FAILURE OF LOCOMOTIVE WHEELS A Critical Analysis

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FAILURE OF LOCOMOTIVE WHEELSA Critical Analysis
Naresh Kumar Director (Vehicle Dynamic Group)
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Introduction

• Wheels It is one of most Critical Safety
  component of a Rolling Stock.
• Criticality increases owing to
• Most intensively loaded Not only static
  dynamic loading but also severe thermal stresses
  during braking.
• No component / system in parallel to wheels for
  support in case of a wheel failure.
• Requirements Hence, wheel design, manufacturing,
  quality control and maintenance to be of highest
  order.

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Wheel Basics

• Wheel Types
• Tyred Consists wheel centre with tyre shrunk fit
  on it. Tyres getting loose is serious problem
  with them. Not suitable for higher speeds.
• Tyre can be replaced when it wears out.
• Cast Manufacture started in 1960s in US. RDSO
  prepared specification for cast wheels in 1979
  RWF started its manufacture in 1980s using
  Griffin Technology.
• Benefit It is economical.
• They are normally used in coaches and wagons.
• Solid Monobloc A single piece wheel forged from
  wheel blank. Consists of hub, web/plate and rim.
  Suitable for high speed operation.
• Whole disc to be replaced when the wheel gets
  worn.

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Wheel Basics

• Understanding IR Locomotive Wheel
• Wheel Specification Metallurgy Stipulations
  for these wheels are laid down in IR Spec. IRS-R
  34.
• The carbon content is 0.57 0.67. They are
  micro-alloyed with 0.06 (max) Mo and 0.10
  (max) Vanadium as grain refiner.
• Wheel Rim Quenching and Residual Stresses
  Beneficial compressive hoop stresses in rim
  developed by rim quenching.
• Wheels in austenitic state are impinged with
  water in a rig fixture under controlled
  conditions on tread.
• These stresses resist initiation as well as
  propagation of service related fatigue cracks.

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Wheel Basics

• Stress Reversals in Rim Residual compressive
  stresses resist formation and propagation of
  fatigue cracks.
• If excessive heat is imparted to the wheel rim,
  reversal of these stresses from compressive mode
  to tensile takes place.
• Thus instead of preventing cracks, they can now
  accelerate the cracks or even help in heir
  propagation.
• Due to repeated brake application, especially on
  ghats, brake block friction heats up the wheel
  tread to such levels, where tread will have
  reduced yield strength and its plastic
  deformation occurs.
• Besides, heated tread tries to expand while
  colder inner rim and plate prevents it. Thus
  tread material comes under tension leading to
  stress reversal.
• It is a major cause for thermal cracks of wheels
  and failures.

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Wheel Basics

• Rim Hardness Rim hardness within prescribed
  range (300 341 BHN) is essential to ensure
  desirable life and reliability.
• Lesser hardness shall certainly give a
  comparatively less life.
• Also, lower yield strength due to wear of
  hardened rim in service can lead to increase in
  failure proneness.
• Fracture Toughness One of main characteristic of
  wheel reliability is critical factor of stress
  intensity i. e. K1C or fracture toughness.
• Measure of wheel capability to sustain shock
  loadings in service.
• Optimisation of heat treatment process to be done
  to achieve improved fracture toughness.
  Accelerated cooling of wheel steel within a
  cooling speed from 0.5 to 10ºC/second results in
  increase of both strength and fracture toughness.
• While increase in carbon content improves
  strength, it adversely affects K1C. Laboratory
  test results show that an increase of carbon
  content by 0.01 results into a decrease of K1C
  by approximately 2.
• Grain refiners help in improving fracture
  toughness.

