Rail Pads and Pressure Plates: Combination and Performance Requirements
- How do under-rail pads and press plates cooperate to fix the rail?
Under-rail pads are laid between the rail and the sleeper to provide elastic support for the rail and adjust the rail height. Press plates are installed on both sides of the rail and fixed on the sleeper by bolts. One end of the press plate presses the rail base, and the other end is connected to the sleeper. The pre-tightening force of the bolts makes the press plate generate lateral pressure on the rail, fixing the rail on the pad to prevent lateral movement of the rail. The two cooperate to ensure the longitudinal and lateral positioning of the rail, and buffer the train load through the elasticity of the pad.
- What are the main performance requirements for under-rail pads?
They have good elasticity, which can absorb vibration and impact generated by train loads. The elastic modulus is generally between 80-150MPa, and different lines have different requirements. High-speed lines require higher elastic precision. They have good wear resistance, can withstand long-term friction between the rail and the pad, and have a service life of not less than 6 years. They have strong aging resistance, with little performance change under the action of environmental factors such as sunlight and temperature changes. For example, rubber pads need to have good ozone aging resistance. In addition, they need to have a certain compressive strength, not easy to produce excessive permanent deformation under long-term load, and the compression permanent deformation should be less than 10%. At the same time, their insulation performance must meet the standard to prevent short circuit of the track circuit, especially for under-rail pads used in electrified railways, the insulation resistance should be not less than 10⁸Ω.
- What are the characteristics of the material and structural design of press plates?
Press plates are mostly made of ductile iron or high-quality carbon steel. Ductile iron press plates have high strength and toughness, with a tensile strength of ≥400MPa, good castability, and can be made into complex shapes; high-quality carbon steel press plates (such as Q345 steel) are formed by forging or stamping, with higher strength, suitable for heavy-haul lines. In structural design, the contact part between the press plate and the rail is mostly arc-shaped, which fits the contour of the rail base to ensure uniform force; the connecting end is provided with bolt holes with high hole position accuracy to ensure alignment with the reserved holes of the sleeper during installation and reduce installation stress.
- What are the requirements for the fitting gap between under-rail pads and press plates?
The gap between the press plate and the rail base should be controlled at 0.3-0.5mm. Too small a gap will cause the rail to be compressed and deformed, and too large a gap will fail to effectively fix the rail. The under-rail pad and the sleeper surface must be closely attached, with a gap not greater than 0.2mm to avoid the pad shaking when the train passes. In curve sections, the gap between the outer press plate and the rail can be appropriately reduced by 0.1-0.2mm to resist the lateral thrust of the rail; the inner gap can maintain the standard value to ensure that the rail is not hindered when expanding and contracting.
- How to select under-rail pads and press plates under different climatic conditions?
In high-temperature areas (rail temperature exceeding 60℃), neoprene pads with high temperature resistance should be selected, which are stable at 100℃, and matched with ductile iron press plates with small thermal expansion coefficient to reduce the impact of temperature deformation. In cold areas, cold-resistant rubber pads (not brittle at -40℃) should be selected, and galvanized press plates should be used to enhance the resistance to freeze-thaw corrosion. In rainy and humid areas, polyethylene pads with low water absorption should be selected, and the press plates should be phosphated and painted to improve corrosion resistance and ensure long-term reliable work in humid environments.