Common Problems and Causes of Magnets in External Rotor Motors

In the structure of an external rotor motor, magnets are typically bonded to the inner wall of the rotor housing. They endure centrifugal force from high-speed rotation over a long period, coupled with effects such as temperature rise and vibration. Consequently, a series of typical issues tend to occur with external rotor magnets in practical applications.

First, magnet detachment is one of the most common and high-risk problems in external rotor motors. The root causes are mostly related to unreliable bonding, such as insufficient temperature resistance grade or shear strength of the adhesive, or process defects including uneven glue application and incomplete curing during production. Unremoved oil stains or oxide layers on the magnet surface can also significantly reduce adhesive adhesion. Combined with long-term thermal cycling, the adhesive layer ages and cracks, easily leading to magnet detachment.

Second, magnet displacement is another frequent problem. Although the magnet is not completely detached, its position or angle shifts, which directly destroys the symmetry of the magnetic field distribution, resulting in torque ripple and increased noise. Such issues are mainly caused by bonding failure, such as improper adhesive selection or an overly thin adhesive layer.

Demagnetization or degradation of magnetic properties is also common. External rotor motors generate a certain temperature rise during operation; if this exceeds the temperature resistance grade of the magnetic material, irreversible demagnetization occurs, leading to reduced motor torque and efficiency. In addition, under abnormal working conditions such as high-current surges or control failures, a strong reverse magnetic field may be generated, which also causes demagnetization of the magnets.