Analysis of the source of noise in feed processing and control measures
Lin Chuanxing1, Zhang Xiaoming2
1. College of Animal Science and Technology, Jiangxi Agricultural University; 2. School of Pharmacy, Jiangxi Science and Technology Normal University
The safe production of feed mills is a problem that cannot be ignored in feed production. Noise is generated in many aspects of feed processing, such as crushing of materials, cleaning of raw materials, and screening. The noise of the feed mill is the second largest public hazard after dust. There are many sources of noise in the feed factory, mainly due to mechanical vibration, electromagnetic vibration, air vibration and material impact, collision, friction and deformation during the production process, especially in the process of screening, grinding and vacuuming. The amount of noise is generally above 85dB, and some even above 100dB. Therefore, special attention should be paid to the hazard of noise in feed production, and practical measures are taken to control the spread of noise. The following is an overview of the sources of noise and its control measures during feed processing, aiming to provide a theoretical reference for the treatment of feed noise.
1 Source of noise
1.1 Mechanical noise
Mechanical noise is caused by the mechanical stress of impact, friction and strain, which is caused by mechanical high-speed operation, which causes vibration of internal parts and liquids of the machine. The precision of each component is not high enough, unbalanced, improperly assembled, and in the process of cleaning, grinding and pulverizing the feed, friction and impact generated between materials and equipment, materials and materials will produce various noises. Such as the noise generated by the crusher and the crusher, the noise generated by the flow of corn in the metal slide tube, and the like. Excessive concentration of noise can cause noise pollution that cannot be ignored, generally between 80dB and 90dB.
1.2 Dynamic noise
During the flow of air, it collides with various equipments, causing eddy currents, shocks or sudden changes in pressure, resulting in airflow noise caused by various mechanical devices. The noise level is related to the speed of the air compressor, the shape of the impeller structure, and the size and shape of the intake and exhaust pipes. The noise generated by the feed plant's pneumatic conveying device, air compressor, centrifugal fan, etc. belongs to this category, among which the high-pressure fan produces the highest noise. To study the surface, the noise of the pulverizer at no-load is mainly composed of solid noise generated by machine vibration and noise generated by aerodynamics, and aerodynamic noise becomes its main noise.
1.3 Electromagnetic noise
In motors, electrical components, etc., changes in current or magnetic field cause the motor to interact alternately in the air, causing vibrations of the armature housing and the core and other related components to radiate noise. Noise generated by generators, motors, transformers, and contactors is electromagnetic noise. For feed mills, the noise generated by different equipment is also different. For example, the wind turbine is mainly aerodynamic noise, and the crusher is both aerodynamic noise and mechanical power noise. Among them, the noise of the pulverizer is the strongest, which determines the noise level of the feed mill. Therefore, electromagnetic noise is very polluting to the production environment and the surrounding environment.
2 noise control
2.1 Noise source control method
The sound source control method first determines the sound source of the noise, and then adopts methods and measures to reduce the noise. It is the most direct, effective and economical method in noise control. Reducing the noise of all major equipment can be considered from the design point of view, such as product design, manufacturing, installation and so on. When selecting the equipment model, the feed mill designer can select mechanical equipment with relatively low noise and good performance. However, the equipment produced by different manufacturers has different performance due to different manufacturing processes and means. Moreover, for some equipment such as shredders, fans, etc., it is expensive to reduce the noise below the standard level. Therefore, the feed factory can selectively purchase related equipment and instruments according to the actual situation of the enterprise, which can save money while reducing noise.
2.2 Noise Propagation Control Method
2.2.1 Sound absorption and noise reduction technology
Sound absorption and noise reduction technology is the use of porous materials, such as glass wool, slag wool, foam, felt, asbestos, wood wool and sound-absorbing bricks, such as sound-absorbing and sound-absorbing materials, is the most Commonly used methods. The principle is that the sound absorbing material is made into a sound absorbing body, and is installed on the inner wall surface and the inner wall of the sound insulating cover to reduce the reverberation sound, thereby achieving the purpose of noise reduction. The key to sound absorption lies in the choice of sound absorbing materials. In actual production, the performance and price of sound absorbing materials can be comprehensively evaluated and selected according to specific conditions.
