Page 45 - NSK_CAT_E1102m_A7-141

FITS AND INTERNAL CLEARANCES

Table 9.17 Axial Internal Clearances in Combined Angular Contact Units : μm (2) Decrease in Radial Internal Clearance Caused
Ball Bearings (Measured Clearance) by Temperature Differences between Inner and
Outer Rings and Effective Clearance
Nominal Bore Axial Internal Clearance & : Effective Clearance
Diameter. The frictional heat generated during operation &= &f − δt
Contact Angle 30° Contact Angle 40° is conducted away through the shaft and housing. δ fe : Decrease in clearance due
d (mm) Since housings generally conduct heat better than to fit between outer ring
CN C3 C4 CN C3 C4 shafts, the temperature of the inner ring and the rolling Outer ring and housing bore
elements is usually higher than that of the outer ring Roller
over incl. min. max. min. max. min. max. min. max. min. max. min. max. by 5 to 10°C. If the shaft is heated or the housing & (=&De)
is cooled, the difference in temperature between the & f & 0 & 0 : Theoretical internal
⎯ 10 9 29 29 49 49 69 6 26 26 46 46 66 inner and outer rings is greater. The radial clearance clearance
decreases due to the thermal expansion caused by the (Geometrical
10 18 10 30 30 50 50 70 7 27 27 47 47 67 temperature difference between the inner and outer clearance)
rings. The amount of this decrease can be calculated
18 24 19 39 39 59 59 79 13 33 33 53 53 73 using the following equations:

24 30 20 40 40 60 60 80 14 34 34 54 54 74 & f :Residual clearance
30 40 26 46 46 66 66 86 19 39 39 59 59 79
40 50 29 49 49 69 69 89 21 41 41 61 61 81

50 65 35 60 60 85 85 110 25 50 50 75 75 100 δ tHα & t De. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (9.6) & f = & 0− δ fi − δ fe
65 80 38 63 63 88 88 115 27 52 52 77 77 100 δ fi : Decrease in clearance
80 100 49 74 74 99 99 125 35 60 60 85 85 110
due to fit between

100 120 72 97 97 120 120 145 52 77 77 100 100 125 inner ring and shaft (=&Di )

120 140 85 115 115 145 145 175 63 93 93 125 125 155 δ t : Decrease in clearance due
to temperature difference
140 160 90 120 120 150 150 180 66 96 96 125 125 155 where δ t : Decrease in radial clearance due to
between inner and outer rings
temperature difference between inner and
160 180 95 125 125 155 155 185 68 98 98 130 130 160
outer rings (mm)
180 200 110 140 140 170 170 200 80 110 110 140 140 170
α : Coefficient of linear expansion of bearing
Remarks This table is applicable to bearings in Tolerance Classes Normal and 6. For internal axial clearances in bearings in
tolerance classes better than 5 and contact angles of 15° and 25°, it is advisable to consult NSK. steelH12.5 × 10−6 (1/°C)

Table 9.18 Axial Internal Clearance in Four-Point Standard operating conditions are defined as those & t : Temperature difference between inner and
Contact Ball Bearings where the inner ring speed is less than approximately outer rings (°C)
(Measured Clearances) 50% of the limiting speed listed in the bearing tables,
the load is less than normal (PH 0.1Cr), and the De : Outer ring raceway diameter (mm)
bearing is tight-fitted on the shaft.
As a measure to reduce bearing noise for electric For ball bearings Fig. 9.2 Changes in Radial Internal Clearance of Bearings
motors, the radial clearance range is narrower than
Units : μm the normal class and the values are somewhat smaller 1 (4D+ d) ..................... (9.7)
for deep groove ball bearings and cylindrical roller 5
Nominal Bore Axial Internal Clearance bearings for electric motors. (Refer to Table 9.13.1 and DeH
CN C3 9.13.2)
Dia. d (mm) C2 C4 Internal clearance varies with the fit and temperature For roller bearings
differences in operation. The changes in radial
over incl. min. max. min. max. min. max. min. max. clearance in a roller bearing are shown in Fig. 9.2. 1 (3D+ d) ..................... (9.8) Table 9. 19 Examples of Clearances for Specific
4 Applications
(1) Decrease in Radial Clearance Caused by Fitting DeH
10 18 15 55 45 85 75 125 115 165 and Residual Clearance
18 40 26 66 56 106 96 146 136 186 The clearance after substracting this δ t from the Operating Conditions Examples Internal
40 60 36 86 76 126 116 166 156 206 When the inner ring or the outer ring is tight-fitted on Clearance
a shaft or in a housing, a decrease in the radial internal residual clearance, & f is called the effective clearance,
60 80 46 96 86 136 126 176 166 226 clearance is caused by the expansion or contraction & . Theoretically, the longest life of a bearing can When shaft deflection Semi-floating rear C5 or equivalent
80 100 56 106 96 156 136 196 186 246 of the bearing rings. The decrease varies according to be expected when the effective clearance is slightly is large. wheels of automobiles
100 140 66 126 116 176 156 216 206 266 the bearing type and size and design of the shaft and negative. However, it is difficult to achieve such an
housing. The amount of this decrease is approximately ideal condition, and an excessive negative clearance Dryers in paper making
140 180 76 156 136 196 176 246 226 296 70 to 90% of the interference (refer to Section 15.2, will greatly shorten the bearing life. Therefore, a When steam passes machines C3, C4
180 220 96 176 156 226 206 276 256 326 Fits (1), Pages A130 to A133). The internal clearance clearance of zero or a slightly positive amount, instead through hollow shafts or C3
220 260 115 196 175 245 225 305 285 365 after subtracting this decrease from the theoretical of a negative one, should be selected. When single-row roller shafts are heated. Table rollers for rolling
internal clearance &0 is called the residual clearance, angular contact ball bearings or tapered roller bearings mills
& f. are used facing each other, there should be a small
260 300 135 215 195 275 255 335 315 395 effective clearance, unless a preload is required. When When impact loads and Traction motors for C4
300 350 155 235 215 305 275 365 345 425 two cylindrical roller bearings with a rib on one side vibration are severe or railways C3, C4
350 400 175 265 245 335 315 405 385 475 are used facing each other, it is necessary to provide when both the inner and
400 500 205 305 285 385 355 455 435 525 adequate axial clearance to allow for shaft elongation outer rings are tight- Vibrating screens C4
during operation. fitted. C4
The radial clearances used in some specific Fluid couplings
9.2.2 Selection of Bearing Internal Clearances applications are given in Table9.19. Under special
operating conditions, it is advisable to consult NSK. Final reduction gears for
Among the bearing internal clearances listed in the tractors
tables, the CN Clearance is adequate for standard
operating conditions. The clearance becomes When both the inner and
progressively smaller from C2 to C1 and larger from outer rings are loose- Rolling mill roll necks C2 or equivalent
C3 to C5. fitted

When noise and vibration Small motors with C1, C2, CM
restrictions are severe special specifications

When clearance is Main shafts of lathes CC9, CC1
adjusted after mounting
to prevent shaft
deflection, etc.

A 94 A 95