Technical Data
8.
Bearing Internal Clearance and Preload
8.1
Bearing internal clearance
8.2
Bearing internal clearance (initial clearance) is the amount of
internal clearance a bearing has before being installed on a
shaft or in a housing.
As shown in Fig. 8.1, when either the inner ring or the outer
ring is fixed and the other ring is free to move, displacement
can take place in either an axial or radial direction. This amount
of displacement (radially or axially) is termed the internal
clearance and, depending on the direction, is called the radial
internal clearance or the axial internal clearance.
When the internal clearance of a bearing is measured, a slight
measurement load is applied to the raceway so the internal
clearance may be measured accurately. However, at this time,
a slight amount of elastic deformation of the bearing occurs
under the measurement load, and the clearance measurement
value (measured clearance) is slightly larger than the true
clearance. This discrepancy between the true bearing
clearance and the increased amount due to the elastic
deformation must be compensated for. These compensation
values are given in Table 8.1. For roller bearings the amount of
elastic deformation can be ignored.
Internal clearance selection
The internal clearance of a bearing under operating conditions
(effective clearance) is usually smaller than the same bearing’s
initial clearance before being installed and operated. This is
due to several factors including bearing fit, the difference in
temperature between the inner and outer rings, etc. As a
bearing’s operating clearance has an effect on bearing life,
heat generation, vibration, noise, etc.; care must be taken in
selecting the most suitable operating clearance.
Effective internal clearance:
The initial clearance differential between the initial clearance
and the operating (effective) clearance (the amount of
clearance reduction caused by interference fits, or clearance
variation due to the temperature difference between the inner
and outer rings) can be calculated by the following formula:
δ eff = δ o − (δ f + δ t )LLLLLLLLLL(8.1)
where,
δeff : Effective internal clearance mm
δo : Bearing internal clearance mm
δf : Reduced amount of clearance due to
interference mm
δt : Reduced amount of clearance due to
temperature differential of inner and outer
rings mm
The internal clearance values for each bearing class are shown
in Tables 8.3 through 8.10.
δ2
δ
Reduced clearance due to interference:
When bearings are installed with interference fits on shafts
and in housings, the inner ring will expand and the outer ring
will contract; thus reducing the bearings’ internal clearance.
The amount of expansion or contraction varies depending on
the shape of the bearing, the shape of the shaft or housing,
dimensions of the respective parts, and the type of materials
used. The differential can range from approximately 70% to
90% of the effective interference.
δ1
Radial
clearance = δ
δ f = (0.70 ~ 0.90) • ∆ deff LLLLLLLL(8.2)
Axial clearance = δ1+δ2
Fig. 8.1 Internal clearance
where,
Table 8.1 Adjustment of radial internal clearance based
on measured load
Unit µm
Nominal Bore
Diameter
(mm)
d
over
incl.
10
18
50
18
50
200
Measuring
Load
Radial Clearance
Increase
Reduced internal clearance due to inner/outer ring temperature
difference:
(N)
24.5
49
147
δf : Reduced amount of clearance due to
interference mm
∆deff : Effective interference mm
C2
Normal
C3
C4
C5
3~4
4~5
6~8
4
5
8
4
6
9
4
6
9
4
6
9
A-64
During operation, normally the outer ring will be from 5° to 10°
cooler than the inner ring or rotating parts. However, if the
cooling effect of the housing is large, the shaft is connected to
a heat source, or a heated substance is conducted through
the hollow shaft; the temperature difference between the two
rings can be even greater. The amount of internal clearance is
thus further reduced by the differential expansion of the two
rings.
δ t = α • ∆ T • Do LLLLLLLLLLL(8.3)
where,
δt : Amount of reduced clearance due to heat
differential mm
α : Bearing steel linear expansion coefficient
12.5×10-6/°C
∆T : Inner/outer ring temperature differential °C
Do : Outer ring raceway diameter mm
Outer ring raceway diameter, Do, values can be approximated
by using formula (8.4) or (8.5).
Table 8.2 Examples of applications where bearing
clearances other than normal clearances are used
Applications
With heavy or
shock load,
clearance is great.
