What Is The Seamless Rail of Train Track?

Seamless rail of train track, also known as welded long rail track, is a long rail line formed by welding standard-length rails together. It is an important new technology in track structure and has developed rapidly in various countries around the world.

On ordinary lines, rail joints are one of the weak links of the track. Due to the existence of rail joints, trains experience impact and vibration when passing through, accompanied by striking noise. The impact load generated can be up to three times that of the non-joint area. The impact force of the joint affects the smoothness of train operation and passenger comfort, and leads to the destruction of the ballast, deterioration of the line condition, shortened service life of rails and connecting parts, and increased maintenance labor costs. Maintenance and repair costs in the joint area account for more than 35% of the total maintenance budget; the number of rails replaced due to damage at the rail ends is 2 to 3 times that of other parts; 60% of severely damaged rails occur in the joint area. With the continuous increase in train axle load, speed and density, its disadvantages will become more prominent, and it will be unable to meet the needs of modern high-speed and heavy-haul transportation.

To improve the working condition of rail joints, since the 1930s, people have been dedicated to research and practice in this area, using various methods to weld rails together to form seamless lines. In the process, they first encountered problems with joint welding quality; secondly, the strength and stability of long rails under the combined action of train dynamic forces and temperature forces; and there were also a series of theoretical and technical issues such as seamless line design, long rail transportation, laying and construction, maintenance and repair. With the gradual resolution of these problems, seamless lines have been widely used in various countries around the world.

Seamless lines, by eliminating a large number of joints, have a series of advantages such as smooth train operation, passenger comfort, reduced maintenance costs for locomotives, vehicles and tracks, and longer service life. A large amount of research data shows that, calculated from the perspective of labor savings and equipment life extension, seamless lines can save maintenance costs by 30% to 70% compared to jointed lines.

The length of long rail sections in seamless lines can theoretically be infinitely long, which is the theoretical basis for the development of cross-interval seamless lines. The length of ordinary seamless line rail sections is generally limited by factors such as signal machine positions, turnouts, and long bridges, and is usually only 1 to 2 kilometers. With the development of two key technologies, namely rail adhesive insulated joints and seamless turnouts, cross-interval seamless lines spanning block sections and across stations have been realized. With the improvement of the quality of new railway embankment filling and the significant reduction of post-construction settlement, as well as the ballast density and stability meeting the design speed requirements, cross-interval seamless lines can be laid on new lines in one go, eliminating the “memory diseases” caused by joints in ordinary lines and significantly improving the smoothness of the track. The successful laying of cross-interval seamless lines on the new Qinshen Passenger Dedicated Line marks a new era in the development of seamless lines in China’s railways.

The advantages of cross-interval seamless track are very obvious: the long rail sections run through the intervals and are welded to the turnouts at the stations, eliminating the buffer zones and fully realizing the seamless nature of the track, comprehensively improving the smoothness and overall strength of the line; after the elimination of the buffer zones, the wear of track components and the maintenance workload are further reduced; the elimination of rail joints further improves the train operation conditions; the temperature force peaks at the junctions of the expansion zones and fixed zones and the excessive expansion of the expansion zones that cannot be reset due to temperature cycles disappear with the disappearance of the expansion zones. Cross-interval seamless track has a strong anti-crawling ability, the longitudinal force distribution is relatively uniform, the locked rail temperature is easy to maintain, and the safety and reliability of the line are improved; the temperature force of the long rail sections in cross-interval seamless track rises and falls smoothly without forming temperature force peaks, allowing for a moderate increase in the locked rail temperature, thereby enhancing the stability of the track. For this reason, China’s “Main Railway Technical Policies” propose that high-speed and heavy-haul lines should prioritize the development of cross-interval super-long seamless track; the “Railway Eleventh Five-Year Plan” proposes to promote the technology of one-time laying of cross-interval seamless track.

Types of Seamless Track

Seamless track can be classified into two types based on the way the internal temperature stress of the rails is handled: temperature stress type and temperature stress release type.

1. The temperature stress type of ordinary seamless track consists of a welded long rail and 2 to 4 standard rails at each end, and uses ordinary joints. After the seamless track is locked, the welded long rail is restricted in its free expansion and contraction by the longitudinal resistance of the track, resulting in significant internal temperature stress in the rail, the value of which varies with the rail temperature. The temperature stress type of seamless track has a simple structure and is convenient for laying and maintenance, and is thus widely used. For straight tracks with 50kg/m and 60kg/m rails, 1760 and 1667 concrete sleepers are set per kilometer, respectively, and the allowable rail temperature difference for laying temperature stress type seamless track is 100℃ and 104℃, respectively.

2.The temperature stress release type of seamless track is further divided into automatic release type and periodic release type, and is suitable for areas with large annual rail temperature differences. The automatic release type is designed to eliminate and reduce the internal temperature stress of the rails by allowing the long rails to freely expand and contract, with expansion joints set at both ends of the long rails. Automatic release type seamless track is generally laid on bridges and at the ends of turnouts to release temperature stress, with expansion regulators set at both ends of the long rails. The periodic release type of temperature stress release seamless track has the same structural form as the temperature stress type. According to local rail temperature conditions, the internal temperature stress of the rails is adjusted and released 1 to 2 times a year. During the release, all fasteners of the welded long rails are loosened to allow free expansion and contraction, releasing the internal temperature stress. The necessary rail joints are maintained by replacing different lengths of adjustment rails in the buffer zones. Periodic release type temperature stress release seamless track has been tested in regions with large annual temperature differences in the former Soviet Union and China, but is now rarely used.

Currently, the temperature stress type of seamless track is mainly used in various countries around the world. According to the different laying locations and design requirements of seamless track, it can be classified into ballasted or ballastless track on embankments, seamless track on bridges, and seamless track in turnout areas; according to the length of the rail sections and whether they cross block sections, it can be classified into ordinary seamless track and cross-interval seamless track; according to the connection form of the joints of the long rails, it can be classified into welded seamless track and frozen seamless track.

Supplier

Luoyang Fonyo Heavy Industries Co., Ltd, founded in 1998,is a manufacturer in railway casting parts. Our factory covers an area of 72,600㎡, with more than 300 employees, 32 technicians, including 5 senior engineers, 11 assistant engineers, and 16 technicians. Our production capacity is 30,000 tons per year. Currently, we mainly produce casting, machining, and assembly for locomotive, railcar, high-speed trains, mining equipment, wind power, etc.
We are the railway parts supply to CRRC(including more than 20 branch companies and subsidiaries of CRRC), Gemac Engineering Machinery, Sanygroup, Citic Heavy Industries, etc. Our products have been exported to Russia, the United States, Germany, Argentina, Japan, France, South Africa, Italy and other countries all over the world.
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