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Sound absorbing materials commonly used for sound absorption

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Sound absorbing materials commonly used for sound absorption

Classification:
Technical Knowledge
Source:
2018/11/14 15:38
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[Abstract]:
Glass wool is a category of glass fibers and is an artificial inorganic fiber
Glass wool is a category of glass fibers and is an artificial inorganic fiber. Natural minerals such as quartz sand, limestone and dolomite are used as the main raw materials, and some raw materials such as soda ash and borax are melted into glass. In the melted state, the flocculent fine fibers are blown by an external force, and the fibers and the fibers are three-dimensionally intersected and entangled with each other to exhibit many fine gaps. This gap can be seen as a void. Therefore, glass wool can be regarded as a porous material and has good heat insulation and sound absorption properties.
 
Glass wool is a material that melts glass into a cotton-like material. Its chemical composition is glass. It is an inorganic fiber. It has good shape, small bulk density, thermal conductivity, thermal insulation, good sound absorption and corrosion resistance. Decorative and chemical properties are stable.
 
The main components of mineral wool are blast furnace slag, phosphate slag, fly ash and so on.
 
 
Centrifugal glass wool
 
The inner fiber of the centrifugal glass wool is fluffy and interlaced, and there are a lot of tiny pores. It is a typical porous sound absorbing material and has good sound absorption characteristics. Centrifugal glass wool can be made into wallboard, ceiling, space sound absorber, etc. It can absorb the sound energy in the room in a large amount, reduce the reverberation time and reduce the indoor noise.
 
The sound absorption characteristics of centrifugal glass wool are not only related to thickness and bulk density, but also related to factors such as cover material and structural structure. In the construction application, it is also necessary to take into consideration various aspects such as cost, beauty, fire prevention, moisture resistance, dust, and aging resistance.
 
Centrifugal glass wool is a porous sound absorbing material with good sound absorption properties. The reason why centrifugal glass wool can absorb sound is not because of the rough surface, but because of the large number of tiny pores and pores that communicate inside and outside. When sound waves are incident on the centrifugal glass wool, sound waves can enter the inside of the material along the pores, causing vibration of air molecules in the gap. Due to the viscous resistance of the air and the friction between the air molecules and the pore walls, the acoustic energy is converted into heat energy and lost.
 
Centrifugal glass wool has good sound absorption performance for high frequency in sound. The main factors affecting the sound absorption performance of centrifugal glass wool are thickness, density and air flow resistance. Density is the weight of material per cubic meter. The air flow resistance is the ratio of the air pressure to the air flow rate on both sides of the material per unit thickness. Air flow resistance is the most important factor affecting the sound absorption performance of centrifugal glass wool. The flow resistance is too small, indicating that the material is sparse, the air vibration is easy to pass through, and the sound absorption performance is degraded; the flow resistance is too large, indicating that the material is dense, the air vibration is difficult to be introduced, and the sound absorption performance is also lowered. For centrifugal glass wool, the sound absorption performance has the best flow resistance. In actual engineering, it is difficult to measure the air flow resistance, but it can be roughly estimated and controlled by thickness and bulk density. 1. As the thickness increases, the mid-low frequency sound absorption coefficient increases remarkably, but the high frequency does not change much (high-frequency absorption is always large). 2. The thickness is constant, the bulk density increases, and the sound absorption coefficient of the middle and low frequency also increases;
 
However, when the bulk density is increased to a certain extent, the material becomes dense, the flow resistance is greater than the optimum flow resistance, and the sound absorption coefficient decreases. For centrifugal glass wool with a bulk density of more than 5 cm and a bulk density of 16 kg/m3, the low frequency 125 Hz is about 0.2, and the sound absorption coefficient of medium and high frequency (>500 Hz) is already close to one. When the thickness continues to increase from 5 cm, the sound absorption coefficient of the low frequency gradually increases. When the thickness is more than 1 m, the sound absorption coefficient of the low frequency 125 Hz will also be close to 1. When the thickness is constant and the bulk density is increased, the low-frequency sound absorption coefficient of the centrifugal glass wool will also increase continuously. When the bulk density is close to 110kg/m3, the sound absorption performance reaches the maximum value, 50mm thick and the frequency is close to 0.6-0.7 at 125Hz. When the bulk density exceeds 120kg/m3, the sound absorption performance decreases, because the material becomes dense, and the mid-high frequency sound absorption performance is greatly affected. When the bulk density exceeds 300kg/m3, the sound absorption performance is greatly reduced. The thickness of sound-absorbing glass wool commonly used in architectural acoustics is 2.5cm, 5cm, 10cm, and the bulk density is 16, 24, 32, 48, 80, 96, 112kg/m3. Centrifugal glass wool of 5 cm thick and 12-48 kg/m3 is usually used.
 
