Abstract : The noise measured is up to 114.5dB(A) at a distance of 2m from a DH90-1 centrifugal air compressor. In the case of no downtime, the air compressor body is added with an acoustic enclosure, the air inlet filter is added with muffler louvers, and the air intake pipe is used for sound insulation and bandages. The noise of the corresponding measuring point is reduced to 88.7dB. (A). IL = 10lg(1+ α 10 0.1 TL ) dB (1) Where α is the sound absorption coefficient of the interior sound absorbing material; Custom Reverse Machine,Water Setting Machine,Tubular Tube Fabric Finish Machine,Crease Remove Machine ZHEJIANG LIANKE MACHINERY CO.,LTD , https://www.zjlinkmachinery.com
Wang Jianxin, Li Xia, Zhang Jun (Jinan Iron Steel Group Corporation, Jinan 250101, China)
Key words : air compressor; noise control; sound insulation cover; muffler; sound insulation
CLC number : TB535 Document code : B Article ID : 1004-4620 (2005) 01-0070-01
1 Air compressor noise source analysis
The air compressor is a strong noise device that is seriously polluting the environment. The Jinan Iron and Steel Group Oxygen Plant (referred to as Jigang Oxygen Plant) installed a DH90-1 centrifugal air compressor outside, and the noise measured at 2m away is as high as 114.5dB(A).
Air compressor noise includes aerodynamic noise, mechanical noise, and electromagnetic noise. The radiated noise parts are divided into: noise source of air compressor body; noise source of motor; noise source of intake pipe; noise source of intake port; noise source of exhaust pipe; noise source of exhaust vent. The noise spectrum of each part was measured by the near-field method, indicating that the noise of this type of air compressor is medium-high frequency.
2 Air compressor sound insulation cover design
The most reasonable measure to control the air compressor body noise and motor noise is to add an acoustic enclosure to the air compressor. The noise reduction effect of the acoustic enclosure is expressed by the insertion loss IL , which is calculated by the following formula:
TL - average sound insulation cover wall, TL = 10lgΣ S i / ( Σ S i 10 -0.1 TL i), dB;
S i — the area of ​​the i- th member constituting the cover wall, m 2 ;
TL i — the amount of sound insulation of the component, dB.
In order to ensure the noise reduction effect of the sound insulation cover, it should be noted that: (1) The material of the cover wall should have sufficient sound insulation. The project adopts a multi-layered complex structure, designed to have a sound insulation of 30dB (A); (2) to handle the weak sound insulation of doors, windows, and openings. The project must open a door and a lighting window to design a sound insulation of 30dB (A); the ventilator is equipped with a muffler, and the noise reduction design value of the muffler is 25dB (A). (3) The inner wall is treated with strong sound absorption. This project uses 50mm thick centrifugal glass wool felt as the sound absorbing material, and its high frequency sound absorption performance is excellent, which is consistent with the noise frequency characteristics of the required control. In order to increase the low frequency sound absorption, the sound absorbing material is left with a 50 mm thick air layer.
The air compressor cannot be shut down due to production needs. At the time of design, the reinforced concrete pedestal of the original air compressor was utilized, and the soundproof cover was divided into upper and lower parts. Thanks to the reinforced concrete pedestal, the main keel structure of the acoustic enclosure is simplified and can be easily constructed under machine operation. 70% of the area under the sound enclosure can use brick walls, saving money on treatment. In order to meet the equipment maintenance requirements, the top of the cover is detachable for hoisting mechanical operation; the cover wall of the cooler is designed as a soundproof door at the lower part of the sound insulation cover, which is usually used for management personnel to enter and exit, and the cooler core can be taken out during maintenance.
In order to ensure the heat dissipation effect, the sound insulation cover adopts forced ventilation. Two low-noise exhaust fans are arranged near the motor at the top of the cover, and the upper part of the exhaust fan is connected with an impedance composite muffler to reduce leakage of noise inside the cover through the exhaust port. The muffler has a higher position and also acts as a "chimney", which is beneficial for ventilation inside the hood. The total air volume of the exhaust fan is designed according to the summer season with the most unfavorable weather conditions. It can be opened or fully opened according to the outdoor air temperature.
The sound enclosure has two air inlets located at the lower part of the hood and arranged diagonally opposite the air vents to allow sufficient airflow through the machine surface. A blower-type resistive muffler is provided at the air inlet to reduce air compressor noise leakage. The effective channel area of ​​the muffler is determined according to the wind speed of 5 m/s.
3 air compressor air intake noise reduction design
The air compressor air inlet is provided with an air filter, which has a certain weakening of the airflow noise of the air inlet, but it cannot meet the noise reduction requirement. The measured noise is 96.2 dB(A) at 1 m from the inlet filter. According to the existing conditions, the filter steel frame is used to set the noise reduction page. As rust, with one hundred muffler aluminum alloy plate, sheet perforation rate was controlled at 12%; using a vertical one hundred, so that dust; acoustic louvers centrifugal glass wool with a sound absorbing material, the sound absorption performance and good It is a hydrophobic material suitable for outdoor use, and the louver cross section is designed to be streamlined to reduce ventilation resistance. It was determined that the noise reduction was obtained by 12 dB (A) noise reduction.
4 sound insulation bandage of inlet and exhaust pipes
The noise radiated by the intake pipe and the exhaust pipe includes two parts: one is the airflow noise from the compressor inlet and the exhaust port; the other is the regenerative noise in the pipeline. Inner wrap insulation asphalt selection, bind tightly original tubing which can weaken the pipe vibration damping effect to reduce noise regeneration duct; an outer layer selected galvanized steel sheet 3mm thick, 50mm thick intermediate layer selection, bulk density of 150kg / m 3 Rock wool felt. The sound insulation bandage achieved a noise reduction of nearly 20dB (A).