WO2017090538A1

WO2017090538A1 - Porous sound-absorbing board

Info

Publication number: WO2017090538A1
Application number: PCT/JP2016/084334
Authority: WO
Inventors: 善三山口; 伊知郎山極
Original assignee: 株式会社神戸製鋼所
Priority date: 2015-11-27
Filing date: 2016-11-18
Publication date: 2017-06-01

Abstract

The present invention can improve, by coating, the sound-absorbing properties of a porous board, rather than merely avoiding degradation in sound-absorbing properties. A porous sound-absorbing board (1) has a plurality of through-holes (4). A coating film (7, 7a) is provided on the inner wall surfaces of the through-holes (4) of a porous board (6) that serves as a base material for forming the porous sound-absorbing board (1), and the coating films (7, 7a) form through-hole sections (8) having a volume smaller than that of the through-holes (4).

Description

Porous sound absorbing plate

The present invention relates to a porous plate as a sound absorbing member.

It is known that the sound absorbing performance of a perforated plate as a sound absorbing member, that is, a perforated sound absorbing plate, is improved by reducing the hole diameter. However, since the plate material used as the sound absorbing member is thin, it is difficult to make a hole having a diameter equal to or smaller than the plate thickness in the plate material. On the other hand, in order to apply a porous plate to a sound-absorbing member and establish it as a product, it is often necessary to coat the porous plate from the viewpoint of corrosion resistance, weather resistance, and the like. The porous sound absorbing plate absorbs sound on the principle that the sound is attenuated in the process of sound propagation through the holes formed in the porous sound absorbing plate. Therefore, if the porous plate is coated and the hole is closed, there is a concern that the sound absorbing performance is deteriorated.

As a porous sound absorbing plate obtained by coating a porous plate, for example, there is one described in Patent Document 1. According to the conventional technique, a coating thin film having a thickness of 1 to 10 μm is formed on the surface of the perforated plate so as to close the opening of the through hole. In Patent Document 1, it is said that the coating thin film can prevent dust from entering the through-hole, suppress deterioration due to change with time, and the like, and is excellent in excellent sound absorption characteristics and appearance characteristics.

Japanese Laid-Open Patent Publication No. 2008-233792

There is no particular problem with products that are necessary and sufficient for coating with a thickness of 1 to 10 μm, but for plate materials that require high weather resistance, such as steel plates that make up automobiles, for example, about 20 μm by electrodeposition coating for rust prevention. The coating of the film thickness is given. When the coating film thickness is about this level, the sound absorption performance is greatly deteriorated by the method of closing the through-hole described in Patent Document 1 with a coating film.
In addition, the method of closing the through-hole with a thin coating film having a thickness of 1 to 10 μm described in Patent Document 1 is not intended to improve the sound absorption performance of the perforated plate, and avoids deterioration of the sound absorption performance. It is intended.

The present invention has been made in view of the above circumstances, and its purpose is not to avoid the deterioration of the sound absorption performance, but to improve the sound absorption performance of the porous plate by painting.

The present invention is a porous sound-absorbing plate having a porous plate as a base material in which a large number of through-holes are formed, and has a coating film on the inner wall surface of the through-hole. A through hole having a small volume is formed.

According to the present invention, by reducing the volume of the through hole of the base material by the coating film, it becomes possible to increase the viscous damping due to the hole, and as a result, it is possible to exhibit the sound absorbing performance more than the through hole of the base material. it can. “Viscosity damping” refers to attenuation of sound waves caused by friction between the sound waves passing through the sound and the wall surface.

