Abstract: Through the analysis of the causes of shaft displacement in sliding bearings, a design idea for controlling shaft displacement is introduced.
Keywords: sliding bearings; Axis movement; electric machinery; design
1. Introduction
At present, the bearings used in large industrial motors are all sliding bearings. However, the shaft displacement of motors using sliding bearings can only be controlled within a critical value of ± 1mm in the industry. This is not a problem for most loads. However, for some special loads, when the requirements for shaft displacement are very strict, such as when the motor shaft displacement must be controlled within ± 0.3mm during the entire start stop process, the motor shaft displacement must be controlled through design means.
2. Analysis of the causes of sliding bearing shaft movement
The main factors are the symmetry of electromagnetic tension, the coaxiality of the shaft bearing stopper, the spring-loaded amount of the punching teeth, the uniformity of the air gap, the coaxiality of the two end caps of the machine base, the coaxiality of the end cap stopper, the assembly method, and the alignment of the stator and rotor iron cores.
The above methods all require strict requirements for the production process, which undoubtedly requires an increase in cost to ensure, and cannot fully guarantee the shaft displacement of ± 0.3mm during the entire start stop process. At this time, it is necessary to control the shaft displacement through design.
3. Design concept
(1) On the basis of conventional design, sliding bearings are used to limit the axial displacement of the shaft by using the thrust surface of the bearing shell. The width of the bearing shell is 0.6mm smaller than the shoulder width of the shaft. Therefore, the shaft movement during the entire start stop process of the motor is inevitably ± 0.3mm. However, normally, such a design will result in a high temperature of the bearing shell, even exceeding 80 ℃, which cannot be used. Below are the specific operation methods.
(2) Firstly, according to the normal bearing design, there is a 3mm gap between the bearing and the shaft shoulder on one side, and it is assembled into the whole machine. A C-shaped center hole is drilled at the extension end of the shaft, and a round head bolt is designed and installed on the center hole. At this time, the motor can be debugged. Start the motor to the rated speed and use a dial gauge to measure the Z-large and Z-small values of the shaft displacement at the rated speed. At this time, the shaft displacement value may be affected by the limit of the shaft shoulder and may be inaccurate. Therefore, it is necessary to measure the displacement value of the rotor in the natural stop state after power failure to eliminate the influence of the shaft shoulder limit. If there is a shaft shoulder limit, use the above three data to analyze whether it is the inner or outer shaft shoulder limit. According to the analysis results, add or remove shims on the bearing seat and end cover mating surface to adjust until the shaft shoulder limit is eliminated. Position influence. Then perform a second debugging using the same method as above. Record the Z-large and Z-small values of the shaft displacement at the rated speed, and use these two data to calculate the actual magnetic centerline position of the motor during operation. At this point, use a 0.1mm copper foil gasket to fine tune until it reaches the theoretical calculation of 3mm on one side of the bearing and shaft shoulder.
(3) Then you can replace another set of bearing shells (hereinafter referred to as wide bearing shells), which are slightly wider than the normal bearing shell width. The width of the wide bearing shell is determined by subtracting 0.6mm from the shoulder width of the shaft. When calculating, the tolerance value should be taken into account, and then the third debugging should be carried out. During the rated operation of the motor, monitor the temperature of the bearing shell and the shaft displacement value. If the shaft displacement value is constant and biased towards one side, it is possible that the shoulder of the other side will rub against the bearing shell during operation. The copper foil needs to be increased or decreased according to the shaft displacement value until the shaft can move forward and backward. Then, the temperature of the bearing shell should be detected continuously for two hours. If the temperature does not exceed 80 ℃, it indicates that the adjustment is successful. At this point, the motor experiences a shaft displacement of ± 0.3mm during the entire start stop process.
4. Conclusion
This design can meet the requirement of ± 0.3mm motor shaft displacement for some special loads without increasing material costs.
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