kiln 5 drive system preliminary root cause analysis_rev2

Kiln 5 Drive System FailureRoot Cause Analysis

October 2013

By Thebe Setshedi

Introduction - Background

Apr 15, 2023 Thebe Setshedi 2

Introduction - Background


1. Main motor2. Main gearbox3. Auxiliary motor4. Auxiliary gearbox clutch unit5. Pinion gear6. Pinion coupling7. Girth gear

Introduction – Failure Background


1. Main motor2. Main gearbox3. Auxiliary motor4. Auxiliary gearbox clutch unit (SOUTH)5. Pinion gear6. Pinion coupling (NORTH)7. Girth gear

Problem Description


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


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




Inner ring webs of the South coupling fractured



Auxiliary gearbox seizes



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


System Operation


Brakes

Motor Fluxing Drive Program

System Operation


Auxiliary motor

MainMotor

OverrunsHelps in braking the kiln

System Operation – Truths & Myths


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


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


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


Mode of Failure Analysis – Overrunning clutch/gearbox


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


Main drive speed

Auxiliary brakes

Main brakes

Final Root Cause


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


Conclusion and recommendations - Torque


Root Cause : Brakes failure – brake pads/ brakes calibration

Conclusion and recommendations


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.


Question& Answers

Seconds From Disaster


kiln 5 drive system preliminary root cause analysis_rev2

Documents

thebe setshedi

kiln drive system

auxiliary drive system

auxiliary brakes

kiln shell

main coupling auxiliary

main motor operation

auxiliary drivebrakes