The Design of Rolling Bearing Mountings

97 Two-bearing screen with circle throwOperating dataScreen box weight G = 35 kN; vibration radius r =0.003 m; speed n = 1,200 min –1 ; number of bearingsz = 2 ; acceleration due to gravity g = 9.81 m/s 2 .Bearing dimensioningTwo-bearing screens work beyond the critical speed;thus the common centroidal axis of the screen box andthe unbalanced load does not change during rotation.The bearing load due to the screen box centrifugalforce is:F r = 1/z · G / g · r · (π · n/30) 2 == 1/2 · 35 / 9.81 · 0.003 · (3.14 · 1,200/30) 2 = 84.5 kNTo allow for the unfavourable dynamic stressing, thebearing load should be multiplied by the supplementaryfactor f z = 1.2. Thus, the equivalent dynamic loadP = f z · F r = 1.2 · 84.5 = 101.4 kNWith the index of dynamic stressing f L = 2.72 (L h =14,000 h) and the speed factor f n = 0.34 (n =1,200 min –1 ) the required dynamic load ratingC = f L /f n · P = 2.72/0.34 · 101.4 = 811.2 kN2The recommended index of dynamic stressing f L forvibrating screens is 2.5...3, corresponding to a nominalfatigue life L h of 11,000 to 20,000 hours. Sphericalroller bearings FAG 22324E.T41A with a dynamicload rating of 900 kN are chosen.Machining tolerancesThe eccentric shaft features two spherical roller bearings,one as the locating bearing, the other as floatingbearing. The inner rings are point loaded and mountedwith a shaft tolerance of g6 or f6. The outer rings arecircumferentially loaded and fitted tightly in the housingbore to P6.Lubrication, sealingCirculating oil lubrication. Mineral oils with a minimumviscosity of 20 mm 2 /s at operating temperatureare recommended. The oil should contain EP additivesand anti-corrosion additives.Outer sealing is provided by a grease-filled, replenishablelabyrinth. A flinger ring with an oil collectinggroove prevents oil leakage. A V-ring is providedbetween flinger ring and labyrinth to separate oil andgrease.1Floating bearing1 FestlagerL l97: Two-bearing screen with circle throwLocating bearing139 FAG