Railway vehicle
axles
C3
Vibration screens
C3
With direction
indeterminate load,
both inner and outer
rings are tight-fitted.
Railway vehicle
traction motors
Tractors and final
speed regulators
For roller bearings (except self-aligning),
Do = 0.25( d + 3.0 D)LLLLLLLLL(8.5)
where,
8.3
Bearing internal clearance selection
standards
C4
C3, C4
Rolling mill table
rollers
C3
Clearance fit for both
inner and outer rings.
Rolling mill roll
necks
C2
To reduce noise
and vibration
when rotating.
Micromotors
C2
To reduce shaft
runout, clearance
is adjusted.
Main spindles of
lathes (Double-row
cylindrical roller
bearings)
C9NA, C0NA
d : Bearing bore diameter mm
D : Bearing outside diameter mm
C4
Paper making
machines and driers
Shaft or inner ring
is heated.
For ball bearings and self-aligning roller bearings,
Do = 0.20( d + 4.0 D)LLLLLLLLL(8.4)
Selected
clearance
Operating conditions
Theoretically, to maximize life, the optimum operating internal
clearance for any bearing would be a slight negative clearance
after the bearing had reached normal operating temperature.
Unfortunately, under actual operating conditions, maintaining
such optimum tolerances is often difficult at best. Due to various
fluctuating operating conditions this slight negative clearance
can quickly become a further negative, greatly lowering the
life of the bearing and causing excessive heat to be generated.
Therefore, an initial internal clearance which will result in a
slightly greater than negative internal operating clearance
should be selected.
Under normal operating conditions (e.g. normal load, fit, speed,
temperature, etc.), a standard internal clearance will give a
very satisfactory operating clearance.
Table 8.2 lists non-standard clearance recommendations for
various applications and operating conditions.
A-65
Technical Data
Table 8.3
diameter
over
—
2.5
6
10
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
710
800
900
1000
1120
Table 8.5
C2
d mm
incl.
2.5
6
10
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
800
900
1000
1120
1250
min
over
—
10
18
30
50
80
100
120
150
180
Note:
Normal
max
0
0
0
0
0
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
3
3
3
3
10
10
20
20
20
20
20
6
7
7
9
10
11
11
11
15
15
18
20
23
23
25
30
35
40
45
55
60
70
80
90
100
110
140
160
170
180
190
min
C3
max
4
2
2
3
5
5
6
6
8
10
12
15
18
18
20
25
25
30
35
40
45
55
60
70
80
90
120
140
150
160
170
11
13
13
18
20
20
20
23
28
30
36
41
48
53
61
71
85
95
105
115
125
145
170
190
210
230
290
320
350
380
410
min
10
8
8
11
13
13
15
18
23
25
30
36
41
46
53
63
75
85
90
100
110
130
150
170
190
210
270
300
330
360
390
C4
max
20
23
23
25
28
28
33
36
43
51
58
66
81
91
102
117
140
160
170
190
210
240
270
300
330
360
450
500
550
600
650
min
C5
max
—
—
14
18
20
23
28
30
38
46
53
61
71
81
91
107
125
145
155
175
195
225
250
280
310
340
430
480
530
580
630
—
—
29
33
36
41
46
51
61
71
84
97
114
130
147
163
195
225
245
270
300
340
380
420
470
520
630
700
770
850
920
min
—
—
20
25
28
30
40
45
55
65
75
90
105
120
135
150
175
205
225
245
275
315
350
390
440
490
600
670
740
820
890
C1
d mm
incl.
min
10
18
30
50
80
100
120
150
180
200
C2
Normal
C3
max
min
max
min
max
min
8
8
10
10
11
13
15
16
18
20
6
6
6
8
11
13
15
16
18
20
12
12
12
14
17
22
30
33
35
40
8
8
10
14
17
22
30
35
35
40
15
15
20
25
32
40
50
35
60
65
15
15
20
25
32
40
50
55
60
65
3
3
3
3
3
3
3
3
3
3
The clearance group in the table is applied only to contact angles in the table below.
