Ball and Roller Bearings

Bearing Load Calculation4.4 Equivalent load4.4.1 Dynamic equivalent loadWhen both dynamic radial loads and dynamic axialloads act on a bearing at the same time, the hypotheticalload acting on the center of the bearing which gives thebearings the same life as if they had only a radial load oronly an axial load is called the dynamic equivalent load.For radial bearings, this load is expressed as pureradial load and is called the dynamic equivalent radialload. For thrust bearings, it is expressed as pure axialload, and is called the dynamic equivalent axial load.(1) Dynamic equivalent radial loadThe dynamic equivalent radial load is expressed byformula (4.17).PrXFrYFa4.17where,PrDynamic equivalent radial load, N {kgf}FrActual radial load, N {kgf}FaActual axial load, N {kgf}X Radial load factorY Axial load factorThe values for X and Y are listed in the bearing tables.(2) Dynamic equivalent axial loadAs a rule, standard thrust bearings with a contact angleof 90˚ cannot carry radial loads. However, self-aligningthrust roller bearings can accept some radial load. Thedynamic equivalent axial load for these bearings isgiven in formula (4.18).PaFa1.2Fr4.18where,PaDynamic equivalent axial load, N {kgf}FaActual axial load, N {kgf}FrActual radial load, N {kgf}Provided that Fr / Fa 0.55 only.4.4.2 Static equivalent loadThe static equivalent load is a hypothetical load whichwould cause the same total permanent deformation at themost heavily stressed contact point between the rollingelements and the raceway as under actual loadconditions; that is when both static radial loads and staticaxial loads are simultaneously applied to the bearing.For radial bearings this hypothetical load refers to pureradial loads, and for thrust bearings it refers to pure centricaxial loads. These loads are designated static equivalentradial loads and static equivalent axial loads respectively.(1) Static equivalent radial loadFor radial bearings the static equivalent radial load canbe found by using formula (4.19) or (4.20). The greaterof the two resultant values is always taken for Por.PorXo FrYo Fa4.19PorFr 4.20where,PorStatic equivalent radial load, N {kgf}Fr Actual radial load, N {kgf}Fa Actual axial load, N {kgf}XoStatic radial load factorYo Static axial load factorThe values for Xo and Yo are given in the respectivebearing tables.(2) Static equivalent axial loadFor spherical thrust roller bearings the static equivalentaxial load is expressed by formula (4.21).PoaFa2.7Fr4.21where,PoaStatic equivalent axial load, N {kgf}Fa Actual axial load, N {kgf}Fr Actual radial load, N {kgf}Provided that Fr / Fa 0.55 only.4.4.3 Load calculation for angular contact ballbearings and tapered roller bearingsFor angular contact ball bearings and tapered rollerbearings the pressure cone apex (load center) is locatedas shown in Fig. 4.12, and their values are listed in thebearing tables.When radial loads act on these types of bearings thecomponent force is induced in the axial direction. For thisreason, these bearings are used in pairs. For loadcalculation this component force must be taken intoconsideration and is expressed by formula (4.22).Fa 0.5Fr 4.22Ywhere,Fa: Axial component force, N {kgf}Fr: Radial load, N {kgf}Y: Axial load factorThe dynamic equivalent radial loads for these bearingpairs are given in Table 4.5.aFaFrLoad centerLoad centerFig. 4.12 Pressure cone apex and axial component forceFaaFrA-25