Reinforced concrete sleepers
Long service life, high stability, small maintenance workload, damage rate and scrap rate are much lower than wooden sleepers. On the seamless line, the stability of reinforced concrete sleepers is on average 15~20% higher than that of wooden sleepers, so it is especially suitable for high-speed passenger lines. For example, Japan's Shinkansen and Russia's high-speed trunk line have laid it.
Of course, reinforced concrete sleepers also have disadvantages, especially the weight is much greater than that of wooden sleepers. For example, cement sleepers for mining weigh 285 kilograms each, the United States weighs 280 kilograms, and the German one is lighter with 230 kilograms.
Therefore, it should not be used in unstable roadbeds and newly filled roadbeds; In the winter with frost heave, it is generally not allowed; It is best not to use it in areas where large quantities of coal and ore are transported and where the line bed is heavily dirty.
The United States, which uses the most wooden sleepers, now uses a type of plastic sleeper. This plastic sleeper made of recycled polyethylene is more than three times more resistant to corrosion than wooden sleepers, and it is easier to make its surface "hairy" when processed, and it will not slide when installed on the roadbed. The third advantage is that it is easy to install, and the same equipment and fasteners as wooden sleepers can be used directly. Of course, plastic sleepers are more expensive than wooden sleepers, and once the cost is reduced, it will be quickly promoted.
Sleepers vary in length depending on the range of applications. In China, the length of ordinary sleepers is 2.5m, and the turnout pillows used for turnouts and the sleepers used on steel bridges have a length of 2.6~4.85m. The number of sleepers laid on each kilometer of the line is determined according to the operating conditions such as railway traffic and travel speed, generally speaking, between 1520~1840. It goes without saying that the greater the number of sleepers, the greater the orbital strength.
Sleepers made of wood
Wood sleeper is a sleeper made of wood. Also known as sleepers, antiseptic wooden sleepers, also called oil-filled sleepers. Wooden pillows must be made of tough and resilient wood. Wooden sleepers can be divided into ordinary wooden pillows, fork pillows, and bridge sleepers according to their use.
The standard length of ordinary wooden sleepers is 2 .5 m, and their cross-sectional shapes are divided into two categories, I and II, which are used on different grades of lines. The turnout pillow used on the turnout is wider than the wooden pillow, the length is from 2600mm to 4 800mm, a total of 12 types, each length difference of 200mm, when used according to the actual width of the turnout grouped selection. Used for bridge sleepers, the cross-sectional dimensions of which vary depending on the size of the center spacing of the main beam (or stringer). Wooden pillows have the advantages of good elasticity, easy processing and easy to use. Since the beginning of the railway, wooden sleepers have been the main type of sleeper.
However, due to the use of materials, the elasticity, strength and durability of the wooden sleeper are not uniform enough, which will increase the wheel-rail dynamic effect, and a large amount of high-quality wood is used. The service life of wooden sleepers is short, and there are many reasons for their failure, mainly decay, mechanical wear and cracking. Because wooden pillows are perishable, they are treated with antiseptic treatment before going on the road. Wooden pillows that have not been embalmed are called plain pillows. China's wood resources are relatively scarce and expensive, and have been gradually replaced by concrete pillows on the main trunk lines.
Concrete sleepers
After World War II, countries around the world gradually used reinforced concrete sleepers due to the shortage of wood resources; It was later improved to prestressed concrete sleepers. Since 1957, China's railways have also used a large number of prestressed concrete sleepers, and by the end of 1983, about 64.45 million sleepers had been laid. In 1983, the annual output was more than 4 million, accounting for about a quarter of the world's annual production of prestressed concrete sleepers (about 15 million). In addition to saving a large amount of high-quality steel, the concrete sleeper can also have the advantages of long service life, good track stability, and can meet the requirements of high speed and large capacity. It has played a great role in promoting seamless lines.
Its disadvantages are large stiffness and poor elasticity, which increases the pressure and vibration acceleration of the track bed, thereby aggravating the pulverization of the ballast, causing the sinking of the track to increase, and adversely affecting the rolling stock part. For this purpose, the use of tough ballast and elastic cushioning on the sleepers are required.
The concrete sleeper structure of railways in various countries is different, most of them adopt continuous whole type, and some countries' railways use the structure of two pieces of concrete connected with section steel to support the rail.
In addition, many countries also pay attention to improving the performance of fasteners. China's ω type elastic fastener, the British Pandrol type fastener and the Swiss Fist type fastener are all designed and manufactured for this purpose.
Steel pillows
On railways in the Federal Republic of Germany and Switzerland, steel pillows were widely used. However, due to the fact that steel pillows are easy to rust, the amount of steel used is large, the maintenance cost is high, and the amount of use is gradually reduced.
Special concrete sleepers
Concrete sleeper of special type includes concrete wide sleepers and steel fiber concrete sleepers. Concrete wide pillows are made of reinforced concrete, similar in appearance to concrete pillows, but wider and thinner than concrete pillows, also known as sleeper plates. The appearance of concrete wide pillows is neat and beautiful, generally 2.5m long and 55~60cm wide, and is densely laid on a compacted clean gravel bed.
1760 concrete wide pillows are laid per kilometer, and a pair of fasteners are installed on each wide pillow, and the load transmitted by the rail has a small eccentricity and good stability to the wide pillow. Due to the large supporting area, compared with the concrete pillow, the sinking amount of the track is significantly reduced, which can slow down the accumulation of permanent deformation of the track bed, smooth the line, and reduce the maintenance workload.
Since the elasticity, cross-sectional size, drainage method, etc. of the concrete wide pillow track are different from other structural forms of tracks, the transition section must be set when connected to other tracks so that it changes evenly.
Steel fiber concrete sleeper refers to a concrete sleeper made by mixing a certain amount of steel fiber into concrete. Steel fiber concrete is a new composite material that increases strength and toughness. Steel fiber concrete sleeper can improve the impact toughness and crack resistance, tensile resistance, shear resistance, bending resistance, fatigue strength of the sleeper, so as to extend the service life of the sleeper, suitable for small radius curve and joint parts, can better solve the nail hole longitudinal crack, shoulder damage and other problems.