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Excessive noise mainly causes damage to the human auditory system. According to data introducers, if they are in a noise environment of 85 decibels for a long time, they will cause hearing loss; while noise above 90 decibels may cause deafness or severe deafness. The short-term limit of the human ear to strong noise is about 125 decibels. Low-frequency noise (such as air compressors and low-speed driving sounds of automobile tractors) with audio frequencies below 500 Hz, medium-frequency noise with audio frequencies of 500 to 1000 Hz, and high-frequency noise with audio frequencies above 1000 Hz. The human hearing field is in the range of 20 to 20,000 Hz and is most sensitive to sounds around 1000 Hz.
The noise generated by concrete construction machinery can be divided into noise of power machine (engine, motor, oil pump, etc.) and noise of transmission and actuator. Several noise control measures are described below.
(1) Sound insulation and noise reduction technology: The sound insulation and noise reduction technology mainly uses the sound insulation cover to isolate the sound source from the outside world. The soundproof cover is generally lined with a damping layer or a damping paint to enhance the sound insulation effect. For the heat engine, in order to meet the needs of heat dissipation and ventilation, there must be an air inlet or an exhaust port. At this time, a muffler should be installed on the air inlet and the exhaust port to maintain the sound insulation effect. In this way, noise can generally be reduced by 15~30 decibels.
(2) Vibration isolation and noise reduction technology: Noise is often caused by vibration of machines or fluids. Therefore, slowing down vibration is a more cost-effective method of noise reduction. For example, the noise generated by the operation of the oil pump contains hydraulic noise and mechanical noise. Hydraulic noise is generated by periodic pulsations of pressure flow when holes and liquids in the liquid are discharged; mechanical noise is caused by unbalanced rotating parts, poor bearing, and component resonance.
Generally, hydraulic noise is the main component of pump noise, which increases as the pump speed increases, and the noise frequency increases as the pump speed increases. Improved design of the pump and hydraulic system is the fundamental way to reduce hydraulic noise. An acoustic enclosure can also be used. When the mechanical vibration generated by the power component and its support is obvious, the vibration isolation and noise reduction technology can achieve significant effects.
Rubber damping pads (blocks), springs, and cork are generally used as damping components, and more advanced gas-liquid damping methods such as oil and gas springs. The installation method also has a great influence on the vibration isolation effect. For example, the cab of the Volvo truck uses a double spring damping plus a lined sound absorbing material to achieve a noticeable mute effect in the cab.
(3) Sound absorption and noise reduction technology: a technique for absorbing attenuation of sound energy. The sound absorbing material is generally a porous sound absorbing material. 90% of the porous material is a fine interconnected cavity. These microcavities generate viscous resistance and friction to the vibrating air molecules. The vibrational kinetic energy of the molecule is converted into thermal energy to attenuate the acoustic energy.
(4) Acoustic cancellation technology: The muffling system using sonic cancellation technology consists of a set of acoustic detectors, information processors and sonic synthesizers. The detector sends the data such as noise intensity and direction to the information processor. After analyzing, the information processor instructs the sound wave synthesizer to generate an acoustic signal with the same amplitude and opposite vibration direction as the noise wave, and eliminates the noise. This technology has been applied in the noise reduction of air conditioning systems in the UK, and the noise reduction effect of about 10 decibels is obtained.
Measures for sustainable development of concrete construction machinery 2
3 Measures to reduce the noise of concrete construction machinery With the further deepening of national environmental protection control, the environmental protection departments will gradually phase out the backward construction machinery and construction methods with serious noise pollution. Therefore, further reducing the operational noise of concrete construction machinery is a problem that all concrete machinery manufacturers must pay attention to.