SE536860C2 - A sound absorber - Google Patents

Abstract

SUMMARY A sound absorber comprises a first layer (4), a second layer (6), and an intermediate layer (8), said intermediate layer (8) comprising walls (13) delimiting a number of cells (12, 12a). 12b, 12c, 12d), which are open at a first end (14) and a second end (16), said cells being arranged next to each other, said first open end (14) of said plurality of cells being covered by said first covering layer ( 4), said second open end (16) said plurality of cells being covered by said second covering layer (6). According to the invention, said first layer (4) is provided with at least one micro-slot (10) by mechanical processing, the micro-slot (10) extending through said first layer (4) so that sound waves are allowed to penetrate the micro-slot (10) and penetrate the first of the icicle. open end (14), said walls (13), said first layer (4) and said second layer (6) being made of a cellulosic material. (Fig. 17)

Description

SUMMARY OF THE INVENTION This object has been achieved with the initially described sound absorber, said first layer being provided with at least one micro-slot by mechanical processing, the micro-slot extending through said first layer so that sound waves are allowed to penetrate microslots into the first open end of the cell, said walls being made of a cellulosic material, said first layer being made of a cellulosic material, and said second layer being made of a cellulosic material.

This results in an effective sound absorber, which is cheaper to manufacture. The object has also been achieved with the initially described method, wherein said micro-slot is manufactured by means of mechanical machining with a mechanical tool.

Preferably, the second layer is provided with at least one micro-slot so that sound waves are allowed to penetrate the micro-slot and penetrate into the other open end of the cell.

Suitably the length of the micro-slot is in the range 2 mm - 2 km, more preferably 10 - 1000 mm, most preferably 100 - 1000 mm.

Preferably the width of the slot is in the range 1 μm to 1 mm, more preferably 10 μm to 0.9 mm, most preferably 0.3 to 0.5 mm.

Suitably the wall thickness is in the range 10 μm to 0.5 mm, more preferably 30 μm to 0.3 mm, most preferably 50 μm to 0.2 mm.

Preferably, the walls are designed to form a plurality of cylinders of predetermined opening area and cross-section, each with a substantially constant cross-section. Above all, the cross section is essentially circular. Alternatively, the cross section is polygonal, such as substantially star-shaped. Alternatively, the cylinders have different cross-sectional areas. 10 15 20 25 30 536 860 Such cylinders have a significant effect on the mechanical stability.

Alternatively, or in addition, the walls are designed to form a plurality of cells of varying cross-section, such as a truncated cone or in the shape of an hourglass. This will expand the effective frequency range of the element.

Preferably, at least every other blade is formed of a corrugated blade or plate, each other wall being a substantially flat blade or plate disposed between every other corrugated blade or plate.

Suitably the thickness of the first layer and optionally the thickness of the second layer is in the range 10 μm to 5 mm, more preferably 20 μm to 0.9 mm, most preferably 50 μm to 0.6 mm.

Examples of suitable cellulosic materials are paper, cardboard, veneer, wood, acetylcellulose, cellulose nonwoven, fibreboard, with or without surface treatment.

Preferably the thickness (tc) of the intermediate layer is in the range 1 - 200 mm, more preferably 5 - 50 mm, most preferably 10 - 30 mm. The greater the thickness (tc), the better the low-frequency absorption.

Preferably, the number of cells per square meter of the cross-section of the intermediate layer is 1 to 100,000,000, more preferably 100 to 1,000,000, most preferably 500 to 200,000. It should be noted that the higher the number per unit area, the better the sound absorption.

According to the method, said micro-slot is manufactured by means of mechanical machining with a mechanical tool.

Suitably the method comprises selecting a predetermined material for the intermediate layer, selecting a predetermined layer for the first layer and selecting a predetermined material for the second layer.

Preferably, the first layer is connected, for example by gluing to the intermediate layer before the micro-slots are formed in the first layer. Likewise, the second layer is connected by gluing to the intermediate layer before the micro-slots are formed in the second layer. The adhesive contributes to mechanical stability and to vibration damping of the element.

Conveniently, both the first layer and the second layer are connected by gluing to the intermediate layer before the micro-slots are formed in the first layer. This avoids handling problems of individual bearings in difficult cutting conditions.

