Clamping Torque

[EthanT24]

I am trying to calculate the applied clamping torque for each of 3 jaws that are used to clamp the end of a solid steel bar on a bar peeling machine.
Here is what I know:
1. Cylinder pressure = 1,850 psi
2. Cylinder bore = 14"
3. Clamp #1 has no linkage and the moment arm from point of force to rotation point is 46". Force is at an angle of 70.5 degrees.
4. Clamp #2 has 2 linkage joints. I took the orthogonal combined moment and came up with 84.5". Force at an angle of 91.4 degrees.
5. Clamp #3 has 2 linkage joints. Combined moment is 106.5". Force angle is 68.9 degrees.

My calculation using Torque = Force (Cylinder force) * Moment Arm Length (FT) * sin(Force Angle):

Clamp #1 = 1,072,881.17 ft-lbs
Clamp #2 = -580,761.27 ft-lbs
Clamp #3 = -539,324.03 ft-lbs

This seems high. Did I perform this calculation correctly? If not, suggestions are welcome. I have attached a picture of the carriage and dimensions.

 

[MintJulep]

You need to draw free body diagrams for each link and solve them all simultaneously.

 

[desertfox]

Hi EthanT24

Where is the calculation showing or calculating the sliding friction between the round bar and clamp faces?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[EthanT24]

That, I don't know because I don't know the torque being placed on the bar and acting against the clamps as it is being peeled. The goal here on this problem is to understand how much pressure the clamps are applying. We are having wear pad pre-mature wear pad failures and are concerned that we are applying more pressure to the bar than what the clamp pads can hold up to. By obtaining the clamping forces, I will complete an FEA assessment to see if the pressure is what is causing the pads to crack.

 

[desertfox]

Hi EthanT24

I can’t see enough detail in your post to understand how you are arriving at the forces, however as I see it you need the force acting perpendicular to the clamp pad at each jaw which pressing on the round bar, then you need the sliding coefficient of friction between the bar and clamp jaws, once you have that you can simply use mu= F/R. R being the force from the clamp and F being the friction force. So finally the max torque the clamps can hold will be the friction force F multiplied by the radius of the bar being clamped. The coefficient of friction is independent of any force it’s just a number.



“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Compositepro]

If the pads are failing, it is due to excessive contact pressure, not force. The contact area can be increased by matching the pad shape to the bar shape.

 

[BrianE22]

I believe the OP is only looking for the clamp load, not the friction torque. I'm probably missing it but what is the distance and angle between the pivot points and the normal load on the round bar?