WO1997024492A1 - Absorbent acoustic panels with rubber siftings - Google Patents

Abstract

The invention is the reuse of highly contaminant materials such as used tires, which can be appropriately treated and transformed into rubber siftings with predetermined sizes and thickness in order to be used as filler materials having absorbent acoustic properties (according to international standards) in order to produce noise-absorbing panels or barriers which can be installed on traffic ways for the protection of human habitats against intrusive noise.

Description

ABSORBENT ACOUSTIC SCREENS WITH RUBBER GRANZA

Technical sector: Acoustics, Environment, Construction, Pollutants.

State of the art

The incessant increase, in recent years, of road traffic, both in the roads of penetration to the big cities, as in the fast roads inside them, has resulted in high levels of noise pollution in habitats nearby.

When the distance of the houses to the traffic lanes, due to previous urban planning reasons or due to modifications of the existing roads is too small, the noise attenuation due to spherical divergence is insufficient, so that the regulations established by the administrations are violated premises in relation to noise indices, leaving no other solution than to screen the homes through acoustic barriers.

The introduction of these barriers or reflective acoustic screens, although they protect the neighbors from traffic noise, present the inconvenience of increasing, due to acoustic reflection phenomena, the noise radiated in the opposite direction to the situation of the barrier which increases the noise both on the roads themselves, and in the built-up areas of that side, which affects the drivers and the neighbors of the buildings. When heavy vehicles circulate near these barriers, a multiple reflection effect is created in the heavy vehicles system - a barrier that minimizes its protective effect, if it is reflective, a very frequent situation in our country. In cases where it is necessary to have double screens on either side of the road, Their effectiveness is diminished by the multiple reflections to which they are subjected. Both in these cases and in which traffic is conducted through tunnels, there is interest in having screens of absorbent material to minimize the phenomena described above. They are described as absorbents, those barriers that incorporate elements capable of absorbing a significant portion of the incident acoustic energy, reducing the reflected sound which contributes to lowering the total noise levels in your neighborhood.

There is an abundant bibliography on the improvements introduced by the absorbent acoustic screens on their insertion losses (degree of protection). In this sense are the works of: P. Bar "Matériaux utilises dans les écrans acoustiques en bordure des voix routieres", Bulletin PCM, 4, 19-23, (1980); W. Bowly & L.M. Cohn, "Sound absorptive highway noise barriers", Federal Highway Administration report FHWA-TS-86-214 (1986); A.T. Peplow & D.C. Hothersall, "Of absorbing screens in the presence of high-sided vehicle", Euro Noise'92 Proc. I.O.A., Vol 14, Part. 4 (1992), etc: At present, the acoustic absorbent barriers, could be described as reflective and low absorption, absorbent and highly absorbent following the criteria of the German Ministry of Traffic (Der Bundesminister FFR Verkehr) in its standard "Zusatzliche technische Vorschriften und Richtlinien fur die Ausfurung von Larmschutzwenden an Strassen ", ZTV-Lsw 88, Bonn (1988), norm implicitly assumed by most EU countries and among them Spain.

In the current state of the art, there are several constructive models of modular acoustic screens (simple on-site installation) that could be classified according to the criteria of the aforementioned standard: Reflective: Made up of wood panels, corrugated sheet, cement, etc.

Poorly absorbent: Porous concrete panels. Absorbent and highly absorbent: a) Systems that use panels constructed of porous open pore materials. b) Hollow box systems filled with acoustically absorbent fibrous material. c) Systems containing resonant cavities.

In case 3a), absorption is achieved through a combination of processes that include inertial losses and friction in the gaps of the permeable layer. These include panels made of special cements that make up a light and porous structure; panels made with treated wood chips, agglomerated and compacted with cement and panels constructed with particles cut from flint. Unless these screens are very thick, it is required to cover their rear part of a waterproof acoustic material, in order to obtain the minimum sound insulation to the wave that propagates through it.

In case 3b), the panels are designed in such a way that the face facing the road traffic is perforated in order to allow the transfer of acoustic energy to the fibrous material contained in the box. This fibrous material is generally made of glass wool or rock wool, and is often covered by a thin layer of fiberglass or other stable material so that it is not degraded by ultraviolet radiation. This layer is also used to increase the durability of the material against rain and wind.

In case 3c), the face of the screen directed to the traffic contains slits or holes that connect to the internal cavities. Sound is absorbed at certain frequencies, depending on the dimensions of the cavities (resonators). The cavities can be filled with fibrous or spongy materials in order to increase the range of acoustic absorption frequencies. Generally these units are built in the form of prefabricated ceramics.

Description of the invention

Brief Description of the Invention

The object of the present patent is the realization of medium absorption acoustic screens of the type 3a described in the state of the art, but with better acoustic absorption characteristics and lower energy expenditure in its construction.

