Railway Noise Reduction Technology Using a Damping Material Günther Koller 1, M.T. Kalivoda 2, Martin Jaksch 2, Martin Muncke 3, Takashi Oguchi 4, and Yoshifumi Matsuda 4 1 koocoo technology & consulting gmbh St.-Veit Gasse 28/1/5 1130 Wien, Austria Tel.:+43 676 960 69 54 e-mail: guenther.koller@koocoo.eu 2 psia-consult GmbH Lastenstr. 38/1 1230 Wien, Austria Tel.:+ 43 1 865 6755 e-mail: jaksch@psia.at 3 OBB-Infrastruktur AG Zieglergasse 6 1070 Wien, Austria Tel.:+ 43 1 93000 31928 e-mail: martin.muncke@oebb.at 4 Sekisui Chemical Co., Ltd. 2-2 Kamichoshi-cho Kamitoba Minami-ku Kyoto 601-8105, Japan Tel.:+ 81 75 662 8524 e-mail: matsuda021@sekisui.jp Summary Two effective railway noise reduction technologies using a high-performance damping material have been developed. One is a rail noise reduction system for reducing rolling noise using a combination of damping material and sound isolation and absorption technologies. The other one is an application of a high-performance damping material on the surface of web within a railway bridge structure as a means for reducing structure noise. An actual track-based field test for demonstrating these technologies was performed using a track of Austrian Federal Railways. As a result, the rail noise reduction system was found effective for reducing noise by 2 to 4 db in a normal section (ballast track) and for a bridge section the combined use of the rail noise reduction system and damping material reduced noise by 2 to 4 db of which the rail noise reduction system provided 0.5 to 3.5 db, and the damping material on the bridge web contributed 0 to 1.5 db. 1 Introduction Recently, for reason of energy saving, railway transportation has been considered a more effective mode of transportation than others though noise produced by a T. Maeda et al. (Eds.): Noise and Vibration Mitigation for Rail Trans. Sys., NNFM 118, pp. 159166. springerlink.com Springer-Verlag Berlin Heidelberg 2011
160 G. Koller et al. railway service has been a matter of high concern. Railway noise includes rolling noise, drive-system noise and structure noise [1]. Rolling noise is a typical type of noise that can occur within a normal section and is a consequence of the surface roughness of rails and wheels [2]. Structure noise is a radiation of sound from structures, e.g. steel-made bridge main girders directly below the sleepers that transmit railway vibration produced when a train is running [3]. There is a variety of products available for reducing these types of noise. They include a damping material Calmmoon Sheet developed by Sekisui Chemical and a rail noise reduction system Calmmoon Rail based on the damping material available for reducing rolling noise. This report shows a result of field test using an actual track of Austrian Federal Railways to demonstrate the performance of the rail noise reduction system and the damping material. The test used a normal section (ballast track) for testing the rail noise reduction system and bridge section for testing a combined configuration of the system and additionally installed damping material. 2 Overview of the Noise Reduction Technologies 2.1 Damping Material The damping material consisting of two layers resin layer (t = 1.0 mm) effective for absorbing vibration and metallic layer (t = 0.3 mm) is a constrained layer damping material having a total thickness of 1.3 mm. The adhesive surface of the resin layer, after the separate paper is removed, can be directly attached to the surface of the material without special technology or tools, which leads to higher efficiency in installation work. In this experiment, the damping materials were installed on the surface of a web of a bridge structure to measure how the material could reduce the sound arising from the web. Metallic layer (t=0.3 mm) Enlarged view Fig. 1. Damping Material Resin layer (t=1.0mm Fig. 2. Damping Material Installed 2.2 Rail Noise Reduction System A rail noise reduction system comprises the damping material and consists of a pair of two covers and two fixtures. To install the system, simply place the cover at each side of the rail and then secure it with the fixtures, thus requiring no special tool. The cover consists of metallic plate, sound absorption material, and the damping