It is sectional drawing which shows a sound absorption structure provided with the porous sound-absorbing board which concerns on 1st Embodiment of this invention. It is an enlarged view of the through-hole part of the porous sound-absorbing board shown in FIG. It is a graph which shows the effect by having reduced the volume of the through-hole with the coating film. It is a graph which shows the relationship between a film thickness / hole diameter and an average sound absorption rate increase rate. It is a figure which shows the 1st modification of the through-hole part shown in FIG. It is a figure which shows the 2nd modification of the through-hole part shown in FIG. It is an enlarged view of the through-hole part of the porous sound-absorbing board which concerns on 2nd Embodiment of this invention. It is a figure which shows the 1st modification of the through-hole part shown in FIG. It is a figure which shows the 2nd modification of the through-hole part shown in FIG. It is an enlarged view of the through-hole part of the porous sound-absorbing board which concerns on 3rd Embodiment of this invention. It is a figure which shows the 1st modification of the through-hole part shown in FIG. It is a figure which shows the 2nd modification of the through-hole part shown in FIG.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(Sound absorbing structure using a porous sound absorbing plate)
As shown in FIG. 1, the porous sound-absorbing plate 1 is arranged at a predetermined interval from the closing member 2 so that an air layer 3 is formed between the plate-shaped or wall-shaped closing member 2. Is done. The closing member 2 is a member that is not perforated, that is, the front surface and the back surface are not in communication. The blocking member 2 is disposed on the opposite side of the noise source 5 with the porous sound absorbing plate 1 interposed therebetween.

The porous sound absorbing plate 1 of the present embodiment is a sound absorbing plate in which a coating film 7 is formed on both surfaces of a porous plate 6 as a base material in which a large number of through holes 4 are formed and on the inner wall surface of the through holes 4. Examples of the coating method for forming the coating film 7 include electrodeposition coating, brush coating, spray coating, and the like. The material of the porous plate 6 and the closing member 2 is, for example, aluminum, aluminum alloy, stainless steel, iron, resin, or the like.

(First embodiment)
(Details of through-hole part)
FIG. 2 is an enlarged view of the through hole 4 portion of the porous sound absorbing plate 1 according to the first embodiment shown in FIG. As shown in FIG. 2, the through hole 4 of the porous plate 6 as a base material is a cylindrical hole, and a coating film 7 a is formed on the entire inner wall surface of the through hole 4. The through-hole part 8 smaller than the hole diameter d (diameter d) of 4 is formed. And the volume of the hole of the formed through-hole part 8 is smaller than the volume of the hole in the case of only the through-hole 4 which is not painted. The coating film 7a has, for example, a mountain shape in which the center side is raised (thickened) from the end in the thickness direction due to the surface tension. The film thickness Lmax of the ridge line portion 11 (maximum film thickness portion) is less than ½ of the hole diameter d of the through hole 4.

In this example, the cross section of the through-hole portion 8 perpendicular to the plate thickness direction is circular in any part in the plate thickness direction, but depending on the method of painting, a crushed circle or a crushed rectangle For example, the through hole 8 may not be circular (perfect circle). In the present invention, such a through hole that is not a perfect circle may be used. In this example, the axis of the through-hole 4 and the axis of the through-hole part 8 coincide with each other. However, depending on the way of painting, the axis of the through-hole 4 and the axis of the through-hole part 8 May not match. In the example described above, the axial center of the through hole 4 and the axial center of the through hole portion 8 coincide with each other, so the film thickness Lmax is less than ½ of the hole diameter d of the through hole 4. When the core and the axial center of the through-hole portion 8 do not coincide with each other, that is, when there is uneven coating or unevenness in the circumferential direction of the inner wall surface of the through-hole 4, the film thickness Lmax depends on the location. In some cases, it may be ½ or more of d. What is essential is that, even if the inner wall surface of the through hole 4 is painted, the through hole portion is formed without blocking the hole.

Here, FIG. 3 is a graph showing the effect of reducing the volume of the through hole by the coating film. The dotted line in FIG. 3 shows the sound absorption coefficient in various frequency ranges when the inner wall surface of the through hole 4 is not painted, and the solid line in FIG. 3 shows the case where the inner wall surface of the through hole 4 is painted (painted) And the sound absorption coefficient in various frequency ranges (when the volume of the through hole 4 is reduced). As can be seen from FIG. 3, by reducing the volume of the through hole 4 by the coating film, it becomes possible to increase the viscous attenuation due to the hole, and as a result, in all the frequency ranges, it is more than the through hole of the base material. Sound absorption performance can be demonstrated.

