What a Rail Pad Does
A rail pad (track pad) is the elastic element between the rail foot and the sleeper or baseplate. It distributes the wheel load over a larger bearing area, absorbs impact energy, reduces vibration transmitted to sleepers and roadbed, lowers running noise, and provides electrical insulation where track circuits are used. Pad stiffness directly controls the vertical stiffness of the fastening system, so the pad must be matched to the system type, axle load and line category.
Rail Pads in Seven Fastening System Families
| Fastening System Type | Pad Material and Configuration | Duty and Notes |
|---|---|---|
| Elastic bar clip system | Polyurethane or rubber; heavy-duty grades rated above 300 kN static load | Axle loads above 30 tonnes; clip toe load plus pad distributes load and prevents rail displacement |
| Tool-free quick-install system (Fast-type) | Rubber, polyurethane or EVA with spring steel clips and insulated fixing pins | Rapid installation, shock absorption, insulation, gauge retention |
| Double-elastic clip system | Rubber, polyurethane or EVA, one pad per fastening point | Spring steel clips, ribbed baseplate; resists longitudinal and lateral rail movement |
| Folded-bar clip system | Rubber, polyurethane or EVA; typically two pads per sleeper | Elastic clips plus connecting plates; absorbs impact and maintains gauge |
| E-type elastic clip system | Rubber or polyurethane pads with insulators | Provides elastic support, insulation for track circuits, constant gauge |
| Clamp-type fastening system (KPO-type) | Rubber, polyurethane or EVA; two pads per sleeper with clamps, iron baseplates and bolts | Crane rails and heavy-load industrial track; withstands high bearing pressure |
| WJ-7 ballastless track fastening | Class A and Class B pads; rubber pads on general sections, composite pads on bridges | High-speed ballastless track; works with T-bolts and iron baseplates; controls vertical rail displacement |
Pad Material Specifications
| Property | HDPE | EVA | Rubber |
|---|---|---|---|
| Density (g/cm3) | 0.95-0.98 | 0.95-0.98 | - |
| Tensile strength (MPa) | ≥19 | ≥15 | ≥12.5 (before aging) |
| Elongation (%) | >80 | >500 | ≥250 (before aging) |
| Melting point (deg C) | 170-190 | 170-190 | - |
| Insulation resistance (ohm) | ≥1×10^10 | ≥1×10^10 | ≥1×10^6 |
| Hardness | Shore A ≈98 | Shore A ≈92 | Shore A 72-80 |
| Stiffness (kN) | - | - | 90-130 |
EVA pads are a blend of about 80 percent polyethylene and 20 percent vinyl acetate. Pads are available with or without grooves, and the size designation follows the rail section and fastening system (for example 43-7-7, 50-10-7, 60-10-17). When specifying, always confirm the hardness scale (Shore A, Shore D or IRHD) because the same material can be rated on different scales.
Selection and Installation Points
Match the pad to the fastening system drawing; a pad from one system is rarely interchangeable with another because seating geometry and groove patterns differ.
Check insulation resistance requirements: track-circuit lines need pads with high insulation resistance, verified per EN 13146-4.
Confirm operating temperature range (typically -50 to 70 degrees Celsius for rubber and plastic pads) against the site climate.
Control pad thickness tolerance; a thicker pad softens the track, a thinner one stiffens it and changes rail height.
Store pads away from direct sunlight, heat sources and chemicals; oil and solvents degrade rubber and EVA.
FAQ
Q: Why do some fastening systems use two pads per sleeper?
A: In folded-bar and clamp-type systems, two discrete pads under the two rail feet equalize support on each side of the sleeper.
Q: What is the difference between Class A and Class B WJ-7 pads?
A: Class A pads suit passenger lines that also carry freight; Class B pads are for pure passenger dedicated lines with different stiffness requirements.
Q: Can a polyurethane pad replace a rubber pad in the same system?
A: Only if the stiffness and insulation requirements of the fastening system remain within specification; verify against the system design before substitution.
Q: How do I know which pad size my rails need?
A: The pad designation (for example 60-10-17) encodes the rail section, pad width and thickness; match it to the rail profile and fastening system drawing.
Q: Why is insulation resistance specified for rail pads?
A: To keep track-circuit currents from leaking to ground through the fastening, which would destabilize the signal system.