NTN - Cylindrical and Tapered Roller Bearings

Roller Bearings
l
F Cylindrical Roller Bearings
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Cylindrical roller bearings with with opposed solid ribs on
m
h
the inner and outer rings will support light to moderate
F 3 c
thrust loads.The maximum thrust load that a cylindrical
B
roller bearing will support is defined later in this section.
F (F a ) 1
5 b F2
f
d k F Field experience and laboratory tests have proven that
6
g F 4
as long as as the the applied applied thrust thrust load load is less is than less the than applied the
radial load and less than the limiting thrust rating, the
A a
(F a )
applied radial load and less than the limiting thrust
2
rating,the fatigue life fatigue of the bearing life of the will bearing not be will adversely not be adversely affected.
F 1 affected. Therefore, Therefore,the fatigue life fatigue of a cylindrical life of a cylindrical roller bearing roller
Combine examples 1, 2, and 3.
bearing under such under combined such combined loading loading conditions conditions will will be
V 6 4 4 4 4 4 4 4 44 V7
AA
be
4 4 4 4 4 4 4 4 48
equivalent equivalent to the to the life under life under the applied the applied radial radial load. load. The
2
The Equivalent Equivalent Radial Radial Load Load concept concept is not is not applicable applicable to
2
–F F1 – Fa g – F7
m
cylindrical roller bearings.
1 a + F 3 c + F 5 h F a 2 g F
2 7 m
R
l
to cylindrical roller bearings.
A =
+
l
Tapered Roller Bearings
H
H A
1 2
6 4 4 4 4 4 44 7 A
4 4 4 4 4 4 48
Tapered roller bearings, due to their basic design,
2 ½
F 2
F2 2 b F
b – F 4 d F
4
– F a
a
1 f + F
f 6 k
F6
k
generate a thrust reaction when subjected to a
1
radial load. The magnitude of this thrust reaction
l
(25)
is a function of the load, the included cup angle,
(25) and the size of the load zone within the bearing. For
convenience in load and life calculations, a Y 2
factor
– F1
m 2
has been assigned to each tapered bearing series.
R
B = [(-F 1 + F 3 + F 5 + F 7 V A ) 2 + (F 2 - F 4 - F 6 H A ) 2 ] ½
This factor is defined for single row bearings as:
2
F2 – F4 – F6 m HA
1 2
(26)
Y 2
= 0.4 cot (27)
Suggestions: SUGGESTIONS:
Where = 1/2 included cup angle
1. If the overhanging forces are always located at the
end of each component in the equation, the
possibility of overlooking them and the
accompanying sign change will be reduced.
2. It will be much easier to learn one set of rules and
always use the right hand support as the momentcenter;
however, the left hand support may be used
if it is necessary. When using the left hand support
as the moment-center, the signs for clockwise and
counterclockwise rotation must be reversed. All
other rules remain the same. Be sure to follow the
strict definition of an overhanging force.
COMBINED LOADING EQUATIONS
Bearings are frequently required to support a
combination of radial and thrust loads. In order to
calculate the bearing life under such conditions, it is
necessary to calculate an Equivalent Radial Load. The
theoretical bearing life under combined radial and thrust
loading conditions will be the same as that which would
be expected under a pure radial load equal to the
Equivalent Radial Load.
When the load on bearing (A) is pure radial (R A
) and
the load zone within the bearing is 180° or less, the
approximate thrust reaction (TR A
) is:
TR A
= 0.50 R A
(Y 2
) A
(28)
When the load zone on bearing (B) approaches 360°
due to a combined radial load (R B
) and an external
thrust load, its approximate thrust reaction is:
TR B
= 0.60 R B
(Y 2
) B
(29)
These thrust reactions are a critical part of the
Equivalent Radial Load equations for tapered roller
bearings.
The general ABMA equation for the equivalent
radial load is:
P = X F r
+ Y F a
(30)
Where: P = Equivalent radial load
F r = Applied radial load
F a = Applied thrust load
X = Radial load factor
Y = Thrust load factor
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