SOUND-ABSORBING PANEL, SOUND BARRIER COMPRISING SAID SOUND-ABSORBING PANEL AND METHOD FOR MAKING SAID SOUND- ABSORBING PANEL TECHNICAL FIELD

The present invention relates to a method for making a sound-absorbing panel.

The use of sound barriers near the loudest sources of noise to attenuate the effects of acoustic pollution has become increasingly more common over the past decades .

Sound pollution is normally produced by road, railway, and air traffic and industrial activities, and is often so loud that it can disturb resting and human activities, be dangerous for human health, cause deterioration of ecosystems, material property, monuments etc .

BACKGROUND ART

Sound barriers of the known type comprise a plurality of sound-absorbing panels coupled to one another .

Each sound-absorbing panel comprises at least one wall provided with a plurality of holes.

Sound-absorbing panels are generally made of concrete, wood or aluminum.

Some sound-absorbing panels are made of polymeric material. For example, document DE8023207 describes a sound-absorbing panel made of polymeric material. The panel is obtained by means of an extrusion process and a drilling process after the extrusion process. This type of technique is costly in terms of time and manufacturing costs. In order to obtain a panel with a good sound-absorption level, the panel must be provided with a very high number of holes (at least 35% of the face surface exposed to the source of noise must be perforated) and the diameter of the holes must be different according to the type of sound to be absorbed. Consequently, simultaneous multiple drilling tools having bits of different diameter are needed. Such tools, in addition to being difficult to make, are costly and not very effective.

Document DE 2101233 describes instead a fiberglass panel obtained by means of a molding process . The described molding process includes making a panel provided with a plurality of recesses, from which the holes are then obtained. However, this method is also costly and furthermore the holes obtained by means of this process do not have a well defined contour. This causes a worsening of the sound absorption of the panel.

Furthermore, the sound-absorbing panels of the known type, especially the panels made of polymeric material, are not sufficiently solid and often subject to breakage .

DISCLOSURE OF INVENTION

It is an object of the present invention to make a sound-absorbing panel and a sound barrier, which are easy and cost-effective to manufacture and which, at the same time, are capable of guaranteeing high performance both in terms of robustness and in terms of sound absorption.

In accordance with such objects, the present invention relates to a sound-absorbing panel and to a sound barrier as disclosed in claims 1 and 9, respectively.

It is an additional object of the present invention to provide a simple, cost-effective method for making a sound-absorbing panel, by virtue of which it is possible to obtain a high-performance sound-absorbing panel both in terms of robustness and in terms of sound absorption.

In accordance with such objects, the present invention relates to a method for making a sound- absorbing panel in accordance with claim 10.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will be apparent from the following description of a non- limitative embodiment thereof, with reference to the figures of the accompanying drawings, in which:

figure 1 is a perspective view, with parts removed for clarity, of a sound barrier according to the present invention;

- figure 2 is a perspective view, with parts in section and parts removed for clarity, of a detail of the sound-absorbing panel according to the present invention;

- figure 3 is a section view, with parts removed for clarity, of a detail of the sound barrier in figure 1;

- figure 4 is a diagrammatic view of a detail of the method for making a sound-absorbing panel according to the present invention;

- figure 5 is a diagrammatic view of a detail of the method for making a sound-absorbing panel according to a variant of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, reference numeral 1 indicates a sound barrier comprising a frame 2 and a plurality of sound- absorbing panels 3.

The frame 2 essentially comprises a plurality of uprights 5 adapted to be coupled to a base (not shown in the accompanying figures) .

Each sound-absorbing panel 3 is coupled laterally to two respective uprights 5 and may be coupled to one or more the sound-absorbing panel 3 in vertical direction. The number of sound-absorbing panels 3 superimposed in vertical direction depends on the height determined for the sound barrier 1 during the step of designing.

With reference to figure 2, each sound-absorbing panel 3 extends essentially along a longitudinal axis A and comprises a main body 7, which encloses and protects a layer of sound-absorbing material 8. The main body 7 comprises a first wall 9 facing the source of the noise in use, a second wall 10 opposite to the first wall 9, and a bottom wall 11.

