7. Bearing Fits 7. Fitting For rolling s, inner and outer rings are fixed on the or in the housing so that relative movement does not occur between fitting surfaces during operation or under. This relative movement between the fitting surfaces of the and the or housing can occur in a radial direction, an axial direction, or in the direction of rotation. Types of fitting include tight, transition and loose fitting, which may be selected depending on whether or not there is interference. The most effective way to fix the fitting surfaces between a 's raceway and or housing is to apply a "tight fit." The advantage of this tight fit for thin walled s is that it provides uniform support over the entire ring circumference without any loss of carrying capacity. However, with a tight fit, ease of installation and disassembly is lost; and when using a non-separable as the floating-side, axial displacement is not possible. For this reason, a tight fit cannot be recommended in all cases. 7.2 The necessity of a proper fit In some cases, improper fit may lead to damage and shorten life, therefore it is necessary to make a careful investigation in selecting a proper fit. Some of the failure caused by improper fit are listed below. Raceway cracking, early flaking and displacement of raceway Raceway and or housing abrasion caused by creeping and fretting corrosion Seizing caused by negative internal clearances Increased noise and deteriorated rotational accuracy due to raceway groove deformation Please refer to insert pages A-96 A-99 for information concerning diagnosis of these conditions. 7.3 Fit selection Selection of a proper fit is dependent upon thorough analysis of operating conditions, including consideration of: Shaft and housing material, wall thickness, finished surface accuracy, etc. Machinery operating conditions (nature and magnitude of, rotational speed, temperature, etc.) 7.3. "" or "Loose fit" () For raceways under rotating s, a tight fit is necessary. (Refer to Table 7.) "Raceways under rotating s" refers to raceways receiving s rotating relative to their radial direction. For raceways under static s, on the other hand, a loose fit is sufficient. (Example) Rotating inner ring = the direction of the radial on the inner ring is rotating relatively (2) For non-separable s, such as deep groove ball s, it is generally recommended that either the inner ring or outer ring be given a loose fit. Table 7. Radial and fit Static Illustration Bearing rotation Ring Fit Inner ring: Rotating Outer ring: Stationary Rotating inner ring Inner ring : Unbalanced Inner ring: Stationary Outer ring: Rotating Static outer ring Outer ring : Loose fit Static Inner ring: Stationary Outer ring: Rotating Static inner ring Inner ring : Loose fit Unbalanced Inner ring: Rotating Outer ring: Stationary Rotating outer ring Outer ring : A-49
7.3.2 Recommended Fits Bearing fit is governed by the selection tolerances for diameters and housing bore diameters. Widely used fits for Class tolerance s and various and housing bore diameter tolerances are shown in Fig. 7.. Generally-used, standard fits for most types of s and operating conditions are shown in Tables 7.2-7.7. Table 7.2: Fits for radial s Table 7.3: Fits for thrust s Table 7.4: Fits for electric motor s Table 7.6: Fits for inch series tapered roller s (ANSI Class 4) Table 7.7: Fits for inch series tapered roller s (ANSI Class 3 and ) Table 7.5. shows fits and their numerical values. For special fits or applications, please consult NTN Engineering. 