Dr Stephen Marich - Marich Consulting Services - Module 4: Wheel and rail profiles

Wheel/Rail Interface Forum – Brisbane, May 2014

Wheel and Rail Profiles

The Wheel/Rail Interface


The Basics

For new wheels in equilibrium position (wheelset centre = track centre), R is generally 0

Rolling Radius Differential (R)

R = RLR – RRR = 0

Rail C/L Rail C/L

Left Rail Right

Rail

RLR RRR

Track C/L

Wheelset C/L


The Basics

C/L of Track

Right Rail (Low)Left Rail (High)

RhrRlr

C/L of Wheelset

y

Rolling Radius DifferentialHowever, as wheelset moves towards one rail (Left), RLR > RRR

When RLR > RRR wheelset tries to move back to equilibrium

position (R = 0) Wheelset Steering (Creep Forces)


The Basics

Conicity

Conicity () of wheel = angle between wheel tread and horizontal axis of axle

For cylindrical

wheel = 0

For conical tread

wheel with 1:20

taper = 0.05

Horizontal Line of

Axle

Vertical1:20 Conical Wheel

Tread

Rail Centre

Line

Conicity (1:20)


The Basics

As wheels and rail become worn or special tread profiles areused, the conicity will depend on the lateral location of thewheelset relative to the rail. In this case, the term “effectiveconicity” (eff) is used.

Effective Conicity

C/L of Track

Right Rail (Low)Left Rail (High)

RhrRlr

eff

C/L of Wheelset

y

eff = 0.5 R/y

R = Rhr - Rlr


Rolling Radius Differential Vs Effective Conicity

An increase in R leads to improved wheelset steering in curved track and hence reduced wear but higher creep forces and hence more surface defects.

An increase in R also leads to an increase in eff.

High eff leads to wheelset/bogie instability in shallow curves and tangent track (hunting), which reduces the safe operating speed.

Hence, sharp curves need higher R/higher eff and shallow curves/tangent track need lower R/lower eff..

Conflicting requirements achieved by modifying the rail profiles by grinding

R = Rhr – Rlr eff = 0.5 R/y

The Requirements


The Requirements

As R increases, steering increases.

Hence, sharper curves need wheel/rail profiles that give higher R.

Right/Low Rail

Conical

Wheel

Profiled or worn

Rail/Wheel

Profiled Rail

and Wheel

Track Centre

Wheelset Lateral

Position (y)

Rolling Radius

Difference (r)

Flanging

Left/High Rail

Curved Track

Requirements

Tangent Track

Requirements

Curved Track

Requirements

Tangent Track

Requirements


The Real Life

New Rail/ New

Conical Wheel

High Rails Low Rails

New Rail/ Flange

Worn Wheel

New Rail/ Tread

Worn Wheel

Worn Rail/ Flange

Worn Wheel

Worn Rail/ Tread

Worn Wheel

RhrRlr

RhrRlr

Rhr

Rlr

RhrRlr

Rhr

Rlr

Wide range of R

in established

Systems

Analysis needs to

be representative


Wheel/Rail Profiling

Aim to control R, eff and contact characteristics,

and hence wheelset steering characteristics,

dynamics and contact stresses.


The General Requirements

The wheel and rail profiles

should have conformal contact

to reduce the contact stresses.

Aim to avoid field side contact,

which leads to high contact

stresses and plastic flow.

Also produces rail head rotation

and hence reduced allowable

rail head wear limits.



Field Side Contact – Function of Both Rail and Wheel

Profiles and Maintenance

Rail Rotation

Tread Hollowing

Low Rail Contact

Eccentric Load

Central Contact is

Best

Higher Critical

Stresses



High leg of relatively sharp curves:

Relatively conformal contact between

rail gauge corner and wheel throat

extending almost to the centre of the

rail to:

Reduce contact stresses (hence

RCF)

Reduce two point contact (hence

wear)

Increase rolling radius differential

(hence improve wheelset steering)

A minor undercut in gauge corner

region may also be applied to

reduce contacts (care is required

since excessive undercut will lead

to high wear rate)

Large

Conformal

Contact

Low Stresses


All other rails:

Relatively conformal contact near the centre of the rail to:

Reduce contact stresses (hence RCF)

Avoid gauge corner contact (hence wheelset/bogie stability)

Avoid field side contact (hence reduce rotational bending in the rails)

Overall contact width of 25mm to 40mm (depending on wheel loads)



The General Steps

Choose/Design Appropriate Wheel Profile:

Conical – wheelset/bogie stability and reduced RCF.