The sound absorption performance of centrifugal glass wool is also closely related to the installation conditions. When there is an air layer behind the glass wool board, the sound absorption effect of the glass wool board having the same thickness and no air layer is similar. In particular, the sound absorption performance of the middle and low frequency is much higher than that of the material on the hard bottom surface, and the sound absorption coefficient will increase as the thickness of the air layer increases, but the effect is not obvious after increasing to a certain value.
 
The use of glass wool stacks of different bulk densities together to form a form of increasing bulk density allows for greater sound absorption. For example, a sound absorption effect of a 2.5 cm thick 24 kg/m3 cotton board and a 2.5 cm thick 32 kg/m3 cotton board is better than a 5 cm thick 32 kg/m3 cotton board. The 24kg/m3 glass wool board is made into a 1m-long triangular tip, and the material density increases gradually, and the average sound absorption coefficient can be close to 1.
 
In the construction of centrifugal glass wool, the surface is often attached with a certain sound-permeable finish, such as plastic film less than 0.5mm, metal mesh, window screen, fireproof cloth, glass cloth, etc., can basically maintain the original sound absorption characteristics. Centrifugal glass wool has excellent properties such as fireproofing, heat preservation and easy cutting. It is one of the most commonly used materials for building sound absorption. However, since the surface of the centrifugal glass wool is not decorative, and there is a fiber sprinkling, it is necessary to make various sound absorbing members concealed. The most commonly used and lowest cost construction is the ceiling of a perforated gypsum board or a perforated panel wall filled with centrifugal glass wool. When the perforation rate is greater than 20%, the sound absorption performance of the centrifugal glass wool can be fully utilized. . In order to prevent the glass wool fiber from spilling out, it is necessary to attach a layer of a sound-permeable fabric such as a non-woven fabric or a mulberry paper to the back of the perforated plate, or to wrap the glass wool with a glass cloth, a plastic film or the like. Panels similar to perforated gypsum board are perforated metal sheets (such as aluminum sheets), perforated boards, perforated fiber cement boards, perforated mineral wool boards, and the like.
 
The glass wool board can be processed into a sound absorbing ceiling board or a sound absorbing wall board. Generally, 80-120kg/m3 glass wool board is cured by glue curing, and the fire-proof sound-permeable fabric is formed to form a sound-absorbing wall board which is both beautiful and convenient to install. The common size is 1.2m×1.2m, 1.2m×0.6m, 0.6 m × 0.6 m, thickness 2.5 cm or 5 cm. There is also a sound absorbing ceiling plate formed by directly spraying a sound-permeable decorative material on the surface of the glass wool of 110 Kg/m3. Whether it is a glass wool sound absorbing wall panel or a sound absorbing ceiling panel, it is necessary to use a high bulk glass wool and a certain strengthening treatment to prevent the sheet from being deformed or too soft. This type of building material has good decorative properties and retains the good sound absorption characteristics of centrifugal glass wool. The noise reduction coefficient NRC can generally reach above 0.85.
 
In a large space such as a gymnasium or a workshop, in order to absorb noise and reduce noise, a sound absorbing body using centrifugal glass wool as a main sound absorbing material is often used. The sound absorbing body can be made into a plate shape, a column shape, a cone or other shaped body as required. The sound absorbing body is filled with centrifugal glass wool, and the surface is wrapped with a sound-permeable surface layer. Since the sound absorbing body has a plurality of surface sound absorbing sounds, the sound absorbing efficiency is high.
 
In the road sound insulation barrier, in order to prevent noise reflection, it is necessary to take sound absorption measures on the side facing the vehicle, and often also use centrifugal glass wool as a filling material and a barrier plate whose surface layer is a perforated metal plate. In order to prevent the glass wool from absorbing water and moisture outside, it is sometimes wrapped with PVC or plastic film.