Analysis of the case of motor broken shaft

The problem of motor broken shafts has been found to be related to the manufacture of the motor itself, and to the actual installation, use and working conditions. Today we provide a real case for everyone.

Reason for motor broken shaft

● Improper assembly. When the motor is not in the same direction as the device being driven, the motor is subjected to excessive radial loads, which eventually leads to metal fatigue. When the radial load on the extension end of the motor shaft is too large, the motor shaft is bent and deformed in the radial direction. When the motor rotates, the shaft is deformed by the torsion force in all directions, and finally the motor shaft is broken, and the fracture position is generally close to the bearing.
For the motor with pulley connection, but some customers give the motor output shaft with pulley, because the pulley is too heavy or the belt is installed too tight, it will cause the motor output shaft to continue to be subjected to variable stress during the operation of the motor. The maximum bending moment generated on the shaft is near the fulcrum of the output shaft bearing, and the repeated impact causes fatigue, causing the shaft to gradually crack and eventually completely break.
● The equipment and motor vibration are too large during operation. If the motor is not firmly fixed, such as running on the frame, the whole foundation is unstable, and the operation is swaying, which causes the tension of the motor belt to be unstable, and the tension is large and small, causing damage to the shaft.
● The shaft machining stress groove does not meet the requirements. This problem occurs mostly in the position of the root of the shaft. A large number of case studies can be found that the R angle of the root of the shaft is not standardized, resulting in a relatively concentrated stress at the position. The motor is subjected to axial and radial alternating stress during operation, resulting in fracture. .
● The crack at the welding position of the web shaft is broken. This is mainly for high-power motors. The welding process of the web will lead to stress concentration. The necessary measures should be taken during the manufacturing process, such as smoldering, vibration, processing, stress reduction and other measures to reduce or eliminate stress. If improper operation, Position is the biggest hidden danger of shaft breakage.

Case basic information

A repair company has undertaken a YE3-355-6 380V 50Hz 220kW motor. The motor is actually equipped with crushing equipment. The shaft adopts a web structure. The broken end is at the end of the shaft end plate. The motor has been seriously damaged due to the shaft breakage. The motor is driven by a pulley and is used for about 20 days. The following is a picture of the fracture taken on site:

Basic requirements for motor connection

The motor is allowed to be driven by a coupling, a spur gear and a pulley, but for all 2-pole motors, a 4-pole motor of 37 kW or more, a 6-pole motor of 75 kW or more, and an 8-pole motor of 55 kW or more are not suitable for belt transmission. (If using a pulley drive, it may cause premature bearing damage or shaft breakage.)
When using a pulley drive, the center line of the motor shaft is required to be parallel to the center line of the load shaft, and the center line of the belt is perpendicular to the center line of the shaft. When using the coupling drive, the center line of the motor shaft and the center line of the load shaft should coincide (if the installation is improper, the motor will vibrate when it runs, causing the bearing to be damaged in advance, which will cause damage to the motor and equipment in severe cases).

Reprinted from the network