Ball and Roller Bearings

Bearing Fits7.3.2 Recommended FitsBearing fit is governed by the selection tolerances forbearing shaft diameters and housing bore diameters.Widely used fits for 0 Class tolerance bearings andvarious shaft and housing bore diameter tolerances areshown in Table 7.1.Generally-used, standard fits for most types of bearingsand operating conditions are shown in Tables 7.2 - 7.7.Table 7.2: Fits for radial bearingsTable 7.3: Fits for thrust bearingsTable 7.4: Fits for electric motor bearingsTable 7.6: Fits for inch series tapered roller bearings(ANSI Class 4)Table 7.7: Fits for inch series tapered roller bearings(ANSI Class 3 and 0)Table 7.5. shows fits and their numerical values.For special fits or applications, please consult NTNEngineering.7.3.3 Interference minimum and maximum valuesThe following points should be considered when it isnecessary to calculate the interference for an application:¡In calculating the minimum required amount ofinterference keep in mind that:1) interference is reduced by radial loads2) interference is reduced by differences betweenbearing temperature and ambient temperature3) interference is reduced by variation of fittingsurfaces¡The upper limit value should not exceed 1/1000 ofthe shaft diameter.Required interference calculations are shown below.(1) Radial loads and required interferenceInterference of the inner ring and shaft decreases whena radial load is applied to the bearing. The interferencerequired to secure effective interference is expressed byformulae (7.1) and (7.2).Fr 0.3 Cor! dF 0.08 (dFr / B) 1/2 N 0.25 (dFr / B) 1/2 kgf (7.1)Fr 0.3 Cor! dF 0.02 (Fr / B) N 0.2 (Fr / B) kgf (7.2)Where,! dF : Required effective interference according toradial load md : Bearing bore diameter mmB : Inner ring width mmFr : Radial load NkgfCor : Basic static load rating Nkgfshown in formula (7.3).! dT = 0.0015d!T (7.3)! dT : Required effective interference fortemperature difference m!T : Difference between bearing temperatureand ambient temperature ˚Cd : Bearing bore diameter mm(3) Fitting surface variation and required interferenceInterference decreases because the fitting surface issmoothened by fitting (surface roughness is reduced).The amount the interference decreases depends onroughness of the fitting surface. It is generally necessaryto anticipate the following decrease in interference.For ground shafts: 1.02.5mFor lathed shafts: 5.07.0m(4) Maximum interferenceWhen bearing rings are installed with an interference fit,tension or compression stress may occur along theirraceways. If interference is too great, this may causedamage to the rings and reduce bearing life. You shouldtry to obtain the previously described upper limit.7.3.4 Other details(1) Tight interference fits are recommended for,¡Operating conditions with large vibration or shockloads¡Applications using hollow shafts or housings withthin walls¡Applications using housings made of light alloys orplastic(2) Small interference fits are preferable for,¡Applications requiring high running accuracy¡Applications using small sized bearings or thinwalled bearings(3) Consideration must also be given to the fact that fitselection will effect internal bearing clearanceselection. (refer to page insert A-58)JIS class 0bearing!DmpG6 G7H6H7Loose fitH8Transition fitJ6 J7K6 K7M6 M7Types of fitsHousingTransition fitN6 N7Tight fitP6 P7Tight fit(2) Temperature difference and required interferenceInterference between inner rings and steel shafts isreduced as a result of temperature increases (differencebetween bearing temperature and ambient temperature,!T) caused by bearing rotation. Calculation of theminimum required amount of interference in such cases isJIS class 0bearing!dmpg5g6h5h6k5ShaftsFig 7.1 State of fittingJ5J6k6m5m6n5n6p6A-50