7.3.3 Interference minimum and maximum values The following points should be considered when it is necessary to calculate the interference for an application: In calculating the minimum required amount of interference keep in mind that: ) interference is reduced by radial s 2) interference is reduced by differences between temperature and ambient temperature 3) interference is reduced by variation of fitting surfaces The upper limit value should not exceed / of the diameter. Required interference calculations are shown below. () Radial s and required interference Interference of the inner ring and decreases when a radial is applied to the. The interference required to secure effective interference is expressed by formulae (7.) and (7.2). Fr.3 Cor ΔdF=.8 (d Fr / B) /2 N =.25 (d Fr / B) /2 {kgf }} (7.) Fr >.3 Cor ΔdF=.2 (Fr / B) N =.2 (Fr / B) {kgf }} (7.2) Where, ΔdF: Required effective interference according to radial μm d : Bearing bore diameter mm B : Inner ring width mm Fr : Radial N{kgf} Cor : Basic static rating N{kgf} shown in formula (7.3). ΔdT =.5 d ΔT (7.3) ΔdT : Required effective interference for temperature difference μm ΔT : Difference between temperature and ambient temperature C d : Bearing bore diameter mm (3) Fitting surface variation and required interference Interference decreases because the fitting surface is smoothened by fitting (surface roughness is reduced). The amount the interference decreases depends on roughness of the fitting surface. It is generally necessary to anticipate the following decrease in interference. For ground s:. 2.5μm For lathed s: 5. 7.μm (4) Maximum interference When rings are installed with an interference fit, tension or compression stress may occur along their raceways. If interference is too great, this may cause damage to the rings and reduce life. You should try to obtain the previously described upper limit. 7.3.4 Other details () Tight interference fits are recommended for, Operating conditions with large vibration or shock s Applications using hollow s or housings with thin walls Applications using housings made of light alloys or plastic (2) Small interference fits are preferable for, Applications requiring high running accuracy Applications using small sized s or thin walled s (3) Consideration must also be given to the fact that fit selection will effect internal clearance selection. (refer to page insert A-58) G6 G7 H8 JIS class H7 H6 J6 J7 ΔDmp Loose fit Transition fit K6 K7 M6 M7 N6 N7 Types of fits Housing Transition fit P6 P7 (2) Temperature difference and required interference Interference between inner rings and steel s is reduced as a result of temperature increases (difference between temperature and ambient temperature, ΔT ) caused by rotation. Calculation of the minimum required amount of interference in such cases is JIS class Δdmp h5 g5 g6 h6 k5 Shafts Fig 7. State of fitting J5 J6 k6 m5 m6 n5 n6 p6 A-5
(4) A particular type of fit is recommended for SL type cylindrical roller s. Table 7.2 General standards for radial fits (JIS Class, 6X, 6) Table 7.2 () Tolerance class of s commonly used for radial s (classes, 6X and 6) Inner ring rotational or of undetermined direction Inner ring static Conditions Light or fluctuating Ordinary Heavy or impact Inner ring must move easily over Inner does not have to move easily over Center axial Overall Ball s Over 8 8 4 2 Under 8 2 8 4 2 28 Cylindrical roller Spherical roller Tapered roller Shaft diameter (mm) Over Under Over Under Cylindrical bore (Classes, 6X and 6) 4 4 4 4 2 5 4 2 4 4 2 4 4 2 4 4 2 Overall diameter Overall diameter Overall diameter Overall diameter 4 65 4 28 5 4 4 65 4 28 5 4 2 Shaft tolerance class h5 js6 k6 m6 js5 k5 m5 m6 n6 p6 r6 n6 p6 r6 g6 h6 js6 Tapered