JPH0211320A - Sound absorbing material made of foamed metal - Google Patents

Abstract

PURPOSE:To improve sound absorbing effect by laminating a number of air- permeable thin sheets wherein isolated cells of a foamed metal are used as its penetrated holes and thereby forming a sound absorbing material. CONSTITUTION:Temp. of a molten aluminum 12 is kept at 700 deg.C and a stirrer having a hollow stirring shaft is slantwise immersed in the molten aluminum. TiH2 as a foaming agent is added in the molten aluminum through the hollow stirring shaft and is thoroughly mixed. The molten aluminum and a mold are heated up to 720 deg.C to decompose the foaming agent mixed with the molten aluminum and to generate gas. While some of the foaming still remains, the molten aluminum is cooled to obtain a foamed metal. The porosity of the obtd. foamed metal is 90% and the mean diameter of the included cells therein is 2.6mm. The obtd. foamed metal is cut in a thickness of 2mm to obtain air- permeable thin plates 12 wherein isolated cells are used as their perforated holes 10. Ten sheets of these air-permeable thin sheets 12 are laminated to form a sound absorbing material 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sound absorbing material made of foamed metal and having improved sound absorption properties by laminating a large number of thin foamed metal plates having through holes.

[Prior Art] Foamed metal is a porous metal that contains countless air bubbles, and since it has sound absorbing properties, its use as a sound insulating material or a sound absorbing material has been considered from an early stage. However, since the cells contained in the metal foam are closed cells and lack air permeability, the sound absorption properties have not always been sufficient.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems in sound absorption properties when using foam metal as a sound absorption material, and provides a sound absorption material made of foam metal with excellent sound absorption properties. The purpose is to

[Means for Solving the Problems] As a result of extensive research into the sound absorption properties of metal foam, the inventor discovered that the sound absorption effect is significantly improved when air permeability is imparted to metal foam, and the present invention was completed. did.

The gist of the metal foam sound absorbing material of the present invention is that it is made by laminating a large number of air permeable thin plates with the closed cells as through holes by cutting the foam metal into a thickness thinner than the diameter of the closed cells it contains. .

Foamed metals include not only aluminum but also Zn, Sn, and Pb.
A method for producing zero foam metal that can use low melting point metals such as Nato and high melting point metals such as Fe and Ni is as follows:
Powder metallurgy involves heating a mixture of metal powder and foaming agent to a temperature above the melting point of the metal to foam it. Various methods can be used, such as the molten metal direct mixing method, which involves directly adding a foaming agent to the molten metal to cause foaming.

The amount and size of the bubbles contained in the foamed metal are determined by controlling the viscosity in the thickening process that is performed prior to foaming the molten metal;
It can be freely controlled by the amount of blowing agent mixed into the molten metal. The suitable diameter of the bubbles is 1 to 3 rings, and the pore ratio is preferably 80 to 90%. If the diameter of the bubbles is less than 11, no through holes will be formed when the thin plate is manufactured. This is because if the number of air bubbles exceeds 31, the sweat absorbency deteriorates. In addition, the void ratio is 80
This is because if the pore ratio is less than 90%, the number of through holes will be insufficient, and if the pore ratio exceeds 90%, the sound absorption property will deteriorate.

The thickness of the breathable thin plate cut out from the foamed metal is made thinner than the diameter of the closed cells contained in the foamed metal.

If the bubble diameter is 2 to 3 mm, the thickness of the breathable thin plate should be 1 to 3 mm.
2m+* is appropriate.0 If the thickness of the breathable thin plate is less than 1 mm, the thin plate has insufficient strength and is easily broken.
This is because if the number of rings exceeds 2, a sufficient number of through holes will not be secured. The number of breathable thin plates is preferably about 10 to 15. If the number is less than 10, the sound absorption effect will be insufficient.
This is because if the number exceeds 15, breathability will be inhibited.

[Function] When a sound-absorbing material is formed by laminating a large number of air-permeable thin plates with through-holes formed of closed cells of foamed metal, a large number of fine passages having intricately winding paths pass through the sound-absorbing surface. By connecting these fine passages,
The foamed metal laminate exhibits a high sound absorption effect, and a resonant sound absorption effect can be expected due to the interference effect caused by diffused reflection on the walls of minute passages.

[Example] A preferred embodiment of the present invention will be described below with reference to the drawings.

5 kg of aluminum was melted in a melting furnace and poured into a ladle. 80 as a thickener to the molten aluminum in the ladle.
L kg of A I 203 finely ground to 0 mesh was added and sufficiently stirred to thicken the mixture. At this time, the temperature of molten aluminum was 750°C.

Subsequently, molten aluminium 11 was poured into a tundish with a spherical bottom. The temperature of molten aluminum 12 is set to 70
A stirrer with a hollow stirring shaft and a blade attached to the tip was kept at 0°C and immersed in the molten aluminum at an angle. 05kg of TiHzo as a foaming agent was added to the molten aluminum through the hollow stirring shaft, and the stirrer was turned off. The blowing agent and molten aluminum were thoroughly mixed by rotation.

Next, molten aluminum was poured into a mold that had been previously heated to 500°C. At this time, since the molten aluminum was sticky due to the thickening process, it was squeezed out of the tundish by gas pressure.

Next, the molten aluminum in the mold is heated to 72°C along with the mold.
The temperature was raised to 0° C. and held for 7 minutes, and the molten aluminum was cooled to obtain a foamed metal while some zero foaming, which was caused by decomposing the foaming agent mixed in the molten aluminum and generating gas, still existed. The porosity of the obtained metal foam was 90%, and the average diameter of the bubbles contained was 2.6.

The obtained foamed metal was cut into a thickness of 21 to obtain an air permeable thin plate 12 with through holes 10 made of closed cells, as shown in FIG. A sound absorbing material 14 was formed by layering 10 pieces of this air permeable thin plate 12 as shown in FIG.

In order to test the sound absorption effect of this sound absorbing material 14, a certain sound source such as a generator was shielded with a sound insulating wall using this sound absorbing material 14, and the sound pressure level at a certain distance from the sound insulating wall was measured. For comparison, the same sound source was shielded with a soundproof wall using a conventional foamed metal plate with the same thickness and no air permeability that contained closed cells, and the sound pressure level at a certain distance from the soundproof wall was measured. was measured.

When the measured sound pressure level was compared between the sound absorbing material 14 of this embodiment and a conventional foamed metal, the sound pressure level of the sound absorbing material 14 of this embodiment was about 20% lower than that of the conventional one. It was confirmed that the sound absorption effect was excellent.

[Effects of the Invention] As explained above, the sound absorbing material made of foamed metal TI% of the present invention has the following properties:
It is characterized by laminating a large number of thin air-permeable plates with the closed cells as through-holes by cutting the foamed metal to a thickness thinner than the diameter of the closed-cells it contains, and the thin-air-air-permeable plates are laminated. By providing a large number of fine passages with intricately winding paths formed by holes, there is an excellent effect of exhibiting a high sound absorption effect.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the breathable thin plate, and FIG. 2 is a sectional view of the sound absorbing material. 10. - Through hole, 12... Thin plate, 14. Sound absorbing material

Claims (1)

[Claims] (1) A sound-absorbing material made of metal foam, characterized in that it is made by laminating a large number of thin air-permeable plates with closed cells as through-holes, which are formed by cutting the metal foam to a thickness thinner than the diameter of the closed cells it contains.