Railway Noise Reduction Technology Using a Damping Material 161 material. Each component has its own role for reducing noise, as shown below. The sound arising from the rail can be insulated by the metallic plate. However the metallic plate transmits rail vibration and resonates to radiate sound. The damping material reduces this vibration and vibration-caused sound. The sound absorption material effectively absorbs sound occurring between the metallic plate and rail. An advantage of the system is that a pair of two covers and two fixtures measures as light as 2.3 kg in weight, which permits easier installation. Rail Sound absorption material Damping material Metallic plate Fig. 3. Rail Noise Reduction System Fig. 4. Rail Noise Reduction System Installed Another feature of the rail noise reduction system is, contrary to an existing mass-rubber based rolling noise reduction system mounted on the side of the rail to reduce noise by damping rail vibration [5], that it does not directly affect the rail vibration. Figure 5 shows decay rates measured on an actual track section of Austrian Federal Railways. Decay rate is a measure of reduction of rail vibration in db per m of rail. This figure shows that the rail noise reduction system has little effect on the decay rate. This is because this noise reduction system uses sound insulation and absorption technologies that are not affected by such vibrations. Fig. 5. Vertical Track Decay Rate before and after installation
162 G. Koller et al. 3 Demonstration of the Effectiveness of the Rail Noise Reduction System for Normal Track Section 3.1 Overview of Experiment The experiment was conducted on a normal track section at Deutsch Wagram, north of Vienna, of Austrian Federal Railways. Table 1 shows the track conditions of the section. The rail noise-reduction system was installed in a length of about 40 m in the section. The noise-measuring method per ISO 3095 was employed with a microphone placed 7.5 m horizontally from the track center and 1.2 m above the rail level to measure sound pressure level before and after the system was installed. For this experiment, four different types of trains freight train, ÖBB S-Train (Class 4020), ÖBB Regional-Doubledeck-Train (Class 8033) and ÖBB S-Train (Class 4024) were used. Table 1. Track Conditions of the Normal Section Used for the Test Track configuration Rail Sleeper Train speed Straight S49 Concrete 40 to 120 km/h 3.2 Result Figures 6, 7, 8 and 9 show the equivalent continuous A-weighted sound pressure level (LA, pb) as a function of train speed V in logarithmic presentation. Train speed V is standardized by 80km/h. The solid lines in these figures show approximated curves for measurements before installation of the rail noise-reduction system, while the dotted lines show those after installation of the system. The difference of these lines represents the system s contribution to noise reduction. These figures show that the noise level produced becomes greater as the train runs faster. The freight train and Class 4020 train produced more noise than Class 8033 and Class 4024 trains. Rolling noise depends on the surface roughness of the rails and wheels, which means that trains having wheels whose surface roughness is larger produce more noise when running on the same rail. This can be a reason why the relatively older freight train and Class 4020 train having larger surface roughness of their wheels than the relatively new trains Class 8033 and Class 4024 produce more noise. Fig. 6. Freight Train Speed vs. Noise Level Fig. 7. Class 4020Train Speed vs. Noise Level
Railway Noise Reduction Technology Using a Damping Material 163 Fig. 8. Class 8033Train Speed vs. Noise Level Fig. 9. Class 4024Train Speed vs. Noise Level Figure 10 shows, for each train type, based on the approximate curves shown in Figs. 6 through 9 the difference in noise level between before and after installation of the rail noise-reduction system, and how the train speed affects the noise reduction of the system. Comparing train types, the freight train and Class 4020 train had larger noise reduction at speed of 60 to 70 km/h though the noise reduction effect reduced as the train speed increased. This result suggests that for the freight train and Class 4020 train, when they run at lower speeds, the dominant source of noise is the rail, though the wheel noise, another main source of noise, becomes relatively larger as the train speed increases. As for Class 8033 and 4024 trains, in contrast, the rail and wheel contribution for noise production does not much change throughout the entire range of train speed. And one possible reason for this result is that the Class 4024 train uses smaller wheels that produce smaller radiation sound. Fig. 10. Train Speed vs. Contribution of the Rail Noise Reduction System Figures 11, 12, 13 and 14 show frequency analyses for noise measurements, respectively, for each train type under test. These figures show data for train speed of 80km/h. These figures show that for the freight train, the noise peak is at around 1 khz while for other train types it is between 630 and 800Hz; and the contribution of the rail noise reduction system is largest at 3-7 db between 630Hz and 1.25kHz.
