EP0063715A1

EP0063715A1 - Sound insulating plate

Info

Publication number: EP0063715A1
Application number: EP82102836A
Authority: EP
Inventors: Yoshikazu Nissan Motor Company Ltd. Hayakawa
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1981-04-20
Filing date: 1982-04-02
Publication date: 1982-11-03
Also published as: JPS57178855A

Abstract

A sound insulating plate effectively insulates audible noise produced by a mechanism. The sound insulating plate according to the present invention, which is disposed onto the external surface of the mechanism producing audible noise so as to closely cover the part, comprises a metal base plate, a low-density thermoplastic resin layer fixed to the metal base plate, and an external high-density heat-hardened resin layer obtained by heating the low-density thermoplastic resin layer. The material of the low-density thermoplastic resin layer is a foam resin such as polyurethane or polyamide.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sound insulating plate for insulating audible noise produced by a mechanism, and more specifically to a sound insulating cover plate having two thermoplastic resin layers.

Description of the Prior Art

Mechanisms which produce audible noise are often covered with a sound insulating plate in order to provide noise insulation. In this case the plate is attached to the external surface of the mechanism so as to closely cover it.
There are various sound insulating plates as described above, such as single-layer or double-layer type sound insulating plates.
The prior-art sound insulating plate of single-layer type is formed of a piece of steel plate. The prior-art sound insulating plate of double-layer type is formed of a piece of steel plate and a layer of synthetic resin such as polyurethane.
In prior-art single or double layer type sound insulating plates, however, the sound insulation effect is equal to only the sum of each layer's sound insulation effect, with the result that the insulation effect is not sufficient in many actual cases. In order to increase the insulation effect, it is necessary to attach a heavy, high-damping material such as rubber to the plate, or to increase the thickness of the plate. As a result, there exists a problem in that it is very troublesome to attach the high-damping material to the plate and further the weight and thickness of the sound insulating plate inevitably increase.
The representative prior-art sound reducing plate will be described in more detail hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.

SUMMARY OF THE INVENTION

With these problems in mind, therefore, it is the primary object of the present invention to provide a sound insulating plate having a high noise-reduction effect without increasing the weight or thickness of the plate, and its manufacturing method.
To achieve the above-mentioned object, the sound insulating plate for insulating audible noise produced from a mechanical part according to the present invention comprises a base plate attached to a mechanism which produces audible noise, a low-density resin layer formed on the base plate, and an external high-density heat-hardened resin layer formed on the low-density resin layer by heating its surface.
To achieve the above-mentioned method, the steps of manufacturing the sound insulating plate for insulating .audible noise produced by a mechanism according to the present invention comprises the step of fixing a low-density thermoplastic resin layer to a base plate, and the step of heating the external surface of the low-density thermoplastic resin layer to a temperature at which the low-density thermoplastic resin layer is heat-hardened.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the sound insulating plate for insulating audible noise produced by a mechanism according to the present invention over the prior art sound insulating plates will be more clearly appreciated from the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings in which like reference numerals designate the same or similar elements throughout the figures thereof and in which;

