There is a special phenomenon of rotor shaft shifting in the process of motor use. Motor rotor out of the stator core, the occurrence of axial displacement, known as the rotor shaft. Under normal conditions, both ends of the stator core and rotor core are aligned, or the rotor is slightly shorter than the stator core. When the rotor core moves out of the stator core for 5 mm or more, the three-phase no-load current of the motor will increase significantly. After loading, the stator current will exceed the rated current value, which will overheat the motor. Together, there will be an uneven but regular buzz. If the motor rotor serious shaft shifting, the motor can not drive the load operation.
What is the meaning of motor shaft shifting?
There are two concepts of motor shaft shifting
1. The axial gap of the motor rotor shaft is too large, and it moves back and forth by hand, which is caused by the motor cover gasket being too thick, or the bearing seat hole being worn.
2. The axial displacement between the rotor shaft and the rotor is caused by the excessive knocking force when the rotor is disassembled. This condition often occurs in some small motors and rotors with carbon pivot.
Causes of axial movement
The shaft and rotor are in relative motion. The rotor core and shaft are interference cooperation. If, for some reason, there is a gap between the iron core hole and the motor shaft core position, resulting in the axial and radial relative orientation changes between the rotor core and the shaft, which is manifested as the shaft shifting problem. It is likely that the end cover and the end of the rotor will rub and deform due to the axial movement of the rotor core, which will affect the stator winding in severe cases.
Axial conditioning spring pad is damaged or missing. In the planning process of the whole machine, the thermal expansion factor of the motor material will be considered, and there is a certain gap in the axial direction. In order to avoid the hard contact in the process of axial displacement, the elastic cushion is added. If the assembly process is missing or the quality of the spring pad is defective, it will lead to the axial stop failure, which is directly manifested as shaft shifting.
The motor stator and rotor magnetic neutral line self alignment adjustment caused by the movement. The ideal condition of the motor is that the magnetic center line of the stator and the rotor coincide, but in the actual process, it is difficult to realize the axial alignment of the stator and the rotor. Therefore, the motor will continue to be aligned, offset, aligned, offset, etc The process of self-aligning conditioning, especially about the radial ventilation channel iron core, iron core floating curve, horseshoe and other problems, the repeated conditioning process is more severe, which presents the axial movement.
The axial rotating force of the electric fan. As for the motor with propeller fan or axial fan, the ventilation process will produce corresponding axial force on the motor during the operation of the motor; if the static balance effect of the fan itself is not good, or the fan is damaged, the axial movement of the motor will also be caused.
The end cap bearing chamber moves due to loose cooperation. In the case of larger axial impact, the cooperation between bearing chamber and bearing of end cover is more sensitive, especially for small size motor with sealed bearing. In order to avoid the occurrence of this problem, stop ring for hole should be added on the end cover.
What are the effects of axial movement
The movement of the motor shaft makes the joint parts that should not have relative motion slip, and the gap becomes larger, and the motor presents abnormal conditions such as vibration and noise. The original relatively static joint parts slip → increase vibration → slip weighted shaft → increase vibration → Until the bearing is scattered out of the "scavenging chamber" and the winding is burned. Even if it has not reached the level of winding damage, it will greatly reduce the service life of the motor.
A wave spring pad can be added between the outer edge of the bearing and the end cover for adjustment and buffering;
Real time monitoring and timely maintenance can eliminate the problem of motor shaft shifting before causing major accidents;
The inner cover of bearing table for fixed end bearing is stuck;
Control the links that lead to the motor shaft shifting;
Understand and master the actual working conditions of the motor to avoid bearing axial force.
Source: Jiangmen reducer http://www.ryzmbyq.cn
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