WO2004013545A1

WO2004013545A1 - Noise reducing panel for air duct

Info

Publication number: WO2004013545A1
Application number: PCT/IT2002/000522
Authority: WO
Inventors: Giuseppe Librizzi
Original assignee: Al.P. S.R.L.
Priority date: 2002-08-06
Filing date: 2002-08-06
Publication date: 2004-02-12
Also published as: AU2002334396A1; WO2004013545A8

Abstract

A panel (1) for the production of a sound-deadening conveyor duct (10) which can be incorporated in a conveyor system (20) for aeriform media, in particular for conditioned air, comprises a sound-deadening layer, inner surface (211), a support layer (3) of substantially rigid material connected uniformly to the outer surface (21) of the sound-deadening layer, and a filtering layer (5) which is formed of gas-permeable material and is connected uniformly to the inner surface (211) of the sound-deadening layer (2) and which is intended to delimit a conveying space (15) so as to allow sound waves to pass from the conveying space (15) into the sound-deadening layer (2) and to prevent impurities passing from the conveying space (15) into the sound-deadening layer (2) and from the sound-deadening layer (2) into the conveying space (15).

Description

NOISE REDUCING PANEL FOR AIR DUCT

The subject of the present invention is a panel for the production of a silencing device for attenuating the noise due to the transportation of aeriform media.

More precisely, the invention relates to a panel for the production of a silencing device which can be incorporated in a system for transporting aeriform media, in particular air, in climate-control, air- conditioning, heating, ventilation, and air-extraction and air-exchange systems of the type with forced circulation, for example, by means of a fan, or of the type with natural convection, for example, due to a temperature or pressure difference.

There are many installations in both domestic and industrial situations and also fitted in office premises, which provide for a circulation of air, in particular, of blown air, through ducts, for example, ventilation and air-conditioning systems.

As is well known, these installations have the disadvantage that the circulation of air generates, by various physical effects, noises of greater or lesser intensity and with frequencies which depend upon the specific flow conditions and which are typically between 60 Hz and 2000 Hz. In addition to the air-flow itself, the fans of air-treatment systems (e.g. the air output and intake fans) contribute in particular to the increase in noise generated.

The discomfort caused by these noises consequently greatly prejudices the comfort brought about by the air- conditioning and ventilation. Silencing devices for attenuating the noises generated by the air-flow are known. A device of this type usually comprises a cylindrical, perforated wall disposed inside an outer wall, which is also cylindrical, the annular space between the two walls being filled with a sound-deadening material.

These devices have the disadvantage of being quite complex and expensive. Moreover, the sound-deadening material constitutes a very good bacteriological trap for the impurities transported by the air-flow. To prevent bacteriological dissemination, frequent dismantling and washing of these silencers is therefore necessary, leading to a considerable increase in the running costs of the air-conditioning system.

Moreover, since the silencing devices of the prior art are usually fitted in the conveyor duct, they constitute an obstacle to the air-flow, leading to considerable losses in terms of air speed and flow-rate. In addition to the increase in energy consumption, the installation of more powerful and hence more expensive fans is often necessary.

The object of the present invention is therefore to provide a panel for the production of a silencing device which can be incorporated in a conveyor system for aeriform media having characteristics such as to overcome the disadvantages mentioned with reference to the prior art .

This and other objects are achieved by a panel for the production of a sound-deadening conveyor duct which can be incorporated in a conveyor system for aeriform media, in particular for conditioned air, in which the panel comprises a sound-deadening layer of sound- deadening material having an outer surface and an opposite, inner surface, a support layer of substantially rigid material suitable for ensuring the structural strength of the panel, the support layer being connected uniformly to the outer surface of the sound-deadening layer, and a filtering layer which is formed of gas-permeable material, is connected uniformly to the inner surface of the sound-deadening layer, and is intended to delimit a conveying space, so as to allow sound waves to pass from the conveying space into the sound-deadening layer and to prevent impurities passing from the conveying space into the sound-deadening layer and from the sound-deadening layer into the conveying space, the panel being suitable for forming a wall of the sound-deadening conveyor duct.

