1. Kiln 5 Drive System Failure
Root Cause Analysis
October 2013
By Thebe Setshedi

2. Introduction - Background
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3. Introduction - Background
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1. Main motor
2. Main gearbox
3. Auxiliary motor
4. Auxiliary gearbox clutch unit
5. Pinion gear
6. Pinion coupling
7. Girth gear

4. Introduction – Failure Background
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1. Main motor
2. Main gearbox
3. Auxiliary motor
4. Auxiliary gearbox clutch unit (SOUTH)
5. Pinion gear
6. Pinion coupling (NORTH)
7. Girth gear

5. Problem Description
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What Kiln drive system failed
When On the 26th
September 2013 around 23:00
Where Kiln 5 main coupling & auxiliary clutch
Who Kiln field operators and maintenance team
Why The was an overload on the system
How Coupling fracture and auxiliary seizing

6. System Operation
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Parameter Operating value Maximum Value
Kiln operation speed-main motor 0.33 rpm 0.9 rpm
Kiln speed - Auxiliary motor (1000rpm) 0.024 rpm 0.024 rpm
Kiln feed rate (Ore) 32 tons/hr. 34tons/hr.
Kiln feed rate (coal + dolomite) 16 tons/hr 17 tons/hr
Kiln Motor current output 2850 kW 3050 kW
Main motor operation speed 350 rpm/ 36.7 rad/s 1000 rpm
Main motor torque 1700 N.m 1900 N.m
Environment Temperatures 45 deg. Cel. 65 deg. Cel.

7. Investigation – Failed Components
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8. Investigation – Failed Components
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9. Investigation – Failed Components
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Inner ring webs of the South coupling fractured

10. Investigation – Failed Components
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Auxiliary gearbox seizes

11. Investigation – Failed Components
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Broken auxiliary south brakes –
brake pads shoe broken
Auxiliary south brake
actuators not functioning

12. Investigation - Aspen Results
• Evidence that the motor is not responding to the drive, feedback is not approaching
reference speed for hours – 14/09/2013 from 12:00 – 16:00
• Signs of a kiln slipping back more often
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13. System Operation
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Brakes
Motor Fluxing
Drive Program

14. System Operation
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Auxiliary
motor
Main
Motor
Overruns
Helps in braking the kiln

15. System Operation – Truths & Myths
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Myth : Brakes are designed to prevent the kiln from slipping back
Truth : The electric drive should be programmed such that it slows down the kiln to
a stop, the brakes are just there to hold the kiln in a stationary position – isolation.
Myth : Auxiliary drive/brakes are to act as anti-run system to prevent the kiln from
running back.
Truth : The auxiliary brakes are just there to isolate the auxiliary drive system.
Myth : The drive system is initially designed such that the auxiliary drive is to be a start
– up for the main drive.
Truth : The primary function of the auxiliary drive is to be able to empty the kiln or
slowly rotate the kiln in a case of main drive failure to prevent the kiln shell from
permanently deforming.

16. Why is the Kiln Slipping back
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3000 N.m 3000 N.m
Braking torque needed by
brakes to stop the kiln from
running back –
Assuming 20 deg. burden angle
Neglecting roller friction
Running
back inertia
Current braking torque on each
main brake = 1000.Nm
Braking torque from each
auxiliary brake = 1000 N.m
Electric drives not fluxed
enough to stop the kiln by
slowing it down.

17. Mode of Failure Analysis - Coupling
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Function : Transmit Torque – Transmit energy
Failure : Inner ring webs fracture
FACT : for fracture to happen there must have
been a resultant force beyond what the coupling
can withstand
FACT : This unwanted force can only come from
the difference in torque output of the motors or
change in the weight of the kiln
Deductions : The inner ring was
receiving torque from the motor but the
outer ring was completely stationary
indicating breaking effect.
Coupling
Kiln

18. Mode of Failure
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Obstruction on the 2 pinion
1. Auxiliary motor turning
in the opposite
direction
2. Auxiliary clutch failure
Gearbox Failure
Brakes failure
Motor Failure
Stationary – No energy flow
Energized but not
necessary in motion

19. Mode of Failure
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20. Mode of Failure Analysis – Overrunning clutch/gearbox
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Function : Transmit Torque in one direction and
overruns in another.
Failure : Clutch not overrunning, completely seized,
not even transmitting torque in any direction
FACT : This clutch is NOT designed to run backwards
by the main motor, it is NOT an anti-run back clutch.
FACT : The anti-run back properties of the clutch is
provided by the auxiliary brakes, if the brakes fails,
then the clutch fails.

21. Aspen Results
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Main drive speed
Auxiliary brakes
Main brakes

22. Final Root Cause
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Coupling fracture
Base bolts fracture
Girth gear cover
lifts up
One side (South) of
the drive is stationary
while the north side
is trying to turn
Auxiliary gearbox
is damaged –
bearing seize
Kiln runs/slips
backward when
stopped
Programming on
the drive
Programming on
the drive
WHY
WHY
WHY
WHY

23. Actions
Action Objective Responsible
Person - Date
Put back the auxiliary drive, For more effective braking effect – half Done Danie van der
merwe
Draft a standard for brakes inspection
and also an inspection plan. Strength
the brakes to counteract enertia.
To make sure that the brakes are forever in
good condition, this will prevent the kiln from
running back.
Thebe
30 Nov 2013
Determine the allowable torque that
the entire system can withstand
without interrupting kiln normal
operation.
Help in understanding why certain
components fail and how we can protect
them.
Thebe
30 Nov 2013
Program the drives such that they
don’t allow a torque output high
enough to damage any component in a
system, and make sure that drives are
fluxed to slow a kiln to a stop.
This will trip the kiln before the motor produce
enough torque to damage any component in
the system
Solly Moroosele
-
Design a mechanical fail safe
mechanism
This mechanism will minimize damages by
failing first in a case of system torque
overload.
Thebe
15 Dec 2013
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24. Conclusion and recommendations - speed
Copyright © ArcelorMittal Mar 23, 2015 Thebe Setshedi 24
Root Cause : Brakes failure – brake pads/ brakes calibration

25. Conclusion and recommendations - Torque
Copyright © ArcelorMittal Mar 23, 2015 Thebe Setshedi 25
Root Cause : Brakes failure – brake pads/ brakes calibration

26. Conclusion and recommendations
Copyright © ArcelorMittal Mar 23, 2015 Thebe Setshedi 26
Root Cause : Programming on electric drives.
Recommendation : it is also necessary that the auxiliary system be
put back - if we lose the main drive, the kiln will be forced to wait
longer in one position and permanently deform the kiln and induce
extra torque and eccentricity on the rotation.

27. Copyright © ArcelorMittal Mar 23, 2015 Thebe Setshedi 27
Question
& Answers

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29. Seconds From Disaster
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