Mitsubishi Electric JR Series Instruction Manual page 21

This noise is caused by a resonance of the natural vibration of the vibration
system composed of the ball bearings axial spring and rotor, and the vibration
system formed between this assembly and the bracket. This is caused by the
Groaning
resulting unstable vibration
noise
(7) Bearing clearance
When purchasing bearings from a bearing maker, order the type with the bearing No. noted on the
motor nameplate. Observe the following points when placing the order.
(a) Clarification of clearance symbol
The bearing clearance is very important for the bearing life, noise and vibration. Thus, when
purchasing the bearings, the clearance symbol must be clearly instructed in addition to the
basic bearing No. (ex., 6310, etc.) and shielded symbol (ex., ZZ, etc.). General motors use
bearings with a special clearance to suppress noise and vibration. This clearance is indicated
with the symbol "CM". The relation of each clearance is shown in Table 14. If a special
clearance is used, it is indicated on the motor nameplate. However, the "CM" clearance
symbol is abbreviated. When placing your order, indicate the "motor" or "CM" clearance
symbol. (Ex., 6310ZZ or 6310ZZCM for motor.)
Table 14-1 Radial internal clearance of deep groove ball bearings
Nominal dimension
of bearing bore
diameter (mm)
More Less
than (<) than
10 18
18 24
24 30
30 40
40 50
50 65
65 80
[Remarks] When using the clearance as the measurement clearance, the clearance compensation amount is as
follows to compensate the increase in the radial clearance cause by the measurement load. The
smaller of the C2 clearance compensation amounts is used for the min. clearance and the larger is
used for the max. clearance.
Nominal dimension of
bearing bore diameter (mm) Measurement
More than (<)
(Including) 10
18
50
Cause of noise
C2 Normal
Min. Max. Min.
– 9 3
– 10 5
– 11 5
– 11 6
– 11 6
– 15 8
– 15 10
load (N)
Less than
18 24.5
50
280
Table 13
Clearance (unit : 0.001mm)
CM
Max. Min. Max.
18 4 11
20 5 12
20 5 12
20 9 17
23 9 17
28 12 22
30 12 22
Compensation amount of radial internal clearance
C2 Normal and CM
3 to 4
49 4 to 5
147 6 to 8
- 16 -
Measures
1) Use grease with a good lubrication
performance.
2) Apply an appropriate pre-load
3) Decrease the radial clearance.
4) Loosen the fitting of the outer ring.
5) Increase the axial rigidity of the
bracket.
C3
Min. Max. Min.
11 25 18
13 28 20
13 28 23
15 33 28
18 36 30
23 43 38
25 51 46
(unit : 0.001mm)
C3
4 4
5 6
8 9
C4
Max.
33
36
41
46
51
61
71
C4
4
6
9