What Is Industrial Noise?

Industrial noise refers to noise generated when machinery is operating. According to its noise source characteristics, it can be divided into: airflow noise, mechanical noise and electromagnetic noise. The "Noise Hygiene Standard for Industrial Enterprises" (trial) issued by the Ministry of Health and the State Administration of Labor in 1979 stipulates that the continuous working 8h noise in production workshops and operating sites shall not exceed 90dB. For every 3dB increase in sound level, the operating time is halved, but the maximum cannot exceed 115dB. The standard is primarily to protect the hearing of workers. Promote the use of new technologies, new processes, new equipment and new materials to reduce noise. Newly constructed, expanded, and rebuilt industrial enterprises must design, construct, and start production of noise-controlling facilities and main works simultaneously. In the existing industrial enterprises, all production workshops and operating places with noise exceeding the standard must take control measures to meet the requirements of the specified standard within a time limit.

1.The way the sound source is generated

(1) The aerodynamic noise is caused by

1. Affects rest and work. People need to reduce the ambient noise to less than 45dB during rest. If it is greater than 63.8dB, it will be difficult to fall asleep. Noise distracts people, is prone to fatigue, slow response, affects work efficiency, and also makes work errors.

2. There is a certain limit to the auditory organ's damage to the auditory organ. Working under strong noise for a long time will cause hearing fatigue and hearing loss. Under the repeated effects of strong noise for many years, the ear organs will generate qualitative lesions and noise deafness will occur.

3. Causative noise caused by cardiovascular system diseases can make sympathetic nerves tense, with accelerated heartbeat, arrhythmia, blood pressure fluctuations, and positive electrocardiogram tests.

4. Impact on the nervous system Noise causes neurasthenia syndromes, such as headache, dizziness, insomnia, dreaming, memory loss, etc. The positive detection rate of neurasthenia increases with increasing noise intensity. In addition, noise can cause gastric dysfunction and reduce vision. When the noise exceeds the sound of the alarm signal of the production control system, the alarm sound signal is flooded, which easily leads to an accident.

Noise control program

The ideal noise control work should be predicted before the factory, workshop, unit construction or installation, the amount of noise reduction should be determined according to the predicted results and allowable standards, and then the noise reduction effect, the amount of investment, and the impact on workers' operations and equipment normal work, etc Three aspects are used to select reasonable control measures and carry out construction at the same time as the infrastructure. After the completion, the noise reduction measurement and acceptance will be performed to achieve the expected results, and it can be put into use ^[1-2] .

Noise source control

(1) Reduce the intensity of the sound source Replace the high-noise processes and equipment with silent or low-noise processes and equipment, improve the processing accuracy and installation technology of the equipment, and make the sounding body into a non-sounding body. This is to control the noise The fundamental way. For example, use low-noise fans, motors, compressors, freezers, textile machines, pumps, etc. Silent steel plates are silent and silent. If the components of machinery and equipment are made of silent steel plates, the intensity of the sound source will be greatly reduced.

(2) Reasonable layout to separate high-noise equipment from low-noise equipment; separate operation room, rest room, office and noisy production environment; separate living area from factory area, so that noise will naturally decay with distance. Urban greening also plays a role in controlling noise. A 40m wide forest can reduce noise by 10 to 15dB. However, in many cases, it is often impossible to control noise directly from the sound source due to technical or economic reasons. Therefore, technical measures such as sound absorption, sound insulation, sound attenuation, and vibration isolation are also needed to cooperate ^[2] .

Control of sound transmission channels

(1) Sound absorption If there is a sound source in the room, the sound waves emitted by this sound source will be reflected multiple times from the wall, ceiling, ground and other surfaces. As a result of the reflection, the noise level of the indoor sound source will be 10-15 dB higher than the noise level of the same sound source in the open air. If you use sound-absorbing materials to decorate the surface of the room, or hang a sound-absorbing body in the space, the room noise will be reduced. This method of controlling noise is called sound absorption. Most sound-absorbing materials are relatively soft or porous, and have a large surface area. Commonly used sound-absorbing materials are glass wool, foam plastic, felt, polyamide fiber, slag cotton, sound-absorbing brick, aerated concrete, wood wool board, sugarcane board and so on. Sound-absorbing materials are useful for high-frequency noise and less effective for low-frequency noise. For low frequency noise, a resonant sound absorbing structure is often used. It is the simplest resonance sound absorption structure to perforate some holes in the metal sheet or thin wood board and set a cavity behind it. The perforated plate sound-absorbing structure is both cost-effective and simple. Its disadvantages are strong frequency selectivity and relatively narrow sound-absorbing frequency band. In order to overcome this shortcoming, a micro-perforated plate sound absorption structure has been developed in recent years, which can have a better sound absorption effect in a wide frequency range. Through sound absorption, the noise can generally be reduced by 6-10dB.

