What is rails, Types of rails, Functions and requirements of rails.

 What is rails? :-

A rail is a steel bar extending horizontally between supports which is used as a track for rail road.

Types of rails:-

Following are the types of rails:
  1. Double headed rail ( DH Rail )
  2. Bull headed rail ( BH rail )
  3. Flat footed rail ( FF rail )

1. Double headed rail:-

It consists of three parts
(a). Upper table    (b). Web    (c). Lower table
  • Both the upper and lower tables were identical and they were introduced with the hope of the life of rails.
  • When the upper table is worn out then the rails can be placed upside down reversed on the chair and so the lower table can be brought into use.
  • But experience showed that such indentations were formed in the lower table due to which smooth running over the surface at the top was impossible.
  • Wrought iron was used to manufacture these rails.

2. Bull headed rail:- 

It consists of three parts
a. Head.        b. Web.       c. Foot. 
  • These rails were made of steel. The head is of larger size then foot and the foot is designed only to hold up properly the wooden keys with which rails are secured.
  • Thus, the foot is designed only to furnish necessary strength and stiffness to rails.
  • Two cast iron chairs are required per each sleeper when these rails are adopted.Rail

3. Flat footed rail:-

These rails are also known as Vignols rails.
 it consists of three parts.
a.   Head.        b.   Web.        c.   Foot. 
  • Initially the flat footed rails were fixed to the sleepers directly and no chairs and key were required.
  • Later under heavy loads the foot was found sinking in the wooden sleeper. It requires Steel bearing plate for load distribution.
            
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Figure of rails

Functions of rail:-

  1. Rails transmit the loads to sleepers and consequently reduced pressure on ballast and formation.
  2. Rails provide a pathway which is smooth and has very little friction. The friction between the Steel wheel and the Steel rail is about one fifth of the friction between the the pneumatic Tyre and a metalled road.
  3. Rails provide a continuous and level surface for the movement of trains.

Requirements:-

  1. The rail should have the most economical section consistent with strength, stiffness, and durability.
  2. The centre of gravity of the rail section should preferably be very close to the mid height of the rail so that the maximum tensile and compressive stresses are equal.
  3. A rail primarily consists of a head a web and a foot and there should be an economical and balanced distribution of metal in its various components so that each of them can fulfill its requirement properly.
  4. They are made of high carbon steel to withstand wear and tear.
  5. Rails serve as a lateral guide for the wheels.
  6. Rails bear the stresses developed due to vertical loads transmitted to them through axels and wheels of rolling stock as well as due to braking and thermal forces.
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