Aerovent IM-391 - Manual (Page 7)

Aerovent IM-391 7
Bearing Problems:
Generally speaking, Aerovent uses three types of bearings:
1. Ball bearing with set screw lock.
2. Spherical roller bearings with set screw lock.
3. Spherical roller bearings with adapter lock/taper lock
feature to attach them to the shaft.
Ball bearings – These are self-aligning bearings and should
present no alignment problems with one exception: i.e., on
Sealmaster bearings there is a pin beneath the grease fit-
ting which prevents the bearings outer race from rotating.
Should this pin jam, the bearing loses its alignment feature.
Common failure causes are (1) set screws loosening and
shaft turning within the bearing, and (2) crowned bearing
supports. Loosen one bolt and measure the clearance
between the pillow block and the support. Add shim to
compensate.
Spherical Roller Bearings with Set Screw Lock – The self-
aligning characteristic of these bearings are inherent in the
spherical roller design. The closer that these bearings are
to perfect alignment, the cooler they will operate.
Common failure causes are the same as with ball bear-
ings, mainly set screws loosening and crowned bearing
supports.
Spherical Roller Bearings with Adapter Lock – Again, the
self-aligning feature is inherent in the spherical design.
Good alignment results in a cooler operating bearing. The
faster the bearing operates the more critical this becomes.
A common cause of failure is improper installation practice.
Removing too much clearance from the bearing can result
in preloading the bearing, resulting in premature failure;
and removing not enough can result in the shaft rotating
within the bearing. Properly tightened, this method of at-
taching a bearing to a shaft is second only to a press fit.
Crowned bearing supports can also preload these bearings
and should be checked by loosening one side of the bear-
ing and checking for clearance.
Lubrication – The major cause of bearing failure is con-
tamination of grease, insufficient grease, or incompatibility
of grease. If a fan is to be stored for any length of time
at the job site, the bearings immediately should be filled
with grease while rotating the shaft and then the bearings
should be regreased and rotated monthly. This will pre-
vent moisture, which condenses within the bearing, from
corroding the raceways. Most greases used on fan pillow
blocks are lithium base. Use the greases shown on the
bearing decal. Do not mix the bases without completely
purging out the initial grease.
Initially, follow the lubrication instruction on the side of
the fan. The frequency of lubrication should be adjusted
depending on the condition of the old grease being
purged. This is the responsibility of the user. If the
grease is dirty, the lubrication frequency should be more
often.
a. Noise – If a bearing is increasing in noise intensity
and/or vibration, it will probably result in failure.
b. Temperature – If a bearing temperature begins to
gradually rise, it will generally result in failure. A bear-
ing can operate up to 200 degrees and operate sat-
isfactorily if the temperature remains constant and the
bearing receives adequate lubrication. Remember that
a roller bearing under the same load and speed will
be somewhat more noisy and run warmer than a ball
bearing. This is normal.
Rough handling and/or dropping a fan can result in bri-
nelling the bearing. This appears as a clicking noise at
first, then gradually worsens until failure.
When replacing a bearing, always align the bearings first,
then bolt the pillow blocks to their support, rotate the
shaft, fasten the bearings to it. If the bearing is fastened
to the shaft first, tightening the pillow block bolts may
bind the shaft and preload the bearings.