VIBTOOL 02.2009
32
The carpet value
Surface roughness causes a rapid sequence of minor shock
pulses which together constitute the shock carpet of the
bearing. This can be heard as a background noise level
when pressing a screwdriver to your ear to listen to the
bearing. The magnitude of the shock carpet is expressed by
the carpet value. The carpet value gives important informa-
tion regarding the lubrication of the bearings, how well the
bearings have been mounted and the way in which the
bearings are being loaded (for example, due to misalign-
ment).
The carpet value is directly related to the thickness of the
lubricant film in the rolling interface. The carpet value is
low when the surfaces of rolling elements and raceway are
completely, or almost completely, separated by a lubricant
film (see the diagram below).
0
20
40
60
dB
N
Time
Poor
Reduced
Good
0
20
40
60
dB
N
Time
Poor
Reduced
Good
The carpet value does not give
information regarding damage
to the bearings!
The carpet value has risen as a
direct result of decrease in
lubricant film thickness.
Here, the carpet value is low
when the rolling elements and
raceway are separated by a
generous lubricant film.
The carpet value rises when the lubricant film thickness
decreases and metal to metal contact increases between the
bearing surfaces. The diagram below shows how the carpet
value has risen.
The carpet value helps to analyze the cause of reduced or
poor operating condition.
Bearing diagnosis
To Next Page
Loading...
