adhesion

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Recap

In the last class you have learnt about

• Mechanics of power transfer from motor to driving wheel

• Derivation of tractive effort

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Objectives

On completion of this topic you would be able to know

• Define Coefficient of adhesion

• Typical values of Coefficient of adhesion

• The factors affecting the Coefficient of adhesion

• Methods of improving Coefficient of adhesion

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Coefficient of Adhesion

• When the torque developed by the traction motor is more, the

tractive effort at the driving wheels is also more

• This relation holds good only up to certain extent after which

any increase in motor torque does not increase the tractive

effort but causes driving wheels to slip

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• It has been found that maximum value of tractive

effort at which driving wheels will not slip depends

on the adhesive weight over the driving wheels


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• The weight of the train on the driving axles only is called

adhesive weight

• The gross weight of the train includes weight of the

locomotive to be moved on the track

Adhesive Weight

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Coefficient of adhesion may be defined as

“the tractive effort needed to slip the driving wheels to the adhesive weight”

It is represented by symbol μ

Tractive effort to slip the wheels

μ =

Adhesive weight


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Typical Values of μ

The values of coefficient of adhesion are

μ= 0.25 to 0.33 for clean dry rails

= 0.15 to 0.2 for wet or greasy wheels

= 0.2 to 0.25 for steam drive

= 0.32 to 0.45 for electric drive

μ =0.28, for diesel drive

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Factors Affecting the Coefficient of Adhesion

The value of Coefficient of adhesion is affected by the following two factors

• Speed of the train

• The condition of the rails

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• The higher the speed, smaller is the coefficient of

adhesion

• If the rails are wet and greasy the coefficient of

adhesion is lower to when they are dry and sandy

Factors Affecting the Coefficient of Adhesion

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Methods of Improving Coefficient of Adhesion

• Torque developed by the driving motors should be

uniform

• Driving wheels should be distributed over a much

greater length

• Treatment of track with sodium meta silicate

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• Sand treatment for temporary improvement

• Supressing bogie pitching oscillations

• Using A.C. motors with smooth variation of applied

voltage by Silicon control rectifier

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Methods of Improving Coefficient of Adhesion

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In this class we have discussed about

• Coefficient of Adhesion

• Factors affecting Coefficient of Adhesion

• Methods of improving Coefficient of Adhesion

Summary

adhesion

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