The rotating shaft is a very critical structural component of motor products and is the direct subject of mechanical energy transmission. At the same time, for most motor products, the rotating shaft will also serve as an important component of the motor magnetic circuit and play a certain role in magnetic diversion.

The vast majority of motor shaft materials are steel with magnetic conductivity, especially for large high-speed motors and small and medium-sized induction motors. The motor's rotor core is directly matched with the shaft. Under no-load conditions, the induction frequency of the motor rotor is very low, and the yoke magnetic flux will penetrate deeply into the rotor. The magnetic circuit shunt effect of the shaft is different for different motors and under different conditions.

In the calculation of the motor's magnetic circuit, the motor's shaft is often included in the magnetic circuit, and some basic principles are determined according to the different pole numbers and shaft materials.

The magnetic shunting effect of the shaft of a 2-pole motor is relatively large, mainly due to the matching relationship between the rotor and the shaft of the 2-pole motor, and the special nature of the relatively small outer diameter of the motor rotor. 1/6 of the shaft side of this type of motor, or 1/3 of the diameter, is included in the magnetic circuit calculation, that is, this part of the shaft will be included in the motor magnetic circuit calculation; for motors with 4 poles or more, 1/12 of the shaft side, or 1/6 of the diameter, is included in the magnetic circuit calculation .

In view of the principle of the degree of participation of the shaft in magnetic circuit calculation under different pole numbers, the change of the material of a 2-pole motor has a greater impact on the performance of the motor. For example, if the ordinary shaft of a 2-pole motor is directly replaced with a stainless steel shaft, serious current increase and winding heating problems will occur due to magnetic flux saturation problems. For other multi-pole motors, due to the ratio of the motor shaft diameter to the diameter of the rotor punching, as well as the principles of motor magnetic circuit design, replacing the ordinary shaft with a stainless steel shaft will not have a significant impact on the motor's performance.

Understanding the principles of the motor shaft in the construction of the magnetic circuit can effectively prevent unnecessary mistakes in motor repair.