Page 124 - Rollingbearings

B.4 Lubrication
Overview of main oil Circulating oil without a bath and temperature, the design and layout of
lubrication methods Circulating oil by means of an external oil the oil drainage must ensure that there is no
pump, instead of an oil bath, is mainly used
oil level build-up.
when it is needed to remove heat generated
The oil lubrication methods are: by the bearing and/or other sources. Oil cir- Oil-air
culation is also a good lubricating method for
• oil bath without circulating oil evacuating solid or liquid contaminants from The oil-air lubrication method (ig. 9), also
• oil bath with self-circulating oil through the bearing to ilters and/or oil/liquid separ- called the oil-spot lubrication method, uses
bearing pumping action ators. The design and layout of the oil drain- compressed air to transport small, accurate-
• circulating oil with external pump age must ensure that there is no build-up of ly-metered quantities of oil as small droplets
• oil jet method oil level (Heat low from adjacent parts or along the inside of the feed lines to an injec-
• oil air method process, page 131). tor nozzle, where it is delivered to a bearing.
A basic circulating oil system (ig. 7) This minimum-quantity lubrication method
The choice of the oil lubrication method includes: enables the bearings to operate at very high
depends mainly on: speeds at a relatively low operating temper-
• oil pump ature. The compressed air also cools the
• the bearing speed • ilter bearing and prevents dust or aggressive
• the need to remove heat • oil reservoir gases from entering. For additional informa-
• the need to remove contaminants (solid • oil cooling and/or heating system tion, refer to skf.com/super-precision.
particles or liquid)
Oil jet
SKF offers a wide range of products for oil
lubrication that are not covered here. For The oil jet lubricating method (ig. 8) is an
additional information about SKF lubrication extension of circulating oil systems, and is
systems and related products, refer to used for bearings operating at very high
skf.com/lubrication. speeds. The dimensioning of oil low and
corresponding jet size is selected so that the
Oil bath without circulating oil oil jet speed reaches at least 15 m/s.
Oil injectors must be positioned so that
The simplest method of oil lubrication is the the oil jet penetrates the bearing between
oil bath. The oil, which is picked up by the one of the rings and the cage. To prevent
rotating components of the bearing, is dis-
churning that can cause increased friction
Lubrication tributed within the bearing and then lows Table 10
back to the oil bath in the housing. Ideally,
the oil level should reach the centre of the

bearing is stationary. Oil levels higher than
B.4 lowest rolling element (ig. 3) when the Oil change intervals for mineral oils
recommended will increase bearing temper-
ature because of churning (Bearing friction, Oil lubrication Typical operating Approximate oil change
system
conditions
interval 1)
power loss and starting torque, page 132).
Oil bath or oil Operating temperature < 50 °C 12 months
Oil bath with self-circulating oil pick-up ring (120 °F)
Little risk of contamination
Oil from a bath is forced to circulate by dif-
ferent methods. Here are some examples: Operating temperature 50 to 100 °C 3 to 12 months
(120 to 210 °F)
Some contamination
• Oil is salvaged and directed to the bearings
Operating temperature > 100 °C 3 months
by means of drain and ducts (ig. 4). (210 °F)
• A dedicated component (ring, disc, etc.) Contaminated environment
picks up oil from an oil bath and transports Circulating oil or All Determined by test runs and
it (ig. 5). oil jet regular inspection of the oil
• The pumping effect of some bearing types condition Dependent on how
can be used to circulate the oil. In ig. 6, frequently the total oil quan-
tity is circulated and whether
the spherical thrust roller bearing pumps or not the oil is cooled
oil which returns to the thrust bearing by
connecting ducts located under it.

All designs of such lubricating methods
1) More frequent oil changes are needed if the operating conditions are more demanding.
should be validated individually by tests.
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