Clamping Force on cylindrical object

[MrNut]

Hello, I have some questions regarding clamping force.

I have a two-piece cylindrical clamp which is to be clamped around a cylindrical part. It is a clamp installed on a product during transportation, where lashings go between the clamp and trailer.
The coefficient of friction and surface area between clamp and cylinder is known.

How would I go about finding the necessary clamping force to ensure the clamp does not slide down the cylinder, nor rotates around its own axis? There is to be a tension force applied in the two brackets.

I applied the forces which I believe will have an affect on the clamping force, but I believe the tension force will make the clamping force non-uniformly distributed across the cylinder.

From what I have found so far, the hoop stress may be relevant. I also looked at Roark's Formulas For Stress And Strain, it had a chapter (9.3) about circular rings and arches, this may also be relevant.

This is completely new to me, and I struggle to find good literature about the topic, so any help is greatly appreciated!

 

[EdStainless]

Unless your bracket is stiffer than the cylinder you will get very non-uniform surface pressure.

 

[desertfox]

Hi MrNut

We would need to know the value of the tensile loads which are pulling on the clamp because these appear to be pulling the bottom half of the clamp away from the cylinder. That said if the cylinder is free to drop into the bottom half of the clamp under its own weight then you only need to worry about the top half of the clamp and use the standard sliding friction formula to get the correct loadings for the bolts, apart from the clamp tensile loadings pulling on the clamp what other external forces are acting which might cause the cylinder to slide through the clamp?
If the clamp is a purchased item then just tighten the bolts to the recommended figure from the clamp supplier because that’s all you can do.

 

[mfgenggear]

Op
I would suggest a more robust clamp as well.
Machined from wrought mild sreel.

 

[3DDave]

It may be worthwhile to add a separate clamp below this one that is not subject to forces that would tend to reduce the load on one part of the clamp or provide twisting loads. This separate clamp would prevent this clamp from sliding down the cylinder.

 

[r6155]

What's all this for?
Pipe transportation doesn't require clamps.

 

[Stress_Eng]

The attachment hasn't been checked but it may give you some ideas on how to derive the reaction forces between the band clamp and the pipe due to bolt preloading. As stated previously, contact bearing pressure can be quite variable.

Edit 1 - Added update to calculations, now gives band clamp displacement at bolt position (possible closure of gap).
Edit 2 - Small update and increased thickness of clamp. Changed reactions so all reaction points are in contact [t=5mm, one point no contact (+ve disp't & 0 N reaction). t=6mm, all points in contact (-ve disp'ts)].

 

[rb1957]

try google "pipe clamps"

 

[MrNut]

Hi MrNut

We would need to know the value of the tensile loads which are pulling on the clamp because these appear to be pulling the bottom half of the clamp away from the cylinder. That said if the cylinder is free to drop into the bottom half of the clamp under its own weight then you only need to worry about the top half of the clamp and use the standard sliding friction formula to get the correct loadings for the bolts, apart from the clamp tensile loadings pulling on the clamp what other external forces are acting which might cause the cylinder to slide through the clamp?
If the clamp is a purchased item then just tighten the bolts to the recommended figure from the clamp supplier because that’s all you can do.

Hi, I should have mentioned that the cylinder is vertical, the clamp may only slide downwards if the clamping force is not high enough.
The tensile force is without a safety factor around 12000N, worst case scenario would probably be to assume that this force acts straight downwards.
Assuming M24 bolts with 600Nm of preload, the axial force from each bolt becomes around 125kN.

So it is the vertical component of the tensile force and gravity itself which can move the clamp along the cylinder. Whereas the other components of the tensile force separates the clamping bodies.

 

[MrNut]

What's all this for?
Pipe transportation doesn't require clamps.

Hi, it is for a school project. The cylinder is part of a framework structure of subsea equipment. Additional lashing points was needed to be added to the product during transportation, so this clamp was developed.

 

[MrNut]

Unless your bracket is stiffer than the cylinder you will get very non-uniform surface pressure.

Thanks for the info, the material is the same for the whole clamp.

 

[MrNut]

The attachment hasn't been checked but it may give you some ideas on how to derive the reaction forces between the band clamp and the pipe due to bolt preloading. As stated previously, contact bearing pressure can be quite variable.

Edit 1 - Added update to calculations, now gives band clamp displacement at bolt position (possible closure of gap).
Edit 2 - Small update and increased thickness of clamp. Changed reactions so all reaction points are in contact [t=5mm, one point no contact (+ve disp't & 0 N reaction). t=6mm, all points in contact (-ve disp'ts)].

Wow! Thank you so much, think this will put me in the correct direction!

 

[desertfox]

Hi MrNut

So if the cylinder is vertical and exerts 12kN downward force then you need to generate something like three to four times that figure of preload depending on the coefficient of friction across the two bolts in order to stop any slippage of the cylinder relative to the clamp. Depending on the bolt grade material you can achieve the correct bolt preload but not sure how the clamp bracket will fare.

 

[ctopher]

I have seen tubing crack or distort from this. The 'pinch' force where the ends come together is greater than the diametric force.
If you're only tying to hold the tube in place, add some shims between the clamps, or use something else.

 

[mfgenggear]

As a discussion brain storming.
Increase the width of clamp. To increase Mu
Clamp both sides to distribute static equilibrium.
A body diagram would be helpful

 

[mfgenggear]

I have seen tubing crack or distort from this. The 'pinch' force where the ends come together is greater than the diametric force.
If you're only tying to hold the tube in place, add some shims between the clamps, or use something else.

A trick I would use with tooling is to have a very small gap. But have enough force to clamp.
Clamp or cap fixture was allowed to flex minimal amount.