The first wall 9 and the second wall 10 are coupled to each other, while the bottom wall 11 is coupled to the first wall 9 and to the second wall 10, respectively.

The first wall 9 has an essentially quadrangular shape and has an outer face 12 facing the source of noise in use, an inner face 13 facing the sound- absorbing material layer 8 in use, and a peripheral edge 14, which extends along the three sides 15 (shown in greater detail in figure 1) of the first wall 9.

The peripheral edge 14 may be preferably folded and, as shown in detail below, is coupled to the second part 10 in use.

The side 16 (shown in greater detail in figure 1) of the first wall 9 not provided with the peripheral edge 14 is coupled, as shown in detail below, to the bottom wall 11.

The first wall 9 is provided with a plurality of holes 18 (shown in the enlargement in figure 1) . In the non-limiting example described and illustrated here, the holes 18 are through holes and are uniformly distributed along the outer face 12 and the inner face 13.

This close-knit series of holes 18 (the holes 18 are approximately 17400 and distributed on a surface of 1.5 m ² in average) increases the sound-absorbing properties of the sound-absorbing panel 3 and puts the outside into communication with the inner part of the sound-absorbing panel 3 where the layer of sound- absorbing material 8 is located.

The holes 18 have preferably different diameters to allow the passage of respective wavelengths of the sound waves coming from the source of noise.

In the non-limiting example described and illustrated here, the plurality of holes 18 comprises a first group of holes 20 having a first diameter Dl of approximately 4 mm, a group of second holes 21 having a second diameter D2 of approximately 6 mm, and a group of third holes 22 having a third diameter D3 of approximately 8 mm.

Preferably, a number of first holes 20 is equal to approximately 33% of the total number of holes 18, the number of the second holes 21 is equal to 33% of the total number of holes 18, while the number of third holes 22 is equal to 33% of the total number of holes 18.

With reference to figures 1 and 2, the first wall 9 is provided with two longitudinal recesses 24.

In particular, along the inner face 13, the longitudinal recesses 24 define respective contact surfaces 25, which are arranged in contact with the sound-absorbing layer 8 in use.

The shape of the second wall 10 is essentially identical to the first wall 9, but is not provided with holes for the passage of sound waves. The second wall 10 must indeed not be perforated in order to form, along with the layer of sound-absorbing material 9, a resonance chamber for improving sound deadening.

In particular, the second wall 10 has an essentially quadrangular shape and has an outer face 29, an inner face 30 facing the sound-absorbing material layer 8 in use, and a peripheral edge 31, which extends along the three sides 33 (shown in greater detail in figure 1) of the second wall 9.

The peripheral edge 31 is preferably folded and coupled in use to the first wall 9.

In particular, the peripheral edge 14 of the first wall 9 is partially superimposed on the peripheral edge 31 of the second wall 10.

Preferably, an auxiliary layer is applied between the peripheral edge 14 and the peripheral edge 31, preferably on the inner surface of the two longitudinal edges 14 and 31 in order to guarantee a solid coupling of the bottom wall 11 with the first wall 9 and with the second wall 10.

Preferably, the auxiliary layer is made of a material chemically compatible with the polymeric material of which the wall 9 is made. The expression "chemically compatible material" means a material capable of bonding and/or adhering to the polymeric material of which the wall 9 is made.

In the non- limitative example described and illustrated here, the auxiliary layer is made of a polyester resin base polymeric material.

The side 34 of the second wall 10 not provided with the peripheral edge 31 is coupled, as shown in detail below, to the bottom wall 11.

The second wall 10 also has two longitudinal recesses 36, which define respective contact surfaces 37 along the inner face 30, arranged in use in contact with the layer of sound-absorbing material 8.

The bottom wall 11 is essentially U-shaped, and has an outer bottom wall 39, an inner bottom face 40, facing in use the layer of sound-absorbing material 8, and two longitudinal edges 42 and 43 coupled in use to the sides 16 and 34 of the first wall 9 and of the second wall 10, respectively.

