TCF&B ES-52
7
5. Poor fan inlet conditions.
6. Acoustics or sound measurement procedure incorrect.
Vibration Problems:
1. Misalignment of drive components.
2. Poor foundations or mounting structure (resonances).
3. Foreign material attached to rotating components.
4. Damaged rotating components (bearings, shaft, fan,
wheel, sheaves).
5. Broken, loose or missing set screws.
6. Loose bolts.
7. Vibration transmitted by another source.
8. Water accumulating in airfoil blades.
9. Fan is operating in stall or unstable flow region.
Motor Problems:
1. Incorrect wiring.
2. Speed of fan too high.
3. Parts improperly installed - binding.
4. Bearings improperly lubricated.
5. WR
2
capability of motor too low for application.
6. Protection devices may be improperly sized.
Drive Problems:
1. Belts improperly tensioned.
2. Drive alignment is poor.
Bearing Problems:
Generally speaking, Twin City Fan & Blower 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 fea-
ture to attach them to the shaft
Ball Bearing — 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 fitting
which prevents the bearing’s outer race from rotating.
Should this pin jam, the bearing loses its alignment feature.
Common failure causes are (1) set screws loosening and
the 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 is 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 sup-
ports.
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 prac-
tice. Removing too much clearance from the bearing can
result in preloading the bearing, resulting in premature fail-
ure; and removing not enough can result in the shaft rotat-
ing within the bearing. Properly tightened, this method of
attaching 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 conta-
mination 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 prevent mois-
ture, 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 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 grad-
ually rise, it will generally result in failure. A bearing can
operate up to 200 degrees and operate satisfactorily if
the temperature remains constant and the bearing
receives adequate lubrication. Remember that a roller
bearing under the same load and speed will be some-
what more noisy and run warmer than a ball bearing. This
is normal.
Rough handling and/or dropping a fan can result in brinelling
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.
