Rail wear and the battering of rail ends are the two major defects in rails. However, some other types of defects may also develop in a rail and necessitate its removal in extreme cases. These are described below.
Hogging of rails
Rail ends get hogged due to poor maintenance of the rail joint, yielding formation, loose and faulty fastenings, and other such reasons. Hogging of rails causes the quality of the track to deteriorate. This defect can be remedied by measured shovel packing. (For details, refer to Chapter 20.)
Scabbing of rails
The scabbing of rails occurs due to the falling of patches or chunks of metal from the rail table. Scabbing is generally seen in the shape of an elliptical depression, whose surface reveals a progressive fracture with numerous cracks around it.
Wheel burns are caused by the slipping of the driving wheel of locomotives on the rail surface. As a consequence, extra heat is generated and the surface of the rail gets affected, resulting in a depression on the rail table. Wheel burns are generally noticed on steep gradients or where there are heavy incidences of braking or near water columns.
Shelling and black spots
Shelling is the progressive horizontal separation of metal that occurs on the gauge side, generally at the upper gauge corner. It is primarily caused by heavy bearing pressure on a small area of contact, which produces heavy internal shear stresses.
Corrugation of rails
Corrugation consists of minute depressions on the surface of rails, varying in shape and size and occurring at irregular intervals. The exact cause of corrugation is not yet known, though many theories have been put forward. The factors which help in the formation of rail corrugation, however, are briefly enumerated here.
(a) Metallurgy and age of rails
(i) High nitrogen content of the rails
(ii) Effect of oscillation at the time of rolling and straightening of rails.
(b) Physical and environment conditions of track
(i) Steep gradients
(ii) Yielding formation
(iii) Long tunnels
(iv) Electrified sections
(c) Train operations
(i) High speeds and high axle loads
(ii) Starting locations of trains
(iii) Locations where brakes are applied to stop the train
(d) Atmospheric effects
(i) High moisture content in the air particularly in coastal areas
(ii) Presence of sand
The corrugation of rails is quite an undesirable feature. When vehicles pass over corrugated rails, a roaring sound is produced, possibly due to the locking of air in the corrugation. This phenomenon is sometimes called ‘Roaring of rails’. This unpleasant and excessive noise causes great inconvenience to the passengers. Corrugation also results in the rapid oscillation of rails, which in turn loosens the keys, causes excessive wear to fittings, and disturbs the packing.
Corrugation can be removed by grinding the rail head by a fraction of a millimeter. No method has been standardized on Indian Railways to grind rail surfaces. The problem of corrugation, however, has been tackled in great detail on German Railways, where two types of equipment are normally used for rail grinding.
(i) Hand or motor-driven trollies that move on the rails at slow speeds and grind the individual rails one by one.
(ii) Rail grinding train, which moves at a speed of 30 kmph and grinds both rails simultaneously.