Rail Pad Aging Performance and Replacement Cycle
- What are the main manifestations of aging of under-rail pads?
Rubber pads will show surface cracks and hardening after aging, with reduced elasticity, and rebound slowly when pressed with fingers; polyurethane pads will show volume shrinkage and bubbles after aging, with significantly reduced cushioning performance; severely aged pads will delaminate or break, unable to effectively transmit and disperse loads, leading to uneven stress on the rail.
- What environmental factors affect the aging rate of under-rail pads?
Ultraviolet radiation will accelerate the oxidative decomposition of rubber and polyurethane materials. In areas with strong ultraviolet rays such as plateaus and deserts, the aging rate of pads is 30%-50% faster than that in plain areas; in areas with large temperature changes, pads are prone to fatigue aging due to repeated thermal expansion and contraction; humid environments will make pads absorb water, especially non-closed-cell pads. After absorbing water, they will reduce elasticity, increase weight and accelerate aging; chemical corrosion, such as corrosive gases or liquids emitted by chemical plants near the line, will destroy the molecular structure of the pads and make them age in advance.
- What are the differences in aging life of under-rail pads made of different materials?
The aging life of natural rubber pads in ordinary environments is about 8-10 years, and shortened to 5-6 years in areas with strong ultraviolet rays; the aging life of styrene-butadiene rubber pads is 2-3 years longer than that of natural rubber, reaching 10-12 years in ordinary environments; neoprene pads have good aging resistance, with an aging life of 12-15 years; the aging life of polyurethane pads in dry environments is about 10-12 years, but will drop to 7-8 years in humid environments.
- How to evaluate the aging degree of under-rail pads?
Through hardness testing, use a Shore durometer to measure the hardness of the pad. Compared with the new pad, if the hardness change exceeds 20%, it indicates that the aging is more serious; conduct elastic recovery rate test, apply a certain load and then unload, record the time for the pad to return to its original state. If the recovery time is 50% longer than that of the new pad, it indicates that the elasticity has decreased significantly; appearance inspection, if the surface crack area exceeds 30%, obvious delamination or fracture occurs, it is judged as severe aging.
- How to determine the replacement cycle of under-rail pads?
Natural rubber pads for ordinary railways are replaced every 8-10 years in plain areas; styrene-butadiene rubber or neoprene pads for high-speed railways, due to large loads and high requirements for cushioning performance, are replaced every 6-8 years; pads in plateau areas with strong ultraviolet rays, regardless of material, need to have their replacement cycle shortened by 20%-30%; polyurethane pads for heavy-haul railways, considering the acceleration of aging by loads, are replaced every 5-7 years. During replacement, the pads in the same section must be replaced as a whole to avoid the impact of performance differences between old and new pads on track smoothness.