Preferably, the slot in the second layer is performed after both the first layer and the second layer have been connected to the intermediate layer, before the micro-slot is formed in the first layer.

Suitably the mechanical machining includes punching, said mechanical tool being, for example, a punching knife. Alternatively, the mechanical processing includes slitting by means of a slitting machine, said mechanical tool being a knife. Alternatively, the mechanical machining includes cutting machining, said mechanical tool being a cutting steel with a cutting edge.

Preferably, the method includes selecting a mechanical tool from a tool set to obtain a predetermined slot width, connecting said mechanical tool to a computer controlled numerical machine, and programming the slot length, slot depth and distance between the slots to obtain a predetermined sound attenuation.

It should be noted that the mechanical processing method according to the invention excludes laser processing, cutting with cutting electrode, cutting with cutting torch and chemical processing, such as photoetching, as such methods can destroy parts of the cells, and will then have a negative effect on the sound attenuation.

SUMMARY OF FIGURES In the following, the invention will be described in further detail, with reference to the accompanying drawings, in which Fig. 1 illustrates in part in a cut-away view a sound absorber arranged with a first layer provided with micro-slots, a second layer and an intermediate layer; 10 15 20 25 30 536 860 F ig. 2 is a cross-sectional view of a portion of the intermediate layer taken along the line shown in FIG. 1; Fig. 3 illustrates an intermediate layer of cells of diamond-shaped cross-section; Fig. 4 shows an intermediate layer of cells of square cross-section; Fig. 5 illustrates an intermediate layer of cells with a corrugated cross section; F ig. 6 illustrates an intermediate layer with honeycomb cross-sectional cells; Fig. 7 illustrates an intermediate layer with cells of another type of honeycomb cross-section; Figs. 8A-8C illustrate an intermediate layer of cells of varying cross-section; Fig. 9 is an enlargement of the first layer of micro-slots shown in Fig. 1; Fig. 10 illustrates an equipment for manufacturing the micro-slots shown in Figs. 1 and 9; Fig. 11 illustrates interrupted micro-slots; Figs. 12A and 12B illustrate differently designed sound absorbers; Figs. 13A-13F similarly illustrate differently designed sound absorbers; Fig. 14 illustrates a sound absorber with angled cells; Fig. 15 illustrates sound absorbers mounted in the ceiling; Fig. 16 illustrates a sound absorber in the form of a work of art; and Fig. 17 illustrates different uses of the sound absorber. DETAILED DESCRIPTION Figure 1 shows a sound absorber 2 in the form of a rectangular parallelepiped of substantially uniform thickness T, comprising a first layer 4, a second layer 6 and an intermediate layer 8. The latter likewise has the shape of a rectangular parallelepiped with even core thickness tea.

The first layer 4 is made of a cellulosic material and has a first thickness t1, while the second layer has a second thickness tz. The material of the second layer 6 is also of a cellulosic material, and may be of the same material as the first layer 4, although the first and second layers may be of different cellulosic materials.

The total thickness T of the sound absorber 2 is thus the sum of the first thickness t1, the core thickness tc and the second thickness tz.

The first thickness t, of said first layer is in the range 10 micrometers to 5 mm, more preferably 20 micrometers to 0.9 mm, most preferably 50 micrometers to 0.6 mm. The second thickness 2 of the second layer is preferably in the same area as the first thickness t1, but may be thinner or thicker than said area. On the other hand, the thickness t1 of the second layer may be substantially the same as the first thickness t1.

The first layer 4 and the second layer 6 are arranged on opposite sides of the intermediate layer 8 and are thus parallel to each other.

The intermediate layer 8 comprises a plurality of elongate cells 12, the length of which corresponds to the core thickness tc of the intermediate layer 8. The cells 12 are delimited by walls 13, the thickness of which is in the range 10 micrometers to 0.5 mm, more preferably 30 micrometers to 0.3 mm, most preferably 50 micrometers to 0.2 mm. The walls 13 are made of a cellulosic material.

The core thickness, i.e. the thickness two of the intermediate layer 8, is in the range 1 - 200 10 20 20 30 30 536 860 mm, more preferably 5 - 50 mm, most preferably 10 - 30 mm.

