Amount of preload

The amount of preload should be determined, to avoid an adverse effect on bearing life, temperature rise, friction torque, or other performance characteristic, in view of the bearing application.
Decrease of preload due to wear-in, accuracy of the shaft and housing, mounting conditions, and lubrication should also be fully considered in determining preload.

11-4-1 Preload amount of matched pair angular contact ball bearings

Table 11-2 shows recommended preload for matched pair angular contact ball bearings of JIS class 5 or higher used for machine tool spindles or other higher precision applications.
JTEKT offers four types of standard preload: slight preload (S), light preload (L), medium preload (M), and heavy preload (H), so that preload can be selected properly and easily for various applications.
Generally, light or medium preload is recommended for grinder spindles, and medium or heavy preload for spindles of lathes and milling machines.
Table 11-3 shows recommended fits of highprecision matched pair angular contact ball bearings used with light or medium preload applied.

Table 11-2 Standard preload of high-precision matched pair angular contact ball bearings

Unit : N
Bore diameter No. 7900 C 7000 7000 C 7200 7200 C ACT 000 ACT 000 B
00 5 15 30 30 80 145 6 20 50 100 50 145 245 10 30 80 145 - - - -
01 7 20 40 30 80 145 6 20 50 100 60 145 295 15 40 100 195 - - - -
02 8 25 50 50 145 245 10 30 80 145 80 245 390 15 50 145 245 - - - -
03 8 25 50 60 145 295 15 40 100 165 100 245 540 25 70 145 345 - - - -
04 15 40 80 60 145 295 15 40 100 245 145 295 635 25 80 195 390 - - - -
05 15 50 100 100 245 490 20 60 145 295 145 390 785 35 100 245 490 - - - -
06 15 50 100 145 295 635 25 80 195 390 145 590 930 35 100 295 590 195 345 295 685
07 25 70 135 145 390 785 35 100 245 490 245 785 1270 50 145 390 785 195 390 390 735
08 25 80 145 145 390 785 35 100 295 590 390 880 1570 65 195 440 880 245 440 440 835
09 35 100 195 245 540 980 50 145 345 635 490 1080 1770 85 245 540 1080 245 490 490 930
10 35 100 195 245 635 1180 50 145 390 735 540 1180 2060 85 245 590 1180 295 540 540 1030
11 40 115 235 295 785 1370 65 195 440 880 635 1370 2450 100 295 735 1470 390 685 685 1270
12 40 115 235 390 880 1570 65 195 490 980 785 1470 2940 110 345 785 1670 390 735 735 1420
13 50 145 295 440 980 1770 85 245 540 1080 835 1670 3330 125 390 930 1860 440 835 785 1520
14 65 195 390 490 1080 2060 85 245 635 1270 930 1860 3730 160 490 980 2060 590 1130 1030 2010
15 65 195 390 590 1180 2160 100 295 685 1370 980 2160 3920 195 590 1180 2350 590 1130 1080 2110
16 65 195 390 635 1370 2350 100 295 735 1470 1080 2450 4310 225 685 1370 2750 685 1370 1270 2500
17 85 245 490 735 1570 2550 125 390 880 1770 1270 2940 4900 260 785 1570 2940 735 1420 1320 2600
18 100 295 590 785 1670 2840 145 440 980 1960 1470 3240 5390 260 785 1770 3430 980 1860 1770 3380
19 100 295 590 880 1770 3140 160 490 1080 2060 1670 3430 5880 290 880 1960 3920 980 1960 1860 3530
20 100 345 685 880 1960 3530 175 540 1180 2160 1860 3920 6370 325 985 2160 4410 1030 2010 1910 3680
21 100 345 685 980 2160 3920 195 590 1270 2350 2060 4310 7060 355 1080 2350 4900 1180 2250 2150 3770
22 145 390 785 1080 2380 4410 210 635 1470 2550 2260 4900 7850 385 1180 2450 5290 1320 2600 2450 4760
24 145 490 980 1180 2650 4900 225 685 1670 2840 2450 5390 8830 420 1270 2840 5490 1420 2800 2550 5100
26 195 590 1180 1370 3140 5390 245 735 1770 3140 2750 5880 9320 485 1470 3140 5880 1770 3380 3230 6230
28 195 635 1270 1470 3430 5880 260 785 1960 3920 2940 6370 9810 520 1570 3430 6370 2010 3920 3720 7210
30 245 735 1470 1770 3920 6860 275 835 2160 4410 3330 6860 10300 585 1770 3730 6860 2500 4850 4660 8920
32 245 785 1570 2160 4410 7850 290 880 2350 4900 3630 7350 10800 645 1960 4120 7850 2500 4850 4660 8920
34 345 880 1810 2450 4900 8830 325 980 2450 5390 3920 7850 11800 645 2160 4410 8340 3090 6030 5730 11100

