Coning of wheels | Railway Engineering | Transportation Engineering

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The tread of the wheels of a railway vehicle is not made flat, but sloped likea cone in order to enable the vehicle tomove smoothly on curves as well as on straight tracks.

Coning of Wheels

The tread of the wheels of a railway vehicle is not made flat, but sloped like a cone in order to enable the vehicle to move smoothly on curves as well as on straight tracks.

The wheels are generally centrally aligned on a straight and level surface with uniform gauge, and the circumference of the treads of theinner and outer wheels are equal.

The problem, however, arises in the case of a curve, when the outer wheel has to negotiate moredistance on the curve as compared to the inner wheel.

Due to the action of centrifugal force on a curve, the vehicle tends to move out.

To avoid this the circumference of the tread of the outer wheel is made greater than that of the inner wheel.

This helps the outer wheel to travel a longer distance than the inner wheel.

The wheels of a railway vehicle are connected by an axle, which inturn is fixed on a rigid frame.

Due to the rigidity of the frame, the rear axle has a tendency to move inward, which does not permit the leading axle to take full advantageof the coning.

The rigidity of the frame, however, helps to bring the vehicle back into central alignment and thus works as a balancing factor.The coning of wheels helps to keep the vehicle centrally aligned on a straight and level track also.

Slight irregularities in the track do occur as a result of moving loads and the vagaries of the weather. The wheels, therefore, move from side to side and therefore the vehicles sway.

Due to the coning of wheels, this side movement results in the tread circumference of one wheel increasing over the other.

As both the wheels have to traverse the same distance, this causes one wheel to slide.

Due to the resistance caused by the sliding, any further side movementis prevented.

If there was no coning, the side movement would have continued and the flange of the wheel would have come in contact with the side of the rail, causing jerks and making the ride uncomfortable.

Coning of wheels causes wear and tear due to the slipping action.

It is, however, useful as

(a) it helps the vehicle to negotiate a curve smoothly,

(b)it provides a smooth ride, and

(c) it reduces the wear and tear of the wheel flanges.

As far as the slip is concerned, it can be mathematically calculated as follows.

where ? is the angle at the centre of the curve fixed by the rigid wheel box andGis the gauge in metres.

The approximate value of the slip for broad gauge is 0.029 metre per degree of the curve.

Necessity for Geometric Design of Track

The need for proper geometric design of a track arises because of the following considerations

Introduction

 The geometric design of a railway track includes all those parameters which determine or affect the geometry of the track. These parameters are as follows.

 1.  Gradients in the track, including grade compensation, rising gradient, and falling gradient.

 2.  Curvature of the track, including horizontal and vertical curves, transition curves, sharpness of the curve in terms of radius or degree of the curve, cant or superelevation on curves, etc.

 3.  Alignment of the track, including straight as well as curved alignment.

 It is very important for tracks to have proper geometric design in order to ensure the safe and smooth running of trains at maximum permissible speeds, carrying the heaviest axle loads. The speed and axle load of the train are very important and sometimes are also included as parameters to be considered while arriving at the geometric design of the track.

 Necessity for Geometric Design

 The need for proper geometric design of a track arises because of the following considerations

 (a)  To ensure the smooth and safe running of trains

(b) To achieve maximum speeds

(c)  To carry heavy axle loads

(d) To avoid accidents and derailments due to a defective permanent way

(e)  To ensure that the track requires least maintenance.

(f)  For good aesthetics