2.2.2 Sound insulation and noise reduction technology
The sound insulation and noise reduction technology adopts sound insulation devices, such as solid materials such as bricks, concrete slabs and glass, to isolate sound waves propagating in the air, and to close the sound source body, thereby achieving the purpose of controlling noise propagation. At present, feed factories mostly use noise sources that are centrally placed, such as fans being equal to the enclosed space to control noise diffusion. The establishment of the soundproof room can form a small range of low noise areas, the anti-noise effect is obvious, and the investment cost is low. The wall of the soundproofing room can be made of a layer of air wall or a double wall filled with sound absorbing material, so that the sound wave produces irregular reflection and reduces the intensity of noise.
2.2.3 Vibration isolation and noise reduction technology
Vibration isolation and noise reduction is an vibration isolation device with elastic performance between the vibration source and the equipment, which blocks most of the vibration generated by the vibration source and reduces the interference of the vibration source to the equipment. It solves the noise caused by vibration by eliminating the connection between the vibration source and the base member. There are many types of vibration damping devices, such as coil springs, leaf springs, cylindrical springs, reed steel springs and conical springs. Among them, the steel spring damper is one of the most commonly used dampers, which has the advantages of low natural vibration frequency, large static compression, high temperature resistance, oil resistance, durability, and can withstand large loads. , stable performance.
2.3 Sound source receptor control technology
2.3.1 Muffler
The muffler is a device that uses the absorption, reflection, and interference of sound to achieve the purpose of muffling. The muffler is only effective for air noise. The requirements for the muffler are: large amount of noise reduction, good aerodynamic performance (small resistance), small size and durability. Muffler can generally be divided into three categories: resistive muffler, resistant muffler and anti-composite muffler.
2.3.2 Vibration isolation
Vibration isolation is the process of changing the direction or weakening of the transmitted vibration wave by reflection or other measures. Devices commonly used for vibration isolation include vibration isolating rubber, springs, air cushions, and bumpers. In addition, the vibration transmitted from the vibration source to the foundation is called active vibration isolation, and the vibration transmitted from the foundation to the vibration damping instrument is called negative vibration isolation.
2.3.3 Damping
The vibration damping treatment is to convert the mechanical energy generated by the vibration into heat energy to be absorbed, so that the vibration is limited, and the loss effect of the vibration energy is called damping. Damping materials include various materials such as asphalt, rubber and some polymer coatings. They have internal friction and large internal loss characteristics, and are suitable for preventing solid noise radiated from the thin plate casing of various devices such as air blowers and pneumatic conveying pipes.
2.3.4 Sound Absorption
Sound absorption relies on sound absorbing materials or sound absorbing structures to absorb reverberation sound (no effect on direct sound). This method of "sound absorption and noise reduction" is one of the main measures to control industrial noise. The sound absorbing material is generally decorated on the inner surface of the room, and the sound absorbing material can also be made into a "space sound absorbing body" and suspended under the roof. According to the data, when the area of ​​the air-absorbing body accounts for about 40% of the floor area of ​​the room, the effect similar to the full-sound sound-absorbing finish can be obtained.
2.3.5 Sound insulation
The measure of covering and reflecting sound waves back by the wall and separating the noise source from the receiver is called sound insulation. The sound insulation relies on the compactness of the material, and the sound is reflected by the reflection of sound energy. The solid and heavy wall has better isolation effect against air noise and solid noise. The method of sound insulation is generally to use a sound enclosure to seal the noise source, but sometimes it is convenient for maintenance or is beneficial to the heat dissipation and ventilation of the equipment. The sound barrier can also be used to shield the noise, so that the sound energy radiated by the noise source to the back of the sound barrier is reduced. .
3 Summary
The noise generated in the feed production process not only affects people's hearing, but also causes cardiovascular system dysfunction, and its effect is strong and wide, which has disadvantages for production, environment and humans. Therefore, we should pay attention to the noise problem of feed mills, formulate necessary prevention measures, protect people's physical and mental health, and build a harmonious coexistence between people and society.
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