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Wheel Failures

• Wheels are designed to give a trouble -
  free life till condemning limits are reached.
  But still, they have to replaced in service
  at mid-life as they are susceptible to
• Wheel flange tread wear since tractive
  braking forces are transferred through them
• Wheel diameter reaching the condemning limit due
  to wheel tread re-profiling
• Breakage from punch mark/sprag holes
• The formation of flat and martensitic heat
  affected zones on the running surface, which
  causes cavities and crack networks to develop on
  the tread
• Thermally and mechanically induced fatigue
• Plastic deformation

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Wheel Failures

• Wheels occasionally require to be replaced in
  mid-life for defects like excessive wear,
  breakage of rim, plate or hub, gauge widening
  etc.
• Instances of such out-of-course wheel
  replacements have gone up in recent years due to
  several operational causes / defects.
• To analyse wheel defects failures, following
  line of action was adopted
• Compile detailed database of defects failures
  from Zonal Railways.
• Conduct examination at site followed by MC
  investigations at RDSO.
• Putting forward specific technical logistic -
  related recommendations to achieve failure-free
  performance.

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Wheel Failures

• Wheel failure analysis was undertaken on
  following lines to study the failure pattern,
  probable causes and zero-in on remedial actions
• Year wise failures
• Cause wise failures
• Wheel make wise failures
• Effect of composite brake blocks

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Wheel Failures Year wise
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Wheel Failures Year wise
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Wheel Failures Year wise

• A very high percentage (51) of all the
  locomotive wheel failures in last 53 months have
  occurred in 2007.
• A major chunk of locomotive wheel failures have
  occurred in WDP4 locos.
• 38 of total wheel failures reported in last
  four years have occurred in WDP4 locomotives, out
  of which, 37 failures occurred in 2007 and 2008
  till 16th April. All WDP4 locomotives are fitted
  with 'High Friction' composite brake blocks.
  Also, they normally operate in ghat section.
• 24 of total wheel failures reported in last four
  years have occurred in WAG7 locomotives.
• 63 of total wheel failures reported in last four
  years have occurred in WDP4 WAG7 locomotives.
• Total wheel failure on goods locomotives (WDG3A,
  WAG5 WAG7) contributes 47 of total wheel
  failures of last 4 years.

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Wheel Failures Cause wise
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Wheel Failures Cause wise
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Wheel Failures Cause wise

• Failure from punch mark was a major
  contributor till 2005.
• Place of stamping changed from rim to hub
  which is less stressed area.
• FEA of wheel was undertaken to ascertain
  this less stressed area.
• In 2007 2008, a shift in failure pattern to
  thermal defects was noted in 2007. This was
  also ascertained in MC Investigations.
• This was the time when CC 8 CC 10
  decision was implemented.
• Also, indigenous composite brake blocks
  including ones manufactured by Mysore
  Workshop were widely adopted on locomotives.

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Wheel Failures Make wise
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Wheel Failures Make wise
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Wheel Failures Make wise

• Since the total population of a particular make
  could not be determined easily, this data
  should be taken as indicative only.
• Only 87 wheels out of 112 cases reported
  could be deciphered for their make.
• The instances of failure of DSP wheels on all
  types of locomotives, Bonatrans make on EMD
  locomotives and Ferro Steel make on ABB
  locomotives stand out.
• It is clear from this data that only the wheels
  supplied by M/s Sumitomo, who are also the OEM of
  these wheels for EMD locomotives, as approved by
  M/s EMD, have worked satisfactorily with a very
  low rate of failure.

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Wheel Failures Composite Brake Blocks

• The next step was to examine the use of composite
  brake blocks on these locomotives. It was found
  that initially only the OEM Cobra make brake
  blocks were in use. Subsequently, Rane make brake
  blocks were used after due qualification by RDSO.
  At the same time, Mysore Workshop make brake
  blocks were also introduced by SW Rly, although
  the same had failed the qualification testing at
  RDSO.
• The control on coefficient of friction of these
  brake blocks, inter alia, is very important,
  failing which the wheel may get subjected to very
  high brake force and excessive thermal loading.
• Poor quality of composite brake blocks can cause
  severe thermal problems.

