The present invention relates to a perforated plate as a sound-absorbing member.
It has been known that sound-absorbing performance of a perforated plate as a sound-absorbing member, that is, a perforated sound-absorbing plate, can be improved by reducing diameters of holes in the perforated plate. However, a plate material for use as the sound-absorbing member is so thin that holes whose diameters are not larger than the thickness of the plate material cannot be easily made in the plate material. On the other hand, when a perforated plate is applied to a sound-absorbing member and completed as a product, the perforated plate must be often coated from the standpoint of corrosion resistance, weather resistance or the like. The perforated sound-absorbing plate absorbs sound based on the principle that sound is damped in a process in which the sound is propagated through the holes formed in the perforated sound-absorbing plate. Accordingly, when the perforated plate is coated to close the holes, there is concern that the sound-absorbing performance of the perforated plate deteriorates.
For example, Patent Literature 1 discloses a perforated sound-absorbing plate obtained by coating a perforated plate. In the technique of Patent Literature 1, a thin coating film having a thickness of 1 to 10 μm is formed on a surface of the perforated plate so as to close opening portions of through holes. Patent Literature 1 suggests that, due to the thin coating film, dust can be prevented from invading the through holes, and deterioration caused by aging or the like can be avoided, so that sound-absorbing properties and appearance properties can be improved.
Patent Literature 1: JP-A-2008-233792
There is no particular problem about a product in which the coating with a thickness of 1 to 10 μm is necessary and sufficient. However, a coating film having a thickness of, for example, about 20 μm is applied, by electrodeposition coating or the like for rust prevention, to a plate material needing high weather resistance, such as a steel plate constituting a car. When the coating film reaches such a thickness, the sound-absorbing performance deteriorates on a large scale in the method in which the through holes are closed by the coating film in Patent Literature 1.
In addition, an object of the method described in Patent Literature 1 in which the through holes are closed by the thin coating film having a thickness of 1 to 10 μm is not to improve the sound-absorbing performance of the perforated plate but to avoid deterioration of the sound-absorbing performance.
The present invention has been made in consideration of the aforementioned situation. An object of the present invention is not to avoid deterioration of sound-absorbing performance but to improve sound-absorbing performance of a perforated plate by coating.
A perforated sound-absorbing plate in the present invention includes a perforated plate as a base material in which a large number of through holes are formed, and a coating film is provided on an inner wall surface of the through hole, and a through-hole portion whose volume is smaller than a volume of the through hole is formed by the coating film.
In the present invention, the volume of the through hole in a base material is reduced by a coating film so that viscous damping due to the hole can be increased. As a result, sound-absorbing performance can be made better than that achieved by the through hole in the base material. The “viscous damping” means damping of a sound wave by friction between the sound wave and a wall surface during passing of a sound.
Embodiments of the present invention will be described below with reference to the drawings.
(Sound-Absorbing Structure Using Perforated Sound-Absorbing Plate)
As shown in
The perforated sound-absorbing plate 1 in the present embodiment(s) is a sound-absorbing plate in which a coating film 7 is formed on both sides of a perforated plate 6 as a base material having a large number of through holes 4 and is formed on inner wall surfaces of the through holes 4. Examples of coating methods for forming the coating film 7 include electrodeposition coating, brush coating, spray coating and the like. Examples of materials of the perforated plate 6 and the closing member 2 include aluminum, aluminum alloys, stainless steel, iron, resin and the like.
(Details of Through-Hole Part)
In this example, a section of the through-hole portion 8 orthogonal to the thickness direction is circular at any part in the thickness direction. However, some way of coating may shape the through-hole portion 8 into not a circle (complete round) but a crushed circle, a crushed quadrangle or the like. In the present invention, the through-hole portion 8 may be such a through-hole portion which is not a complete round. In addition, in this example, the axis of the through hole 4 is aligned with the axis of the through-hole portion 8. However, in some way of coating, the axis of the through hole 4 is not aligned with the axis of the through-hole portion 8. In the aforementioned example, since the axis of the through hole 4 is aligned with the axis of the through-hole portion 8, the film thickness Lmax is smaller than ½ of the hole diameter d of the through hole 4. When the axis of the through hole 4 is not aligned with the axis of the through-hole portion 8, that is, when coating has unevenness or irregularity in the circumferential direction of the inner wall surface of the through hole 4, there may be a portion where the film thickness Lmax is not smaller than ½ of the hole diameter d of the through hole 4. It is essential to form a through-hole portion without closing the hole of the through hole 4 in spite of coating on the inner wall surface of the through hole 4.
Here,
The “average sound absorbability” designates an average of sound absorbability at 100 to 500 Hz in a perforated sound-absorbing plate in which holes each having a hole diameter d of 1 mm are made in a plate having a plate thickness of 1 mm, and the inner wall surface of the holes is coated with a coating film having a film thickness L, on the assumption that an aperture ratio in the perforated sound-absorbing plate is defined so that the sound absorbability is 1 at a sound-absorbing peak. The average sound absorbability is generally about 0.5 to 0.7. As the conditions of the through-hole part in
As is understood from the graph on the right side of
The reason why the reflected energy decreases by about 0.1 dB when the average sound absorbability increases by 2% will be explained based on the following formula. Er (dB) designates reflected energy (energy of a reflected wave) before improvement (before increase in average sound absorbability) and Er′ (dB) designates reflected energy after the improvement. A reduction amount of the reflected energy is Δl (dB). Here, α designates average sound absorbability before the improvement (film thickness is zero), and α′ designates average sound absorbability after the improvement. Ei designates energy of an input wave.
When α′=α+0.02α and α=0.5 are substituted into the aforementioned formula. Δl is about 0.1 dB.
