Page 94 - Rollingbearings

B.3 Bearing size
Calculating equivalent Certain thrust bearings, such as thrust Rotating load
dynamic bearing load ball bearings and cylindrical and needle If, as illustrated in diagram 5, the load on the
roller thrust bearings, can only accommodate bearing consists of a load F which is constant
1
The load value, P, used in the bearing rating pure axial loads. For these bearings, pro- in magnitude and direction, such as the
life equations is the equivalent dynamic vided the load acts centrically, the equation weight of a rotor, and a rotating constant
bearing load. The equivalent dynamic bearing is simpliied to load F such as an unbalanced load, the
2
load is deined as: a hypothetical load, con- mean load can be calculated using
stant in magnitude and direction, that acts P = F a
radially on radial bearings and axially and F = f (F + F )
m
m
2
1
centrically on thrust bearings. Information and data required for calculating
This hypothetical load, when applied, the equivalent dynamic bearing load for the Values for the factor f are provided in
m
would have the same inluence on bearing different bearing types is provided in the diagram 6.
life as the actual loads to which the bearing relevant product sections.
is subjected (ig. 2). Peak load
If a bearing is loaded with simultaneously High loads acting for short times (diagram 7)
acting radial load F and axial load F that are Equivalent mean load may not inluence the mean load used in a
r
a
constant in magnitude and direction, the fatigue life calculation. Evaluate such peak
equivalent dynamic bearing load P can be Other loads may vary with time. For these loads against the bearing static load rating
obtained from the general equation. situations, an equivalent mean load must be C , using a suitable static safety factor
0
calculated. s (Size selection based on static load,
0
P = X F + Y F a page 104).
r
Mean load within a duty interval
where Within each loading interval, the operating
P = equivalent dynamic bearing load [kN] conditions can vary slightly from the nominal
F = actual radial bearing load [kN] value. Assuming that the operating conditions,
r
F = actual axial bearing load [kN] such as speed and load direction, are fairly
a
X = radial load factor for the bearing constant and the magnitude of the load
Y = axial load factor for the bearing constantly varies between a minimum value
F min and a maximum value F max (diagram 4),
An axial load only inluences the equivalent the mean load can be calculated using
dynamic load P for a single row radial bearing
Bearing size factor e. With double row bearings, even F m = –––––————
if the ratio F /F exceeds a certain limiting
a
r
F min + 2F max

3
light axial loads inluence the equivalent load
and have to be considered.
The same general equation also applies to
B.3 spherical roller thrust bearings, which can
accommodate both axial and radial loads.
Fig. 2 Diagram 4 Diagram 5

Equivalent dynamic bearing load Load averaging Rotating load

F 1

F
F a
F m
F r P
F max
F min F 2

U

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