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Ball bearing- inner and outer ring - move at two different constant speeds-possible?

  1. Jul 5, 2011 #1
    My regards to all

    I am current doing my thesis for my masters. I have completed my work, but i seemed to have taken one thing for granted.
    lets assume there is a Single Row, Deep Groove Ball Bearing.
    Here what i want to know is CAN the outer ring and inner ring move at two different constant rotations, in the same direction.
    I know it might be quiet simple a question, but i am primarily concerned with the rate at which the balls will wear.

    the specifications of the scenario are as follows
    please refer this picture for nomenclature - http://www.reliance.com/mtr/images/befig4.gif

    let us assume the outer ring to rotate at = x rads/sec
    then inner ring is expected to rotate at = 2x rads/sec
    [the rpm is not supposed to be very high, on the order or max 60 rpm, so its very less]

    I really want to know if under these conditions how long would the ball last - I do agree there should be a great increase in wear as apposed to one of the rings being static, but will it excessive wear so as to make the device impractical.

    SUMMARY - Can the outer and inner rings of a single Row, Deep Groove Ball Bearing rotate at TWO DIFFERENT CONSTANT speeds IN the SAME direction. If so, how bad is the increase in wear of the balls.

    Thanks to all in advance
  2. jcsd
  3. Jul 6, 2011 #2
    Re: ball bearing- inner and outer ring - move at two different constant speeds-possib

    If the loading stays the same, then I don't see why the wear rate would be any different than having one race fixed and the other rotating a x rad/sec. Having both races rotate at different speeds (including opposite directions) isn't all that unusual in some equipments. The bearings for planet gears would be one such situation, although with a much greater speed differential.

    If my understanding is too elementary, I would be very interested in understanding what is happening to change the wear rate.
  4. Jul 6, 2011 #3
    Re: ball bearing- inner and outer ring - move at two different constant speeds-possib

    thanks a million for the reply.. i was having doubts about how i had worded the question.
    I have designed a gear systems for the pedicabs (cycle rickshaws) in India. These people and REALLY very poor and use a fixed sprocket system to pull loads of up to 500kgs.
    So Ive designed a very simple two speed planetary system for this situation. Things is they cant afford maintenance, so Ive designed it to be as sturdy and as maintanence free as possible.
    The only doubts I had was weather dude to my design would the bearings become a major maintenance issue, but i am glad its not going to be.
    Current I am writing the white paper to be published and would really be glad to send you the article.
    I could use all the criticism possible. These people cannot be given a system that is flawed.

    Thanks again
    and my name is Arun btw
  5. Jul 7, 2011 #4
  6. Jul 7, 2011 #5


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    Re: ball bearing- inner and outer ring - move at two different constant speeds-possib

    What causes bearings to wear out is fatigue of the races and balls. As the ball rolls across some point on the race, that point on the race undergoes compression, and then relaxes again.

    As a thought experiment, consider a bearing in which the inner and outer races rotate in the same direction at exactly the same speed. The balls of this bearing wouldn't rotate at all, they would only orbit around the axis, remaining in contact with the inner and outer races in the same location all the time. Now imagine a load on this bearing that rotates at exactly the same speed as the bearing such that the load is always applied at the same point on the races and is always transfered by the same balls. Such a bearing will have a load profile identical to a bearing that isn't rotating and has a static load on it such as a stationary truck. There would be no fatigue because contact stresses on the races wouldn't change, they would remain constant as long as the bearing was loaded in this way. Life would be infinite.

    If the inner and outer races move at different speeds however, there will be cyclic stresses on the balls and races which is a function of how often the load coincides with some point on the race. What is important to the bearing is how often the load passes through that point. So to determine life, use the standard B10 calculations but figure out how often the load is actually rotating relative to either of the races.
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