capacity
and fatigue life of ball bearings
IntroductionSelection GuideEngineeering DataBrochure
The BASIC DYNAMIC
RADIAL LOAD RATING, C, or "dynamic capacity", for a ball bearing
is that calculated, constant radial load at which 90% of a group of
apparently identical bearings with stationary outer rings can statistically
endure 106 revolutions of the inner ring. ANSI/ABMA Standard 9 with
correction factors for race curvatures was used to calculate the catalog
ratings.
The DYNAMIC THRUST
and DYNAMIC MOMENT LOAD RATINGS are also shown in the product tables.
The ratings shown are a guide for the maximum loads under which these
bearings should be operated with either pure thrust or pure moment loading.
Thrust ratings are 2.5 to 3.0 times the radial ratings depending on
the bearing type and cross section. These load ratings are not additive.
For combined radial and thrust loads, an equivalent radial load is to
be calculated.
The BASIC STATIC
LOAD RATING, Co, or "static capacity", is that uniformly distributed
load, which produces a maximum theoretical contact stress of 609,000
psi. At this contact stress permanent deformation of ball and raceway
occurs. This deformation is approximately .0001% of the ball diameter.
The RATING LIFE,
L10, is a statistical measure of the life which 90% of a large group
of apparently identical ball bearings will achieve or exceed. For a
single bearing, L10 also refers to the life associated with 90% reliability.
Median Life, L50, is the life which 50% of the group of ball bearings
will achieve or exceed. Median life is approximately five times the
rating life.
The relationship
between rating life, load rating, and load is:
L10
= (C/P)3 with 
L10
= rating life (106 rev)
C = basic dynamic radial load rating (lbf)
P = equivalent radial load (lbf) 
To obtain the rating
life in hours, use:
L10
hrs = 16667/n * (C/P)3 with n
= speed (rpm) 
The Equivalent Radial
Load is defined as:
P
= XFr + YFa with 
Fr
= radial load (lbf)
Fa = axial load (lbf)
X = see below
Y =see below 
