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9 EXTERNAL SELF ALIGNING BALL BEARING UNITS

SERVICE LIFE OF GREASE
Figure 1: Value of adjustment factor f L according to
Bearing units are pre-filled with appropriate amounts of grease bearing load
and do not need to be relubricated during operation under
normal operating conditions. Even if they do need to be
relubricated, small amounts of grease (approx. 1/2 to 1/3 of the
bearing’s internal volume) are sufficient for relubrication.
The service life of grease varies greatly depending not only on
the type and dimensions of the bearing, but on operating
conditions, operating temperature, ingress of dust, moisture
and gas – and also on the type of mineral oil and soap base of f L
the grease. Figure 1 gives a scale chart for calculating the
service life of grease contained in bearings units. The scale
chart is based on test results and on our long years of
experience, and includes substantial safety margins.
This chart applies only to normal operating conditions. By using
it, the service life of grease can be determined once the type,
bore diameter, and ratio of allowable to actual bearing speed
ratio are found. However this calculated grease service life
does not imply any guarantee. The actual service life of a Example calculation
particular grease will vary according to many different factors
Find the service life of grease for UCP205 when the radial load
are previously described, and the calculated life should be
is 1,000N and the speed is 3,600rpm. First find the n o. The
treated only as a guideline that reflects quite large safety
basic dynamic rated load of UCP205 is Cr = 14,000N. From
margins.
Figure 1:
As operating temperature increases, the service life of grease
CR 14,000
will become shorter. The amount by which service life is
= = 14
PR 1,000
reduced depends on grease type. In general, the service life
can be determined as given in Figure 1 for the operating f L = 1.00 with ball bearing unit A 0 = 250,000
0
0
temperature range of -15 C to 100 C.
Therefore:
A 0 250 000
n o = f L = 1.00 X = 10,000
d 25
n o 10,000
= = 2.78
n 3,600
On the chart in Figure 1, join point A that corresponds to bore
diameter d = 25 and point B that corresponds to n 0/n = 2.78
with a straight line to find the intersection point C. Point C
indicates a service life of 15,000 hours.

n : Speed
Aod
no = f L
For ball bearing units,
Ao = 250,000

Figure 1

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