For a better understanding of the invention, some embodiments thereof will be described below by way of non-limiting example, with reference to the appended drawings, in which:

Figure 1 is a perspective view of a,panel according to the invention,

Figure 2 is an enlarged, schematic view of the detail II of Figure 1, Figure 3 is a schematic view of the production of a panel according to the invention,

Figures 4a, 4b and 4c show the main steps of the method for the production of a sound-deadening conveyor duct portion according to the invention, by means of the panel according to the invention,

Figures 5a and 5b show the main steps of the method for the production of a further sound-deadening conveyor duct portion according to the invention, by means of a further panel according to the invention, Figures 6a to 6f show cross-sections of sound- deadening duct portions produced by means of the panel according to the invention, and

Figure 7 is a partially-exploded, perspective view of a forked sound-deadening duct portion, produced by means of the panel according to the invention.

With reference to Figure 1, a panel for the production of a sound-deadening conveyor duct for aeriform media is generally indicated 1_.. The panel 1 is advantageously prefabricated and comprises a sound- deadening layer 2 of sound-deadening material, having an outer surface 2' and an opposite, inner surface 2'', a support layer 3 of substantially rigid material suitable for ensuring the structural strength of the panel 1, the support layer 3 being connected uniformly to the outer surface 2 ' of the sound-deadening layer 2 , and a filtering layer 5 which is made of gas-permeable material, is connected uniformly to the inner surface 2'' of the sound-deadening layer 2, and is intended to delimit a conveying space 15, so as to allow sound waves to pass from the conveying space 15 into the sound- deadening layer 2 and to prevent impurities passing from the conveying space 15 into the sound-deadening layer 2 and from the sound-deadening layer 2 into the conveying space 15. According to the invention, the panel 1 is suitable for forming a wall of a conveyor duct, rendering it sound-deadening, without the use of further silencing devices .

According to one embodiment, the support layer 3 is made of thermally-insulating material.

The sound-deadening layer 2 is relatively yielding and is connected uniformly to the support layer 3 along its outer surface 2 ' . The. layers 2 , 3 , 5 of the panel 1 advantageously have substantially uniform thicknesses, forming a panel 1 of substantially constant thickness.

According to one embodiment, the panel 1 further comprises a protective sheet 4 of material which is preferably non-inflammable and resistant to water and to ultraviolet light. The protective sheet 4 is associated with the exposed surface of the support layer 3 remote from the surface for connection to the sound-deadening layer 2.

The individual layers 2, 3, 4 and 5 of the panel 1 are advantageously connected to one another to form a substantially flat and self-supporting "sandwich" -type structure. In order to produce specific shapes of the panel 1, the "sandwich" structure may be subjected to a mechanical or thermal treatment in which the layers are shaped together. According to one embodiment, the uniform connection between the sound-deadening layer and the support layer and/or between the sound-deadening layer and the filtering layer is formed by a connection region, for example, a gluing region, extending uninterruptedly over the entire surface. According to a further embodiment, the connection between the layers is discontinuous with connection regions which extend, for example, along parallel lines . This ensures a uniform connection between the layers 2 , 3 , , 5 of the panel 1 and increases its sturdiness.

The filtering layer 5 is advantageously made of flexible material suitable for preventing the reflection of sound waves and for favouring their passage into the sound-deadening layer 2 and their damping. Moreover, the filtering layer 5< advantageously has good abrasion resistance, allowing it to be cleaned by brushing.

According to a further embodiment, the filtering layer 5 also has good fire resistance, forming a fire barrier between the conveying space 15 and the support layer 3 of the panel 1.

According to the preferred embodiment, the filtering layer 5 is formed by a fabric, preferably of glass fibre, the fabric having a thickness of between 0.06 mm and 0.18 mm, preferably 0.12 mm. The sound-deadening layer 2 is advantageously made of mineral fibres, preferably from a glass-wool mat or a glass-wool felt which, like the glass fabric of the filtering layer 5, has the advantage that it cannot be attacked by parasites or rodents, is resistant to sudden changes in temperature, is not hygroscopic, and does not rot, as well as having good dimensional stability and being chemically inert .

The thickness of the sound-deadening layer 2 is preferably between 6 mm and 8 mm, preferably 6 mm. The support layer 3 is advantageously made of a closed-cell expanded material, preferably polyurethane, having a thickness of from 10 to 50 mm, preferably 20 mm.

The protective sheet 4 is preferably made of a metallic material, for example, of aluminium, but could just as well be formed by a sheet of stainless-steel or of galvanized and/or prepainted steel, or a sheet of PVC or other suitable materials.

An advantageous method of producing the panel 1 by rolling on a double continuous belt will be described below with reference to Figure 3.

