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Ball bearings are preferred over other types of bearings for machines rated up to 75 kW. Which of the following is not true for ball bearings?

Ball bearings are preferred over other types of bearings for machines rated up to 75 kW. Which of the following is not true for ball bearings? Correct Answer they require more maintenance

Bearings:

These are used for supporting the rotating parts of the machines and are of two types :

  1. Ball or roller bearings
  2. Sleeve or bush bearings
     

1. Ball Bearings: Upto about 75kW motors, ball bearings are preferred to other bearings because of their following advantages :

  • They have low friction loss
  • They occupy less space
  • They require less maintenance
  • Their use allows a much smaller air gap between the stator and rotor of an induction motor
  • Their life is long.
     

Their main disadvantages are with regard to cost and noise, particularly at high motor speeds.

2. Sleeve Bearings: These are in the form of self-aligning porous bronze bushes for fractional kW motors and in the form of journal bearings for larger motors.

Since they run very silently, they are fitted on super-silent motors used for driving fans and lifts in offices or other applications where noise must be reduced to the absolute minimum.

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