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Bolt Torque to Tension
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Posted by: feenaujm

04/19/2009, 20:26:56

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I am trying to figure out how to convert a given torque on a given thread size to tension (force) in the bolt. I am not finding any standard tables in Machinery's Handbook, etc. Does anyone have torque-tension conversion equations?

Thanks!










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: Bolt Torque to Tension
: Bolt Torque to Tension -- feenaujm Post Reply Top of thread Engineering Forum
Posted by: Heviiguy

05/04/2009, 15:14:38

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Hello feenaujm,

Regardless of the formula offered, one can't "calculate" the residual bolt stress after a bolt has been torqued. At best, one can only make an educated guess. The reason for this is the dreaded "K" factor... The K factor is based on myriad conditions in the field which cannot be predicted. Sure, you can find many tables of K factors on line and elsewhere but, the point is that it's impossible for them to be refleective of reality. This is why Fastener A tightened to the same torque as Fastener B may not exhibit the same residual bolt load as the latter. In fact, one may be overtightened while the other may be undertightened! Trying to relate input torque to final residual bolt stress is like predicting how your new sandwich will taste before taking a bite! You chew it first, let your tongue do its work and only then do you know if it's good or not. Same thing applies to critical bolts: Tighten them and then, measure residual bolt stress.

Best regards, Hevii Guy










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: Bolt Torque to Tension
: Bolt Torque to Tension -- feenaujm Post Reply Top of thread Engineering Forum
Posted by: Kelly Bramble

04/19/2009, 23:47:09

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Welcome to the Engineers Edge!

See - /calculators/torque_calc.htm










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: : Bolt Torque to Tension -- Kelly Bramble Post Reply Top of thread Engineering Forum
Posted by: rams

04/24/2009, 03:41:00

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Bolt torgue is a function of two parameters
1. Friction Coefficient between the flange and the bolt
2. Nominal Diameter of the Bolt

Torque = Friction_coefficient * Nominal_diameter_of_the_bolt*Pretension_Force.

Normally for steel flanges and bolts, the friction co-efficeint is 0.12 to 0.14.










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