True or false?

Many people believe that after tightening part of the torque still remains in the bolt.

The Truth: The torque is a force multiplied by a moment arm. The force is applied at the moment arm (e.g. a wrench) and then rotates around the bolt axis. The moment arm is the length from the centre of the axis to the point where the force is being applied. Once the tightening is complete this external force is reduced to zero and with it the torque.

During tightening the bolt will work as a torsional spring and twist. The twisting will result in some residual torsion stress in the bolt that will work to unscrew the bolt. This can be interpreted as residual torque left in bolt.

To keep the residual torque as small as possible a low friction co­efficient inside the bolting would be desirable. However, since friction is the only reason why the bolt does turn loose under its own preload, the friction coefficient should remain as high as possible.

The Nord-Lock group offers two ideal solutions for this dilemma. If torquing is the preferred tightening method, our wedge-locking washers will prevent the residual torque from unscrewing the bolting. Alternatively, twisting can be avoided completely by using Superbolt MJTs for torsion-free, purely axial preloading. Rely on our bolting experts to help you make the right choice.

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