Broken shaft
The motor shaft breakage occurs mostly at the root of the shaft extension and the root of the shaft extension end bearing position.
If the motor has a shaft fracture, the shaft fracture surface should be macroscopically observed and microscopically analyzed to find out the location of the fracture crack source and the cause, and fundamentally restrain the problem.
The reasons for the fracture of the motor shaft are summarized
The fracture of the motor shaft is the result of the superposition of multiple factors.This article lists several common reasons:
1. Manufacturing potential quality problems.The fracture form of the motor shaft belongs to low-stress rotating bending fatigue fracture. The root cause is defects in the production and processing of the motor shaft, such as no process control requirements for the transition fillet of the shaft shoulder, no heat treatment after welding, and super inclusions in the surfacing layer. The stress of the shoulder fillet is concentrated, and fatigue cracking occurs under the action of the rotating bending moment, which eventually leads to the fracture of the motor shaft.
2. Installation problems.If the belt pulley is used for transmission, the belt tension is larger than the value recommended by the belt manufacturer), which increases the load on the motor shaft, which is a contributing factor to the breakage of the motor shaft.For motors installed with couplings, if the coaxiality between the motor and the equipment axis cannot be guaranteed, the shaft will also be fatigued and fractured.
3. The web axis is broken.Excluding installation factors, the web shaft often has irregular cracks at the welding position of the web. Most motor manufacturers solve the problem of this type of shaft by processing stress grooves at the two ends of the web and the main shaft through the annealing process. Broken shaft problem.
Axis shift
No matter what motor should not move shaft at any time, a slight amount of movement has little effect on the motor itself. When the amount of movement is large to a certain extent, the current will increase, the temperature of the motor will rise, and the mechanical shock will increase. Affect other equipment and other specific issues.
Analysis of the cause of the motor shaft shifting
1. The mechanical center is inconsistent with the magnetic field center.When the motor is running, its rotor will be positioned at the center of the magnetic field, and there is a mechanical center between the rotor main shaft and the two bearings (that is, the position where the distance between the shoulders of the motor rotor at both ends and the bearings is equal).The two centers may be inconsistent. If the shaft shoulder spacing is adjusted based on the mechanical center during installation, when the motor is started, the rotor will automatically be positioned at the center of the magnetic field, and the axial movement of the motor shaft will damage the original installation.的axial spacing.When this deviation is not large, for gear couplings, the reserved axial clearance of the inner and outer gear sleeves can be compensated; if the reserved axial clearance of the coupling is exceeded, the coupling and the driven shaft will suffer An axial force exerts harmful effects such as friction on the end face of the component and heat generation.
2. For sliding bearing motors, errors occur when the rotating shaft system is centered according to the coupling.The misalignment of the shaft in the bearing will add a lot of additional torque to the bearing. Because the motor rotor can move back and forth in the axial direction within a certain range, when the shaft center is not correct, the coupling will produce a fixed direction of axial separation. The force causes the rotor to push to one side against the force of the magnetic field under the action of the axial component force, resulting in dynamic and static friction between the oil retaining shoulder blade of the motor rotor and the babbitt alloy outside the bearing.
3. The lift at both ends of the motor rotor does not meet the requirements.The unreasonable rise of the shaft journals at both ends of the motor rotor will cause the motor rotor to overcome the magnetic field force and slide to the end with a small rise under the action of the axial component of its own gravity.Therefore, reasonable lift at both ends of the motor shaft is the key to eliminating the axial component of force.
The rotor has static deflection due to its own weight, which is manifested as the two ends or journals will rise upward when the rotor is placed horizontally.This lift value measured with a precision level is customarily called the rotor lift.
In view of the various reasons of motor shaft shifting, problems should be avoided in the process of motor design, manufacturing and installation. It is also very important to restrain and prevent the occurrence of problems through some necessary means in the actual process.
● Choose an interference fit for the fit between the shaft and the rotor.If the movement occurs due to the fitting problem, it is mostly due to the problem of the machining size of the shaft, because the inner diameter of the rotor shaft hole is determined by the punching die, and theoretically there will be no major problems.
● The wave spring washer at both ends of the bearing is not installed, or there is a problem with the quality of the wave spring washer.Some motor operating conditions have relatively strict requirements on the amount of shaft movement. Motor manufacturers solve the problem by adding wave spring washers, and some manufacturers add stop rings on the end caps for small motors with sealed bearings.
● The axial force generated by the fan, that is, the axial force of the wind on the fan blade when the motor is running, but the amount of movement caused by this is very small.
● The matching selection of the bearing and the end cover is inappropriate, or there is a large gap between the two due to processing quality problems.
