The Core Matching of Shore Hardness and Temperature Adaptability of Rail Pads
What hazards are caused by the increase in Shore hardness of under-rail pads in low-temperature environments (below -20℃)?
Below -20℃, rubber and polyurethane materials undergo a "glass transition", with Shore hardness increasing by 10°-15° and elastic modulus rising sharply. After hardness increase, the elastic deformation capacity of the pad drops drastically, the overall track stiffness increases, and the wheel-rail impact load rises by more than 20%. At the same time, the brittleness of the pad increases, making it prone to cracking and chipping under train load impact, and the vibration reduction performance decreases by more than 50%. For rubber pads, increased hardness also reduces the bonding force with sleepers, making pad slippage prone to occur and damaging the geometric stability of the track.
What impact does the decrease in Shore hardness of under-rail pads have in high-temperature environments (above 60℃)?
Above 60℃, the molecular chain movement of the under-rail pad material intensifies, Shore hardness decreases by 8°-12°, and the material's resistance to compression set is significantly reduced. After hardness decrease, the plastic deformation of the pad under train load increases by more than 30%, leading to uneven rail settlement and deteriorated track smoothness. At the same time, the creep rate of the pad accelerates; after long-term service, "collapse" occurs, causing a regional decrease in track stiffness and exacerbating wheel-rail uneven wear. In addition, pads with low hardness are easily extruded and deformed by elastic clips or pressure plates, losing their elastic support function.
What are the differences in the Shore hardness selection standards for under-rail pads in different service temperature regions?
Frigid regions (minimum temperature ≤-30℃) need to select low-hardness rubber pads with Shore A 50°±5° or modified polyurethane pads to lower the glass transition temperature and ensure elasticity at low temperatures. High-temperature regions (maximum temperature ≥60℃) need to select high-hardness polyurethane pads with Shore A 90°±5° to improve the heat resistance of the material and reduce high-temperature plastic deformation. Temperate regions (-20℃ to 60℃) can use standard-hardness rubber or polyurethane pads, balancing elasticity and heat resistance. Alpine high-speed lines need to select special elastomer pads with Shore D 30°±3° to balance low-temperature elasticity and high-temperature stability.
What is the quantitative relationship between Shore hardness and the vibration reduction performance of under-rail pads?
Within the standard hardness range, the vibration reduction performance of under-rail pads is negatively correlated with Shore hardness-for every 5° decrease in hardness, the vibration reduction efficiency increases by 8%-10%. When the hardness of the rubber pad decreases from Shore A 60° to 55°, the vibration reduction efficiency increases from 25% to about 33%. However, when the hardness is lower than 50°, the improvement of vibration reduction efficiency slows down, and plastic deformation intensifies due to insufficient pad strength. When the hardness is higher than 65°, the vibration reduction efficiency drops sharply to below 15%, failing to meet the track vibration reduction requirements. Therefore, each pad material has its optimal hardness range; it is not that the softer the pad, the better the vibration reduction effect.
How to quickly detect the Shore hardness of under-rail pads on site to judge whether their temperature adaptability is qualified?
On site, a portable Shore hardness tester (Type A for rubber, Type D for high-hardness polyurethane) can be used to measure multiple points in the non-stressed area of the pad, and the average value is taken as the test result. During testing, the ambient temperature must be close to room temperature (25℃) to avoid the impact of temperature on hardness measurement. If the measured hardness exceeds the standard range of ±5°, it indicates that the pad material is aged or improperly selected, and the temperature adaptability is unqualified. In addition, combined with the appearance state of the pad-if cracks appear at low temperatures or viscous deformation at high temperatures-even if the hardness is qualified, the pad suitable for the temperature must be replaced.