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14. BEARING HANDLING
14.1 Precautions for Proper Handling of
Bearings
Since rolling bearings are high precision machine
parts, they must be handled accordingly. Even if high
quality bearings are used, their expected performance
cannot be achieved if they are not handled properly.
The main precautions to be observed are as follows:
(1) Keep Bearings and Surrounding Area Clean
Dust and dirt, even if invisible to the naked eye, have
harmful effects on bearings. It is necessary to prevent
the entry of dust and dirt by keeping the bearings and
their environment as clean as possible.
(2) Careful Handling
Heavy shocks during handling may cause bearings to
be scratched or otherwise damaged possibly resulting
in their failure. Excessively strong impacts may cause
brinelling, breaking, or cracking.
(3) Use Proper Tools
Always use the proper equipment when handling
bearings and avoid general purpose tools.
(4) Prevent Corrosion
Since perspiration on the hands and various other
contaminants may cause corrosion, keep the hands
clean when handling bearings. Wear gloves if possible.
Pay attention to rust of bearing caused by corrosive
gasses.
14.2 Mounting
The method of mounting rolling bearings strongly
affects their accuracy, life, and performance, so
their mounting deserves careful attention. Their
characteristics should first be thoroughly studied, and
then they should be mounted in the proper manner.
It is recommended that the handling procedures for
bearings be fully investigated by the design engineers
and that standards be established with respect to the
following items:
(1) Cleaning the bearings and related parts.
(2) Checking the dimensions and finish of related
parts.
(3) Mounting
(4) Inspection after mounting.
(5) Supply of lubricants.
Bearings should not be unpacked until immediately
before mounting. When using ordinary grease
lubrication, the grease should be packed in the
bearings without first cleaning them. Even in the case
of ordinary oil lubrication, cleaning the bearings is not
required. However, bearings for instruments or for
high speed operation must first be cleaned with clean
filtered oil in order to remove the anti-corrosion agent.
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After the bearings are cleaned with filtered oil, they
should be protected to prevent corrosion.
Prelubricated bearings must be used without cleaning.
Bearing mounting methods depend on the bearing type
and type of fit. As bearings are usually used on rotating
shafts, the inner rings require a tight fit.
Bearings with cylindrical bores are usually mounted
by pressing them on the shafts (press fit) or heating
them to expand their diameter (shrink fit). Bearings
with tapered bores can be mounted directly on tapered
shafts or cylindrical shafts using tapered sleeves.
Bearings are usually mounted in housings with a loose
fit. However, in cases where the outer ring has an
interference fit, a press may be used. Bearings can be
interference-fitted by cooling them before mounting
using dry ice. In this case, a rust preventive treatment
must be applied to the bearing because moisture in the
air condenses on its surface.
14.2.1 Mounting of Bearings with Cylindrical Bores
(1) Press Fits
Fitting with a press is widely used for small bearings.
A mounting tool is placed on the inner ring as shown
in Fig. 14.1 and the bearing is slowly pressed on
the shaft with a press until the side of the inner ring
rests against the shoulder of the shaft. The mounting
tool must not be placed on the outer ring for press
mounting, since the bearing may be damaged. Before
mounting, applying oil to the fitted shaft surface is
recommended for smooth insertion. The mounting
method using a hammer should only be used for small
ball bearings with minimally tight fits and when a press
is not available. In the case of tight interference fits or
for medium and large bearings, this method should not
be used. Any time a hammer is used, a mounting tool
must be placed on the inner ring.
When both the inner and outer rings of non-separable
bearings, such as deep groove ball bearings, require
tight-fit, a mounting tool is placed on both rings as
shown in Fig. 14.2, and both rings are fitted at the
same time using a screw or hydraulic press. Since the
outer ring of self-aligning ball bearings may deflect a
mounting tool such as that shown in Fig. 14.2 should
always be used for mounting them.
In the case of separable bearings, such as cylindrical
roller bearings and tapered roller bearings, the inner
and outer rings may be mounted separately. Assembly
of the inner and outer rings, which were previously
mounted separately, should be done carefully to align
the inner and outer rings correctly. Careless or forced
assembly may cause scratches on the rolling contact
surfaces.
Fig. 14.1 Press Fitting Inner Ring (2) Shrink Fits
Since press fitting large bearings requires a large force,
Fig. 14.2 Simultaneous Press Fitting of Inner and Outer Rings a shrink fit is widely used. The bearings are first heated
in oil to expand them before mounting.
μm This method prevents an excessive force from being
imposed on the bearings and allows mounting them in
240 a short time.
220 r6 The expansion of the inner ring for various temperature
Bore Expansion differences and bearing sizes is shown in Fig. 14.3.
Temperatur&e6T0Di7=°ff0Ce8r°0eCn°ceC200 The precautions to follow when making shrink fits are
as follows:
180 50 °C p6
160 40 °C (a) Do not heat bearings to more than 120˚C.
(b) Put the bearings on a wire net or suspend them in
140 30 °C n6
120 an oil tank in order to prevent them from touching
the tank's bottom directly.
100 20 °C m5 (c) Heat the bearings to a temperature 20 to 30˚C
higher than the lowest temperature required for
80 k5 mounting without interference since the inner ring
will cool a little during mounting.
(d) After mounting, the bearings will shrink in the
axial direction as well as the radial direction while
cooling. Therefore, press the bearing firmly against
the shaft shoulder using locating methods to avoid
a clearance between the bearing and shoulder.
NSK Bearing Induction Heaters
Besides heating in oil, NSK Bearing Heaters, which
use electromagnetic induction to heat bearings, are
widely used. (Refer to Page C7.)
In NSK Bearing Heaters, electricity (AC) in a coil
produces a magnetic field that induces a current inside
the bearing that generates heat. Consequently, without
using flames or oil uniform heating in a short time is
possible, making bearing shrink fitting efficient and
clean.
In the case of relatively frequent mounting and
dismounting such as cylindrical roller bearings for roll
necks of rolling mills and for railway journal boxes,
induction heating should be used for mounting and
dismounting inner rings.
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60 j5
40 180 250 315 400 500
20 Bore Diameter mm
80 120
Fig. 14.3 Temperature and Thermal Expansion of Inner Ring