SKF - Rolling Bearings

Lubrication
Relubrication
Rolling bearings have to be relubricated if the
service life of the grease is shorter than the
expected service life of the bearing. Relubrication
should always occur while the existing
lubricant is still satisfactory.
The time at which the bearing should be relubricated
depends on many related factors.
These include:
• bearing type and size
• speed
• operating temperature
• grease type
• space around the bearing
• bearing environment
It is only possible to base recommendations on
statistical rules. The SKF relubrication intervals
are defined as the time period, at the end
of which 99% of the bearings are still reliably
lubricated. This represents the L 1 grease life.
SKF recommends using experience based
data from actual applications and tests,
together with the estimated relubrication
intervals provided.
For many applications, there is a temperature
limit for standard greases when the bearing
ring with the highest temperature exceeds
an operating temperature of 100 °C (210 °F).
Above this temperature, special greases
should be used. In addition, the temperature
limits of the bearing and adjacent machine
components, such as external seals, should
be taken into consideration.
For additional information about high temperature
applications, contact the SKF application
engineering service.
Relubrication intervals
The relubrication intervals t f for bearings with
a rotating inner ring on horizontal shafts under
normal and clean operating conditions can be
obtained from diagram 4 († page 256) as a
function of:
• the speed factor A multiplied by the relevant
bearing factor b f
where
A = n d m [mm/min]
b f = bearing factor dependent on bearing
type and load conditions († table 5,
page 257)
d m = bearing mean diameter [mm]
= 0,5 (d + D)
n = rotational speed [r/min]
• the load ratio C/P
The relubrication interval t f is the estimated
number of operating hours that a high-quality
grease, consisting of mineral oil and a lithium
base thickener, can perform adequately when
the operating temperature is 70 °C (160 °F).
When bearing operating conditions differ, the
relubrication intervals († diagram 4,
page 256) need to be adjusted († Adjustments
of relubrication intervals due to operating
conditions and bearing types).
If the speed factor A exceeds 70% of the
recommended limits († table 5, page 257),
verify the influence of the selected lubricant
on the speed limits that are provided under
Speeds († page 117) and check whether the
rotational speed is within these limits.
When using high performance greases,
an extended relubrication interval and grease
life may be possible.
For grease life of capped bearings, refer to
the relevant product chapters.
For additional information, contact the SKF
application engineering service.
Adjustments of relubrication intervals
due to operating conditions and bearing
types
Operating temperature
To account for the accelerated ageing of
grease with increasing temperature, SKF
recommends halving the obtained intervals
(† diagram 4, page 256) for every 15 °C
(27 °F) increase in operating temperature
above 70 °C (160 °F). The high temperature
performance limit HTPL for the grease
(† diagram 1, page 245) should not be
exceeded.
252