A NOISE DAMPER AND A METHOD FOR PRODUCING A NOISE DAMPER

Abstract

A noise damper for reducing noise from a vibrating element which vibrates at a vibrational frequency, wherein the noise damper is configured to be in contact with the vibrating element such that when the noise damper is in contact with the vibrating element a noise amplitude at a point in a surrounding of the vibrating element is given by an attenuation factor times the noise amplitude at the point in the surrounding when the noise damper is disconnected from the vibrating element, the noise damper comprising: a polymer matrix, the polymer matrix being in a solid phase and forming a shape; a plurality of hollow particles dispersed in the polymer matrix, each hollow particle having a shell encapsulating a gas filled cavity, each hollow particle having a hollow particle size, and the plurality of hollow particles being dispersed at a hollow particle concentration in the polymer matrix; wherein the hollow particle size and the hollow particle concentration are configured to set the attenuation factor below an attenuation factor threshold at the vibrational frequency of the vibrating element, the hollow particle size being in a range wherein the largest dimension is between 20 μm and 2000 μm.

Claims

1. A noise damper for reducing noise from a vibrating element which vibrates at a vibrational frequency, wherein the noise damper is configured to be in contact with the vibrating element such that when the noise damper is in contact with the vibrating element a noise amplitude at a point in a surrounding of the vibrating element is given by an attenuation factor times the noise amplitude at the point in the surrounding when the noise damper is disconnected from the vibrating element, the noise damper comprising: a polymer matrix, the polymer matrix being in a solid phase and forming a shape; a plurality of hollow particles dispersed in the polymer matrix, each hollow particle having a shell encapsulating a gas filled cavity, each hollow particle having a hollow particle size, and the plurality of hollow particles being dispersed at a hollow particle concentration in the polymer matrix; said noise damper being characterized in that the hollow particle size and the hollow particle concentration are configured to set the attenuation factor below an attenuation factor threshold at the vibrational frequency of the vibrating element, the hollow particle size being in a range of 20 μm to 2000 μm, the hollow particle size and the hollow particle concentration being further configured such that the polymer matrix with the dispersed hollow particles has a tan delta between 0.1 and 15, wherein tan delta is the loss modulus divided by the storage modulus for a viscoelastic material.

2. The noise damper of claim 1, wherein the attenuation factor is frequency dependent and the hollow particle size and the hollow particle concentration are further configured to set the attenuation factor to have a local minimum within a first vibrational interval, said first vibrational interval comprising the vibrational frequency of the vibrating element, said first vibrational interval being the vibrational frequency ±10% of the vibrational frequency.

3. The noise damper of claim 1, wherein the noise damper is configured to act as an acoustic attenuator which attenuates a sound wave originating from the vibrating element as the sound wave is transmitted through the noise damper when it is in contact with the vibrating element, wherein the hollow particle size and the hollow particle concentration are further configured to set an acoustic attenuation coefficient of the noise damper above an acoustic attenuation coefficient threshold at the vibrational frequency of the vibrating element.

4. The noise damper of claim 3, wherein the acoustic attenuation coefficient is frequency dependent and the hollow particle size and the hollow particle concentration are further configured to set the acoustic attenuation coefficient to have a local maximum within a second vibrational interval, said second vibrational interval comprising the vibrational frequency of the vibrating element, said second vibrational interval being the vibrational frequency ±10% of the vibrational frequency.

5. The noise damper of claim 1, wherein the noise damper is configured to act as a part of a vibration isolation system, the noise damper being configured to be attached to an object as well as to the vibrating element, wherein the noise damper, the vibrating element and the object together form the vibration isolation system when the noise damper is attached both to the vibrating element and the object, the vibration isolation system controlling an amplitude of vibrations transmitted from the vibrating element to the object.

6. The noise damper of claim 5, wherein the hollow particle size and the hollow particle concentration are further configured to set a natural frequency of the vibration isolation system such that the ratio between the vibrational frequency and the natural frequency of the vibration isolation system is above a frequency ratio threshold.

