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.

Turbomachines

Turbomachines are rotary type machines where the transfer of energy is brought about by dynamic action. Here impervious boundary containing the fluid does not exist. In a  turbomachine, energy exchange is brought about by hydrodynamic forces that appear between a moving fluid and the rotating and stationary elements of the machine. Here a dynamic energy exchange is taking place between one or several rotating elements and a rapidly moving fluid. The main components of a turbomachine are a vane carrying rotating element which operates in a fluid stream, some stationary elements acting as guide vanes for the proper control of flow direction and the energy conversion process, two shafts and housing. A turbomachine creates thermodynamic and dynamic action between a slow moving surface and a static fluid. This action involves a change in either volume or displacement of the fluid. Some characteristics of turbomachine are high rotational speed, simple design, less weight and almost vibration free.