The Stockholm intercity (SL) trains on the Roslagsbanan line make too much noise, according to a ruling by the Environmental court following complaints from residents who live nearby. Trials are now being carried out on a train that has been modified to reduce the noise at source – by means of sound-deadening aluminium skirts fitted to the sides of the carriages.
SL has previously tried to solve the noise problem by erecting screens along the rail embankment and installing triple glazing on those properties that get most exposure. However this solution is expensive and not sufficiently effective at rail crossings and bridges.
In response, SL is attempting to reduce noise from the trains themselves.
The task went to engineering company Caran, which has extensive experience of product development in the automotive industry.
Their suggestion was to install sound-deadening panels, or skirts, on locomotives and carriages. In combination with bellows between the carriages, the skirts muffle the sound from every side of the train.
“We had to come up with a design that was rigid but able to deform, so that if a panel fell off and was run over it would not derail the train,” says Klaus Knudsen, project manager for Caran.
Caran narrowed down the choice of material for the skirts to a selection of composites, steel and aluminium.
The need for low weight and recyclability swayed them in favour of aluminium. This was also a less costly solution than composites.
“Each carriage is also slightly different, so the panels require skilled fitting. That’s easier to do with aluminium,” says Knudsen.
Caran contacted Sapa, who provided technical guidance on the detailed construction of the panels.
“The partnership with Sapa worked very well. My team and I had never done any design work with extruded aluminium before,” says Knudsen.
He reckons that this method is very well suited to series production and points out that with profiles the same tool can be used to produce panels of any required length.
On the trial train each panel is just over a metre long and is mounted on the lower part of the body. The inside is lined with a micro-perforated plate that is specially designed to dampen noise at particular frequencies. This is a proven solution and is used for sound deadening on contracting machinery, for example. This is the first time it has been used on a train, however.
“If it turns out well there will be a big market for this type of solution. It will appeal to a lot of train operators,” believes Knudsen.
Each panel weighs 11 kilograms and is designed so that it can be raised and lowered by service staff, which made the design a little more difficult. The panels also have to be lockable.
“Since getting the original request to develop a panel profile we’ve now produced twenty different items for this project. The external appearance is exactly what Caran wanted and we’ve also met the sound-deadening requirements,” says Crister Roswall, from Sapa’s Region North sales team.
As part of the design process Sapa also developed an aluminium frame profile to support the bellows between the carriages. Caran’s solution includes a new front section with impactabsorbing beams, with aluminium profiles used to transfer the energy of impact.
The trial train has been in service on the Roslagsbanan line since April, and noise level metering has now started. The sound-deadening skirts will be tested over the summer and winter period, before the final evaluation is completed, hopefully in spring 2009. One of the factors to evaluate is performance during heavy snow.
“If everything works as intended this could be part of a refurbishment project for all the rolling stock on the Roslagsbanan line, which includes around thirty train sets,” says Mats Knutsson, noise specialist at SL.
The skirts on the trains will also be supplemented by other noise-reduction methods. The same noise-deadening technique that is used on the panels has been used to design low platform screens. These will be installed on stretches where the rail embankment has a camber and where higher noise levels are produced through wheel contact with the rails.
Text: Nils Sundström
Photos: Mauro Rongione