On the mechanical equipment noise muffling problem, is due to the operation of mechanical equipment, there is an imbalance, the mechanical spindle concentricity deviation, the size of the components between the deviation or surface defects and mutual impact, friction generated by the alternating mechanical force so that the equipment metal plate, bearings, gears, or other parts of the movement of the vibration and radiation of noise muffling sound source is called the noise muffling source of mechanical equipment. Here are some examples to illustrate the various types of mechanical equipment noise sources.
Friction noise muffling
Objects in contact with each other under a certain force to produce movement, friction between the objects, friction in the direction of anti-movement in the direction of the movement of the moving objects on the contact surface, thereby stimulating the vibration of the object to produce noise muffling. Such as the subway to the station when the brakes issued by the sound, etc..
Friction noise muffling in the main friction caused by the object's relaxation vibration noise muffling, when the vibration frequency and the object's intrinsic vibration frequency is the same, the friction noise muffling will reach the maximum.
Impact noise muffling
Because of the impact of the role of the impact force will make the machinery produce a strong impact noise muffling. Such as forging hammer work its mechanical energy is divided into four parts, the first part of the work, the second part is converted into thermal energy, the third part of the foundation through the form of solid sound to the surrounding ground propagation, the fourth part of the vibration energy is converted into the elastic deformation of the machine parts. Part of the vibration energy of the elastic deformation of the machine parts and then in the form of sound waves to the surrounding space radiation, the formation of impact noise muffling, this noise muffling can also be broken down into the moment of impact produced by the jet noise muffling, pressure impulse noise muffling and structural noise muffling. Among them, the structure noise muffling produces the greatest impact, and the radiation noise muffling time is the longest.
Impact noise muffling has the following characteristics: when the impact occurs between the harder smooth objects, the action time is short, the force is large, then the frequency band of excitation is wide, the vibration mode of excitation object itself is more, is a wide-band impact noise muffling; if the impact occurs between the softer non-smooth objects, the action time is relatively long, the force is small, the frequency band of excitation is narrow, the vibration mode of excitation is less.
Structural noise muffling
Mechanical equipment noise muffling is due to mechanical vibration system forced vibration and intrinsic vibration *** with the same cause, in which the intrinsic vibration plays a major role in the intrinsic frequency of vibration is the main component of the noise muffling, and the vibration of the system of the intrinsic frequency of vibration depends on the system's structural characteristics and parameters, so this noise muffling is known as the structural noise muffling.
Any noise muffler is a structural noise muffler.
Any mechanical component has its inherent vibration mode, different vibration mode corresponds to different vibration frequency. The vibration mode and frequency are related to the physical properties of the component or material, the structural shape of the component and the boundary conditions of vibration. The greater the modulus of elasticity of the material, the thicker the material, the thicker, the higher the intrinsic frequency; the greater the area of the material, i.e., the longer the rod, the greater the area of the plate, the lower the intrinsic frequency.
Gear noise muffling
Meshing gear pair or gear group, due to mutual collision or friction can be provoked by the vibration of the gear body, the noise muffling radiated in this case is called gear noise muffling.
Excited noise muffling
Generally generated by the periodic force of rotating machinery. The simplest periodic force is the eccentric force caused by the static and dynamic imbalance of the rotating system such as the rotating shaft and flywheel. This force is proportional to the mass of the rotating system and the static and dynamic synthetic eccentricity, but also proportional to the square of the rotational angular velocity. When the rotational speed of the rotating system reaches its critical speed, the system itself will produce great vibration, and will be transmitted to the vibration force connected to other parts of the machinery, provoking a strong noise muffler. Excitation of noise muffling will increase with the presence of gaps in the machine parts, structural rigidity or friction is not enough.
Bearing noise muffling
The friction and vibration between the parts in relative motion within the bearing, or the imbalance of the rotating part (embodied in the case of the shaft is not concentric), the impact between the parts in relative motion, etc., will lead to the generation of bearing noise muffling.
Mechanical equipment muffling, the installation of muffling devices in the exhaust port. Silencer selection is very important, it is appropriate to choose the muffling performance for low frequency, low mid-frequency wide band of resistance silencer, generally choose impedance composite silencer. Impedance composite muffler refers to the sound absorption and sound reflection properly combined with the muffler. It has the characteristics of both resistive muffler to eliminate middle and high frequency noise and resistive muffler to eliminate low and middle frequency noise, and it has the effect of wide-band muffling. Mechanical equipment sound insulation, the main attention when installing the sound barrier is the distance of the sound barrier from the air inlet of the mechanical equipment in about 1m to ensure that the mechanical equipment ventilation air inlet is not blocked, so as to make the cooling effect of the mechanical equipment better. In order to prevent noise bypassing and affect the acoustic effect of the noise deflector, you can install a certain length of sound barrier near the noise deflector to play an auxiliary role in noise reduction. Equipment in the use of the process will produce greater heat, so that the temperature in the sound insulation room rising, so that the motor and other equipment can not run normally, according to the actual situation of the equipment, can be installed in the mouth of the material ventilation muffler pipeline for heat dissipation.
Mechanical equipment vibration damping: to solve the vibration and noise of mechanical equipment, the most economical and effective method of mechanical equipment to damping treatment. Mechanical equipment vibration is mainly through the foundation and piping system to the outside, body vibration control measures include: the use of professional vibration isolation; arrangement of floating sound-isolating ground; set up vibration isolation ditch; piping system vibration control can be considered to add a rubber flexible receiver, elastic hangers, vibration damping and sound isolation materials wrapped pipeline. However, the requirements for horizontal installation are very high when the mechanical equipment is working. Therefore, when the vibration damping program is not properly designed, the mechanical equipment will sway or produce elastic waves under the reaction force of the shock absorber. For this reason, it is very important to accurately calculate the horizontal and vertical rigidity of mechanical equipment when carrying out the vibration damping design of mechanical equipment.
Finally, mechanical equipment noise management and mechanical equipment vibration noise reduction program, the need for professional acoustic design companies to conduct field surveys of the sound source and the environment, and analysis and design, based on the results of the analysis of the combination of site conditions, the use of high-performance noise reduction products, equipment in order to make the most reasonable mechanical equipment noise reduction management program.