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Thread: Calculation question

  1. #1
    Associate Engineer
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    Calculation question

    Hi there,

    Hopefully someone much better at calcs than me can help, I'm looking for a way to calculate 2 problems. I have attached a sketch which will hopefully illustrate what I'm after.
    I have various large flanges of different diameters widths and masses acting down on fixed rollers of different centres.
    What I'm looking for are calculations that give me;
    a) the reaction force on the roller
    b) the maximum torque that can be applied to the flange before the torque would overcome the friction between the flange and roller.

    Note: Both rollers and flange are steel and unlubricated.

    Thanks in advance,
    Chris
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  2. #2
    Technical Fellow jboggs's Avatar
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    Your question is theoretical in nature. It is basic force vector calcs. And you are really just looking for the equations to use.
    All of which cause me to suspect that this is a homework question. Is it?

    Be that as it may, if the supports are truly "rollers", there will be no friction between them and the flanges.

  3. #3
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    jboggs

    It's not homework I'm far too long in the tooth for that it's for a real situation, the rollers are basically used to turn the large flange and when I say large actually from 26' to 35' diameter. The reason I need to know the friction is that sometimes the flange has an out of balance torque load and at lighter loads there is a potential for slippage. I am looking for the calcs as maths is not my strong point, I should have paid more attention in school. I've attached a picture of the type of equipment
    Any help would be appreciated, thanks.
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  4. #4
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    The reaction force on each roller depends on the angle between the vertical centerline of the the drum and rollers and any outside forces applied tom the drum (for example, the horizontal forces associated with winding a cable or wire on the drum which will bias the loading toward the two rollers on the pulling force side .

    Assuming no applied outside forces, the reaction on each roller from the loaded drum alone can be calculated by the below formula.

    F = 1/4 x loaded drum weight x L /Lv

    where:
    L = the direct distance from the drum C/L to the roller C/L
    Lv = the vertical distance from the drum C/L to the roller C/L

    A published general friction factor for clean dry steel against dry steel is 0.8 but to address the effects of contamination and roller hardening to would probably be best to use a factor no greater than 0.4. (For reference: lubricated steel on steel has a factor of .16; and, any coatings or paint can definitely reduce the friction factor)
    Last edited by JAlberts; 08-22-2014 at 11:35 PM. Reason: formula rewritten due to paragraph width

  5. #5
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    Thanks JAlberts, much appreciated.

  6. #6
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    Hi Tollie / JAlberts

    currently i have a simular project but i have no idea how to calculate the torque require to rotate this system. can anyone of you help me on this.

  7. #7
    Technical Fellow jboggs's Avatar
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    The torque required to bring it up to speed and the torque required to maintain speed are two different things. One involves acceleration and friction. The other just involves friction. The rotary inertia of the system can be calculated. The friction of the system will be an educated estimate. It can be deduced from how long it takes the system to slow to a free-wheeling stop when all drivers are disconnected.

  8. #8
    I have a similar issue with loaded drum. i appreciate if some one can help me with this.
    we have a drum 60" Diameter and 30,000Lbs
    It is positioned on four trundles of which two are idler and two are drive ones. These trundles are 12" OD They are all steel. i want to know what length the trundles must be to be able to rotate the drum rotation speed 1 RPM
    appreciate if you can help out.
    Thanks

  9. #9
    Technical Fellow jboggs's Avatar
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    Your question makes no sense to me. How can the length of the trundles affect the speed of the drum?

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