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Viscoelastic biadhesive helps reduce railway noise pollution

3M Europe : 26 March, 2003  (New Product)
Increasingly stringent rules governing noise emissions led Lucchini Sidermeccanica, a leading Italian manufacturer of railway products, to investigate how the noise generated by rolling stock could be reduced. The company
The project involved the examination of a range of noise reducing options, conducted using the same set of procedures, and included the testing of methods such as those involving friction rings and tuned absorbers applied under the wheel rim. Ultimately the solution developed by Lucchini and designated Syope, after the Greek for ‘Silence’, exhibited superior performance compared with more complex and more costly alternatives.

Syope is a noise-damping treatment that can be applied to any disc-braked wheelset. Consisting of a constrained aluminium or steel damping plate, Syope is attached to a wheel by a viscoelastic biadhesive polymer. Lucchini selected this fixing technique, which is widely used in many industries, because it provides a high performance fixing system that eliminates the need for metal fastenings or welding. Moreover, in the Syope application, it did not require any modification of either the wheel structure or geometry.

Developed by 3M, the special polymer, which is an extension of the company’s VHBTM (very high bond) product family, gives long-term, high, consistent adhesive resistance. Additionally, in tests conducted by Lucchini and 3M that encompassed adhesion resistance, accelerated and outdoor weathering, thermal cycling and fatigue performance, the 3M polymer has shown to provide the wheel web surface with protection against corrosion.

Higher performance

3M VHB viscoelastic polymer tapes have been prominent for over 20 years in the engineering manufacturing industries. In fixing applications they eliminate the need for drilling, riveting, welding, screw fastening, cleanup, grinding and refinishing, and help achieve seamless designs as well as contribute to a reduction in labour and material costs.

The viscoelastic properties of 3M VHB polymer, result both from the viscous flow of VHB into the microstructure of the substrates that are being bonded, and its inherent elastic nature. Use of this material results in a finished product that is lighter, quieter, more efficient and reliable, as well as aesthetically improved. Furthermore, peel adhesion and tensile holding power of VHB products are significantly higher than those of typical pressure sensitive tapes.

Key characteristics of the viscoelastic polymer in the Syope application were its ability to compensate for differential thermal expansion and contraction, which is essential in the joining of dissimilar materials. Also its unique ability for energy absorption and stress relaxation, both of which are important for dynamic strength and vibration damping. Moreover, in contrast to mechanical fastners which result in a concentration of stress, the continuous bond of the polymer fixing allows the even distribution of stress over the entire bonded surface.

Quietly succesful

Because laboratory tests could not replicate the real in-use acoustic behaviour of a rolling wheel, long-term testing programmes were conducted with Syope in two different railway environments. One involving ETR 500 high-speed trains, and one the 950mm gauge Circumvesuviana Railway around Naples where wheelsets would be exposed to high temperatures in a potentially corrosive sea-air environment.

After almost two years of daily service at speeds up to 250km/h, over a cumulative distance of 400.000km, inspections of the Syope wheelsets have revealed no defects. Importantly, testing over the period, conducted in conjunction with the national railway companies DB, SNCF and Trenitalia, showed that compared with standard wheels, the bogies equipped with Syope wheelsets gave a noise reduction of around 4 dB (A). Syope will shortly be supplied in its first commercial application in Class 680 Pendolino trainsets built for the Czech Railways by French engineering leader Alstom.
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