Sound absorption
The sound wave is partly reflected and partially projected into the foam aluminum at the interface of the foam aluminum. If the surface of the foam aluminum is not closed, the destructive wave will be destroyed. Aluminum foam, especially open cell aluminum foam, can scatter, interfere and diffuse inside the material when the sound is transmitted into the foam aluminum, causing the internal skeleton to vibrate. Acoustic waves in the open cell aluminum foam, many times beautiful air pressure through the channel. When airflow passes through the channel, air rubs against the wall of the hole and forms turbulence. Therefore, the sound energy is partly converted into heat energy and consumed through heat transfer, thus playing the role of sound absorption. The power consumption factor of aluminum foam is one order of magnitude higher than that of aluminum. When the pore size of open cell aluminum foam is between 0.1--0.5mm, its sound absorption effect is optimal.
The sound absorption property of foamed aluminum can be measured by sound absorption coefficient. The greater the absorption coefficient, the better the sound absorption performance. The sound absorption property of foam aluminum mainly depends on the pore characteristics, and the sound absorption performance of the through hole is better than that of the nostril. The larger the porosity and the smaller the aperture, the better the sound absorption performance. When the closed cell aluminum foam is extruded, there will be enough cracks and other hole wall defects. In this way, closed cell aluminum foam also has better sound absorption properties.
Sound absorption and shock absorption is a very important research field in automobile industry. The use of foam aluminum can make the noise emitted by the car itself not spread to the surrounding environment, and the noise from the external sound source is isolated outside the vehicle.
| Sound absorption | |
| Demand for Noise Reduction of Submarine Muffler and Missile Destroyer |
The sound absorption box made of foam aluminum acoustic board and the cavity behind it is installed in the engine room of the submarine, which can reduce noise by more than 20 decibels, and is conducive to making mute submarine. Missile destroyers and other ships also need to use foam aluminum acoustic board to reduce noise and make partition walls in the engine room. |
| Noise Reduction in Highway Tunnels | The 10mm thick perforated foam aluminum sound absorbing board is used to make noise and noise reduction wall around highway and river tunnel, and 60mm thick cavity behind can effectively absorb low-frequency noise generated by vehicles. The foam aluminum material keeps good sound absorption and noise reduction effect without moisture absorption, and the side wall of foam aluminum can absorb impact kinetic energy and vibration wave to protect the tunnel inner wall. Aluminum foam material is non corrosive, non burning and safe to use. |
| Noise Reduction of Submarine Tunnel | The 10mm thick perforated foam aluminum sound absorbing board is used to create the sound absorption and noise reduction enclosure of the undersea tunnel, with 60mm thick cavity behind it. The moisture in the subsea tunnel is large, and the foam aluminum material does not absorb moisture. It still maintains good sound absorption and noise reduction effect, and the side wall of the foam aluminum can absorb impact kinetic energy and vibration wave to protect the inner wall of the tunnel. The surface of the foam aluminum sound absorbing board can be treated by nickel plating and plastic spraying to resist seawater corrosion. |
| Muffler for Ventilation Port of Metro Tunnel | The sound absorption grid made of foam aluminum sound absorbing board can effectively reduce the noise of tunnel ventilation. |
| Making Mufflers | The muffler of freight cars, passenger cars and cars is made of aluminum foam sound absorbing board, and the aluminum foam sound absorbing board can be applied to the exhaust temperature at 500~600 degrees after fire treatment. The noise reduction effect is 2-3 times of that of the expanded impedance muffler and the parallel resonance muffler, and the weight is reduced by about 1/3. |
| Noise Reduction in Engine Chamber of Ordinary Tugboat and Freight Ship | The sound absorption lining of the engine room is made of aluminum foam sound absorbing board. The thickness of the aluminum foam sound-absorbing board is 10mm, and the cavity behind it is 30 to 60mm, which can reduce noise by 20 dB or more. |
| Making Electrical Cabinet | Using aluminum foam sandwich panels (0.5mm aluminum plate /5 ~ 10mm foam aluminum plate /0.5mm aluminum plate) to produce generators, motors, frequency converters, central air conditioners and other electrical appliances that produce noise and electromagnetic wave equipment, it can reduce noise by more than 20 decibels, shielding electromagnetic waves by more than 90 dB. |
| Make sound absorption lining of metro station | The side wall and the top sound absorbing board of the subway station are made of perforated foam aluminum sound absorbing board. The thickness is 10mm, and the 20mm thick cavity behind them is maintained. Even in the damp environment of the subway station, the sound absorption and noise reduction effect is still better than that of other sound absorbing materials, and the noise reduction effect is more than doubled. |
| Making High Speed Railway Sound-proof Screen | Production of high-speed railway noise barrier, height of 2800mm, perforated aluminum sound absorbing board thickness of 10mm, behind the 20mm thick air layer, the rear plate is galvanized steel. The inner side of the sound barrier is aluminum foam bare surface, which can be sound-absorbing, and the whole wall can be soundproof, so as to achieve the effect of high efficiency and noise reduction. After the aluminum foam is drenched by rain water, the noise reduction function will not be reduced. Foam aluminum can absorb energy and shock, and the rivet will not loose after the train vibrate, so it will be safe for a long time. |
| Making Sound Absorbing Lining for Buildings | Using foam aluminum sound absorbing board (thickness 10mm) to make recording room, dubbing room, concert hall, conference hall, stadium and gymnasium, etc., to avoid noise generated inside the lining, and 20 ~ 40mm thickness cavity behind the aluminum foam sound absorbing board. The noise and noise reduction effect is good. |
| Making Absorbing Wall of Swimming Pool | Because of the high humidity in the swimming pool, the sound absorption ability of ordinary sound-absorbing materials is greatly reduced after absorbing water. Noise reduction in swimming pools has been a long-standing problem in the construction industry. The sound absorption rate of the perforated foam aluminum sound absorbing board is high, and the sound absorption rate is not reduced under the moist environment, and the noise reduction effect is good. The thickness of the aluminum foam sound absorbing board is 10mm, and 20mm thick cavity is set behind it. |
| Making Soundproof Floor | Building insulation is a difficult problem. 5mm thick plank /10 to 15mm thick foam aluminum floor composite floor is adopted, and the sound insulation between floors is more than 20 decibels. |
| Making Road Noise Barrier | The sound barrier of the elevated road and viaduct can be effectively reduced by using the foam aluminum acoustic board. The thickness of the aluminum foam sound-absorbing board is 10mm, and the 60mm thick cavity behind it is 2800mm, which is two times higher than that of the ordinary louvered sound barrier. |
