Thursday, 25 February 2016

Sleepers

Sleeprs in Railway Track

Sleepers are members generally laid transverse to the rails, on which the rails are fixed to transfer the loads from the rails to the ballast and the subgrade.

Main Functions of Sleepers

1)Holding rails to correct gauge and alignment.
2)Firm and even support to rails.
3)Transferring the load evenly from rails to wider area of ballast.
4)Elastic medium between rails and ballast.
5)Providing longitudinal and lateral stability.

 Requirements of Sleepers

1)Sleepers used should be economical, they should have minimum possible initial and maintenance cost.
2)Operations such as lifting ,packing,removal and replacements of sleepers should be easily handled .
3)The weight of sleepers should have moderate weight.
4)The design of sleepers should be in such a way that the gauge the alignment of track and the levels of the rails can be easily adjusted.

       TYPES OF SLEEPERS

Wooden Sleepers


 2)Metal Sleepers
     a)Cast-iron sleepers
      b)Steel sleepers

3)Concrete sleepers
     a)Reinforced concrete
     b)Pre stressed concrete

Wooden Sleepers

Wooden sleepers are regarded to be best  as they fulfill almost all the requirements of an ideal sleeper.
The life of these sleepers depends upon the ability to resist 
             1.Wear 
             2.Decay
             3. Attack of vermin(white ants)

Advantages/disadvantages of wooden Sleepers

Advantages:-
1)Easy to manufacture and handling.
2)Suitable for track circuited area.
3)Can be used with or without ballast.
4)Suitable for bridges, Points/Crossings.
5)Resists the shocks and vibrations due to heavy moving loads and also gives less noisy track
6)Alignment can be easily corrected.

Disadvantages:-
1) Lesser life.
2)) Liable to damage by beater packing.
3) Difficult to maintain the gauge.
4) Susceptible to fire hazards.

 Description of wooden Sleepers:-

Size of wooden sleepers in mm :
 B.G. : For ordinary track :-
                2750x250x130 (9’x10”x5”) 
Durable and non durable types of sleepers.
Life of Sleeper:
 Durable –19 years (B.G.)/ 31 years (M.G.)
 Non-Durable- 12 to16 years.

Metal Sleepers


Types of cast iron Sleepers:-
1)Pot/bowl Sleepers
2)C S T-9 Sleepers


Advantages of Cast Iron Sleepers:
  i) Lesser corrosion.
  ii) Easy handling due to light weight.
  iii) Higher Scrap value.
 Disadvantages of Cast Iron Sleepers:-
  i) Not suitable for high speed route.
  ii) Difficult to maintain the Gauge.
  iii) Lesser lateral stability.
  iv) Not fit for track circuited area.
  v) Not suitable for mechanical maintenance.
  vi) Tie bars weakened by corrosion.

Usual Defects in CST-9 Sleepers:-
1) Cracks at rail seats or fracture
2) Wear of lug and rail seat
3) Tie bars weakened by corrosion, broken or damaged by falling of wagon parts.
4) Corrosion of tie bars inside the cast iron plates.

Steel Sleepers

C/S:-

Types of S.T. Sleepers
 i) ST sleepers with Pressed up lugs.
 ii) ST Sleepers with loose jaws.
 iii) Bolt and clip type ST Sleepers.






 Disadvantages of ST Sleepers:
 i) Liable for corrosion.
ii) Not fit for track circuited area.
 iii) Develops cracks at rail seat during   service.
 iv) Can only be used for rails for which it is manufactured.

Advantages of ST Sleepers:
 i) Longer life
 ii) Better Stability
 iii) Lesser damage during handling                     /Transport
 iv) Easy to maintain Gauge
  v) Simple Manufacturing Process
  vi) High Scrap value 

Usual defects in ST Sleepers
1) Rusted and corroded metal
2)Cracks at rail seat or near the lugs
3)Elongation of holes

Inspection of sleepers- Over 20 years old
Precautions during maintenance
Reconditioning of sleeper.

Concrete Sleepers:-

  Types of concrete Sleepers:
   i) Prestressed Concrete Sleepers.
        a) PSC-12 for 52 Kg Rails
        b) PSC-14 for 60 Kg Rails
  ii) Reinforced concrete Sleepers.

i)
C/s-


ii)
C/S:-



 Advantages of concrete Sleepers:
 i) Greater stability.
 ii) Track geometry maintained for much. longer duration hence economical.
 iii) Best suited for machine maintenance.
 iv) Suitable for Track circuiting area.
 v)  No chances of damage by fire/            corrosion.
 vi) No possibility of theft.
vii) No chances of gauge widening.
viii) 60 Kg Sleeper can be used for 52 Kg    rail.
 ix) Best suited for LWR track.
  x) Best performance on P & C, S.E.J. Guard rails , Level Crossings, Check rail in curve.

   *Disadvantage :
i)Handling and laying is difficult being heavy.
ii)Damage is very heavy in case of derailment.
iii)No scrap value.
iv)Not suitable for manual packing.

*Conditions for laying Concrete Sleepers:
i) Track should be deep screened.
ii) Cuttings having rocky bed should have clean ballast cushion of at least 300 mm.
iii)On Arch bridges formation cover min. 1 m.
iv) On other bridges ballast cushion not less than 300 mm.

*Spacing Of Sleepers as follows:-

The space between two adjacent sleepers determines the effective span of the rail over the sleepers.
The spacing of sleepers depends on
                 1)   Axle load    
                 2)   Lateral thrust of locomotive
 The number sleepers per rails varies in India from M+4  to  M+7 (where M=length of rail in meteres)

Sleeper Density:-
It is the number of sleepers per rail length.
It is specified as M+x,
  where,
       M = is the length of the rail in meteres
        x = is the number varying according to
                  certain factors.

Factors Governing The Sleeper Density:-
i)Axle load and speed.
ii)Type and section of rails.
iii)Type of ballast and ballast cushion.
iv)Type and strength of sleepers.
v)Nature of foundation.

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