164 G. Koller et al. Fig. 11. Frequency Analysis for Freight Fig. 12. Frequency Analysis for Class 4020 Fig. 13. Frequency Analysis for Class 8033 Fig. 14. Frequency Analysis for Class 4024 4 Demonstration of the Effectiveness of the Rail Noise Reduction System/Damping Material for Bridge Section 4.1 Overview of Experiment The experiment was conducted on part of the line to Hainburg about 40 km east of Vienna, consisting of bridge sections alternating with normal track sections. Table 2 shows the track conditions for this experiment. The rail noise reduction system was installed at each of the three bridge sections to cover a total installation length of 60 m. The damping materials were installed on each side of about 15-m-long part of the bridge webs as additional measures to the rail noise reduction system. As with measurement at normal sections, the noise-measuring method per ISO 3095 was employed. The experiment used trains of ÖBB S-Train (Class 4020) and ÖBB S-Train (Class 4024). Table 2. Track Conditions of the Bridge Section Used for the Test Track configuration Rail Sleeper Train speed Straight S49 Synthetic sleeper 30 to 65 km/h
Railway Noise Reduction Technology Using a Damping Material 165 4.2 Result Figures 16 and 17 show the equivalent continuous A-weighted sound pressure level (LA, pb) as a function of the train speed in logarithmic presentation. The solid lines in these figures show approximated curves for measurements before installation of the rail noise-reduction system. The dotted lines represent those after installation of the system. The chain lines represent those after installation of both the rail noise reduction system and damping material. These figures show that the Class 4020 train produced more noise than Class 4024 trains. The reason for the difference in noise production level again is the abovementioned difference in wheel roughness between the two vehicle types. Class 4020 train sets are cast iron block braked with high surface roughness of wheels while modern class 4024 train sets are disc braked with thick small wheels. Fig. 15. Class 4020 Train Speed vs. Noise Level Fig. 16. Class 4024 Train Speed vs. Noise Level Figure 17 and 18 show, for each train type, how the train speed affects the noise reduction of the rail noise reduction system and damping material. These figures show that the rail noise reduction system and damping material contribute to noise reduction by 0.5 to 3.5 db and 0 to 1.5 db, respectively; therefore, the combined use of these two measures leads to noise-reduction by 2 to 4 db in total. These figures also show that the rail noise reduction system contributes to larger noise reduction when the train runs at higher speed; however, the damping material has less effect on noise reduction at higher train speed. This is probably because,the bridge structure generates more noise than the rail at low train speeds; however, the rail noise becomes greater as the train speed increases. Another finding is that the Class 4024 train that has small wheels that produce smaller sound radiation is given a larger noise reduction contribution of the rail noise reduction system, and the damping material s contribution is not affected by the particulars or operating characteristics of the trains.
166 G. Koller et al. Fig. 17. Noise Reduction for Class 4020 Train Fig. 18. Noise Reduction for Class 4024 Train 5 Conclusion The high-performance damping material intended for railway noise reduction was tested in cooperation with Austrian Federal Railways using its actual tracks. The rail noise-reduction system based on this damping material has proved effective for reducing noise by 2 to 4 db when it was applied for a normal section (ballast track). For a bridge section, combined use of the rail noise reduction system and damping material can reduce noise by 2 to 4 db as a sum of 0.5 to 3.5 db by the rail noise-reduction system and 0 to 1.5 db by the damping material. To further reduce noise, train maintenance for keeping the wheel surface roughness at lower level and use of smaller wheels should be taken into consideration in addition to direct rail noise-reduction measures such as those mentioned here. References [1] Railway Technical Research Institute: Measuring and Evaluation Technologies for Railway Noise Annoyance (October 2003) [2] Kitagawa, T.: An investigation on the Influence of Wheel and Track Parameters upon Rolling Noise. RTRI Report 22(5) (May 2008) [3] Zenda, Y., Tanaka, S., Nagakura, K., Obara, T., Satou, K., Minami, H.: Effect of Rail/Wheel Roughness and Wheel Shape on Rolling Noise. RTRI Report 22(5) (May 2008) [4] Asmussen, B., Stiebel, D., Kitson, P., Farrington, D., Benton, D.: Reducing the Noise Emission by Increasing the Damping of the Rail: Results of a Field Test. In: Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 99, pp. 229235 (2008)