bearing and its failure

1. GUIDED BY – SUBMITTED BY-
DR. R.K. PATEL ABID ALI (2016PD13)
M.TECH
MNNIT ALLAHABAD

2. Introduction
 Bearing is a mechanical element that permits relative motion
between two parts, such as shaft and housing with minimum
friction.
 The bearing holds the shaft or axle in the correct position.
 Bearing take up the forces that act on the shaft or axle and
transmits them to the foundation or the frame. Bearings are
used as a mechanical component to transfer the power and to
move a certain part.

3. Types of bearing
 Bearings can be classified into two major groups, namely,
Rolling Contact Bearings and Sliding Contact Bearings.
 Apart from this Magnetic bearings and Jewel bearing are the
other type of bearing.

4. Rolling Contact Bearings
 A bearing’s smooth performance is assured by a combination
of four basic working parts
• Outer race (also called outer ring or cup)
• Inner race (also called inner ring or cone)
•Rolling elements (either balls or rollers)
• Separator

5. Rolling Contact Bearing Failures
Rolling contact bearing failures are divided into two categories
 Failure relating to bearing rings
 Failure relating to bearing cages
Failure relating to bearing rings
1. Wear damage
2. Smearing
3. False brinelling
4. Damage due to Corrosion

6. Wear damage
 Wear may, occur due to presence of foreign particles into the
bearing or when, the lubrication is unsatisfactory.
 Small indentations around the raceways and rolling elements.
Dull, worn surfaces.
 Cause : Ineffective seals, contaminated Lubricants.
 Action: Keep workshop clean and use clean tools, improve the
sealing

7. Smearing
 When two inadequately lubricated surfaces slide against each
other under load, material is transferred from one surface to the
other. This is known as smearing.
 Cause: Sliding/rolling under heavy axial loading and with
inadequate lubrication.
 Ring rotation relative to shaft or housing.
 Action: More suitable lubricant, Improve the bearing
clearance, Improve the sealing mechanism

8. False Brinelling
 False brinelling is a bearing damage caused by fretting, that
causes imprints that look similar to brinelling, but are caused
by a different mechanism.
 Shinny marks and recesses on the raceway surface
 Cause: Vibrations in stationary machines – leads to micro-
motion in the contact areas
 Action: provide vibration
Insulation to machine

9. Damage due to Corrosion
 Rust will form if water or corrosive agents reach the inside of
the bearing.
 Cause: Entry of corrosive gas or water or Improper lubricant.
 Actions: Improve the sealing mechanism, Anti-rust treatment
for periods of non-running part of bearing

10. Damage relating to bearing cages
1. Cage wear due to starved lubrication and contamination
2. Wear in ball bearing cages due to tilting
3. Cage fracture

11. Cage wear due to starved lubrication and contamination
 Wear in the pockets, Poor rolling element guidance due to
wear.
 Cause: Lubricant contaminated with hard foreign particles
Too little or unsuitable lubricants.
 Filter lubricants.

12. Wear in ball bearing cages due to tilting
 Bearing rings tilting towards one another led to high
constraining forces between balls and cage which, in turn, led
to fracture.
 Cause: Excess misalignment of the bearing rings to one
another.
 Action: Avoid tilting as much as possible, Select self-aligning
bearings or bearings

13. Cage fracture
 Fracture of cage side edges.
 Causes: Mounting damage,
Exceeded the permissible speed,
Poor lubrication,
Moment load too high or tilting of ball bearings.
Action: Mount carefully, Avoid misalignment or shaft deflection,
Increase lubricant flow

14. Sliding Contact Bearings
 The sliding contact bearings having surface contact between
two contacting surfaces. Type of sliding bearing as shown in
chart Sliding
contact
Bearings
According to
Load
Axial load or
Thrust Bearing
Pivot Bearing
Flat pivot
Conical pivot
Collar Bearing
Flat collar
Conical collar
Radial load or
Journal bearing
According to
Lubrication
Thin film Thick film
Hydrodynamic
Bearing
Hydrostatic
Bearing
Solid film

15. JOURNAL BEARING FAILURES
1. Bearing Seizure
2. Wear
3. Oil Whirl Instability
4. Oil Whip Instability

16. Bearing Seizure
 Seizure is the stopping of relative motion as a result of inter-
facial friction. As a result of seizure, the operation of the
system is interrupted and the contacting elements are damaged.
 Causes:
a) loss of clearance due to thermal expansions of the journal
and bearing.
b) loss of clearance due to build-up of wear debris.
c) metal-metal contacts.