The absorbent material that constitutes the filling of the screen (which can be made of sheet metal, light concrete or any other bearing structure and modular manufacturing), is constituted by rubber pellets of waste tires. This results in not only an absorption greater than that presented by the materials described in 3a, but also helps to solve the problem of environmental pollution that the enormous amounts of vehicle tires represent; problem not satisfactorily solved in the current technological state.

It is well known the high stability of the tires in the event of inclement weather, which is why it represents advantages over wood chips and / or other agglomerated with cement, of medium / short duration due to atmospheric agents and pollution by flue gases .

On the other hand, it implies the use of waste products of non-recyclable materials, using soft technology, thus providing a solution to this serious problem in developed countries. Its cost can be considered as very Low and due to the high density of the material it is possible to make screens with smaller thicknesses than the traditional ones of this group.

The manufacture of 2x1 m ² carrier modules (eg) has the same advantages of transport and installation, through right feet in the form of double T, like the other screens in use.

Detailed description of the invention

Acoustic absorption through porous rigid skeleton materials such as those described in 3b, is based on a process of degradation of acoustic energy through inertial losses and friction in the gaps of the permeable layer. The skeleton of these materials is quite rigid, being constituted by cement or other binder component. In turn, particles of aggregate material cannot be too small to not fill it, resulting in an absorbent material displaced towards high frequencies.

In the case of the present patent, the size of the voids in which the sound absorption occurs can be regulated at will in a wide range, through the size of the grains of the pellets. Since the material does not have a rigid skeleton, the acoustic energy losses are increased through inertial processes in the pellets themselves, since it is a system with three degrees of freedom. As a consequence, the absorption band increases its frequency range, being able to shift the maximum absorption frequencies, especially by matching them with the frequency spectrum of the traffic noise, which significantly increases the acoustic performance of the process. The screen would consist of modules of adequate dimensions to the transport and installation facilities. For example, an embodiment in modules of 2 m in length and 1 m in height, formed as drawers with varying thicknesses (depth of the filling) depending on the desired degree of absorption, is susceptible. In the aforementioned drawers, the rubber pellet is deposited, covering it with a metal grid. Grid that for greater use of the material (sheet metal) can be made by incisions and stretching, which avoids the losses by punching, as well as the problems that occur with the remains of material that formed the holes of other types of perforated materials.

The assembly can be painted at the factory or on-site, without damaging the absorbing characteristics of the assembly.

With this type of absorbent material, it is possible to manufacture a device suitable for the type of noise on which it is desired to act, which is a function of the agent producing it (road traffic, railways, or other agents, such as industrial plants, etc.) .

In the case at hand, acoustic absorption has focused on the preponderant frequencies of the traffic noise spectrum weighted in dBA (ISO 717, part II), that is, at frequencies close to the third octave of 630 Hz.

The high density of the product ensures intrinsic insulation losses compatible with the ZTV Lsw 88 standard. If, due to design reasons, a thin thickness pellet layer is desired, the insulation can be increased by adding a blanket of bituminous elastic material, easy to Find in the market. Example of embodiment of the invention

One of the biggest advantages of not having a rigid skeleton is its speed and low economic cost in the design of prototypes and laboratory tests on Kundt tube specimens. These tests offer perfectly acceptable results compared to those performed in the Reverberant Chamber as set by the German standard ZTV Lsw 88, according to which the qualifying index of the sound absorption of an absorbent acoustic screen is expressed through the relationship:

Análogos valores de absorción total, se obtienen a través de la expresión propuesta por el proyecto de norma europea CEN/TC226/WG6/TG1:

Similar total absorption values are obtained through the expression proposed by the draft European standard CEN / TC226 / WG6 / TG1:

Thus, Figure 1 represents the variation of the absorption spectrum measured in Kundt tube, of a 7 mm diameter rubber pellet sample, as a function of the thickness of the sample. The displacement of the maximum absorption towards the low frequencies can be observed, as the sample thickness increases.

Figure 2 shows, for the same depth of the specimen (in all cases 9 cm), the variation of the absorption coefficient as a function of the diameter of the pellet.

The qualification, according to the ZTV Lsw 88 standard, of the specimens in all these cases is ABSORBENT. Figure 3 presents a possible embodiment of absorbent screen as described in 4.2., In which a section of a module, filled with granzo (A), as well as the assembly, which from different modules make up the screen, is presented.

Claims

Claims 1) Absorbent acoustic screens made with rubber pellets, formed in modular structure, panel type, which are characterized in that the absorbent material that constitutes the filling of the screen is rubber pellet of waste tires. 2) Acoustic screens according to claim 1 characterized in that the pellet is contained in its housing by means of a perforated mesh or panel. 3) Acoustic screens characterized in that the pellet is contained in its housing by a thin net, consisting of thin layers of glass wool.