EP0255473B1 - Method for manufacturing a sound-absorbing element - Google Patents
Method for manufacturing a sound-absorbing element Download PDFInfo
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- EP0255473B1 EP0255473B1 EP87810287A EP87810287A EP0255473B1 EP 0255473 B1 EP0255473 B1 EP 0255473B1 EP 87810287 A EP87810287 A EP 87810287A EP 87810287 A EP87810287 A EP 87810287A EP 0255473 B1 EP0255473 B1 EP 0255473B1
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- European Patent Office
- Prior art keywords
- resonance
- protuberances
- sound
- vibration
- element according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 238000000034 method Methods 0.000 title claims description 10
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- 238000010521 absorption reaction Methods 0.000 claims description 29
- 229920003023 plastic Polymers 0.000 claims description 15
- 239000004033 plastic Substances 0.000 claims description 15
- 239000000463 material Substances 0.000 claims description 9
- 238000002485 combustion reaction Methods 0.000 claims description 5
- 230000001419 dependent effect Effects 0.000 claims description 5
- 241000826860 Trapezium Species 0.000 claims 1
- 239000011148 porous material Substances 0.000 claims 1
- 239000004743 Polypropylene Substances 0.000 description 7
- -1 polypropylene Polymers 0.000 description 7
- 239000004800 polyvinyl chloride Substances 0.000 description 7
- 229920000915 polyvinyl chloride Polymers 0.000 description 7
- 229920001155 polypropylene Polymers 0.000 description 5
- 239000002985 plastic film Substances 0.000 description 4
- 229920006255 plastic film Polymers 0.000 description 4
- 230000010355 oscillation Effects 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 229920000573 polyethylene Polymers 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000011358 absorbing material Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- XECAHXYUAAWDEL-UHFFFAOYSA-N acrylonitrile butadiene styrene Chemical compound C=CC=C.C=CC#N.C=CC1=CC=CC=C1 XECAHXYUAAWDEL-UHFFFAOYSA-N 0.000 description 1
- 229920000122 acrylonitrile butadiene styrene Polymers 0.000 description 1
- 239000004676 acrylonitrile butadiene styrene Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 230000003116 impacting effect Effects 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 230000003534 oscillatory effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Images
Classifications
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B1/00—Engines characterised by fuel-air mixture compression
- F02B1/02—Engines characterised by fuel-air mixture compression with positive ignition
- F02B1/04—Engines characterised by fuel-air mixture compression with positive ignition with fuel-air mixture admission into cylinder
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/24521—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness with component conforming to contour of nonplanar surface
- Y10T428/24537—Parallel ribs and/or grooves
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/2457—Parallel ribs and/or grooves
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/24612—Composite web or sheet
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24628—Nonplanar uniform thickness material
- Y10T428/24661—Forming, or cooperating to form cells
Definitions
- the present invention relates to a method for producing an airborne sound-absorbing component which has a plurality of cup-shaped protuberances made of compact PVC film or foamed PP film, the cover surfaces of which are effective as resonance surfaces and are excited to vibrate by impacting sound energy, the sound energy being at least partially is absorbed and converted into heat, as well as a component produced by this method and a preferred use of this component.
- Components of the type described are usually made from a plastic film. They have a dense surface, a low mass and are resistant to most acids, oils, solvents as well as to relatively high temperatures and are therefore preferably used for the absorption of airborne noise in noisy workshops and for lining the housing of noise sources, especially internal combustion engines.
- the best known embodiments of such components can be assigned to one of two different groups.
- one group DE-OS 27 58 041
- the rear openings ie the openings of the protuberances facing away from the incident sound field
- the rear openings of the protuberances are closed, so that the mass of the vibrating cover surface with the enclosed air forms a physical mass-spring system with a clear resonance frequency.
- CH 626 936 the rear openings of the protuberances are not closed.
- the components of both groups are preferably arranged in front of and at a distance from a sound-reflecting wall.
- the resonance frequency of the cover or resonance surface depends on the shape, size and mass of this surface, on the height of the protuberance and on the mechanical loss factor and the modulus of elasticity of the used material is dependent. Practical experience has confirmed that even relatively small differences in the dimensions of the protuberances severely impair the course of both the sound absorption depending on the frequency of the incident sound and the strength of the sound absorption. Despite these findings, no method for producing such components is known to date which enables the shape and dimensions of the resonance surfaces to be optimized for a given use, taking into account the material properties.
- the maximum permissible height of the protuberances is often predetermined by the shape and dimensions of the sound source or its cladding and is usually smaller than in the known embodiments mentioned above.
- the present invention was therefore based on the object of creating a method which enables the production of airborne sound-absorbing components which have optimal absorption properties as a function of the permissible height of the protuberances.
- the method according to the invention makes it possible to form the values important for effective sound absorption by resonance vibrations, namely the thickness and the size of the resonance surface as a function of the height of the protuberance, and thus to systematically and reproducibly achieve values of sound absorption that have hitherto not been achieved or, at best, at random.
- FIGS 1a and 1b are not drawn to scale for clarity.
- the airborne sound absorbing component shown in FIGS. 1a and 1b contains a base area 10, the peripheral edge of which is provided with a stabilizing frame 11.
- the base area has a plurality of similar truncated pyramidal protuberances, of which simply the protuberance 12 is simply identified by a reference symbol.
- Each protuberance contains four lateral surfaces 13, 14, 15 and 16 and a cover surface 17.
- the sizes of the protuberances which are important for the present invention are their height h and the thickness d and the size A of the cover surface which acts as the determining resonance surface. Sound absorption measurements have shown that the horizontal distance between adjacent protuberances and the angle of inclination of the side walls to the base surface have little influence on the course of the sound absorption coefficient depending on the frequency.
