Many manufacturers continue to use torque control technologies as the primary method to specify and control how they tighten threaded fasteners. However, torque measurement alone may be misleading.
Every fastener, hole dimension, material strength and lubrication condition differ, making each assembly a unique event. Manufacturers that rely on torque alone may not achieve the target clamp load and face potential rework or safety-critical errors.
A fastener behaves similarly to a stiff elastic band. The more a fastener stretches, the more force reacts to return the fastener to its original position. This ‘clamping’ force is what holds the joint components together and helps the assembly remain secure. It is vital that the ‘elastic’ fastener stretches enough to apply the proper clamp load but not so much that the joint components or fastener becomes damaged.
As a bolt rotates, it stretches and the joint compresses. The amount of angle rotation and the thread pitch of the fastener dictate the axial distance equivalent to the stretch and compression.