กก
1 Introduction
With the growing awareness of environmental protection, noise pollution
problems more and more attention. In recent years, the construction of
expressway, urban viaduct and urban light rail has developed rapidly.
The number of urban motor vehicles has increased dramatically, and the
problem of traffic noise has become more and more serious. It has become
one of the most serious and widespread pollution affecting people's
lives. Among the various measures to combat traffic pollution, the
establishment of road noise barriers is an effective method, has been
widely used in developed countries. China's application in this area is
still relatively small, the use of results is not ideal, mainly for the
sound-absorbing material is not high sound absorption, sound absorption
properties of instability and the durability of the material in the
field is not high, the production process is complex, higher. At
present, in many large cities in the construction or proposed light rail
project in the design of the noise barrier. Therefore, the development
of a highly efficient sound absorption, high durability and low cost of
new road sound-absorbing screen special sound-absorbing material is of
great significance.
2 sound absorption principle 2.1 sound absorption evaluation sound
can be calculated according to the following formula: LI = 10lg (I / I0)
Where: LI - sound intensity level, dB; I - a point of sound intensity, W
/ m2; I0 - reference sound Strong, 10 -12 W / m2. Sound intensity is the
sound energy per unit area, commonly used sound intensity level to
represent the sound size. When the sound is absorbed by 1/2, the sound
intensity decreased by 1/2, from the above equation we can see the sound
intensity level reduced by about 3dB; sound is absorbed 90%, the
intensity level reduced 10dB. The human ear can generally feel the sound
changes the minimum value of 3 ~ 5dB, so if the absorption of
sound-absorbing material is not high efficiency, there is no use of
significance. Sound absorption of materials with sound absorption
coefficient (the sound energy absorbed by the material and the ratio of
all the sound energy), it is related to the sound frequency, engineering
generally take 125,250,500,1000,2000,4000Hz and other six frequencies
Under the sound absorption coefficient that the material's sound
absorption performance. 2.2 Sound absorption mechanism Sound-absorbing
material can be divided into porous, leaving the cavity of the plate,
film and flexible materials and other types of sound absorption
mechanism vary. The sound absorption performance of the porous material
is achieved by a large number of interconnected microvoids and voids.
When the sound waves along the pore or gap into the material, the
excitation of the pores or gaps in the air vibration, air and the hole
wall friction heat conduction, due to the viscosity of the air in the
pores or gaps in the corresponding viscous Resistance, so that the
energy of the vibration of the air is constantly being converted to heat
and consumption, the sound can be reduced, so as to achieve the purpose
of sound absorption. The pore structure is required to be fine and
interconnected. 2.3 Sound absorption structure Sound absorption
structure can produce a higher sound absorption value, the main use of
this cavity resonant sound absorption structure and strong sound
absorption structure. 2.3.1 Cavity Resonance Sound-absorbing Structure
The sound absorption mechanism of this structure is that when the
incident sound frequency and the system natural frequency are equal, the
main column in the aperture will vibrate violently due to the resonance,
and the air column and the hole side wall friction will consume Sound
energy. 2.3.2 Strong sound absorption structure Strong absorption
structure that is cleavable sound absorption structure, the structure at
a relatively low frequency can produce more than 0.99 absorption
coefficient. The use of cutting-edge sound-absorbing wedge structure of
the sound absorption performance is not, but it is conducive to product
stability and durability.
3 Experimental and analysis 3.1 The use of
resonant sound-absorbing structure Expanded perlite particles on the
surface there are many semi-open holes, which constitute the resonant
cavity sound absorption structure, and thus its own strong sound
absorption. Part of the water absorbed by the expanded perlite particles
is rapidly extruded and some of the slurry is concentrated near the
point of contact with the particles during the mixing, extrusion and
curing processes with the cement. Part of the orifice was cement sealed,
lost part of the resonance cavity sound absorption function. Therefore,
to meet the strength requirements under the premise of the cement
content to be as low as possible. In this study, gas-generating agents
were used to improve the sound absorption properties of the materials.
