Analysis of Roots Vacuum Pump Noise

The synthesis of the important zero components of the Roots pump, and the analysis of the noise source during the application of the vacuum pump and the cause of the noise generated by the opposite bearing. Explain the corresponding measures to increase the above noise.
The Roots vacuum pump (referred to as the Roots pump) is a winding variable displacement vacuum pump without internal compression. In the pumping chamber, as shown in Fig. 1, there are two symmetrical braids in the pump chamber, and the shape of the coil has two leaves, three leaves and four leaves. The two pronations wrap around each other at the same position. The synchronous rotation is driven by the shaft end gear. The spinners are not in contact with each other, and the loops are not in contact with the pump chamber wall, and there is usually a gap of 0.15 to 1.0 mm therebetween, and the pump wall is sealed by a gap. Usually the change of the gap is also an important cause of noise, and the backlash between the transmission gears is an indirect cause of the heat generated by the gearbox. The same sound of heat will also generate noise. The relationship between the two is not enough.
1. Internal and rising measures of noise The noise of a Roots pump usually refers to the noise level measured when the pump is running stably. It covers the noise of the pump itself and the noise of the motor. In terms of the part of the sound, the pump noise has the following possible numbers.
1 bearing noise;
2 gear noise;
3 The change of the gap between the spinner and the side cover causes the noise generated by the friction of the spinner and the side cover and the noise of the gas flow generated thereby.
In addition to the noise generated by the built-in error of the bearing and the gear, the most important noise is actually the accumulation of the error of the rotor, side cover and bearing housing of the pump. Reflected in the bearing, the coaxiality of the bearings at both ends becomes larger. as shown in picture 2.
Because of the parallelity error of the end faces of the pump body, the perpendicularity error between the end face of the side cover and the inner hole of the socket, the coaxiality error between the inner hole and the outer circle of the bearing seat, and the position error of the lateral cover and the rotor when positioning. The final consequence is reflected In the bearing, the accumulative error of the inner hole of the front and rear bearings accumulates. That is, the spine shaft emerges. Figure 3 (b) Condition: The shaft receiving force is not misaligned, causing the twisted shaft to be distorted, the twister is shocked, the bearing is hot and the sound is emerging. The double row bearing emerges from the scene. More obvious. Therefore, the single-row bearing is thin, and there is no strong double-row bearing when it restricts the rotational freedom of the shaft.
The company has made similar attempts. On the rigid fulcrum tops of 5 ZJP-1200 Roots pumps, the double row deep groove ball bearings made by Oman are equipped with imported roller bearings at the floating fulcrum end. The noise is large and the average is 85.7dB. (A); replace the double row deep groove ball bearing at the rigid fulcrum end and install it in Germany (the price is 1 times higher than that produced by Oman). The noise is slightly larger than that produced by Oman, and the uniformity is 86.3dB(A). The cause is that German bearings have higher precision and the accumulation of zero component errors is more obvious. Remove the bearings at both ends and replace them with single row deep groove ball bearings. The vibration is reduced and the noise is obviously increased, which is 82.7dB (A). Then we continue to improve the manufacturing process of the zero components, select special facilities to process the important machine, continue to grind the bearing housing to reduce the manufacturing error, and the noise of the Roots pump with the double row bearing is also increased. The uniformity is 82.3dB (A). This consequence is sufficient to indicate that the processing accuracy of important zero components is not necessary for the noise level of the Roots pump.
The noise generated by the gear is the opposite of the cause of the noise generated by the bearing. However, it has a greater relationship with the precision of the gear itself, because there is an error in the coaxiality between the outer teeth of the gear and the inner circle. When a pair of gears mesh with each other, a pair will emerge. All the teeth mesh tightly, that is, the backlash between them is too small, and is looser than the absolute one. In this kind of situation, one of the gears can be unloaded, and the gear is wound 180 degrees along the rotary shaft, and the coaxiality error between the outer teeth and the inner circle of the gear is canceled, and the gap between the gears can be evenly distributed. It can eliminate the noise when the gear meshes. It is only the invalid measure to increase the noise of the Roots pump.
The heat generated in the compression of the Roots pump operation is transmitted to the rotor and the pump body. It is difficult for the rotor to transfer heat to the outside of the pump, and the heat of the pump body is easily dissipated to the surrounding atmosphere. Therefore, the rotor and the pump body The difference between the two is deepening. The heat shrinkage of the spinner is deepened.
If the screwdriver is not stuck in the middle of the operation, it is necessary to make a clearance between the rotary table and the pump chamber between the rotary table and the end cap in order to compensate for the vacuum pump construction and disassembly. Inaccuracy and deformation caused by heat, and the shape of the rotor is symmetrical, the dynamic misalignment performance is good, can reduce the vibration noise and heat.
The whole machine noise of the Roots vacuum pump is regulated, the motor noise must be lower than this sound level, so the two sound sources are very close, so the motor noise is lower than the whole machine noise by 3~4dB (A) is completely redundant, in order to achieve domestic The degree of sophistication, such a setting is a must.