Joint development between Durel GmbH and DSM Engineering Plastics has resulted in a range of railway side buffer springs, draft gears and, in more demanding safety applications, crash buffers capable of absorbing large amounts of energy. The designs combine metal with Arnitel® thermoplastic polyether elastomer (TPEE). Acting as a spring, Arnitel TPEE absorbs and releases energy in predictable ways over a long service life, helping trains to start, accelerate, decelerate and stop smoothly. Unlike metal springs, Arnitel TPEE does not rust, deteriorate, fracture or lose its springiness. In contrast to rubber, Arnitel TPEE does not lose its ability to act as a spring over time -- the DSM material has a field life of at least 20 years versus 5-10 for rubber.

Draft gear & buffers serve to smooth out train movement, providing comfort for passengers and protection against damage to freight goods from acceleration or deceleration shock. Crash buffers provide further protection, mandated on tank wagons carrying dangerous goods built after January 1st, 2005, as defined by “Règlement concernant le transport International ferroviaire des marchandises Dangereuses” (transport of dangerous goods or RID) regulations. The UIC/RID mandate (leaflet 573) also requires the retrofitting of existing European tank wagon fleets by 2010.

“Our elastomer spring design objectives were three-fold,” said Michael Schnaufer, Director of Durel GmbH. “The first was of course to dampen energy, meeting systems specifications and customer requirements. The second was to provide new levels of effectiveness in the same footprint of earlier components. Size, weight and cost considerations are paramount for installation on both new and existing rolling stock in a market with ever increasing demands. Finally, we needed a product lifecycle measured not in years but in decades—locomotives and railcars stay in service for very long times.”

The Durel components have been incorporated in systems produced by Saalfelder Hebezeugbau GmbH for draw gear and hydraulic components; SMW (Spezialmaschinen und Werkzeugbau) GmbH & Co. KG for buffers; and in equipment from many other railway component suppliers.

Crash buffers from EST Eisenbahn-Systemtechnik GmbH uniquely combine Arnitel TPEE with steel components that fully maintain buffer geometry and functionality in normal use, but “peel back” sacrificially in a crash, absorbing very large amounts of energy protecting people, lading, rolling stock and locomotives from damage.

“We knew Arnitel thermoplastic elastomers performed well in railway applications,” said André Oosterlaken, Manager Application Development Technical Service for Arnitel TPEE. “For example, it is used in vibration damping pads between rails and concrete sleeper ties, outperforming competitive elastomers for durability and consistency in all climates and under high load conditions; heavy freight traffic and high speed. However this performance is dramatically exceeded by the unique combination of the Arnitel raw material and the Durel spring manufacturing technology. We worked in tandem, combining Arnitel with Durel technology, to make these high-performance springs possible.”

Elastomer springs made of Arnitel TPEE have a range of characteristics and offer advantages over other solutions tried over the years. These include the following:

• Excellent flexural fatigue endurance

• High load bearing capability with low creep

• Applicable in temperature range from –60°C to +80°C  

• Good resistance against chemicals, grease, oil and solvents

• Good resistance against ozone and radiation

• Good resistance against ultraviolet (UV) and hydrolysis for all-climate performance

Durel chose Arnitel TPEE as the best material in class for its patented Durel springs. Durel springs are known for their durability, and their unbeaten record of highest energy absorption efficiency for a given system weight or volume. This enables higher dynamic capacity in the often limited space and travel available in coupler systems compared to competitive systems

Compared to metal spring systems, Durel springs based on Arnitel TPEE do not corrode or exhibit catastrophic failure due to metal fatigue. While elastomers can suffer more compression set than metals, this potential down side is fully compensated in the unique and patented Durel spring manufacturing technology.

Compared to metal systems, wear does not lower the efficacy of the Durel design. Further, with its over 1:6 weight ratio for the same dynamic capacity, the low mass of Durel designs makes them superior to steel spring systems. Finally, Durel springs work lubrication-free.

Durel springs can also be combined with traditional metal dry friction systems (for example in friction draft gears) and with hydraulic systems, to reach very high capacity levels required for the ever-increasing lading capacities of heavy freight trains. The combination of the unique properties of Arnitel and the Durel spring manufacturing technology contributes to products that require minimal maintenance and outperform and outlast traditional spring systems based on metal-to-metal friction, rubber and/or hydraulics.