atight fit is obtained by machining the cylinder journalto k4 (k5). With a tapered bearing seat, an interferencefit is also obtained by axial displacement.The outer ring is mounted with a K5 or K6 fit or reducedtolerances (with a slight interference).114: Triple ring bearing for a blanket cylinderFAG 164