(2) Sound insulation Enclose the sound-producing machine or a place that requires quietness in a small space to isolate it from the surrounding environment. This method is called sound insulation. Typical sound insulation equipment is a sound insulation cover, a sound insulation panel and a sound insulation screen. Sound insulation should use sound insulation materials with large sound transmission loss (average sound insulation volume). Heavy and dense materials (such as steel plates, brick walls, concrete, etc.) are good sound insulation materials. Intermediate interlayer can reduce the transmission of vibration, and it is better to fill the middle with sound-absorbing material.

The sound insulation cover is composed of sound insulation material, damping paint and sound absorption layer. If 2ram thick steel plate and 5cm thick sound absorbing material are used, the noise can be reduced by 10-30dB. There are two types of soundproof rooms: fixed soundproof rooms and mobile soundproof rooms. The fixed sound insulation is a brick wall structure, and the movable sound insulation room is assembled. The sound insulation room not only needs an ideal sound insulation wall, but also considers the sound insulation of doors and windows and whether there is any sound leakage from the pores. The door shall be made of a double-layered sound insulation door filled with sound absorbing material. The sound insulation window is preferably made of a double-layer non-parallel and unequal-thickness structure. Doors and windows should be sealed with elastic materials such as rubber and felt. Better noise reduction between the noise can reach 25 ~ 30dB.

Sound insulation screens are mainly used in large workshops where direct sound is dominant. The sound insulation screen is very effective for reducing the high-frequency noise of the motor and the chainsaw, and it can reduce the noise by 5-15dB.

(3) Noise reduction Noise reduction is the process of reducing sound energy using a muffler. A muffler is a device that allows airflow to pass or prevent sound transmission. It is the main technical measure to reduce aerodynamic noise. Generally, the muffler is installed on the fan inlet and exhaust duct. Currently, there are four types of mufflers: resistive muffler, resistant muffler, impedance composite muffler and micro-plate muffler.

Resistive muffler. The resistive muffler uses sound-absorbing material attached to the inner tube wall of the airflow channel to absorb sound energy. When sound waves enter the muffler, the air molecules in the sound-absorbing material on the pipe wall are vibrated. Due to frictional resistance and viscous resistance, the sound energy becomes thermal energy to achieve the effect of muffler. Its function is similar to the resistance in the circuit, so it is called a resistive muffler. The characteristic of the resistive muffler is that it has a significant muffler effect on the middle and high frequency noise. It is simple to manufacture and has stable performance. The disadvantage is that it has a short service life in high temperatures, water vapor, and gases that have a corrosive effect on sound-absorbing materials, and has a poor effect on low-frequency noise.

Resistive muffler. The resistant muffler is manufactured according to the principle of acoustic filtering, which can significantly eliminate noise in certain frequency bands. Expansion mufflers, resonance mufflers, interference mufflers, and perforated mufflers are common resistant mufflers. The advantages of resistant muffler are good low and medium frequency muffler performance, simple structure, high temperature resistance and gas corrosion resistance. The disadvantage is that the muffler frequency band is narrow and the effect on high frequency muffler is poor.

Impedance compound muffler. This muffler is composed of sound-absorbing materials, such as sound-absorbing materials, expansion chambers, and perforated screens. In fact, it is a combination of a resistive muffler and a resistive muffler, which concentrates its advantages. The muffler effect is relatively good. It is suitable for a wide range of frequencies and can be used at high, medium and low frequencies.

Microplate muffler. The structure of this muffler is to drill a thin metal plate at a perforation rate of 2.5% to 3.5%, with a hole diameter of 0.5 to 1mm, as a lining material for the muffler. According to the requirements of the intensity, frequency range and aerodynamic performance of the noise source, a suitable single-layer or double-layer micro-well plate member is selected as the sound absorbing material of the muffler. The micro-plate muffler is suitable for various occasions, such as high-pressure fans, air conditioners, axial and centrifugal fans, diesel engines, and places containing water vapor and corrosive gases. Light weight, small size, not afraid of water and oil pollution.

(4) Isolation and damping In order to prevent the machine from transmitting vibration to other buildings through the foundation and radiating the machine noise, the usual method is to prevent the machine from being rigidly connected to the foundation and other structural components. This method is called isolation Zhen. It has the following three forms:

Install shock absorbers, such as rubber, spring or air shock absorbers, between the machine and the foundation;

Lay a certain elastic lining material between the machine and other structures, such as rubber board, cork, felt, fiberboard, asbestos board, etc. Dig a deep trench around the machine, fill in sawdust, expanded perlite, etc. Damping is to apply a layer of damping material to the hood, duct, and duct made of metal plates to prevent the board from vibrating violently and radiating strong noise due to vibration transmission. The currently used damping materials include asphalt asbestos damping, pulp cork heat insulation and vibration damping pulp. Mostly used in cars and various machinery and equipment.

personal protection

Due to technical and economic reasons, wearing high-noise personal protective equipment is an important measure to protect the auditory organs of workers from high-noise situations that are difficult to solve with the above methods. The ideal anti-noise products should have a high sound insulation value, be comfortable to wear, and have no harm to the skin. In addition, it is best not to affect language conversation. Common anti-noise products include soft rubber (or soft plastic) earplugs, soundproof cotton earplugs, earmuffs and helmets, etc., which can be selected according to the actual situation ^[3] .