Torque to Force relation

[rlara]

Hi there:

Im trying to determine the force to torque relationship for a bolted surface. This surface should maintain a certain pressure (e.g. 8000 psi). Usually 4 bolts are used, so i determined the axial force needed from each bolt. My problem is how to determine how much torque needed to reach that axial force. I have found T=K*D*F and also another equation used in power screws that involves picth angles. I would apreciate any help with this.

Also bolt material is stronger that taped surface (Bolt= Stainless steal 35 ksi; Surface: Aluminum T6-6061 32 ksi) can I make the same analysis on the aluminum as the one i used for the bolt?

Thanks

Rudy

 

[motorman]

T= k*D*F, But in the real world, the actual torque that the bolt gets is hard to verify because an unknown amount of torque goes into over coming friction instead of stretching the bolt. Go to this other forum and browse and submit your question there

forum725

 

[jackboot]

rlara,

I have used that equation in the past, but in order to obtain anything useful from it you must know "K". I tried to used "K" values in my old engineering book- they were not even close. However, I was approaching the yield strength of the bolt for my application.

If you can determine your bolt strain- and therefore your stress/preload- you might be better off.

Try Ultra-sonic length measurements or use a micrometer if space permits.

jackboot

 

[rlara]

Thanks for the pointers:

I have posted the question on forum 725. I looks like this analysis is more involved that i thought hopefully i can get an aproximate k value if not I see in to ultrasonic measurements.

Thanks for your help

Rudy

 

[poetix99]

You ought to review Thread 404-27748 as well.

Friction, friction, friction!!! Thread friction (no pun intended) and bearing surface friction.

Even with well lubricated fasteners, the amount of torque going into friction related strain energy is commonly regarded to be between 50% and 90% of the torque work.

 

[poetix99]

p.s. hit

http://www.boltscience.com

for some discussion of clamped "systems" and the effects of differing relative stiffness of fastener vs. "foundation" (abutment).