Noise control scheme of air compressor

Air compressor plays an important role in production, but it is a kind of equipment with strong noise. The noise of air compressor mainly comes from air inlet, exhaust port, mechanical port and electromagnetic port. Air compressor noise has high sound level, prominent low frequency, long transmission distance and large pollution range. In particular, the frequency of some noise is close to the natural frequency of human internal organs, causing resonance, which causes dizziness, nausea, tachycardia, hypertension and other symptoms, which not only leads to the decline of people's work and life quality, but also easily leads to safety accidents and interpersonal relationships.

How to reduce the noise of air compressor inlet

To control the intake noise of air compressor, the muffler can be installed. As the noise of air compressor inlet is low frequency, the reactive muffler should be used. The reactive muffler is a kind of muffler which can reflect part of the sound wave to the direction of echo source through the sudden change of acoustic characteristics in the pipeline, so as to achieve the purpose of noise elimination. It is mainly used to reduce the noise of low frequency and low middle frequency band. Its forms are: expansion type, resonance type, expansion chamber type, micro perforation plate type, thousand step type and so on.

Fixed air compressor is usually installed on the indoor floor, but some of the air inlet of the air compressor are indoor and some are outdoor. When the air inlet of the air compressor is indoor, the noise of the air inlet should be reduced to a little lower than that of the machine body, and the noise reduction amount of the air inlet muffler should be about 15dB (a); when the air inlet of the air compressor is outdoor, the noise of the air compressor inlet should be reduced to the requirements of the environmental noise standard according to the environmental conditions around the machine room, and the noise reduction amount of the muffler should be more than 20dB (a).

In order to ensure the muffler's muffling effect, the intake muffler should generally use reactive silencers, such as no fiber, no foam plastics and other loose materials, resistant micro perforated panel muffler or micro perforated plate muffler. The common air compressor intake resistance muffler is to open some uniform small holes on the pipe wall of the air inlet, and connect the closed cavity with its diameter of 3-4 times. The air column in the small hole and the cavity form a common vibration system. Under the resonance frequency, the vibration speed of the air column is very high, which overcomes the friction resistance, consumes a large amount of sound energy, forms a resistance resonance, and has the effect of low-frequency sound reduction.

Some air compressors are equipped with air filters at the air inlet. The air filters can attenuate the air flow noise to a certain extent, but they can not meet the requirements of noise reduction. Therefore, it is still necessary to add noise reduction devices. In general, the filter steel frame can be used to set up a noise elimination hundred page, which is made of aluminum alloy plate, mainly for rust prevention; the vertical type is beneficial to dust prevention; the sound absorption material in the noise elimination page is hollow glass wool, which has good sound absorption performance and is hydrophobic material, which is suitable for outdoor use.

How to reduce the noise of air compressor exhaust port

Due to the high exhaust noise produced by the air compressor with high exhaust pressure and large flow rate, a special muffler should be set up in the exhaust system for control. The exhaust muffler requires a large amount of noise elimination and a wide range of noise elimination frequency band. It can reduce the pressure drop of exhaust and vent, so as to reduce the exhaust noise.

For the air compressor with flow rate less than 20 m 3 / min, the noise is not high and mainly high frequency, so resistance muffler can be used generally. The advantage of resistive muffler is that it can eliminate noise in a wide range of medium and high frequency, especially for high frequency sound wave. The dissipative muffler uses porous sound absorption materials (often called resistive materials) with different structures in the airflow duct to absorb sound energy and reduce noise. It is the most widely used muffler among all kinds of mufflers, and has a wide range of noise elimination frequency, especially in the middle and high frequency band. Resistance muffler has the following types: tube muffler, elbow muffler, chamber muffler, disc muffler.

However, for the air compressor with high exhaust pressure and large flow rate, due to the high sound pressure level of noise, there are both medium and low frequency noise and high frequency noise. The effect of resistance muffler is not ideal. Composite muffler is an effective way to solve the problem. The forms of composite muffler include: resistance composite type, resistance and resonance composite type, resistance and micro perforated plate composite type, etc. The composite muffler synthesizes the former advantages. Although the resistive muffler has excellent middle and high frequency noise elimination performance, the low-frequency noise elimination performance is poor and difficult to improve. On the contrary, the expansion type and resonance type muffler have good noise elimination performance in low and medium frequency, and the high-frequency noise elimination effect is generally poor.

If the two kinds of silencing principles of resistance and resistance are combined into one kind of muffler, satisfactory silencing effect can be obtained in a wide frequency range. This kind of muffler has acoustic filter elements such as resonant cavity, expansion chamber, perforated screen, etc., and also has sound absorption material with holes, which can eliminate noise at different frequencies.

