Page 54 - needle bearings

Bearing Handling
NTN

10.3 Post-installation running test
Bearing running test must be conducted on an installed
bearing to check whether it was installed correctly. In this
case, accelerating immediately the running speed up to
the rated speed must be avoided absolutely. Doing so
could result in damage of the bearing in the case of
imperfect installation and seizure of the bearing in the
case of inadequate lubrication. In testing, therefore, the
shaft or the housing must first be rotated by hand and
thereafter the shaft be rotated at low speed under no-load
condition by the driving power, unless any failure is
detected upon checking. After that, the running speed
Good example Bad example and load on the bearing must be accelerated and
increased gradually while checking the running condition.
Fig.10.2 Press-fit Running sound level and tone of a bearing can be
checked by a sound scope held in contact with the
bearing housing. The sound is normal if it is a pure sound
(3) Shrinkage fit
upon checking. In this case, high metallic sound or
This shrinkage fit method is to fit the inner ring on a irregular sound from the bearing, if any, reveals
shaft after dipping it in hot oil for thermal expansion of
occurrence of somewhat failure. In such a case, possible
its bore. This method is also widely used for cause of the failure can be presumed by measuring
installation of bearings. In heating the inner ring, low-
quantitatively vibration amplitude and frequency using a
corrosive mineral oil or the like is used. In this case, vibrometer.
the heated inner ring is natural-cooled down after
Generally bearing temperature is presumed from the
shrinkage-fit, but simultaneously it shrinks in axial circumferential temperature of a housing. However, it can
direction, too. Therefore, the inner ring must be
be judged more exactly if possible to measure directly the
pressed to the shaft shoulder until adequate cool- outer ring temperature by utilizing the oil hole thereof, etc.
down, so as not to allow a clearance between the
Needless to say, bearing temperature rises with elapse
inner ring and the shoulder. of the running time and reaches a constant level after a
In any case, however, it is not allowed to heat the
certain time. Rapid bearing temperature rise or continued
inner ring up to over 120˚C. temperature rise in excess to the constant level or
Fig. 10.3 shows the relationship of inner ring bore
abnormally high bearing temperature would reveals
thermal expansion to heating temperature. occurrence of somewhat failure. In such a case, careful
check is required.
Table 10.1 shows the required check items.
Required rising temperature = Heating temperature - room temperature
280 280 Table 10.1
260 80˚C 70˚C 60˚C 260 Variation in torque Imperfect installation
240 Rising temperature 90˚C 50˚C 40˚C 30˚C 240 Hand Over-torque Under-clearance, great seal friction, etc.
Thermal expansion of inner ring bore Жm 180 r6 180 Power Abnormal noise Inclusion of dust and other foreign matter,
operation Chattering
Indent and flaw on raceway surface
220
220
Inclusion of dust and other foreign matter
Abnormal sound
200
200
indent on raceway surface,over-clearance,
and vibration
inadequate lubrication
160
160
operation
Abnormal
Use of improper lubricant, imperfect

temperature
p6
140
140
installation, under-clearance
120
120
n6
100
80
80
Some related bearings are removed from each shaft,
60
60 k5 m6 100 10.4 Bearing removal (dismounting)
incurred by periodic disassembly or incidental trouble of a
40 j5 40
machine. In this case, these bearings must be handled
20 20 with good care similarly to the case of installation, when
they are reused or the condition thereof is examined after
50 100 150 200 250 300 350 400 450 500 550 600 removed (dismounted). Too tight fit of a bearing would
Bearing bore diameter mm
incur difficulty in dismounting and, therefore, the bearing-
Fig. 10.3 Rising temperature required for shrinkage fit of inner ring related construction must be fully considered in design of
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