voestalpine Railway Systems and Getzner Werkstoffe are researching new turnouts to combat rail noise in populated areas. Switch frogs filled with highly damping polyurethane composites show the potential for reduced sound radiation and thus a higher level of living comfort for residents.
The acoustically clearly perceptible impact, which is caused by the longer lying time of the switch frog in the track, is very disturbing for residents in the vicinity as well as for railroad operators. Various measures such as noise barriers or soundproof windows continue to ensure the living comfort of the residents.
voestalpine Railway Systems and Getzner Werkstoffe set out to analyze this problem and find new innovative solutions. They investigated whether a modification to the switch frog itself can change the acoustic properties to such an extent that an audible or measurable reduction in shocks can be achieved while maintaining the same function and quality.
Turnout frogs made of hard manganese steel castings have several cavities on the underside facing the ballast. On the one hand, these cavities are production-related, on the other hand they also offer the possibility of material and weight reduction. The idea behind this project was to fill these cavities of the switch frogs with a highly damping PUR composite material and thus achieve a reduction in primary noise emission while maintaining the same performance and maintenance properties.
The first prototype was tested under laboratory conditions. It was recognized that the introduced attenuation begins to take effect from about 100 Hz, but the greatest differences can only be observed from about 700 Hz.
Together with ÖBB, the first field test was started in July 2021 in Pfaffstätten, Lower Austria on the Südbahn line and a transfer point was equipped with test frogs. Turnout frogs of the type "60E1 500 1:12" were used and damped in turnouts W1 and W4. Turnouts W2 and W3 did not receive any damping of the turnout frogs and serve as a reference in order to be able to directly compare the differences. The measurements were to be on passenger trains only. The first measurement took place in September 2021, with all turnout frogs still in optimal condition in their overflow geometry. The following graphics show the measurements of the "Railjet" train type.
Since there were no signs of wear on the switch frogs at the time of measurement, those measurements are only to be evaluated as an inventory in the new condition. As expected, the measured differences are relatively small.
At the pre-assembly site of voestalpine Railway Systems in Zeltweg, a measurement was also carried out by means of impulse hammer excitation on the pre-assembled switch hearts. An improvement of the excitation-normalized sound level by 60 % could be determined in the sum level. However, environmental conditions (background noise from factory operation) still have to be taken into account here. However, the sound of the damped switch frog was perceived to be significantly duller and not reverberant.
Due to the continuous wear of the switch frog, an audible impact is expected with an increasing tendency. This audible shock at the switch frog would subsequently drown out the pure rolling noise and at this point the difference to the damped frog will become noticeable. A corresponding wear should be given after about 12 to 18 months. This means that the next measurement on the potential of damped switch frogs will probably take place in winter 2022 or spring 2023.
