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Thread: Help with Centrifugal Force

  1. #1
    Associate Engineer
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    Help with Centrifugal Force

    We have spin cast units with a liquid pumped into the center of a mold and then spin the mold until the material cures to make a hollow cylinder up to 24 inch diameter x 24 feet long.

    I am looking for the proper name to determine the force exerted on the frame that holds the mold. My predecessor used F=WrC and the value of C is 0.000028416. I can't determine what or where the value for C came from. The reason I am looking for this value is determine what the frame must with stand to hold together and not bow or bend.

    Thank you for any response.

  2. #2
    Administrator Kelly Bramble's Avatar
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    W is typically the total load or force applied, r might be radius, F is typically force, I agree C is unknown..

    You should consider just redoing the equations and calculations to be sure of what you are doing..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    To convert rpm to radians per second, multiply by .10472
    The obtain centrifugal force you need to square the rotating speed so to convert to rpm^2 use .10472^2 or .010966
    You also need to convert lbs to mass units in that case we divide lbs by 386 in/sec^2. the gravitational acceleration.
    .019066/386 = .00002841 There's your C.

    The usual formula for a single point mass centrifugal force is mass x radius x speed squared.

    I don't see the speed (rpm) number in your formula.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by Hudson View Post
    To convert rpm to radians per second, multiply by .10472
    The obtain centrifugal force you need to square the rotating speed so to convert to rpm^2 use .10472^2 or .010966
    You also need to convert lbs to mass units in that case we divide lbs by 386 in/sec^2. the gravitational acceleration.
    .019066/386 = .00002841 There's your C.

    The usual formula for a single point mass centrifugal force is mass x radius x speed squared.

    I don't see the speed (rpm) number in your formula.
    Awesome..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
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    Quote Originally Posted by Kelly Bramble View Post
    W is typically the total load or force applied, r might be radius, F is typically force, I agree C is unknown..

    You should consider just redoing the equations and calculations to be sure of what you are doing..
    Thank you Kelly.

  6. #6
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    Hudson,
    That helps a lot. So to determine the correct rectangle tube to withstand the mass I used a stress strength calculator. I need to identify the shear force in lbf and the bending moment in lbf*in.

    Using the calculation from above F=WrC with our data will the F be the same as shear force? Calculation is 1,014 lbf using the data below???
    RPM = 26^2 or 676
    W = 1776 lbs or W*C 0.050
    r = 30 in
    C = .00002841

  7. #7
    Principle Engineer
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    You have not presented a clear picture of the problem or exactly how your equation came to be. We went from casting a cylinder to a rectangular tube of unknown dimensions and we added a speed but there is no axial length. 0.050 came from where? Sorry, I can't help.

    If you cannot figure it out, call the manufacturer of the casting equipment or a local engineer or engineering professor from a nearby school.

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