Welding processes

Various welding processes that can be used for joining the metal parts are solid phase welding, arc welding, resistance welding, thermit welding, ultrasonic welding, electron beam welding, laser beam welding and explosive welding. Solid state phase welding can be further classified into five categories- forge welding, butt welding, oxyacetylene pressure welding, flash butt welding and friction welding. In forge welding, the parts to be welded are heated in a furnace and then hammered together to form the weld. Electric current is used in Butt welding. An Oxyacetylene ring burner is used in oxyacetylene pressure welding. In flash butt welding, the parts are brought in contact with a light pressure and followed by the passage of an electric current. Heat due to friction is employed in friction welding.

Concrete sleepers used in railway lines

Economic considerations and changing traffic patterns forced railway industry to introduce concrete sleepers. The problem with wooden sleepers was shortage in material and expensive. In the initial stages RCC sleepers were used. After some time, block-type RCC sleepers connected by a steel tie bar were introduced. Latest in this category are prestressed concrete blocks and steel or an articulated concrete tie bar. The advantages of concrete sleepers are strength, stability, resistance to the buckling of the track, better packing, better alignment, improved cross leveling, better gauging, easy maintenance, less electrical conductivity, non-flammable, less damage, longer lifespan and can be produced in bulk. The main disadvantages are handling and transportation difficulties due to large weights, less scrap value, difficulty in beater packing etc. While designing a concrete sleeper, we have to consider the following factors: forces acting on sleeper, effects of geometric form, provision of failure on a damage and effect of the characteristics of fastenings used. The different varieties of concrete sleeper used by Indian railways are BG monoblock sleeper, BG twin block sleeper and MG twin block sleeper.