By
There are several structural similarities between vertical and horizontal motors; both types use bearings for the support of the rotor. The bearings play an important role in providing a smooth operation of the motor by absorbing the forces caused by the weight of the rotor. Despite the structural similarities, the orientation of the motor plays a significant role in the distribution and bearing of these forces.
The orientation of the motor determines the nature of the forces on the bearings. In a horizontal motor, the weight of the rotor acts as a radial load on the bearings at both ends and is shared equally between them. In the case of a vertical motor, the weight of the rotor becomes an axial load. This shift requires the bearings to handle a different type of force, impacting their design and selection.
In horizontal motors, the bearings have a major load radial to the bearings due to the rotor’s gravity. This radial load, acting perpendicular to the axis of the shaft, is equally shared between the two bearings. This way, the rotor remains balanced and runs with efficiency while the bearings support it with stability.
In vertical motors, gravity pulls the rotor along the motor shaft. While in horizontal motors, the bearings bear the radial loads, in vertical motors, the bearings are set to bear this axial force of the rotor. In turn, this means bearings must be capable of handling substantial axial loads to keep the rotor in place and keep the motor running properly.
Simplified, it is assumed that the motor is not subjected to external axial and radial forces, other than the rotor’s weight. Also, for slight misalignments of the stator and rotor centerlines, which easily can occur in normal operational conditions, any asymmetric air gap would result in a radial load. These are assumptions only necessary to simplify the basic explanation of the main forces affecting the bearings and give more clarity to their role at different motor orientations.
Bearings in motors are generally arranged so that one end is located and the other end is free. The locating end bearing is designed to accept axial loads, maintaining proper alignment of the rotor. The free-end bearing can accept radial loads and allows for some thermal expansion and slight misalignment without placing additional stresses on the bearings.
The fixed or positioning end bearing supports axial and radial loads while providing stability and precise alignment to the rotor. On the other hand, the floating end bearing manages the major part of radial loads, allowing axial movement caused by thermal expansion or other causes. In vertical motors, the weight of the rotor applies an axial force to the positioning end bearing, and this bearing must be designed to accept this load without significant wear or failure.
To put it clearly, the terms “shaft extension end” and “non-shaft extension end” are defined. The shaft extension end is that with which the motor shaft sticks out of the motor housing, which is usually used in connecting to other mechanical parts. The non-shaft extension end is on the opposite side of the motor.
Whether the extended end of the shaft is at the top or the bottom, there are similar principles in bearing configuration and load distribution for a vertical motor. The basic concern is having the bearing at the positioning end suitably designed to take the axial load to hold the weight of the rotor and extra forces when operational.
Three aspects to note:
1. Selection of bearings at both ends
Since the positioning end bears axial force, a bearing that can bear axial force shall be selected at the positioning end. It doesn’t matter for the non-positioned end. The most common selection is that deep groove ball bearings and angular contact ball bearings, etc., which can bear axial loads, can be used as positioning ends; NU/N series cylindrical roller bearings cannot bear axial loads and cannot be used as positioning ends. The spherical roller bearings can bear axial loads, but when bearing axial loads, one of the two rows of rollers will be overloaded so easily, and thus the specific actual problems must be analyzed in particular.
2. There is a radial load on the shaft extension end.
In other words, if there is an external radial load at the end of the shaft extension, the bearing bears the gravity of the rotor, and thus the axial force will be relatively large. At the same time, if viewed from another end, the non-shaft extension end appears not to have any load. When this is the case, then the bearing size on the extending end will be bigger and that of the non-extending end smaller. This kind of bearing size matching will make its performance and cost disproportionate. Not economical, and it might give some problems to the bearing either. 3. Convenience in maintenance In bearing maintenance, the load condition of the bearing on one end and the other end.
3. Convenience of maintenance
Since the positioning end bearing will bear the combined loads in axial and radial aspects, it tends to need more frequent maintenance and will be more frequently disassembled.
Then, when locating the bearing that requires higher maintenance at the non-extension end of the shaft, during maintenance, one must consider if there are additional steps in disassembling the fan, windshield, and other components. We cannot answer in one word whether it is better to put the positioning end bearing of a vertical motor on the top or bottom. Each choice needs to adapt to the corresponding working conditions. Only after understanding the basic principles can we adapt to changes and make appropriate choices.
Conclusion
An understanding of the structural similarities and differences between vertical and horizontal motors, with particular attention to bearing forces and configurations, is important. A comprehensive analysis of the forces on bearings, along with considering the implications of various bearing configurations, will be beneficial in making informed decisions for motor design optimization and maintenance. This approach will ensure that efficient and reliable motor operations occur in many applications.
