Material Properties and Selection of Rail Pads
- What are the commonly used materials for under-rail pads? What are their characteristics?
Commonly used materials for under-rail pads include rubber, polyethylene (PE), polyurethane and styrene-butadiene rubber. Rubber pads have good elasticity and can effectively absorb vibration, but their aging resistance is general, with a service life of 5-8 years; PE pads have strong wear resistance and good chemical corrosion resistance, suitable for acid-base environments, but their elasticity is slightly lower; polyurethane pads have excellent comprehensive performance, with good elasticity and wear resistance, and a service life of 10-15 years, but the cost is higher; styrene-butadiene rubber pads have good cold resistance and can maintain good elasticity at -30℃, suitable for use in cold regions.
- What are the hardness requirements for under-rail pads for different line types?
High-speed railway lines require under-rail pads with a hardness of Shore A 60-65 degrees, which can ensure sufficient elasticity and control rail displacement within 0.5mm; the hardness of pads for ordinary railway trunk lines is Shore A 55-60 degrees, taking into account both buffering and bearing capacity; freight dedicated lines require pad hardness to be increased to Shore A 65-70 degrees due to large loads to reduce deformation; the hardness of pads for urban rail transit (such as subways) is Shore A 50-55 degrees, focusing on shock absorption and noise reduction to improve ride comfort.
- How to determine the thickness of under-rail pads?
The thickness of under-rail pads should be determined according to the rail type and line settlement requirements. The common thickness for 60kg/m rails is 10-12mm, and for 50kg/m rails is 8-10mm; in areas with large settlement, thickened pads (12-15mm) can be used to compensate for settlement through their own compression; the thickness deviation of pads for high-speed railway lines must be controlled within ±0.5mm to ensure track smoothness; the thickness of pads in turnout areas is determined according to actual height adjustment requirements, and pads of different thicknesses can be used in 叠加,but the total thickness should not exceed 20mm.
- What is the impact of the elastic modulus of under-rail pads on the track system?
Too low elastic modulus (＜80MPa) will lead to excessive compression of the pad, increase the rail sinking amount, and affect the track geometric dimensions; too high elastic modulus (＞150MPa) results in poor buffering effect, and the train vibration load is directly transmitted to the sleeper, accelerating sleeper damage; the appropriate elastic modulus is 100-120MPa, which can effectively absorb vibration and ensure track stability; in curve sections, the elastic modulus of the outer under-rail pad can be appropriately increased by 5%-10% to resist greater lateral force.
- How to select under-rail pad materials according to environmental conditions?
In high-temperature and high-humidity areas (such as southern coastal areas), polyurethane pads with resistance to 湿热 aging should be selected, whose performance attenuation rate in 90% humidity and 60℃ environment is ＜10% per year; in cold regions (such as Northeast China), styrene-butadiene rubber or rubber pads with cold-resistant agents are preferred to ensure no embrittlement at -40℃; in acid-base soil areas, PE pads are selected, whose chemical corrosion resistance can reduce the impact of soil erosion; the environment in tunnels is closed, and flame-retardant under-rail pads (oxygen index ≥32) can be selected to reduce fire risks.