The elongate cells 12 as such have first and second open ends 14, 16, but are covered by the first layer 4 and the second layer 6.

The first layer 4 is provided with a plurality of substantially parallel micro-slots 10, which penetrate the first layer 4 substantially through the first thickness t, to the intermediate layer 8, and connect the cells 12 to the ambient air.

To obtain a desired sound attenuation, the number of cells per square meter of a cross section of the intermediate layer 8 is in the range 1 to 100,000,000, more preferably 100 to 1,000,000, most preferably 500 to 200,000.

Figure 2 shows in cross section along the lines ll-ll in Fig. 1 a number of cells 12 of different geometries; each cell 12a is bounded by a wall 13 of circular cross-section 18a, while each cell 12b is bounded by a wall 13 of a star-shaped cross-section 18b. The star-shaped cells 12b are placed between the circular cells 12a to thereby fill the remaining space between the circularly shaped cells, in order to improve the sound attenuation compared to if the spaces were filled with, for example, glue.

Figure 3 shows cells 12 of yet another form. A plurality of corrugated blades 20a, 20b are formed with sharp cams 22 and valleys 24 (ie zigzag shape) and are connected to each other by the cams 22 of the second corrugated blade 20a and the valleys 24 of the first corrugated blade abutting against each other.

In this way, each cell 12 is delimited by walls 13 which together have a diamond or rhomboid cross-section 18c.

Alternatively, a flat blade is located between the first and second corrugated blades 20a, 20b, while the valleys 24 of the first corrugated blade 20a are connected to one side of the flat blade, while the ridges 22 of the blade 20b are connected to the opposite side of the flat blade. As a result, each cell 12 is delimited by the flat blade and the walls 13, and the cross section of the cells will become triangular. It should be noted that for manufacturing reasons it is preferable to arrange the valleys and ridges of the first and second blades 20a, 20b in a mirrored manner so that the valleys and ridges can be connected simultaneously to the flat blade, for example by means of point - or line welding.

Figure 4 shows cells 12 of yet another form. A plurality of corrugated blades 20a, 20b, are formed into a square waveform. A first flat blade 26a and a second flat blade 26b are connected to each side of the corrugated blade 20a.

Hereby the cells 12d are delimited by the walls 13, which together form a square cross-section 18d.

Alternatively, if the corrugated square wave blades 20c are connected to each other directly above each other, the cross section of the cells will be square.

According to another alternative, the corrugated square wave blades 20c can be connected to each other without the blade 26a, 26b (corresponding to the method shown in Fig. 3), whereby the cross section of the cells will be rectangular.

Figure 5 shows an alternative embodiment according to which the flat blades 26a, 26b, 26c, etc. are arranged between sinusoidal wave-shaped blades. The cross section of the cells then becomes a half sine wave or essentially a semicircular shape.

It should be noted that for manufacturing reasons it is preferable to arrange the valleys and ridges of the first and second leaves 20a, 20b in a mirror-shaped manner so that the sine waves of the valleys and ridges can be connected simultaneously to a flat blade e.g. by spot or line welding.

If the embodiment according to Fig. 5 is used without flat blades between the sine waves, with connection of the valleys directly to the ridges of adjacent sine wave blades, the cross section of the cells will instead be lemon-shaped (or substantially circular or oval).

Figure 6 shows another variant of the cells 12, according to which a plurality of the first corrugated blades 20d are formed with flat ridges 22 and sharp valleys 24, while a plurality of other corrugated blades 20d are formed mirror-inverted 536 860 i.e. with sharp ridges 22 and flat valleys 24 and placed relative to each other as shown in Fig. 3. As a result, the cross section of the cells 12 (formed by the walls 13) between the flat ridges 22 and the flat valleys 24 becomes hexagonal, while the cells between the sharp ridges 22 and sharp valleys 24 become diamond, rhomboid or square shaped. Also in this case a flat blade can of course be arranged between the corrugated blades. Figure 7 shows an opportunity to obtain cells of different sizes. In this way a varying sound attenuation can be obtained.

The cells 12 shown in Figures 1-7 are all cylindrical, i.e. the cross-section of the longitudinal extent of the cell 12 from the first open end 14 to the second open end 16 is constant.

Figures 8A-8C show an alternative configuration of cells with varying cross-sections.