- the protuberances are therefore preferably as close to one another and the side walls are designed to be as slightly inclined as the manufacturing process and practical requirements allow.
- a plastic film can simply be thermoformed to produce the component. However, it is also possible to manufacture the component in plastic injection molding or to glue or weld protuberances formed from individual sub-areas connected to one another on a carrier film.
- Suitable plastics are, for example, polyvinyl chloride, polyethylene, polypropylene, acrylonitrile-butadiene-styrene polymer or polycarbonate, which can be used both in compact and in foamed form.
- the optimal thickness d of the resonance surface becomes smaller as the height h of the protuberance increases.
- the curves confirm that the thickness d of the resonance surface is within the range of the height h of the protuberance which is important for the practical use of the component, i.e. between 10 and 35 mm is most dependent on this height.
- the optimal size A of the resonance surface is approximately proportional to the resonance surface thickness d.
- Curve 30 shows the typical course of the sound level as a function of the frequency for an internal combustion engine (four-stroke gasoline engine) with four cylinders and at idle at about 800 revolutions / minute. It goes without saying that the exact course of this curve is determined not only by the type of engine mentioned, the number of revolutions and the load, but also by specific design features, the operating temperature and other parameters. However, measurements on different motors under different operating conditions have shown that the curve 30 corresponds to an average value. Curve 30 shows that the sound level is low at frequencies up to 1000 Hz, increases with increasing frequencies, reaches the maximum value at 1600 Hz, slowly decreases until around 2500 Hz and rapidly decreases at even higher frequencies.
- FIG. 4 shows the strength of the sound absorption as a function of the frequency of the incident sound for three different embodiments of airborne sound absorbing components. All three components have truncated pyramid-shaped protuberances on the back, as in the 1a and 1b is shown. In all three embodiments, the plastic foils were deep-drawn in such a way that the side surfaces are inclined by approximately 20 ° from the vertical and the protuberances are 5 mm apart in the plane of the base surface.
- the height of the protuberances and the size of the resonance surfaces are the same for all three embodiments and are 30 mm and 35 cm2. In these embodiments, the resonance surfaces are rectangular and have an aspect ratio of approximately 0.8: 1.
- Curve 41 shows the sound absorption of a component made of foamed polyethylene, in which the thickness of the resonance surface is 1.5 mm. This curve rises evenly from values of low sound absorption at low frequencies to a maximum sound absorption corresponding to ⁇ s ⁇ 0.8 at 1000 Hz, then drops only slightly up to frequencies of around 1250 Hz and then drops steeply to ⁇ s up to around 1500 hz ⁇ 0.3.
- Curve 42 shows the sound absorption of a component made of compact PVC, in which the thickness of the resonance surface is 0.15 mm.
- the curve begins at higher frequencies than curve 41, rises steeply and reaches a relatively narrow maximum value of ⁇ s ⁇ 0.9 for a frequency of 1000 Hz and then drops steeply again until ⁇ s ⁇ 0.45 at 1500 Hz.
- Curve 43 shows the sound absorption of a component made of foamed polypropylene, in which the thickness of the resonance surfaces is 3 mm. This curve rises to frequencies of approximately 1250 Hz similar to curve 41, but then continues to rise to a maximum value of more than 0.95 in the frequency range around 1500 Hz and then falls more flatly than curves 41 and 42 and reaches a value of ⁇ s ⁇ 0 , 5 at a frequency of 4000 Hz.
- the method according to the invention and a component produced using this method can be adapted to special working conditions or uses. It has already been mentioned that instead of the films used for the exemplary embodiments described, other plastic films with similar properties can also be used. It is also possible to design the component differently than the simple plastic film provided with protuberances. For certain uses, it may be advantageous to cover the back of the component with a porous, sound-absorbing material or to insert or put a "cover” of such material in or on the rear openings of the protuberances. It is also possible to produce a combined component with two components of the type described. Of the simple components used for this, one is to be provided with protuberances that are somewhat higher and whose base area is somewhat larger than the other.
- protuberances enables the components to be placed on one another in such a way that only the webs of the base surfaces arranged between the protuberances lie on one another. Then the overlapping protuberances form a closed and a rearwardly open resonance space, with which the sound absorption and its frequency range can be further improved or expanded. Finally, it is also possible to produce a combined component from more than two components.
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Soundproofing, Sound Blocking, And Sound Damping (AREA)
- Vehicle Interior And Exterior Ornaments, Soundproofing, And Insulation (AREA)
- Laminated Bodies (AREA)
- Building Environments (AREA)
- Transducers For Ultrasonic Waves (AREA)
Description
Die vorliegende Erfindung betrifft ein Verfahren zum Herstellen eines Luftschall absorbierenden Bauelements, das eine Mehrzahl rückseitig offener becherförmige Ausstülpungen aus kompakter PVC-Folie oder geschäumter PP-Folie aufweist, deren als Resonanzflächen wirksame Deckflächen von auftreffender Schallenergie zu Schwingungen angeregt werden, wobei die Schallenergie mindestens teilweise absorbiert und in Wärme umgewandelt wird, sowie ein nach diesem Verfahren hergestelltes Bauelement und eine bevorzugte Verwendung dieses Bauelements.The present invention relates to a method for producing an airborne sound-absorbing component which has a plurality of cup-shaped protuberances made of compact PVC film or foamed PP film, the cover surfaces of which are effective as resonance surfaces and are excited to vibrate by impacting sound energy, the sound energy being at least partially is absorbed and converted into heat, as well as a component produced by this method and a preferred use of this component.