bore (class ) (with adapter or withdrawal sleeve) Remarks When greater accuracy is required js5, k5, and m5 may be substituted for js6, k6, and m6. Alteration of inner clearances to accommodate fit is not a consideration with single-row angular contact s and tapered roller s. Therefore, k5 and m5 may be substituted for k6 and m6. Use s with larger internal clearances than CN clearance s. When greater accuracy is required use g5. For large s, f6 will suffice for to facilitate movement. When greater accuracy is required use h5. Generally, and inner rings are not fixed using interferance. 2 2 h9/it5 h/it7 will suffice for power transmitting s. Table 7.2 (2) Fit with (fits for tapered bore s (Class ) with adapter assembly/withdrawal sleeve) All s All types All diameters Tolerance class 2 h9 / IT5 2 h/ IT7 Standards for light s, normal s, and heavy s Light s: equivalent radial.6cr Normal s:.6cr equivalent radial.2cr Heavy s:.2 Cr equivalent radial 2 IT5 and IT7 show roundness tolerances, cylindricity tolerances, and related values. General applications Transmission s, etc. Note: All values and fits listed in the above tables are for solid steel s. A-5
Table 7.2 (3) Tolerance class of housing bore commonly used for radial s (classes, 6X and 6) Housing Conditions Types of Outer ring axial 2 direction movement Tolerance class of housing bore Remarks Single housing or divided housing All types of s Yes H7 Light or ordinary Yes H8 G7 can be used for large s or s with large temperature differential between the outer ring and housing. Outer ring static Shaft and inner ring become hot Easily G7 F7 be used for large s or s with large temperature differential between the outer ring and housing. Requires precise rotation under light or ordinary s As a rule, cannot move. Yes K6 Js6 Primarily applies to roller s. Primarily applies to ball s. Requires low noise operation Yes H6 Single housing Indeterminate Light or ordinary Ordinary or heavy High impact Yes As a rule, cannot move. No Js7 K7 M7 If high accuracy is required, Js6 and K6 are used in place of Js7 and K7. Light or fluctuating No M7 Outer ring rotational Ordinary or heavy Heavy or large impact with thin wall housing No No N7 P7 Primarily applies to ball s. Primarily applies to roller s. Standards for light s, normal s, and heavy s Light s: equivalent radial.6 Cr Normal s:.6 Cr equivalent radial.2 Cr Heavy s:.2 Cr equivalent radial 2 Indicates whether or not outer ring axial movement is possible with non-separable type s. Note : All values and fits listed in the above tables are for cast iron or steel housings. 2: If only center axial is applied to the, select a tolerance class that provides clearance for the outer ring in the axial direction. A-52
Table 7.3 Standard fits for thrust s (JIS Class and 6) Table 7.3 () Shaft fits Bearing type Load conditions Fit Shaft diameter mm over incl. Tolerance class All thrust s Centered axial only Transition fit All sizes js6 or h6 Spherical roller thrust s Combined Inner ring static Inner ring rotating or Indeterminate Transition fit Transition fit All sizes 2 2 4 4 js6 k6 or js6 m6 or k6 n6 or m6 Table 7.3 (2) Housing fits Bearing type Load conditions Fit Combined Tolerance class Remarks All thrust Select a tolerance class that will provide clearance between outer ring and housing. Centered axial only s Loose fit H8 Greater accuracy required with thrust ball s Outer ring static H7 Spherical roller thrust Indeterminate K7 Normal operating conditions s or outer ring Transition fit rotating M7 For relatively large radial s Note: All values and fits listed in the above tables are for cast iron or steel housings. Table 7.4 Fits for electric motor s Bearing type Deep groove ball s Cylindrical roller s Shaft fits Shaft diameter mm over incl. Tolerance class 8 8 6 4 46 6 2 j5 k5 m5 k5 m5 n6 Housing fits Housing bore diameter Tolerance class All sizes All sizes H6 or J6 H6 or J6 A-53