As seen in Figures 8A-8B, the wall 13 forming each cell 12 has a waist 30 or an hourglass shape. At the first open end 14, the cell 12 has a first cross section 18 ”. The cross section decreases to approximately the middle longitudinal extent of the cell 12 and then widens towards the second open end 16 to a second cross section 18 ". The first cross section 18 'is substantially the same as the second cross section 18", and the waist 30 is substantially halfway between the first one end and the other end.

Of course, the waist 30 may be located closer to the first open end 14 or the second open end 16. Likewise, the first cross-section 18 "may be larger than the second cross-section 18" and vice versa.

As shown in Figure 8C, the cross-section 18 may instead be in the form of a truncated cone 32, i.e. the cross-section is circular, the diameter varying continuously from the first open end 14 to the second open end 16. The first end 14 860 cross section 18 'is larger than the other end 16 cross section 18 "or vice versa.

Fig. 9 shows a section of the first layer 4. As shown, the micro-slot 10 has the width a and is arranged parallel to and with the distance b from each other, and as shown in Fig. 10, the micro-slots have the length L.

Figure 10 further shows the manufacture of micro-slots in a sound absorber 2. A robot 50 controlled by a microcomputer 52 is programmed to control the movements of a robot arm 54. A tool holder 56 is provided with a replaceable cutting tool 58, such as a cutting steel or a knife.

Alternatively, the tool as such may be oscillating, such as a saw, or rotating, such as a circular saw or an end mill. Alternatively, the tool can be a punching knife. In both cases, the robot only needs a reprogramming of the computer.

A cutting tool 58 for cutting a micro-slot of width a is selected in such a way that the cut micro-slot obtains a width a within a range 1 micrometer to 1 mm, more preferably 10 micrometers to 0.9 mm, most preferably 0.3-0 , 5 mm.

The computer 52 of the robot 50 is programmed in such a way that it will control the robot arm to perform longitudinal movements and cut slits at a distance b from each other, so that adjacent slits are cut at a distance b within a range 1 micrometer to 10 mm, more preferably 10 micrometers to 5 mm, most preferably 0.5 - 2 mm.

The computer 52 is further programmed to control the robot arm to cut the slits to a length L in the range 2 - 2000 mm, more preferably 10 - 1000 mm, most preferably 100 - 1000 mm.

As can be seen in Figure 11, each of a plurality of aligned slots 10 may have a length L, while together they have a total length Lu, which may be within a range of 4 mm up to several meters; only the size of the sound absorber 2 sets the upper limit. Figures 10A-12B show a circular sound absorber 2 with a plurality of parallel slots 10. In the case shown in Figure 12A, the diameter of the circular sound absorber 2 sets the upper limit of the length of each slot L (or in the case of a plurality of aligned slots (cf. Fig. 11) the total length Lu).

In the variant shown in Fig. 12B, instead a helical single slot 10 is arranged in the first layer 4. Depending on the distance between adjacent turns of the coil, the length of the slot L can be many meters.

In all the embodiments described above, the intermediate layer has been shown with a constant thickness tc so that the first layer 4 and the second layer 6 are parallel to each other.

As shown in Figures 13A-13F, the thickness of the intermediate layer tci may be anything but constant, and thus the first layer 4 and the second layer 5 will not be parallel.

In Fig. 13A, the intermediate layer 8 is concave 60 on the side facing the first layer 4 in such a way that also the first layer 4 will be concave, while the opposite side of the intermediate layer 8 is flat and thus also the second layer 6 flat.

In Fig. 13B, the intermediate layer 8 is concave 60 also on the side facing the second layer 4 and thus both the first and second layers 4, 6 are concave 60.

In Fig. 13C, the intermediate layer 8 is instead convex 62 on the side facing the first layer 4, in such a way that also the first layer 4 will become convex 62, while the opposite side 8 of the intermediate layer 8 is flat, and thus is also the second layer 6 flat.

In Fig. 13D, the intermediate layer 8 is convex 62 also on the side facing the second layer 6, and thus both the first and the second layer 4, 6 are convex 62.

In Fig. 13E, the intermediate layer 8 is concave 60 on the side facing the first layer 4 in such a way that also the first layer 4 is caused to become concave 60, while the opposite side of the intermediate layer 8 is convex 62, and thus is also the second layer 6 convex 62. Another concave-convex shape is shown in Fig. 17.

