The magnetic field of the motor is mainly reflected in the gap between the stator and the rotor, which is what we call the air gap magnetic field. When the motor rotor moves to a certain position along the axial direction, the magnetic lines of the air gap magnetic field are all perpendicular to the motor shaft and have no axial component. The magnetic centers between the stator and the rotor are in an aligned state. At this time, the specially processed notches on the motor shaft extension end are The line position is called the magnetic centerline.

For large and medium-sized motors using sliding bearings, when the motor is stopped and running, the rotor can be seen to move significantly in the axial direction. This process is the alignment process of the magnetic centerline. In order to avoid additional axial force causing damage to the equipment or affecting operating accuracy, the shaft must be powered on and idle before coupling, and the magnetic centerline position must be calibrated, and then the coupling must be installed.
 
Theoretically, the axial geometric centers of the motor stator and rotor should coincide. However, due to actual assembly operations and machining errors of parts, it is difficult to ensure the axial symmetry of the magnetic field or the alignment of the magnetic centerline. Due to these errors, after the motor is powered on, the rotor of the motor will move toward the center of the magnetic field due to the magnetic field, correcting the deviation after actual assembly. If calibration is not performed, when the motor is running, the motor shaft will be subject to the interaction between the equipment installation tightening force and the axial electromagnetic force, resulting in axial reciprocating motion, which is what we call axial movement.
 
The reciprocating process of continuous centering and deflection of the above magnetic force lines will cause the intensity of the motor's axial vibration to be larger or smaller depending on the level of the deviation of the magnetic centerline. In severe cases, the harm to the motor body and the dragged equipment can be fatal.
 
Simply put, after the motor is powered on, it will automatically complete the centering adjustment of the magnetic center line, that is, correct the misalignment of the stator and rotor caused by various factors, and decide the installation adjustment plan accordingly.
 
In the production and manufacturing process of the motor, if there are problems such as the motor core springing out, horseshoeing, misalignment of the stator and rotor, uneven air gap between the stator and the rotor, etc., after the motor is powered on, the rotor part will also experience varying degrees of axial movement. In addition to the relative movement of the axial positions of the stator core and the rotor core, the bearing system of the motor will also be affected. When the axial displacement exceeds the allowable axial clearance, the operating condition of the bearing itself will deteriorate, causing noise, heat and other undesirable phenomena. If the movement is severe, the grease in the bearing will be thrown out, thus causing the Bearings burn out due to poor lubrication in a relatively short period of time.