Contact angle symbol
Nominal contact angle
C
A1)
B
15°
30°
40°
Applicable clearance group
C1, C2
C2, Normal, C3
Normal, C3, C4
1) Usually not to be indicated
A-66
max
—
—
37
45
48
53
64
73
90
105
120
140
160
180
200
230
265
300
340
370
410
460
510
570
630
690
840
940
1040
1150
1260
Unit µm
Radial internal clearance of double row and duplex angular contact ball bearings
Nominal bore
diameter
Unit µm
Radial internal clearance of deep groove ball bearings
Nominal bore
C4
max
22
24
32
40
50
60
75
80
90
100
min
22
30
40
55
75
95
110
130
150
180
max
30
40
55
75
95
120
140
170
200
240
Table 8.6 Radial internal clearance of cylindrical roller bearings, needle roller bearings
Table 8.6 (1) Cylindrical Bore Interchangeable Radial Clearance ISO Cylindrical Roller Bearings ONLY
Nominal bore
diameter
over
0
10
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
C2
d mm
incl.
10
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
1400
min
Normal
max
0
0
0
5
5
10
10
15
15
15
20
25
35
45
45
55
55
65
100
110
110
120
140
145
150
180
200
220
230
270
25
25
25
30
35
40
45
50
55
60
70
75
90
105
110
125
130
145
190
210
220
240
260
285
310
350
390
430
470
530
min
20
20
20
25
30
40
40
50
50
60
70
75
90
105
110
125
130
145
190
210
220
240
260
285
310
350
390
430
470
530
C3
max
min
45
45
45
50
60
70
75
85
90
105
120
125
145
165
175
195
205
225
280
310
330
360
380
425
470
520
580
640
710
790
35
35
35
45
50
60
65
75
85
100
115
120
140
160
170
190
200
225
280
310
330
360
380
425
470
520
580
640
710
790
Unit µm
C4
max
60
60
60
70
80
90
100
110
125
145
165
170
195
220
235
260
275
305
370
410
440
480
500
565
630
690
770
850
950
1050
min
50
50
50
60
70
80
90
105
125
145
165
170
195
220
235
260
275
305
370
410
440
480
500
565
630
690
770
850
950
1050
C5
max
75
75
75
85
100
110
125
140
165
190
215
220
250
280
300
330
350
385
460
510
550
600
620
705
790
860
960
1060
1190
1310
min
max
—
65
70
80
95
110
130
155
180
200
225
250
275
305
330
370
410
455
510
565
625
—
—
—
—
—
—
—
—
—
—
90
95
105
125
140
165
190
220
245
275
300
330
365
395
440
485
535
600
665
735
—
—
—
—
—
—
—
—
—
Unit µm
Table 8.6 (2) Tapered Bore Interchangeable Radial Clearance
Nominal bore
diameter
over
0
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
C2
d mm
incl.
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
Normal
min
max
15
20
20
25
30
35
40
50
55
60
75
85
95
105
115
130
145
165
185
205
40
45
45
55
60
70
75
90
100
110
125
140
155
170
185
205
225
225
285
315
C3
min
max
min
30
35
40
45
50
60
70
90
100
110
125
140
155
170
185
205
225
255
285
315
55
60
65
75
80
95
105
130
145
160
175
195
215
235
255
280
305
345
385
425
40
45
55
60
70
85
95
115
130
145
160
180
200
220
240
265
290
330
370
410
A-67
C4
max
65
70
80
90
100
120
130
155
175
195
210
235
260
285
310
340
370
420
470
520
C5
min
max
50
55
70
75
90
110
120
140
160
180
195
220
245
270
295
325
355
405
455
505
75
80
95
105
120
145
155
180
205
230
245
275
305
335
365
400
435
495
555
615
min
max
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Technical Data
Table 8.7
Radial internal clearance of cylindrical roller bearings, needle roller bearings (Non-interchangeable)
Bearing with cylindrical bore
Nominal bore
diameter
d mm
over
—
10
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
incl.