Fig. 13F shows another embodiment of the sound absorber 2, the intermediate layer having a double-sloping side facing the first layer 4, so that the first layer is also double-sloping, while the opposite side of the intermediate layer facing the second layer 6 is flat.

Of course, the intermediate layer 8 side, which faces the second layer 6, can also be double-sloping.

In the figures referred to above, the layers 8 of the cells have been shown with a length corresponding to the core thickness te of the intermediate layer 8.

As can be seen in Figure 14, the cells 12 may instead be angled relative to a normal to the layers 4 and 6. The angle d may be in the range 0 ° - 30 °.

Figure 15 shows recangular sound absorbers 2 connected to the ceiling with fastening means 72, which hang down from the ceiling. In this case, when sound is to be absorbed from two sides, not only the first layer 4 must be provided with micro-slots 10, but also the second layer 6.

In addition, as shown in Fig. 15, the elongate slits may be arranged diagonally opposite the edges of the recangular sound absorber. Of course, all the variants of sound absorbers 2 shown above can be provided with slots arranged at an angle to and in the plane of the first (or the second) layer.

Figure 16 shows a sound absorber 2 with a pattern of micro-slits 10 which also has an aesthetic effect. 12 10 15 20 25 30 536 860 Figure 17 shows a room arranged with different kinds of sound absorbers 2 provided with micro-slots 10 in the first as well as the second layer 4, 6 and also arranged on racks 80. This type of sound absorber 2 is suitable for e.g. open office landscapes.

Fig. 17 also shows sound absorbers 2 in the form of works of art 82, 84, where the pattern of the micro-slits is such that they give an aesthetic effect of the object 82 (the surface preferably has a uniform color, such as white, to emphasize the pattern of the micro-slits), while the object 84 is provided with an image on the surface of the first layer, the micro-slots being arranged on the image. The micro-slots 10 will in this case become more or less invisible depending on the character and color of the image.

List of reference numerals used 2 sound absorber 4 first layer 6 second layer 8 intermediate layer 10 micro slot 12,12a, 12b, 12c, 12d cell 13 wall 14 first open end 16 second open end 18,18a, 18b, 18c, 18 ', 18 " cross section 20a, 20b, 20c, 20d corrugated sheets 22 comb 24 dal 26,26a, 26b, 26c flat blade 30 waist 32 truncated cone 50 robot 52 microcomputer 54 robot arm 13 56 58 60 62 80 82 84 10 15 Qïl-um-lrlvs' 536 860 tool holder cutting tool concave convex fastener set artwork artwork first thickness second thickness core thickness total thickness width distance total length angle 14

Claims (29)

1. A sound absorbent comprising a first layer (4), a second layer (6) and an intermediatelayer (8), said intermediate layer (8) comprising walls (13) delimiting a plurality of cells(l2,l2a,l2b,l2c,l2d) open in a first end (14) and a second end (16), said cells beingarranged adjacent one another, said first open end (14) of said plurality of cells beingcovered by said first cover layer (4), said second open end (16) of said plurality of cellsbeing covered by said second cover layer (6), characterised in that said first layer (4) isprovided with at least one micro-slit (10) by mechanical machining, the micro-slit (10)extending through said ñrst layer (4), such that sound waves are allowed to penetrate said micro-slit (10) and to enter the first open end (14) of said cell.

2. A sound absorbent according to claim 1, wherein said second layer (6) is providedwith a at least one micro-slit (10), such that sound waves are allowed to penetrate said micro-slit and to enter the second open (16) end of said cell.

3. A sound absorbent according to claim 1 or 2, wherein the length (L) of said micro-slitis in the range of2 mm - 2 km, more preferably 10 - 1000 mm, most preferably 100 -1000 mm.

4. A sound absorbent according to any one of claims 1 to 3, wherein the width (a) ofsaid slit is in the range of 1 micrometer to 1 mm, more preferably 10 micrometer to 0,9 mm, most preferably 0,3 - 0,5 mm.

5. A sound absorbent according to any one of the preceding claims, wherein thethickness of said wall (13) is in the range of 10 micrometers to 0,5 mm, more preferably 30 micrometers to 0,3 mm, most preferably 50 micrometers to 0,2 mm.