Preferably, an auxiliary layer is applied between the two longitudinal edges 42 e 43 in order to guarantee a solid coupling of the bottom wall 11 with the first wall 9 and with the second wall 10.

Preferably, the auxiliary layer is made of a material chemically compatible with the polymeric material of which the wall 9 is made. The expression "chemically compatible material" means a material capable of bonding and/or adhering to the polymeric material of which the wall 9 is made.

In the non- limitative example described and illustrated here, the auxiliary layer is made of a polyester resin base polymeric material. The bottom wall 11 has a longitudinal recess 45, which defines, a respective contact surface 44 along the inner bottom face 40, arranged in use in contact with the layer of sound-absorbing material 8.

Preferably, the longitudinal recess 45 is shaped so as to accommodate a respective portion 46 of a second sound-absorbing panel 3 so as to allow to stabily stack the sound-absorbing panels 3, as shown in figure 3.

The bottom wall 11 may be optionally provided with holes (not shown in the accompanying figures) to drain any residues of water accumulating within the sound- absorbing panel 3 in case of rain.

The first wall 9, the second wall 10 and the bottom wall 11 are made of a reinforced polymeric material, preferably reinforced with fiber.

In the non-limiting example described and illustrated here, the reinforced polymeric material comprises a resin reinforced with glass fibers, preferably having an interlaced fiber structure; in all cases, other types of fiber may be used to reinforce the resin, such as, for example, Kevlar fibers, carbon fibers, or hybrid fibers (Kevlar or carbon weave and glass warp) .

The resin is preferably a styrene unsaturated polyester resin. Such a resin is fireproof and characterized by absence of halogens in the formula, which guarantees low fume emissions and low toxicity of the same. Finally, this type of resin is characterized by a nearly total absence of shrinkage. This allows to make artifacts characterized by high dimensional stability and accurate model reproduction.

A variant includes that the second wall 10 and/or the bottom wall 11 are made of a different material from that of which the first wall 9 is made, e.g. concrete, aluminum or wood.

The layer of sound-absorbing panel 8 is thus fully contained within the main body 7, rests on the contact surfaces 25, 37 and 44 and is preferably made of polyester fiber.

Preferably, the layer of sound-absorbing panel 8 is coupled to a layer of sound-absorbing material 50, e.g. of bituminous material, along the face facing the second wall 10.

Advantageously, the sound-absorbing panel 3 according to the present invention is characterized by high mechanical strength, and at the same time by minimum thickness and weight.

The very high mechanical strength is obtained by virtue of the use of reinforced polymeric material and the adoption of a particular type of coupling between the walls which define the sound-absorbing panel 3. The fact that the peripheral edge 14 of the first wall 9 is superimposed on the peripheral edge 31 of the second wall 10 makes the structure more rigid and more solid than the structure of the panels of the prior art. Furthermore, the application of a layer of plaster, preferably of the same material of which the walls are made (polystyrene) , between the peripheral edges of the walls which define the sound-absorbing panel 3 improves the robustness of the structure of the sound-absorbing panel 3 even more .

By virtue of the fact that weight and thickness of the sound-absorbing panel 3 are low, it is possible to make sound-absorbing panels having longer than standard lengths, i.e. 4 or 6 meters, to optimize underpinning costs.

The use of a resin reinforced with fibers makes the sound-absorbing panel 3 according to the present invention particularly resistant to atmospheric and chemical elements and to temperature variations .

Furthermore, the sound-absorbing panel 3 may be made with colors covering the entire RAL range and which are not subject to substantial chemical alterations over time .

Furthermore, the maintenance costs of the sound- absorbing panel 3 are essentially equal to zero and the panel is characterized by an excellent quality-price ratio .

Each sound- bsorbing panel 3 is made in accordance with the method for making a sound-absorbing panel according to the present invention.

In particular, such a method essentially includes carrying out the following operations in sequence:

- making the wall 9; - making the wall 10;

- making the bottom wall 11;

- assembling the walls 9, 10 and 11, the sound- absorbing panel 8 and the layer of sound-absorbing material 50.