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Wheel Failures Composite Brake Blocks

• RDSO also undertook a special surprise check on
  samples of composite brake blocks used on other
  locomotives two samples of all makes were picked
  up randomly from locomotive sheds and subjected
  to full product testing in the Brake Dynamometer
  laboratory at RDSO.
• It was very disturbing to find that the samples
  of M/s Escorts and M/s Hindustan Composites
  faired very poorly, with a very high percentage
  of readings showing coefficient values above the
  specified band.
• It is indicated that poor quality control on
  locomotive composite brake blocks could well be
  one of the reasons for this spurt in failure of
  wheels due to thermal loading.

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Recommendations to Redress Problem of Wheel
Failures

• The following action is proposed in respect of
  composite brake blocks / brake system
• Strict control should be exercised on the quality
  of composite brake blocks now being used in
  locomotives. The coefficient of friction of
  composite brake blocks should strictly be within
  the prescribed limits. It should be ensured that
  the composite brake blocks are procured as per
  relevant RDSO specifications from RDSO approved
  sources only.
• Discontinue use of Mysore make brake blocks.
• Reintroduce Cobra make brake blocks as the
  majority supplies(being OEM for GM locomotive),
  particularly on EMD locomotives, with only
  limited procurement form M/s Rane, for EMD
  locomotives.
• Conduct stringent audit of the manufacturing
  quality and product compliance for various
  sources of brake blocks.
• Reduction in brake cylinder pressure during
  automatic brake application

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Recommendations to Redress Problem of Wheel
Failures

• To study the effect of reduction in brake
  cylinder pressure on wheel temperature rise and
  Emergency Braking Distance (EBD) during
  automatic braking, simulation studies and FE
  Analysis have been undertaken considering one
  WDP4 locomotive and 26 LHB coaches.

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Recommendations to Redress Problem of Wheel
Failures

• It must be ensured that dynamic brake is
  available and kept effective in all locomotives.
  Blending of pneumatic brakes with electric
  brakes to be ensured, as in case of WDP4,
  which minimizes the use of tread brakes. Similar
  project is in hand for WDM3D locomotives for
  incorporation of CCB along with blended brakes.
• RDSO has taken up pioneering project of
  developing an S-shaped wheel as and analysis had
  shown that the thermal and mechanical stress
  bearing capability of these wheels would be 50
  15 more respectively compared to straight plate
  wheels.
• Procurement of wheels from manufacturers with
  questionable field performance should be done
  with due care.
• Hence, it is recommended that a structured system
  of vendor approval for wheels be introduced like
  the procedure followed for other safety
  critical items, a list of duly approved
  manufacturers to be identified from which the
  wheel supplies can be obtained.

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Recommendations to Redress Problem of Wheel
Failures

• Due care to be taken during bogie
  maintenance as follows
• Proper Brake Block alignment clearances to be
  ensured.
• Axle box clearances to be maintained within
  prescribed limits.
• Bearing clearances should be maintained as
  prescribed.
• End cap bolts of bearings to be tightened with
  torque wrench as recommended ensuring proper
  clamping forces on bearing components and proper
  rolling of wheels.
• Any welding work on locomotive to be undertaken
  only after providing a conductive path for return
  current above the axle box level to avoid any
  possibility of bearing failures due to weld
  pitting on rollers or races.

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Recommendations to Redress Problem of Wheel
Failures

• Use of Disc brakes
• WAP5 are having disc brakes and
  conveniently giving a wheel life of not
  less than 6 7 years.
• No wheel failures have been reported in
  WAP5 since introduction on IR.
• It is a mandatory requirement for speeds
  above 200 kmph.

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Conclusion

• Some of these important recommendations have
  already been implemented on IR since August
  2008.
• Results can be tabulated as follows

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Conclusion
Thus, it can be seen that with implementation
of many of these recommendations, the wheel
failures in locomotives have considerably come
down since August 2008. Thanx