Acoustics – Sound-modifying means – Housing or enclosure
Reexamination Certificate
2002-03-28
2003-08-12
Hsieh, Shih-Yung (Department: 2837)
Acoustics
Sound-modifying means
Housing or enclosure
C181S284000, C181S290000, C181S291000, C181S294000
Reexamination Certificate
active
06604603
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to soundproofing for insulating sound generating devices or parts of systems particularly vibrating conveyers with insulation elements that are bordered by an inner face in the direction of the sound source and by an outer face in the direction away from the sound source; and the insulation elements comprising layers of insulation material with a hollow cavity component. Such insulation is used for acoustic insulation and optionally also thermal insulation of equipment, installation parts, motors or machines, in particular for vibration conveyers. This invention preferably includes soundproofing that can be removed quickly by hand and reinstalled again in the event of inspections, repairs, problems, etc.
BACKGROUND OF THE INVENTION
The known insulation systems have various disadvantages. The most common type of insulation is so-called cassette insulation, such as that described as thermal insulation in German Patent 36 36 341. However, cassettes of similar design are also widely used for soundproofing. A cassette is understood to be a housing made of steel plate or chrome steel plate with an open inside. To achieve a sound absorbing effect, insulation mats are inserted into the cassette from the inside. The surface of the insulation mats facing inward may be flat or may optionally have a three-dimensional structure. The air movements of the sound waves are hindered or attenuated in the insulation mat. If it is assumed that sound is reflected on the sheet metal wall of the cassette housing, the maximum air movements are at a distance of one-quarter wavelength from this reflective surface. To be able to optimally dampen these air movements, the thickness of the insulation mat would have to be in the range of one-quarter wavelength. With a justifiable layer thickness, this is possible only at a high frequency, because wavelengths in the low frequency range down to approx. 500 Hz are more than 60 cm, so the quarter wavelength would be more than 15 cm accordingly. At 2 kHz, the quarter wavelength is approx. 4 cm, which is thus within the range of the insulation material layer thicknesses conventionally used. Accordingly, the known soundproofing is effective only in the high frequency range with a frequency of more than 1 kHz.
If devices are enclosed in such cassettes, metallic housing side edges extend from the inside of the insulation to the outside in the contact area between adjacent cassettes or between a ring of cassettes and a cover element adjacent to this ring. Such housing side edges form sound bridges which greatly promote unwanted transmission of sound toward the outside. Accordingly, such a soundproofing system does not provide an adequate noise reduction effect even in the high frequency range.
The absorption coefficients of various materials and wall structures depend on the frequency. Essentially, fiber material has a high absorption coefficient in the range of 1 kHz. For example, measurements on a concrete wall coated with a fiber material have yielded absorption coefficients of 0.14, 0.20, 0.79 and 0.37 at frequencies of 125 Hz, 250 Hz, 1 kHz and 4 kHz. A plywood board has an elevated absorption coefficient in the low frequency range. Absorption coefficients of 0.60, 0.30, 0.09 and 0.09 have been determined for frequencies of 125 Hz, 250 Hz, 1 kHz and 4 kHz by performing measurements on a plywood board. The greater absorption in the low frequency range can be explained by resonance and the energy absorbing internal friction of the plywood board. The low absorption in the high frequency range shows that high frequency vibrations have little effect on friction because of the small amplitudes.
In addition to cassettes that are open toward the inside, cassettes which include a perforated plate as the inner face, so that a sheet metal face is adjacent to the soft insulation layer on both the inside and outside, are also used. In this way, absorption in the low frequency range should be combined with absorption provided by fiber mats in the high frequency range. Sound absorbing resonators are formed and kept open between the two metal plates due to the holes in the perforated plate arranged on the inside. The resonators and the insulation layer guarantee sound absorption in the respective frequency ranges according to the respective dimensions of the resonators and the absorption property of the insulation material. The cohesive area of the perforated plate arranged on the inside forms a reflective surface at least for the high frequency range. The sound component reflected on this reflective surface can excite resonance that is radiated outward over sound bridges, depending on the shape of the interior space adjacent to the insulation, for various frequency ranges.
The known soundproofing system for sheathing equipment usually guarantees a relevant sound absorbing effect only in certain portions of the high frequency range. However, since many types of equipment generate sound with frequency components in frequency ranges that are far apart, at least individual frequency components are not absorbed enough. In the case of equipment with very high sound levels, the ambient air quality standards or guideline values cannot be met with the known insulation, in particular when various types of such equipment are set up in one working area.
International Patent application WO 97/48943, a patent application by the present applicant, describes insulation which is in direct contact with the three-dimensional outside surface of structural components. It includes a contact layer or a friction layer made of sheet metal and/or wire mesh which is in contact with the structural component. To achieve stability of the insulation elements and to be able to absorb axial forces between adjacent insulation elements, solid supporting half-rings arranged on the end faces of the insulation elements are in contact with the structural component and extend over the entire thickness of the insulation element. These supporting half-rings or solid ribs form unwanted sound bridges which extend essentially over the entire thickness of the insulation elements and thus transmit sound from the interior of the insulation to the environment. Another disadvantage of the insulation according to International Patent WO 97/48943 is that it can only be mounted directly on the structural component, not at a desired distance from it. In addition, this insulation is designed mainly as thermal insulation and does not have the desired damping properties over the entire frequency range.
Vibrating conveyers or so-called vibrators that transmit vibrations have the object of supplying components that are used in an automatic assembly operation, such that they are supplied serially and in particular in the proper cycle. To do so, these vibrators are in the form of a vessel with a curved bottom and a conical side wall. At least one spiral-shaped ramp is provided on the conicalside wall. Vibration of the vessel is induced by magnet-metal spring packages which are arranged between the vessel and a solid base. Because of this vibration, the loose parts accommodated in the vessel are moved toward the wall of the vessel and on the ramp toward the output end of the ramp. The noise emitted by the vibrators has two different sources. First, a low frequency hum, the so-called transformer hum, is emitted by the magnet-metal spring packages. The sound level of this low frequency component is very high. For example, a sound pressure level of 90 dB(A) has been measured at 16 Hz. On the other hand, the moving loose parts produce noise in the high frequency range. This noise is formed by relative movement between the loose parts and the vibrating vessel or ramp and by collisions between abutting parts of the loose parts. There are also parts with a natural resonance that can be excited by the vibration. Other noise sources include blast nozzles or deflection devices which are optionally present and guarantee for example a desired conveyance of the isolated loose parts.
Depending on the loose
Etis AG
Harness & Dickey & Pierce P.L.C.
Hsieh Shih-Yung
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