Page 46 - needle bearings

Lubrication
NTN

8.1.8 Grease replenishment deem the intersection point with the vertical line ! as A.
Lubrication grease must be replenished at an proper Thereafter, connect no /n=3 point B on the vertical line @
interval because its lubrication performance deteriorates and said A point together, with a straight line, and
with elapse of the bearing running time. However, this determine the intersection point C with the vertical line #.
replenishing interval differs depending on bearing type, And the grease replenishing interval of approximately
dimension, rotational speed, bearing temperature, kind of 4600 hours can be read from the intersection point C.
grease used, etc.
Fig.8.2 gives the replenishing interval chart as a
guideline. This chart is subject to use of a grease for 8.2 Oil lubrication
ordinary rolling bearings under usual operating In general, oil lubrication is more suitable for high
conditions. speed running application or high temperature application
Needless to say, the grease replenishing interval must than grease lubrication. Oil lubrication is suitable for the
be the shorter as the bearing temperature gets higher. As case where heat value generating from a bearing or heat
an approximate guideline, when the bearing temperature value being transferred to a bearing must be discharged
is 80˚C or more, the replenishing interval shall be outside the bearing.
shortened by 1/1.5 whenever the bearing temperature
rises by 10˚C. 8.2.1 Lubrication method
ʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕ (1) Oil bath lubrication
[Ex.] Determine the grease replenishing interval This oil bath lubrication is the most common of the
in the case when bearing NA4910R is in running currently available oil lubrication methods, which is
under the conditions of radial load Pr 5kNʨ510kgfʩ applied to bearings running at low or medium speed.
and rotational speed n 1 600r/min. An important point in this method is control of oil level
ʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕʕ in an oil bath.
d =50mmɼ For that, when bearings are installed on a horizontal
no =4700 is determined from NA4910R shaft, it is common that a point close to the center of
Cr =48kN (4900kgf) and allowable rotational speed the rolling element in the lowest position should be
=4,700 r/min in the Dimensions Table. deemed as the oil level to be secured during
Accordingly, shutdown. In this case, the housing must be designed
in such a profile as to minimize variation in oil level
no 4700
ʕʕ ʕʕʕ˺2.9 therein. Furthermore, it is desirable to provide the
n 1600
housing with an oil gauge to facilitate level check
Plot a line horizontally from d =50 point in Fig. 8.2 and during running as well as shutdown.
When bearings are installed on a vertical shaft, it is
no /n okay if 50 to 80% of the rolling elements are dipped in
@ an oil bath under low speed running, but in the cases
20.0
Grease refilling of high speed running and bearings used in multiple

deadline 15.0 rows it is desirable to adopt the drip lubrication and
h circulating lubrication methods, and others described
#
Shaft diameter d ! 30 000 10.0 hereunder.
mm 9.0
8.0
20 000
400 7.0 (2) Spray lubrication
300 6.0
200 This method sprays lubrication oil by an impeller of
10 000 5.0
100 A simple structure, which is mounted on the shaft,
50 4.0
40 5 000 C without directly dipping a bearing in an oil batch. This
30
20 can be applied to bearings running at considerably
4 000
10 3.0 B
5 3 000 high speed.
2 000
2.0 (3) Drip lubrication
1 000 This lubrication method is used where bearing runs at
1.5 comparatively high speed and medium and less loads
500 act on thereon. In this method, oil drips from an oiler
400
provided on the top of a bearing unit strikes the rolling
300
elements in its housing for atomizing lubrication (Fig.
1.0
8.3) or otherwise
0.9
a small amount of oil passes through the bearing. In
0.8 many cases bearing is lubricated with several drips
noɿAllowable rotational speed (See Dimensions Table)
per minute though the number of oil drips per specific
n ɿOperating rotational speed
0.7 unit differs depending on bearing type and dimension.
Fig.8.2 Chart for determination of grease replenishing interval
A-42