The Development History of Rail Profiles and Fixed Lengths

The Development History of Rail Profiles and Fixed Lengths

The Origin of Rail Profiles
Rail profiles and fixed lengths are manifestations of the development of railways and the progress of metallurgical technology. Since the establishment and operation of the Hanyang Iron Works in 1894, China has had a history of 127 years in rail production. In the past, rail profiles were called rail types or styles. In the 1950s, rail standards were referred to as varieties (such as heavy rail varieties and light rail varieties, etc.). Now, according to the standard TB/T2344.1, they are called rail profiles, mostly expressed in kg/m (nominal unit weight). The standard specifies the cross-sectional dimensions of different rail profiles (the cross-sectional dimensions refer to theoretical dimensions without considering tolerances). The terms for rail profiles vary in different countries. In the United States, they are called rail sections; in Europe, rail profiles; and in Japan, rail types. Modern railway rails are all I-shaped. The I-shaped cross-section was first designed by the American engineer Stevens in 1830. In China, it is called the I-shaped cross-section, while in foreign countries, it is called T-shaped rails. The shape of the I-shaped rail has been used until now, but there have been continuous improvements in unit weight, the distribution of metal in the rail head, rail web, and rail base, and the shape of the rail head crown. Due to the requirements of force and processing, turnout rails are classified into three types in the European standard: asymmetric rails, symmetrical thick-web rails, and symmetrical full-web rails. Currently, only asymmetric rails such as 50AT1 and 60AT1 are included in the standards for turnout rails in China. Besides the above-mentioned cross-sectional rails, there are also light rails (9-30kg/m rails), tramway rails, and crane rails. According to the current standards, the classification of heavy and light rails is as follows: rails of 38kg/m and above are heavy rails (actual rail types include 38, 43, 50, 60, and 75kg/m); rails below 38kg/m are light rails (actual rail types include 9, 12, 15, 18, 22, 24, and 30kg/m).

The Development of Rail Profiles in China

2.1 Symmetrical Cross-Section Rails

Over the past 100 years, China has used many types of rail profiles, but there have been less than 15 types that were manufactured and used in China and included in the standards.
【Hanyang Rails】
The Hanyang Iron Works was established and began operation in 1894 and completely ceased production in 1922. During this period, the Hanyang Iron Works produced various types of rails for China’s railway construction. Among them, the 85-pound rail based on the British standard was included in China’s first rail standard, “The Regulations for the Manufacture and Acceptance of 85-Pound Rails and Accessories”.
【38-50kg/m Rails (referred to as P38-P50)】
In December 1950, the former Ministry of Railways issued the “Draft Specification for Railway Rails and Accessories”, which stipulated that there were five types of rail profiles: Chinese 30-type, Chinese 33-type, Chinese 38-type, Chinese 43-type, and Chinese 50-type. In 1953, the former Ministry of Heavy Industry and the former Ministry of Railways jointly formulated the “Heavy Rail Varieties” (variety refers to rail profile and specification based on the Soviet standard), including three types of rail profiles: 38, 43, and 50kg/m. The cross-sectional dimensions of the rails in GB181-1963 “Cross-Sectional Dimensions of 50kg/m Rails”, GB182-1963 “Cross-Sectional Dimensions of 43kg/m Rails”, and GB183-1963 “Cross-Sectional Dimensions of 38kg/m Rails” followed the provisions of the “Heavy Rail Varieties”. In 1981, the standard GB2585-1981 “Technical Conditions for 38-50kg/m Rails for Railway Use” was formulated, in which the cross-sectional dimensions of the rails followed the 1963 standards, but the dimensional tolerances were modified (see the compilation instructions of GB2585-1981). TB/T2344.1—1993 “Dimensions of 43kg/m Rail Type”, TB/T2344.2—1993 “Dimensions of 50kg/m Rail Type”, and TB/T2344.3—1993 “Dimensions of 60kg/m Rail Type” were the first to include 60kg/m rails, while the rail types of 38~50kg/m remained unchanged.
Since Chongqing Iron and Steel Company (referred to as Chongqing Steel) first developed and produced P38 rails in 1951, by the 1960s, the cross-section of Chinese rails had evolved from P38 to P50. These three rail types form a series, with the rail head composed of three arcs of R13, R300, and R13mm, and the side of the rail head has no slope. This design has been in use until now, and the cross-section has not changed (in 2020, the lower jaw arc of the rail head of P43 and P50 rails was changed from R2mm to R5mm, while other dimensions remained unchanged).
【60~75kg/m Rails (referred to as P60~P75)】
To meet the needs of railway development, P60 rails were developed and produced in the 1970s, and P75 rails were developed and produced in the 1980s.
The cross-sectional dimensions of P60 rails were designed by the Railway Building Research Institute of China Railway Science Corporation Limited (referred to as CRSC Railway Building Institute), mainly referring to the European UIC60 (60E1) rail, except for the rail height, which is 4mm higher, all other dimensions are basically the same. The railhead is composed of three arcs, namely R13, R80, and R300mm; the side of the railhead has a 1:20 slope starting from 14.2mm below the top surface.
The CRSC Railway Building Institute designed the cross-sectional dimensions of P75 rails, which are exactly the same as the Soviet P75 rail cross-section. The railhead is composed of three arcs, namely R15, R80, and R500mm; the side of the rail head has a 1:20 slope starting from 16.6mm below the top surface.
【New Rail Head Profile Rails】
To improve the wheel-rail matching relationship, enhance the stability of EMU operation, reduce wheel-rail contact stress, lower rail maintenance costs, and extend the service life of wheel-rail while meeting the needs of high-speed and heavy-haul railway development, in 2011, the CRSC Metal and Chemical Research Institute designed the new rail head profile rail P60N (N is the abbreviation of the English word NEW), in 2013, designed P75N rail, and in 2020, designed P50N rail. To facilitate rail interchangeability, the new rail head profile rails only modified the dimensions of the rail crown, while other dimensions remained the same as the original rails.

