Track Pad Stiffness Classification and Application Specifications
Why are low-stiffness under-rail pads selected for high-speed railways?
High-speed railways of 350km/h have extremely high requirements for driving smoothness and vibration and noise reduction. Low-stiffness (20-30kN/mm) under-rail pads can better absorb wheel-rail impact force and reduce vibration transmission. Low-stiffness pads have better elasticity, which can effectively buffer high-frequency vibration during high-speed train operation and improve passenger comfort. It can make the track elastic distribution more uniform, reduce excessive local stress on rails, and extend the service life of rails. At the same time, the low-stiffness design can reduce the dynamic-static stiffness ratio of the track structure, improve the wheel-rail contact state, and reduce wear. In addition, the insulation performance of low-stiffness pads is more stable, which can meet the insulation requirements of track circuits and ensure reliable signal transmission.
What impact does the aging resistance of under-rail pads have on the line?
Under-rail pads are exposed outdoors for a long time, subject to temperature changes, rain erosion and load extrusion. Insufficient aging resistance will lead to material cracking, hardening and loss of elasticity. After the pad ages, the track elasticity will decrease, vibration will increase, wheel-rail impact will intensify, and the damage of rails and sleepers will be accelerated. The insulation performance of aging pads may fail, affecting the normal operation of track circuits and causing signal failures. At the same time, the aging pad cannot effectively disperse pressure, leading to local stress concentration on sleepers, which is prone to cracking and damage. In addition, frequent replacement of aging pads will increase maintenance costs and line outage time, affecting operational efficiency.
What are the advantages of composite under-rail pads compared with rubber pads?
Composite under-rail pads combine the elasticity of rubber with the rigidity of metal or engineering plastics, with stronger stiffness stability and less susceptibility to temperature changes. Its wear resistance and tear resistance are higher, and its service life is more than 30% longer than that of ordinary rubber pads, reducing replacement frequency. Composite materials have better oil resistance and corrosion resistance, and can adapt to complex track environments, such as oil pollution and chemical medium pollution. In terms of bearing capacity, composite pads can bear larger loads with smaller deformation, suitable for heavy-haul and high-speed lines. At the same time, the insulation performance of composite materials is more excellent, which can meet the higher standard insulation requirements of track circuits.
What factors need to be considered when selecting the stiffness of under-rail pads?
First, it is necessary to combine the design speed of the line. Class B low-stiffness pads are selected for 350km/h passenger dedicated lines, and Class A medium-stiffness pads are selected for 250km/h lines that also carry freight. Line load conditions are crucial. Heavy-haul lines need to appropriately increase pad stiffness to ensure bearing capacity and avoid excessive deformation. The type of track structure also needs to be considered. Ballastless tracks have higher requirements for pad stiffness uniformity, and ballasted tracks can be flexibly adjusted according to ballast elasticity. In terms of geological conditions, slightly lower stiffness pads can be selected for lines with soft foundations to offset part of the settlement impact. In addition, local climate conditions should be considered. Pads with good stiffness stability are preferred in areas with extreme temperature differences.
How to detect whether the stiffness of under-rail pads meets the standard?
Special stiffness testing equipment is required for detection, simulating the actual stress state of the pad, applying different loads, measuring the corresponding deformation, and calculating the stiffness value. During the test, the ambient temperature must be controlled within the standard range (23℃±2℃) to avoid the impact of temperature on material elasticity. According to relevant standards, the pad needs to be tested under specified load cycles to ensure that the stiffness change does not exceed 25% and meets the fatigue performance requirements. For laid lines, the track smoothness detection and vibration data collection can be used to indirectly evaluate whether the pad stiffness has attenuated. During regular sampling inspection, pads in different laying positions and service durations should be covered to ensure overall performance meets the standard.