The Design of Rolling Bearing Mountings

69 Guide rollsGuide rolls guide, as the name indicates, and turn thewire and felt cloth in the wet end and dryer sections ofa paper machine. The same bearings are used for theguide rolls in both areas. Lubrication and sealing differ,however, depending on the place of application.In older machines the wet end section is usually lubricatedwith grease, and the dryer section with oil.In modern machines both sections have oil circulationlubrication. Due to different operating conditionsseparate oil circuits are necessary for the wet end anddryer sections.The larger the machine the more often it is found tobe faster. For this reason the bearing inner rings aremounted with a tapered bore directly on the taperedroll journal.Wet end sectionDepending on the positions of the bearings in the machinethey are subject to a small or large degree ofmoisture. Water must not penetrate the housing particularlywhen machines are being high-pressurecleaned.Dryer sectionEnvironmental temperatures of about 95 °C lead togreat length variations and place high demands onlubrication. The operating temperature of the bearingscan be 115 °C.Operating dataUseful width 8,800 mmRoll diameter 700 mmPaper speed 1,650 m/min (n = 750 min –1 )Roll weight F G ≈ 80 kNPaper pull 1 kN/m (tensile load F z ≈ 9 kN)Wrap angle 180°Bearing temperature approx. 105 °CBearing selection, dimensioningThe bearings must be able to accommodate loads andcompensate for misalignment at the same time (misalignment,bending). An increased radial clearanceaccording to C3 is necessary due to temperature differences.Spherical roller bearings FAG 22330EK.C3 aremounted.Bearing load:P = (F G + F z )/2 = (80 + 9)/2 = 44.5 kNThe diameter of the roll journal is determined by theroll rigidity required. As a result there is a high index ofdynamic stressing f L corresponding to a nominal life L hof well over 200,000 hours. The attainable life is evenhigher with such good lubrication conditions.The housings can be in standing or suspended positionor can be laterally screwed on. They are designed foroil circulation lubrication.Machining tolerancesThe inner rings have circumferential load and are directlyfitted to the tapered roll journal. The roll journalhave oil ducts so the bearings can be mounted and dismountedwith the hydraulic method.Roundness tolerance IT5/2 (DIN ISO 1101); taperangle tolerance AT7 (DIN 7178).Bearing seats in the housing bore according to G7.LubricationIn the dryer section: see example 68 (Dryer rolls) sincethe bearings are connected to the oil circuit of thedryer rolls. Minimum flow rate 0.9 l/min.In the wet end section: see example 66 (Suction rolls)and 67 (Central press rolls), since the bearings are connectedto the oil circuit of the wet section rolls.Minimum flow rate 0.5 l/min.SealingGap-type seals, which are non-rubbing and maintenance-free,prevent oil from escaping through the coverpassages in the dryer section.The bearings in the wet end section must have relubricatablelabyrinth seals to prevent water from penetrating.Remaining oil is thrown off by splash grooves intocollecting chambers and directed back. Cover sealsmake the housing oilproof.FAG 96