How is the high-speed rail installed using seamless steel rails?
seamless steel rails
High-speed rail uses seamless steel rails, how is it installed? What to do in case of thermal expansion and contraction?
Ordinary railway tracks are section by section, and there will be a gap of 6 mm between the track and the track, which can avoid the problem of thermal expansion and contraction, and prevent the track from climbing due to thermal expansion and contraction.
Now in China’s high-speed rail system, seamless steel rails are used, and now it has to face the problem of thermal expansion and contraction.
So China’s high-speed rail uses seamless steel rails, how is it installed? What should I do if I encounter thermal expansion and cold contraction?
How to install high-carbon steel rail
seamless steel rails installation
The seamless steel rails used in high-speed railways are welded, or more precisely, the rails are “cast” section by section. There were gaps in the previous rails, in addition to considering the problem of thermal expansion and contraction, as well as the impact of welding on the material.
If the steel is heated, its properties will change, it will start to soften, or there will be more severe metal fatigue. When such a rail is welded, the weld seems to be “seamless”, but the metal strength has been greatly affected.
With the progress of my country’s welding technology over the years, high-speed rail has dared to use “welding” technology to make seamless rails. There are three main ways of welding high-speed rail in my country, which are aluminothermic welding, air pressure welding, and flash welding.
As for which one to use, it depends on the actual needs of the construction site. China’s land area is more than 9.6 million square kilometers, and the mainland is more than 5,000 kilometers deep from north to south. The requirements for high-speed rail construction vary greatly from place to place.
The “welding” process of seamless steel rails is to first take 5 sections of 100-meter-long steel rails indoors and weld these 5 sections of steel rails into a section of 500-meter-long steel rails. These 500-meter-long steel rails are then transported to the construction site, where 4 500-meter-long steel rails are welded together into 2-kilometer-long steel rails each.
At this point, each 2km long rail can be fitted with sleepers. After that, the rails with the sleepers are welded together, and then the welds are polished smooth, and the construction is completed.
Material of high-speed rail
As for how high-speed rails cope with thermal expansion and contraction, it can be described in two words, that is, “hard resistance”.
The biggest problem brought by thermal expansion and cold contraction to the rail is climbing, that is, the rail expands after being heated, and then the entire rail is deformed and “crawls up and down” on the sleepers. If conventional steel is used, seamless steel rails can easily cause rail climbing, but a breakthrough in material science is different.
my country’s rail material is a kind of steel with relatively small thermal expansion and cold contraction. Even if no other method is used, the problem of “climbing the rail” in summer will not be too serious.
During construction in my country, we basically choose the time when the weather is moderate (usually spring and autumn). At this time, the volume of the rail affected by the temperature change is moderate, and there is no need to worry about the problem of climbing the rail after the sleeper is installed.
After the problem of thermal expansion is solved, there is no need to worry too much about the problem of cold shrinkage. Conventional steel will shrink after being cooled. If the two ends of the rail are fixed, the middle of the rail may crack during the shrinking process.
However, the strength of the steel used in my country’s high-speed rail is very high, so there is basically no need to worry about this problem. So to put it simply, my country’s high-speed rail technology is to forcibly “press” the steel rail to the ground, and the steel rail can eliminate the influence of thermal expansion and contraction due to the strength of the material itself.
How to avoid thermal expansion and contraction of high-speed rail
In addition to material solutions, my country has also taken some measures on the high-speed rail to prevent it from climbing. The first measure is the simplest and crudest method, and that is watering. If the weather is really too hot, the rail system will send rail linemen to water the track to cool it down. This method is not very technical, but it is very effective.
The second is to use a high-pressure buckle to control the stress. As we said above, the most important means of preventing thermal expansion and contraction of seamless steel rails is to “press” the rails on the sleepers after solving the material problem. This requires the use of high-pressure buckles, and there will be such a high-pressure buckle every few tens of centimeters on the rail so that the rail can be “pressed”.
When the high-speed rail was built, the entire rail was not straight, it was an “S” shape. It’s just that this bend is so tiny that it’s so small that it’s invisible to the naked eye. In our eyes, the high-speed rail track is straight.
If the temperature change is too great, you can release the high-pressure button and let it deform naturally. Because of the breakthrough in materials, this deformation will be within a controllable range. If the temperature becomes lower, the “S” will be stretched straight. If the temperature gets higher, this “S” will be more pronounced.
After the high-pressure buckle is released to allow the rail to deform naturally, the rail is relieved of stress. When the temperature changes to a suitable range, and then the high-pressure buckle is fastened, the stress of the rail can be the same as before the temperature change. Through these measures, the influence of temperature changes on the seamless rail can be greatly reduced, and its service life can be extended.
