Slip friction can be a telltale sign of inade-
quate lubrication. Rolling- element bearings are
multi-element tribosystems with many rollers,
two races and one cage. For elastohydrodynamic
lubrication between the rollers and races, the
required fluid film thickness is approximately 1
micron. For hydrodynamic lubrication between
the rollers and cage, the necessary fluid film
thickness is approximately 100 microns. ere-
fore, inadequate lubrication shows up first in
the cage. Since the loading between the roller
and cage is very light, ultrasonic stress waves
may reveal slip friction before the onset of
physical damage.
Slip Contact, Sliding Contact,
Impact, Cavitation and
Turbulence
Properly lubricated tribosystems are buoyed
by lubricant film strength. Static and dynamic
compression loads are transferred between
adjacent components. Interfacial shear forces
are rendered insignificant by a strong lubricant
film. Under these conditions, the DNA500
waveform reports a strong acceleration score
corresponding to machine dynamics, while the
DNA12 acceleration score remains well below
25 percent of the DNA500 acceleration score.
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Graph showing a slip event in undecimated DNA12 and DNA500 waveforms
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