Bauelemente der beschriebenen Art werden gewöhnlich aus einer Kunststoffolie hergestellt. Sie haben eine dichte Oberfläche, eine geringe Masse und sind beständig gegen die meisten Säuren, Oele, Lösungsmittel sowie gegen relativ hohe Temperaturen und werden darum vorzugsweise für die Absorption von Luftschall in lärmigen Werkhallen und zum Auskleiden der Gehäuse von Lärmquellen, insbesondere Verbrennungsmotoren, verwendet.Components of the type described are usually made from a plastic film. They have a dense surface, a low mass and are resistant to most acids, oils, solvents as well as to relatively high temperatures and are therefore preferably used for the absorption of airborne noise in noisy workshops and for lining the housing of noise sources, especially internal combustion engines.
Die bekanntesten Ausführungsformen solcher Bauelemente lassen sich einer von zwei unterschiedlichen Gruppen zuordnen. Bei der einen Gruppe (DE-OS 27 58 041) sind die rückseitigen, d.h. dem einfallenden Schallfeld abgewandten Oeffnungen der Ausstülpungen verschlossen, damit die Masse der schwingenden Deckfläche mit der eingeschlossenen Luft ein physikalisches Masse-Feder-System mit einer deutlichen Resonanzfrequenz bildet. Bei der anderen Gruppe (CH 626 936) sind die rückseitigen Oeffnungen der Ausstülpungen unverschlossen.The best known embodiments of such components can be assigned to one of two different groups. In one group (DE-OS 27 58 041) the rear openings, ie the openings of the protuberances facing away from the incident sound field, are closed, so that the mass of the vibrating cover surface with the enclosed air forms a physical mass-spring system with a clear resonance frequency. In the other group (CH 626 936) the rear openings of the protuberances are not closed.
Bei der Verwendung werden die Bauelemente beider Gruppen vorzugsweise vor einer schallreflektierenden Wand und von dieser beabstandet angeordnet.When in use, the components of both groups are preferably arranged in front of and at a distance from a sound-reflecting wall.
In den Publikationen, die Ausführungsformen dieser beiden Gruppen von Bauelementen betreffen, wird erwähnt, dass die Resonanzfrequenz der Deck- bzw. Resonanzfläche von der Form, der Grösse und der Masse dieser Fläche, von der Höhe der Ausstülpung sowie vom mechanischen Verlustfaktor und dem Elastizitätsmodul des verwendeten Materials abhängig ist. Dazu hat die praktische Erfahrung bestätigt, dass auch relativ geringe Unterschiede der Abmessungen der Ausstülpungen den Verlauf sowohl der Schallabsorption in Abhängigkeit von der Frequenz des auftreffenden Schalls als auch die Stärke der Schallabsorption stark beeinträchtigen. Trotz dieser Erkenntnisse ist bisher noch kein Verfahren zum Herstellen solcher Bauelemente bekannt, das es ermöglicht, die Form und Abmessungen der Resonanzflächen unter Berücksichtigung der Materialeigenschaften für eine vorgegebene Verwendung zu optimieren.In the publications that relate to embodiments of these two groups of components, it is mentioned that the resonance frequency of the cover or resonance surface depends on the shape, size and mass of this surface, on the height of the protuberance and on the mechanical loss factor and the modulus of elasticity of the used material is dependent. Practical experience has confirmed that even relatively small differences in the dimensions of the protuberances severely impair the course of both the sound absorption depending on the frequency of the incident sound and the strength of the sound absorption. Despite these findings, no method for producing such components is known to date which enables the shape and dimensions of the resonance surfaces to be optimized for a given use, taking into account the material properties.
Bei der Verwendung schallabsorbierender Bauelemente in unmittelbarer Nähe einer Schallquelle ist die maximal zulässige Höhe der Ausstülpungen oft durch die Form und Abmessungen der Schallquelle bzw. deren Verkleidung vorgegeben und ist meistens kleiner als bei den oben erwähnten bekannten Ausführungsformen. Der vorliegenden Erfindung lag darum die Aufgabe zugrunde, ein Verfahren zu schaffen, das die Herstellung von Luftschall absorbierenden Bauelementen ermöglicht, die in Abhängigkeit von der zulässigen Höhe der Ausstülpungen optimale Absorprionseigenschaften aufweisen.When using sound-absorbing components in the immediate vicinity of a sound source, the maximum permissible height of the protuberances is often predetermined by the shape and dimensions of the sound source or its cladding and is usually smaller than in the known embodiments mentioned above. The present invention was therefore based on the object of creating a method which enables the production of airborne sound-absorbing components which have optimal absorption properties as a function of the permissible height of the protuberances.
Ausgehend von der Ueberlegung, dass die Schallabsorption eines schwingungsfähigen Systems, bestehend aus biegeschwingenden Flächen und einer dahinterliegenden Luftschicht am grössten ist, wenn die Resonanzfrequenz f₀ reell und ungefähr gleich der spezifischen Impedanz Z₀ der Luft ist, wurden theoretische und experimentelle Untersuchungen durchgeführt, um ein Verfahren zum Herstellen eines schallabsorbierenden Bauelements zu schaffen, bei dem die Schallabsorption für einen den praktischen Anforderungen entsprechenden Bereich der Höhe der Ausstülpungen optimiert ist und im Bereich der Resonanzfrequenz nur eine geringe Frequenzabhängigkeit aufweist.Based on the consideration that the sound absorption of an oscillatory system, consisting of bending-vibrating surfaces and an air layer behind it, is greatest when the resonance frequency is real and approximately equal to the specific impedance Z Luft of the air, theoretical and experimental investigations were carried out to create a sound-absorbing component in which the sound absorption is optimized for a range of the protuberances corresponding to practical requirements and has only a low frequency dependence in the range of the resonance frequency.
