The stress relief process in seamless rail welding can prevent the seamless rail from expanding with heat and contracting with cold, that is, the stress inside the rail is evenly distributed on the rail to prevent the rail from breaking when the temperature is too low and expanding when the temperature is too high.
In fact, seamless rail has been widely used in our country, which is really not a new technology.
Slotted track
I believe that many friends used to hear the sound of "clang, clang" when they took the green leather train, and they could obviously feel the regular vibration of the vehicles on the rails. With the development of the times, China's railways have experienced several speed increases, and the previous tremor is gone, and one of the important means to eliminate this tremor is seamless rail.
The standard lengths of rails in China are12.5m and 25m. In the past, railway trunk lines generally used 50kg/m rails, and some used 60kg/m rails. The standard lengths of these two rails are 12.5 meters and 25 meters. When the railway was built, several rails of standard length were connected, and then the rail gap appeared.
Rail gap refers to the gap reserved between the two ends of the rail for rail expansion. Because the railway tracks are exposed and exposed all the year round, they are greatly affected by temperature. When laying rails, it is necessary to reserve rail joints. When the rail temperature reaches the highest local rail temperature, the rail gap should be greater than or equal to zero, so that the rail end will not be squeezed and the rail expansion caused by excessive temperature and pressure will be prevented. When the rail temperature reaches the local minimum rail temperature, the rail gap should be less than or equal to the structural rail gap, so that the joint bolt is not sheared and the rail joint bolt is prevented from bending or breaking. Structural rail gap refers to the maximum gap at the rail end that can be realized in structure due to the size limitation of rail, joint splint and bolt.
Seamless rail principle
As the key equipment for train speed-up, the localization rate of seamless rail is close to 100%, and within the range of 1.5m m, the flatness error at the rail interface is less than 0.2mm.
When the wheel travels to the joint of two rails, one part of the wheel tread presses on the first rail, while the other part of the wheel tread presses on the second rail at the same time, so that the two rails are stressed at the same time, and the wheel smoothly passes through the joint of the two rails without vibration.
When laying rails, two 500-meter-long rails are towed by tractors to slide to corresponding positions, and dozens of engineers and technicians assist the tractors to unload the rails and locate them accurately. After the rail is laid, the locomotive can push the flat car group consisting of 37 flat cars along the rail.
After the tractor lays the rails on the ballastless track, another seamless rail welding construction team will immediately weld the rails laid in front into seamless rails.
With the development of China's railways, two new members have been introduced into the rail family, 50m and 100m, which are rails for laying seamless tracks.
In fact, the so-called seamless rail is not completely seamless, but reduces the number of rail gaps compared with the original seamless rail. When people take the seamless rail train, it is not that they can't feel the slight vibration of the car body caused by the rail gap, but that the number of rail gaps is greatly reduced than before, and this feeling is not obvious.
50m, 100m or even 500m long seamless rails used in high-speed railways are generally welded by several short rails in turn. At this time, a friend will ask: the rail gap has decreased, so how to solve the rail expansion problem just mentioned?
There are generally two methods to solve the problem of rail expansion by jointless track. One is that the long rail section itself bears all the temperature stress and locks the long rail on the sleeper so that it will not expand and contract due to temperature changes. This method is suitable for places such as southern China where the temperature is not much different throughout the year.
Another method is that in areas with large temperature difference throughout the year, the long track section itself does not bear the temperature stress, but automatically releases the stress or periodically releases the stress, so that the long track section can freely contract with the temperature rise and fall. When laying rails, try to choose the best temperature to keep the expansion value of rails within the minimum range, so that the expansion value of rails can be controlled within a reasonable range no matter whether the temperature rises or falls.
Construction of seamless rail
Take the construction and laying of 500-meter-long rails as an example. During the construction of seamless rail, the newly produced 100-meter fixed-length rail is welded to 500 meters in the rail welding factory, and then the 500-meter-long rail is transported to the laying site. During track laying on site, two 500-meter-long rails were towed by tractors and slid to corresponding positions. With the help of dozens of engineers and technicians, the tractor successfully unloaded the rail and positioned it accurately in the laying position.
After the rail laying is completed, the locomotive will continue to lay the rail along the newly laid track. At this time, the seamless rail welding construction team will weld the previously laid rails. Under normal circumstances, it is customary to weld 500-meter-long rails into 2000-meter-long management units during site construction in China.
In the welding process of seamless rail, there needs to be a process to relieve stress, that is, to solve the problem of thermal expansion and cold contraction of seamless rail mentioned above, and to evenly distribute the stress inside the rail to prevent the rail from breaking when the temperature is too low and expanding when the temperature is too high.
Finally, the adjacent 2000-meter-long track management units are welded together. This continuous welding formed the seamless line we use now.
Compared with jointless track, jointless track can improve the ride comfort of trains, reduce the damage of trains to track components and greatly reduce the maintenance workload of field staff. According to statistics, jointless track can save at least 15% maintenance cost and prolong the service life of rails by 25% every year. At the same time, when we take the train, we can no longer hear the sound of "clang, clang".