What if the shaft sleeve of screw vacuum pump is locked?

Screw vacuum pump is a positive displacement pump with unique structure. It is mainly composed of drive motor and reducer, connecting rod and connecting rod box, stator and rotor, etc. According to the analysis of shaft sleeve locking of screw vacuum pump, the requirements of medium and rotating speed on shaft sleeve clearance are analyzed, and the rectification scheme to solve shaft sleeve locking is put forward.

What if the shaft sleeve of screw vacuum pump is locked?

1、 Cause analysis of shaft sleeve locking of screw vacuum pump
According to the working conditions of sliding bearing, the fit between bushing hole and shaft is generally clearance fit. The dimensional deviation between the shaft diameter and the bushing hole in a part is usually determined by ensuring a reasonable gap change between the shaft and the bushing hole at an average operating temperature of 20. There are many factors affecting the overheating of sliding bearings. Under the condition of reasonable bearing structure design and correct material selection, the overheating of sliding bearing is mainly caused by improper assembly and use of bearing radial clearance.

The influence of journal bearing radial clearance on bearing overheating fault. The radial clearance of sliding bearing is the difference between the diameter of bearing hole and the diameter of journal. The sliding bearing shall have a certain radial clearance. Its functions are as follows: it is the minimum condition to realize the movable connection between shaft and bearing; It is the guarantee of the operation accuracy of the control shaft. This is an important condition for the formation of liquid lubrication. Therefore, the radial clearance of sliding bearing is very important. Too large or too small is extremely harmful. If the clearance is too small, it is difficult to form lubricating oil film, and the friction heat is not easy to take away. In serious cases, the bearing will overheat and “hold the shaft”. If the clearance is too large, the oil film is difficult to form, which will reduce the operation accuracy of the machine, produce serious vibration and noise, and even lead to tile burning accidents.
In the actual use of the bearing, the friction heat is not easy to take away due to the small clearance. In addition, the lubricating oil is medium residual oil and contains many impurities, which is easy to enter the gap and lead to bearing overheating. In serious cases, the bearing will “hold the shaft” and burn the tile.

2、 Prevention and improvement measures of shaft sleeve locking of screw vacuum pump
In order to prevent the bearing from overheating, if the radial clearance increases, = 0.03mm. At this time, although the mating pair of the bearing can work normally, its service life is greatly shortened. Therefore, when determining the radial clearance of the bearing, the bearing should be as small as possible on the premise of normal operation. After the bearing is assembled, the running in and running in shall be carried out according to the running in test and running in specifications, and then gradually loaded and accelerated to make the convex part of the shaft and bearing mating surface smooth, and finally put into normal operation. Otherwise, even if the clearance is not small, because there is no test run after assembly, the bearing will operate normally, resulting in overheating and even Bush burning. For this reason, the radial clearance of sliding bearing should be controlled between 0.10mm and 0.15mm

The radial clearance of sliding bearing has a great influence on Bearing Overheating and service life. Therefore, the radial clearance must be strictly controlled within a reasonable range. When determining the radial clearance of bearing, the factors affecting the radial clearance should be fully considered. In addition to the diameter, speed, load and accuracy of the machine, the following points should be considered:

a. Bearing material of screw vacuum pump. Bearing material is different, expansion coefficient is different, clearance is also different.

b. Roughness of shaft and bearing surfaces.

c. Geometric shape and mutual position error of journal and bearing (i.e. roundness, cylindricity, coaxiality, etc.).

d. Working temperature of bearing of Shenzhen screw vacuum pump.

f. Sudden changes in starting conditions.

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