Weather resistance test and life assessment of rail pads
- What are the main items of weather resistance testing for under-rail pads?
High - and low - temperature cycle testing simulates extreme temperature changes, cycling 50 - 100 times in the range of - 40 - 70℃, with each cycle lasting 8 hours (4 hours at high temperature, 4 hours at low temperature). It detects the change of elastic modulus of the pad, with a qualified standard of change ≤15% to avoid embrittlement or softening. UV aging testing exposes the pad to UVB - 313 灯管 with an irradiance of 0.71W/m² for 1000 - 2000 hours, detects surface cracks and elastic changes. It is qualified if there are no cracks and the elastic retention rate ≥80%, evaluating applicability in high - altitude and other strong ultraviolet areas. Damp - heat aging testing places the pad in an environment of 40℃ and 95% relative humidity for 500 - 1000 hours, detects weight and volume changes. Weight change ≤5% and volume change ≤3% to prevent deformation caused by moisture absorption. Pads in coastal areas must pass this test. Salt spray corrosion testing (5% NaCl solution) lasts 500 hours, detects the insulation performance and appearance of the pad. Insulation resistance ≥10⁸Ω and no obvious corrosion, which is mandatory for electrified railway pads.
- What impact do different environmental factors have on the weather resistance of under-rail pads?
Strong ultraviolet rays will accelerate the aging of rubber pads, and molecular chain 断裂 will lead to decreased elasticity. The ultraviolet intensity in plateau areas is 30% - 50% higher than that in plain areas, and the pad life is shortened by 20% - 30%. It is necessary to add carbon black and other anti - ultraviolet additives. High temperature and high humidity environments make rubber pads easy to absorb moisture, and plasticizer loss accelerates, with hardness increasing by 10 - 15 Shore A and elastic modulus increasing by 20% - 30%. The aging speed of pads in the plum rain season in the south is significantly accelerated. Low temperature will make rubber pads crystallize and harden, and the glass transition temperature rises. At - 30℃, the elasticity of ordinary rubber pads decreases by more than 50%, while that of cold - resistant pads (such as EPDM rubber) has an elasticity retention rate ≥70% at low temperatures. Chloride ions in saline - alkaline environments will erode pads, especially damaging natural rubber, causing bubbles and cracks on the pad surface. Such damage in coastal areas appears 2 - 3 years earlier than in inland areas.
- How to evaluate the service life of under-rail pads through test data?
Predict according to the change rate of elastic modulus. Pads with an annual increase of elastic modulus ≤5% at room temperature can have a life of 8 - 10 years; if the annual increase is 10% - 15%, the life is only 3 - 5 years, which needs to be adjusted according to the service environment. In UV aging testing, 1000 hours of testing is equivalent to 1 year outdoors. Pads with an elastic retention rate ≥80% can have an outdoor life ≥8 years; those with a retention rate of 60% - 80% have a life of 5 - 7 years; those with a retention rate lower than 60% have a life of < 5 years. After high - and low - temperature cycle testing, if the pad has cracks or elastic loss > 20%, the actual life may be shortened to 50% - 60% of the design value, which needs to be focused on in cold areas. Comprehensive multi - environment test results, using a weighted scoring method, pads with a total weather resistance score ≥80 points (100 - point system) have a life ≥8 years; 60 - 80 points have a life of 5 - 8 years; < 60 points need to shorten the replacement cycle.
- What are the differences in weather resistance among under-rail pads of different materials?
EPDM rubber pads have the best weather resistance, with an elastic retention rate ≥85% after high - and low - temperature cycles, no cracks after 2000 hours of UV aging, suitable for extreme environments such as plateaus and cold areas, with a life of 10 - 15 years, 30% - 50% higher cost than natural rubber. Natural rubber pads have medium weather resistance, with rapid elastic decline in high temperature and high humidity, 25% - 30% increase in elastic modulus after 5 years, suitable for temperate dry areas, with a life of 5 - 8 years and low cost. Chloroprene rubber pads have balanced weather resistance, good high - and low - temperature resistance and UV resistance, with an elastic retention rate ≥80% (5 years), suitable for rainy or coastal areas, with a life of 7 - 10 years. Polyurethane pads have poor weather resistance, easy to soften at high temperatures and embrittle at low temperatures, with elastic loss ≥30% after 500 high - and low - temperature cycles, only suitable for mild climate areas, with a life of 3 - 5 years.
- What are the suggestions for replacement cycles of under-rail pads in different climate zones?
In cold temperate zones (- 30 - 20℃), it is recommended to use EPDM rubber pads with a replacement cycle of 8 - 10 years. Because low temperature causes great damage to ordinary rubber, weather - resistant materials are needed, and elastic changes must be detected every year. In subtropical zones (0 - 40℃, rainy), chloroprene rubber pads are recommended with a replacement cycle of 7 - 9 years. High temperature and high humidity accelerate aging, and weight and volume changes must be detected every 2 years. In plateau areas with strong ultraviolet rays, UV - resistant pads (such as EPDM with UV stabilizers) must be used with a replacement cycle of 6 - 8 years. Surface cracks and elasticity must be detected every 1.5 years to avoid premature failure. In tropical zones (20 - 50℃), heat - resistant EPDM rubber is selected with a replacement cycle of 5 - 7 years. High temperature lasts for a long time, so the detection cycle must be shortened, and the elastic retention rate must be evaluated every year.