17.  Controlling parameters
a) Surface temperature and Interface pressure.
b) Temperature due to frictional heating.
c) Clearance change due to thermal expansion.

18. Wear
 The most common root cause of machine wear and failure is
lubricant contamination by particles and moisture.
 Abrasive particles such as dirt, dust, and debris slowly rub
away critical machine surfaces until clearances are breached
and the machine fails.
 Corrective measure: Dirt and water are the primary root
causes of machine and lubricant degradation. Monitoring them
on-site ensures that they are controlled.

19. Oil Whirl Instability
 Oil whirl is probably the most common cause of instability in
hydrodynamic journal bearings.
 Causes : due to external vibratory forces transmitting into the
unit or from sources within the machinery itself.
 An increase in oil pressure or oil Temperature
 Excessive bearing wear or clearance.

20. Corrective Measure
Temporary corrective measures
 Changing the temperature of the oil (thus, the oil viscosity).
 Grooving the bearing surface to disrupt the lubricant wedge.
 Changing the oil pressure.
 Permanent corrective measures
 Installing a new bearing shell with proper clearances
 Completely changing the bearing type to oil film bearings that
are less susceptible to oil whirl.

21.  The tilting pad bearing is a good choice because each segment
or pad develops a pressurized oil wedge, tending to center the
shaft in the bearing and thereby increase the system damping
and overall stability.

22. Oil Whip Instability
 Oil whip occurs during the later stages of an oil whirl when the
oil whirl frequency coincides with the system’s natural
frequency. At this point, the oil whip frequency remains the
same, independent of the rotor rpm.
 The amplitude will be larger than the amplitude noted during
oil whirl because the shaft uses up the entire bearing clearance,
as an oil wedge can no longer be established by the rotor and
the shaft is in direct metal-to-metal contact with the bearing.

23. Research Work in Bearing
 Oil lubricated bearings have been widely used in variety of
turbo machinery, though it has its own limitations such as
thermal degradation of oil over temperature, complicated
oil lubrication system and their maintenance.
 Air foil bearing come into action. . Absence of external
pressurizing and lubricating system makes the system light and
compact. Simple construction, low friction drag and reliability
at high speed operations are few more advantages of the foil
bearings.

24.  Microturbomachinery has demanded light weighted, compact,
extreme temperature and high speed operation.
 Air foil journal bearing:
 Air foil journal bearing self-acting hydrodynamic fluid film
bearings uses air as lubricant which is not degraded by extreme
temperatures.

26.  Air Foil Thrust Bearing

27. Conclusion
 The failure modes that cannot be fully avoided is to be
: Wear in both rolling and sliding contact bearing.
 Air Foil bearing gives a new ideas of bearing where
pressurising and lubricating systems are absent.
But it also have some problem
 Problem related to cooling of upper foil of Air foil
bearing.
 Not suitable for large thrust load.
 And problem related to designing of corrugated shape
in bump foil.

28. Bump foil

29. References
 ‘Seizure failure of journal-bearing conformal contacts’ by Q Wang -
Wear, 1997 – Elsevier.
 ‘Journal Bearing Failure Monitoring (JBFM)’ by Y Zhang -
Encyclopedia of Tribology, 2013 - Springer.
 Dykas, B., Bruckner, R., DellaCorte, C., Edmonds, B., and Prahl, J.,
2008, "Design, Fabrication, and Performance of Foil Gas Thrust
Bearings for Microturbomachinery Applications," ASME Turbo
Expo 2008, Berlin, Germany, June 9-13, ASME Paper number
GT2008-50377.
 “Failure Analysis Of Bearing In Wind Turbine Generator Gearbox”
by Sanskar S., Nataraj M. and Prabhu Raja V. in Journal of
Information Systems and Communication Vol-III, 2012.
 “Bearing Failures and its Causes” published by SKF bearings
Sweden