Diese Aufgabe wurde mit einem Verfahren gemäss Anspruch 1 gelöst, bei dem für eine optimale Schallabsorption durch Resonanzschwingungen die Dicke d der Resonanzflächen entsprechend der Formel
und die Flächengrösse A jeder Resonanzfläche entsprechend der Formel
ausgebildet werden, in welcher Formel h die Höhe der Ausstülpungen bzw. der Abstand von einer schallreflektierenden Wand und f₀ die Resonanzfrequenz ist und K₁, K₂ und K₃ vom Material des Bauelements und von der Schwingungsform der Resonanzfläche abhängige Konstante sind.This object was achieved with a method according to claim 1, in which the thickness d of the resonance surfaces according to the formula for optimal sound absorption by resonance vibrations
and the area size A of each resonance area according to the formula
are formed, in which formula h is the height of the protuberances or the distance from a sound-reflecting wall and f Reson the resonance frequency and K₁, K₂ and K₃ are dependent on the material of the component and the shape of the resonance surface dependent.
Als Schwingungsform s = 1 werden nachfolgend solche Schwingungen bezeichnet, die im Längsschnitt durch eine an ihren seitlichen Kanten befestigte Resonanzfläche nur einen Schwingungsbauch aufweisen, als Schwingungsform s = 2 werden Schwingungen bezeichnet, die im gleichen Längsschnitt drei Schwingungsbäuche (und dazwischen zwei Schwingungsknoten) zeigen.In the following, vibrations form s = 1 are those vibrations that have only one antinode in longitudinal section due to a resonance surface attached to their lateral edges, oscillation form s = 2 are oscillations that show three antinodes (and in between two oscillation nodes) in the same longitudinal section.
Zahlenwerte für die Konstante K₁, K₂ und K₃ für zwei gebräuchliche unterschiedliche Materialien und die beiden Schwingungsformen s = 1 und s = 2 sind in der folgenden Tabelle angegeben:
Das erfindungsgemässe Verfahren ermöglicht, die für eine wirksame Schallabsorption durch Resonanzschwingungen wichtigen Werte, nämlich die Dicke und die Grösse der Resonanzfläche in Abhängigkeit von der Höhe der Ausstülpung auszubilden und damit bisher nicht oder bestenfalls zufällig erreichte Werte der Schallabsorption systematisch und reproduzierbar zu verwirklichen.The method according to the invention makes it possible to form the values important for effective sound absorption by resonance vibrations, namely the thickness and the size of the resonance surface as a function of the height of the protuberance, and thus to systematically and reproducibly achieve values of sound absorption that have hitherto not been achieved or, at best, at random.
Nachfolgend wird das erfindungsgemässe Verfahren anhand einiger Ausführungsformen von Luftschall absorbierenden Bauelementen und mit Hilfe der Figuren erläutert. Es zeigen:
- Fig. 1a
- die perspektivische Draufsicht auf einen Teil eines typischen zur Absorption von Luftschall geeigneten Bauelements mit pyramidenstumpfförmigen Ausstülpungen,
- Fig. 1b
- den Schnitt durch das in Fig. 1a gezeigte Bauelement längs der Linie X-X,
- Fig. 2a
- die grafische Darstellung der erfindungsgemäss bestimmten Werte für die optimale Dicke d und die optimale Grösse A einer Resonanzfläche aus kompakter PVC-Folie in Abhängigkeit von der Höhe h der Ausstülpung und für eine Resonanzfrequenz von f₀ = 1000 Hz,
- Fig. 2b
- die zur Fig. 2a analoge Darstellung für eine Resonanzfläche aus geschäumter Polypropylen-Folie und für eine Resonanzfrequenz von f₀ = 1600 Hz,
- Fig. 3
- den Verlauf des Schallpegels des von einem Verbrennungsmotor erzeugten Lärms in Abhängigkeit von der Frequenz, und
- Fig. 4
- den Schallabsorptionskoeffizienten für ein Bauelement der bisher bekannten Art und für zwei erfindungsgemässe Bauelemente, ebenfalls in Abhängigkeit von der Frequenz.
- Fig. 1a
- the perspective top view of a part of a typical component suitable for the absorption of airborne sound with truncated pyramids,
- Fig. 1b
- the section through the component shown in Fig. 1a along the line XX,
- Fig. 2a
- the graphical representation of the values determined according to the invention for the optimal thickness d and the optimal size A of a resonance surface made of compact PVC film as a function of the height h of the protuberance and for a resonance frequency of f₀ = 1000 Hz,
- Fig. 2b
- 2a for a resonance surface made of foamed polypropylene film and for a resonance frequency of f₀ = 1600 Hz,
- Fig. 3
- the course of the sound level of the noise generated by an internal combustion engine as a function of the frequency, and
- Fig. 4
- the sound absorption coefficient for a component of the previously known type and for two components according to the invention, also as a function of the frequency.
Die Figuren 1a und 1b sind der deutlicheren Darstellung wegen nicht massstäblich gezeichnet.Figures 1a and 1b are not drawn to scale for clarity.
