Page 93 - Rollingbearings

Size selection based on rating life
Basic dynamic load Dynamic load rating for SKF Equivalent dynamic
rating, C Explorer bearings bearing load, P

SKF Explorer bearings have undergone
The basic dynamic load rating C is used for design, material and manufacturing When calculating the bearing rating life, a
calculating basic rating life and SKF rating improvements that require adjusted factors value for equivalent dynamic bearing load is
life for bearings that rotate under load. The C to calculate the dynamic load ratings in required for both basic bearing life and SKF
value is deined as: the bearing load that will accordance with ISO 281. The SKF Explorer bearing life equations.
result in an ISO 281 basic rating life of adjusted dynamic load ratings, which are The loads acting on a bearing are calcu-
1 000 000 revolutions. It is assumed that the higher than the ratings for SKF basic design lated according to the laws of mechanics
load is constant in magnitude and direction bearings, are veriied by extensive endur- using the external forces – such as forces
and is radial for radial bearings and axial, ance testing. from power transmission, work forces, gravi-
centrically acting, for thrust bearings. To fully utilize the improved performance tational or inertial forces – that are known or
The basic dynamic load ratings for SKF of SKF Explorer bearings, the SKF rating life can be calculated.
bearings are determined in accordance with calculation including the life modiication In real-world circumstances, the loads
the procedures outlined in ISO 281, and factor a SKF is recommended. In fact, it is the acting on a bearing may not be constant, can
apply to bearings made of chromium bearing modiied rating life of the bearing, L 10m , act both radially and axially, and are subject
steel, heat treated to a minimum hardness of rather than the dynamic load rating, C, that to other factors that require the load calcula-
58 HRC, operating under normal conditions. provides the most valuable information tions to be modiied or, in some cases,
regarding the endurance performance of a simpliied.
bearing. For detailed information, refer to
Life modiication factor, a SKF , page 94.

Table 4
Unit conversion factors for bearing life

γ
1
3 0
2 The complete oscillation = 4 γ
4 (= from point 0 to point 4) Bearing size

Basic units Conversion factor
Million Operating Million Million
revolutions hours kilometres oscillation cycles 1) B.3

6
10 π D 180
1 million revolutions 1 —— —— ——
3
60 n 10 2 ү
60 n 60 n π D 180 x 60 n
1 operating hour ——– 1 ————– ————–––
6
6
9
10 10 2 ү 10
3
3
10 10 180 x 10
9
1 million kilometres —–– —–––––– 1 —–––––––
π D 60 n π D 2 ү π D

6
1 million oscillation 2 ү 2 ү 10 2 ү π D 1
cycles 1) –––– –––––––— –––––––—
3
180 180 ¥ 60 n 180 x 10
D = vehicle wheel diameter [m]
n = rotational speed [r/min]
γ = oscillation amplitude (angle of max. deviation from centre position) [°]
1) Not valid for small amplitudes (y < 10°).

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