The Design of Rolling Bearing Mountings

25 Rolls for a plastic calenderPlastic foils are produced by means of calenders comprisingseveral rolls made of chilled cast iron or steelwith polished surfaces which are stacked on top ofeach other or arranged side by side.Hot oil or steam flows through the rolls, heating theO.D.s, depending on the material, to up to 220 °C(rigid PVC), which ensures a good processibility of thematerial. Rolls 1, 2 and 4 are subjected to deflectionunder the high loads in the rolling gap. In order to stillachieve the thickness tolerances of the sheets in the micrometerrange, the deflection is compensated for byinclining of rolls 1 and 3 and by counterbending ofrolls 2 and 4. Moreover, the narrow tolerance of thefoil thickness requires a high radial runout accuracy ofthe bearings and adequate radial guidance of roll 3which is only lightly loaded; this is achieved by preloadingthe main bearing arrangement by means ofcollaterally arranged, separate preloading bearings.Roll arrangement 1 to 41 234Operating dataType: four-roll calender, F-shapedUseful width 3,600 mmRoll diameter 820 mmRolling gap 1st step 1.5...2 mm2nd step 1...1.5 mm3rd step 0.25...1 mmRoll speed n = 6...24 min –1Inner ring temperature 170 °CRoll mass 18 t (weight ≈ 180 kN)Bearing systemTo accommodate the radial and thrust loads, the fourrolls are supported at both ends by the same type ofmain bearing arrangement. It consists of two doublerowcylindrical roller bearings forming the floatingbearing and of two double-row cylindrical roller bearingsplus one deep groove ball bearing forming thelocating bearing at the drive end. In addition, rolls 2and 4 have to accommodate counterbending forces,and roll 3 has to accommodate preloading forces.These counterbending and preloading forces are supportedat both roll ends in spherical roller bearings.Bearing selectionMain bearing arrangementThe radial pressure by load of 1,620 kN resulting fromthe maximum gap load of 4.5 kN/cm, as well as thecounterbending and preloading forces, are accommodatedby the main bearing arrangement at each end ofrolls 1, 2 and 4. The radial loads and the axial guidingloads are accommodated by double-row FAG cylindricalroller bearings (dimensions 500 x 650 x 130 mm)and deep groove ball bearings FAG 61996M.P65.At the locating bearing end the radially relieved deepgroove ball bearing accommodates only axial guidingloads.At the floating bearing end, heat expansions are compensatedby cylindrical roller bearings. Misalignmentsresulting from shaft deflections and roll inclination arecompensated for by providing a spherical recess for thebearing housings in the machine frame. The bearingsmust be dimensionally stable up to 200 °C as theirinner rings may heat up to 180 °C as a result of rollheating.The high radial runout accuracy (≤ 5 µm) is achievedby grinding the bearing inner rings and the roll bodyto finished size in one setting at a roll surface temperatureof 220 °C.The inner rings and the roll body canbe ground together due to the fact that the inner ringsof the cylindrical roller bearings – in contrast to thoseof spherical or tapered roller bearings – can be easilyremoved and mounted separately.The dimension of the inner ring raceway after grindinghas been selected such that no detrimental radialpreload is generated even during the heating processwhen the temperature difference between outer andinner ring is about 80 K.FAG 38