Acoustics – Sound-modifying means – Sound absorbing fence or screen
Reexamination Certificate
1998-11-24
2001-07-03
Nappi, Robert E. (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing fence or screen
C181S293000, C105S452000, C238S382000
Reexamination Certificate
active
06253872
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a noise control device for tracks comprising sound absorbing slabs mounted at the rails of the track, the slabs being supported on the rails via elastic sections, the slabs arranged between the rails self-supportingly bridging the space between the rails. Furthermore, the invention relates to sound-absorbing slabs for such a noise control device.
In a noise control device of the above-mentioned type known from DE 36 02 313 A1, the slabs arranged between the rails of the track consist of three plies or layers supported on the rail base, on the rail web and on the lower side of the rail head via elastic sections. The upper layer consists of a passable woven steel wire whose rim is glued, welded or vulcanized into the section. The middle layer forms a sound absorption layer and consists of glass wool or rock wool. This sound absorption layer rests on the lower layer which is a perforated wall or grate and is supported in a recess of the section in the region of the rail base. According to a further embodiment, the slabs are also arranged on the rail outer side and upwardly angled at their ends so as to form a lateral noise control wall. Such slabs of mineral wool do provide sufficient silencing at high frequencies, yet at low frequencies their silencing is insufficient. Furthermore, this construction has the disadvantage that under higher and repeated loads, the passable perforated layer of woven steel wire may become detached from its anchoring in the sections so that the sound absorbing layer arranged therebelow may become damaged. Moreover, the dust penetrating the perforated layer may deposit on the upper side of the sound absorption layer and thus the silencing effect may increasingly deteriorate.
From NL-A-9400910 a noise control device for tracks is known, in which slabs made of wood fiber concrete are arranged between the rails of the track, which slabs rest on the sleepers of the track and laterally abut on the rails with elastic strips interposed. There is no self-supporting mounting of these slabs.
SUMMARY OF THE INVENTION
The invention has as its object to provide a noise control device for tracks comprising sound absorbing slabs which have good sound absorption or silencing over the entire range of frequencies essential for the noise levels of rail traffic, wherein also a lasting mechanical strength of the device is to be ensured.
In the noise control device of the initially defined type, according to the invention this object is achieved in that the slabs are comprised of particles of porous lightweight building material combined by a binder and that the slabs have an embedded reinforcement and are arranged without cover. By this design, the aforementioned objects can be met well. The airborne sound particularly arising from the wheels of a rail vehicle and from the rails is absorbed at the surface of the slabs by the pores of the particles, and even when a structure having fine gaps between the particles is chosen, the sound can penetrate more deeply into the slab via gaps or channels present between the particles so as to be gradually completely silenced there. By reinforcing the slabs, also their passability is ensured.
To further improve the sound absorption properties of the slabs, it is advantageously provided that the upper side of the slabs is structured, and even better results being obtainable if the structuring is irregular.
Preferably, the upper side of the slabs is provided with ribs extending in parallel to the rails, resulting in a structuring which is easy to be constructed.
It is also advantageous if the ribs have a trapezoidal cross-section, since thus obliquely incident sound waves can be better absorbed.
An additional improvement of the sound absorption properties of the slabs is obtained in that cavity resonators having tubular sound apertures directed to the upper side of the slabs are formed in the slabs. In this manner, certain frequency ranges of the impacting sound waves purposefully can be better absorbed.
To increase the silencing effect of the cavity resonators, it is suitable if the walls of the cavity resonators and their sound apertures are provided with a silencing structuring, and/or if the walls of the cavity resonators and their tubular sound apertures are provided with a silencing layer.
According to a structurally simple embodiment it is provided that the cavities forming the cavity resonators are designed such that they widen downwardly and are open, and are covered by a lower plate. In a different, also structurally simple embodiment it is provided that the cavities forming the cavity resonators are designed such that they widen downwardly and are open and form a resonance cavity together with the rail bedding.
In practice, it has proven to be suitable if the dampened resonance frequency of the cavity resonators lies within a frequency range of from 150 to 1,000 Hz, preferably between 500 and 1,000 Hz.
Within the scope of the invention also a special embodiment is provided in which the installation and removal of the slabs to be provided between the two rails of a track can be effected in a very simple manner. This embodiment of the noise control device is characterized in that the space present between the two rails of a track is bridged with slab parts arranged in pairs, each engaging by at least one carrying rib in the fishing surfaces of the rails, the slab parts of each slab pair being supported on each other at their facing rims, carrying portions and resting portions following each other in meander-like alternating fashion at each slab part along the rim facing the other slab part, the carrying portions being formed by indentations originating from the slab upper side and extending as far as to the rim facing the other slab part, upwardly directed indentations originating from the slab lower side being formed below the resting portions, which indentations are shaped complementary to the indentations of the carrying portions, and that the resting portions of the one slab part rest on the carrying portions of the other slab part, and that the resting portions of the other slab part rest on the carrying portions of the one slab part With slab parts in a folded-up position, the hinge-like assembled zones of the slab parts of each slab pair can be simply nested in each other, whereupon the slab parts can be inserted between the rails without any problem by levelling the slab pair, and neither will the slab parts be pressed apart under the action of loads.
A preferred type of the last-mentioned embodiment, which is characterized in that at those surfaces on which the slab parts of one slab pair contact each other, projections and indentations shaped complementary to the projections are formed, the projections latchingly engaging in the indentations for a mutual latching of the slab parts, has the advantage that the positive fit of the slab parts of a slab pair will be ensured over very long periods of time even if unfavorable vibrations act on the slab parts.
In terms of as simple an insertion procedure as possible of the slab parts between the rails, which is to be effected with little expenditure of force, and in terms of a possible simple removal of the slab parts it is advantageous if it is provided that the carrying surfaces provided in the carrying portions, starting from the rim facing the other slab part of the slab pair, at first rise steeply, starting from the slab lower side, and then flatten. There, it is furthermore suitable and also advantageous for ensuring a stable positive fit of the slab parts over extended periods of time in their installed state, if it is provided that the carrying surfaces provided in the carrying portions have a crowned shape, which shape inhibits a mutual movement of these slabs in the direction of the slab plane in the levelled position of the slab parts of the respective slab pair. Such a crowned shape may be formed on one slab part by a surface portion originating from the rim facing the other slab part of the slab pair, which sur
Gmundner Fertigteile Gesellschaft m.b.H & Co., KG
Martin Edgardo San
Nappi Robert E.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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