Fig. I is a perspective view of a prior-art sound insulating plate;
Fig. 2 is an illustration for explaining a manufacturing step for the prior-art sound insulating plate;
Fig. 3 is a longitudinal cross-sectional view of a first embodiment of the sound insulating plate according to the present invention;
Figs. 4 and 5 are longitudinal cross-sectional views for explaining a first manufacturing method for the sound insulating plate according to the present invention;
Fig. 6 is a longitudinal cross-sectional view for explaining a second manufacturing method for the sound insulating plate according to the present invention;
Fig. 7 is a longitudinal cross-sectional view for explaining the first manufacturing method for the modified embodiment of the sound insulating plate according to the present invention;
Fig. 8 is a longitudinal cross-sectional view for explaining a third manufacturing method for the modified embodiment of the sound insulation plate according to the present invention; and
Fig. 9 is a graphical representation showing the sound insulation effect of the sound insulating plate according to the present invention in comparison to the effects of the prior-art single-layer and double-layer sound insulating plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To facilitate understanding of the present invention, a brief reference will be made to a representative prior-art sound-insulating plate, with reference to the attached drawings.
A prior-art sound insulating plate is shown in Fig. 1. This sound insulating plate is formed of a piece of steel plate 1, that is, of a single layer.
As shown in Fig. 2, this single layer sound insulating plate is usually formed by pressing a cold- or hot-worked steel plate 1 with a press machine provided with a male die 2 and a female die 3.
Another prior-art sound insulating plate is a double-layer sound insulating plate having a layer of synthetic resin, such as polyurethane, fixed to the surface of a steel plate, which is usually made by press work.
In these prior-art single- or double-layer sound insulating plates, however, since the total sound insulation effect is equal to only the sum of the effects due to the steel plate and the synthetic resin, the effect of sound insulation is not great. Therefore, in order to increase the sound insulation effect, it is necessary to attach a heavy, high-damping material such as rubber to the plate or to increas. the thickness of the plate itself. As a result, there exists a problem in that it is very troublesome to attach the high-damping material, and, in addition, the weight and thickness of the sound insulating plate inevitably increase.
In view of the above description, reference is now made to a first embodiment of the sound insulating plate for insulating audible noise produced by a mechanism according to the present invention. Fig. 3 shows a first embodiment of the sound insulating plate according to the present invention.
First, the configuration thereof will be described. The reference numeral 10 denotes a steel plate. A layer of low-density thermoplastic resin is fixed to one surface of the steel plate 10. This thermoplastic resin .layer 11 is of a low-density foam type such as polyamide, polyurethane, etc., which will fuse and condense when partially melted or treated with high heat. The reference numeral 12 denotes a high-density external layer, which is formed by heating the external surface of the low-density thermoplastic resin layer 11 to a temperature at which a heat-hardened layer can be formed.
Now, the method of manufacturing such a sound insulating plate will be described.
Figs. 4 and.5 show some manufacturing steps for the sound insulating plate according to the present invention.
First, as shown in Fig. 4, the low-density thermoplastic resin foam layer 11 of predetermined thickness is fixed to the surface of the steel plate 10. Next, as shown in Fig. 5, a heat plate 13 heated with a heater H is brought near the surface of the thermoplastic resin layer 11 with an appropriate clearance, in order to heat, contract, and harden the surface of the thermoplastic resin layer 11. After that, when the heat plate 13 is removed, an external high-density heat-hardened layer 12 will cover the resin layer 11.
In order to obtain an effective audible noise reduction effect as explained later, the thickness and the density of the external heat-hardened layer 12 are adjusted by controlling the temperature of the heat plate 13, the distance between the heat plate 13 and the thermoplastic .resin layer 11, and the length of time for which the heat plate 13 is heated.
According to experimental results, an appropriate specific gravity for the external heat-hardened layer 12 is in the range 0.8 to 1.2 and an appropriate specific gravity for the thermplastic resin layer 11 is in the range of 0.01 to 0.5.
Fig. 6 shows a second manufacturing method of the sound insulating plate according to the present invention, in which it is possible to accurately conform the surface of the layer 12 with a uniform density. In the figure, steel plate 10 provided with the thermoplastic resin layer 11 thereon is first mounted on a supporting base 14, and next the heat plate 13 is heated to a high temperature after being brought into pressure-contact with the surface of the thermoplastic resin layer 11. In this case, it is possible to form the external heat-hardened layer 12 quickly.
Fig. 7 shows a modified sound insulating plate according to the present invention, and Fig. 8 shows a third manufacturing method for the modified sound insulating plate according to the present invention.
In this embodiment, the external heat-hardened layer 12 covering the thermoplastic resin layer 11 is formed in an appropriate shape so as to fit the mechanism to be insulated.
As shown in Fig. 7, when an irregular profile is required for the surface of the external heat-hardened layer 12, the irregular external layer 12 can be formed by bringing a heat plate 13 having a plurality of projections 15 near the surface of the thermoplastic resin layer 11, in order to heat, partially melt, and harden the layer 11, and after that, separating the heat plate 13 from the newly-formed heat-hardened layer 12.
When it is necessary to accurately, conform the surface of the layer 12 with a uniform density, as shown in Fig. 8, the steel plate 10 with the thermoplastic resin layer 11 fixed thereon is first mounted on a supporting base 14 and a finishing model plate 20 having projections 19 is fixed to the lower surface of the heat plate 13, and next the heat plate 13 is heated to a high temperature after being brought into pressure contact with the surface of the thermoplastic resin layer 11.
When the sound insulating plate is formed in such a way that the heat plate 13 or the finishing model plate 20 is formed into a shape similar to that of the surface of a mechanism to which the sound insulating plate is to be attached, for instance, when the sound insulating plate is formed into the same shape as that of an engine, even though the profile of the engine is irregular, it is possible to fit the sound insulating plate onto the engine with an appropriate constant clearance therebetween; that is, it is possible to muffle audible noise produced by the engine without deteriorating engine performance.
Fig. 9 shows the sound insulation curve of the sound insulating plate c according to the present invention, and includes the curves for the 'prior-art single-layer plate a and double-layer plate b for comparison.
In this figure, the abscissa represents the frequency (f KHz) and the ordinate represents the effect of sound insulation effect (dB). Therefore, in the figure, the greater the numeral value of sound insulation dB, the higher the sound insulation effect.
In the case of the characteristic curve a of the prior-art single-layer sound insulating plate, the sound insulation effect is about 20 dB at a frequency of 0.5 KHz and is about 40 dB at 5 KHz. The sound insulation effect between 0.5 and 5 KHz is roughly proportional to frequency, in accordance with inertial effects. To facilitate comparison of the sound insulation effects, the sound insulation effect values at a frequency of 5 KHz will. referred to hereinafter as the representative values. The representative value of the steel plate is X₅ = 40 dB, as can be clearly understood from Fig. 9.
As shown by the characteristic curve b, in the case of the prior-art double-layer sound insulating plate in which a synthetic resin layer is formed on a steel plate, the sound insulation effect is about 20 dB at a frequency of 0.5 KHz, but is about 50 dB at 5 KHz. The sound insulation effect between 0.5 KHz and 5 KHz is roughly proportional to frequency, similar the characteristic curve a. The representative value of the double-layer plate is X_s + Y_s = 40 dB + 8 dB = 48 dB.
That is to say, an additional sound insulation effect of Y₅ (= 8 dB) is obtained at frequencies near 5 KHz, in comparison to the sound insulation effect X₅ (= 40 dB) obtained when only a steel plate is used. This is due to the additional sound damping effect Y due to the synthetic resin; that is, the sound waves are attenuated as they pass through the synthetic resin. Therefore, as compared with the case of the single-layer sound insulation plate, the sound insulation effect increases by 8 dB.
In the case of the sound insulating plate according to the present invention, the sound insulation effect is about 27 dB at a frequency of 0.5 KHz, but is about 62 dB at 5 KHz. The sound insulation effect between 0.5 KHz and 5 KHz is roughly proportional to frequency, similar to the characteristic curves a and b. In this case, the representative value of the insulating plate of the present invention is X₅ + Y₅ + Z _{5 =} 40 dB + 8 dB + 14 dB = 62 dB.
That is to say, the high-density thermoplastic heat-hardened resin layer formed by applying heat to the low-density thermoplastic resin layer disposed on the steel plate results in an additional sound insulation effect Z₅ (= 14 dB at a frequency of 5 KHz).
In the case of the sound insulating plate .according to the present invention, in addition to the sound damping effect due to the low-density foam thermoplastic resin layer, which is roughly the same as that Y due to the synthetic resin layer on the prior-art double-layer sound insulation plate, there is an additional sound insulation effect Z based on cover effect due to the fact that sound waves within the thermoplastic resin layer are repeatedly reflected and attenuated between the high-density external layer and the steel-plate. Therefore, in spite of having roughly the same thickness and weight as that of the prior-art double-layer sound insulation plate, the sound insulation plate of the present invention has an improved sound insulation effect.
As described above, in the sound insulation plate according to the present invention, since there is a low-density thermoplastic resin layer having a predetermined thickness on the surface of a metal plate, and further since there is a high-density external heat-hardened layer - on the low-density thermoplastic resin formed by heating the external surface of the thermoplastic resin layer, in addition to the sound insulation effect or sound damping effect due to the low-density thermoplastic resin layer, there exists another sound insulation effect based on a covering effect due to the external heat-hardened layer such that the sound waves of noise within the thermoplastic resin layer are repeatedly reflected and attenuated between the high-density external heat-hardened layer and the steel .plate, thus improving sound insulation effect compared with the case in the prior-art sound insulating plate. Further, since the sound insulation effect of the plate according to the present invention is great, it is possible to reduce the thickness and the weight of the sound insulation plate.
It will be understood by those skilled in the art that the foregoing description is in terms of preferred embodiments of the present invention wherein various changes and modifications may be made without departing from the spirit and scope of the invention, as set forth in the _appended claims.

