Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1998-09-18
2001-02-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S131000, C428S132000, C428S137000
Reexamination Certificate
active
06194052
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a soundabsorbing element, how to manufacture it and how to use it.
BACKGROUND OF THE INVENTION
Different kinds of soundabsorbing elements are known in the technical field. Damping materials that are mounted in the ceiling often consist of a perforated plate with a soundabsorbing material in the form of absorbing felt or some other fiberbased material, placed on the backside of the plate. These plates are placed at a certain distance from the actual ceiling. This, and the fact that the soundabsorbing material itself requires space means that the available height in the room is reduced. Other types of acoustical tiles made of fibres, glassfibers or asbestos have disadvantages mainly during installation but, also during removal as handling them is health-hazardous. Foamed plastics are also used as absorbing elements. These materials have the obvious drawback that they are flammable. Plastic foams often have a short life following which they fall apart.
THE KNOWN PRIOR ART
In the Swedish patent 207 484 a soundabsorbing element for ceilings, walls or similar applications is described. The element according to the patent consists of a single plate or a long coil of material, that is given a great many openings arranged in parallel rows where the parts of the element lying between adjacent and parallel slits are pressed out of the plane of the plate, and said parts connected to the element by flaps. All the protruding parts are hereby situated in a plane parallel to but outside the plane of the plate. The openings are thus constituted by a similarly sized slits oriented perpendicular to the plane of the material. Each slit is thus adjacent to the plate and to the protrusion connected by flaps to the plate. These protrusions are oriented essentially parallel to the plate. If the upper surface of the pressed out protrusions still would be below the plates lower surface, the patent claims that no slits have been created, i.e. a solely vertically oriented slit through the plate is not considered included in the patent claims but the protrusion must be created in a way so that the protrusion essentially is pressed out beyond the surface of the plate.
A similar construction is known from the Swedish laid open publication 394 126 where a metal sheet is described which has a great number of protruding segments shaped like parallel ribs, each of the protruding segments consisting of a part of the metal plate that lies between two longitudinally oriented slits and where the cut surfaces of each protruding the segment are pushed out beyond the central plane of the plate.
Combinations of plates with penetrating slits of varying shapes in combination with a layer of soundabsorbing additional material are also known for instance form the Swedish laid open publication 325 694 and U.S. Pat. No. 2,009,512.
In addition to above mentioned plates there are various absorbent panels of pressed fibers and porous materials, in combination with plates, or separate.
A common feature in the known art is that the sound penetrates the plate through holes and slits of rather large size and that the plate itself works as a resonant absorber. In order to increase the energy losses further i.e. to increase the soundabsorption, an airflow resistance layer is placed behind the holes or slits.
These earlier types of perforated acoustic tiles are of the Helmholtz resonator type, i.e. a resonant absorber where a plate equipped with holes is arranged at a certain distance from a rigid wall.
In an article by H. V. Fuchs, Einsatz mikroperforierter Platten als schallabsorber mit inhärenter Dämpfung, Acustica vol. 81 (1995), p. 107-116 the theory of another type of sound absorbers is described.
In the article it is described how a microperforated plate can be used to achieve a broadband absorption. The theory behind this is that the vibrations in the air (=the sound) is effectively damped by the influence of the shearforces inside the small holes and that in this way a broadband absorption is achieved without using additional fibres or other porous materials. The holes in the article are produced by using a laser beam.
In the above cited article it is concluded, however, that the cost for producing these plates is considerable and when using stiff and or thick materials cost considerations make their use impossible. The theory of microholes has been discussed since 1950 but the difficulties of making so many and so small perforations has prevented the practical use of micro-holes as a sound absorbing means.
Thus it has been shown that sounddamping elements according to the state of the art, for instance Helmholtz type resonators, beside the first mentioned drawbacks, also have the disadvantage that a combination of materials must be used in order to achieve a desirable absorption over a wide frequency range.
I has also been shown that sounddamping elements using microperforations are very expensive to manufacture by for instance using a laser beam as in the above mentioned article.
OBJECTS OF THE INVENTION
The main object with this invention is to achieve a soundabsorbing element, having broadband absorption characteristics, that consists of a single plate that is easy to install and easy to manufacture, and requires no additional layer of fiber or the like.
Another object is to achieve a soundabsorbing element that easily can be formed in two or three dimensions, that is weldable and that is easily cleaned even with high pressure spray objects or other cleaning techniques including different kinds of detergents.
Another object is to achieve a soundabsorbing element that is economically advantageous because of the way it is manufactured.
Another object is to achieve a soundabsorbing element which is fire-resistant and can withstand hard conditions e.g. corrosive environments.
Yet another purpose is to achieve a soundabsorbing element that has a decorative effect.
SUMMARY OF THE INVENTION
It has now been surprisingly shown that with a soundabsorbing element according to the invention, and a way to produce this soundabsorbing element it is possible to achieve excellent sound absorption over essentially the whole of the actual band width. The above shown purposes are achieved by an element and a way of producing it which are characterised by the characterising parts of claims
1
and
8
.
With the element and the process a simple and uncomplicated element is achieved that is easy to produce and mount and that withstands high temperatures, that withstands demanding chemical environments and that is self-supporting.
The element according to the invention is formable and can be welded and is thin, lightweight, and flexible to mount.
The element according to the invention is moreover adjustable to different acoustic requirements by varying number of slits per m
2
and also by varying the slit shape. Moreover it is possible to foresee the performance which means that an element or element system can be tailored to different needs.
The element has also shown to be very effective at damping machine noise. It can thus be used in engine compartments, in machine tools and vehicles. When used in soundmufflers, part or the whole muffler, can be made of the element according to the invention.
The suitability of the element for the above mentioned applications does not only depend on the excellent formability and the possibility to join the element to metal constructions by well-known techniques as for instance welding, but also on properties such as fire resistance and washability.
Additional features of the element and the process according to the invention are claimed in the dependent claims.
REFERENCES:
patent: 1536666 (1925-05-01), Franz
patent: 2132642 (1938-10-01), Parsons
patent: 3734234 (1973-05-01), Wirt
Jones Deborah
Miranda Lymarie
Young & Thompson
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