Noise generation and control of centrifugal fan 

 By detecting, analyzing and studying the noise of centrifugal fan, the main source of the noise and its transmission path are determined, and effective noise control measures are taken to reduce or cut off the transmission path or elimination of the noise The purpose of removing the noise source. The centrifugal fan commonly used in ceramic industry is the key equipment of ventilation and dust removal device, such as the dry grinding process of ceramic raw materials, Raymond mill, hammer mill, squirrel cage mill and other grinding equipment The core fan will reach the specified size requirements of the ceramic powder discharged out of the machine; Spray dryer tunnel dryer chamber dryer Chain dryer and kiln and other equipment use centrifugal fans for heat exchange in order to improve products Heating speed and heating quality, etc.; Cyclone dust collector and bag dust collector use centrifugal fans to dust the production workshop, to ensure that the production workshop clean and bright and civilized production, the use of centrifugal fans can also be To complete the transmission of ceramic powder and other noise is the fatal defect of centrifugal fans commonly used in ceramic industry. In fact, noise is an irregular and chaotic combination of different frequencies of sound, which seriously damages people's physical and mental health It reduces productivity. Therefore, active research and discussion of the causes of centrifugal fan noise in ceramic industry harm and control ways, to protect the health of operators and improve the economic benefits of enterprises Have profound and important significance. Noise generated by centrifugal fans can usually be divided into mechanical noise, motor noise and aerodynamic noise. 2.1 Mechanical noise The impeller of centrifugal fans commonly used in the ceramic industry is usually installed directly on the motor shaft or connected with the motor shaft through the coupling fan shaft or through the belt pulley fan shaft and drive belt, and accompanied by the motor The shaft rotates at high speed. Although the design and manufacture of centrifugal fans commonly used in the ceramic industry meet the requirements of strength and stiffness, the rotating parts of the fan shaft, fan impeller coupling and pulley have been strict when the fan leaves the factory Grid static balance and dynamic balance correction qualified before assembly into a table. But because of the high speed of the centrifugal fan, the production environment is harsh, the air is humid and the dust is flying, and the ceramic powder and dust are the main components of solid particles It is still quartz and or stone quartz, and its hardness is particularly high, so the centrifugal fan is commonly used in the ceramic industry, the fan impeller and other rotating parts are easy to wear and produce mechanical noise, now the following aspects of the fan impeller Uneven wear, under the action of fan pressure, leads to the deformation of the fan impeller, and mechanical noise is generated due to the unbalance of the fan impeller when the fan is working. Due to the wear of the fan bearing, the bearing rolling body forms a large gap with its contact working surface, resulting in mechanical noise. In serious cases, the inner and outer rings of the bearing and the fan shaft bearing seat will also form a large gap Produce mechanical noise. Some fans usually use multiple belts to work at the same time. If the length and size of the belts differ greatly, some belts will be tensioned while others will not be tensioned, resulting in mechanical noise The sound. Mechanical noise is caused by improper installation of fan or loose connection bolts of working parts. Due to the high speed rotation of the fan, some parts of the fan produce resonance and cause mechanical noise. 2.2 Motor noise Motor is an important part of centrifugal fan. Generally, the motor used by fan manufacturers is provided by professional motor manufacturers, and fan manufacturers usually do not carry out internal operations on the motor Process, but use directly. In fact, there are many kinds of motor noise, usually mainly due to the following aspects of mechanical noise caused by the poor accuracy of motor bearings. Electromagnetic noise caused by the excitation of the radial alternating electromagnetic force inside a motor. Mechanical noise caused by the commutator commutator carbon brush rubbing the conductive ring and the commutator itself. Due to the vibration of some parts, its natural frequency is close to the frequency of the exciting force and produces resonance, resulting in noise. Noise caused by the unbalance of the motor rotor or the axial component of the electromagnetic force generated by axial channeling. 2.3 Aerodynamic Noise The aerodynamic noise generated by centrifugal fans can usually be divided into rotation noise, eddy current noise and collision noise Strike noise. 