Recip Compressor drive Motor Steady
Bearing Damage
Case History Number 12
K4420-3 is a two stage in-line
reciprocating compressor which is driven by a two speed (960/400 rpm) Laurence Scott
electric motor via a 9 belt pulley system giving a compressor speed of either 345 rpm or
144 rpm respectively.
This machine forms part of a monthly vibration monitoring schedule and is one of a team of
three identical units that produce CO2 for the chlorine liquefaction
process, Figure 1 below shows the layout of the machine.
Figure
1 - Two stage reciprocating compressor.
Historically,
the overall vibration levels throughout the machine had been consistently low (around 1.4
mm/s rms) and had never given any cause for concern, however, the overall vibration levels
recorded on the 30th September 1997 at the motor drive pulley outboard steady
bearing exhibited a marked increase in the axial direction (position 3A), see Figure 2
below.
Figure 2 - Motor outboard
pulley steady bearing.
Examination of the
vibration spectrum collected from this location exhibited several harmonic peaks across
the 500 Hz bandwidth indicating a possible bearing defect at this location, see Figure 3
Figure 3 - Vibration spectrum
indicating bearing damage.
The site Mechanical Engineer was
immediately made aware of the change in the vibration levels with a recommendation to
replace the bearing as soon as possible. The machine was subsequently taken off line and
the bearing replaced. On examination of the original bearing, a large area of flaking
(spalling) was evident on the outer race, see Figure 4.
Figure 4 - Photograph showing bearing outer race damage.
Due to the accurate analysis and
prompt action by the Engineering Department a catastrophic failure had been prevented with
a mechanical cost saving of several thousand pounds.
A clear
case of ‘Machines Talk and it Pays to LISTEN’
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