The Design of Rolling Bearing Mountings

118 ExhausterThe exhauster is of the double-flow type; rotor weight22 kN; speed 1,200 min –1 ; exhaust gas temperatureapprox. 180 °C.Bearing selection, dimensioningThe use of plummer blocks for mounting the rotorshaft is simple and economical. The shaft diameter isdictated by strength considerations, and determinesplummer block and bearing size.The shaft is mounted on spherical roller bearings FAG22226E.C3 fitted in housings FAG LOE226BF andFAG LOE226AL. Due to the exhaust gas temperatureof +180 °C and the relatively high exhauster speed, thebearings feature an increased radial clearance C3. Thisprevents the bearings from running under preloadwhen there are major temperature differences betweeninner and outer ring. In addition, cooling discs are requiredto limit the bearing temperature. The plummerblock at the drive end is designed as the locating bearingwith a shaft opening (design BF), and that at theopposite end as the floating bearing with end cap (designAL).With the specified operating data the calculated indexof dynamic stressing f L ≈ 10; an f L value of 4...5 (correspondingto 55,000...100,000 h) would be adequate.Thus, the bearings are very safely dimensioned with regardto fatigue life. However, premature wear can becaused by slippage, ending the actual service life of thebearings before the calculated fatigue life has beenreached.The plummer blocks are made of grey cast iron. Thehousing bodies are split to simplify mounting.Machining tolerancesShaft to m6; housing to G6.Lubrication, sealingThe LOE housings feature an oil bath. A ring oilersupplies the bearings with oil. The design of the lateralhousing covers (oil collecting pockets and returnducts) allows excess oil to return to the sump.A grease chamber is provided as an additional sealingbetween cover and labyrinth ring; the chamber is replenishedwith grease at regular intervals.118: Rotor mounting of an exhauster169 FAG