2.3.1 Rotating noise Rotating noise, also known as blade noise, is the noise generated by the pulsation of gas pressure and speed caused by the periodic pressure generated by the impeller blade of a high-speed rotating fan. this When the fan impeller blade rotates in free space, the gas at a fixed position adjacent to it will be affected by the exciting force of the fan impeller blade and its pressure field, resulting in the fluctuation of gas pressure. Due to fan When rotating at high speed, the impeller blades of the fan frequently pass through the position one by one, and the gas pressure pulsation is generated correspondingly, and the noise is formed by radiation to the surrounding area. 2.3.2 Eddy noise Eddy noise is also known as eddy noise. When the air flow enters the centrifugal fan from the shaft disk and the front disk of the inlet, the gas will be violently compressed or expanded due to the rapid change of the gas flow path And form eddy noise; On the other hand, vortex noise will be generated when the air flows through the fan impeller blade passage due to the deflow of the gas boundary layer. 2.3.3 Impact noise The impact noise generated by centrifugal fans is the impact noise generated when the air flow enters and leaves the impeller blade of the centrifugal fan, and the whistle noise generated when the air flow flows through the volute cochlear tongue, etc Yes. 3.1 Noise affects psychology and induces a variety of diseases. Noise interferes with People's Daily conversation, study, work and rest, and seriously damages people's health. If you live in a ring of noise for years and years In the environment, people are very easy to get tired of temper, such as over time will also damage the deaf. Clinical experience shows that the development and deterioration of heart disease, hypertension, gastroenteropathy and cancer are closely related to the intensity of noise The relationship between. 3.2 Noise affects safe production and reduces work efficiency Due to the interference of noise, people are easy to be tired, distracted, reduced energy, etc., which affects the work quality and work efficiency. Due to the masking effect of noise , people are not easily aware of the existence of the omen of the accident and various warning signals, which is easy to cause equipment damage and personal injury accidents, seriously endangering the safety of production. The noise generated by centrifugal fans commonly used in the ceramic industry is usually transmitted to space through the air inlet pipe, the air inlet shell, the air exhaust pipe, the air outlet and the fan foundation, and seriously endangers people The living environment. For this reason, the government issued a draft of the health standards for industrial enterprises noise. The International Standardization Organization 150 also stipulated that the noise of industrial and mining enterprises could not exceed 85 decibels. According to people's ability to withstand the noise, the closest distance from the ceramic industry production plant requires that the noise should not exceed 40, 45 dB 4. In fact, it was measured within 1.5 distance of centrifugal fans commonly used in the ceramic industry The noise is usually as high as 90,100 decibels and sometimes 105 decibels. Therefore, we must effectively control and control the noise of centrifugal fans. The control ways are described as follows. 4.1 Ways to control mechanical noise Fan impeller fan shaft belt pulley and coupling and other rotating parts shall be strictly corrected for static and dynamic balance, and can be assembled into a table and approved for delivery after qualified. Regularly check whether the connecting bolts and anchor bolts of all parts of the fan are loose, whether the bearing is abnormally worn or poorly lubricated, and whether the transmission belt is tensioned. If the situation is abnormal, it should be stopped immediately. During installation, soft materials such as rubber cork board or felt board should be padded between the fan and the reinforced concrete foundation so that the vibration transmitted by the centrifugal fan to the reinforced concrete foundation can be minimized or eliminated. A rubber hose is installed at the air inlet and the air outlet of the fan to minimize or eliminate the vibration transmitted by the centrifugal fan to the air duct at the rubber hose. 4.2 Ways to control the motor noise Motor cooling fan blades must be strictly calibrated for static balance and dynamic balance, before assembly into a platform approved for delivery. At the same time, motor cooling fan blades and The gap between the wind guide can effectively reduce the rotating noise of the motor cooling fan blade. The eddy current noise of motor cooling fan can be effectively reduced by choosing the shape and diameter of motor cooling fan blade reasonably. If the motor produces low frequency electromagnetic noise, the motor stator has eccentricity and the air gap is uneven, the motor stator can be repaired or replaced to eliminate the low frequency electromagnetic noise produced by the motor; If the motor produces high-frequency electromagnetic noise If the motor rotor is defective, the high frequency electromagnetic noise generated by the motor can be eliminated after the motor rotor is repaired or replaced. 