Latvian Maritime academy

Frequency f
2
is caused with the shaft „leaping” above each rolling body.
The frequency of rotation bodies rolling along the running slot of the inside ring (Formula 4).
f
1 d4
( f1
f3)*
Z f1(1
cos
)* ;
(3)
2 d3
4
Z
f f f * Z
At this 4 1
. This frequency appears if the inside ring of the bearing (or of the shaft) is not
of ideal round form.
f the frequency of the separator rotation (Formula 4).
3
2
f
1
f
2
d
(1
d
1
cos
) f
2
4
3 1
h
3
;
(4)
This harmonic component appears in the case is one of the rolling bodies has a larger or smaller diameter.
Then rotating the shaft is „leaping” or „falling in”.
f the frequency of the rotation of the rolling bodies (Formula 5).
f
5
1 2
d3
d4
f *(1 *cos
2
1
) . (5)
2
2 d d
5
4
3
This frequency appears is the rolling bodies are of a facetted form. Usually this harmonic component
evinces its even harmonics. The number of the even harmonics and their order depend on the number of
sides of the rolling bodies. Let us consider the example of bearing of the average model 60305 with the
rotation frequency f 1 =1420 min -1 and outside diameter of the outside ring 72 mm. The typical
frequencies will be equal: f 2 = 4311 Hz; f 4 = 7049 Hz; f 5 = 2772 Hz; f 3 = 539 Hz.
Figure 2А demonstrates the spectrum of the frequencies of the forward bearing of the fan electric
motor at the beginning of the examination, Figure 2В – the same in 500 hours of uninterruptable
operation (3 weeks).
Figure 2. The spectral distribution of the bearing unit
The amplitude of the harmonics is given in relative units. For one the amplitude of 4311 Hz
harmonic component is accepted on the frequency of rotation of the rolling bodies along the outside ring
of the bearing of the defect-free motor (frequency № 2). The defect motor has the amplitude of all the
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