Table 7.5 Numeric value table of fitting for radial of class Table 7.5 () Fitting against Nominal bore diameter of d mm Mean bore diameter deviation Δdmp over incl. high low g5 g6 h5 h6 j5 js5 j6 3 6 8 3 5 8 6 8 3 5 8 2-8 -8-8 - -2-5 -2 4T 9L 3TL 2T4L 3T6L 3T2L 5T23L 8T27L 4T2L 3T4L 2T7L 3T2L 3T25L 5T29L 8T34L 8T 5L 8T 6L 8T 8L T 9L 2TL 5T3L 2T5L 8T 8L 8T 9L 8TL T3L 2T6L 5T9L 2T22L 2 4 4 6-25 T32L T39L 25T8L 25T25L 6 8 8 2 2 225-3 5T35L 5T44L 3T2L 3T29L 225 25 25 28 28 35-35 8T4L 8T49L 35T23L 35T32L 35 355 355 4-4 22T43L 22T54L 4T25L 4T36L 4 45 45 5-45 25T47L 25T6L 45T27L 45T4L Above table is not applicable to tapered roller s whose bore diameter d is 3mm or less. T 2L 2T 2L 3T 3L 5T 4L 8T 5L 2T 7L 26T 9L 32TL 37T3L 42T6L 47T8L 52T2L.5T 2.5L T 3L 2T 4L 4.5T 4.5L 7.5T 5.5L 2.5T 6.5L 27.5T 7.5L 34T 4T 9L L 46.5T.5L 52.5T2.5L 58.5T3.5L 4T 2L 5T 2L 6T 3L 9T 4L 23T 5L 27T 7L 33T 9L 39TL 46T3L 5T6L 58T8L 65T2L Table 7.5 (2) Fitting against housing Nominal outside diameter of 2 Mean outside diameter deviation D ΔDmp mm over incl. high low 6-8 G7 H6 H7 J6 J7 Js7 K6 housing housing housing housing housing housing housing 5L 28L 7L 23L 4T3L 8 3 5 8 2 5 8 25 35 4 8 3 5 8 2 5 8 25 35 4 5-8 -9 - -3-5 -8-25 -3-35 -4-45 6L 32L 7L 37L 9L 45L L 53L 2L 62L 4L 72L 4L 79L 5L 9L 7L4L 8L5L 2L28L 9L 22L 27L 32L 37L 43L 5L 59L 67L 76L 85L 26L 3L 36L 43L 5L 58L 65L 76L 87L 97L 8L 5T4L 5T7L 6T2L 6T26L 6T3L 7T36L 7T43L 7T52L 7T6L 7T69L 7T78L 2 Above table is not applicable to tapered roller s whose outside diameter D is 5mm or less. Note: Fitting symbol "L" indicates clearance and "T" indicates interference. 7T6L 8T8L 9T2L T25L 2T3L 3T37L 4T44L 4T5L 6T6L 6T7L 8T79L 2T88L 7.5T 5.5L 9T 7L.5T 9.5L 2.5T 23.5L 5T 28L 7.5T 32.5L 2T 38L 2T 45L 23T 53L 26T 6L 28.5T 68.5L 3.5T76.5L 7TL 9TL TL 3T4L 5T7L 8T9L 2T22L 2T29L 24T35L 27T4L 29T47L 32T53L A-54
A-55 2T 2.5T 3.5T 6.5T 2T 24.5T 3T 4L 4.5L 5.5L 6.5L 8L 9.5L L 4T 5T 7T 2T 25T 3T 38T T T T 2T 2T 2T 3T 7T 8T 2T 25T 3T 36T 45T T T T 2T 2T 2T 2T 7T 2T 23T 27T 32T 39T 48T 4T 6T 7T 8T 9T T 3T Nominal bore diameter of d mm js6 k5 k6 m5 Unitm 2T 23T 26T 3T 37T 45T 55T 4T 6T 7T 8T 9T T 3T m6 24T 27T 3T 38T 45T 54T 65T 8T T 2T 5T 7T 2T 23T n6 28T 32T 37T 45T 54T 66T 79T 2T 5T 8T 22T 26T 32T 37T p6 r6 37.5T2.5L 44.5T4.5L 5T 6L 65T 2L 58T 8L 46T3T 54T4T 62T4T 69T4T 77T5T 53T3T 63T4T 8T4T 9T4T 7T4T 58T5T 67T7T 78T2T 86T2T 95T23T 65T5T 76T7T 87T2T 97T2T 8T23T 77T27T 9T3T T34T 3T37T 25T4T 93T43T 9T5T 23T56T 38T62T 53T68T 3T 5T 8T 63T 65T 68T 36T 39T 43T 77T 8T 84T 6T 65T 94T 98T 84T 9T 8T 4T 2T 27T 26T 32T 3 6 8 3 5 8 6 8 3 5 8 2 2 4 6 4 6 8 8 2 225 2 225 25 25 28 28 35 35 355 355 4 4 45 45 5 over incl. T 2T 5T 8T 2T 25T 28T 28T 33T 36T 4T 45T 3L 4L 5L 8L 22L 25L 3L 37L 43L 5L 57L 63L 5T 8T 2T 25T 3T 35T 4T 4T 46T 52T 57T 63T 8L 8L 9L L 3L 5L 8L 25L 3L 35L 4L 45L 9T 23T 28T 33T 39T 45T 52T 52T 6T 66T 73T 8T 4L 3L 2L 3L 4L 5L 6L 3L 6L 2L 24L 28L 24T 29T 35T 42T 5T 59T 68T 68T 79T 88T 98T 8T T 3T 5T 6T 8T 9T T 3T 3T T T 6 8 3 5 8 2 5 8 25 35 4 8 3 5 8 2 5 8 25 35 4 5 Nominal outside diameter of D mm K7 M7 N7 P7 Unitm over incl. housing housing housing housing