6. A sound absorbent according any one of the preceding claims, wherein the walls (13)is shaped to form a plurality of cylinders of predetermined opening areas and cross- sections, each one ofa substantially constant cross-section (18, 18a, 18b, 18c). 16

7. A sound absorbent according to claim 6 wherein the cross-section is substantially Circular.

8. A sound absorbent according to claim 6, wherein the cross-section is polygonal.

9. A sound absorbent according to any one of claims 6 to 8, wherein the cross-section is substantially star-shaped.

10. A sound absorbent according any one ofclaims 6-9, wherein the cylinders have different cross-sectional areas.

11. ll. A sound absorbent according to any one of claims l ~ 5 wherein the walls areshaped to form a plurality of cells of a varying cross-section, such as a truncated cone or a time-glass shape.

12. A sound absorbent according to claim 6, wherein at least every second sheet isshaped by a corrugated sheet or plate (20a, 20b, 20c, 20d), every second wall being asubstantially plane sheet or plate (26, 26a, 26b, 26c) arranged between every secondcorrugated sheet or plate (20a, 20b, 20c, 20d).

13. A sound absorbent according to any one of the preceding claims, wherein thethickness (t,) of said first layer is in the range of 10 micrometers to 5 mm, more preferably 20 micrometers to 0,9 mm, most preferably 50 micrometers to 0,6 mm.

14. A sound absorbent according to any one of the preceding claims, wherein thethickness (tg) of said second layer is in the range of 10 micrometers to 5 mm, more preferably 20 micrometers to 0,9 mm, most preferably 50 micrometers to 0,6 mm.

15. A sound absorbent according to any one of the preceding clams, wherein said sheets (13) are made of a cellulose material, polymer material or metal.

16. A sound absorbent according to any one of the preceding clams, wherein said first layer (4) is made of a cellulose material, polymer material or metal. 17

17. A sound absorbent according to any one of the preceding clams, wherein said second layer (6) is made of a cellulose material, polymer material or metal.

18. A sound absorbent according to any one of the preceding claims, wherein the thickness (tc) of said intermediate layer is in the range of 1 - 200 mm, more preferably 5 - 50 mm, most preferably 10 - 30 mm.

19. A sound absorbent according to any one ofthe preceding claims, wherein the ratio ofcells per square meter of a cross-section of the intermediate layer (8) is within the range of 1 to 100 000 000 more preferably 100 to 1 000 000, most preferably 500 to 200 000.

20. Method of manufacturing a sound absorbent according to any one of the preceding claims, whereby said micro-slit (10) is made by mechanical machining by a mechanical tool.

21. Method according to claim 20, including choosing an intermediate layer of a predetermined material, choosing a first layer (4) of a predetermined layer and choosing a second layer (6) of a predetermined material.

22. Method according to claim 21, whereby the first layer (4) is connected e.g. by gluing to the intermediate layer (8) before the micro-slits are made in the first layer (4).

23. Method according to claini 21, whereby the second layer is connected e.g. by gluing to the intermediate layer (8) before the micro-slits (10) are made in the second layer (6).

24. Method according to claim 21, whereby the first layer (4) as well as the second layer (6) are connected e.g. by gluing to the intermediate layer (8) before the micro-slits are made in the first layer (4).

25. Method according to claim 21, whereby the slit in the second layer (6) are madeafter said first layer (4) as well as said second layer (6) are connected to the intermediate layer (8), before the micro-slit (10) is made in the first layer (8). 18

26. Method according to claim 21, whereby mechanical machining includes punching, whereby said mechanical tool is e.g. a punch knife.

27. Method according to claim 21, whereby mechanical machining includes slitting by means ofa slitting machine, whereby said mechanical tool is a knife.

28. Method according to claim 21, whereby mechanical machining includes cutting, whereby said mechanical tool is a cutting blade with a cutting edge.

29. Method according to any one of claims 21 - 27, including choosing a mechanicaltool out of a set of tool sizes to achieve a predetermined slit width, connecting saidmechanical tool to a computer numerical control machine, and programming the slit length, the slit depth and the distance between the slits to achieve a desired sound attenuation.