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