10
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
C1NA
NA1)
C2NA
C3NA
min
max
min
max
min
max
min
5
5
5
5
5
5
5
10
10
10
15
15
15
20
20
25
25
30
30
35
45
50
10
10
10
10
12
15
15
20
25
25
30
35
35
40
45
50
55
60
65
75
85
95
10
10
10
10
12
15
15
20
25
25
30
35
35
40
45
50
55
60
65
75
85
95
20
20
20
25
25
30
35
40
45
50
60
65
75
80
90
100
110
120
135
150
170
190
20
20
20
25
25
30
35
40
45
50
60
65
75
80
90
100
110
120
135
150
170
190
30
30
30
35
40
45
50
60
70
80
90
100
110
120
135
150
165
180
200
225
255
285
35
35
35
40
45
50
55
70
80
95
105
115
125
140
155
170
185
205
225
255
285
315
C4NA
max
45
45
45
50
55
65
75
90
105
120
135
150
165
180
200
215
240
265
295
330
370
410
C5NA
min
max
min
max
45
45
45
50
55
65
75
90
105
120
135
150
165
180
200
215
240
265
295
330
370
410
55
55
55
60
70
80
90
110
125
145
160
180
200
220
240
265
295
325
360
405
455
505
—
65
65
70
80
95
110
130
155
180
200
225
250
275
305
330
370
410
455
510
565
625
—
75
75
80
95
110
130
150
180
205
230
260
285
315
350
380
420
470
520
585
650
720
1) For bearings with normal clearance, only NA is added to bearing numbers. Ex. NU310NA, NN03020KNAP5
Table 8.4
Radial internal clearance of self-aligning ball bearings
Bearing with cylindrical bore
Nominal bore
diameter
over
2.5
6
10
14
18
24
30
40
50
65
80
100
120
140
d mm
incl.
6
10
14
18
24
30
40
50
65
80
100
120
140
160
C2
Normal
C3
min
max
min
max
min
1
2
2
3
4
5
6
6
7
8
9
10
10
15
8
9
10
12
14
16
18
19
21
24
27
31
38
44
5
6
6
8
10
11
13
14
16
18
22
25
30
35
15
17
19
21
23
24
29
31
36
40
48
56
68
80
10
12
13
15
17
19
23
25
30
35
42
50
60
70
A-68
C4
max
20
25
26
28
30
35
40
44
50
60
70
83
100
120
min
15
19
21
23
25
29
34
37
45
54
64
75
90
110
C5
max
25
33
35
37
39
46
53
57
69
83
96
114
135
161
min
21
27
30
32
34
40
46
50
62
76
89
105
125
150
max
33
42
48
50
52
58
66
71
88
108
124
145
175
210
Table 8.7
(Cont.) Radial internal clearance of cylindrical roller bearings, needle roller bearings (Non-interchangeable)
Unit µm
Bearing with tapered bore
C0NA2)
C9NA
min
5
5
5
5
5
5
5
10
10
10
15
15
15
20
20
25
25
30
30
35
45
50
C1NA2)
Nominal bore
C2NA
max
min
max
min
max
min
5
10
10
10
12
15
15
20
25
25
30
35
35
40
45
50
55
60
65
75
85
95
7
7
7
10
10
10
10
15
20
20
25
30
30
30
35
40
40
45
45
50
60
70
17
17
17
20
20
20
20
30
35
35
40
45
45
50
55
65
65
75
75
90
100
115
10
10
10
10
12
15
15
20
25
25
30
35
35
40
45
50
55
60
65
75
85
95
20
20
20
25
25
30
35
40
45
50
60
65
75
80
90
100
110
120
135
150
170
190
20
20
20
25
25
30
35
40
45
50
60
65
75
80
90
100
110
120
135
150
170
190
NA1)
max
30
30
30
35
40
45
50
60
70
80
90
100
110
120
135
150
165
180
200
225
255
285
min
35
35
35
40
45
50
55
70
80
95
105
115
125
140
155
170
185
205
225
255
285
315
C3NA
max
45
45
45
50
55
65
75
90
105
120
135
150
165
180
200
215
240
265
295
330
370
410
min
max
45
45
45
50
55
65
75
90
105
120
135
150
165
180
200
215
240
265
295
330
370
410
55
55
55
60
70
80
90
110
125
145
160
180
200
220
240
265
295
325
360
405
455
505
diameter
d mm
over
incl.
