Page 20 - needle bearings

Load Rating and Life
NTN

2.4.3 Life adjustment factor for operating conditions a3 1.0
The life adjustment factor for operating conditions a3 is
used for adjustment(compensation) of the bearing life,
where the lubricated bearing condition gets worse and the
lubricant deteriorates or foreign matter is included in the
bearing, caused by the rotational speed, temperature rise, Hardness factorɹf H 0.5
etc. of the bearing in running.
Generally the life adjustment factor in the case of good
lubricated bearing condition is a3=1 and, particularly
where the lubricated bearing condition is good and other
factors for the bearing are normal, a3>1 can be applied to HRC 59 57 55 53 51 49 47 45
adjustment of the bearing life. However, a3<1 is applied in
Fig. 2.2 Hardness factor
the following cases.
¡Low viscosity of lubrication oil under bearing
temperature in running 2.6 Life of bearing with oscillating motion
Radial needle roller bearing 13mm /s and less
2
The life of bearing with oscillating motion can be
2
Thrust needle roller bearing 20mm /s and less
¡Particularly low rotational speed determined by formula (2.8).
(The product of rotational speed n r/min by pitch circle Losc ʹ ЊLRot ⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯(2.8)
diameter dp mm of rolling element is dpɾn<10000.)
¡High operating temperature of bearing where,
High operating temperature of bearing would cause the Losc : Life of bearing with oscillating motion
raceway hardness to reduce, whereby bearing life LRot : Life rating subject to rotational speed r/min
would be shortened, In such a case, the bearing life is identical to oscillation frequency cpm
adjusted (compensated) by multiplying the value shown Њ : Oscillation factor (showing the relation with
in Fig.2.1 as the life adjustment factor for operating half angle Ќ of oscillation angle per Fig.2.3).
conditions depending on operating temperature.
¡Inclusion of foreign matter in lubricant Generally Fig.2.3 is applied when the oscillation angle
In the case of special operating conditions, feel free to exceeds critical angle 2Ќ. This critical angle is nearly
contact NTN for inquiry. For a bearing manufactured determined by design of bearing internals ʕmainly the
using the specially improved material and number of rolling elements included in single row bearing.
manufacturing process/technique, usually a2 ʷ a3<1 is Where a bearing with oscillating motion is used at
applied unless the lubricating condition is good, even below the critical angle, its life is shorter than the lifetime
though the life adjustment factor is a2>1. value calculated using Fig.2.3. When the critical angle is
unknown, determine Њ, assuming Ќ=Ќ C. Feel free to
1.0 contact NTN for inquiry about the critical angle of
Life adjustment factor for operating conditions a3 0.6 30
individual bearings.
0.8

0.4
20
0.2

100 150 200 250 300 10 7 Ќ
Operating temperature ˚C 5
Oscillation factor Њ 2
Fig. 2.1 Life adjustment factor for operating conditions 4
depending on operating temperature 3

2.5 Affect on basic dynamic load rating by
raceway surface hardness 0.7 1
When a bearing rolls on shaft surface/housing surface 0.5
as its raceway surface, the surface layer must be 0.4
0.3
hardened to HRC58 to64 in proper hardening depth.
Ordinary quenching, carburizing or induction 0.2
quenching, etc. are available as the raceway hardening
method, but low hardness of the raceway would cause to 0.1 3 4 5 7 10 20 30 50 70 100 200 300 500 7001000
the bearing fatigue lifetime to reduce. In such a case, the Half angle of oscillation angle Ќ
basic load rating is adjusted by multiplying the hardness
factor shown in Fig.2.2. Fig. 2.3 Relationship of oscillation angle Ќ to factor Њ

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