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Thread: Moment force on bearing in swivelcastor

  1. #1
    Associate Engineer
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    Question Moment force on bearing in swivelcastor

    Hello all, first time here and i'm excited to see if you can help me with a calculation i face.

    I designed a swivel castor, and i calculated the mass and friction force once pushed around loade with 200kg of weight on it. (Blue arrow is 1962N, and the red arrow 24.5N) which causes a moment in the bearing off 50.5 Kn*mm.
    I have no idea if the bearing can hold this, i know things for axial and radial forces but not for a moment.

    Also, later i want to play with the maximum swivel offset since that makes it easier to turn the cart.

    Is there anyone who can help me with this?

    Noud
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  2. #2
    Technical Fellow jboggs's Avatar
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    The type of bearing you're using is not intended for this type of application. It is intended for mainly radial loads with lesser thrust loads. In this case the thrust loads are the primary forces. You need a thrust bearing with a captured center to absorb the off-center loads created by the offset swing radius. Do a Google search for "swivel caster cross section" and look at the images. You'll see what I mean.

    Which brings up a question - why are you even designing a device that is in such wide use already? You could probably buy a proven design off the shelf somewhere.

  3. #3
    Associate Engineer
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    Thank you for your reply,

    I know these bearings aren't ideal for this situation, but due costs and assembling-time it's almost mandatory to use these 'simple' bearings for this configuration.

    Though the question should be asked more in a general way, this is only one (the simplest) of many 'swivelheads' we designed. For higher loads, we have bearingcombination with tapered roller bearings and thrustbearings for way more loadcapacity. But i can not theoratically substantiate that some combinations can hold more load then others. Due to the information about moments on bearings i miss. If we get asked why a swivelhead can hold (for example) 500 kg, we can only say that 'it never broke before' or 'that's how everyone is doing it'..

    That's why i wanted to calculate forces on the swivelheads, but it seems rather complicated to me.

  4. #4
    Administrator Kelly Bramble's Avatar
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    There's a statics modeler / calculator here:
    https://www.engineersedge.com/calcul...d-modeling.htm

    It's a simple statically indeterminate problem. Sum the forces in the x and y solve for the unknowns.

    You can also find a similar too example equations and calculators here:
    https://www.engineersedge.com/beam_calc_menu.shtml
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
    Technical Fellow jboggs's Avatar
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    Unless I'm reading this incorrectly it appears that you are looking for a rating that normally does not appear on rotary ball bearings, a max moment load. At least I do not recall seeing such a rating. I would expect that type bearing in that application to deteriorate and fail fairly quickly. If you insist on using that type of bearing in this application my best advice would be to talk directly to the application engineers at the bearing manufacturers.

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