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Common types of motor shafts
- Feb 11, 2019 -

The shaft is an important part of the motor. It acts as a link between the electromechanical energy conversion between the motor and the device, supporting the rotating parts, transmitting torque and determining the relative position of the rotating parts to the stator. Therefore, the motor shaft must have reliable strength and rigidity to ensure the implementation of the pre-set design function.

Type of shaft and its applicability

1. According to the classification of the ladder on the axis. Can be divided into optical axis and stepped axis. The optical axis is often made of cold drawn round steel, which reduces the man-hours for machining the outer circumference of the shaft and is sometimes used in micromotors. Stepped shafts can be easily and securely mounted with many different components, so most motors use this type of shaft.

In the stepped shaft, depending on the direction of the step, it can be divided into a one-way stepped shaft (the step diameter is gradually reduced from one end of the shaft to the other end) and a two-way stepped shaft (the step diameter is stepped from the middle to the both ends of the shaft) Reduce).

2.Classify according to the manufacturing method of the shaft blank. It can be divided into round steel shafts (shafts made of hot rolled round steel), forged shafts (shafts made of forged parts) and welded shafts (shafts with welded ribs).

The shaft made of hot-rolled round steel is the most common shaft in small and medium-sized motors. The material of the shaft is usually 45 high quality carbon structural steel. For small power motors, some use Q235 ordinary carbon steel. The blank diameter is selected according to the maximum diameter of the shaft plus the machining allowance. Therefore, the amount of cutting is relatively large.

Forged shafts are preferred for shafts over 100 mm in diameter. The forged steel has high mechanical strength and the general shape of the stepped shaft can save raw materials and cutting man-hours. For large shafts with high mechanical strength requirements, such as the shaft of a turbo generator, alloy steel forging is commonly used.

The welding shaft replaces the rotor bracket with the radial ribs, which can increase the ventilation area of the rotor inner cavity. However, when the rib is welded, the shaft is easily deformed and must be annealed after welding. It is not continuous cutting when machining on the machine tool, which is not good for the tool. Due to the presence of welds, the fatigue strength of the shaft is significantly reduced and is therefore not suitable for high speed motors.

3.According to the combination of the shaft and the core. It can be divided into a central knurled shaft, a hot sleeve shaft and a central keyway shaft. The knurled shaft is used for small motors up to 10 kW, eliminating the need for machining and keyways. However, when the shaft is pressed into the core, it is easy to deform the shaft. During the operation of the motor, some of the knurled rotor cores move axially. This kind of shaft deformation is caused by the over-tightening of the core and the shaft, and the axial displacement is caused by insufficient interference between the two.

The middle portion of the hot sleeve shaft is neither knurled nor keyed. There is a certain amount of interference between the shaft and the inner hole of the core, and the core is inserted into the shaft in the hot state. The combination of the rotor core and the shaft is very reliable as long as the interference is properly selected.

The shaft with the keyway in the middle can be divided into a section with a groove and a two-stage keyway. The shaft with a keyway is used for small motors. A shaft with two keyways is used for medium to large motors. The rotor core (or bracket) and the shaft are keyed. The core is axially fixed, the shoulder is added at one end, and the other end is clamped in the annular key groove on the shaft by a curved key. This kind of shaft can transmit a large torque, and is often used for motors with high power and motors that are frequently reversed during operation or that the rotor core is not suitable for hot sets.

4.Classify according to the shape of the shaft extension. It can be divided into a cylindrical shaft extension shaft, a conical shaft extension shaft and a shaft with a shaft coupling half coupling. The cylindrical shaft is easy to machine and is used most in the motor. The round-shaped shaft has a fastening bolt and a large amount of processing. However, the fitted transmission wheel is convenient to load and unload, and is mostly used in special motors. The shaft with the half coupling is mainly used for hydroelectric generators and large DC motors.

Classify according to the shape of the axis. It can be divided into a solid shaft, a shaft with a deep hole at one end, and a shaft with a center through hole. Solid shafts are most commonly used in motors. A shaft with a deep hole at one end is mainly used for a wound-type asynchronous motor, so that the lead wire on the rotor is connected to the slip ring outside the end cover through the hole. The shaft with the central through hole is mainly used for large motors: in the dual water cooled turbine generator, the central through hole is also used as part of the cooling water circuit.

5.According to the axis guide magnetic classification. Can be divided into a magnetic axis and a non-magnetic axis. The magnetic guide shaft is mainly used in a steam turbine generator. The shafts of other motors usually do not require magnetic guidance.

6.Other classification methods. According to the number of shaft extensions, it can be divided into single shaft extension shaft and double shaft extension shaft; according to the number of bearings, it can be divided into single bearing shaft, double bearing transmission and multi-bearing shaft.

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