fmea of steel transfer car

Failure Modes of

Steel Transfer Car at LD1

Ambarish AmbujMT(Technical) ’11

Guide: Kumar VarunSr Manager, LD1

Scheme of the Presentation

• Project Objectives and Achievements• About Steel Transfer Car• Failure Data• Failure Modes

– Mode 1: Wheel Assembly Damaged– Mode 2: Spring Assembly Damaged– Mode 3: Tie Rod Assembly Damaged– Mode 4: Derailment (Breakdown on 16th April ’12)– Mode 5: Brass Bush Failure– Mode 6: Axle Cracked

• Road Ahead

Project Objectives & Achievements

Objectives

1. To understand the steel transfer car

2. To collect the failure data and analyse it

3. To study different failure modes

4. To suggest measures to prevent failure

Achievements

1. Design and working of steel car understood

2. Failure data collected and analysed

3. Different failure modes studied and analysed

4. Preventive measures suggested for significant failure modes

About Steel Transfer Car

Function: Transfers Ladle containing Liquid Steel from Vessel

Area to Ladle Furnace AreaCapacity: 260t Weight: 100tNumber: 2Equipment Owner: MHS MechanicalDesigner: Design CellManufacturer: TGSDrive Mechanism: Motor Driven with Gear

Transmission


• Components:– Car Frame– Ladle Stool– Cable Mast– Wheel-Axle

Assembly– Spring Assembly– Motor– Gearbox


Wheel-Axle Assembly

Spring Assembly

Motor & Gearbox Assembly

Track Stopper

Failure Data

Date Problem Correction

04-05-2000East side Wheel collar got

deformed and its width became 258mm

Wheel assembly changed

27-07-2000West Side frame got damaged and wheel got jam as ladle got

through in the car

wheel assembly changed & frame repaired

09-02-2001West side frame got damaged as ladle punctured in the car

Frame repaired

North-east Spring assembly damaged

changed the spring assembly

Track stopper damaged Welding doneSouth-west Spring Assembly

damagedchanged the spring

assemblyTrack stopper damaged Welding done

All 4 spring assemblies brokenchanged the spring

assemblyWest side both top half bush

worn outchanged top half bush and

lubricated

Planned ShutdownWest side wheel assembly changed and housing slot

increased to 120 from 100

Fixed guide block found 7mm thinner (88 instead of 95mm)

All four fixed guide blocks changed

Maintenance Log: Steel Transfer Car #1

07-08-2009

04-06-2003

21-09-2002

28-06-2001

S No Component Failures % Occurrence1 tie rod assembly 13 28.262 wheel assembly 10 21.743 spring assembly 10 21.744 Brass Bush 5 10.875 gearbox 4 8.706 coupling 2 4.357 Axle 2 4.35

46

Failure Summary

tie rod assembly

28%

wheel assembly

22%

spring assembly

22%

Brass Bush11%

gearbox9%

coupling4%

Axle4%

Failure Data

020406080

100120140160180

Risk

Prio

rity

No

Failure Mode RPNwheel assembly 175spring assembly 150tie rod assembly 120

Derailment 72Axle 48

Brass Bush 45gearbox 32coupling 24

Show Calculation

SOD Analysis

*Basis

Failure Mode Sever Occurr Detect RPNtie rod assembly 4 6 5 120wheel assembly 7 5 5 175spring assembly 6 5 5 150

Brass Bush 3 3 5 45gearbox 2 2 8 32coupling 3 1 8 24

Axle 6 1 8 48Derailment 9 1 8 72

SOD Basis

Rating occurrence Severity Detection10 45% and above breakdown >24hrs can not be detected9 40-45% breakdown >16hrs8 35-40% breakdown >8hrs can be detected in proper inspection7 30-35% shutdown, very high cost6 25-30% shutdown, high cost5 20-25% shutdown, medium cost observable trends in inspection4 15-20% shutdown, low cost3 10-15% shutdown, very low cost2 5-10% shutdown, major repair easily visible 1 0-5% shutdown, minor repair

Mode 1: Wheel Assembly Damaged

Wheel Collar Cracked

Foreign Particle (steel lump) on/near track strikes already flared wheel

Why Steel Lump Why Wheel flared

Liquid steel splash during

tapping, solidifies near

track

Wheel Pressing Against Track

Wheel Rubbing Against Frame

Adequate Track Cleaning

Misalignment Wheel-frame Clearance

15mm

Change Spring Design

Why

Why

Improper Wheel AssemblyFrame SkewedUnbalanced

force on wheels

Track Stopper Inadequate Improve Wheel Assembling SOP

Use sensor to stop car at right time and pneumatic stopper to absorb shock

Why

False Flange Contact

When the centre of the track and that of wheel do not match, car has tendency to turn

