Holiday travel confusion: Where did the "clang" sound I made when riding on the train as a child go?

Review expert: Wang Shengwei, Senior Engineer, Beijing Municipal Engineering Design and Research Institute Co., Ltd.

The Dragon Boat Festival is approaching, and many people choose to go out for travel, with rail travel becoming the first choice.

I remember when I was a kid, I could always hear the "clang, clang" sound when the wheels collided with the rail joints when the train passed through the track gap. Over time, this sound gradually became the iconic sound of the train in people's memory. Today, this sound is gradually disappearing. Not only does the high-speed train have no "clang" sound, but it is also rarely heard on many express and ordinary trains, greatly improving the comfort of passengers.

Aren't you curious? Where did the "clang" sound go? Today, let's walk into the story of trains and rails!

PART.01

The source of the train's "clang" - seamed rails

The "clang" sound you hear while riding on a train mainly comes from the collision between the train and the rails . In the past, the railway lines used segmented rails , each 25 meters long, and the rails were connected with plywood and bolts.

Train in motion Source: Shenyang Railway

In the past, due to limitations in production technology and transportation conditions, in order to prevent thermal expansion and contraction of the rails from affecting the smoothness of the line, an 18 mm gap was left between the rails on the line. When a train passed through the gap, the wheels collided with the rails, making a "clang" sound.

The use of seamed rails is not only due to thermal expansion and contraction, but also related to various factors such as the funds, steel materials, construction conditions, construction technology, etc. at the time. With the development of China's industry and the blessing of new quality productivity, the construction of railway tracks has been improved, and the rails of railways have gradually changed from seamed rails to seamless rails .

PART.02

Seamless rails do not "bang"

With the rapid development of railway track construction, passengers' requirements for travel comfort are also constantly increasing. With the support of new quality productivity, railway construction has developed rapidly, and railway track technology has been continuously improved. The rails have been changed from seamless to seamless, the matching of wheels and tracks has been optimized, and the vehicle sound insulation technology has been improved , making the trains less "clacking".

Seamless lines are made by connecting sections of rails together using a special welding process to form long rails up to 100 meters long. When laid on the line, they are welded using pneumatic welding, thermite welding or a mobile flash rail welding vehicle to connect the long rails into a whole, forming a seamless line for the entire section. The rail seams are thus eliminated, and the "clang" sound disappears as well.

How can seamless rails eliminate temperature stress? How can seamless rails avoid deformation due to thermal expansion and contraction? First, the material standards of rails can be improved to reduce the deformation due to thermal expansion and contraction. Secondly, the rails can be prestressed and stretched in advance. Then, the track laying method can be changed , and the rails can be forcibly "locked" on the sleepers through rail connectors and anti-climbing equipment, and the stress can be offset through reinforced concrete sleepers. At the same time, the track temperature can be controlled during construction, and the track can be locked when the temperature in the area is at the middle value of the year-round temperature.

Through the improvement of these new materials, new processes and new technologies, deformation of seamless steel rails of dozens or even hundreds of kilometers due to thermal expansion and contraction can be effectively avoided. For areas with large temperature differences, stress can also be released by setting up buffer zones and expansion zones .

PART.03

From seamless lines to high-speed railways

High-speed railways were designed with seamless lines from the beginning, so passengers naturally do not hear any "clang" sound when riding on high-speed railways.

At present, the steel rails used in high-speed railways are 100 meters long when they leave the factory. After passing the inspection, they are transported to the rail welding factory for welding. Every 5 rails are welded together, and each rail is transformed from 100 meters long to 500 meters long. Then the rails "take" the rail transport vehicle to arrive at the laying site.

Railway workers will lay the rails one section at a time on the track and perform secondary welding to eventually form an entire seamless railway.

Rail welding is a delicate job! It has to go through more than a dozen precise processes such as drying water vapor, degreasing and rust removal, rail welding, straightening, fine grinding, welding nodules, flaw detection, etc., before a smoother seamless line can be created.

In addition, the high-speed rail is powered by electricity , so it is relatively quiet when running. At the same time, the design of the high-speed rail carriages and tracks also takes into account the factors of shock absorption and sound insulation , which further reduces the noise during running. Therefore, the high-speed rail is relatively quiet when running, without the "clang clang" sound of the green train.

PART.04

Rail weight upgrade experience

In addition to making the seams seamless and eliminating the "clanging" sound, the weight of the rails has also been upgraded.

In the early days of the founding of New China, due to the actual situation at the time, the weight of the steel rails was only 38 kg/m, commonly known as "38 rails".

Under this type of rail condition, the train can only run at a speed of 30 to 45 kilometers per hour. With the development of railway construction, the weight of rails has gradually increased, and "43 rails", "50 rails", "60 rails" and "75 rails" have been introduced one after another.

Today, almost all conventional railway lines have been replaced with "60-gauge", while some high-speed railway lines and heavy-load railways will use heavier "75-gauge", which has greater wear resistance and bearing capacity.

The use of heavier rails has not only greatly increased the speed, but also made passenger trains run more smoothly and provide a more comfortable riding experience; in terms of freight transportation, it can also carry heavier freight trains.

As a major infrastructure with national strategic significance, leadership and key role, railway is the backbone of the national economy, an important livelihood guarantee project, and the core pillar of the comprehensive transportation system. It occupies a pivotal position in economic and social development. With the support of new quality productivity, railway engineering construction has been continuously developed at a high speed. New quality productivity provides new impetus for the high-quality development of railways and promotes the process of railway modernization.

Driven by the new productivity, my country's rail transit industry has developed rapidly, from being poor in history to becoming a transportation powerhouse today. From railways to highways, road networks, water transportation and many other aspects, China is leading the world! I believe that in the future, my country's railway industry will achieve more efficient, intelligent and green operations, providing more convenient and comfortable services for people's travel.