Crossties, also known as sleepers, are also a kind of railway accessories. But the materials used today are not just wood. So the railway sleepers
are more scientific. Despite the monotonous and uniform shape of the train track sleeper, its function is not small. Railway sleepers should support the rails, keep the rails in position, and transfer the enormous pressure from the rails to the ballast bed. It must be flexible. It can not be too hard or too soft. When a train passes by, it can deform appropriately to cushion the pressure. But the train has to be restored as much as possible.
Classification of Railway Sleepers
1. Reinforced concrete sleepers
The utility model has the advantages of long service life, high stability, small maintenance workload, much lower damage rate and scrap rate than wooden pillows. On CWR, the stability of reinforced concrete sleepers is 15-20% higher than that of wooden sleepers, so it is especially suitable for high-speed passenger lines. For example, it is laid in Shinkansen of Japan and high-speed trunk lines of Russia. Of course, reinforced concrete sleepers also have shortcomings, especially the weight is much larger than wooden sleepers.
2. Hardwood sleepers
Since the existence of railways, wooden sleepers have been the main type of sleepers. However, the elasticity, strength and durability of wooden sleepers are not uniform enough due to the reasons of taking materials, which will increase the dynamic effect of wheel and rail, and a large number of high-quality wood will be used. The service life of wooden pillows is short. There are many reasons for their failure, mainly decay, mechanical wear and tear. Because of its perishability, wooden pillows should be treated with anticorrosion before going up the road. Unpreserved wooden pillows are called vegetable pillows. China's timber resources are scarce and expensive, and concrete pillows have gradually replaced them on major trunk lines.
3. Concrete sleepers
After the Second World War, because of the shortage of wood resources, reinforced concrete sleepers were gradually used in the world. After that, it was improved to the prestressing concrete sleeper.
4. Special concrete sleepers
Including concrete wide pillow and steel fiber reinforced concrete pillow.
Compared with the concrete pillow, the track subsidence is obviously reduced, which can slow down the accumulation of permanent deformation of the track bed, smooth the track and reduce the maintenance workload. Because the elasticity, section size and drainage mode of concrete wide sleeper track are different from those of other track structures, it is necessary to set transition section when connecting with other track to make it change evenly.
Steel fiber reinforced concrete sleeper refers to the concrete sleeper made by mixing a certain amount of steel fiber into concrete. Steel fiber reinforced concrete (SFRC) is a new kind of composite material which can increase strength and toughness. Steel fiber reinforced concrete sleepers can improve the impact toughness and crack resistance, tension, shear, bending and fatigue strength of sleepers to prolong the service life of sleepers. They are suitable for small radius curves and joint positions, and can better solve the problems of longitudinal cracks in nail holes and shoulder damage.