Page 47 - needle bearings

Lubrication
NTN

(4) Circulating lubrication 8.2.2 Lubrication oil
This circulating lubrication method is adopted to cool Mineral oils such as spindle oil, machine oil, turbine oil,
down bearings or to lubricate automatically many etc. are mostly used as the lubrication oil for bearings.
lubricating portions by a centralized lubrication However, synthetic oils such as diester oil, silicone oil,
system. In more detail, as the features of this method fluorocarbon oil, etc. are used under the operating
the oil feed line is equipped with a cooler to cool down conditions wherein bearings are subjected to running at
the lubrication oil and, in addition, provided with an oil high temperature of 150˚C and over or low temperature of
filter to purify the lubrication oil. -30˚C and less.
Under this circulating lubrication system, the For lubrication oil, its viscosity is one of the important
lubrication oil must securely be discharged from each characteristics that determine the lubrication
bearing after having passed through it. For that, it is performance. Too low viscosity of lubrication oil would
important to provide an oil inlet and an oil outlet on cause imperfect forming of an oil film and finally cause
each bearing in opposite position and to make the oil damage of bearing surface, while too high viscosity of
discharge port size as large as possible or otherwise lubrication oil would cause great viscosity resistance,
to discharge the oil compulsorily. (Fig.8.4) which would then lead to temperature rise and increase of
friction loss.
(5) Others Generally lubrication oil of lower viscosity is used for
Jet lubrication, oil mist lubrication, air-operated oil the faster rotational speed of bearing, while lubrication oil
lubrication, etc. are available as other lubrication of higher viscosity is used for the heavier bearing load.
methods. Lubrication of bearings needs the oil viscosity every
each operating temperature which is specified in Table
8.4. Fig. 8.5 shows the lubrication oil viscosity -
temperature characteristic chart, which is referred to in
selecting a lubrication oil of optimal viscosity under actual
operating temperature.
Furthermore, Table 8.5 shows the criterion for selection
of the lubrication oil viscosity according to the actual
bearing operating conditions.

Table 8.4 Oil viscosity required for each bearing type
Bearing type Required mm /s
2
viscosity
Radial needle roller bearing 13
Thrust needle roller bearing 20

3,000
2,000
*40 7(
1,000
*40 7(
500 *40 7(
300 *40 7(
200
*40 7(
Fig. 8.3 Drip lubrication 100 *40 7(
Viscosity mm 2 /s 30
*40 7(

50
20
15
10
8

6
5

4

3
- 30 - 20 - 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Temperature ˚C
Fig. 8.5 Lubrication oil viscosity - temperature characteristic chart

Fig.8.4 Circulating lubrication

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