Special Issue; Products for Industrial Machinery - NTN

Development of New RCT Bearing for Axleboxes and Insulated Bearing with Shields
Test conditions
Table 4 Test condition of light contact seal
Radial load (kN)
Axial load (kN)
Bearing speed (min -1 )
Run pattern
Test results
Standard
seal
Bearing speed (rpm)
Train speed (km/h)
Radial load (kN)
Axial load (kN)
Cooling air speed (m/s)
Run duration (h)
Fig. 7 Test machine for Journal bearing
Table 6 Test condition of EN standard
Running-in operation
554 1108
83 165
3.4
68.3
13.6
2216 (equivalent to train operation at 330 km/h)
Repeated forward/backward running cycles
(according to EN standard)
Table 5 Test result of light contact seal
Max
Ave
Outer ring
A row
Light Max 44.2 46.4 45.9 52.8 41.5
contact
seal Ave 41.3 42.7 43.0 49.6 38.7
Note: data converted to equivalent value in a 20˚C environment
2.5 Result of EN standard running test
The samples were subjected to a running test that
conforms to the relevant EN standard. As a result, it
has been verified that the new RCT bearing satisfies
the EN standard.
Test conditions
Outer ring
B row
1662
248
68.3
2216
330
Endurance
test
2216
330
6.8 10.2 13.6 13.6
Approx. 10 (0 when no rotation is in progress)
24 for each step
Seal
A row
Seal
B row
Axlebox
56.6 56.5 73.9 78.4 50.5
50.3 49.9 65.2 69.6 45.2
2910
Axial loading: One loading cycle consists of a 5-second loading period and a
5-second no-loading period (bi-directional)
Test results
Running-in
operation
Endurance
test
Table 7 Test result of EN standard
Peak value
Value at
stable state
Value at
stable state
(average value)
Inner ring
Outer ring
Inner ring
Outer ring
Inner ring
Outer ring
Difference in outer ring temperature
between Bearing 1 and Bearing 2
Difference in outer ring temperature
between adjacent cycles
Bearing
1
Bearing
2
EN
standard
97.9 98.8
80.1 78.5
45.7 47.9 5°C or lower
37.3 36.8 for 2 hours
43.9
34.1
15 or lower
90 or lower
20 or lower
10 or lower
20 or lower
2.6 Summary
By adopting a resin cage, a light contact seal and
an anti-fretting measure, NTN has realized a journal
bearing that satisfies the EN standard and is capable
of extending maintenance intervals while ensuring a
high degree of reliability.
3. Sealed Insulated Traction Motor
Bearing
In order to realize higher train speeds as well as to
promote increased use of LRVs, electric motors that
are more compact are greatly needed to realize lighter
trains. At the same time, railway companies are
demanding extended maintenance intervals to
decrease maintenance costs.
Currently, traction motor bearings are relubricated
after every 600,000 to 900,000 km of operation. The
maintenance intervals of traction motors are usually
governed by the lubrication lives of the bearings, and
can vary depending on whether or not the traction
motor is a brushless design and whether or not the
lubricant is an insulating type. Therefore, until now,
long-life greases have been developed in an attempt
to extend lubrication life. Since bearing life is extended
only when the bearing is effectively lubricated for a
long period, the importance of the structure around the
bearing, including the grease pockets, has been
attracting attention.
NTN has recently developed a sealed insulated
bearing that allows compact design and does not
need maintenance work for up to 1,200,000 operating
km.
3.1 Features of sealed insulated bearings
The traction motors for rolling stock, such as those
on Shinkansen high-speed trains, use insulated
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