How to reduce the noise of air compressor

To control the body noise and motor noise of air compressor, the control technology of sound insulation and sound absorption is often considered. The measure is to install sound insulation cover or make sound insulation room for compressor to prevent the transmission of noise. This is because the radiated noise and electromechanical noise can not be controlled only by noise elimination measures.

When the noise of air compressor inlet decreases by 10 ~ 20dB (a), the radiated noise from the casing will become the main sound source. For small mobile air compressor, the control measures of sound insulation cover are often used; for large or multiple air compressors, sound insulation room can be made in the machine room and operation room.

In order to improve the sound insulation effect of the sound insulation cover, the sound absorption layer is usually attached. If there is no sound absorption material in the enclosure, the noise source will be continuously reflected by the steel plate and not absorbed, and a reverberation field will be formed in the enclosure, which will increase the sound level in the enclosure. The greater the sound absorption coefficient of a material, the better its sound absorption ability. The sound absorption coefficient varies with frequency, thickness and density.

Heat dissipation should be considered for sound insulation cover and sound insulation room, and intake muffler and exhaust muffler are usually set on the sound insulation body. The convenience of maintenance shall be considered for sound insulation equipment. Sound insulation door and observation window shall be set to facilitate disassembly, and the joint shall be tight after installation. The sound insulation loss of sound insulation door, sound insulation window and intake muffler is close to the enclosure. In order to improve the noise reduction effect of sound insulation cover, the design of sound insulation cover should meet the following requirements: the sound insulation cover plate should be made of materials with sufficient sound insulation capacity, such as thin metal plate; the weak sound insulation links such as doors, windows and openings should be well handled; the inner wall should be treated with strong sound absorption, and appropriate sound absorption materials should be selected.

The noise of air tank is usually eliminated by hanging sound absorber. When the compressed air enters the tank, the sound absorber in the tank absorbs the sound energy, so as to achieve the effect of noise reduction. In order to reduce the noise of exhaust pipe, the method of wrapping up the pipe or burying the pipe in the ground is as follows: the inner layer is wrapped with asphalt felt, which can weaken the vibration of the pipeline and reduce the regeneration noise of the pipeline; the outer layer is made of 3 mm thick galvanized steel plate, and the middle layer is made of 50 mm thick rock wool felt with volume density of 150 kg / M 3. Nearly 20dB (a) of noise reduction is obtained by sound insulation wrapping.

How to reduce the vibration noise of air compressor body

To control the noise of air compressor, vibration must be controlled. The vibration of air compressor is mainly transmitted through the foundation and pipeline system. Vibration control is mainly to take vibration isolation control. The main measures are as follows:

1. Use vibration isolator

The vibration isolator forms elastic connection between the air compressor and the foundation to reduce the amplitude to achieve vibration isolation, which is the most critical link of vibration isolation.

2. Adopt vibration isolation joint to suspend the foundation

The vibration isolation joint suspended foundation cuts off the transmission way of air compressor vibration to soil. The vibration isolation joint is 150-200 mm wide and filled with dry sand. Dry sand and industrial felt are laid under the foundation with a thickness of 20-40mm.

3. Vibration isolation ditch is adopted

In some cases, surface trenching can be used to cut off the vibration of surface wave propagating along the ground.

Control the vibration of air compressor pipe and reduce the noise of air compressor

In the noise control of air compressor, there are usually two problems to be solved: vibration and radiation noise. The reason of pipeline vibration of air compressor is that the vibration of air compressor is transmitted to the pipeline, and another reason is the vibration caused by air flow pulse in the pipe. When the vibration frequency is 20 ~ 20kHz, it is connected with the sound and forms the sound radiation of the pipeline. The measures to control pipeline vibration and acoustic radiation are as follows:

1. The length of the resonance tube on the common wall. When the excitation frequency of the air compressor coincides with the natural frequency of the pipe fitting system, the resonance occurs, and the length of the pipe is the length of the resonance tube.

2. Add orifice plate in the pipe. The ratio of orifice diameter to pipe diameter d $L / D is 0.43-0.50. The thickness of orifice plate is h = 3-5mm. The orifice plate is installed at the inlet and outlet with large pulse and enough air volume.

3. Add soft hose connection to cut off the vibration along the pipeline. That is to change a section of metal pipe into rubber tube, and the length is usually more than 0.5m.

4. Elastic fixation shall be adopted at the fixed position of pipeline to avoid vibration transmission to support.

5. Set buffer muffler.

6. Wrap the pipeline with damping material. For example, wrapping air compressor pipeline with asphalt cloth can effectively reduce radiation noise.