HIGH-PRECISION TPE SPRINGS TAKE ON THERMOSET ELASTOMERS IN RAILWAY BUFFERS

Tielt, Belgium – June, 2007 – Thermoplastic elastomers are replacing conventional rubbers and steel in high performance springs used in railway rolling-stock buffers, draw gears and draft gears. German company DUREL is in the vanguard of this trend, manufacturing spring pads from rods and tubes supplied by Quadrant Engineering Plastic Products (Quadrant EPP) in Arnitel® thermoplastic polyether elastomer (TPEE) from DSM Engineering Plastics.

Draft gears and buffers serve to smooth out train movement, providing comfort for passengers and protection against damage to freight goods, by separating the movements of individual railcars during acceleration and braking.

TPEEs combine the strength and processing characteristics of engineering plastics with the performance of thermoset elastomers, providing benefits in processing and productivity. Arnitel® has exceptional flexibility and outperforms conventional rubber and steel springs.

DURELS’s production process requires it to use spring pads formed from very high precision extrusions. It has found that Quadrant EPP is one of the very few companies that can meet its very precise and demanding quality requirements.

Quadrant EPP uses two extrusion processes to make the extrusions. Tube extruders equipped with vacuum calibrators ensure that the outside dimensions meet very tight tolerances. Equal accuracy can be obtained by using cold die extrusion, which the company uses for rods and a limited number of tubes, but this requires the line to run at a lower speed.

“The quality of the extrusion is critical to the application,” says Quadrant EPP sales engineer Françoise Donovan. “The surface of the rods and tubes must be absolutely smooth in order to prevent the spring from cracking or even exploding during the forming and machining operations that occur before assembly. Even a small fissure invisible to the naked eye would not meet DUREL’s specifications.” She says that when DUREL worked with other suppliers, it had to machine the stock shapes again in a lathe in order to achieve this perfection. “Working with Quadrant EPP saves them time and money.”

Quadrant EPP dedicates one extrusion line on a full time basis to production of stock shapes for DUREL, and can allocate a second line when necessary. Total output amounts to between 20 and 30 tonnes per month. “DUREL used to work with another extrusion company, but it was not able to meet those demands,” says Donovan.

“Quadrant EPP is our biggest elastomer supplier, it is capable of supplying high quality product, and it is flexible in production quantities,” says DUREL general manager Christian Georg. “They are highly responsive to our special needs.”

In the springs, a series of doughnut-like pads made of Arnitel® are sandwiched between annular metal plates along a metal rod, rather like a kebab. DUREL uses a patented process to make the springs, which entails pre-compressing the pads to improve their elastic response. “Pads that don’t undergo our forming process have a relatively low level of spring behaviour,” says Georg. “After we have powered them up, their properties improve by a factor of around three.”

Quadrant EPP says Arnitel®-based springs should last for several decades, providing the most efficient energy absorption systems for a given railcar weight. The springs deliver high energy absorption, freedom from maintenance, and also toughness when exposed to extreme climatic conditions (temperature range from -60 to +50°C). Their predictable absorption and release of energy helps trains to start, accelerate, decelerate and stop smoothly. The pads do not rust, fracture or lose their springiness.

DUREL is not the only company to make composite metal/elastomer springs, but it is the first to use Arnitel®. According to Georg, the TPE is one of very few materials in the world that have the energy density to make the springs work.

Quadrant EPP says the technology used for making the springs could be extended to numerous other heavy duty shock or vibration absorbing and noise reduction applications. For the moment, however, DUREL is concentrating on the railway business. “We are working at full capacity,” says Georg.

Arnitel® is a registered trademark of Royal DSM.

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Notes for editors

About Quadrant EPP

Quadrant Engineering Plastic Products (Quadrant EPP) is the world's leading manufacturer of engineering plastics in stock shapes (rod, plate, tube) for machining. Other specialities include custom nylon castings and finished parts. Quadrant EPP's catalogue of General and Advanced Engineering Plastics covers the broadest range (in terms of materials and dimensions) of standard and custom shapes for machining. Products are available through a worldwide network of branch offices, technical support centres and authorized dealers.

Learn more about Quadrant EPP at www.quadrantplastics.com

About the Quadrant group

Quadrant, a global leader in high-performance polymer materials in the form of semi-finished and finished products with locations in 18 countries, generates annual sales of over CHF 800 million. The specialty engineering thermoplastics and composites manufactured and marketed by more than 2’400 employees worldwide are superior in performance to metals and other materials and are used in a growing number of applications, primarily in the capital goods industry. Together with leaders in a wide range of customer markets, Quadrant is continuously developing new areas of application. Thanks to its clear strategic orientation and focus, Quadrant has generated substantial added value for customers and shareholders since it was established in 1996 and is well prepared to continue expanding its market leadership in future.