FIG. 4 is a graph showing the relationship between the film thickness L / hole diameter d and the average sound absorption rate increase rate. In addition, the through hole 4 of the base material of the porous sound absorbing plate to be analyzed has a cylindrical shape. The “film thickness L” of the film thickness L / hole diameter d on the horizontal axis in FIG. 4 is the film thickness when a coating film having a uniform thickness is formed on the entire inner wall surface of the cylindrical through-hole 4. When the thickness of the coating film is different in the plate thickness direction as shown in FIG. 2, it is the maximum film thickness Lmax.

The “average sound absorption coefficient” is a perforated sound absorbing plate in which a hole having a hole diameter d = 1 mm is formed in a plate having a thickness of 1 mm and the inner wall surface of the hole is coated with a film thickness L. This is the average of the sound absorption coefficient of 100 to 5000 Hz of the porous sound absorption plate whose aperture ratio is determined so that the sound absorption coefficient is 1. Generally, the average sound absorption coefficient is about 0.5 to 0.7. As conditions for the through-hole portion in FIG. 4, the average sound absorption coefficient is 0.5, and there is no coating unevenness in the circumferential direction of the inner wall surface of the through-hole 4, that is, the axial center of the through-hole 4 and the inside thereof It is assumed that the axial center of the through-hole portion formed by the coating film coincides. The graph on the right side in FIG. 4 is an enlarged view of the portion where the film thickness L / hole diameter d in the left graph is 0 to 0.05.

As can be seen from the graph on the right side in FIG. 4, when the film thickness L / pore diameter d is changed from 0 to 0.02, the average sound absorption rate increases by 2%. When the average sound absorption coefficient is increased by 2%, the reflected energy is reduced by about 0.1 dB, so that a significant difference begins to appear in the sound absorption coefficient. That is, the film thickness L / hole diameter d is preferably 0.02 (1/50) or more.

The reason why the reflected energy is reduced by about 0.1 dB when the average sound absorption rate is increased by 2% will be described based on the following equation. The reflected energy (energy of the reflected wave) before improvement (before the increase of the average sound absorption coefficient) is Er (dB), and the reflected energy after improvement is Er ′ (dB). The amount of reduction in the reflected energy is ΔI (dB). Here, α is an average sound absorption rate before improvement (film thickness is zero), and α ′ is an average sound absorption rate after improvement. Ei is the energy of the input wave.
ΔI = Er−Er ′
_{= 10log 10 (1-α)} Ei-10log 10 (1-α') Ei
= 10log ₁₀ ((1-α) / (1-α '))
Substituting α ′ = α + 0.02α and α = 0.5 into the above equation yields ΔI = about 0.1 dB.

In addition, although it is preferable that the diameter of the through-hole part formed with a coating film is small, since sound-absorbing performance will reduce if the through-hole 4 is obstruct | occluded with a coating film, film thickness L / hole diameter d is 0. Less than 5 (1/2). In order to more reliably prevent the through hole 4 from being blocked by the coating film, it is preferable to set the film thickness L / hole diameter d to 1/3 or less.

Moreover, in embodiment shown in FIG. 2, the coating film thickness of the center side (coating film thickness direction center side) becomes thicker than the edge part (edge part of the coating film in a board thickness direction) of a board thickness direction. ing. Thereby, compared with the case where the cross section of the hole by a uniform coating film is constant, the length in the plate | board thickness direction of the part (area | region) where a hole diameter becomes small becomes short. As a result, the viscous damping effect by the holes can be improved, and the number of holes for exhibiting the same sound absorbing performance can be reduced. In addition, regarding the micro perforated plate to which the present invention is applied, the thickness of the coating film formed on the inner wall surface of the through hole 4 (in the case of a uniform thickness coating film, the thickness is not uniform) The thickness of the maximum film thickness portion) is preferably 10 to 100 μm, and the hole diameter d is preferably 0.5 mm or less.

