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What is a Railway Sleeper?Railway sleepers are the components on which the rails are arranged with proper gauge. These sleepers generally rests on ballast and is also called as ties in some regions. The load from rails when train passes, is taken by these sleepers and is distributed it to the ballast.
Functions of Railway SleepersThe basic functions of Railway sleepers are to:
- hold the rails strongly and to maintain uniform gauge.
- transfer the load from rails to the ballast or ground.
- reduce the vibrations coming from rails.
- offer longitudinal and lateral stability.
Classification of Railway SleepersBased on the materials used, railway sleepers are classified into following types.
- Wooden sleepers
- Concrete sleepers
- Steel sleepers
- Cast iron sleepers
- Composite sleepers
Wooden SleepersThese are sleepers made of wood. Wooden sleepers are used since olden days. These are still widely using in some western countries. Either hardwood or softwood can be used to make wooden sleepers. However, hardwood sleepers made of oak, jarrah, teakwood are more famous.
Benefits of Wooden Sleepers
- Wood sleepers are cheaper than others and easy to manufacture.
- They are light in weight so, they can be easily transported and handled while installing.
- Fasteners can be easily installed to wooden sleepers. They are good insulators so, rails are well protected.
- Any type of gauge can be maintained by wooden sleepers.
- They are suitable for all types of rail section.
- They are well suitable for tracks in coastal areas.
Drawbacks of Wooden Sleepers
- Life of wooden sleepers is very less compared to others.
- Weak against fire.
- Easily affected by humidity which will cause dry rot, wet rot etc.
- Vermin attack can be possible if it is not properly treated.
- Poor creep resistance.
- Good Attention is required even after laying.
Concrete SleepersConcrete sleepers are manufactured by concrete with internal reinforcement. Concrete sleepers used in many countries due to its high stability and small maintenance. These are more suitable for high speed rails. Most of the concrete sleepers are made from pre-stressed concrete in which internal tension is induced into the sleeper before casting. Hence, the sleeper withstand well against high external pressure.
Benefits of Concrete Sleepers
- Concrete sleepers are heavier than all other types hence, gives good stability to the rails.
- They have long life span so, economically preferable.
- They have good Fire resistance.
- Corrosion is not occurred in concrete sleepers.
- Vermin attack, decay etc. are not occurred. Hence, they are suitable for all types of soil and moisture conditions.
- Bucking strength is more.
- Concrete is good insulator so, this type of sleepers are more suitable for circuited tracks.
- Concrete sleepers holds the track strongly and maintains gauge.
Drawbacks of Concrete Sleepers
- Because of heavy weight, handling is difficult.
- For tracks on bridges and at crossings, concrete sleepers are not suitable.
- Damage may occur while transporting.
Steel SleepersSteel sleepers are more often used because of stronger than wood and economical than concrete. They also have good life span. They are molded in trough shape and placed on ballast in inversed trough shape.
- They are light in weight so, easy to transport, to place and to install.
- They are recyclable hence possess good scrap value.
- Life span of steel sleepers is more and is about 30 years.
- They are good resistant against fire.
- They have good resistance against creep
- They cannot be attacked by vermin etc.
- They are well suitable for tracks of high speeds and larger loads.
- They holds the rail strongly and connecting rail to the sleeper is also simple.
- Steel can be effected by chemicals easily.
- Steel sleepers requires high maintenance.
- They are not suitable for all types of ballast which is provided as bed for sleepers.
- If derailment is happened, they damaged very badly and not suitable for re using.
- These are not suitable for all types of rail sections and gauges.
Cast Iron SleepersCast iron sleepers are widely used in the world especially in Indian railways. They are available in 2 types, pot type sleepers and plate type sleepers. Pot type sleepers are not suitable for curves sharper than 4 degrees. CST 9 type sleepers more famous in Indian railways.
- Cast iron sleepers can be used for long period up to 60 years.
- Their manufacturing is also easy and it can be done locally so, there is no need for longer transportation.
- Vermin attack is impossible in case of cast iron sleepers.
- They provide strong seat to the rail.
- Damaged cast iron sleepers can be remolded into new sleepers hence, scrap value of cast iron is good.
- Creep of rail can be prevented by cast iron sleepers.
- Cast iron is brittle in nature and it can be damaged easily while handling. So, transportation, placing is difficult to deal.
- Cast iron sleepers can be easily damaged and corroded by salt water so, they are not suitable for coastal regions.
- They may damage badly when derailment happened.
- Cast iron is expensive in market when compared to some other sleeper materials. Hence it is uneconomical.
- So many fastening materials are required to fix the rail to the sleeper.
- Proper Maintenance is required.
Composite SleepersComposite sleepers are modern type sleepers which are made from waste plastic and rubber. Hence, it is also called as plastic sleepers. They have many combined properties of all other types.
- Composite sleepers are serviceable for longer spans about 50 years.
- Composite sleepers are eco-friendly sleepers.
- They are light in weight but possess great strength.
- Their scrap value is good because of recyclable property of composite sleepers.
- They can be resized easily like wooden sleepers. So, they can be used for any type of rail section.
- Vibrations received from rails are reduced well by these composite sleepers.
- Composite sleepers are not that much good against fire.
- The cost of sleepers may increase for large scale production.