ball and roller bearings - NTN Bearing Corporation of

TECHNICAL
INFORMATION
Bearing Materials
The reliability and high capacity of NTN ball and
roller bearings is the result of developments in metallurgy,
manufacturing techniques, and our strict methods
of quality control.
Contact surfaces of the bearing rings and rolling
elements are subjected to repeated heavy stresses, yet
must be able to maintain high precision and rotational
accuracy. To accomplish this, the rings and rolling elements
must be made of material that has high hardness,
is resistant to rolling fatigue, is wear resistant and has
good dimensional stability.
High carbon chromium bearing steel, which can be
deep hardened, and case hardened steel with a hardened
carburized outer layer are used for the rings and
rolling elements of standard bearings. Case hardened
steels have excellent shock resistance properties and
are often used where impact loads are present.
The most common cause of fatigue cracking in
bearings is the inclusion of non-metallic impurities in
the bearing material. By using clean materials, the rolling
fatigue life of the bearing is lengthened. For all its
bearings, NTN uses steel of the highest cleanliness, and
refined by a vacuum degassing process.
Bearing cage materials must have the strength to
withstand rotational vibrations and shock loads. These
materials must also have a low friction coefficient, be
light weight, and be able to withstand bearing operating
temperatures. Common cage materials are low carbon
steel, bronze/brass alloy, or injection molded plastic. For
additional information, please contact your NTN representative.
Handling & Installation
Improper handling practices prior to and during
installation can easily damage the performance and precision
built into NTN ball and roller bearings. It is necessary
that certain precautions are taken to prevent such
damage.
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The most important factor to keep in mind when
handling bearings is cleanliness. NTN bearings are
assembled under immaculate conditions, then carefully
packaged for protection against contamination and oxidation.
A strong effort should be made to keep the bearings
in this condition prior to final assembly. The bearing
package should remain closed until ready for immediate
installation. If it is necessary to unwrap bearings before
that, they should be placed in a clean, dry area. Do not
stack unpackaged bearings.
Bearings should be installed in an area where a
clean atmosphere exists. Dirty conditions in the bearing
installation area can easily lead to contamination and a
premature failure. In addition, assembly benches and
tools must be kept clean to prevent contaminants such
as dust, grit and steel chips from entering the bearing. It
is much easier to keep a bearing clean than it is to wash
it clean enough for service.
The shaft, housing and other machine elements
should be cleaned and inspected prior to bearing installation.
The bearing mounting must be properly designed
from a functional standpoint, and must have correct
shaft and housing fits and shoulder heights. The design
should be such that the bearings can be installed as
easily as possible.
Proper assembly procedures and tools such as
arbor presses, pullers, and sleeves will not only facilitate
assembly, but will also avoid damage to the bearings.
When a bearing is pressed on a shaft, the inner ring
must be started squarely. A “cocked” ring may score the
shaft and damage the bearing. The pressure must be
applied directly on the ring being mounted. The bearing
must not be tapped in place with direct blows on the
bearing ring. The preferred practice is to place a sleeve
between the bearing ring and the hammer and to tap the
sleeve lightly all around. (Illustration A)
Sometimes a larger size bearing must be heated so
that it can be more easily assembled on a shaft. A convenient
method of doing this is to insert a heat source