The Design of Rolling Bearing Mountings

66 Suction rollsSuction rolls are found in the wire or press section of apaper machine. They are hollow cylinders up to 10 min length which have several small holes all aroundtheir circumference. Some water is removed from theweb due to the rotating roll shell and the vacuum insidethe roll. The suction box, as interior axle, is stationary.The roll shell is driven by planet wheels inmodern paper machines.Operating dataRoll length 7,800 mm; roll diameter 1,600 mm; rotation278 min –1 (speed 1,400 m/min); roll weight270 kN; wire tension 5 kN/m.Bearing selection, dimensioningThe diameter of the suction box is decisive for the sizeof the bearing. We recommend bearings with a dynamicload rating as low as possible; the higher specificbearing load reduces the danger of slippage. Self-aligningbearings are necessary as misalignment could arise.Roll weight, wire tension and rotational speed are themain criteria for dimensioning the bearings.FAG spherical roller bearings FAG 239/850K.MB.C3with tapered bore (K 1:12) and increased radial clearanceare used. The bearings are mounted directly onthe tapered shaft seats for running accuracy reasons.The hydraulic method is applied to facilitate mounting.The locating bearing provides axial guidance for therolls while the floating bearing compensates for anyFloating bearinglength variations caused by displacement of the outerring in the housing bore.The nominal life for both bearings is L h > 100,000 h.The attainable life reaches over 200,000 h when theoperating temperature is 60 °C and oil ISO VG 68(viscosity ratio > 2; factor a 23 = 2.2) is used.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 due to point load at theouter ring.LubricationThe spherical roller bearings are supplied by circulationlubrication with a mineral oil quantity of 8 l/min.A mineral oil with sufficient viscosity and EP additives isselected. Additives with good anti-corrosive propertiesand water separation ability are also required. An effectivelubrication is achieved with an oil supply to thecentre of the bearing.SealingAny oil which escapes is thrown off via splash groovesinto oil collecting chambers and directed back. At theroll side a baffle plate and multiple grease-filled labyrinthwith integrated V ring prevent water penetratingfrom the outside.Locating bearing66: Suction roll bearingsFAG 92