Due to the passage of moving loads and friction between the rail and the wheel, the rail head gets worn out in the course of service. The impact of moving loads, the effect of the forces of acceleration, deceleration, and braking of wheels, the abrasion due to rail-wheel interaction, the effects of weather conditions such as changes in temperature, snow, and rains, the presence of materials such as sand, the standard of maintenance of the track, and such allied factors cause considerable wear and tear of the vertical and lateral planes of the rail head. Lateral wear occurs more on curves because of the lateral thrust exerted on the outer rail by centrifugal force. A lot of the metal of the rail head gets worn out, causing the weight of the rail to decrease. This loss of weight of the rail section should not be such that the
stresses exceed their permissible values. When such a stage is reached, rail renewal is called for.
In addition, the rail head should not wear to such an extent that there is the possibility of a worn flange of the wheel hiting the fish plate.
Type of Wear on Rails
A rail may face wear and tear in the following positions:
(a) on top of the rail head (vertical wear)
(b) on the sides of the rail head (lateral wear)
(c) on the ends of the rail (battering of rail ends)
Wear is more prominent at some special locations of the track. These locations are normally the following:
(a) on sharp curves, due to centrifugal forces
(b) on steep gradients, due to the extra force applied by the engine
(c) on approaches to railway stations, possibly due to acceleration and deceleration
(d) in tunnels and coastal areas, due to humidity and weather effects
Measurement of Wear
Wear on rails can be measured using any of the following methods.
(a) By weighing the rail
(b) By profiling the rail section with the help of lead strips
(c) By profiling the rail section with the help of needles
(d) By using special instruments designed to measure the profile of the rail and record it simultaneously on graph paper
Methods to Reduce Wear
Based on field experience, some of the methods adopted to reduce vertical wear and lateral wear on straight paths and curves are indicated below.
(a) Better maintenance of the track to ensure good packing as well as proper alignment and use of the correct gauge
(b) Reduction in the number of joints by welding
(c) Use of heavier and higher UTS rails, which are more wear resistant
(d) Use of bearing plates and proper adzing in case of wooden sleepers
(e) Lubricating the gauge face of the outer rail in case of curves
(f) Providing check rails in the case of sharp curves
(g) Interchanging the inner and outer rails
(h) Changing the rail by carrying out track renewal
Rail End Batter
The hammering action of moving loads on rail joints batters the rail ends in due course of time. Due to the impact of the blows, the contact surfaces between the rails and sleepers also get worn out, the ballast at places where the sleepers are
joined gets shaken up, the fish bolts become loose, and all these factors further worsen the situation, thereby increasing rail end batter.
Rail end batter is measured as the difference between the height of the rail at the end and at a point 30 cm away from the end. If the batter is up to 2 mm, it is classified 'average', and if it is between 2 and 3 mm, it is classified as 'severe'. When rail end batter is excessive and the rail is otherwise alright, the ends can be cropped and the rail reused.
Rail lubricators are provided on sharp curves, where lateral wear is considerable. The function of lubricators is to oil the running face of the outer rail in order to reduce the friction. It has been noticed that this considerably reduces the wear, by up to 50%. There are many mechanical devices that can be attached to the wheels to provide such lubrication. In these mechanical arrangements, the wheels of moving trains normally cause the lubricant to flow on the side of the rail either by the action of the wheels pressing the plunger up and down or by ramps on account of the rails being depressed by wheels. Sometimes the movement of trains also cause lubricants to flow. Based on the principle of the plunger being pressed by moving wheels, P and M type lubricators have been provided on curves in some sections such as the 'Ghat section' of Central Railway and these are working very satisfactorily. For more details on wear, including limit of wear, refer to Chapter 23.