Table 7.6 General fitting standards for tapered roller s using US customary unit (ANSI class 4) Table 7.6 () Fit with Operating conditions Inner ring rotational Outer ring rotational Ordinary Heavy Impact Inner ring does not have to move easily over with ordinary. Inner ring must move easily over with ordinary. Nominal Bore diameter Shaft diameter bore diameter tolerance tolerance Fitting d mm Δds over incl. high low high low max min 76.2 76.2 34.8 34.8 69.6 69.6 94.4 76.2 76.2 34.8 34.8 69.6 69.6 94.4 76.2 76.2 34.8 34.8 69.6 69.6 94.4 76.2 76.2 34.8 34.8 69.6 69.6 94.4 +3 +5 +3 +5 +3 +5 +3 +5 + 3 + 25 + 5 + 76-3 - 25-5 - 76 3T 25T 5T 3L 25L 5L 76T 76L 3L 5L 2L 52L Remark Unitm + 38 + 64 + 27 + 25 + 38 + 76 38T 64T 27T 2T 3T 25T Applicable when slight impact is applied + 9 + 4 9T 38T as well. + 64 + 38 38T 2T.5 m mean interference per mm of inner ring bore diameter. Minimum interference is 25 m. Tolerance for the is adjusted to match tolerance of bore diameter. Not applicable when impact is applied. Table 7.6 (2) Fit with housing Operating conditions Inner ring rotational Outer ring rotational When used on floating- or fixed side When outer ring is adjusted in axial direction When outer ring is not adjusted in axial direction When outer ring is not adjusted in axial direction Nominal outer diameter Outer diameter tolerance Housing bore diameter tolerance Fitting D mm ΔDs over incl. high low high low max min 76.2 76.2 27. 27. 34.8 34.8 69.6 69.6 94.4 76.2 76.2 27. 27. 34.8 34.8 69.6 69.6 94.4 76.2 76.2 27. 27. 34.8 34.8 69.6 69.6 94.4 76.2 76.2 27. 27. 34.8 34.8 69.6 69.6 94.4 +5 +5 +5 +5 + 76 + 76 + 76 + 52 + 229 + 25 + 25 + 5 + 76 + 27-3 - 25-25 - 25-25 - 3-25 - 25-25 - 25 + 5 + 5 + 5 + 2 + 52 26 + + 5-38 - 5-5 - 76-2 - 38-5 - 5-76 -2 26L 26L 26L 76L 76L 76L 5L 52L 76L 229L 25T 25L 25T 25L 25T 5L 25T 76L 25T 27L 63T 3T 76T 25T 76T 25T 27T 25T 78T 25T 63T 3T 76T 25T 76T 25T 27T 25T 78T 25T Unitm Types of fit loose fit transition fit tight fit Fitting symbol "L" indicates clearance and "T" indicates interference. A-56
Table 7.7 General fitting standards for tapered roller s using US customary unit (ANSI classes 3 and ) Table 7. () Fit with Operating conditions Inner ring rotational Outer ring rotational Precision machine tool spindles Heavy Impact High-speed rotation Precision machine tool spindles Nominal Bore diameter Shaft diameter bore diameter tolerance tolerance Fitting d mm Δds over incl. high low high low max min 34.8 34.8 69.6 +3 + 3 + 64 + 8 + 38 3T 64T 5T 3T 69.6 94.4 + 2 + 64 2T 26T 76.2 +3 76.2 34.8 34.8 69.6 +3 Minimum interference is.25 m per mm of inner ring bore diameter. 69.6 94.4 34.8 34.8 69.6 +3 + 3 + 25 3T 64T 5T 3T 69.6 94.4 + 2 2T 26T Note: For class, bore diameter d applies to 24.3 mm or less. Unitm Table 7.7 (2) Fit with housing Operating conditions Inner ring rotational Outer ring rotational When used for floating-side When used for fixed side When outer ring is adjusted in axial direction When outer ring is not adjusted in axial direction Ordinary When outer ring is not adjusted in axial direction Nominal outer diameter Outer diameter tolerance Housing bore diameter tolerance Fitting D mm ΔDs over incl. high low high low max min 52.4 52.4 34.8 34.8 69.6 69.6 94.4 52.4 52.4 34.8 34.8 69.6 69.6 94.4 52.4 52.4 34.8 34.8 69.6 69.6 94.4 52.4 52.4 34.8 34.8 69.6 69.6 94.4 52.4 52.4 34.8 34.8 69.6 69.6 94.4 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 Fitting symbol "L" indicates clearance and "T" indicates interference. Note: For class, outer diameter D applies to 34.8 mm or less. + 38 + 38 + 64 + 89 + 25 + 25 + 5 + 76 + 3 + 3 + 25 + 38-3 - 3-3 - 3 + 25 + 25 + 38 + 5 + 3 + 3 + 25 + 38-3 - 25-25 - 38-25 - 38-38 - 5 2L 2L 3L 3L 3T 3T 25T 38T 26T 38T 5T 76T 38T 5T 63T 89T 38L 38L 64L 89L 25L 25L 5L 76L 3L 3L 25L 38L 3T 3T 3T 3T Unitm Type of fit loose fit transition fit tight fit A-57