4.3 Ways to control aerodynamic noise 4.3.1 Install silencer at the air inlet and exhaust outlet of the fan. The silencer uses porous sound absorbing materials to absorb sound energy. When the sound wave passes through the air inlet and exhaust outlet lined with porous sound absorbing materials, the sound wave will stimulate more The air molecules in the numerous holes in the porous sound absorbing material move violently, and most of the sound energy is used to overcome the friction and viscous resistance and is converted into heat energy and consumed, thus reducing the production of centrifugal fans Aerodynamic noise. In practice, the installation of a muffler at the intake and exhaust vents of centrifugal fans can usually reduce the aerodynamic noise generated by the intake and exhaust vents by about 20 and 30 decibels. 4.3.2 Setting a rectification Device at the air inlet of the fan Because the size of the exhaust outlet of the impeller blade of the centrifugal fan is usually larger than the size of the air inlet at the front panel, the air flow in the fan will be in the arc section of the air inlet A lot of vortices are formed in the air inlet, and the vortices will collide with the volute of the fan and the parts of the air inlet repeatedly and frequently, resulting in the formation of aerodynamic noise. If the air inlet of the fan is located in the outer part of the fan volute interior design and production prevention The rectifier device that generates eddy current, that is, the rectifier ring and baffle are added, can effectively prevent the airflow from forming eddy current at the inlet of the fan, so as to reduce the aerodynamic noise generated by the centrifugal fan. 4.3.3 Improving the structure of the fan volute The function of the centrifugal fan volute is to collect the high-speed air flow from the fan impeller and guide the high-speed air flow to the exhaust outlet. In this process, centrifugation is commonly used in the ceramic industry The structure of the fan accelerated airflow will impact the fan volute and generate aerodynamic noise. By optimizing and improving the production technology of the volute, and precisely making the fan volute with the linear logarithmic spiral spiral curve, it can effectively Reduce the aerodynamic noise produced by centrifugal fans. picture 4.4.4 Improving the gas flow passage of the fan impeller and controlling the wind speed at the inlet of the centrifugal fan impeller can effectively reduce the flow velocity of the gas flow passage of the fan impeller and reduce the aerodynamic noise generated by the centrifugal fan. ruofan The impeller blade is designed and made into a swept-back twisted blade, that is, the impeller blade of the fan tilts moderately forward at the exhaust air outlet and moderately backward at the inlet air outlet, so as to avoid the sharp change of the gas flow passage and prevent the gas The volume generates eddy currents to reduce the aerodynamic noise generated by the centrifugal fan. 4.4 Other ways to control noise Usually sound through uniform and dense wall materials, the sound energy will be weakened or eliminated, the more weakened the sound energy, the better the sound insulation effect. If sound absorbing material is used to make sound insulation Cover or sound insulation room, the centrifugal fan is closed in a small space, can prevent its noise from spreading to the outside world, reduce the centrifugal fan produced. At present, the noise generation and control of centrifugal fan commonly used in the ceramic industry is the subject of common concern of the ceramic scientists and manufacturers. We think it should be optimized in the design and manufacture of centrifugal fans And improve the centrifugal fan structure, elaborate production, as far as possible to reduce the generation of aerodynamic noise; The rotating parts of fan impeller fan shaft pulley and coupling should be strictly corrected for static balance and dynamic balance to reduce Less mechanical noise caused by fan vibration. However, due to the high speed of the impeller of the centrifugal fan, the ceramic production environment, the air humidity and dust flying, the impeller blade of the centrifugal fan is easy to grind when the centrifugal fan is working Damage and form noise. We should detect, analyze and study the noise of centrifugal fan, determine the main source of the noise and its transmission way, and take effective noise control measures to reduce or cut off the noise transmission Or eliminate the noise source, to ensure the maximum reduction of centrifugal fan noise pollution to the surrounding environment, so as to improve the working environment, improve production efficiency.