Page 39 of Needle Roller Bearings by NTN Corporation Japan

bearing fits ntn 6.5 interference calculation 1 load and required interference when radial load acts on a bearing the interference required to prevent a clearance between its inner ring and a steel solid shaft can be expressed in formulas 6.1 and 6.2 for fr 0.3 cor d b fr 0.25 d b fr where dt required effective interference for temperature difference m t difference between bearing temperature and ambient temperature °c d bearing bore diameter mm 3 fitting surface roughness and required interference the fitting surface is smoothed surface roughness is made less by bearing fits so that the interference reduces correspondingly the interference reduced value differs depending on the fitting surface roughness and generally the following reduction values must be prospected for ground shafts 1.0 to 2.5mm for lathe-turned shafts 5.0 to 7.0 mm 4 maximum interference bearing ring fitted with interference on a shaft or in a housing results in tensile stress or compressive stress over-interference could cause cracking /splitting of bearing and short fatigue life of bearing therefore in general the maximum interference is secured at 1/1000 and less of shaft diameter or otherwise it is secured so the circumferential maximum stress generating on the fitting surface comes to 130mpa or less see table 6.4 5 stress and deformation caused by interference when bearing ring solid is fitted with interference it deforms elastically and this elastic deformation results in stress see fig.6.2 the fitting surface pressure of bearing ring circumferential tensile stress inner ring compressive stress outer ring and radial expansion of raceway inner ring and shrinkageouter ring can be calculated from table 6.4 df 0.08 6.1 for fr 0.3 cor fr b 0.2 fr b df 0.02 6.2 where df required effective interference mm d bearing bore diameter mm b inner ring width mm fr radial load n kgf c0r basic static load rating n kgf 2 temperature rise and required interference when temperature rise of bearing difference between bearing temperature and ambient temperature is inevitable incurred by bearing running the interference required to prevent a clearance between the inner ring and a steel shaft can be expressed in formula 6.3 df 0.0015 d t 6.3 table 6.4 deformation and stress caused by bearing fit item surface pressure pi p mpa circumferential maximum stress i mpa radial elastic deformation of i raceway where k d di k0 d0 d h de h0 d d d0 e 2 pi 1 inner ring deff d k 2 2 outer ring 2 1 k 1 2 2 k0 2 pe e 2 deff d 2 1 h2 deff h 1 1 h2 1 h h0 2 2 h02 1 k k0 1 k deff tensile stress 1 1 k0 2 e pe compressive stress 1 h0 2 p k k2k02 expansion e h2h02 shrinkage remarks symbol representation d d0 di deff d d0 de deff e inner ring bore diameter shaft diameter mm hollowed shaft bore diameter for solid shaft d0 0 mm inner ring raceway diameter mm effective interference for inner ring mm outer ring outer diameter housing hole diameter mm housing outer diameter for sufficient housing size d0 mm outer ring raceway diameter mm effective interference for outer ring mm modulus of elasticity young factor 6 2.07 10 21200 mpa kgf/mm2 fig.6.2 a-35

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