Summary:
Noise of rotary vane vacuum pump usually refers to the noise level measured under the limit vacuum when the temperature is stable.
It includes the noise of the pump itself and the motor noise for users. It also cares about the noise of the start-up stage when the pump temperature is not stable and the noise of the operation under different inlet pressure, as well as the noise of the air-conditioning station. Therefore. A variety of factors should be considered.
The noise of the pump can be divided into the following aspects:
(1) The impact of the rotor on the cylinder block, the residual volume of the pump and the sound of the pressure oil in the exhaust dead gap;
(2) Impact of exhaust valve disc on seat and support;
(3) Echo and bubble burst in the box;
(4) Bearing noise;
(5) Noise caused by large amount of gas and oil impacting the oil baffle;
(6) Others. Such as noise caused by transmission, fan noise of air-cooled pump, etc.
(7) Motor noise, which is a crucial factor.
The proposals for the design treatment scheme are as follows:
1. The impact of the rotary blade on the cylinder wall.
If improper design, manufacture or material is used, the sliding of the rotary blade is not smooth, or because of the existence of exhaust dead gap, incompressible oil causes the head of the rotary blade to not always run close to the cylinder wall, which will cause the impact sound of the rotary blade on the cylinder wall. Therefore, the circular arc surface should be used to separate the intake and exhaust ports. Eliminate dead gap with exhaust guide groove. When using line separating structure, the distance between exhaust end point and tangent point should be shortened as far as possible. For rotary vane pumps below 70L/s, considering the actual thickness of the rotary vane, it is suggested to take 7-lOmm and large pump. Too close, due to rotation
There is only one narrow band contact between the sub-rotating vane groove and the head of the vane. Once the sealing effect is not good when the vane turns to the cutting point, it will affect the pumping speed and even the limit pressure of the pump. It can be seen that this structure can not completely eliminate the exhaust dead gap and limit the noise reduction level.
It should be pointed out that too much clearance between the rotor and the groove will degrade the performance. Therefore, it is necessary to ensure reasonable tolerance fit and tolerance value of form and position, pay attention to the thermal expansion of the rotary blade, avoid the brushing of the rotary blade and groove, pay attention to the cold oil viscosity of the oil, and design enough spring force of the rotary blade. When using circular arc surface separation, the additional eccentricity value of the rotor center should not be too large. Otherwise, when the blade passes through two circular arcs, there will be a tendency to break away from the cylinder wall at the intersection point, which will cause impact noise instead. Generally, small pumps are 0.20-0.25 mm, and large pumps can be enlarged appropriately.
The sound of pressure oil in exhaust dead gap and pressure oil in residual volume. When the pump reaches the limit pressure, the two pressure oils will be injected into the vacuum chamber at high speed when connected with the vacuum chamber, and impact with the rotor and cylinder wall to produce sound.
The size and location of the two volumes are related to noise.
2. Impact Noise of Valve Plate on Seat and Support
The larger the amount of inhaled gas, the more the circulating oil of the pump, the greater the noise of the valve plate, the higher the valve jump, the larger the area of the valve, the greater the noise of the valve plate, and the material of the valve plate has a certain impact. The noise of rubber valves should be better than that of steel plates or laminates. Therefore, to control the oil inflow, the valve should be closed in time and tightly. Pay attention to the material selection and structure of the valve.
3. This noise will increase with the increase of echo and bubble burst volume in the chamber. Therefore, this noise will increase obviously when the air is opened or in the atmosphere. If the gas ballast can be adjusted, the gas ballast can be adjusted reasonably.
4. Noise emitted when a large amount of gas and oil are discharged and impacting parts such as oil baffles. If the parts are not rigid enough or not tightened, vibration and collision will occur, which will increase the noise. Therefore, not only should the oil baffle be rigid enough and tightened, but also when contacting with other parts (such as oil tank), rubber clamping method can avoid collision noise caused by vibration and improve the oil-retaining effect.
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