The better bearing solution for industrial fans

1 The better bearing solution for industrial fans HIGHEST RELIABILITY OPTIMUM PERFORMANCE MINIMISED MAINTENANCE COSTS Берг АБ Тел. (495)-228-06-21, факс (495) Берг АБ Тел. (495)-228-06-21, факс (495) 223-30712 Yesterday s solutionsThe most common bearing solution for industrial fans ,until now, has been to use two double-row self-aligningbearings in separate plummer block housings eitherself-aligning ball bearings for light loads and highspeeds, or spherical roller bearings for heavy loads andmoderate bearing solutions allow a wide range of oper-ating conditions, whilst accommodating the misalign-ment which inevitably occurs in such a machine due, forinstance, to machining tolerances, assembly errors.

2 Ordeflection under load. However, they have one shortfall:in order to allow axial expansion of the shaft due tochanges in temperature etc., the outer ring of one bearingon each fan shaft (the free or non-locating bearing )must be able to slide axially inside the order to achieve axial sliding, the housing bores aremachined to give a loose fit for the bearing . This is amajor compromise in the design, since with the typicallight and imbalanced loads which often occur in fans , atight fit would be preferred to prevent the bearing outerring turning in the housing, and thus avoid extra vibra-tion, temperature, and wear of the more importantly, a loose fit does not guaranteethat the bearing will slide easily; due to friction betweenthe bearing and housing as a result of radial load, someaxial (thrust) force is generated within the bearing sys-tem.

3 This thrust force creates vibration and high tem-peratures, resulting in reduced bearing occursto some extent even under ideal ( normal ) external factors such as corrosion, wear, deflection,distortion or machining/mounting errors on the supportsurface mean that the bearing outer ring is preventedfrom sliding, then the real friction will be much higher,and the effect on the bearing system much more severe(see fig 1).Today s solutionsThe disadvantages/compromises with the old bearingsystem solution can be avoided completely by replacingthe non-locating bearing with CARB , the toroidal rollerbearing from SKF.

4 The spherical roller bearing or self-aligning ball bearing at the locating position remains 1An uneven housing support may cause problems whennot using CARB bearings .. leading to cross-located bearings, temperature increase and vibrationAn uneven bearing housing support .. gives distorted housing and pinched bearing ..shaft Берг АБ Тел. (495)-228-06-21, факс (495) Берг АБ Тел. (495)-228-06-21, факс (495) 223-30713021345670,050,10,150,20,25 Fig 2 Non-locating arrangement with and without CARB toroidal roller bearing .

5 The toroidal roller bearing arrange-ment does not induce any axial loadsFig 3 This bearing system life comparison shows that a toroidal roller bearing arrangement always has a higher basicrating life than an arrangement with only spherical roller bearings due to the absence of axial loads generated withinthe bearing systemCARB is a purely radial bearing , and cannot carryany axial loads. It accommodates the axial expansionwithin the bearing itself, with negligible friction, at thesame time as it allows misalignment. Therefore, the typical high vibration levels, elevated temperatures, andreduced bearing lives seen in fans , are avoided.

6 CARB toroidal roller bearings can be used with thesame standard housings and accessories as other self-aligning bearings. An extra benefit is that tight fits maybe used in the housings, eliminating wear and furtherreducing vibration levels. This is done with no adverseeffects on the standard housings, such as SNL plummer blocks,can be supplied with non-standard bore tolerances onrequest to give the bearing outer ring a tight 3 shows comparative calculated combined fatigue(L10) lives of an optimised bearing arrangement usingone spherical roller bearing and one CARB toroidal roller bearing , and a conventional bearing arrangementusing two spherical roller bearings.

7 The chart assumes noexternally applied loads on the system and that the coef-ficient of friction between the free spherical roller bear-ing and housing remains constant. The actual coefficientof friction is very hard to determine; a normal assump-tion for an ideal bearing housing is that = 0,1 0, does however vary significantly. Higher values of arecommon and if the bearing becomes jammed in the hous-ing, then will be greater than 1, : A bearing arrangement using one CARB toroidal roller bearing (C 2220 K) and one spherical roller bearing (22220 EK) is compared with an arrange-ment using two spherical roller bearings (22220 EK).

8 = 0,12. Life increase is then 2,4 times (see diagram).L10new solutionL10old solutionC 30 seriesC 22 seriesC 31 seriesC 23 seriesFriction coefficient (outer ring housing) Берг АБ Тел. (495)-228-06-21, факс (495) Берг АБ Тел. (495)-228-06-21, факс (495) 223-3071 SKF recommended bearing solution for industrial fans the complete package Locating bearing : spherical roller bearing orself-aligning ball bearing Non-locating bearing : CARB toroidal rollerbearing Standard housings (optional tight fits) Locating rings Adapter sleeves / lock nuts Seals Lubricants System 24 automatic lubricators Condition monitoring equipment4 Benefits of CARB toroidal roller bearingin industrial fans true free/held bearing arrangementThe internal axial freedom of a toroidal rollerbearing eliminates the risk of failure from outer rings sticking in the housing bore due to distortions from non-flat mounting surfaces.

9 Outer rings are axially fixed and can have a light press fit in the housing bore, reducing the risk of creeping as a result of unbalancedloading. reduced vibration and noiseMomentary axial load changes or changes in gas temperature will not lead to increased axial vibrations, due to the absence of inter-action between the locating and non-locatingbearings. less sensitive to minimum loadThe design allows the bearing to function properly where the applied loads are typically lighter than those required by similar size spherical roller bearings.

10 Lower operating temperature longer service life improved grease life less sensitive to imbalanceImbalance loads in fans can produce wear of housings with loosely fitted bearings CARB toroidal roller bearings can be mounted with a tight fit thereby eliminating housing wear uses the same standard housings as spherical roller and self-aligning ball bearingsNote: Boththe non-locating and locating bearingsbenefit from all these improvementsFig 4 When not using a CARB toroidal roller bearing , loosefits in housing are used to allow the free bearing to moveaxially.