CREEP OF RAILS

Creep of rails:-

Definition:

It is a horizontal movement of rails in a track. It can be minimized but cannot be stopped.               

                            OR

Longitudinal movement of rails in a track .

Cause of creep:-

1)There are three main causes of Creep wave motion of trains.

2)Expansion and contraction of rails due to variation in temperature.

3)Due to starting, accelerating, slowing down (decelerating) and stopping of trains.  

Wave Motion:-

*When train passes on a track, the portion of rail length under the wheel of train will under more stresses and little depression will exist.

*As a result, this depression will cause (set) a wave motion in the rail or track 

Alignment Of Track:
Creep is more on curve track than on a tangent portion (straight track).

Grades:
In upgrades tracks, creep will be less and in down grades track creep will be more.

Direction of movement of trains:
Creep will be more in the direction to which the loaded train moves more.


Extent of Creep:-
1)Creep does not vary at some constant rate. (it is not constant)

2)Creep does not continue in one direction only.

3)Creep for two rails of the track will not be in equal amount.

Result of creep:-
1)Expansion gap is reduced, buckling of track take place.
2)Sleepers are moved out of a square.
3)Crossing points get disturbed.

Creep Prevention:-
Pulling back the rails:
  1)using crow bars and hooks through fish
     bolt holes
   2)slow and tedious process
   3)practicable for only small lengths
Use of steel slippers:
    1)steel through sleepers are best
    2)Increase in number of sleepers can help
 
Using Anchors/Anti-creepers:
 1)4 anchors  per rails if creep is 7.5cm to 15cm/month.
 2)6 anchors per rail if creep is 22.5 to 25cm/month.
 3)Used at levels crossings,in yards and places of heavy brake application.

       SOME IMPORTANT POINTS
1) Should be able to resist the movement of the rails
2)Fixed to good sound sleepers.
3)Should butt against the sleepers.
4) Should not to be used on bridges.