7. The noise damper of claim 5, wherein the hollow particle size and the hollow particle concentration are further configured to set a transmissibility of the vibration isolation system at the vibrational frequency below a transmissibility threshold, wherein the transmissibility is the ratio of an amplitude of a vibrational response and an amplitude of a vibrational input of the vibration isolation system.

8. The noise damper of claim 5, wherein the hollow particle size and the hollow particle concentration are further configured to set a damping ratio above a damping ratio threshold, wherein the damping ratio is the ratio between the damping coefficient and the critical damping coefficient of the vibration isolation system.

9. The noise damper of claim 1, wherein the noise damper is a rail boot, the rail boot being configured to be attached to a rail of a railroad, wherein the rail is the vibrating element.

10. The noise damper of claim 1, wherein the hollow particles are temperature expandable particles and wherein the hollow particle size has been set by elevating the temperature of the hollow particles to a size defining temperature during the production of the noise damper, the size defining temperature being a temperature which expands the hollow particles to a predefined size.

11. The noise damper of claim 1, wherein the noise damper is a vibrational element clip, wherein the shape of the polymer matrix has a form which grips the vibrating element such that the vibrational element clip is configured to be attached to the vibrating element by clipping it on to the vibrating element.

12. A method for producing a noise damper for reducing noise from a vibrating element which vibrates at a vibrational frequency, wherein the noise damper is configured to be in contact with the vibrating element such that when the noise damper is in contact with the vibrating element a noise amplitude at a point in a surrounding of the vibrating element is given by an attenuation factor times the noise amplitude at the point in the surrounding when the noise damper is disconnected from the vibrating element, the method comprising: heating an amount of a polymer matrix material such that it melts and forms a melted polymer matrix material; dispersing an amount of hollow particles in the melted polymer matrix material, wherein each hollow particle has a shell encapsulating a gas filled cavity; shaping and cooling the melted polymer matrix material with the dispersed hollow particles such that the melted polymer matrix material solidifies into a polymer matrix with a shape, the shape comprising a plurality of the hollow particles with a hollow particle size dispersed at a hollow particle concentration in the polymer matrix; wherein the amount of polymer matrix material and the amount of hollow particles are configured to define the hollow particle concentration in the solidified polymer matrix, said method being characterized in that the hollow particle size and the hollow particle concentration are configured to set the attenuation factor below an attenuation factor threshold at the vibrational frequency of the vibrating element, the hollow particle size and the hollow particle concentration being further configured such that the polymer matrix with the dispersed hollow particles has a tan delta between 0.1 and 15, wherein tan delta is the loss modulus divided by the storage modulus for a viscoelastic material.

13. The method for producing a noise damper according to claim 12 wherein: each hollow particle is a temperature expandable particle which is expandable to a size which is temperature dependent; the method further comprising: elevating the temperature of the melted polymer matrix material with the dispersed hollow particles to a size defining temperature such that the hollow particles expand, wherein the size defining temperature is configured to define the hollow particle size in the solidified polymer matrix.

14. The method for producing a noise damper according to claim 13 wherein an extrusion process is used in which: the steps of heating an amount of polymer matrix material and dispersing an amount of hollow particles in the melted polymer matrix material are performed by feeding a barrel of an extruder with polymer matrix material and unexpanded hollow particles and elevating the temperature in the barrel above the melting temperature of the polymer matrix material; the step of elevating the temperature of the melted polymer matrix material with the dispersed hollow particles to a size defining temperature is performed at an extruder die of the extruder wherein the die is a point where the melted polymer matrix material with the dispersed hollow particles leaves the extruder.

15. The noise damper of claim 6, wherein the hollow particle size and the hollow particle concentration are further configured to set a transmissibility of the vibration isolation system at the vibrational frequency below a transmissibility threshold, wherein the transmissibility is the ratio of an amplitude of a vibrational response and an amplitude of a vibrational input of the vibration isolation system.

