Rolling Element Bearing Components
For Vibration Analysis Diagnostics
To separate the rolling elements, is the chief function
of the bearing cage, permitting safe operation at a variety
of operating speeds. The cage reduces rolling element sliding,
contact and wear. Cages facilitate uniform load distribution
by the elements in the bearing but carry no load.
The Fundamental Train Frequency (FTF)
or cage frequency physically relates to
the centerline of the rolling elements or the speed of the
bearing pitch circle. The analyst to derive the cage speed
ratio with respect to inner or outer raceway rotation is
allowed by bearing kinematics, based on physical bearing
geometry (θ Thrust Contact Angle, BD Ball Diameter, PD Pitch
Diameter and NB Number of Rolling Elements)
IRR = Inner Race Rotation
FTFIRR = ½ (1-(BD / PD) cos θ)
FTFIRR.approx = (½ - (1.2/ NB))
0.33x - 0.48x RPM of Inner Race
ORR = Outer Race Rotation
FTFORR = ½ (1 + (BD / PD) cos θ)
FTFORR.approx = (½ + (1.2/ NB))
0.52x - 0.67x RPM of Outer Race
To determine spectrum frequency, defect coefficient calculations
must be multiplied by 1x RPM.
Typical Cage Faults in Velocity Spectrum
