Wang Yong
Vertical motors and horizontal motors have similar structures in terms of bearings, but the forces are different.
It is assumed that there is no axial force or radial force outside the motor. In a horizontal motor, the bearings at both ends bear the gravity of the rotor, and this force is a radial load on the bearings.
If the motor becomes a vertical motor, the gravity of the rotor becomes an axial load without bearing any external load. At this time, the two bearings have no radial load. Here we do not consider the radial load caused by the air gap asymmetry due to the offset of the stator and rotor centerline. Therefore, the bearings at both ends of the vertical motor bear axial force and no radial force.
The configuration of motor bearings is generally such that one end is positioned and the other floating. Regardless of whether the bearing is in the positioning end or the floating section, it can bear radial load; while the axial load is borne by the fixed end bearing, and the floating end bearing does not bear axial load.
Based on the above, all the weight of the vertical motor rotor is used as axial force and is exerted on the positioning end bearing, while the floating end bearing neither bears the axial force nor the radial force it bears.
Based on this principle, we can analyze the question. Should the positioning end of the vertical motor be at the upper end or the lower end?
In the following, we will use the terms "shaft extension end" and "non-shaft extension end" to describe it. As for whether the shaft extension end is placed above or below, the principle is the same.
Three aspects to note:
1, selection of bearings at both ends
Since the positioning end bears axial force, the positioning end needs to select a bearing that can withstand the axial force. The non-positioned end does not matter.
The most common selection is that deep groove ball bearings, angular contact ball bearings, etc. can withstand axial loads and can be used as positioning ends; NU/N series cylindrical roller bearings cannot withstand axial loads and cannot be used as positioning ends. Spherical roller bearings can bear axial loads, but when bearing axial loads, one of the two rows of rollers will easily be overloaded, so specific analysis of actual problems is required.
2, there is a radial load on the shaft extension end.
If there is an external radial load on the shaft extension end, when the bearing is also subjected to the rotor gravity (axial force), the force on the shaft extension end bearing will be relatively large; looking at the other end, there seems to be no load on the non-shaft extension end. When this happens, the bearing size at the bearing end will be larger, while the bearing at the non-extension end will be smaller. Such bearing size matching will cause an imbalance in performance and cost. Not only is it not economical, it may also cause bearing problems.
3, ease of maintenance
When maintaining bearings, consider the load conditions of the bearings at both ends. Since the positioning end bearing bears combined loads (axial and radial), it requires more maintenance and will face more frequent disassembly.
Then, when the bearing that requires more maintenance is placed at the non-shaft extension end, when performing maintenance, it is necessary to consider whether there will be additional steps in disassembling the fan, windshield and other components.
We cannot answer in one word whether it is better to place 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.
Article source: Lubrication standardization and practical fault diagnosis technology
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