16. The noise damper of claim 6, wherein the hollow particle size and the hollow particle concentration are further configured to set a damping ratio above a damping ratio threshold, wherein the damping ratio is the ratio between the damping coefficient and the critical damping coefficient of the vibration isolation system.

17. The noise damper of claim 7, wherein the hollow particle size and the hollow particle concentration are further configured to set a damping ratio above a damping ratio threshold, wherein the damping ratio is the ratio between the damping coefficient and the critical damping coefficient of the vibration isolation system.

18. The noise damper of claim 2, wherein the noise damper is configured to act as an acoustic attenuator which attenuates a sound wave originating from the vibrating element as the sound wave is transmitted through the noise damper when it is in contact with the vibrating element, wherein the hollow particle size and the hollow particle concentration are further configured to set an acoustic attenuation coefficient of the noise damper above an acoustic attenuation coefficient threshold at the vibrational frequency of the vibrating element.

19. The noise damper of claim 4, wherein the noise damper is configured to act as a part of a vibration isolation system, the noise damper being configured to be attached to an object as well as to the vibrating element, wherein the noise damper, the vibrating element and the object together form the vibration isolation system when the noise damper is attached both to the vibrating element and the object, the vibration isolation system controlling an amplitude of vibrations transmitted from the vibrating element to the object.

20. The noise damper of claim 2, wherein the noise damper is a rail boot, the rail boot being configured to be attached to a rail of a railroad, wherein the rail is the vibrating element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0085] FIG. 1 illustrates a noise damper in the form of a rail boot attached to a rail.

[0086] FIG. 2 illustrates a hollow particle.

[0087] FIG. 3 illustrates a hollow particle.

[0088] FIG. 4 illustrates a rail boot being clipped on to a rail.

[0089] FIG. 5 illustrates a rail boot attached to a rail which is partially encased in a concrete roadway.

[0090] FIG. 6 illustrates a vibration isolation system.

[0091] FIG. 7 illustrates a transmissibility curve.

[0092] FIG. 8 illustrates noise dampers in the form of expansion joints.

[0093] FIG. 9 illustrates a noise damper in the form of an expansion joints for a bridge.

[0094] FIG. 10 illustrates a method for producing a noise damper.

DETAILED DESCRIPTION

[0095] In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit the claimed scope. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0096] FIG. 1 illustrates a noise damper 1, in the form of a rail boot 50, attached to a vibrating element 2, in the form of a rail 52. The rail boot 50 comprises a polymer matrix 10 in which hollow particles 20 are dispersed, as seen in the enlarged portion of the figure. The rail boot 50 in the figure has a shape which conforms to the surface of the rail 52.

[0097] FIGS. 2 and 3 illustrates a hollow particle 20 having a shell 24 encapsulating a gas filled cavity 22. FIG. 2 illustrates a semi-transparent hollow particle 20 while FIG. 3 illustrates a semi-transparent hollow particle 20 wherein a portion of the shell 24 has been cut out for illustrative purposes. However, in a hollow particle 20 according to the inventive concept, the shell 24 fully encapsulates the cavity 22. One example of a hollow particles 20 is Expancel particles which have a polymer shell. Another example of hollow particles 20 is Deep Springs Technology particles which may have a shell of e.g. glass, oxide ceramics, carbides etc. Another example of hollow particles 20 is 3M glass bubbles like iM16K.

[0098] FIG. 4 illustrates a rail boot 50 being clipped on to the rail 52. The polymer matrix 10 into which the hollow particles 20 are dispersed herein offers enough flexibility for the rail boot 50 to be distorted during the installation process. Once installed, the rail boot 50 reverts to its original form and grips the rail 52 by embracing the rail 52 tightly. Thus the rail boot 50 works as a vibrational element clip which may be attached to the vibrating element by clipping it on to the vibrating element.

