What Are the Common Materials of Railway Plastic Dowels?
Nov 10, 2025
What a Plastic Dowel Does
A railway plastic dowel is a sleeve cast into the concrete sleeper to receive the screw spike. It does three jobs: it gives the spike a durable thread that can be screwed and unscrewed many times during maintenance, it protects the concrete from the local stresses of the spike, and it electrically insulates the spike and the fastening system from the sleeper. The dowel is one of the least visible parts of the track but one of the most difficult to repair, because it is embedded in the concrete. Choosing the right material and the right dimensions is therefore a one-time decision for the life of the sleeper.
Reinforced PA66: The High-Performance Choice
Glass-fibre-reinforced PA66 (nylon 66) is the premium dowel material. A typical formulation is about 69.6% PA66 resin with 30% glass fibre and 1% processing modifiers. The glass fibre raises the strength dramatically: tensile strength 170 MPa minimum and flexural (bending) strength 250 MPa minimum, with a density of 1.3-1.45 g/cm3. The material keeps its stiffness up to a melting point of 250-270 °C, offers insulation resistance of 10^8 Ω minimum, and reaches a Rockwell hardness of 110 HRR minimum. PA66 dowels are impact- and ageing-resistant and are the preferred choice for high-speed and heavy-haul railways, where the spike is loaded and unloaded millions of times.
HDPE: The Cost-Effective Option
High-density polyethylene (HDPE) is the economical alternative. Its density is 0.95-0.98 g/cm3, tensile strength 19 MPa minimum and elongation over 80%, with a melting point of 170-190 °C. HDPE is an excellent insulator - insulation resistance of 10^10 Ω minimum - and resists acids and alkalis, which matters in industrial environments. Its hardness is about 98 Shore A minimum. HDPE dowels are easy to process and install and are suitable for medium- and low-speed lines, industrial sidings and projects where the load on the fastening is moderate.
Reference Dimensional Data
| Type | Length (mm) | Outer dia. (mm) | Inner dia. (mm) | Pull-out force (kN) |
|---|---|---|---|---|
| 207 | 110 ±1 | 53 ±0.5 | 31 | 80 min |
| 111 | 119 ±0.2 | 35 | 25 | 50 min |
| WJ-2 | 135 | 24.5 | 31 | 50 min |
| Type D (39.5 OD) | 165 ±1 | 39.5 | 24.5 | 75 min |
The pull-out force is the practical acceptance value: it measures how firmly the spike stays anchored in the sleeper under traffic. The type code refers to the fastening-system family the dowel is made for, and the dimensions are always confirmed against the sleeper drawing and the spike specification.
How the Material Choice Is Made
The choice follows the fastening system and the line duty. High-speed and heavy-haul systems with high spike loads and frequent maintenance use reinforced PA66, because the glass fibre keeps the thread from stripping after repeated spike insertion. Medium- and low-speed lines use HDPE, which is sufficient for the loads and significantly cheaper. For aggressive chemical environments, the acid and alkali resistance of HDPE is an argument in its favour. The supplier should offer material selection advice and dimension adaptation, and every batch is delivered with the dimensional and property test results.
Frequently Asked Questions
Q1. Why is glass fibre added to PA66 dowels?
The 30% glass fibre raises the tensile and bending strength of the nylon so that the dowel keeps its thread and shape under the repeated loads of the screw spike.
Q2. Can HDPE dowels be used on high-speed lines?
HDPE is normally chosen for medium- and low-speed lines. High-speed and heavy-haul systems use reinforced PA66 for its higher strength and better thread retention.
Q3. What pull-out force is required?
Acceptance values are set per dowel type, typically from 50 kN minimum for light systems up to 80 kN minimum for heavy-duty systems.
Q4. Do dowels provide electrical insulation?
Yes. Both PA66 and HDPE are insulating; HDPE offers about 10^10 Ω and PA66 about 10^8 Ω minimum resistance, which is part of the insulated fastening system.
Q5. How is the dowel installed in the sleeper?
The dowel is cast into the concrete sleeper at the factory, positioned by the mould, so that the spike is screwed into it on site.
Q6. Are dowels supplied with matching screw spikes?
Yes. Fastener suppliers normally supply the dowel together with the screw spike, the anchor bolt and the rest of the fastening set so that the thread and the dimensions match.