(First modification of the first embodiment)
FIG. 5 is a diagram showing a first modification of the through hole portion shown in FIG. In the porous sound absorbing plate 1 shown in FIGS. 1 and 2, both surfaces of the porous plate 6 are coated. However, in this embodiment, only one surface of the porous plate 6 is coated, whereby the inner wall surface of the through hole 4 is obtained. A coating film 7b is formed on a part of the film. In addition, although the coating film 7b is a mountain-shaped coating film similarly to the coating film 7a shown in FIG. 2, it is not restricted to this, The coating film of uniform thickness may be sufficient in each part of a plate | board thickness direction.

By forming the coating film 7 b only on a part of the inner wall surface of the through hole 4, the through hole portion having a volume smaller than the diameter of the through hole 4 of the base material and smaller than the volume of the through hole 4 of the base material The sound absorbing performance of the base material through hole 4 or more can be exhibited. In addition, by forming the coating film 7b in a chevron shape by surface tension or the like, the length in the plate thickness direction of the portion (region) where the hole diameter becomes smaller compared to the case where the cross section of the hole by the uniform coating film is constant is shortened. Therefore, the viscous damping effect by the holes can be improved, and the number of holes for exhibiting the same sound absorbing performance can be reduced.

In addition, the through-hole part 8 is a hole part formed with the coating-film 7b surface and the surface (surface which is not painted) of the inner wall surfaces of the through-hole 4 without the coating-film 7b (base material). The same applies to other embodiments described later in which a part of the inner wall surface of the through hole is coated.

(Second modification of the first embodiment)
FIG. 6 is a view showing a second modification of the through hole portion shown in FIG. In this embodiment, the both-ends part 4a of the through-hole 4 of the perforated plate 6 which is a base material is chamfered. Therefore, the coating film 7c formed on the inner wall surface of the through hole 4 has a larger degree of curvature than the coating film 7a of FIG. 2 and a region in which the hole diameter is reduced by painting in the plate thickness direction (region around the ridge line portion 11). ) Is less than in the case of the porous plate 6 shown in FIG. 2 in which the hole ends are not chamfered. Thereby, the viscous damping effect by a hole can be improved more and the number of holes for exhibiting the same sound absorption performance can be reduced more.

(Second Embodiment)
FIG. 7 is an enlarged view of a through hole portion of the porous sound absorbing plate 21 according to the second embodiment of the present invention. The through holes 4 formed in the porous plate 6 which is the base material shown in FIGS. 2, 5 and 6 are all cylindrical holes, whereas the porous plate 6 (base material) of the present embodiment. The through-holes 9 formed in the shape of a truncated cone are holes. The through-hole 9 has a maximum hole diameter portion 12 formed on one surface of the porous plate 6 and a minimum hole diameter portion 13 formed on the other surface of the porous plate 6. As it goes to 12, the pore diameter gradually increases.

In addition, although the through-hole 9 of this embodiment is classified into the shape of a right truncated cone (axisymmetric truncated cone) in the truncated cone shape, it may be a through-hole having an oblique truncated cone shape. Furthermore, the through hole is not limited to the truncated cone shape, and as described above, it is sufficient if the hole diameter gradually increases from the minimum hole diameter portion 13 toward the maximum hole diameter portion 12 (third described later). The same applies to the truncated cone hole 14b of the through hole 14 in the embodiment).

A coating film 7d is formed on the entire inner wall surface of the through-hole 9, and a through-hole portion 10 having a volume smaller than the volume of the through-hole 9 is formed by the coating film 7d.

By making the shape of the through hole 9 tapered, the portion where the hole diameter is minimized can be limited to the minimum hole diameter portion 13, so there is a risk that the hole will be blocked due to the accuracy of the hole shape, variations in coating film thickness, etc. Can be small.

Regarding the arrangement of the porous sound absorbing plate 21, the surface on the minimum hole diameter portion 13 side may be on the noise source 5 side, or the surface on the maximum hole diameter portion 12 side may be on the noise source 5 side (FIG. 8 to FIG. 8). The same applies to the porous sound-absorbing plate having the through-hole portion shown in FIG.

