The Experts: Should I change my tightening torque with Nord-Lock?
Q: Does the use of Nord-Lock washers affect my tightening routines? How?
A: When a tightening torque is applied to create a clamp load in a joint, friction under the bolt head (or nut) and in the threads must be overcome before any torque goes to achieving the clamp load.
Since the Nord-Lock washers feature serrations, the coefficient of friction under the bolt head (or nut) will be slightly increased. The thread friction remains unchanged. A slightly higher tightening torque is therefore required to achieve the same clamp load as for a flat faced joint.
Nord-Lock’s general tightening guidelines are taking the increased friction into account and permit to achieve a very accura te tightening.
Some users choose to keep their torque values when implementing Nord-Lock washers. It will result in a somewhat lower (-10% to -20%) but still acceptable preload.
It is also important to remember that friction varies significantly depending on bolt grade, bolt size, lubricant and joint material so real torque values may actually differ from torque guidelines.
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