SKF - Rolling Bearings

Lubrication
Relubrication procedures
The relubrication procedure generally depends
on the application and on the relubrication interval
t f . SKF recommends one of the following
procedures:
• Replenishment is a convenient and preferred
procedure if the relubrication interval
is shorter than six months. It enables
uninterrupted operation and provides, when
compared with continuous relubrication,
a lower steady state temperature.
• Renewing the grease fill is generally recommended
when the relubrication interval is
longer than six months. This procedure is
often applied as part of a bearing maintenance
schedule.
• Continuous relubrication is used when the
estimated relubrication intervals are short
due to the adverse effects of contamination,
or when other relubrication methods are inconvenient
because access to the bearing is
difficult. SKF does not recommend continuous
relubrication for applications with high
rotational speeds since the intensive churning
of the grease can lead to very high operating
temperatures and destruction of the
grease thickener structure.
When using different bearings in a bearing arrangement,
it is common practice to apply the
lowest estimated relubrication interval for all
bearings in the arrangement. The guidelines
and grease quantities for the three alternative
procedures are provided below.
Suitable quantities for replenishment from the
side of a bearing can be obtained from
G p = 0,005 D B
and for replenishment through the bearing
outer or inner ring from
G p = 0,002 D B
where
G p = grease quantity to be added when
replenishing [g]
B = total bearing width [mm]
(for tapered roller bearings use T,
for thrust bearings use height H)
D = bearing outside diameter [mm]
Fig. 1
Fig. 2
Replenishment
As mentioned in the introduction of Lubrication,
the free volume in the bearing should be
completely filled during installation, while the
free volume in the housing generally should
be partly filled. Depending on the intended
method of replenishment, SKF recommends
the following grease fill percentages for this
free volume in the housing:
• 40% when replenishing from the side of the
bearing († fig. 1).
• 20% when replenishing through the lubrication
holes in the bearing inner or outer ring
(† fig. 2).
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