(First Modification of Second Embodiment)
FIG. 8 is a diagram showing a first modification of the through hole portion shown in FIG. In the present embodiment, the coating is applied only to the surface on the minimum hole diameter portion 13 side of the perforated plate 6, whereby the coating film 7 e is formed only on the minimum hole diameter portion 13 side of the inner wall surface of the through hole 9. According to this configuration, it is possible to achieve the above-described effect that the risk of the hole being blocked due to the accuracy of the hole shape, the variation in the coating film thickness, and the like can be reduced with a smaller coating amount.

(Second Modification of Second Embodiment)
FIG. 9 is a view showing a second modification of the through hole portion shown in FIG. In the present embodiment, the coating is applied only to the surface of the perforated plate 6 on the side of the maximum pore diameter portion 12, thereby forming the coating film 7 f only on the maximum pore diameter portion 12 side of the inner wall surface of the through hole 9. According to this configuration, while maintaining the diameter of the minimum hole diameter portion 13, the hole diameter can be reduced as a whole by the coating film 7f (the volume of the hole can be reduced), and the viscous damping at the hole is improved. Can be made.

Of the through-hole portion 10 formed on the coating film 7f surface and the surface without the coating film 7f (uncoated hole surface), the inner diameter of the coating film 7f portion is smaller than the inner diameter of the minimum hole diameter portion 13. That is, the through-hole part 10 has a diameter part smaller than the minimum diameter of the through-hole 9 of a base material with the coating film 7f. Here, the sound absorption effect is determined by the pressure loss when the sound wave passes through the hole, and this pressure loss is greatly influenced by the smallest part of the hole. Therefore, as in this embodiment, the inner wall surface of the through-hole 9 is coated to reduce the hole volume and to form a hole smaller than the minimum hole diameter portion 13 of the through-hole 9 of the base material. A sound absorption effect can be obtained.

(Third embodiment)
FIG. 10 is an enlarged view of the through hole portion of the porous sound absorbing plate 31 according to the third embodiment of the present invention. The through hole 14 formed in the porous plate 6 (base material) of the present embodiment has a maximum hole diameter portion 12 formed on one surface of the porous plate 6 and a minimum hole diameter formed on the other surface of the porous plate 6. Part 13. This is the same as the through hole 9 shown in FIGS. In this embodiment, the through-hole 14 is initially formed as a cylindrical hole 14a having the same diameter as the minimum hole diameter portion 13 from the minimum hole diameter portion 13 toward the maximum hole diameter portion 12, and a cone whose diameter gradually increases from the middle. A trapezoidal hole 14b is formed. The cylindrical hole 14 a is a part that maintains the same diameter as the minimum hole diameter part 13.

A coating film 7 g is formed on the entire inner wall surface of the through hole 14, and a through hole portion 15 having a volume smaller than the volume of the through hole 14 is formed by the coating film 7 g.

According to the porous sound absorbing plate 31 of the present embodiment, as in the case of the porous sound absorbing plate 21 of the second embodiment shown in FIG. Since it can limit to the part 13, the risk that a hole is obstruct | occluded by the precision of a hole shape, the dispersion | variation in a coating-film thickness, etc. can be made small. In addition, by changing the length of the cylindrical hole 14a having the smallest diameter in the plate thickness direction, attenuation of sound waves in the hole can be easily controlled.

(First Modification of Third Embodiment)
FIG. 11 is a diagram illustrating a first modification of the through hole portion illustrated in FIG. 10. In the present embodiment, coating is applied only to the surface on the minimum hole diameter portion 13 side of the porous plate 6, thereby forming the coating film 7 h only on the minimum hole diameter portion 13 side of the inner wall surface of the through hole 14. According to this configuration, it is possible to achieve the above-described effect that the risk of the hole being blocked due to the accuracy of the hole shape, the variation in the coating film thickness, and the like can be reduced with a smaller coating amount. By changing the length in the plate thickness direction of the cylindrical hole 14a having the smallest diameter, there is an effect that the attenuation of the sound wave in the hole can be easily controlled.

