Needle Roller Bearings - Ntn-snr.com

Load Rating and Life
NTN
When the oscillation angle 2 is very small, difficulty in
forming an oil film on the contact surface of rolling ring to
rolling element could result in fretting corrosion.
In the case of inner ring oscillation, the critical
oscillation angle is expressed in formula (2.9).
360˚ dp
Critical oscillation angle ⋯⋯(2.9)
Z dpDa cos
Where,
Z : Number of rolling elements (per row)
dp : Pitch circle diameter (PCD) of rolling element
Dp: Rolling element diameter
e : Contact angle
(In the case of outer ring oscillation, the right side
denominator is dp + Da cos .)
2.7 Life of bearing with linear motion
In the case of bearings with linear motion such as linear
ball bearing, linear flat roller bearing, etc., the relationship
among axial travel distance, bearing load and load rating
can be expressed in formulas (2.10), (2.11).
When the rolling elements are balls;
L 50 Cr 3
Pr
⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯(2.10)
When the rolling elements are rollers;
L 100 Cr 10/3
⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯(2.11)
Pr
where,
L Load rating km
CrBasic dynamic load rating N (kgf)
PrBearing load N (kgf)
Fig.2.4 shows the relationship of Cr/Pr to L.
Furthermore, when the travel motion cycle and travel
distance remain unchanged, the lifetime of bearing can
be determined by formulas (2.12), (2.13).
When the rolling elements are balls;
Lh 50103 Cr 3 (2.12)
60S Pr
When the rolling elements are rollers;
Lh 100103 Cr 10/3
(2.13)
60S Pr
where,
Lh: Travel life h
S : Travel distance per minute m/min
S =2Ln
L : Stroke length m
n : Stroke cycle N (kgf)
2.8 Various factors influencing bearing life
Bearing life is influenced by not only bearing load and
rotational speed but also various factors such as
lubricating condition, internal clearance, surface
roughness and hardness of raceway, heat-treated
structure, misalignment, etc. In using bearings, therefore,
these influence factors must be taken into full
consideration. Table 2.4 shows the bearing operating
conditions as a guideline. (For the detail refer to
Commentary" described in Bearing Dimensions Table
every each bearing type.)
Table 2.4 Guideline of the bearing operating conditions
Allowable rotational speed (r/min)
Surface roughness of raceway
Surface hardness of raceway
Misalignment
Radial internal clearance
See Dimensions Table
within 0.2a
HRC58 to 64
Note: Refer to Subsection 7.5 for
various materials and heat-treated
hardness thereof.
1/2000 or less (for radial bearing)
Ordinary level (C2, C3, C4)
Cr /Pr
10
8
6
5
4
3
2
Ball bearing
Roller bearing
0.05 0.1 0.2 0.3 0.4 0.6 0.8 1 2 3 4 6 8 10 20 30 40 60 100
L10 3 km
Fig. 2.4 Life of bearing with axial motion
A-17