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Developing a Motor Bearing Regreasing Strategy
James Oldach, Asset Management Consultant, New
Dimension Solutions
There are several factors that will determine if any motor is
to be included in the lubrication program:
1. Bearing type (Open, single shielded, double shielded, or sealed)
2. Size of motor (some smaller horsepower motors may not deserve
the attention)
3. Criticality (even if it's small it may be critical enough
to include in program) The following is the MOST effective methodology
to be used to identify motors that should be regreased:
A. Create a list all motors that are critical to process or are
larger than 30 HP (this HP size is subjective).
B. Identify bearing types for all motors on the list. This is
done as follows: If bearing ID number is on nameplate use AFBMA
bearing identification cross reference to determine bearing type.
If bearing id includes letters that indicate bearing is either
double shielded or sealed (eg. 2Z, or JJ indicates double shielded
bearing) motor is not capable of being regreased in field. Note
- although most motor manufacturers recommend regreasing all motor
bearings, bearing manufacturers have performed tests showing regreasing
a double shielded bearing can only damage the bearing. I have
a letter from SKF North America stating test results. If bearing
ID is not listed (in many cases) motor serial number, model number,
etc. must be collected and submitted to motor manufacturer for
bearing type determination.
C. Based on bearing type, operating frequency, and environment
establish a regreasing/no regreasing policy for all motors on
the list. For motors with non regreasable bearings, remove grease
fittings.
D. For critical motors with non-regreasable bearings, establish
an appropriate failure prevention policy using vibration monitoring,
ultrasonic monitoring, thermography, or in some cases, periodic
motor or bearing replacement. In my experience, motors with double
shielded bearings will last 6-8 years without regreasing (less
if you regrease).
E. For the motors that are not included on the list (smaller
non critical motors), consider a run to failure policy or address
the bearing identification as time permits.
F. Perhaps one of the most important steps that is overlooked
is to set procurement standards for motors and their bearing types.
If this is not done, as motors are replaced in the plant the original
list will become outdated. Motors with regreasable bearings may
be installed where a motor with double shielded bearings was installed.
Maintenance should dictate the types of bearings preferred in
new motors, either regreaseable or non-regreaseable.
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