Das in den Fig. 1a und 1b gezeigte Luftschall absorbierende Bauelement enthält eine Grundfläche 10, deren umlaufender Rand mit einem stabilisierenden Rahmen 11 versehen ist. Die Grundfläche weist eine Mehrzahl gleichartiger pyramidenstumpfförmiger Ausstülpungen auf, von denen einfacherweise nur die Ausstülpung 12 mit einem Bezugszeichen identifiziert ist. Jede Ausstülpung enthält vier seitliche Flächen 13, 14, 15 und 16 und eine Deckfläche 17. Für die vorliegende Erfindung wichtige Grössen der Ausstülpungen sind deren Höhe h sowie die Dicke d und die Grösse A der als bestimmende Resonanzfläche wirksamen Deckfläche. Schallabsorptionsmessungen haben gezeigt, dass der horizontale Abstand zwischen benachbarten Ausstülpungen und der Neigungswinkel der Seitenwände zur Grundfläche den Verlauf des Schallabsorptionskoeffizienten in Abhängigkeit von der Frequenz wenig beeinflussen. Für eine möglichst grosse Gesamtschallabsorption sind darum die Ausstülpungen vorzugsweise so nahe benachbart und die Seitenwände so wenig geneigt auszubilden, wie es das Herstellverfahren und praktische Bedürfnisse ermöglichen.The airborne sound absorbing component shown in FIGS. 1a and 1b contains a
Zur Herstellung des Bauelements kann einfacherweise eine Kunststoffolie tiefgezogen werden. Es ist aber auch möglich, das Bauelement im Kunststoffspritzguss herzustellen oder aus einzelnen miteinander verbundenen Teilflächen gebildete Ausstülpungen auf eine Trägerfolie zu kleben oder zu schweissen. Geeignete Kunststoffe sind beispielsweise Polyvinylchlorid, Polyäthylen, Polypropylen, Acrylnitril-Butadien-Styrol-Polymerisat oder Polykarbonat, die sowohl in kompakter wie in geschäumter Form verwendet werden können. Ausgehend davon, dass die Wahl eines für einen gegebenen Verwendungszweck bestgeeigneten Kunststoff ebenso wie dessen Verarbeitung im Bereich fachmännischen Könnens liegen, wird auf eine ausführliche Beschreibung der brauchbaren Materialien und deren Verarbeitung ausdrücklich verzichtet.A plastic film can simply be thermoformed to produce the component. However, it is also possible to manufacture the component in plastic injection molding or to glue or weld protuberances formed from individual sub-areas connected to one another on a carrier film. Suitable plastics are, for example, polyvinyl chloride, polyethylene, polypropylene, acrylonitrile-butadiene-styrene polymer or polycarbonate, which can be used both in compact and in foamed form. Outgoing from the fact that the choice of a plastic that is best suited for a given purpose as well as its processing are within the range of expert knowledge, there is no detailed description of the usable materials and their processing.
In den Fig. 2a und 2b sind die Membrandicke d und die Membranfläche A in Abhängigkeit von der Höhe h der Ausstülpung für einen kompakten bzw. einen geschäumten Kunststoff dargestellt.2a and 2b show the membrane thickness d and the membrane surface A as a function of the height h of the protuberance for a compact or a foamed plastic.
In Fig. 2a entspricht die Kurve 21 der erfindungsgemäss optimalen Dicke d der als Resonanzfläche wirksamen Deckfläche der Ausstülpung in Abhängigkeit von der Höhe h der Ausstülpung für die Schwingungsform s = 1 und einen kompakten PVC-Kunststoff. Die Kurve 22 zeigt ebenfalls die optimale Dicke d der gleichen Fläche in Abhängigkeit von der Höhe h, aber für die Schwingungsform s = 2. Beide Kurven gelten für eine optimale Resonanzfrequenz bzw. optimale Schallabsorption im Frequenzbereich f₀ ≃ 1000 Hz.In FIG. 2a, curve 21 corresponds to the optimal thickness d according to the invention of the cover surface of the protuberance, which is effective as a resonance surface, depending on the height h of the protuberance for the vibration form s = 1 and a compact PVC plastic.
Die Kurve 23 entspricht der erfindungsgemäss optimalen Grösse A der Resonanzfläche in Abhängigkeit von der Höhe h der Ausstülpung für die Schwingungsform s = 1 und einen kompakten PVC-Kunststoff. Die Kurve 24 zeigt ebenfalls die optimale Fläche A in Abhängigkeit von der Höhe h, aber für die Schwingungsform s = 2. Auch diese beiden Kurven gelten für eine Resonanzfrequenz im Bereich f₀ ≃ 1000 Hz.
In Fig. 2b ist die erfindungsgemässe optimale Dicke d der Resonanzfläche in Abhängigkeit von der Höhe h der Ausstülpung und für die Schwingungsform s = 1 durch die Kurve 25 sowie für die Schwingungsform s = 2 durch die Kurve 26 für ein Bauelement aus geschäumtem Polypropylen-Kunststoff dargestellt. Beide Kurven gelten für eine Resonanzfrequenz bzw. eine optimale Schallabsorption im Frequenzbereich f₀ ≃ 1600 Hz.2b, the optimal thickness d of the resonance surface according to the invention is a function of the height h of the protuberance and for the waveform s = 1 by the curve 25 and for the waveform s = 2 represented by
Weiter zeigt die Kurve 27 die erfindungsgemäss optimale Grösse A der Resonanzfläche in Abhängigkeit von der Höhe h der Ausstülpung für die Schwingungsform s = 1 und die Kurve 28 die gleiche Grösse für die Schwingungsform s = 2 für einen geschäumten Polypropylen-Kunststoff. Beide Kurven gelten für eine Resonanzfrequenz bzw. eine optimale Schallabsorption im Frequenzbereich f₀ ≃ 1600 Hz.Furthermore,
Aus diesen Kurven ist zu ersehen, dass die optimale Dicke d der Resonanzfläche kleiner wird, wenn die Höhe h der Ausstülpung grösser wird. Die Kurven bestätigen, dass die Dicke d der Resonanzfläche in dem für die praktische Verwendung des Bauelements wichtigen Bereich der Höhe h der Ausstülpung, d.h. zwischen 10 und 35 mm am stärksten von dieser Höhe abhängig ist. Die Kurven bestätigen weiter, dass für Schwingungsformen s = 2 Ausstülpungen mit Höhen im gezeigten Bereich von 10 bis 50 mm die optimale Dicke d auf Werte sinkt, bei denen die geforderte mechanische Stabilität des fertigen Bauelements nicht mehr gewährleistet ist.It can be seen from these curves that the optimal thickness d of the resonance surface becomes smaller as the height h of the protuberance increases. The curves confirm that the thickness d of the resonance surface is within the range of the height h of the protuberance which is important for the practical use of the component, i.e. between 10 and 35 mm is most dependent on this height. The curves further confirm that for waveforms s = 2 protuberances with heights in the range from 10 to 50 mm shown, the optimum thickness d drops to values at which the required mechanical stability of the finished component is no longer guaranteed.
