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Thread: PV Calculations

  1. #1
    Associate Engineer
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    Feb 2017
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    Arrow PV Calculations

    Hi everyone,

    I hope someone can shed some light on this for me. I have to prove that a bearing that I am using in a valve component (rotating 90 degrees) conforms to requirements.

    I have come across this calculation that a company use that calculates the resultant pressure on the bearing under load.

    the Pressure (on each bearing) being easy to calculate, matches what I have on FEA (25 MPa).

    I have two questions:
    1) Am I right by applying a force to only Half of the ID of the Bearing used. I.e. assuming that contact is only made on half of the ID area of the bearing at all times.
    2) The link I have provided seems pretty good, My only concern is that It takes into account the material of the shaft, however it doesn't account for the material of the bearing. Would I be right in assuming that the calculator some how works out a coefficient of friction between the bearing and shaft contact surfaces. By using the "application characteristics" section. By assuming heat dissipation and temperature?


    Figure 1 - Application Characteristics

    Any help I would really appreciate,

    Thanks

    Ryan
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Feb 2011
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    Bold Springs, GA
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    1) Am I right by applying a force to only Half of the ID of the Bearing used. I.e. assuming that contact is only made on half of the ID area of the bearing at all times.
    Probably ~ if the loading applied is normal to the bearing and accounting for a bending moment is not required.

    2) My only concern is that It takes into account the material of the shaft, however it doesn't account for the material of the bearing. Would I be right in assuming that the calculator some how works out a coefficient of friction between the bearing and shaft contact surfaces.
    Static bearing? bushing or rollering bearing being used?

    Often in bearing and shaft designs the perspective materials used are different. The stiffness, hardness, etc.. will be different therefore we analyze or design to the weakest of the two. I know this is not typically an academic approach which would be to micro analyze all frictions and interactions of applied loading, stress, thermal effects and so on.. As you're aware the FOS and ultimately functional testing proves an application in service.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
    Join Date
    Feb 2017
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    Thanks for the reply Kelly, it is more of a journal bearing. The bearing stays still and the shaft oscillates through 90 degrees to open and close (uni-directional load).




    Thanks Ryan
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