[0099] FIG. 5 illustrates a rail boot 50 according to the inventive concept. The rail boot 50 in the figure is attached to a rail 52 and the rail 52 with the rail boot 50 is partially encased in a concrete roadway 8. Thus, the rail 52, the rail boot 50 and the concrete roadway 8 forms a vibration isolation system 30. The amplitude of vibrations transmitted from the rail 52 to the concrete roadway 8 may thus be reduced. When the rail 52, with the rail boot 50 attached, is encased in the concrete roadway 8, the noise amplitude at a point 4 in the surrounding of the rail 52 is given by an attenuation factor times the noise amplitude in the surrounding when the rail 52, without the rail boot 50 attached, is encased in the concrete roadway 8. The point 4 in the surrounding of the rail 52 may be a point 4 in the concrete roadway 8, in the ground adjacent to the concrete roadway 8, or a point 4 in the air in the vicinity of the rail 52.

[0100] For the polymer matrix 10 of the rail boot 50 a variety of polymer matrixes 10 may be used. The polymer matrix 10 may e.g. be a thermoplastic polymer. The polymer matrix 10 may e.g. be TPS (styrenic block copolymers), TPU (thermoplastic polyurethanes), or TPV (thermoplastic vulcanizates). The hollow particles 20 may have a shell 24 made of e.g. a thermoplastic polymer. The shell 24 may encapsulate a hydrocarbon gas, e.g. isopentane. Examples of hollow particles are Expancel particles, e.g. Expancel 920 MB 120, Expancel 950 MB 80, and Expancel 930 MB 120. Other examples are Deep Springs Technology particles or 3M glass bubbles.

[0101] The hollow particle size and the hollow particle concentration in the polymer matrix 10 may be customized to an expected vibrational frequency such that the attenuation factor is set below an attenuation factor threshold. FIG. 6 illustrates a model of a vibration isolation system 30. The vibration isolation system 30 comprises a vibrating element 2 with mass m, a noise damper 1 according to the inventive concept, and an object 32, wherein the noise damper 1 is attached both to the vibrating element 2 and the object 32. The noise damper 1 may herein be modelled as a spring 34 with stiffness k and a dash-pot 36 with damping coefficient C. The hollow particle size and the hollow particle concentration may affect k and C and thereby control the properties of the vibration isolation system, e.g. the natural frequency (f.sub.n), and the transmissibility (T), of the system.

[0102] FIG. 7 illustrates transmissibility curves 40 for three vibration isolation systems 30. The figure illustrates that the ratio between the vibrational frequency (f.sub.d) and the natural frequency determines if the vibration isolation system is in the region of isolation or amplification. When f.sub.d/f.sub.n>√{square root over (2)} the vibration isolation system is in the region of isolation wherein T<1. Lower stiffness and higher damping coefficient may reduce the natural frequency such that the vibration isolation system 30 operates in the region of isolation. If the vibrational frequency is so low that it is not possible to shift the vibration isolation system 30 into the region of isolation the magnitude of the amplification in the region of amplification may be reduced by increasing the ratio between the damping coefficient (C) and the critical damping coefficient (C.sub.c). The figure illustrates that increasing the C/C.sub.c ratio reduces the transmissibility in the region of amplification.

[0103] FIG. 8 illustrates noise dampers 1 in the form of expansion joints 60. The expansion joints 60 acts as acoustic attenuators placed in the gaps between e.g. two wall segments 62 or a wall segment 62 and a ceiling segment 64 in a building. A noise source 6 on one side of the wall creates a sound wave which has to go through the expansion joint 60 to reach the other side. The hollow particle size and the hollow particle concentration are configured to set the acoustic attenuation coefficient of the expansion joint 60 above an acoustic attenuation coefficient threshold at the vibrational frequency of the vibrating element, the vibrating element being the air at the side of the wall facing the noise source 6. By setting the acoustic attenuation coefficient of the expansion joint 60 above the acoustic attenuation coefficient threshold at the vibrational frequency it is possible to ensure that with a given thickness a certain acoustic attenuation coefficient may be achieved.