Aus der Darstellung ist ersichtlich, dass sich die optimale Grösse A der Resonanzfläche ungefähr proportional zur Resonanzflächendicke d verhält. Die Kurven zeigen ferner, dass die optimale Fläche A für die Schwingungsform s = 2 kleiner ist als für die Schwingungsform s = 1 und dass die dem erfindungsgemässen Verfahren entsprechenden Werte der Dicke d und der Grösse A der Resonanzfläche wesentlich unter den Werten liegen, die bisher gebräuchlich waren und in den eingangs genannten Publikationen aufgeführt sind.It can be seen from the illustration that the optimal size A of the resonance surface is approximately proportional to the resonance surface thickness d. The curves also show that the optimal area A for the waveform s = 2 is smaller than for the waveform s = 1 and that the values of the thickness d corresponding to the method according to the invention and the size A of the resonance area are significantly below the values that were previously used and are listed in the publications mentioned at the beginning.
Schliesslich zeigt der Vergleich der Kurven in den Fig. 2a und 2b, dass die Abhängigkeit der für eine optimale Schallabsorption bestimmten Dicke und Grösse der Resonanzfläche von der Höhe der Ausstülpung für eine Resonanzfläche aus geschäumtem Kunststoff sehr viel stärker ist als für eine Resonanzfläche aus kompaktem Kunststoff.Finally, the comparison of the curves in FIGS. 2a and 2b shows that the dependence of the thickness and size of the resonance surface, which is intended for optimal sound absorption, on the height of the protuberance is much stronger for a resonance surface made of foamed plastic than for a resonance surface made of compact plastic .
Die Fig. 3 zeigt den typischen Verlauf des Schallpegels in Abhängigkeit von der Frequenz für einen Verbrennungsmotor (Viertakt-Ottomotor) mit vier Zylindern und im Leerlauf bei etwa 800 Umdrehungen/Minute. Dabei versteht sich, dass der genaue Verlauf dieser Kurve nicht nur von der genannten Motorenart, der Umdrehungszahl und der Belastung, sondern auch von spezifischen Konstruktionsmerkmalen, der Betriebstemperatur und weiteren Parametern bestimmt wird. Messungen an unterschiedlichen Motoren bei unterschiedlichen Betriebsbedingungen haben jedoch gezeigt, dass der Verlauf der Kurve 30 einem Mittelwert entspricht. Die Kurve 30 zeigt, dass der Schallpegel bei Frequenzen bis 1000 Hz klein ist, mit zunehmenden Frequenzen ansteigt, bei 1600 Hz den Maximalwert erreicht, bis etwa 2500 Hz langsam und bei noch höheren Frequenzen rasch absinkt.3 shows the typical course of the sound level as a function of the frequency for an internal combustion engine (four-stroke gasoline engine) with four cylinders and at idle at about 800 revolutions / minute. It goes without saying that the exact course of this curve is determined not only by the type of engine mentioned, the number of revolutions and the load, but also by specific design features, the operating temperature and other parameters. However, measurements on different motors under different operating conditions have shown that the
Die Fig. 4 zeigt die Stärke der Schallabsorption in Abhängigkeit von der Frequenz des auftreffenden Schalls für drei verschiedene Ausführungsformen von Luftschall absorbierenden Bauelementen. Alle drei Bauelemente weisen rückseitig offene, pyramidenstumpfförmige Ausstülpungen auf, wie es in den Fig. 1a und 1b gezeigt ist. Bei allen drei Ausführungsformen wurden die Kunststoff-Folien derart tiefgezogen, dass die Seitenflächen um ca. 20° gegenüber der Senkrechten geneigt sind und die Ausstülpungen in der Ebene der Grundfläche einen Abstand von 5 mm haben.4 shows the strength of the sound absorption as a function of the frequency of the incident sound for three different embodiments of airborne sound absorbing components. All three components have truncated pyramid-shaped protuberances on the back, as in the 1a and 1b is shown. In all three embodiments, the plastic foils were deep-drawn in such a way that the side surfaces are inclined by approximately 20 ° from the vertical and the protuberances are 5 mm apart in the plane of the base surface.
Die Höhe der Ausstülpungen und die Grösse der Resonanzflächen ist für alle drei Ausführungsformen gleich und beträgt 30 mm bzw. 35 cm². Die Resonanzflächen sind bei diesen Ausführungsformen rechteckig und weisen ein Seitenverhältnis von etwa 0,8 : 1 auf.The height of the protuberances and the size of the resonance surfaces are the same for all three embodiments and are 30 mm and 35 cm². In these embodiments, the resonance surfaces are rectangular and have an aspect ratio of approximately 0.8: 1.
