Effect of thrust force on torque?

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Discussion Overview

The discussion revolves around the effect of axial thrust force on the torque produced by a motor turning a shaft. It explores the implications of large axial forces on motor performance, bearing requirements, and the relationship between axial force and torque in the context of motor design and operation.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the effect of a large axial force on the motor, specifically whether it influences the torque (T) and the overall performance of the motor.
  • Another participant suggests that large axial forces can lead to rapid wear of the bearings, indicating a potential issue with motor longevity.
  • A different viewpoint emphasizes the necessity of a thrust bearing to accommodate large axial forces, noting that many motors may not include such bearings.
  • Further, it is mentioned that vertical motors typically incorporate thrust bearings to handle axial loads, contrasting them with horizontal motors that may lack such features.
  • One participant asserts that the air gap torque is fixed by the magnetic circuit and is unaffected by axial force, while also stating that increased axial force raises friction in the thrust bearing, which could reduce the motor's available output torque.

Areas of Agreement / Disagreement

Participants express differing views on the impact of axial force on torque and motor performance. There is no consensus on the necessity of thrust bearings in all motor designs, nor on the specific effects of axial force on torque output.

Contextual Notes

Participants discuss various types of bearings and their roles in motor performance, highlighting differences between vertical and horizontal motor configurations. The implications of axial force on friction and torque are noted, but the discussion does not resolve the complexities involved.

Who May Find This Useful

This discussion may be of interest to engineers, motor designers, and students studying mechanical systems, particularly those focused on motor performance and bearing applications.

PCarson85
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If I have a motor that is turning a shaft with only a small torque required but the shaft is also being forced into the motor, axially at a large force, what is the effect on the motor here?

If Faxial is large, does this effect T and how does this effect the motor?

Scan - 2020-04-20 10_00_16.jpeg
 
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Depending on the bearings, it will wear out pretty soon ! :wink:
 
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PCarson85 said:
only a small torque required but the shaft is also being forced into the motor, axially at a large force, what is the effect on the motor here?
If there is a large axial force, you need a thrust bearing to accommodate that force. I don't think many motors include a thrust bearing (I could be wrong), but if you use a motor with a "double shaft", you can put the thrust bearing on the end of the shaft that protrudes out the back of the motor...

https://ae01.alicdn.com/kf/H800cb6f513b9434c94ca5c1d24e0ee0et.jpg

1587396663271.png
 
BTW, with a little Google searching, it looks like motors with thrust bearings are used in the vertical orientation (where you would expect more axial shaft loading). Here is a good starting point:

https://www.efficientplantmag.com/2018/04/understand-vertical-motor-bearings/

Vertical motors differ from horizontal units in various ways, including their oil-leak risks.

By Jim Bryan, Electrical Apparatus Service Association (EASA)

Bearing construction is a key difference between vertical motors and horizontal motors that are mounted vertically. Vertical motors typically drive pumps using thrust bearings. Horizontal motors rarely have those types of bearings. Understanding relevant construction and configuration factors is crucial when confronting lubrication-related issues that can be associated with vertical-motor bearings.

VERTICAL-MOTOR-BEARING CONSTRUCTION
Vertical motors commonly have a thrust bearing and a guide bearing. The thrust bearing is usually at the top of the motor and may consist of one or more angular contact bearings, a spherical roller bearing, or a hydrodynamic plate bearing. The force and direction (upward, downward, or balanced) of the applied axial load dictate the type and number of thrust bearings needed to obtain optimum performance and service life.
 
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The air gap torque is fixed by the magnetic circuit and is not affected by Faxial. Faxial is going to increase the friction in the thrust bearing and this in turn will reduce the available output torque of the motor.
 
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