The equipment is a three blade roots blower, and the working chamber and bearing seat are sealed with carbon rings. The rear end bearing is a support bearing, which bears the radial force and axial force of the rotor. The front end bearing is a support bearing, which bears the radial force of the rotor. The front end cover and shaft are sealed by skeleton. There is a pair of helical gears at the tail as synchronous gears. The power transmission mode is belt pulley transmission. The axial positioning of Roots blower is ensured by the production of parts. Axial positioning needs to be adjusted, and the adjustment of rotor axial positioning is related to the operation of the whole fan, so it is particularly important.
1. Axial clearance
The main function of axial positioning of roots blower is that when the fan is running, the shaft system will produce linear expansion and body expansion due to rotor heating. The volume expansion reserve is guaranteed by axial processing, and the linear expansion reserve is determined by axial positioning. If the axial reserve is too large, the fan efficiency will be reduced; If the axial reserve is too small, the fan housing and bearing will be heated and damaged.
In general, the following faults are not allowed for axial clearance:
In order to understand the effect of axial positioning, the problems caused by wrong positioning are systematically analyzed:
1) Bearing pedestal end face damaged
There are two main reasons for bearing end face damage. First, the probability of foreign matter entering the rotor and bearing pedestal end face is too small, so it will not be analyzed here. Second, the axial clearance is insufficient, resulting in the contact damage between the rotor and the bearing end face during online expansion. We know that molecules of any substance are doing irregular thermal movement, so molecules have speed and kinetic energy. Microscopically explain that the pressure of gas is the collision of a large number of molecules on the wall of the container, and the temperature is the measurement of the average kinetic energy of the thermal movement of a large number of molecules. The higher the temperature is, the greater the average thermal motion of the molecule is, and the greater the molecular speed is. As we all know, the higher the speed, the stronger the collision, that is, the greater the pressure of the gas. When the fan produces pressure, the opposite gas produces temperature. The temperature causes the rotor to stretch. If the clearance is not enough, the rotor will rub against the housing.
The axial clearance is too small, resulting in damage to the end cover and impeller end face
At the same time, the friction generates heat, which increases the bearing temperature through heat conduction and damages the bearing and seal ring.
2) Reduce fan efficiency
Excessive axial clearance will reduce fan efficiency. Roots blower is a volume fan, and its wind pressure is related to the system, but not to others. In other words, it is related to the characteristics of the outlet pipeline. The flow has a lot to do with the fan speed. However, if the axial clearance is slightly larger, the impeller end face and the bearing seat end face will form a gas channel. The gas channel will make the variable pressure gas return to the suction port of the fan through it, so that the fan is constantly busy rationing, reducing the air volume and efficiency of the fan.
3) Fan vibration
When the clearance is too small, the impeller end face will rub with the bearing seat end face. The unit will produce strong vibration due to friction between sound positions. Excessive vibration is likely to cause friction in the sound part, and then cause devastating consequences. Friction occurs on the seal ring of the shaft, which will lead to the thermal bending of the rotor, further increase the vibration, form a malignant, leading to the bending of the rotor. Vibration and shaft bending will cause bearing damage, gear damage, impeller damage, and even the whole roots blower scrapped.
2. Adjustment skills
2.1 Positioning principle
Axial clearance positioning is mainly determined by bearing positioning. The bearing positioning mode of ROBOX roots blower is fixed end free end. The tail of roots blower is fixed end, and the front end is free end. Through the fixed end, the rotor can expand freely to the free end under the premise of hot state.
2.2 Calculation of Voids
Calculate the linear expansion of rotor in hot state:
C=1.2 Δ TL/100
C Thermal expansion elongation (mm);
Δ Difference between temperature and ambient temperature during operation of T-axis; Length of the L axis.
When calculating the value of C, the linear expansion of axis C is axis
2.3 Air conditioning skills
The axial clearance adjustment of Roots blower is mainly based on the calculation data, and the tail positioning bearing is used to adjust the entire clearance.
1) Measure the distance X between the two ends of the housing;
2) Measure the distance Y between the two end faces of the rotor;
4) The inner ring of the bearing is in contact with the shaft shoulder, and there is a clearance S between the outer ring of the bearing and the locating ring outside the bearing seat. When the outer end cover is fastened with bolts, the bearing pushes the entire rotor to the front end, and the value of&2 gradually increases. Therefore, add shims at clearance S to make it possible& 1,&2 values meet the required clearance.
5) In daily work, the shim thickness can be determined in two ways. One is the measurement method, which mainly uses a deep micrometer to measure the S value, and then measure the S value S -&2=K. K This is the thickness of the shims. The other method is the additional test method. The additional test method is a fake shaft sleeve. The diameter of the shaft sleeve is 1mm smaller than the outer ring of the positioning bearing, and the inner diameter is 1mm larger than the shaft. The thickness is the standard bearing thickness. Try to add shims to the shims every time, then tighten the shaft sleeve according to the standard, and measure the&2 value with a feeler gauge until the&2 value reaches the standard value.
6) The relationship between&1 and&2 is 2:1. That is, when it is used as& When 1 is 0.30mm, the value of&2 is 0.15mm. The purpose is to increase the expansion clearance at the free end of the rotor.
Axial clearance positioning of roots blower is the key point of maintenance during installation of roots blower. The installation quality is related to the smooth operation of the equipment. Due to the inaccurate adjustment of the axial clearance, the roots blower has been damaged one after another. Therefore, it is particularly important to master the skills of adjusting the axial clearance of roots blower. In the maintenance of rotating machinery and equipment, all reference standards should be based on data, and any wrong method judged by human experience should be abandoned.
