Overview of the application of aramid products in the field of rail transit
Aramid productsApplication overview in the field of rail transit
0 Preface
Our country has the characteristics of a large geographical area, uneven population distribution, and unbalanced regional economic development. These characteristics determine the irreplaceable role of rail transit in the development of the national economy and the important position of key materials in the field of rail transit. With the development of high-speed railways, as the transportation speed increases, the quality of its key materials also needs to be further improved, and there is an urgent need for upgrading. In October 2014, in order to support the development of the rail transit industry, the National Development and Reform Commission, the Ministry of Finance, and the Ministry of Industry and Information Technology jointly issued the “Implementation Plan for the Key Materials Upgrading Project.” Among them, aramid paper was selected as an “urgently needed material in the advanced rail transit industry” due to its good performance and broad market space.
Aramid paper was first invented by DuPont in the United States, and its trade name is Nomex. It uses aramid chopped fibers and aramid fibrid fibers as raw materials and is prepared using a unique papermaking and hot pressing process. It can be used as key insulating materials for transformers, motor slots, magnetic coils, and electromagnetic coils used in high-speed rail, urban rail, and subway to ensure the safe operation of electrical equipment; aramid paper can also be used to prepare aramid honeycombs, which can be used to manufacture high-speed rail As well as the doors, partitions, luggage racks, floors and other components of high-speed trains, they play a major role in lightweighting in the field of rail transit.
1 Application of aramid paper in train motors
Aramid paper has the characteristics of high strength, high insulation level, flame retardancy, high temperature resistance, moisture resistance, and chemical corrosion resistance. It can be used as insulation material for high-speed train motors and transformer systems. Compared with other insulating materials, aramid paper has a limiting oxygen index of >28 and will not support combustion, explosion or combustion, and will not release toxic gases, which improves the safety and stability of high-speed trains; aramid paper has high heat resistance , can reduce the cooling space of the transformer, making the transformer compact and reduced in size; aramid paper has excellent moisture resistance and can increase the life of electrical equipment. Although domestic units such as Yantai Minstar, Shanghai Shengou, and Shenzhen Longbang have carried out industrialization, due to limitations in industrial scale and technical capabilities, the domestic high-end electrical insulation market is still monopolized by DuPont.
1.1 Transformer
Aramid paper can be widely used in the insulation parts of various dry-type and oil-immersed transformers, including wire wrapping paper, layer insulation, phase insulation, core wire insulation, wire end insulation, electrostatic rings, stays and spacers, etc. Aramid paper and cardboard can also be used with high-temperature oils such as Midel, R-Temp and silicone to form high-temperature insulation systems that have been used in railway system traction equipment and roadside distribution transformers. Nomex insulation system transformers are used on the American high-speed train “Acela Express”. The application of Nomex has reduced the volume of the train’s transformer by 15% to 20%, reduced its maintenance workload, and increased its safety.
In the manufacturing process of traction transformers, aramid insulating paper is partially used to replace ordinary insulating paper, which can reduce the capacity level of the transformer and effectively reduce the operating cost of electrical equipment. Li Qiang of Beijing Jiaotong University uses Nomex insulating paper to partially replace the ordinary insulating paper of traction transformers, which can improve the overload capacity of the transformer, reduce basic capacity fees, and reduce the operating costs of electrified railways.
Hybrid insulation refers to the use of aramid paper and cardboard in the high-temperature parts of the transformer coil, while cellulose paper is used in other less hot parts. This technology is currently used in Europe, North America, Australia and other countries. my country’s Chengdu Railway power supply system uses a 13.5 MV hybrid insulated rectifier transformer to replace the original two 10 MV conventional rectifier transformers, which greatly saves costs.
1.2 Motor
As my country’s railway electrification and the construction of urban subways and light rails accelerate, motors are developing towards high voltage levels, high power, large capacity, and high performance, which has led to a surge in demand for meta-aramid insulating paper. Aramid paper is widely used in rotating equipment such as generators and motors. Its specific applications include wire wrapping paper, slot insulation lining, stays in the middle and top of wedges, phase insulation, pole pieces and coil supports, commutator V ring, lead insulation and ground insulation.
In the high-speed motor trial produced by Xiangtan Electric Machinery Company, aramid fiber-epoxy resin composite material is used for the rotor guard ring of the high-speed engine. The tensile yield limit is 1498 MPa, which can meet the requirements of high-speed operation of the motor and solve the problem of traditional glass fiber rotor guard rings. The problem of insufficient ring strength. Tianjin Huazhiyang Special Cable Company invented a closed motor lead wire, which is composed of a metal conductor, an inner braided layer, an outer braided layer and a wrapping layer. The inner and outer braided layers are both made of aramid. The braided motor lead wire is completely suitable for It is used in high-temperature and high-pressure refrigerant and lubricating oil applications in enclosed motors.
2 Application of aramid honeycomb in trains
Aramid honeycomb is made of aramid paper through glue coating, paper cutting, lamination, hot pressing, stretching, dipping, shaping, sheet cutting and other processes. A certain process is used to combine carbon fiber panels, glass fiber panels, aluminum panels, etc.The traditional design concept of stressed members has expanded its application scope to a new field.
2.3.2 Used in manufacturing train load-bearing parts
Aramid honeycomb can also be used to manufacture the main load-bearing parts of high-speed trains, including high-speed train roofs, car bodies, driver’s cabs and other components. The roof of the Italian ETR500 train is made of glass fiber/carbon fiber fabric reinforced phenolic resin prepreg to make a sandwich structure panel, using 48 kg/m3 aramid fiber honeycomb with a thickness of 12.5 mm as the core material, and using vacuum bagging and hot pressing. Using the can molding process (autoclave pressure is 0.25 MPa, curing temperature is 135°C), a composite sandwich structure car that meets the requirements for high-speed train roof bending stiffness, flame retardant and environmental aging resistance, and joint fatigue life is prepared. Top, the mass is reduced from the original 1080kg to 512kg. To increase the passenger capacity of the Disneyland Florida railcar, the car body was redesigned using a variety of composite materials, including honeycomb, carbon and fiberglass, and epoxy and phenolic resins. Compared with traditional aluminum structures, the weight of this monorail car body is reduced by more than 40%. And it is estimated that its cost is 9% cheaper than that of aluminum, mainly due to the reduction in workload and scrap materials.
3 Conclusion
With the acceleration of railway electrification and the construction of urban subways and light rails, higher requirements have been put forward for the safety of electrical equipment of railway vehicles and the lightweight of vehicles. The batch use of aramid paper and aramid honeycomb is The development of high-speed rail technology is inevitable.
1) On the one hand, domestic aramid paper manufacturers should strengthen the localization of key equipment such as papermaking and hot pressing. On the other hand, they should make joint efforts to overcome the key technologies of aramid paper raw materials, reduce the cost of aramid insulating paper, and enhance its on-track Competitiveness in the transportation field, occupying the high-end electrical insulation market.
2) Before designing aramid honeycomb components, finite element analysis and other software should be used to simulate them to analyze whether their strength, stiffness and fatigue resistance meet the requirements; the application of aramid honeycombs requires strengthening the research and design of new installation processes, giving full consideration to Its bonding, opening and splicing processes of aramid honeycomb sandwich materials; developing different types of panels to fully meet the needs of different applications.
3) Since high-speed EMUs belong to different imported models, involve different materials and specifications, and are distributed among different OEM manufacturers, it is impossible to establish a unified material evaluation system and collect statistics on the demand for related aramid products. Therefore, it is necessary to establish a supply and demand service platform as soon as possible to solve the problems existing in the application of aramid products and promote the development of the aramid industry.
