Page 21 - needle bearings

Load Rating and Life
NTN

When the oscillation angle 2Ќ is very small, difficulty in When the rolling elements are balls;
forming an oil film on the contact surface of rolling ring to 50ʷ10 3 Cr 3
rolling element could result in fretting corrosion. Lh ʹ ʢ ʣʜʜʜʜʜʜʜʜʜʜ(2.12)
60ɾS Pr
In the case of inner ring oscillation, the critical
oscillation angle is expressed in formula (2.9).
When the rolling elements are rollers;
360˚ dp 100ʷ10 3 Cr 10/3
Critical oscillation angleВʾʕʕʕɾʕʕʕʕʕʕʕʕʕ ⋯⋯(2.9) Lh ʹ ʢ ʣ ʜʜʜʜʜʜʜʜ(2.13)
Z dpʵDa cosЋ 60ɾS Pr
where,
Where, Lh: Travel life h
Z : Number of rolling elements (per row) S : Travel distance per minute m/min
dp : Pitch circle diameter (PCD) of rolling element S =2ɾLɾn
Dp: Rolling element diameter L : Stroke length m
e : Contact angle n : Stroke cycle N (kgf)
(In the case of outer ring oscillation, the right side
denominator is dp + Da cos Ћ.) 2.8 Various factors influencing bearing life
Bearing life is influenced by not only bearing load and
2.7 Life of bearing with linear motion
rotational speed but also various factors such as
In the case of bearings with linear motion such as linear lubricating condition, internal clearance, surface
ball bearing, linear flat roller bearing, etc., the relationship roughness and hardness of raceway, heat-treated
among axial travel distance, bearing load and load rating structure, misalignment, etc. In using bearings, therefore,
can be expressed in formulas (2.10), (2.11). these influence factors must be taken into full
When the rolling elements are balls; consideration. Table 2.4 shows the bearing operating
conditions as a guideline. (For the detail refer to
Cr 3
L ʹ50ʷʢ ʣ ⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯(2.10) Commentary" described in Bearing Dimensions Table
Pr
every each bearing type.)
When the rolling elements are rollers;
Cr 10/3 Table 2.4 Guideline of the bearing operating conditions
L ʹ100ʷʢ ʣ ⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯(2.11)
Pr Allowable rotational speed (r/min) See Dimensions Table
where,
Surface roughness of raceway within 0.2a
L ɿLoad rating km
HRC58 to 64
CrɿBasic dynamic load rating N (kgf)
Surface hardness of raceway Note: Refer to Subsection 7.5 for
PrɿBearing load N (kgf) various materials and heat-treated
hardness thereof.
Fig.2.4 shows the relationship of Cr/Pr to L. Misalignment 1/2000 or less (for radial bearing)
Furthermore, when the travel motion cycle and travel Radial internal clearance Ordinary level (C2, C3, C4)
distance remain unchanged, the lifetime of bearing can
be determined by formulas (2.12), (2.13).

10
8
6
5
4 Ball bearing
Cr /Pr 3
Roller bearing
2

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
Lʷ10 3 km
Fig. 2.4 Life of bearing with axial motion

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