A mixture 8 of polyisocyanates composed of polyols and isocyanates, which is to form the support layer 3, is deposited on the surface of an aluminium sheet with a thickness of from 50 to 500 micrometers, which forms the protective sheet 4.

Naturally, the protective sheet 4 may also be formed by a stainless-steel sheet or by another suitable material . If the support layer 3 is already sufficiently protective per se the protective sheet 4 may even be omitted.

The mixture 8 is polymerized, in the presence of catalysts, surfactants, flame • retardants, .and liquid expanding agents, by propagation reactions which increase the molecular weight and the viscosity of the reagents. During the polymerization process, the polymer, which up to this point was soluble and fusible, is rendered insoluble and infusible by means of further cross-linking reactions.

The heat generated by the reaction which, as a whole, is endothermic, vaporizes the expanding agent, forming a gas which remains trapped in the form of very small bubbles in the polymer being formed, determining its density and thermally-insulating properties.

According to a particularly advantageous embodiment, the thermally insulating support layer 3 is constituted by expanded polyurethane having a density of from 30 kg/m³ to 60 kg/m³, preferably from 44 kg/m³ to 50 kg/m³, and even more preferably of about 48 kg/m³. In the course of the polymerization process or subsequently thereto, the sound-deadening layer 2, which is preferably a glass-wool felt mat having a thickness of about 6 mm, is applied, by means of its outer surface 2 ' , to the exposed surface of the support layer 3 which is being formed. The inner surface 2'' of the sound- deadening layer, remote from the outer surface 2 ' , is advantageously already covered with a glass fabric which will form the filtering layer 5. After a pressing step with subsequent cooling, the continuous sandwich panel is cut into substantially rectangular individual panels 1. The final dimensions of the panels 1 depend substantially on transportation requirements . The main steps for the production of a sound- deadening duct 10 for aeriform media by means of a panel 1 according to the invention are described below with reference to Figures 4a-4c and 5a-5b.

One or more panels 1 which are to form the walls of the sound-deadening duct 10 are formed from a panel 1 of larger dimensions by cutting along outlines 11. Preferably, the cutting surfaces 12 are not perpendicular to the plane of the panel 1 but are inclined so as to form a larger connection area. The panels 1 are then connected along opposed sides 13 , 13 ' , advantageously without the use of f rther connection members or of reinforcing means, to form a gas-tight, tubular body 14 which delimits the conveying space 15, by means of the filtering layer 5. The individual panels 1 are advantageously connected by gluing of the opposed sides 13, 13' over the entire cutting surface 12.

During the connection of the panels 1, a joint crack is formed between the lateral edges 9, 9' of the filtering layers and is sealed ' in a leaktight manner by a substantially impermeable sealing material, for example, with silicone.

The panels 1 are advantageously glued by means of a glue based on neoprene rubber, synthetic resins, and organic solvents, such as aliphatic hydrocarbons and esters.

Even more advantageously, in particular with regard to use in the food and hospital fields, the panels 1 are glued by means of a completely solvent-free glue, for example, based on water and modified rubber latex.

In the embodiment of Figure 4c, the sound-deadening conveyor duct 10 has a rectangular cross-section formed by four panels 1.

To form extensive and branched sound-deadening conveyor systems, the individual duct portions 10 are connected to one another along end edges 16 to form a tubular structure substantially impermeable to gas. Whereas the formation of the cross-section of the sound- deadening duct 10 by gluing of the panels 1 is final and substantially irreversible, the longitudinal connection between the various duct portions 10 may advantageously be releasable, for example, by means of suitable connecting, .members which can render the conveyor system very versatile and adaptable to structural or functional modifications of the building in which it is installed. The connection members may comprise metal flanges which can be fixed to the end edges 16 of the sound- deadening duct portions 10 and can be connected to one another by geometrical coupling or by means of further connection elements.

Naturally, the sound-deadening ducts 10 may be connected to one another and to non-sound-deadening ducts of the air-conveyor system. In practice, the sound-deadening ducts are used mainly in the vicinity of the fans, in order to deaden their noise.

Figure 5a shows a panel 1 by means of which elbowed duct portions 10 are formed, advantageously by means of the same process as was described above with reference to Figures 4a-4c. The panels 1 which form the curved walls may be shaped irreversibly, for example, by means of a plurality of folds 17 substantially parallel to the bending axis, or may be held in the deformed configuration by gluing to the substantially flat side panels.

