The tread or rim of railway vehicles are not made flat but are sloped and this sloping surface along the circumference forms part of a cone (with a slope of about 1 in 20). This is known as coning of wheels.
On straight and level track, the wheel remains central and circumference of treads of both wheels are equal.
On the level track as the axle moves towards one rail, the diameter of wheel tread over the rail increase while it decreases over the other rail. This prevents the further movement of axle retreat back to original position with equal diameters and equal pressure on both rails.
On curved track, outer wheel has to travel greater length than the inner wheel. Vehicle on a curve has the tendency to move sideways towards the outer rail, so the circumference of the tread on the outer rail towards inner edge of the wheel becomes greater than that on the inner rail. This helps outer rail to cover a greater distance than the inner rail.
Conicity of wheel is equals to the angle between tread and horizontal axis of axle.
Advantages of coning of wheel
- It helps vehicle to negotiate curves smoothly.
- To keep the train just in central position in a level track.
- To provide for possibility of lateral movement of axle with its wheels.
- To prevent wheels from slipping to some extent.
- To reduces wear and tear of the wheel flanges.
Disadvantages of Coning of Wheel
The pressure of the horizontal component of the force near the inner edge of the rail has a tendency to wear the rail quickly.
The horizontal component of the force tends to turn the rail outwards and hence the gauge is widened sometimes.
If no base plates are provided, sleepers under the outer edge of the rail may get damaged.
Canting of Rails
- In order to minimize the disadvantages due to coning of wheels, canting of rails is done which means that rails are not laid flat but are tilted inwards.
- This reduces wear on the rail as well as on the tread of the wheel.
- The slope of the base plate is 1 in 20 which is also the slope of the wheel flange.
- Tilting of rails can be achieved by
- Adzing of Sleepers
- Use of Canted Sleepers
Adzing of Sleepers
A groove (having angle of 1 in 20) is being cut on the top of the sleepers. The rail is being seated into this groove in such a manner that it remains fixed in this location.
This sort of angle making in sleepers so as to seat the rail is known as adzing of sleepers.