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Thread: Roller bearing data help

  1. #1

    Question Roller bearing data help

    Hello,

    I am looking at deep grove ball bearing catalogs and I came across some data that doesn't seem to make sense.

    For some bearings (SKF Explorer series) dynamic load rating is much higher than static load rating. How is this possible and which figure should I use for an intermittent 25 rpm load.

    Thanks.
    Last edited by roketman; 09-05-2012 at 03:07 AM.

  2. #2
    Technical Fellow jboggs's Avatar
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    I know the answer to your question but that's because I called them and asked years ago.
    Did you try that?

  3. #3
    Hi jboggs,

    I have written to forum first as I thought many people may had the same question at some point. Can you share what you learnt from the firm please?

  4. #4
    Administrator Kelly Bramble's Avatar
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    A simple search on the interent revealed...

    "Dynamic Load Capacity of a bearing

    The dynamic load capacity of a bearing any bearing can be selected from the manufacturer's bearing catalogue where all details pertaining to the particular bearing are given. The dynamic load capacity of the bearing is unique and has been determined based on various empirical formulas which the manufacturer has developed based on the years of experience and research carried out.

    The dynamic load capacity is a value which has a unit of ‘N’ or ‘kN’ (Newtons or Kilo Newtons). The Dynamic Load capacity can be defined as the load that will give a life of one million revolutions of the inner race. The dynamic load rating hence plays a vital role for the bearing life. The relation between the bearing life and the dynamic load capacity is expressed as follows:


    L = (C/P) ^3 - for Ball bearing
    L = (C/P) ^10/3 – for Roller bearings
    Here L = Bearing L Life,
    P = Equivalent Radial Load, Newtons
    C = Dynamic Load capacity of the bearing, Newtons

    Since we normally know the expected life for a bearing and the equivalent radial load on the bearing, it would be easy for us to determine the value of C, the dynamic Load capacity of the bearing. All that we need to do is to select a bearing, whose dynamic load capacity value, C is greater than the value calculated.

    Static Load Capacity:

    The static load capacity of the bearing is denoted by Co. The unit is Newtons (N). This value is given to ensure that the equivalent radial load does not exceed the static load capacity of the bearing. This denotes the amount of load the bearing will be able to withstand in standstill condition without creating any deformation in the bearing i.e. to the inner race, outer race or the rolling elements. By experiments it has been concluded that when a bearing is subjected to this load i.e. the maximum of the Static Load capacity, it tends to produce a deformation of 0.0001 times the diameter d of the rolling element. "

    References Machine Design Article Lamar Stonecypher

    You should size your bearing such that the static and dynamic ratings exceed your application requirements.

  5. #5
    Hi, what's quoted above is the definition of load ratings. It doesn't explain how dynamic can be higher than static.

  6. #6
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by roketman View Post
    The dynamic load capacity of the bearing is unique and has been determined based on various empirical formulas which the manufacturer has developed based on the years of experience and research carried out.
    I suggest that you contact the manufacturer and ask what the above statement means in terms of "various empirical formulas " and "Reasearch".

  7. #7
    I think I found the answer to my question. I have been in two training sessions, one form Timken Bearings and the other from GRW. I asked my question to both companies. GRW said having higher dynamic rating than static did not make sense however when ISO standards used for testing and calculations such results may be obtained. In short, dynamic load rating is only a theoretical value is not significant before application of load factors. Timken said they correct the ISO standards with their proprietary formulas so static load rating is always higher than dynamic one.
    I hope this is clear for everyone. Thanks to all who have replied.

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