—
10
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
10
18
24
30
40
50
65
80
100
120
140
160
180
220
225
250
280
315
355
400
450
500
2) C9NA, C0NA and C1NA are applied only to precision bearings of class 5 and higher.
Unit µm
Bearing with tapered bore
C2
min
—
—
—
—
7
9
12
14
18
23
29
35
40
45
Normal
max
min
—
—
—
—
17
20
24
27
32
39
47
56
68
74
—
—
—
—
13
15
19
22
27
35
42
50
60
65
max
—
—
—
—
26
28
35
39
47
57
68
81
98
110
Nominal bore
C3
min
—
—
—
—
20
23
29
33
41
50
62
75
90
100
C4
max
—
—
—
—
33
39
46
52
61
75
90
108
130
150
min
—
—
—
—
28
33
40
45
56
69
84
100
120
140
A-69
diameter
C5
max
—
—
—
—
42
50
59
65
80
98
116
139
165
191
min
—
—
—
—
37
44
52
58
73
91
109
130
155
180
max
—
—
—
—
55
62
72
79
99
123
144
170
205
240
d mm
over
incl.
2.5
6
10
14
18
24
30
40
50
65
80
100
120
140
6
10
14
18
24
30
40
50
65
80
100
120
140
160
Technical Data
Table 8.8
Axial internal clearance of metric double row and duplex tapered roller bearings
(Except series 329X, 322C, 323C)
Contact angle α≤27° (e≤0.76)
Nominal bore
diameter
d mm
C2
Normal
C3
C4
over
incl.
min
max
min
max
min
max
min
max
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
500
25
25
25
20
20
20
45
45
45
60
80
100
120
160
180
200
220
260
300
75
75
95
85
85
110
150
175
175
200
220
260
300
360
400
440
480
560
600
75
75
95
85
110
130
150
175
175
200
240
260
300
360
400
440
500
560
620
125
125
165
150
175
220
260
305
305
340
380
420
480
560
620
680
760
860
920
125
145
165
175
195
240
280
350
390
400
440
500
560
620
700
780
860
980
1100
170
195
235
240
260
325
390
480
520
540
580
660
740
820
920
1020
1120
1280
1400
170
195
210
240
280
325
390
455
500
520
600
660
720
820
920
1020
1120
1280
1440
220
245
280
305
350
410
500
585
630
660
740
820
900
1020
1140
1260
1380
1580
1740
Note: Radial internal clearance is approximately obtained from:
e
∆r =
∆a
1.5
A-70
where
∆r =radial internal clearance, µm
∆a =axial internal clearance, µm
e =constant, see bearing tables
Table 8.8
(Cont.) Axial internal clearance of metric double row and duplex tapered roller bearings
(Except series 329X, 322C,Unit
323C)
µm
Contact angle α>27° (e>0.76)
C2
Normal
Nominal bore
C3
min
max
min
max
min
max
10
10
10
10
10
10
20
20
20
30
—
—
—
—
—
—
—
—
—
30
30
40
40
40
50
70
70
70
100
—
—
—
—
—
—
—
—
—
30
30
40
40
50
60
70
70
70
100
—
—
—
—
—
—
—
—
—
50
50
70
70
80
100
120
120
120
160
—
—
—
—
—
—
—
—
—
50
60
70
80
90
110
130
150
160
180
—
—
—
—
—
—
—
—
—
70
80
100
110
120
150
180
200
210
240
—
—
—
—
—
—
—
—
—
Table 8.10 Radial internal clearance of bearings for electric
motor
Unit µm
Nominal bore
diameter
d mm
over
103)
18
24
30
40
50
65
80
100
120
140
160
180
incl.
18
24
30
40
50
65
80
100
120
140
160
180
200
Radial internal clearance CM1)
Deep groove
ball bearings
min
4
5
5
9
9
12
12
18
18
24
24
—
—
Cylindrical2)
roller bearings
max
min
11
12
12
17
17
22
22
30
30
38
38
—
—
—
—
15
15
20
25
30
35
35
40
50
60
65
diameter
C4
max
—
—
30
30
35
40
45
55
60
65
80
90
100
1) Suffix CM is added to bearing numbers.