Die Kurve 41 zeigt die Schallabsorption eines Bauelements aus geschäumtem Polyäthylen, bei dem die Dicke der Resonanzfläche 1,5 mm beträgt. Diese Kurve steigt von Werten geringer Schallabsorption bei niedrigen Frequenzen gleichmässig an bis zu einer maximalen Schallabsorption entsprechend αs ∼ 0,8 bei 1000 Hz, fällt dann bis zu Frequenzen von etwa 1250 Hz nur wenig und danach bis etwa 1500 hz steil ab auf αs ∼ 0,3.Curve 41 shows the sound absorption of a component made of foamed polyethylene, in which the thickness of the resonance surface is 1.5 mm. This curve rises evenly from values of low sound absorption at low frequencies to a maximum sound absorption corresponding to α s ∼ 0.8 at 1000 Hz, then drops only slightly up to frequencies of around 1250 Hz and then drops steeply to α s up to around 1500 hz ∼ 0.3.
Die Kurve 42 zeigt die Schallabsorption eines Bauelements aus kompakten PVC, bei dem die Dicke der Resonanzfläche 0,15 mm beträgt. Die Kurve beginnt bei höheren Frequenzen als die Kurve 41, steigt steil an und erreicht für eine Frequenz von 1000 Hz einen relativ schmalen Maximalwert von αs ∼ 0,9 und fällt danach wieder steil ab bis αs ∼ 0,45 bei 1500 Hz.Curve 42 shows the sound absorption of a component made of compact PVC, in which the thickness of the resonance surface is 0.15 mm. The curve begins at higher frequencies than curve 41, rises steeply and reaches a relatively narrow maximum value of α s ∼ 0.9 for a frequency of 1000 Hz and then drops steeply again until α s ∼ 0.45 at 1500 Hz.
Die Kurve 43 zeigt die Schallabsorption eines Bauelements aus geschäumtem Polypropylen, bei dem die Dicke der Resonanzflächen 3 mm beträgt. Diese Kurve steigt bis zu Frequenzen von etwa 1250 Hz ähnlich an wie die Kurve 41, steigt dann aber weiter bis zu einem Maximalwert von mehr als 0,95 im Frequenzbereich um 1500 Hz und fällt danach flacher als die Kurven 41 und 42 ab und erreicht einen Wert von αs ∼ 0,5 bei einer Frequenz von 4000 Hz.Curve 43 shows the sound absorption of a component made of foamed polypropylene, in which the thickness of the resonance surfaces is 3 mm. This curve rises to frequencies of approximately 1250 Hz similar to curve 41, but then continues to rise to a maximum value of more than 0.95 in the frequency range around 1500 Hz and then falls more flatly than curves 41 and 42 and reaches a value of α s ∼ 0 , 5 at a frequency of 4000 Hz.
Die gezeigten Kurven machen deutlich, dass die Schallabsorption von geschäumtem Kunststoff höhere Werte erreicht und in einem breiteren Frequenzbereich wirksam ist als diejenige von kompaktem Kunststoff und dass ein Bauelement mit erfindungsgemäss dimensionierten Ausstülpungen (Kurve 43) eine Schallabsorptionskurve aufweist, die sehr gut mit dem Schallpegel eines Verbrennungsmotors (Fig. 3) übereinstimmt.The curves shown make it clear that the sound absorption of foamed plastic achieves higher values and is effective in a wider frequency range than that of compact plastic and that a component with protuberances dimensioned according to the invention (curve 43) has a sound absorption curve which is very good at the sound level of a Internal combustion engine (Fig. 3) matches.
Es versteht sich, dass das erfindungsgemässe Verfahren und ein nach diesem Verfahren herstelltes Bauelement an spezielle Arbeitsbedingungen oder Verwendungen angepasst werden kann. Es wurde bereits erwähnt, dass anstelle der für die beschriebenen Ausführungsbeispiele verwendeten Folien auch andere Kunststoff-Folien mit ähnlichen Eigenschaften verwendet werden können. Es ist auch möglich, das Bauelement anders als die beschriebene einfache, mit Ausstülpungen versehene Kunststoff-Folie auszubilden. Für bestimmte Verwendungen kann es vorteilhaft sein, die Rückseite des Bauelements mit einem porösen, schallschluckenden Material zu belegen oder in bzw. auf die rückseitigen Oeffnungen der Ausstülpungen einen "Deckel" aus solchem Material ein- oder aufzusetzen. Weiter ist es möglich, mit zwei Bauelementen der beschriebenen Art ein kombiniertes Bauelement herzustellen. Von den dafür verwendeten einfachen Bauelementen ist das eine mit Ausstülpungen zu versehen, die etwas höher und deren Grundfläche etwas grösser ist als bei dem anderen. Diese Ausbildung der Ausstülpungen ermöglicht, die Bauelemente derart aufeinanderzulegen, dass nur die zwischen den Ausstülpungen angeordneten Stege der Grundflächen aufeinanderliegen. Dann bilden die übereinanderstehenden Ausstülpungen einen geschlossenen und einen rückwärtig offenen Resonanzraum, womit die Schallabsorption und deren Frequenzbereich nochmals verbessert bzw. erweitert werden können. Schliesslich ist es auch möglich, aus mehr als zwei Bauelementen ein kombiniertes Bauelement herzustellen.It goes without saying that the method according to the invention and a component produced using this method can be adapted to special working conditions or uses. It has already been mentioned that instead of the films used for the exemplary embodiments described, other plastic films with similar properties can also be used. It is also possible to design the component differently than the simple plastic film provided with protuberances. For certain uses, it may be advantageous to cover the back of the component with a porous, sound-absorbing material or to insert or put a "cover" of such material in or on the rear openings of the protuberances. It is also possible to produce a combined component with two components of the type described. Of the simple components used for this, one is to be provided with protuberances that are somewhat higher and whose base area is somewhat larger than the other. These Formation of the protuberances enables the components to be placed on one another in such a way that only the webs of the base surfaces arranged between the protuberances lie on one another. Then the overlapping protuberances form a closed and a rearwardly open resonance space, with which the sound absorption and its frequency range can be further improved or expanded. Finally, it is also possible to produce a combined component from more than two components.