(Second Modification of Third Embodiment)
FIG. 12 is a view showing a second modification of the through hole portion shown in FIG. In the present embodiment, the coating is applied only to the surface on the side of the maximum hole diameter portion 12 of the porous plate 6, thereby forming the coating film 7 i only on the maximum hole diameter portion 12 side of the inner wall surface of the through hole 14. According to this configuration, while maintaining the diameter of the minimum hole diameter portion 13, the hole diameter can be reduced as a whole by the coating film 7i (the volume of the hole can be reduced), and the viscous damping at the hole is improved. Can be made. By changing the length in the plate thickness direction of the cylindrical hole 14a having the smallest diameter, there is an effect that the attenuation of the sound wave in the hole can be easily controlled.

(Modification)
A cylindrical hole is illustrated in FIGS. 2, 5, and 6 as the through-hole 4 formed in the porous plate 6 that is a base material. It is good also as a hole, and it is good also as a through-hole whose cross section is an ellipse or an ellipse. In addition, although the truncated cone-shaped holes are illustrated in FIGS. 7 to 12 as the through-

holes

9 and 14 formed in the porous plate 6 which is the base material, the truncated pyramid-shaped through-holes may be used instead. What is essential in the porous sound-absorbing plate of the present invention is that the inner wall surface is coated without blocking the through-holes formed in the base material.

In any of the above embodiments, the coating film is formed over the entire circumferential direction of the inner wall surfaces of the through

holes

4, 9, 14 in any embodiment. A coating film may be formed only on a part, and a through-hole portion having a volume smaller than the volume of the through-hole 4 may be formed by the coating film.

This application is based on a Japanese patent application filed on November 27, 2015 (Japanese Patent Application No. 2015-231451) and a Japanese patent application filed on June 16, 2016 (Japanese Patent Application No. 2016-120172), Its contents are incorporated herein by reference.

1: porous sound absorbing plate 2: blocking member 3: air layer 4: through-hole 5: noise source 6: perforated plate (base material)
7: Coating film 8: Through-hole part (hole formed by coating film)

Claims

A porous sound absorbing plate having a porous plate as a base material in which a large number of through holes are formed,
A porous sound-absorbing plate having a coating film on an inner wall surface of the through-hole, wherein a through-hole portion having a volume smaller than the volume of the through-hole is formed by the coating film.
The porous sound absorbing plate according to claim 1,
The porous sound absorbing plate, wherein the through hole portion has a diameter portion smaller than a minimum diameter of the through hole by the coating film.
The porous sound absorbing plate according to claim 1,
The through hole is a cylindrical hole,
The porous sound-absorbing plate, wherein the thickness of the coating film is thicker in the center side in the plate thickness direction of the coating film than the end of the coating film in the plate thickness direction.
In the porous sound-absorbing plate according to claim 3,
A porous sound absorbing plate, wherein a hole end portion of the through hole is chamfered.
In the porous sound-absorbing plate according to claim 3,
A porous sound absorbing plate, characterized in that a coating having a coating thickness of less than ½ of the diameter of the through hole is applied to the inner wall surface of the through hole.
In the porous sound-absorbing plate according to claim 5,
A porous sound absorbing plate, characterized in that a coating having a coating thickness of 1/50 or more of the diameter of the through hole is applied to the inner wall surface of the through hole.
The porous sound absorbing plate according to claim 1,
The through hole is
A maximum pore diameter portion formed on one surface of the porous plate;
A minimum pore diameter portion formed on the other surface of the perforated plate,
A porous sound absorbing plate, wherein the hole diameter gradually increases from the minimum hole diameter part toward the maximum hole diameter part.
The porous sound absorbing plate according to claim 1,
The through hole is
A maximum pore diameter portion formed on one surface of the porous plate;
A minimum pore diameter portion formed on the other surface of the perforated plate,
A porous sound-absorbing plate characterized in that, as it goes from the minimum hole diameter portion to the maximum hole diameter portion, the same diameter is initially maintained, and the hole diameter gradually increases from the middle.
The porous sound-absorbing plate according to any one of claims 1 to 8,
A porous sound absorbing plate comprising the coating film on a part of an inner wall surface of the through hole.