Torque (Pitch/Bolt) to Axial Force
Torque (Pitch/Bolt) to Axial Force
(OP)
I have an assembly in which I must translate torsional force (a torque from screwing in a piece), that pushes against a silicon ring, which pushes against a metal piece. I'm interested to see if the piece will deform or fracture.
I do not have the specs for the spring constant for the silicon ring. I'm just going to do calculations assuming the piece that is being torqued is directly pushing on the metal piece. I'm not entirely sure on how to go about calcuating this.
I know of the torque to axial force equation that is:
F=.2*D*T
However, this does not account for pitch....
I've included a hand calculation my boss did. I'm not sure if it is correct or not...
I will include the hand calculations with an illustration, as well as two pictures of the assembly modelled in CAD if it helps.
The torque is 15 in-lbs. The thread is a 7/8 - 32 pitch.
I do not have the specs for the spring constant for the silicon ring. I'm just going to do calculations assuming the piece that is being torqued is directly pushing on the metal piece. I'm not entirely sure on how to go about calcuating this.
I know of the torque to axial force equation that is:
F=.2*D*T
However, this does not account for pitch....
I've included a hand calculation my boss did. I'm not sure if it is correct or not...
I will include the hand calculations with an illustration, as well as two pictures of the assembly modelled in CAD if it helps.
The torque is 15 in-lbs. The thread is a 7/8 - 32 pitch.





RE: Torque (Pitch/Bolt) to Axial Force
RE: Torque (Pitch/Bolt) to Axial Force
RE: Torque (Pitch/Bolt) to Axial Force
The hand calculation is way off. The torque (15 in-lb) can be applied by your fingers, yet the thread diameter is almost an inch in diameter, so there is no way it could generate > 1000 lb of force.
You can find equations to calculate torque-tension relationship in MIL-HDBK-60 Threaded Fasteners - Tightening to Proper Tension, available free of cost here:
http://assist.daps.dla.mil/quicksearch/
RE: Torque (Pitch/Bolt) to Axial Force
http://euler9.tripod.com/fasteners/preload.html
which derives the 0.2 factor, and includes the effect of pitch.
i suggest that in your case, because you're compression a Si gasket, the your "joint" stiffness is much reduced ... maybe the derivation shows you how to account to that; maybe you need to determine your joint stiffness by test (controlled clamping of the joint).
RE: Torque (Pitch/Bolt) to Axial Force
RE: Torque (Pitch/Bolt) to Axial Force
another site ... the pic is why i thought to post it
RE: Torque (Pitch/Bolt) to Axial Force
If I use the T= k*d*F, I get a value of about 83 lbf. This is much lower than my bosses estimated 1500 lbf...
RE: Torque (Pitch/Bolt) to Axial Force
Using the 15lbf-in torque on a 7/8" diameter screw I get a load of 2.625lbf with the formula you have provided.
Normally to create a seal with an 'o' ring you compress the thickness or cross section of the 'o' ring by a %, usually off the top of my head about 15-30% of the section size.
One full turn of your screw will compress the ring by 0.031".
Your design as it stands does not appear to have any great control on how much the 'o' ring gets compressed, given the error on using torque setting your 'o' ring could get severly over or undercompressed.
In your last post you appear to be working out torque with your formula but your answers are in lbf.
regards
desertfox
RE: Torque (Pitch/Bolt) to Axial Force
I am getting the 85.71 lbf from
F= T/(K*D) = 15 in-lb/(.2*.875) = 85.71 lbf
Thanks for the help, I will look into the O-Ring compression.
RE: Torque (Pitch/Bolt) to Axial Force
I found why I got a different figure from you, in your original post you put:-
know of the torque to axial force equation that is:
F=.2*D*T
I should have checked and didn't I just used it.
So I agree with your later figures now.
regards
desertfox