Aging detection and replacement cycle of rail pads
- What are the typical characteristics of under-rail pad aging?
Surface cracks are common, initially fine mesh cracks, expanding to through cracks with aging, especially at edges and stress - concentrated areas. Rubber pads tend to show this after 5 years of use. Reduced elasticity is manifested by decreased rebound under load. Detected by a pressure testing machine, the rebound rate of aged pads is over 30% lower than new ones, failing to absorb vibration effectively, increasing track vibration. Hardness changes significantly: rubber pads' hardness usually increases by 10 - 20 Shore A (e.g., from 60 to 70 - 80) after aging; plastic pads may harden and become brittle due to plasticizer loss, more obvious in low temperatures. Dimensional shrinkage or expansion: length/width changes over 1% after aging, increasing fitting gaps with rails and sleepers, affecting load transfer, more likely in areas with large temperature changes.
- How to detect under-rail pad aging on - site with simple methods?
Press test: press the pad surface hard with fingers. If rebound is slow and leaves obvious indentation (not recovered after 3 seconds), elasticity decreases, indicating aging. Visual inspection: check for cracks, chalking or discoloration. Cracks over 5mm in length or covering over 10% area are moderate aging; through cracks are severe aging. Caliper measurement: regularly measure pad thickness. If thickness reduces over 10% of original (e.g., 10mm pad to below 9mm), indicating severe wear and aging, replacement is needed. Tap and listen: tap the pad with a small hammer. Aged pads make crisp "ding - ding" sounds due to increased hardness; new ones make dull "dong - dong" sounds, assisting judgment.
- What are the differences in replacement cycles of under-rail pads of different materials?
Natural rubber pads have a replacement cycle of 6 - 8 years in dry ordinary railway environments, shortened to 4 - 6 years in humid environments due to easy oxidation and microbial erosion. Chloroprene rubber pads have better aging resistance, with a replacement cycle 30% - 40% longer than natural rubber: 8 - 12 years in ordinary environments, 6 - 10 years in coastal humid areas. EPDM rubber pads have strong UV resistance and weatherability, with a replacement cycle of 15 - 20 years, maintaining stable performance even in high - altitude strong UV areas, a long - life choice. Polyurethane pads in heavy - haul railways have a replacement cycle of 5 - 8 years due to long - term compression; though wear - resistant, elasticity decays quickly, needing adjustment based on load.
- How is the under-rail pad replacement cycle related to railway traffic volume?
Low - traffic railways with annual traffic below 10 million tons: pads suffer little load impact, replacement cycle can be extended by 20% - 30% (e.g., natural rubber pads to 8 - 10 years). Medium - traffic railways with annual traffic 10 - 50 million tons: replace according to regular cycles, e.g., chloroprene rubber pads every 8 - 12 years, with annual elasticity tests. High - traffic railways with annual traffic over 50 million tons: frequent load cycles accelerate aging, replacement cycle shortened by 15% - 20% (e.g., EPDM rubber pads to 12 - 18 years), with increased testing frequency (every 6 months).
- What on - site factors need to be considered when formulating under-rail pad replacement plans?
Track type: ballastless track pad replacement is difficult, requiring plans 3 - 6 months in advance, constructed during line skylights; ballasted track replacement is flexible, arranged according to regular cycles. Surrounding environment: rainy areas need 10% - 15% shorter cycles, prioritizing water - resistant materials; alpine areas focus on winter pad hardness changes, completing replacement before freeze - thaw periods. Maintenance conditions: lines with frequent maintenance and timely testing can dynamically adjust cycles based on actual aging, not strictly fixed years; remote lines with inconvenient testing can shorten cycles appropriately to ensure safety.