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Kiln 5 Drive System FailureRoot Cause Analysis
October 2013
By Thebe Setshedi
Introduction - Background
Apr 15, 2023 Thebe Setshedi 2
Introduction - Background
Apr 15, 2023 Thebe Setshedi 3
1. Main motor2. Main gearbox3. Auxiliary motor4. Auxiliary gearbox clutch unit5. Pinion gear6. Pinion coupling7. Girth gear
Introduction – Failure Background
Apr 15, 2023 Thebe Setshedi 4
1. Main motor2. Main gearbox3. Auxiliary motor4. Auxiliary gearbox clutch unit (SOUTH)5. Pinion gear6. Pinion coupling (NORTH)7. Girth gear
Problem Description
Apr 15, 2023 Thebe Setshedi 5
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
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.
Investigation – Failed Components
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Investigation – Failed Components
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Investigation – Failed Components
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Inner ring webs of the South coupling fractured
Investigation – Failed Components
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Auxiliary gearbox seizes
Investigation – Failed Components
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Broken auxiliary south brakes – brake pads shoe broken
Auxiliary south brake actuators not functioning
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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System Operation
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Brakes
Motor Fluxing Drive Program
System Operation
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Auxiliary motor
MainMotor
OverrunsHelps in braking the kiln
System Operation – Truths & Myths
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Myth : Brakes are designed to prevent the kiln from slipping backTruth : 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.
Why is the Kiln Slipping back
Apr 15, 2023 Thebe Setshedi – 12 months Appraisal 16
3000 N.m 3000 N.m
Braking torque needed by brakes to stop the kiln from running back – Assuming 20 deg. burden angleNeglecting 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.
Mode of Failure Analysis - Coupling
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Function : Transmit Torque – Transmit energyFailure : Inner ring webs fractureFACT : 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
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
Mode of Failure
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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 directionFACT : 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.
Aspen Results
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Main drive speed
Auxiliary brakes
Main brakes
Final Root Cause
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Coupling fracture Base bolts fractureGirth 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 driveProgramming on the drive
WHY
WHY
WHY
WHY
ActionsAction Objective Responsible
Person - DatePut 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.
Thebe30 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.
Thebe30 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.
Thebe15 Dec 2013
Apr 15, 2023 Thebe Setshedi 23
Conclusion and recommendations - speed
Copyright © ArcelorMittal 15 Apr 2023 Thebe Setshedi 24
Root Cause : Brakes failure – brake pads/ brakes calibration
Conclusion and recommendations - Torque
Copyright © ArcelorMittal 15 Apr 2023 Thebe Setshedi 25
Root Cause : Brakes failure – brake pads/ brakes calibration
Conclusion and recommendations
Copyright © ArcelorMittal 15 Apr 2023 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.
Copyright © ArcelorMittal 15 Apr 2023 Thebe Setshedi 27
Question& Answers
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Seconds From Disaster
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