Elasticity adjustment and selection of rail pads
- What indicators are used to measure the elasticity of under-rail pads, and what are their ranges?
Elastic modulus is the main indicator, in MPa. The elastic modulus of ordinary rubber pads is 80 - 150MPa, which can meet the needs of ordinary railways; high - speed railway special pads are 50 - 100MPa, with better elasticity, which can reduce vibration transmission. Static stiffness (kN/mm) is also commonly used, defined as the force required for unit deformation. The static stiffness of ordinary railway pads is 15 - 30kN/mm, and that of high - speed railways is 10 - 20kN/mm. The smaller the stiffness, the better the elasticity, but the stability needs to be balanced. Rebound rate is an indicator of elastic recovery ability. High - quality pads have a rebound rate ≥80%, that is, they can recover more than 80% of deformation after unloading, natural rubber pads can reach 85% - 90%, and plastic pads about 70% - 75%. The dynamic - static stiffness ratio (dynamic stiffness/static stiffness) should be ≤1.5. A too large ratio indicates poor dynamic buffering performance. High - speed railway pads need to be controlled at 1.2 - 1.4 to ensure good elasticity when trains pass at high speed.
- How to adjust the elasticity of under-rail pads to adapt to different scenarios?
Changing the thickness is a simple method. For every 1mm increase in thickness, the elastic modulus can be reduced by 5% - 8%. For example, a 10mm thick pad has an elastic modulus of 120MPa, and a 12mm thick pad can be reduced to 100MPa. Heavy - haul railways can increase stiffness by reducing thickness. Adjusting the material formula, increasing the proportion of natural rubber in rubber pads (from 50% to 70%), the elastic modulus can be reduced by 10% - 15%, suitable for high - speed railways; adding carbon black can increase stiffness, used in heavy - haul railways. Using a composite structure, such as rubber + metal interlayer, adjust elasticity by changing the thickness of the metal sheet. The thicker the metal sheet, the greater the stiffness, which can be customized according to needs. This kind of adjustable elastic pad is commonly used in turnout areas. Reserve compression amount, make the pad pre - compressed by 5% - 10% during installation, which can ensure initial elasticity and cope with later aging. Ordinary railways are pre - compressed by 5%, and high - speed railways by 8% - 10%.
- What impact does the elasticity of under-rail pads have on train operation?
Insufficient elasticity will increase track vibration, increase train operation noise by 5 - 10dB, reduce passenger comfort, and at the same time, the impact force on sleepers and ballast will increase by 20% - 30%, accelerating damage. Excessive elasticity will increase rail displacement, and the gauge deviation will exceed the allowable range (high - speed railway ±2mm), affecting driving safety, especially in curve sections, excessive elasticity may lead to excessive lateral displacement of rails. Appropriate elasticity can extend wheel - rail life. Compared with 50MPa, the rail wear of pads with elastic modulus 100MPa is reduced by 15% - 20%, and the wheel life is extended by more than 10% due to low vibration and impact force. Elastic uniformity is very important. The elastic deviation of pads in the same section should be ≤10%, otherwise it will cause uneven track stiffness, and the train will bump when passing, affecting stability. Elastic indicators need to be sampled during installation.
- How to consider the elastic changes of under-rail pads in different seasons?
High temperature in summer (≥35℃) will soften rubber pads, and the elastic modulus will decrease by 10% - 15%. It is necessary to select heat - resistant formulas, such as adding anti - aging agents, to control the elastic change within 5% and avoid excessive stiffness reduction. Rubber will harden at low temperature in winter (≤-10℃), and the elastic modulus will increase by 15% - 20%. Cold - resistant pads (such as EPDM rubber) change only 5% - 10%, suitable for northern regions, and can maintain stable elasticity. The temperature difference in spring and autumn is large, and the elastic fluctuation of pads is frequent. It is necessary to select materials with good weather resistance, such as chloroprene rubber pads. When the temperature changes by ±20℃, the elastic modulus changes by ≤8% to ensure stable track performance. Rubber pads will absorb a small amount of water in rainy seasons, and the elastic modulus will decrease by 5% - 8%. It is necessary to select waterproof formulas, such as adding paraffin, to reduce water absorption, which is more important in coastal areas.
- What track parameters need to be considered when selecting under-rail pads?
Gauge is the basis. 1435mm standard rails use standard size pads (such as length 180mm), and broad or narrow rails need to be customized to ensure matching with rails and sleepers, with a deviation ≤1mm. Axle load determines stiffness. Heavy - haul railways with axle load ≥25t need to select high - stiffness pads (static stiffness ≥25kN/mm), and those with axle load < 16t select low stiffness (≤20kN/mm) to balance buffering and stability. Different track types have different requirements. Ballasted tracks can use ordinary rubber pads, and ballastless tracks need high - precision, low - stiffness pads (static stiffness 10 - 15kN/mm) to ensure close fit with track slabs. Train speed has a great impact. Speed ≥200km/h needs low elastic modulus (50 - 100MPa), and speed < 120km/h can select 100 - 150MPa, taking into account cost and performance.