Following are the 16- top listed reasons for bearing failure or damages
1-Lubrication:
Following are the 7 major reasons for bearing failures
related to lubrication
1-Lack of lubrication
2-Less lubrication
3-Over lubrication
4-Contaminants in lubricants
5-Wrong method of lubrication
6-Poor quality of lubricants
7-Selection of wrong lubrication
8-Lubricant failure
2-Bearing clearance:
Bearings may fail if the clearance between rolling elements
& race is too less & too more. Lesser bearings clearance than desired
creates friction & temperature rise.
More bearing clearance creates vibrations
3-Operating the
bearings at higher vibrations for long time:
Bearings can operate satisfactory at the vibrations range up
to 5 mm/sec, vibrations more than this reduces the bearing life &
eventually failure.
Operation range: 0.5 to 3 mm/sec
Alarm Range: 3 to 5mm/sec
Trip range: > 5mm/sec
High vibrations in machine or bearings are due to;
1-Axial vibrations due to misalignment
2-Horizontal vibrations due to imbalance in machine
3-Vertical vibrations are due to looseness in foundation
bolts
4-Shaft run out
4-Operating the bearing
at excessive loads:
Excessive load on bearings leads to premature fatigue, over
loading creates other side problems like bearing overheating, damage to rolling
elements.
Brinelling occurs when loads
exceed the elastic limit of the ring material. Brinell marks show as
indentations in the raceways which increase bearing vibration (noise]. Severe
brinell marks can cause premature fatigue failure.
5-Overheating
Overheating & damage of the bearings is due to;
1-Lack of lubrication
2-Over lubrication
3-Improper cooling of bearings
4-Excessive loads
6-Smaller clearance between
rolling elements & race
Operating the boilers at higher temperature (>90 deg C
for ball bearings & sump cooling) will lead to annealing the races & rolling
elements that, eventually fails the bearings.
7-Miss alignment
Running the equipments at misaligned condition creates vibrations
& excessive loads on bearings in axial, vertical & horizontal directions
that causes bearing failures.
Misalignment also leads into failure of couplings &
equipments parts like seals, impellers, pulley etc
8-Frequent start &
stops of machine
Leads to jerk load on bearings & leading to reduction of
its life
9-Not following of
equipment/machine SOP:
If machine SOP (standard operating procedure) is being not followed,
then it could cause not only bearing failure but also machine other elements.
For example if pump is not
started with discharge valve closed or not stopped without closing discharge
valves, it could cause jerk loads on bearings & impellers. After some cycle
it will reflect it effect on misalignment, vibrations etc
10-Reverse rotation of
machine or reverse loading of bearing element:
Some machines & bearings are not recommended for reverse
rotation.
For example: Boiler feed pumps & screw compressors are
meant to rotate in only one direction
Also Angular contact ball bearings are meant to take load
only in one direction
11-Corrosion in
Bearings:
Red brown areas on balls, raceways, cages, or bands of ball
bearings are symptoms of corrosion. This condition results from exposing the bearings
to corrosive fluids or a corrosive atmosphere. The usual result is increased
vibration followed by wear, with subsequent increase in radial clearance or
loss of preload. In extreme cases. Corrosion can initiate early fatigue
failures.
12-Loose & tight
fittings of bearings:
Fitting of bearings loose on shaft or loose in housing leads
to rotation of bearings outer race in housing, this causes rubbing &
bearing damage.
As like loose fitting, very tight fit can also cause
excessive load on rolling elements which eventually creates overheating &
vibrations
13-Entry of water in
bearings grease
14-Material or
manufacturing defects in bearings cause bearing failure as soon as it is been
installed.
15-Leakage current in
VFD motor bearings lead to bearing failure
16-Carrying out welding
near bearings or Plummer blocks without proper earthing can lead to
flow of currents through bearings, which ultimately causes bearing failure
CHAIN CONVEYOR MAINTENANCE GUIDE
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