SL trains get aprons against noise
The trains on the Roslagsbanan railway are too noisy. House owners in Danderyd and Täby have repeatedly reported their opinion that the trains are not as silent as one could wish. Noise screens and upgrading of windows along the affected sections of the railway used to be the only possible solutions offered by SL, the Bigger Stockholm Local Traffic Company. Currently, a new solution is being tested – aprons made of aluminium profiles.
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The taped up profiles are fastened along the bottom edge of the train as noise reducing aprons. |
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Slits and screw ports are the only things that are required in order to install the solution in place. |
A few years ago, an environmental court ruled a decision against SL, which required that further steps against noise should be taken. But noise screens are an expensive method. Can the problem be solved in a better way and at a lower cost? Mats Knutsson, a noise specialist at SL, contacted Klaus Knudsen at Caran to get help in finding an overall solution. Caran is an engineering company working in the field of industrial design with a large experience in product development for the automotive industry. SL wanted to use some of this knowledge. Klaus Knudsen at Caran says: – Our solution means that we attack the noise issue at the source. Noise is changing pressure waves and with the help of micro-perforated sheet metal we are able to reduce noise in certain frequency bands. This solution has been tested in other applications. It is used, among other things, in engine compartments to make cars quieter. The micro-perforated sheet metal, with holes having the size of a fraction of a millimetre, is made of aluminium. Two aluminium profiles hold the sheet metal in place and the entire “package” is attached with hinges and double locks, thus building an apron on the train.
Why aluminium?
– In the first place, it is about reducing the weight, which is necessary if you want to reduce the energy consumption, explains Klaus. Apart from this, SL required that the material should be easy to recycle. Aluminium requires quite a lot of energy at the primary production stage, but remelting is a simple process with low energy requirements.
Why profiles?
– When we choose profiles, we can use the same die, no matter whether we need just a few metres or several kilometres of profiles. We only need to cut the profiles into sections of required length. The cost of the die is low and the delivery time is short compared to other solutions. A solution based on plastic or composite material would require some kind of a frame structure, which would result in a more expensive and heavier product, adds Klaus.
The prototype developed by Caran is now being tested on a trial train. The apron consists of two profiles that are taped up together, a technique that is commonly used when building aeroplanes. A slit in the profile holds the perforated sheet metal in place. The end parts are fastened with the help of screw pockets which are integrated in the profiles. In this way, the solution is dismountable. The profiles are slightly rounded in order to obtain a certain rigidity and eliminate the risk of self-oscillation.
The solution developed by Caran includes, among other things, a new front assembly with a beam system which can collapse and absorb energy. Today, a stone, for example, can damage the wheel axles, the engine or the chassis of a train. The impact energy is transferred with the help of aluminium profiles.
How do you perceive the co-operation with Sapa?
– None of our team members has worked with profile-based solutions before. We explained clearly to Sapa that we did not know much about profiles, but we wanted to do this and that. The ideas are ours, but the Sapa technicians have contributed to every stage of the development work and have helped us to solve the engineering problems that have arisen. To put is simply, the co-operation has been very fruitful.
What will happen next?
– The noise issues are getting more and more attention and the requirements are going to increase. If noise emission rights are going to be introduced in the future, the railway operators are going to get a stronger incentive to get a grip with the problem. And this solution is an alternative to buying new trains. In a short time, a trial train using our solutions will be on track. It is all prototypes, but here we can put the equal sign between prototype and series production. All the dies that we have developed can be used for mass production, concludes Klaus.
Text: lg.linden/text
Updated: 2008-03-12