2) Non-interchangeable clearance.
3) This diameter is included in the group.
A-71
min
70
80
90
110
130
150
180
210
210
240
—
—
—
—
—
—
—
—
—
max
90
100
120
140
160
190
230
260
260
300
—
—
—
—
—
—
—
—
—
d mm
over
incl.
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
500
Technical Data
Table 8.9
Radial internal clearance of spherical roller bearings
Bearing with cylindrical bore
Nominal bore
diameter
over
14
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
d mm
C2
Normal
C3
incl.
min
max
min
max
min
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
1400
10
10
15
15
20
20
30
35
40
50
60
65
70
80
90
100
110
120
130
140
140
150
170
190
210
230
260
290
320
350
20
20
25
30
35
40
50
60
75
95
110
120
130
140
150
170
190
200
220
240
260
280
310
350
390
430
480
530
580
640
20
20
25
30
35
40
50
60
75
95
110
120
130
140
150
170
190
200
220
240
260
280
310
350
390
430
480
530
280
640
35
35
40
45
55
65
80
100
120
145
170
180
200
220
240
260
280
310
340
370
410
440
480
530
580
650
710
780
860
950
35
35
40
45
55
65
80
100
120
145
170
180
200
220
240
260
280
310
340
370
410
440
480
530
580
650
710
780
860
950
A-72
C4
C5
max
min
max
min
max
45
45
55
60
75
90
110
135
160
190
220
240
260
290
320
350
370
410
450
500
550
600
650
700
770
860
930
1020
1120
1240
45
45
55
60
75
90
110
135
160
190
220
240
260
290
320
350
370
410
450
500
550
600
650
700
770
860
930
1020
1120
1240
60
60
75
80
100
120
145
180
210
240
280
310
340
380
420
460
500
550
600
660
720
780
850
920
1010
1120
1220
1330
1460
1620
60
60
75
80
100
120
145
180
210
240
280
310
340
380
420
460
500
550
600
660
720
780
850
920
1010
1120
1220
1330
1460
1620
75
75
95
100
125
150
180
225
260
300
350
390
430
470
520
570
630
690
750
820
900
1000
1100
1190
1300
1440
1570
1720
1870
2080
Table 8.9
Unit µm
(Cont.) Radial internal clearance of spherical roller bearings
Bearing with tapered bore
C2
Normal
Nominal bore
C3
C4
min
max
min
max
min
max
—
15
20
25
30
40
50
55
65
80
90
100
110
120
140
150
170
190
210
230
260
290
320
350
390
440
490
530
570
620
—
25
30
35
45
55
70
80
100
120
130
140
160
180
200
220
240
270
300
330
370
410
460
510
570
640
710
770
830
910
—
25
30
35
45
55
70
80
100
120
130
140
160
180
200
220
240
270
300
330
370
410
460
510
570
640
710
770
830
910
—
35
40
50
60
75
95
110
135
160
180
200
220
250
270
300
330
360
400
440
490
540
600
670
750
840
930
1030
1120
1230
—
35
40
50
60
75
95
110
135
160
180
200
220
250
270
300
330
360
400
440
490
540
600
670
750
840
930
1030
1120
1230
—
45
55
65
80
95
120
140
170
200
230
260
290
320
350
390
430
470
520
570
630
680
760
850
960
1070
1190
1300
1420
1560
C5
min
max
min
max
—
45
55
65
80
95
120
140
170
200
230
260
290
320
350
390
430
470
520
570
630
680
760
850
960
1070
1190
1300
1420
1560
—
60
75
85
100
120
150
180
220
260
300
340
370
410
450
490
540
590
650
720
790
870
980
1090
1220
1370
1520
1670
1830
2000
—
60
75
85
100
120
150
180
220
260
300
340
370
410
450
490
540
590
650
720
790
870
980
1090
1220
1370
1520
1670
1830
2000
—
75
95
105
130
160
200
230
280
330
380
430
470
520
570
620
680
740
820
910
1000
1100
1230
1360
1500
1690
1860
2050
2250
2470
A-73
diameter
d mm
over
14
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
incl.
