Most Developed Polymers Used in Rail Transportation
- Updated on January 10, 2022
The continuous improvement of the running speed of railway vehicles not only further increases the requirements for running stability and ride comfort, but also puts forward higher requirements for flame retardancy, environmental protection, light weight, vibration reduction and noise reduction. Therefore, more and more polymeric materials are used in rail transportation. Today, some advanced polymers commonly used in rail transit are listed.
Polyurethane Elastomer
Compared with general-purpose rubber, polyurethane has better wear resistance and toughness, and is known as "wear-resistant rubber". Due to the customizability of polyurethane molecules, by controlling the composition and structure, it develops in the direction of functionalization and high performance.
MDI Polyurethane
At present, MDI polyurethane microcellular elastomer damping pads and polyurethane elastomer expansion joints have been successfully applied to China's high-speed railway.
Polyurethane composite sleepers have the advantages over wooden or concrete ones, and make up for the defects of both. They not only have excellent mechanical properties, flexural strength and shear strength, but also can reduce vibration, reduce noise, improve driving comfort and safety, protection of track beds, etc. At the same time, the polyurethane sleeper also has the advantages of good electrical insulation and no need to install insulating pads.
NDI-based Polyurethane
NDI-based polyurethane has stronger molecular chain rigidity than benzene ring due to its naphthalene ring structure, and its macroscopic performances include higher compressibility, higher deformability, better dynamic fatigue resistance, and lighter weight.
Silicone Foam Material
Silicone refers to a compound containing Si-O bonds and at least one organic group directly connected to the silicon atom. Its structure contains both "organic groups" and "inorganic structures", so it has both organic and inorganic properties. .
Silicone materials can be used for a long time at -70 ~ 150 ℃(-94~302F) and have excellent electrical insulation properties, oxidation resistance stability, weather resistance, flame retardancy, water repellency, corrosion resistance, non-toxic and tasteless, etc. The characteristics of flammability and non-toxicity make it widely used in rail transportation.
At present, the representative products of silicone foam are seat cushions and subway floor vibration damping pads. Silicone foam is used as a floor vibration damping pad, which not only has a good vibration damping effect, but also acts as a sound-isolating bridge, and has a good noise reduction effect.
With the higher flame retardant requirements for rail vehicle seat cushions, at present, some export-oriented rail vehicles developed by CRRC Tangshan Rail Passenger Car and CRRC Changchun Rail Passenger Car and Jing-Xiong High-speed Railway developed by CRRC Qingdao Sifang business-class seats are equipped with silicone foam seat cushions.
In addition, the Hong Kong subway and the buses of the new airport demonstration lines in Beijing and Shanghai all use silicone materials, and some foreign rail transit equipment also gradually require their seats to use silicone foam materials.
Featured Nylon
Nylon has been widely used as the basic material of high-speed rail fasteners. In order to ensure the safe operation of high-speed railways in alpine regions, fasteners must meet higher standards, especially low-temperature fatigue resistance. Therefore, higher requirements are put forward for nylon's low temperature toughness, processing fluidity, wrapping ability and encapsulation of fillers such as glass fiber.
Low temperature resistant copolymerized nylon can combine high toughness and high fluidity, and can be used in rail transportation.
Aramid Insulation Material
Aramid is the abbreviation of aromatic polyamide fiber, which was invented by DuPont. It has the advantages of heat resistance, flame retardant, light weight, high strength and good wear resistance. Meta-aramid products have a wide range of uses in high-end electrical insulation and lightweight honeycomb structures, and have now become an important basic material in the fields of electrical machinery and power transmission.
High-quality aramid is the key main insulating material in high-power motors, transformers, and electrical equipment in rail transit, and is used in wrapping insulation, slot insulation, inter-turn insulation and other areas. Especially in the motors and transformers of high-speed EMUs, the amount of insulation system is huge. Foreign commercialized meta-aramid paper mainly includes DuPont's Nomex and Japan's Teijin.
At present, the development of aramid fiber products has been completed in China, and various products such as laminated board, insulating paper, and aramid honeycomb paper have been applied in various fields such as rail transit. The figure below shows the application of aramid insulating paper in the slots and turns of transformers and motor coils.
Composite Material
Composite materials in a narrow sense mainly refer to fiber-reinforced composite materials and sandwich structure composite materials, which have the characteristics of light weight, high strength, fatigue resistance, and corrosion resistance.
At present, domestic rail transit composite materials are mainly used in non-load-bearing structures such as interior parts, among which the driver's interior, driver console, hood, passenger seat surface, side wall panels, roof panels, door pillar covers and other structures are using fiberglass composite.
With the development of railways in the direction of high speed, safety and light weight, the role of polymer materials is becoming more and more important. Rail transit systems will become an important field for the development of modified plastics in the future, and high-performance PA composites have become the most promising application products.
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