Torque Guide
It has been reported that approximately 50% of applied torque is needed to overcome the friction caused by the nut/bolt bearing surface being applied against the mating joint surface. Approximately 40% of the applied torque is needed to overcome the friction of the mating thread surfaces. Therefore, only approximately 10% of the applied torque produces tension in the bolt.
Many variables can affect the torque tension relationship. The following are some known examples of factors that can influence the actual pre-load achieved by a given application torque:
- Joint design
- The hardness and type of materials of the mating joint members
- Natural variation of joint/fastener dimensions due to manufacturing processes
- Surface finish of the parts
- Percentage of thread flank engagement
- Hole clearance
- Perpendicularity of the contact surfaces
- Supplemental coatings, thickness and lubricity
- High performance additional lubricants
- Cut vs. rolled threads
- Interference caused by burrs, thread nicks, dirt etc.
- Type and accuracy of tool used to tighten the fastener
- The speed of tightening
- Where torque is applied (head of bolt vs. nut)
- Operator influence
- Job conditions
Any values supplied by American Bolt Corp. are intended to provide only a target torque. The only accurate way to establish a specific pre-load is through torque tension testing of the fasteners to be used in the actual joint.