The panel 1 according to the invention permits the construction of sound-deadening conveyor ducts 10 with cross-sections of any shape, as can be seen, for example, from Figures 6a to 6f. Figure 6f shows, for example, a sound-deadening duct section ^' 10 which comprises two conveying spaces 15 and 15', separated by a dividing wall 18 formed by means of a panel 1 provided with two sound-deadening layers 2 and filtering layers 5, disposed on both surfaces of the support layer 3. The operation of a conveyor system 20 according to the invention, provided with a sound-deadening duct 10 according to the invention, formed by the panels 1 according to the invention, is described below.

The panels 1 are advantageously transported to the installation site in the form of rectangular elements with dimensions suitable for transportation. Once they have arrived on site, the panels 1 are cut and glued to form substantially gas-tight, self-supporting and thermally-insulating, tubular, sound-deadening duct portions. These sound-deadening ducts 10 are connected to one another and/or to further, not necessarily sound- deadening ducts, to form a conveyor system 20, for example, for conditioned air, in which any branches and forks are formed by forked portions 10' which can also advantageously be produced by means of the same panels 1, as shown, for example, in Figure 7. After the conveyor system 20 has been connected to the other modules of the air-conditioning system, it is ready for use. In operation, the conveyor system 20 comprising sound-deadening ducts 10 produced by means of the panels 1, has highly advantageous characteristics.

The sound waves inside the conveying space 15 pass though the filtering layer without being reflected, deforming it at the cost of an energy loss, and are then trapped in the sound-deadening layer 2 which greatly attenuates' the amplitude of the sound waves.

Effective prevention not only of the noise due to the flow of the air transported, but also of the transmission of the noise of the fans of the conveyor system itself, as well as of the acoustic connection between different areas of a building or industrial installation, is thus achieved.

By virtue of the fact that the filtering layer 5 is made of a material which is resistant to abrasion and to corrosion in general, damage to the surface delimiting the conveying space 15 and the formation of recesses, which are responsible for the deposition of dirt and the formation of colonies of bacteria, are prevented. These characteristics render the panel 1 usable particularly in critical areas such as hospitals, in the food industry, in the semiconductor industry, and the like.

The conveyor system 20 according to the invention. also has extremely uniform sound-deadening, thermally- insulating and structural characteristics which in turn permit a precise calculation of its acoustic behaviour, and of the heat and pressure losses, and thus economic and reliable operation of the conditioning system. Moreover, the panel 1 has characteristics such as to permit the production of sound-deadening conveyor ducts 10 of any desired shape, ensuring a high level of impermeability and structural strength.

The panel 1 is suitable for the production of low- pressure, medium-pressure and high-pressure conveyor systems. By virtue of the fact that the panel itself is sound-deadening, thermally-insulating and self- protective, it presents no difficulty with regard to its assembly, fitting, and insulation in spaces to which access is difficult. Moreover, the panel 1 according to the invention requires no reinforcing sections.

The conveyor system 20 formed by means of the panel

1 according to the invention is particularly quiet and has a conveying space 15 which, by virtue of the characteristics of the filtering layer 5, can be cleaned by brushing and with the use of detergents and steam.

Moreover, the sound-deadening duct 10 according to the present invention has no sudden changes in cross- section or inserts which could increase resistance to the air-flow, and consequently completely prevents losses in flow-rate and flow speed which occur in silencing devices of the prior art, leading to an energy saving and, in some cases, to the use of less powerful and hence less expensive fans. The continuity of cross-section and the absence of inserts in the sound-deadening duct 10 according to the invention also enables the duct to be cleaned by brushing and/or washing machines, the use of which is not permitted by the devices of the prior art . Since it is a prefabricated product, the panel 1 and consequently also the sound-deadening duct 10, naturally have all of the related advantages with regard to quality, tolerances and, in particular, limitation of rejects during assembly. Moreover, inspection openings and other accessories can be installed, according to specific requirements, either during the prefabrication of the panel 1 or on site.

Naturally, in order to satisfy contingent and specific requirements, a person skilled in the art may apply to the panel 1 according to the present invention further modifications and variations all of which, however, are included within the scope of protection of the invention as defined by the appended claims .