[0104] FIG. 9 illustrates a noise damper 1 in the form of an expansion joint 60 for a bridge. The expansion joint 60 is placed in a gap between two road segments 66 of a bridge. The expansion joint 60 in the figure may act as part of a vibration isolation system which absorbs mechanical vibrations at the joint of the road segments 66. The expansion joint 60 in the figure may also act as an acoustic attenuator preventing acoustic noise from passing between the two road segments 66. The expansion joint 60 may be optimized for a mechanical vibrational frequency, e.g. an expected frequency originating from vehicles or pedestrians travelling on the bridge. The expansion joint 60 may also be optimized for an acoustic frequency, e.g. a resonant frequency of the space below the bridge or an expected frequency originating from vehicles travelling below the bridge.

[0105] FIG. 10 illustrates a method 100 for producing a noise damper 1. The method 100 comprises the step of heating 102 polymer matrix material such that it melts and forms a melted polymer matrix material. The polymer matrix material may herein be e.g. TPS, TPU, or TPV. The method 100 further comprises the step of dispersing 104 an amount of hollow particles 20 in the melted polymer matrix material.

[0106] The hollow particles 20 may be of a fixed size wherein the size of the particles does not change substantially from the point when they are mixed into the melted polymer matrix material to the point when the melted polymer matrix material has solidified. However, in some embodiments the hollow particles 20 are temperature expandable particles. An example of temperature expandable particles is Expancel particles. Temperature expandable particles expand when subjected to heat. The heat may herein soften the shell 24 and expand the gas in the gas filled cavity 24. The temperature expandable particles have a start temperature at which expansion starts and a max temperature at which the temperature expandable particles starts to degrade through e.g. rupture.

[0107] In an optional step of the method 100 the temperature of the melted polymer matrix material with the dispersed hollow particles 20 is elevated 106 to a size defining temperature. The size defining temperature herein lies between the start temperature and the max temperature.

[0108] In a further step of the method 100 the melted polymer matrix material with the dispersed hollow particles 20 is shaped and cooled 108 such that the melted polymer matrix material solidifies into a polymer matrix 10 with a shape.

[0109] According to the method 100 the amount of polymer matrix material and the amount of hollow particles 20 are configured to define the hollow particle concentration in the solidified polymer matrix 10. According to the method 100 the size of the hollow particles 20 in the finished noise damper 1 may be the same as the size of the hollow particles 20 when they were dispersed 104 in the melted polymer matrix material. When temperature expandable particles are used the size of the hollow particles 20 in the finished noise damper 1 may be defined by the size defining temperature. It should be understood that the size defining temperature may be the highest temperature the hollow particles 20 during the production of the noise damper 1.

[0110] In one embodiment an extrusion process is used to implement the method 100. Herein the steps of heating 102 an amount of polymer matrix material and dispersing 104 an amount of hollow particles 20 in the melted polymer matrix material are performed by feeding a barrel of an extruder with polymer matrix material and unexpanded hollow particles 20 and elevating the temperature in the barrel above the melting temperature of the polymer matrix material. In the extruder one or more screws may provide heat through shear heating to melt the polymer matrix material. The screw/screws may also mix the melted polymer matrix material with the hollow particles 20 as well as force the mixture towards an extruder die. Herein the extruder die is an opening where the melted polymer matrix material with the dispersed hollow particles leaves the extruder, the opening defining the shape of cross-section of the extruded noise damper 1. It may be advantageous to use a single screw extruder to avoid too high shear forces which may rupture the hollow particles 20. However, a twin screw extruder or a melt pump extruder may also be used.

[0111] In the extrusion process the step of elevating 106 the temperature of the melted polymer matrix material with the dispersed hollow particles 20 is performed at the extruder die. The temperature may be controlled by heating elements at the barrel and at the at the extruder die. The barrel may be kept at a lower temperature than the extruder die such that the temperature of the melted polymer matrix material with the dispersed hollow particles 20 is elevated as the melted polymer matrix material passes the extruder die. The temperature in the barrel may be set e.g. slightly above the start temperature and the temperature at the extruder die may be set between the start temperature and the max temperature or between the barrel temperature and the max temperature.

[0112] In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.