Claims

1. A sound insulating plate for insulating audible noise produced by a mechanism, which comprises:

(a) a base plate;

(b) a low-density thermoplastic resin layer fixed to said base plate; and

(c) a high-density heat-hardened resin layer on the surface of said low-density thermoplastic resin layer, said high-density resin layer being formed by heating said low-density resin layer.

2. A sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 1, wherein said low-density thermoplastic resin is a foam resin.

3. A sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 2, wherein said foam resin is polyamide.

4. A sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 2, wherein said foam resin is polyurethane.

5. A sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 1, wherein the specific gravity of said low-density . thermoplastic resin layer lies between about 0.02 and 0.5.

6. A sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 1, wherein the specific gravity of said external high-density heat-hardened resin layer lies between about 0.8 and 1.2.

7. A method of manufacturing a sound insulating plate for insulating audible noise produced by a mechanism, which comprises the following steps of:

(a) forming a low-density thermoplastic resin layer on a base plate; and

(b) heating the external surface of the low-density thermoplastic resin layer to a temperature at which the low-density thermoplastic resin layer is heat-hardened.

8. A method of manufacturing a sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 7, wherein said step of heating the external surface of the low-density thermoplastic resin layer is achieved by bring a heated plate having a surface which is an approximate reflection of the desired contour of the external surface of the sound insulating plate into close proximity to the external surface of the low-density resin layer.

9. A method of manufacturing a sound insulating plate for insulating audible noise produced by a mechanism as set forth in claim 8, wherein the heated plate is brought into close contact with the external surface of the low-density layer.