Lubrication and maintenance

Oil lubrication

When oil is the lubricant, the oil bath or oil

recirculating methods are the two most

common.

Oil bath

This is the most simple method of oil lubrica-

tion († fig. 1). The oil, which is picked up by

the rotating components of the bearing, is

distributed within the bearing and then flows

back to the oil sump.

The oil level should be such that it almost

reaches the centre of the lowest roller when

the bearing is stationary. Even under optimum

operating conditions, the oil must be changed

at least once a year.

Circulating oil

In a recirculating system, the oil can be con-

tinuously filtered and/or cooled († fig. 2).

This significantly increases the service life of

the oil, helping to avoid frequent oil changes.

The circulation can be produced by a pump.

In a recirculating system, ducts must be ad -

equately dimensioned so that the oil exits

from the housing after passing through the

bearing.

An intermediate form of oil circulation is

one where the oil is splashed up from the oil

bath by other components, e.g. gears in a

gearbox.

Grease lubrication

Today’s modern greases enable an increasing

number of maintenance-free bearing applica-

tions to be lubricated for life. Here, the selec-

tion of sealed SKF spherical roller bearings is

the optimum choice, both technically and eco-

nomically. These bearings are filled with SKF

LGEP 2 grease with a lithium thickener, before

leaving the factory († table 1) and are ready

to mount and operate.

In cases where the operating conditions are

so harsh that very frequent relubrication is

needed or where sealed SKF spherical roller

bearings are not available, SKF offers a full

range of greases and tools to enable proper

lubrication of the bearing († section “Lubri-

cants and lubrication equipment” on page 66).

Relubrication

It is only possible to determine relubrication

intervals statistically. SKF bases its relubrica-

a seemingly identical lot of bearings are still

reliably lubricated, i.e. they correspond to an

L1 grease life which is the relubrication inter-

val tf. The L10 grease life is approximately

twice the L1 life.

If the L10 grease life corresponds to, or

exceeds, the L10 life of the bearing, the bear-

ing is considered to be lubricated for life and

relubrication is not required.

The following recommendations are based

on the results of long-term tests in various

applications. They do not apply where water

and/or particulate contaminants can pene-

Fig. 2

Fig. 1

Spherical roller bearing application lubricated by an oil bath

Spherical roller bearing application lubricated by circulating oil

Table 1

Thickener Lithium

Colour Light brown

Base oil type Mineral

NLGI consistency class 2

Temperature –20 to +110range, °C (°F)1) (–4 to +230)

Dropping point toISO 2176, °C (°F) min. 180 (356)

Base oil viscocity, mm2/s at +40 °C (105 °F) 200 at +100 °C (210 °F) 16

1) The safe bearing operating temperature according to “The SKF traffic light concept”, where the grease will function reliably, lies within +40 to +110 °C (105 to 230 °F)