Thread engage/disengage torque
Thread engage/disengage torque
(OP)
I am seeking information to understand the relationship between tightening and losening a threaded connection. Does it take more or less torque to lossen a bolted connection than it does to tighten it? The level of detail I am seeking is that which will allow me to calculate fastener combinations for product design comparisons. Thanks





RE: Thread engage/disengage torque
On the same joint, I have seen breakaway torques of 120%-60% of the original assembly torque (single bolt - no interaction between bolts).
Are you trying to determine joint relaxation? A return to mark check can provide a good estimate of remaining preload. (Mark the fastener to abutment orientation after tightening, loosen the retighten to the mark). For better results you will have to use ultrasonic or strain measurement techniques.
RE: Thread engage/disengage torque
RE: Thread engage/disengage torque
In Handbook of Bolts and Bolted Joints edited by Bickford and Nassar, equations are shown for the tightening torque and loosening torque. They are functions of the bolt tension, thread flank angle, thread helix angle, friction coefficient for threads, friction coefficient for bearing surface, mean bearing diameter, mean thread contact diameter. Assuming identical variables for tightening and loosening (not necessarily true for friction coefficients), I got a tightening/loosening ratio of 1.3.
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