The Material Composition of Track Pads and Their Impact on Track Vibration and Noise Reduction
What are the formulation advantages of natural rubber-styrene butadiene rubber blended pads?
The typical ratio of natural rubber-styrene butadiene rubber blended pads is 60% natural rubber + 40% styrene butadiene rubber, which balances the high elasticity of natural rubber and the wear resistance of styrene butadiene rubber with outstanding cost performance. The damping coefficient of the blended rubber material can reach 0.15-0.20, which can effectively attenuate wheel-rail vibration, reduce track vibration noise by 8-12 decibels, and is suitable for conventional speed railways and urban rail transit. The rebound rate of the pad with this formula is ≥65%, which is not prone to permanent deformation under long-term load, and the service life can reach 8-10 years. The carbon black reinforcing agent added in the blending process can increase the tensile strength of the pad to more than 18MPa, and the tear resistance is significantly enhanced. In addition, the anti-aging agent added in the formula can delay rubber aging, maintain stable performance in the temperature range of -30℃ to 60℃, and adapt to different climate zones.
What performance advantages do polyurethane (PU) pads have over rubber pads?
The hardness of polyurethane pads can be precisely adjusted between Shore A 50-90, which can be customized according to the vibration reduction needs of different lines and is suitable for full-scenario applications from conventional speed to high speed. Its compressive strength is ≥30MPa, more than twice that of ordinary rubber pads, with excellent resistance to compressive permanent deformation, and the deformation is ≤5%, far lower than the 15% standard of rubber pads. Polyurethane pads have outstanding wear resistance, with a wear loss of only 0.08cm³/1.61km, and a service life of more than 15 years, greatly reducing the replacement frequency. This material has stronger oil resistance and chemical corrosion resistance, suitable for track use in special polluted environments such as mines and chemical parks. At the same time, the insulation resistance of polyurethane pads is ≥10¹⁰Ω, which is better than that of rubber pads, and is more suitable for electrified railways with high voltage levels.
Why are ethylene propylene diene monomer (EPDM) pads suitable for use in alpine regions?
The glass transition temperature of ethylene propylene diene monomer is as low as -55℃, so it will not be brittle in the extreme low temperature environment of alpine regions, and can still maintain good elasticity and vibration reduction performance. This material has excellent weather resistance and strong UV aging resistance. Under the intense UV radiation in alpine regions, the performance attenuation rate is no more than 3% per year. EPDM pads have excellent ozone resistance, can resist ozone erosion in the thin air of alpine regions, and avoid cracking of the pads. The cold-resistant plasticizer added in its formula can further improve low-temperature toughness. When subjected to compression test at -40℃, the rebound rate can still be maintained above 60%. In addition, EPDM pads have outstanding waterproof performance, which can prevent water from melting ice and snow from penetrating into the pad, avoiding pad damage caused by frost heave.
What special requirements do urban rail transit have for the vibration and noise reduction indicators of under-rail pads?
Urban rail transit mostly operates in urban centers, with strict requirements for noise control. Under-rail pads need to reduce wheel-rail noise to below 65 decibels to meet urban environmental noise standards. The vertical static stiffness of the pad should be controlled at 20-40kN/mm, which can effectively reduce vibration and avoid track settlement caused by insufficient stiffness. Urban rail trains start and stop frequently, so the pad must have excellent fatigue resistance. After 10 million alternating load tests, the stiffness attenuation rate is ≤10%. Since most urban rails are underground lines with humid environment and poor ventilation, the pads must have mildew and antibacterial properties to inhibit performance degradation caused by mold growth. In addition, urban rail pads must adopt a flame-retardant formula with an oxygen index ≥28% to prevent fire spread in case of fire accidents and ensure operational safety.
How to judge whether the vibration reduction performance of under-rail pads meets the standard through testing?
A vibration test bench can be used to simulate wheel-rail impact load, measure the vibration transmissibility of the pad. If the transmissibility is ≤30%, the vibration reduction performance is judged to meet the standard, and the lower the value, the better the vibration reduction effect. Use a universal testing machine to test the static stiffness of the pad, compare it with the design value to judge whether it meets the line vibration reduction needs, and the deviation should be controlled within ±10%. Conduct noise testing, measure the noise value when the train passes at a distance of 5 meters from the track to ensure that it meets the noise emission standard of the area. Through the compression permanent deformation test, compress the pad at 70℃ for 22 hours, measure the deformation, and a deformation ≤8% is qualified to verify its long-term use stability. In addition, on-site drop hammer test can be carried out to record the rebound of the pad after drop hammer impact, and intuitively evaluate the actual performance of the vibration reduction effect.