Page 51 - NSK_CAT_E1102m_A7-141

LUBRICATION

(2) Replacement of Grease the discharge side is made larger than the partitioned (4) Grease Life of Sealed Ball Bearings (b) Operating Temperature, T
Grease, once packed, usually need not be replenished side so it can retain the old grease, which is removed For general purpose grease (1)
for a long time; however, for severe operating periodically by removing the cover. When grease is packed into single-row deep groove
conditions, grease should be frequently replenished ball bearings, the grease life may be estimated using 70 °C≤T≤110 °C
or replaced. In such cases, the bearing housing should (3) Replenishing Interval Equation (12.1) or (12.2) or Fig. 12.3:
be designed to facilitate grease replenishment and (General purpose grease (1)) For wide-range grease (2)
replacement. Even if high-quality grease is used, there is
When replenishment intervals are short, provide deterioration of its properties with time; therefore, ( )n n 70 °C≤T≤130 °C
replenishment and discharge ports at appropriate periodic replenishment is required. Figs 12.2 (1) and
positions so deteriorated grease is replaced by fresh (2) show the replenishment time intervals for various log t = 6.54 – 2.6 Nmax – 0.025 – 0.012 Nmax T When T<70 °C assume T = 70 °C
grease. For example, the housing space on the grease bearing types running at different speeds. Figs.12.2 (1) ……………………(12.1)
supply side can be divided into several sections with and (2) apply for the condition of high-quality lithium (c) Bearing Loads
partitions. The grease on the partitioned side gradually soap-mineral oil grease, bearing temperature of 70°C, (Wide-range grease (2)) The bearing loads should be about 1/10 or less of the
passes through the bearings and old grease forced and normal load (P/C=0.1). basic load rating Cr.
from the bearing is discharged through a grease valve · Temperature n n
(Fig. 12.1). If a grease valve is not used, the space on If the bearing temperature exceeds 70°C, the Notes (1) Mineral-oil base greases (e.g. lithium soap
replenishment time interval must be reduced by half Nmax 0.018 – 0.006 Nmax base grease) which are often used over a
A for every 15°C temperature rise of the bearings. ( )log t = 6.12 – 1.4 – T temperature range of around – 10 to 110 °C.
· Grease
A-A A In case of ball bearings especially, the replenishing ……………………(12.2) Notes (2) Synthetic-oil base greases are usable over
Fig. 12.1 Combination of Partitioned Grease time interval can be extended depending on used a wide temperature range of around – 40
Fig. 12. 1 Reservoir and Grease Valve grease type. (For example, high-quality lithium soap- where t : Average grease life, (h) to 130 °C.
synthetic oil grease may extend about two times of n : Speed (min–1)
replenishing time interval shown in Fig.12.2 (1). If 12.2.2 Oil Lubrication
the temperature of the bearings is less than 70°C, the Nmax : Limiting speed with grease lubrication
usage of lithium soap-mineral oil grease or lithium (min–1) (1) Oil Bath Lubrication
soap-synthetic oil grease is appropriate.) (values for ZZ and VV types listed in the
It is advisable to consult NSK. bearing tables) Oil bath lubrication is a widely used with low or
· Load medium speeds. The oil level should be at the center
The replenishing time interval depends on the T : Operating temperature °C of the lowest rolling element. It is desirable to provide
magnitude of the bearing load. a sight gauge so the proper oil level may be maintained
Please refer to Fig.12.2 (3). Equations (12.1) and (12.2) and Fig. 12.3 apply under (Fig. 12.4)
If P/C exceeds 0.16, it is advisable to consult NSK. the following conditions:

(a) Speed, n

n

0.25 ≤ Nmax ≤ 1

when n <0.25, assume n = 0.25 (2) Drip-Feed Lubrication

Nmax Nmax Drip feed lubrication is widely used for small ball
bearings operated at relatively high speeds. As shown
Radial Ball Bearings h in Fig. 12.5, oil is stored in a visible oiler. The oil drip
Cylindrical Roller Bearings rate is controlled with the screw in the top.
h 10 000
h
20 000 150 000
100 000
7 000 General purpose grease
5 000 50 000 Wide-range grease
4 000
20 000 10 000Grease Replenishment Interval, t 3 000
8 000f
2 000
6 000 Grease Replenishment Interval, t
10 000 5 000 f1 000
8 000 4 000 Average grease life, t800
d=20 30600 20 000 T=70 T=70
6 000 3 000 40 50500 80
5 000 60 70400 10 000 90 80
4 000 2 000 80 100300 5 000 100 90
121060142000 3 000 100
3 000 240 280200 2 000 110
340 420 110
2 000 1 000 500 1 000 120
800 500
d=10 20 130
30 40
600 50 60
500 7100104810080121062020
400 260 300

1 000 300
800

600

400 200 4 000 6 000 10 000 20 000 100 200 300 400 600 1 000 2 000 4 000 6 000 10 000
200 300 400 600 800 1 000 2 000 100
min–1
Speed n min–1 Speed n 200
0.25 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
(1) Radial Ball Bearings, Cylindrical Roller Bearings (2) Tapered Roller Bearings, Spherical Roller Bearings Fig. 12.5 Drip Feed
n/N max Fig. 12.4 Oil Bath Lubrication Fig. 12.5 Lubrication
(3) Load factor P/C ≤0.06 0.1 0.13 0.16
Load factor 1.5 1 0.65 0.45 Fig. 12.3 Grease Life of Sealed Ball Bearings

A 106 Fig. 12.2 Grease Replenishment Intervals A 107