Inspector 400 Applications
General Mechanical Inspection / Detection
Inspector 400 Ultrasonic Probe
2 - 11
User Manual
Ultrasonic inspection of bearings is a useful tool in
recognizing:
•
The beginning of fatigue failure.
•
Brinelling of bearing surfaces.
•
Flooding of or lack of lubricant.
In ball bearings, as the metal in the raceway, roller or
ball bearing begins to fatigue, a subtle deformation
begins to occur. This deforming of the metal
produces an increase in the emission of ultrasonic
sound waves.
Changes in amplitude from 12 to 50 times the original
reading is indication of incipient bearing failure. When
a reading exceeds any previous reading by 12 db, it
can be assumed that the bearing has entered the
beginning of the failure mode.
This information was originally discovered through
experimentation performed by NASA on ball bearings.
In tests performed while monitoring bearings at
frequencies ranging from 24 through 50 kHz, they
found that the changes in amplitude indicate incipient
bearing failure before any other indicators including
heat and vibration changes. An ultrasonic system
based on detection and analysis of modulations of
bearing resonance frequencies can provide subtle
detection capability similar to the proven SKF method
of "Acceleration Enveloping;" whereas conventional
vibration monitoring methods are incapable of
detecting very slight faults. As a ball passes over a pit
or fault in the race surface, it produces an impact. A
structural resonance of one of the bearing
components vibrates or “rings” by this repetitive
