Oil Aging Resistance of Rail Pads and Adaptation Design to the Hydraulic Oil Contamination Environment of Switch Areas
Why does hydraulic oil in switch areas cause significant aging damage to ordinary under-rail pads?
Ordinary under-rail pads are mostly made of natural rubber or general-purpose polyurethane, whose molecular chain structure is compatible with mineral oil-based hydraulic oil. Hydraulic oil penetrates the rubber molecular gaps, disrupting the cross-linked structure and causing swelling-volume expansion rate can reach 10%-30%, with a significant decrease in hardness. For polyurethane pads, hydraulic oil triggers solvation, creating internal micropores and reducing the elastic modulus. Under long-term immersion, pads lose cushioning performance, even undergoing viscous flow deformation and complete failure.
What are the core evaluation indicators for pad oil aging resistance, and how does Chinese standard specify them?
Core indicators include volume change rate, hardness change rate, and tensile strength retention rate. According to the Chinese standard "Under-Rail Pads for Railway Switches," after immersion in hydraulic oil (70℃×72h), the pad's volume change rate shall be within ±5%, hardness change rate ≤±10%, and retention rates of tensile strength and elongation at break shall both be ≥80%. Switches-specific pads have stricter requirements: volume change rate ≤±3% and strength retention ≥85% to withstand long-term oil contamination.
How to optimize pad materials at the formulation level to enhance oil aging resistance in switch areas?
The core of material optimization is "molecular modification to block compatibility." For rubber pads, nitrile butadiene rubber (NBR) or fluororubber replace natural rubber-acrylonitrile groups in NBR effectively resist mineral oil erosion, while fluororubber offers superior oil resistance but higher cost. For polyurethane pads, polyether-based polyurethane replaces polyester-based polyurethane; polyether molecular chains have far better oil resistance and hydrolysis resistance than polyester. Additionally, oil-resistant agents and reinforcing fillers are added to form a dense protective layer, further reducing hydraulic oil penetration rate.
How do "oil-proof isolation grooves" in structural design assist in protecting under-rail pads in switch areas?
Oil-proof isolation grooves are annular groove structures designed at pad edges or beneath point machines, with the core function of intercepting and diverting hydraulic oil. When a point machine leaks, the isolation groove intercepts hydraulic oil outside the pad's contact area, preventing large-area immersion. Simultaneously, the groove connects to the switch drainage system, rapidly diverting intercepted oil out of the track bed. Furthermore, the grooves increase the pad's edge stiffness, reducing warpage deformation after swelling and extending the failure cycle.
How to quickly judge oil aging failure of pads via appearance features on-site?
Oil-aged failed pads exhibit typical appearance characteristics, identifiable through a three-step "visual inspection, touch test, and measurement" method. Visual inspection: Check for blisters, cracks, or abnormally enlarged contact marks with rails-swollen pads show obvious volume increase. Touch test: Touch the pad; a sticky, soft surface, significantly reduced hardness, or permanent indentations after finger pressure indicate oil aging. Measurement: Use calipers to measure pad thickness and width; a thickness increase of over 3% compared to the original size confirms swelling failure, requiring immediate replacement.