2.2 Asymmetric Cross-Section Rails

To meet the force requirements of turnouts and the need for turnout processing, since the 1970s, the CRSC Railway Building Institute has designed 50AT and 60AT rails in China. Here, AT is the abbreviation of the Chinese term for “low-profile special cross-section”, and the numbers 50 and 60 represent the rails used for 50 and 60kg/m tracks, respectively. The unit weights of these rails are 69.3 and 82.2kg/m, respectively.
With the development of high-speed railways and the introduction of turnout technology, China’s railway and metallurgical departments have also developed three types of turnout rails: 60AT2 (60D40), 60AT3 (Zu1-60), and 60TY (special cross-section for wing rails). Among them: 60AT2 is the same as 60E1A5 in the European standard (EN13674.2); 60AT3 is the same as 60E1A1 in the European standard (EN13674.2), and 60TY is a cross-section independently designed in China, which is based on the 60kg/m rail and has a wider rail head and rail waist thickness.
Unification of Rail Head Profiles
To reduce wheel-rail contact stress, decrease grinding workloads, and extend the service life of rails, the United States has also optimized rail head profiles. Firstly, the 136RE (68kg/m) rail was optimized and included in the AREMA standard for the first time in 2003 and was modified again in 2007. In 2011, the new rail head profile was applied to the 115RE and 141RE new steel rails commonly used in the US railway, and in 2017, it was also applied to the 132RE steel rails, forming a unified rail head profile. The four new rail head profile rail crowns are mainly composed of several arcs, such as approximately R200, R44, and R14mm (8, 1.75, and 9/16 inches). After the new profile rails were included in the standards, the old profile rails were deleted from the standards.

The P50, P65, and P75 rails used in Russia also have a unified rail head profile, and their rail crowns are composed of three arcs of R15, R80, and R500mm.

Since 2016, the national railway network in China has basically adopted P60N rails, but the turnout areas have not adopted them, mainly relying on rail grinding to optimize the rail head profile. P50N rails have also not been widely promoted and applied in the national railway. It can be seen that even in the national railway network, a unified rail head profile has not been formed, which brings certain difficulties to the optimization management of the wheel-rail relationship, and related work to unify the rail head profile needs to be continued.

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