[S : slight preload, L : light preload, M : medium preload, H : heavy preload]

Table 11-3 Recommended fits for high-precision matched pair angular contact ball bearings with preload applied

(1) Dimensional tolerance of shaft

Unit:µm
Shaft diametermmInner ring rotationOuter ring rotation
overup toTolerance of shaft diameterInterference between shaft and inner ring1)(matching adjustment)Tolerance of shaft diameter
610 - 2 0 - 2 0
- 6 - 4
1018 - 2 0 - 2 0
- 7 - 5
1830 - 2 0 - 2.5 0
- 8 - 6
3050 - 2 0 - 2.5 0
- 9 - 7
5080 - 2 0 - 3 0
-10 - 8
80120 - 2 0 - 4 0
-12 -10
120180 - 2 0 - 5 0
-14 -12

[Note]
1)Matching adjustment means to measure of bore diameter the bearing and match it to the measured shaft diameter.

(2) Dimensional tolerance of housing bore

Unit:µm
Housing bore diametermmInner ring rotationOuter ring rotation
Tolerance of housing bore diameterClearance between housing1)and outer ringTolerance of housing bore diameter
overup toFixed-side bearingFree-side bearing
1830 ± 4.5 + 9 2 - 6 - 6
0 -12
3050 ± 5.5 +11 2 - 6 - 6
0 -13
5080 ± 6.5 +13 3 - 8 - 8
0 -16
80120 ± 7.5 +15 3 - 9 - 9
0 -19
120180 ± 9 +18 4 - 12 -11
0 -23
180250 ±10 +20 5 - 15 -13
0 -27
250315 ±11.5 +23 6 - 18 -16
0 -32

[Note]
1)Lower value is desirable for fixed side; higher value for free side.

11-4-2 Amount of preload for thrust ball bearings

When a thrust ball bearing is rotated at high speed, balls slide on raceway due to centrifugal force and the gyro moment, which often causes the raceway to suffer from smearing or other defects.
To eliminate such sliding, it is necessary to mount the bearing without clearance, and apply an axial load (preload) larger than the minimum necessary axial load determined by the following equation.
When an axial load from the outside is lower than 0.001 3C0a, there is no adverse effect on the bearing, as long as lubrication is satisfactory.

Generally, deep groove and angular contact ball bearings are recommended for applications when a portion of rotation under axial load is present at high speed.

11-4-3 Amount of preload for spherical thrust roller bearings

Spherical thrust roller bearings sometimes suffer from scuffing, smearing, or other defects due to sliding which occurs between the roller and raceway surface in operation.
To eliminate such sliding, it is necessary to mount the bearing without clearance, and apply an axial load (preload) larger than the minimum necessary axial load.
Of the two values determined by the two equations below, the higher should be defined as the minimum necessary axial load.

  • Thrust ball bearing (contact angle : 90°)
a_116_001.png
  • Spherical thrust roller bearing(the higher value determined by the two equations should be taken.)
a_116_002.png
a_116_003.png
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