Claims

1. A panel (1) for the production of a sound- deadening conveyor duct (10) which can be incorporated in a conveyor system (20) for aeriform media, in particular for conditioned air, in which the panel (1) comprises:

- a sound-deadening layer (2) of sound-deadening material having an outer surface (2') and an opposite, inner surface (2''), a support layer (3) of substantially rigid material suitable for ensuring the structural strength of the panel (1), the support layer (3) being connected to the outer surface (2') of the sound-deadening layer, - a filtering layer (5) which is formed of gas- permeable material and is connected to the inner surface

(2¹') of the sound-deadening layer (2) and which is intended to delimit a conveying space (15) , so as to allow sound waves to pass from the conveying space (15) into the sound-deadening layer (2) and to prevent impurities passing from the conveying space (15) into the sound-deadening layer (2) and from the sound- deadening layer (2) into the conveying space (15) .

2. A panel (1) according to Claim 1, comprising a protective sheet (4) associated with a surface of the support layer (3) remote from the sound-deadening layer (2) , the protective sheet (4) being intended to form the outer casing of a conveyor duct (10) of the conveyor system (20) .

3. A panel (1) according to Claim 1 or Claim 2 in which the support, sound-deadening and filtering layers have substantially uniform thicknesses.

4. A panel (1) according to any one of the preceding claims in which the support, sound-deadening and filtering layers are shaped together.

5. A panel (1) according to any one of the preceding claims in which the support layer (3) and the sound-deadening layer (2) and/or the sound-deadening layer (2) and the filtering layer (5) are connected to one another continuously over their entire surface.

6. A panel (1) according to any one of the preceding claims in which the filtering layer (5) is made of flexible and abrasion-resistant material.

7. A panel (1) according to any one of the preceding claims in which the filtering layer (5) is made of fire-resistant material.

8. A panel (1) according to any one of the preceding claims in which the filtering layer (5) is formed by a fabric, preferably of glass filament.

9. A panel (1) according to any one of the preceding claims in which the filtering layer (5) is formed by a glass-fibre fabric.

10. A panel (1) according to Claim 9 in which the fabric has a thickness of between 0.06 mm and 0.18 mm, preferably 0.12 mm.

11. A panel (1) according to any one of the preceding claims in which the sound-deadening layer (2) is formed of a material selected from the group of mineral fibres .

12. A panel (1) according to any one of the preceding claims in which the sound-deadening layer (2) is formed by a glass-wool mat.

13. A panel (1) according to any one of the preceding claims in which the support layer (3) comprises a layer of a thermally-insulating material.

14. A panel (1) according to any one of the preceding claims in which the material - of the support layer (3) is selected from the group of closed-cell expanded resins .

15. A panel (1) according to any one of the preceding claims in which the support layer (3) comprises an expanded polyurethane layer.

16. A panel (1) according to any one of the preceding claims, when dependent on Claim 2, in which the protective sheet (4) is made of aluminium.

17. A panel (1) according to any one of the preceding claims, when dependent on Claim 2, in which the protective sheet (4) is made of stainless steel.

18. A panel (1) according to any one of the preceding claims in which the panel (1) is prefabricated.

19. A panel (1) according to any one of the preceding claims, produced from a panel (1) of larger dimensions by cutting along outlines (11) .

20. A sound-deadening conveyor duct (10) comprising one or more panels (1) according to any one of the preceding claims in which one or more panels (1) are connected in a substantially gas-impermeable manner along opposed sides (13, 13") to form a tubular body delimiting the conveying space (15) by means of the filtering layer (5) .

21. A sound-deadening conveyor duct (10) according to Claim 20 in which the panels (1) are connected by gluing of the sides over the entire cutting surface (12), preferably with a glue based on neoprene rubber and synthetic resins.

22. A sound-deadening conveyor duct (10) according to Claim 20 or Claim 21 in which a joint crack formed between the lateral edges (9, 9') of the filtering and/or sound-deadening layers is sealed in a leaktight manner by a substantially impermeable sealing material.

23. A sound-deadening conveyor duct (10) according to Claim 22 in which the sealing material comprises silicone.

24. A sound-deadening conveyor duct (10) according to any one of Claims 20 to 23 having a substantially rectangular cross-section formed by four panels (1) .

25. A conveyor system (20) comprising one or more sound-deadening conveyor ducts according to Claims 20 to 24, connectible to one another and to further conveyor ducts of the conveyor system (20) along end edges (16) to form a tubular structure which is substantially impermeable to gases, except for the openings provided.

26. A conveyor system (20) according to Claim 25 in which the sound-deadening conveyor ducts, and/or the further conveyor ducts are connected to one another along sides to form a branched tubular structure.

27. A conveyor system (20) according to. Claim 25 or Claim 26 in which the conveyor ducts can be connected releasably.