This causes collar to touch the track

Reaction force, causing flare in the wheel

wheel

track

Wheel Rubbing with Frame

• Marks on the frame, indicating the rubbing of wheel with frame

Wheel-Frame Clearance Inadequate

Clearance between the wheel and the plate supporting the car-support-spring is just 15mm

Spring Design Change required to increase the clearance

Increasing Wheel-Frame Clearance

Spring 1 Spring 2

Spring 3 Spring 4

Increase the gap between spring 3 & 4 so that the gap between spring 1 & 2 can be decreased, consequently increasing the clearance between wheel and spring

The Wheel Assembly

Critical dimension

Improper Assembly

Track Stopper is Problematic!

– If there is mass imbalance in the frame, axle will deviate from the position normal to track length to nullify the imbalance created by frame.

– If the track stopper is damaged, as the car approaches the stopper, one wheel strikes stopper before the other one, creating unbalanced force on wheels, deflecting the axle.

Consequently, wheels will not be aligned properly, touching the outer frame and rubbing against it

Changing the track stopper

• Existing track stopper welded at the end of the track• The car strikes stopper at significant speed• This can be avoided by stopping motor at right moment• Sensor can be used to trip the motor at exact time• Also, pneumatic stopper can be used in place of traditional stopper to

stop the car smoothly and absorb the shock

Rail Adhesion

• While starting the car, tangential force on the track-wheel contact greatly increases shear force.

• Fine sand provides some ‘lift’ which assists starting the car

Mode 2: Spring Assembly Damaged

Spring Assembly Damaged

Material Defect

Shock Load on Spring

Steel Lump on Track

Track Cleaning not Adequate

Install Track Cleaners

Car Strikes Track Stopper

Motor not Stopped at Right Time

Install Sensor & PLC to Stop

Motor at Right Time

Spring Under-designed

why

why

why

why

why

X

X

Mode 3: Tie Rod Assembly Damaged

Tie Rod Assembly Damaged

Material Defect

Shock Load on Spring

Car Strikes Track Stopper

Motor not Stopped at Right Time

Install Sensor & PLC to Stop

Motor at Right Time

Eliminate Tie Rod Assembly (Attach Drive

unit Base Rigidly to Frame)

Spring Under-designed

X

X

why why why

X

Mode 4: Derailment

As it Happened:• On 16th April ’12, around 7am, Steel Transfer Car #1 derailed from track. • Upon inspection of the site, track was found damaged.• Caterpillar, used to clean the track, uprooted the clamp and displaced track• Track was repaired and the Car was placed back on the track.• Vessel was down for 16hrs Reasons:• The person at job can’t see the shovel properly while track cleaning• The shovel of new caterpillar is long and sharp, increasing the chances of

damage to track.Preventive Measures:• Careful cleaning of the track. One person to assist (give directions) during

cleaning• Inspection of track after cleaning• Change in shovel design to minimise the chances of clamp uprooting

Mode 5: Brass Bush Failure

• Was a significant problem• The axle rubbed with top-

half bush resulting in wearing out

• Back in 2007, design changed. Two greasing points in top-half bush

• No failures after that

Mode 6: Axle cracked

• Occurred twice in 2003• Information not available on the causes• Defective Material or unbalanced forces might have been the

culprit• NDT has been installed • No failure in last 8 years

Road Ahead

• Change spring design to increase wheel-frame clearance• Install sensor and PLC to stop car at right time• Installation of pneumatic/hydraulic stopper• Change in shovel design of caterpillar• Create SOP for wheel assembly so as to avoid any imbalance• Create revised SOP for track cleaning and assign one helper

References

• Railway Track Engineering by JS Mundrey• Interface, The Journal of Wheel/Rail Interaction

– What Kind of Rail Materials Will Survive in Heavy-Haul Service? By James R. Hornaday, Jr.

– Understanding Stresses in Rails By Jude Igwemezie

Acknowledgements

• Mr. Kalyan Prasad, HOMM, LD1• Kumar Varun, Sr. Manager, LD1• S. Samantha, Foreman, MHS, LD1

Thank You