18
24
30
40
50
65
80
100
120
140
160
180
200
225
250
280
315
355
400
450
500
560
630
710
800
900
1000
1120
1250
1400
Technical Data
8.4
Preload
Normally, bearings are used with a slight internal clearance
under operating conditions. However, in some applications,
bearings are given an initial load; this means that the bearings’
internal clearance is negative before operation. This is called
“preload” and is commonly applied to angular ball bearings
and tapered roller bearings.
8.4.1
Purpose of preload
Giving preload to a bearing results in the rolling element and
raceway surfaces being under constant elastic compressive
forces at their contact points. This has the effect of making the
bearing extremely rigid so that even when load is applied to
the bearing, radial or axial shaft displacement does not occur.
Thus, the natural frequency of the shaft is increased, which is
suitable for high speeds.
Preload is also used to prevent or suppress shaft runout,
vibration, and noise; improve running accuracy and locating
accuracy; reduce smearing, and regulate rolling element
rotation. Also, for thrust ball and roller bearings mounted on
horizontal shafts, preloading keeps the rolling elements in
proper alignment.
The most common method of preloading is to apply an axial
load to two duplex bearings so that the inner and outer rings
are displaced axially in relation to each other. This preloading
method is divided into fixed position preload and constant
pressure preload.
Bearing II
8.4.2
Preloading methods and amounts
The basic pattern, purpose and characteristics of bearing
preloads are shown in Table 8.11. The definite position preload
is effective for positioning the two bearings and also for
increasing the rigidity. Due to the use of a spring for the constant
pressure preload, the preload force can be kept constant, even
when the distance between the two bearings fluctuates under
the influence of operating heat and load.
Also, the standard preload for the paired angular contact ball
bearings is shown in Table 8.12. Light and normal preload is
applied to prevent general vibration, and medium and heavy
preload is applied especially when rigidity is required.
8.4.3
Preload and rigidity
The increased rigidity effect preloading has on bearings is
shown in Fig. 8.5. When the offset inner rings of the two paired
angular contact ball bearings are pressed together, each inner
ring is displaced axially by the amount δo and is thus given a
preload, Fo, in the direction shown. Under this condition, when
external axial load Fa is applied, bearing I will have an increased
displacement by the amount δa and bearing II’s displacement
will decrease. At this time the loads applied to bearing I and II
are Fi and Fii, respectively.
Under the condition of no preload, bearing I will be displaced
by the amount δb when axial load Fa is applied. Since the
amount of displacement, δa, is less than δb, it indicates a higher
rigidity for δa.
Bearing I
Fa
Fo
Fo
δo
Outer ring
Steel ball
Inner ring
(1) Under free from
preload
Bearing II
δo
δo δo
δa
Bearing I
δb
δo
(2) Under preloading Fo
Fa
δa
(3) Under preloading
and applied load
Axial load
δo
Fa
δa Inner ring
displacement
FII
FI
Fo
Fa
FII
FI = FII + Fa
δI
δo
δa
Fig. 8.5 Fixed position preload versus axial displacement
A-74
δII
δo
Axial
displacement
Table 8.11 Preloading methods and characteristics
Method
Basic pattern
Applicable
bearings
Object
Characteristics
Applications
Fixed position preload
Precision
Maintaining
angular contact accuracy of
ball bearings
rotating shaft,
preventing
vibration
increasing
rigidity
Preload is accomplished by
a predetermined offset of the
rings or by using spacers. For
the standard preload see Table
8.12
Tapered roller Increasing
bearings, thrust bearing rigidity
ball bearings
angular contact
ball bearings
Preload is accomplished by
Lathes, milling
adjusting a threaded screw.
machines,
The amount of preload is set by differential
measuring the starting torque or gears of
axial displacement.
