The Design of Rolling Bearing Mountings

67 Central press rollsThe paper web runs through the press rolls on a feltcloth and a large amount of water is pressed out of it.Modern press sections consist of one central press rollagainst which one or more (suction) press rolls arepressed. The central press roll is solid, made of granite/steelor steel with a protective coating.Operating dataRoll length 8,800 mm; roll diameter 1,500 mm; speed1,450 m/min; roll weight 750 kN. Pressure by 3 rollsat 30°, 180° and 210°; bearing temperature about60 °C. Direct drive.Bearing selection, dimensioningSelf-aligning spherical roller bearings of the series 231or 232 with a very high load carrying capacity are chosendue to the high radial load and the misalignmentwhich is possible between the bearing locations. A lowcross section height is also important for these bearingssince the height of the housing is restricted by the rolldiameter. The roll weight and the load components ofthe pressure rolls yield a resulting bearing load F r =300 kN.A spherical roller bearing FAG 231/600K.MB.C3 ismounted at every bearing location. The bearings withtapered bore (taper 1:12) are pressed directly onto thetapered shaft seat by means of the hydraulic method.The floating bearing at the operator's end permits temperature-dependinglength variations of the roll byshifting the outer ring in the housing. The locatingbearing is at the drive end.The nominal life calculated is L h > 100,000 h with aspeed of 308 min –1 . With good lubrication (viscosityratio ≈ 3, basic factor a 23II = 3) and improved cleanliness(contamination factor V = 0.5) in the lubricatinggap L hna 100,000 h according to the adjusted ratinglife calculation.Machining tolerancesThe inner ring has circumferential load and is attachedto the tapered bearing seat of the shaft.Roundness tolerance IT5/2 (DIN ISO 1101); taperangle tolerance AT7 (DIN 7178).Housing bores according to G7 since there is pointload at the outer ring.LubricationThe spherical roller bearings are supplied with a minimumoil quantity of 7 l/min by circulation lubrication.A mineral oil of sufficient viscosity (ISO VG 100) andEP additives is used. Additives with good anti-corrosiveproperties and water separation ability are also required.An effective lubrication is achieved with an oilsupply to the centre of the bearing.Oil returns to both sides of the bearing via oil collectingpockets and connecting holes.SealingOil splash grooves in the roll journal prevent oil escapingat the cover passage.Non-rubbing and maintenance free gap-type seals protectthe bearings from environmental influences.Locating bearingFloating bearing67: Central press roll bearings93 FAG