# Help with Centrifugal Force

• 01-21-2020, 11:04 AM
dougdean
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.
• 01-21-2020, 01:34 PM
Kelly Bramble
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..
• 01-22-2020, 11:01 PM
Hudson
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.
• 01-23-2020, 07:59 AM
Kelly Bramble
[QUOTE=Hudson;16319]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.[/QUOTE]

Awesome..G:J
• 01-23-2020, 09:35 AM
dougdean
[QUOTE=Kelly Bramble;16310]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..[/QUOTE]

Thank you Kelly.
• 01-23-2020, 09:54 AM
dougdean
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
• 01-23-2020, 11:30 AM
Hudson
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.