Claims (8)
- Method of manufacturing a sound-absorbing element, which has a plurality of rearwardly open, beaker-shaped protuberances of compact PVC sheet or foamed PP sheet, the top surfaces of which, acting as resonance surfaces, are excited into vibration by impinging sound energy, the sound energy being at least partly absorbed and converted into heat, characterized in that, for an optimum sound absorption by resonance vibrations, the thickness d of the resonance surfaces is constructed according to the formula
Material Constant Form of vibration s = 1 s = 2 Compact PVC sheet K₁ (ms⁻¹) 1.1 0.12 K₂ (m²s⁻²) 1.6 0.17 K₃ (ms⁻¹) 4.7x10³ 2.2x10⁴ Foamed PP sheet K₁ (ms⁻¹) 3.2 0.3 K₂ (m²s⁻²) 70.6 7.5 K₃ (ms⁻¹) 1.6x10³ 7.5x10³ - Sound absorbing element manufactured according to the method of Claim 1, characterized by at least one compact or foamed plastics sheet, from which the beaker-shaped protuberances are moulded out in one piece.
- Element according to Claim 2, characterized in that two or more plastics sheets having different heights and base areas of the protuberances are laid upon one another in such a manner that only the webs of the base surfaces disposed between adjacent protuberances touch one another.
- Element according to Claim 2, characterized in that the top or resonance surfaces of the protuberances have the form of a rectangle, a trapezium, a parallelogram, a circle or a regular polygon.
- Element according to Claim 4, characterized in that the beaker-shaped protuberances taper towards the top surface.
- Element according to Claim 2, characterized in that the inner openings of the beaker-shaped protuberances are closed by a layer of porous material.
- Use of the element according to Claim 2 for at least partly internally lining the casing of a machine, especially an internal combustion engine.
- Use of the element according to Claim 2 for at least partly internally lining a space or room.
Applications Claiming Priority (2)
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CH2006/86 | 1986-05-16 | ||
CH200686A CH671848B (en) | 1986-05-16 | 1986-05-16 |
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EP0255473A1 EP0255473A1 (en) | 1988-02-03 |
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US5904318A (en) * | 1996-12-18 | 1999-05-18 | Towfiq; Foad | Passive reduction of aircraft fuselage noise |
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US6471157B1 (en) * | 1999-03-22 | 2002-10-29 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Device and method for reducing aircraft noise |
US6598701B1 (en) | 2000-06-30 | 2003-07-29 | 3M Innovative Properties Company | Shaped microperforated polymeric film sound absorbers and methods of manufacturing the same |
FR2823467B1 (en) * | 2001-04-17 | 2005-07-15 | Sofitec Sa | THERMOFORMED PRODUCT FOR ACOUSTIC AND / OR THERMAL INSULATION PANEL |
US7434660B2 (en) * | 2001-06-21 | 2008-10-14 | Kabushiki Kaisha Kobe Seiko Sho | Perforated soundproof structure and method of manufacturing the same |
DE10323045A1 (en) * | 2003-05-20 | 2004-12-09 | Behr Gmbh & Co. Kg | Housing, in particular air guide housing and method for producing such |
EP1571650B1 (en) * | 2004-03-03 | 2009-05-13 | Rolls-Royce Deutschland Ltd & Co KG | Device for producing acoustic fields with a defined modal composition |
JP2007223341A (en) * | 2006-02-21 | 2007-09-06 | Nagoya Oil Chem Co Ltd | Sealing material for door |
ITRA20100013A1 (en) * | 2010-05-04 | 2011-11-05 | Simone Meneghel | "FRANGI-ONDA SOUND INSULATION PANEL" |
RU2593733C1 (en) | 2012-07-06 | 2016-08-10 | Си Энд Ди ЗОДИАК, ИНК. | Interior panel of aircraft with acoustic materials |
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CN112735368A (en) * | 2020-12-24 | 2021-04-30 | 江苏建声影视设备研制有限公司 | Environment-friendly fireproof acoustic board |
CN113757817B (en) * | 2021-10-22 | 2022-11-29 | 广东美芝制冷设备有限公司 | Sound insulation structure, air condensing units and air conditioner |
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1986
- 1986-05-16 CH CH200686A patent/CH671848B/de not_active IP Right Cessation
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1987
- 1987-05-07 ES ES198787810287T patent/ES2030092T3/en not_active Expired - Lifetime
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- 1987-05-07 EP EP87810287A patent/EP0255473B1/en not_active Expired - Lifetime
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- 1987-05-15 BR BR8702500A patent/BR8702500A/en not_active IP Right Cessation
- 1987-05-15 CA CA000537264A patent/CA1277922C/en not_active Expired - Fee Related
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JPH0818389B2 (en) | 1996-02-28 |
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CA1277922C (en) | 1990-12-18 |
US4755416A (en) | 1988-07-05 |
ES2030092T3 (en) | 1992-10-16 |
JPS6327242A (en) | 1988-02-04 |
EP0255473A1 (en) | 1988-02-03 |
CH671848B (en) | 1989-09-29 |
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