(2) due to the higher hydration temperature of the cement and the
formation of the pore structure, the pore size of the cement slurry can
be improved by the expansion of the cement slurry, (3) The slurry is
enriched in the vicinity of the particle contact point, and then the
strength is increased.
The micropores produced by the gassing agent and their openings vary in
size, resulting in a wider frequency range for sound absorption (see
Figure 2). Figure 2 shows that the introduction of gas bubbles,
significantly improved the following 1000Hz the following low-frequency
sound absorption, which is common for the ordinary gas-breathing agent;
Expanded perlite products are generally difficult to achieve. In the
porous sound-absorbing material behind the cavity, can produce a similar
cavity resonance absorption structure of the sound absorption effect,
effectively improve the absorption of low-frequency sound, the
experimental results shown in Figure 3. Figure 3 behind the cavity of
the sound-absorbing material on the absorption coefficient of 1 - behind
the paste real; 2-cm behind the back of this simple process to enhance
the sound absorption effect is remarkable, can be composite special
sound-absorbing material or its Paste the appearance of the substrate
design to achieve. 3.2 The use of sound-absorbing wedge structure of the
sound-absorbing surface of the products designed to wave-shaped, can
form a sound-absorbing wedge structure, cutting the tip of the waves to
highlight the strong sound absorption of the sharp wedge effect, but
Structure of the firm. The enhanced sound absorption effect shown in
Figure 4. Figure 4, the structure of the wedge-enhanced sound absorption
1-tip wall structure; 2-level surface can be seen from Figure 4, the
experimental design of the wedge structure can be produced from 500Hz or
more close to a strong sound absorption, and In the low-frequency also
has some enhanced sound absorption. If the sound-absorbing structure
density gradually increased from outside to inside, but also play the
role of sound-absorbing wedge. The actual production by the paste facing
the sound surface compression, you can make the structure from the sound
surface to the paste surface gradually dense, similar to the sharp split
of the sound-absorbing structure. 3.3 pore structure of the control
particle size of the formation of different pore sizes of different
sizes to form a different air flow resistance. The effect of particle
size on sound absorption is shown in Fig. The particle size of 1 ~ 3mm;
2-particle size of 1 ~ 5mm; 3-particle size of 3 ~ 5mm can be seen when
the particle size of 1 ~ 3mm when the best sound absorption. Particle is
too fine, its own cavity resonant sound absorption structure is reduced,
and the need to increase the amount of cement, sound absorption
performance will be reduced. Excessive or too small particle sizes do
not produce optimum porosity. Adjust the molding compression ratio is an
effective means to control the air flow resistance. The influence of
different compression ratio on the sound absorption coefficient is shown
in Fig. Figure 6 compression ratio on the absorption coefficient of 1 -
compression ratio of 1.5; 2 - compression ratio 2; 3 - compression ratio
2.2 compression ratio in the general range of major low - frequency
impact. The compression ratio is too large to make the sound wave more
smooth through; too small is not conducive to the sound waves into the
loss of porous materials, sound absorption characteristics. Experimental
results show that the compression ratio of 2.0 can produce the highest
sound absorption value. 4 Conclusion (1) the use of gas-generating agent
and through a special exterior design can form a resonant cavity sound
absorption structure. (2) According to the strong sound-absorbing
structure, the wave-type sharp-split sound-absorbing structure is
designed, and the similar wedge structure can be obtained by the
pressing process. (3) By controlling the particle size of raw materials
and molding the compression ratio and other means, can form the most
conducive to enhance the sound absorption of the porosity. (4) According
to the principle of material preparation, the sound absorption
coefficient of the expanded perlite products can reach 0.7 or above by
combining various sound absorption structures, and the sound absorption
coefficient indexes of the six frequencies are reached. The
international advanced level.
.
.
.