“Worn” – improved wheelset/ bogie steering and hence reduced rail and wheel wear.

Determine flange thickness required to give appropriate flange clearance.

Design suitable rail profiles.

Implement and monitor general wheel/rail contact characteristics and fine tune rail profiles to account for wheel wear and rail deformation.

Increased

Steering

Narrow Contact – Needs Broadening


The Flange Thickness

70 60 50 40 30 20

10 0

-40 -30 -20 -10 0 10 20 30 40

a x x

b c c 16mm

a = wheelset back to back (say 1358mm)

h = track gauge (say 1435mm)

c = flange thickness (say 29mm)

x = flange clearance (9.5mm)Best flange clearance = 9mm to 12mm

Lower values increase dynamic lateral response.

Higher values increase angle of attack and risk of field side contacts.


The Implementation

Now accepted practice in majority of Systems

Rail Grinding


The Monitoring – Manual


The Monitoring – Automatic

Laser based Systems.

Currently mostly used for general wear analysis, for example:

Rail gauge face and wheel flange wear.

Rail running surface wear.

Wheel tread hollowing.


If You Get It Right

Improve wheel/rail interaction characteristics.

Control of corrugations, dipped welds and joints.

Control of RCF and other defects.

Increase allowable rail wear limits.

Improve wheelset/bogie dynamics (hunting).

Reduce adverse influence of „rogue‟ wheels/bogies.

Control track gauge.

Reduce noise/vibrations.

Moderate adverse influence of higher axle loads.


The Benefits – Wear

For poor profiles note:

Increased wear rate (x 2-4)

Increased curve radius of flanging wheels

General Effect of Profiles on Flange Energy (Wear),

Lubricated

0

20

40

60

80

100

120

140

160

180

200

200 300 400 500 600 700 800 900 1000

Curve Radius (m)

Fla

ng

e E

nerg

y (

Wear)

(N

m/m

)

Narrow Conformal Gauge Corner Contact

Broad Conformal Gauge Corner Contact

Mild Gauge Corner Undercut

Heavy Gauge Corner Undercut


The Benefits – Allowable Wear Limit

C/L

22.5mm15mm

Offset vertical loading –

15mm from the rail C/L is indicative of

well maintained rails and wheels

22.5mm from the rail C/L is indicative

of poorly maintained rails and wheels


The Benefits – Allowable Wear Limit

Note: Control of wheel/rail contact

increases allowable rail head wear limit in SC rails from 27% to

45%

Effect of Wheel Load Eccentricity on Rail Stresses and

Wear Limits

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Percentage Rail Head Loss

Str

ess (

MP

a)

L/V=0.2, @ 15mm load eccentricity

L/V=0.2, @ 22.5mm load eccentricity

347 MPa, Stress Limit

for SC Rails


0.0

0.5

1.0

1.5

2.0

2.5

40 45 50 55 60 65 70 75 80 85 90

Speed (kph)

Conformal Contact

Two Point Contact

Conformal Contact + Friction Mod

Hu

nti

ng

Severi

ty I

nd

ex

Severe

Hunting

The Benefits – Reduced Hunting


Getting it Wrong

Insufficient metal removal from contact surface (required to control surface defects).

Out of tolerance profiles.

Excessive undercutting in the rail gauge corner region.

Excessive time between maintenance cycles in both wheels and rails.

Insufficient time for completion of maintenance (poor planning).

Introduction (rather than removal) of surface irregularities.

Note: Profiles can last a long time and hence the consequences


Surface Condition After Grinding


Concluding Remarks –

Wheel/Rail Profiles

Wheel and rail profiles have a very substantial influence on a wide range of factors, including:

Wheel and rail lives.

Defect development

Noise and vibration.

Wheelset and bogie dynamics (and hence operating speeds).

The main stages of establishing the best profiles strategy are:

Identify main requirements:

Wear and Lubrication Vs Defects and Stability

Design of the profiles (consider actual track/vehicle condition)

Implementation, monitoring of performance and fine tuning.

Planning of the required rail maintenance activities.

Commitment to a long term maintenance strategy.

Dr Stephen Marich - Marich Consulting Services - Module 4: Wheel and rail profiles

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Transcript of Dr Stephen Marich - Marich Consulting Services - Module 4: Wheel and rail profiles