What is noise:
To know why a cylinder needs to be equipped with a muffler, you first need to understand what noise is?
Noise includes mechanical noise, electromagnetic noise and aerodynamic noise. The noise generated by solid vibration is mechanical noise. In the electromagnetic coil, the moving iron core vibration caused by alternating current is electromagnetic noise. When the gas has a vortex or a sudden change in pressure, it will cause the gas to vibrate, which is aerodynamic noise.
Factors affecting noise:
The compressed air on the exhaust side of the cylinder is usually discharged into the atmosphere through the exhaust port of the reversing valve. Due to the high residual pressure and the maximum exhaust velocity near the speed of sound, the air expands sharply, causing the gas to vibrate, resulting in strong exhaust noise. The size of the noise is related to the exhaust speed, exhaust volume and the shape of the exhaust passage.
The size of the noise:
The magnitude of the noise is measured in decibels (dB). Generally, the noise in the machining workshop is 70~85dB, and the noise from pneumatic tools such as air riveting guns is about 100dB. According to international standards, for eight hours a day, the allowable continuous noise is 90dB; the time is halved and the noise is allowed to increase by 3dB, but 115dB is the maximum limit. Anything higher than 85dB should try to reduce noise.
People's perception of noise is also related to the frequency of noise. Generally, the audio frequency range that can be heard is 20~20001z, and the audio frequency of normal speech is 500~200Hz. Noise with the same decibel number sounds much louder than low-frequency noise. On a gas tank with a volume of 24L and an internal pressure of 0.5MPa, there is a solenoid valve with an effective cross-sectional area of 48.5m㎡. When the solenoid valve is opened to vent air to the outside, the measured noise is 1m away from the outlet of the solenoid valve .General exhaust noise is 80~120dB.
The adverse effects of noise on people:
Working in a noisy environment for a long time will make people feel tired and reduce work efficiency; reduce people’s hearing
Power, affect human health. Therefore, measures must be taken to reduce noise. Good noise reduction performance means that there is sufficient noise reduction in the frequency range of the generated noise.
The working principle of cylinder muffler:
Two noise reduction principles are introduced below:
1) The absorption type allows compressed air to pass through the porous sound-absorbing material, and generates heat by friction with the airflow, so that the pressure energy of the gas is partially converted into heat energy, thereby reducing exhaust noise. Absorptive muffler has good performance in eliminating medium and high frequency noise.
Generally, the noise can be reduced by more than 25dB. Most of the sound-absorbing materials use polyvinyl chloride fiber, glass fiber, sintered copper beads, etc.
1) Expansion interference type This muffler has a larger diameter than the exhaust aperture. The air flow diffuses, collides and reflects inside, interferes with each other, reduces the noise intensity, and finally discharges into the atmosphere from the porous shell with a larger aperture. Mainly used to eliminate medium and low frequency noise.
2) Lead some of the gas discharged by the valve to the main exhaust pipe with a large enough inner diameter. The outlet of the main exhaust pipe can be installed with an exhaust cleaner, or the outlet of the exhaust pipe can be set outdoors or in a trench to reduce The noise in the working environment is called the centralized exhaust method.
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