Although it is preferred that the diameter of the through-hole portion formed by the coating film is smaller, the sound-absorbing performance is reduced when the through hole 4 is closed by the coating film. Therefore, the ratio of the film thickness L to the hole diameter d is smaller than 0.5 (½). In order to more surely prevent the through hole 4 from being closed by the coating film, it is preferred that the ratio of the film thickness L to the hole diameter d is ⅓ or less.
In addition, in the embodiment shown in
(First Modification of First Embodiment)
When a coating film 7b is formed only on a part of the inner wall surface of the through hole 4, a through-hole portion whose diameter is smaller than the diameter of the through hole 4 in the base material and whose volume is smaller than the volume of the through hole 4 in the base material can be formed so that sound-absorbing performance can be made better than that achieved by the through hole 4 in the base material. In addition, when the coating film 7b is formed into a mountain-like shape by use of surface tension or the like, the length in the thickness direction of a part (region) having a small hole diameter is shorter than the case where the hole has a fixed section due to a uniform coating film. As a result, the effect of viscous damping due to the hole can be improved to obtain an effect that the number of holes can be reduced to obtain the same sound-absorbing performance.
The through-hole portion 8 is a hole portion formed by the surface of the coating film 7b and, of the inner wall surface of the through hole 4, the surface where the coating film 7b is absent (the surface which has not been coated) (the same can be applied to other embodiment(s) in which a part of an inner wall surface of a through hole in a base material is coated as will be described later).
(Second Modification of First Embodiment)
The through hole 9 in this embodiment is classified into a shape like a right circular truncated cone (circular truncated cone symmetrical about its own axis) of a shape like a circular truncated cone. However, the through hole 9 may be a through hole formed into an obliquely circular truncated cone. Further, the shape of the through hole 9 is not limited to the circular truncated cone, but any shape may be used as long as the hole diameter is increased gradually from the minimum hole diameter portion 13 toward the maximum hole diameter portion 12, as described above (the same can be applied to a circular truncated cone-like hole 14b of a through hole 14 in the third embodiment which will be described later).
A coating film 7d is formed all over the inner wall surface of the through hole 9, and a through-hole portion 10 whose volume is smaller than the volume of the through hole 9 is formed by the coating film 7d.
When the shape of the through hole 9 is tapered, the place where the hole diameter is smallest can be limited to the minimum hole diameter portion 13. Thus, it is possible to reduce the risk that the hole may be closed due to accuracy in hole shape, a variation in coating film thickness or the like.
The perforated sound-absorbing plate 21 may be disposed so that the surface on the minimum hole diameter portion 13 faces the noise source 5 or the surface on the maximum hole diameter portion 12 faces the noise source 5 (the same can be applied to perforated sound-absorbing plates having through-hole parts shown in
(First Modification of Second Embodiment)
(Second Modification of Second Embodiment)
Of the through-hole portion 10 formed by the surface of the coating film 7f and the surface where the coating film 7f is absent (the hole surface which has not been coated), the inner diameter of the coating film 7f portion is smaller than the inner diameter of the minimum hole diameter portion 13. That is, due to the coating film 7f, the through-hole portion 10 has a diameter portion whose diameter is smaller than the minimum diameter of the through hole 9 as a base material. Here, a sound absorbing effect is determined by a pressure loss generated when a sound wave passes through the hole. The pressure loss depends largely on the smallest part of the hole. Therefore, a larger sound absorbing effect can be obtained when the inner wall surface of the through hole 9 is coated to reduce the hole volume while a hole portion whose diameter is smaller than that of the minimum hole diameter portion 13 of the through hole 9 in the base material is formed.
A coating film 7g is formed all over the inner wall surface of the through hole 14, and a through-hole portion 15 whose volume is smaller than the volume of the through hole 14 is formed by the coating film 7g.
In the perforated sound-absorbing plate 31 in this embodiment, the shape of the through hole 14 is tapered so that the place where the hole diameter is smallest can be limited to the minimum hole diameter portion 13, in the same manner as in the perforated sound-absorbing plate 21 in the second embodiment shown in
(First Modification of Third Embodiment)
(Second Modification of Third Embodiment)
Although a columnar hole is illustrated in
In the aforementioned embodiments, a coating film is formed circumferentially all over the inner wall surface of the through hole 4, 9 or 14. However, the coating film may be formed only on a part, in the circumferential direction, of the inner wall surface of the through hole 4, 9 or 14 so that a through-hole portion whose volume is smaller than the volume of the through hole 4 is formed by the coating film.
The present application is based on Japanese patent application No. 2015-231451 filed on Nov. 27, 2015, and Japanese patent application No. 2016-120172 filed on Jun. 16, 2016, the contents of which are incorporated herein by reference.
Number | Date | Country | Kind |
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JP2015-231451 | Nov 2015 | JP | national |
JP2016-120172 | Jun 2016 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2016/084334 | 11/18/2016 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2017/090538 | 6/1/2017 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
6206136 | Swindlehurst | Mar 2001 | B1 |
6977109 | Wood | Dec 2005 | B1 |
20090038883 | Kim | Feb 2009 | A1 |
Number | Date | Country |
---|---|---|
S58-88700 | Jun 1983 | JP |
S60-123000 | Aug 1985 | JP |
2004264372 | Sep 2004 | JP |
2008-233792 | Oct 2008 | JP |
2008-544119 | Dec 2008 | JP |
2012168415 | Sep 2012 | JP |
Entry |
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International Search Report issued in PCT/JP2016/084334; dated Feb. 7, 2017. |
Written Opinion issued in PCT/JP2016/084334; dated Feb. 7, 2017. |
Number | Date | Country | |
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20190112805 A1 | Apr 2019 | US |