The first wall 9, the second wall 10 and the bottom wall 11 are made by molding, preferably by using the so- called "RTM light (Resin Transfer Molding)" technique. Such a technique includes depositing dry glass fibers on the open mold (shown in figure 4 and in figure 5) , closing the mold with a counter mold and injecting the resin by means of an injection line 57 (only shown in figure 5) and of aspirating air by means of a suction line 58 provided with a vacuum pump 59 (only shown in figure 5) . The vacuum pump 59 provides two levels of vacuum: a first level of approximately -0.9 bars to obtain the closing of the mold and of the counter mold, and a second level of approximately -0.5 bars for assisting the flowing of the resin during injection. By virtue of the low injection pressures, the making of the molds is simple and rapid and the molds are lighter and, above all, less expensive.

The making of the wall 10 and of the bottom wall 11 essentially includes using molds and counter molds shaped so as to generate a wall 10 and a bottom wall 11 having the required shape .

A step of milling of the edges is preferably provided at the end of the step of molding. With reference to figure 4, the making of the wall 9 includes using a mold 60 and a counter mold 61 shaped so as to generate a provisional wall 62 provided with a plurality of recesses 65, uniformly distributed along the wall 9, starting from a layer of reinforcement fibers .

The provisional wall 62 is thus fed to a milling station. In the milling station, the provisional wall 62 is sectioned along a plane b (shown with a dashed line in figure 4) so as to transform the plurality of recesses 65 into the holes 18 of the wall 9 described above .

Preferably, the recesses 65 will have different diameters so as to obtain holes 18 of different diameter capable of allowing the passage of respective wavelengths of the sound waves coming from the source of noise .

A variant of the present invention shown in figure 5 include making the wall 9 by using a mold 160 and a counter mold 161.

The mold 160 is provided with a plurality of holes 162 having substantially the same distribution and the same diameter as the holes 18, 20, 21, 22 which must be made along the wall .

The counter mold 161 is provided with a plurality of punches 163 provided with an end 164 sufficiently pointed to pierce the reinforcement fiber layer 165 deposited on the mold 160 during the approach of the counter mold 161 to the mold 160.

The punches 163 are arranged so that each punch 163 of the counter mold 161 engages a respective hole 162 of the mold 160 during the approach of the counter mold 161 to the mold 160.

In practice, the layer of reinforcement fibers 165 is perforated during the approach of the mold 160 against the counter mold 161.

The step of approaching the mold 160 to the counter mold 161 includes that the mold 160 is approached to the counter mold 161 until there is a predetermined distance d between mold 160 and counter mold 161. Such a distance corresponds to the thickness of the wall 9 which is obtained at the end of the procedure .

After having perforated the layer of reinforcement fibers 165, polymeric material is injected between mold 160 and counter mold 161 by means of RTM technique which includes, as mentioned before, the injection of resin by means of the injection line 57 and the intake of air by means of the suction line 58.

The step of assembling the walls 9, 10 and 11, the layer of sound-absorbing material 8 and the layer of insulating material 50 essentially includes:

- applying the insulating layer 50 on the layer of sound-absorbing material 8;

- resting the layer of sound-absorbing material 8 on wall 9 or wall 10;

- assembling walls 9, 10 and bottom wall 11. The step of assembling the walls 9, 10 and the bottom wall 11 includes, as described above, the use of a plaster, preferably made of polyester. Alternatively, riveting techniques associated to the application of plaster may be used or not for coupling the walls 9, 10 and the bottom wall 11.

Advantageously, the making of the wall 9 in accordance with the newly described variant illustrated in figure 5 allows to obtain a wall 9 ready for use and provided with 17400 holes having the required diameters in a single molding process step.

The wall 9 thus obtained indeed does not require further steps of machining with evident advantages from the economic point of view. Indeed, by virtue of this solution, the sound-absorbing panel may be made in series by means of fully automated processes which guarantee mass production and high product quality at the same time.

It is finally apparent that changes and variants can be made to the sound-absorbing panel 3, the sound barrier 1 and the method for making the sound-absorbing panel 3 without departing from the scope of protection of the appended claims.