DuPont™ Hytrel® pads keep railways on track
By GU, LINDA JIE LIN, Global Railway Segment Leader, DuPont Performance Polymers
In many countries, rail travel is still the most popular mode of transportation, linking population centers with commerce districts and city centers with the open countryside. For rail operating companies, the upkeep of the rail infrastructure is vital, but can be a real challenge. Breakdowns and closures can simply not be tolerated.
If you look at a modern railway and pay close attention to the track, especially the way it is attached to the sleepers, chances are you will not notice anything particularly special. However, this simple mounting arrangement has undergone some remarkable changes since the introduction of the steam locomotive in the early 19th century. Hidden in this simple joint is some incredibly detailed design work, precision manufacturing and, in many cases, some clever engineering polymer technology from DuPont.
The rail-fastener-sleeper combination serves an incredibly important function. The major elements all work in combination to not only secure the rail at the correct gauge, but also to spread the enormous loads and forces experienced. It is in the dispersion of these forces that serious problems can arise. However, thanks to rail pads made from DuPont™ Hytrel®, railways across the globe are experiencing many years of trouble-free operation. The pads perform their task admirably, while showing negligible wear when compared to their brand-new state.
One country with a significant over- and underground rail infrastructure is China. Three of the country's metro lines—Hangzhou Metro Line 1, Xian Metro Line 2 and Suzhou Metro Line 1—all exploit rail pads developed by the Beijing ZKYT Shock Absorption Technical Co. Ltd. The pads, made from Hytrel®, are designed to combat the stresses of heavy, high-speed trains by absorbing some of the loads and forces before they damage the sleeper.
Many types and designs of rail pads exist, including those made of simple steel, but the success of Hytrel® in this type of application has seen it deployed throughout the world. According to Ms. Wei Pei, president of ZKYT, "From our findings, the overall performance of Hytrel® is better than other brands, with its higher-yield stress limit providing larger flexibility for product design. The technical and pre-market support we received from DuPont is also better than others. DuPont provided technical support and shared samples, demonstrating the stiffness of the products."
Ms. Wei Pei continues, "All products have been operating well since 2004, and no unnecessary changes have had to be made. The pads used for the Shanghai Metro Line 3 and Guangzhou Metro Line 1 (all in trial sections) were checked and tested after three or four years of operation, and their stiffness level was virtually identical to that when they were new. With new track being laid all the time, between 2010 and 2012 around 2,000,000 rail pads made with Hytrel® have been laid down along 300 kilometers of track."
Hytrel® has seen action in similar applications across the globe—from metro lines, to commuter lines, to heavy transport lines—with some operating in extreme temperatures. This incredibly flexible thermoplastic polyester elastomer provides the flexibility of rubbers, the strength of plastics and the processability of thermoplastics.
Hytrel® is ideal for parts requiring excellent flex fatigue and broad-use temperature. It resists tearing, flex-cut growth, creep and abrasion. It also offers strength, stiffness and outstanding toughness, while resisting hydrocarbons and many other fluids. Hytrel® can be processed easily by conventional thermoplastic processes, such as injection molding, blow molding, calendaring, rotational molding, extrusion and melt casting. If you have a part that needs to bend, flex, twist, open, compress, turn, squeeze or simply just move, speak to us; chances are we already know how to help.
Beijing ZKYT Shock Absorption Technical Co. Ltd.
Room 510, 1 building, No. 13 Beiertiao, Zhongguancun, Haidian District,
Beijing, China. 100080E