automotives,
Relationship between the
printing
starting torque M and preload T machines,
is approximately given by the wheel axles
following formulas: for duplex
angular contact ball bearings:
M=
dp • T
330 ~ 430
Grinding
machines,
lathes, milling
machines,
measuring
instruments
N • mm1)
for duplex tapered roller
bearings:
M=
Constant pressure preload
∆
∆
d p 0.8 • T
54 ~ 107
N • mm1)
Angular contact
ball bearings,
deep groove
ball bearings,
precision
tapered roller
bearings
Maintaining
accuracy and
preventing
vibration and
noise with a
constant
amount of
preload without
being affected
by loads or
temperature
Preloading is accomplished by Internal
using coil or belleville springs. grinding
Recommended preloads are as machines,
follows:
electric motors,
for deep groove ball bearings: high speed
(4 to 8) d N
shafts in small
for angular contact ball
machines,
bearings:
tension reels
see Table 8.12
Tapered roller
bearings with
steep angle,
spherical roller
thrust bearings,
thrust ball
bearings
Preventing
smearing on
raceway of
non-loaded
side under
axial loads
Preload is accomplished by
Rolling mills,
using coil or belleville springs. extruding
Recommended preloads are as machines
follows:
for thrust ball bearings:
T = 0.42(n • Coa ) × 10 −13 N 2)
1.9
T = 0.00083 Coa N 2)
whichever is greater for
spherical roller thrust bearings:
T = 0.025 Coa 0.8 N 2)
Note: In the above formulas,
dp=pitch diameter of bearing, mm
dp=(Bore+Outside dia)/2
d=bearing bore, mm
n=number of revolutions, r/min
T=preload, N
Coa=basic static axial load rating, N
The starting torque M however, is greatly influenced by lubricants and a period of run-in time.
A-75
Technical Data
Table 8.12 Standard preloads for angular contact ball bearings
Nominal bore
diameter
d
Bearing series
mm
78C
Heavy
Light
Normal
—
—
200
300
500
600
800
1000
1000
1500
1500
1500
2000
2500
3000
3000
3000
4000
4000
6000
20
20
30
50
50
100
100
150
150
150
200
200
200
300
300
500
500
500
600
600
30
30
80
150
150
200
300
400
400
400
600
600
600
800
800
1000
1000
1000
1500
1500
100
100
150
300
300
500
700
1000
1000
1000
1500
1500
1500
2000
2000
2500
2500
2500
3500
3500
150
200
300
600
700
1000
1500
2000
2000
2000
2500
2500
2500
4000
4000
6000
6000
6000
7000
7000
20
20
50
80
100
150
200
300
300
300
400
400
400
500
500
700
700
700
800
800
50
50
100
200
300
400
500
700
700
700
1000
1000
1000
1500
1500
2000
2000
2000
2500
2500
Heavy
Medium
—
—
100
200
250
300
400
500
500
700
700
700
900
1000
1500
1500
1500
2000
2000
3000
Medium
Normal
—
—
—
—
20
50
30
80
40 100
50 120
80 200
100 250
100 250
120 300
120 300
120 300
150 400
200 500
250 700
250 700
250 700
300 900
300 900
500 1300
Light
—
—
150
150
200
400
400
600
600
600
600
1000
1000
1300
1500
1500
2000
2000
2500
2500
72C, BNT2
Heavy
—
—
80
80
100
200
200
300
300
300
300
500
500
600
800
800
1000
1000
1300
1300
70C, BNT0, HSBOC
Medium
—
—
30
30
50
100
100
150
150
150
150
200
200
300
400
400
500
500
600
600
Normal
—
—
10
10
20
30
30
50
50
50
50
80
80
100
150
150
150
150
200
200
Light
Heavy
12
18
32
40
50
65
80
90
95
100
105
110
120
140
150
160
170
180
190
200
Medium
—
12
18
32
40
50
65
80
90
95
100
105
110
120
140
150
160
170
180
190
Normal
incl.
79C, HSB9C
Light
over
Units: (N)
100 200
150 300
300 500
500 800
600 1000
800 1500
1000 2000
1500 3000
2000 4000
2000 4000
2500 5000
2500 5000
2500 5000
3000 6000
3000 6000
4500 8000
4500 8000
4500 8000
5000 10000
5000 10000
Note: Symbols /GL, /GN, /GM and GH are suffixes on NTN bearing part numbers indicating Light, Normal, Medium and Heavy
preloads, respectively.
A-76