WELDING OF RAILS
Purpose of providing welding:-
1)To increase the length of rail
2)To repair the damage rail thus increase their life.
3)To build up worn out points and rails on sharp curves.
4)To build up the burnt portion of rail head.
Advantages of welding:-
1)It increases the life of rails.
2)It reduces the creep due to increase in length of rail.
3)It reduces expansion effect due to temperature.
4)Welding facilitates track circuiting on electrified tracks.
5)Welding rails provides on large bridges for the span length are helpful as they result in better performance.
6)The cost of track construction by welding of rails decreases due to less number of rail joints.
TYPES OF WELDING RAILS:-
In India the present practice is to use following types :
1)Short welded rails (SWR)
2)Long welded rails(LWR)
3)Continuous welded rails(CWR)
METHODS OF WELDING RAILS:-
1)Electric arc welding(metal arc welding)
2)Oxy-acetylene welding(gas pressure welding)
3)Flash butt welding
4)Chemical or thermite welding
Electric Arc Welding:-
In this method the current is passed through the rail and at the same time through a thin rod known as electrode. As the electrode approaches the rail ,an electric arc is formed and with its heat the electrode gets melted and finally the molted metal of the electrode gets deposited on the rail providing a firm bond.
Flash Butt Welding:-
In this method powerful current is passed through two rails, the end of which are to be join together. The width of the gap between two rails is varied till both the ends get heated upto a required temperature . Then they are brought in contact with each other resulting in flash
In this method intense heat is produced by combining the oxygen and acetylene gas which melts the electrode and deposits the molten metal on the rail.
This method like electric arc welding is used for repairing damage parts of points and crossings
here is figure of oxy acetylene welding
Length Of Welding Rails:-
As a result the use of longer length of rails ensures smooth running of trains and comfort to passengers and therefore the length of rail should be as long as possible. However its length is limited by the following factors:-
1)The length of rail is governed by the facilities available for the manufacture of rails at reasonable costs.
2)The length of rails should be such that they can be transported using longest wagon available with railways.
3)The length of rails is also limited by the available machinery facilities for lifting and handing the rails.
Chemical or Thermite welding:-
It involves use of aluminium and iron oxide, and then mix together in powder form and ignited. After ignition the below chemical reaction takes place