Causes of motor shaft breakage classification

● Improper assembly. When the motor is not concentric with the equipment it is dragging, the motor is subjected to excessive radial load, which eventually leads to metal fatigue. When the radial load on the motor shaft extension is too large, the motor shaft will bend and deform in the radial direction. When the motor rotates, the shaft is subjected to torsion in all directions and deforms, which eventually causes the motor shaft to break. The fracture position is generally near the bearing.

 

For motors connected by pulleys, some customers equip the motor output shaft with pulleys. Because the pulley is too heavy or the belt is installed too tightly, the motor output shaft will be continuously subjected to variable stress during operation. This stress produces a maximum bending moment on the shaft near the output shaft bearing fulcrum. Repeated impact causes fatigue, causing the shaft to gradually crack and eventually break completely.

 

● Excessive vibration of the equipment and motor during operation. If the motor is not firmly fixed, such as running on a rack, the entire foundation is unstable and shakes during operation, resulting in unstable tension of the motor belt, and the tension is sometimes large and sometimes small, causing damage to the shaft.

 

● The stress groove of the shaft does not meet the requirements. This problem often occurs at the root of the shaft extension. A large number of case analyses show that the R angle processing at the root of the shaft extension is not standardized, resulting in relatively concentrated stress at this position. When the motor is running, it is affected by the alternating stress of the shaft diameter and radial direction, resulting in fracture.

 

● Cracks and fractures at the welding position of the web plate shaft. This is mainly for high-power motors. The web plate welding process will cause stress concentration. Necessary measures should be taken during the manufacturing process, such as smoldering, vibration, and processing should be used to reduce or eliminate stress due to stress grooves. If the operation is improper, this position is the biggest hidden danger of shaft fracture.

 

Basic information of the case

A repair company undertook a YE3-355-6 380V 50Hz 220kW motor. The motor is actually equipped with crushing equipment. The shaft adopts a web plate structure. The fracture is at the end of the web plate at the end of the shaft extension. Because the shaft is broken, the motor has been severely swept; the motor is driven by a pulley and has been used for about 20 days. The following are pictures of the fracture taken on site: