The Experts: Can I yield my bolt by over-tightening?

Do I risk yielding my bolt, due to over-tightening, when using Nord-Lock wedge-locking solutions?

It is true that the clamp load increases during untightening, as a result of the so-called “wedge effect”. During dismantling, the cams slide against each other, thereby increasing the distance between the washers. This stretches the bolt and creates an increase in clamp load. This increase is at a maximum when the washers pass over the top of a cam.

However, the rises of the cams have been optimised to make it impossible to overstretch the bolts during untightening, provided that tightening guidelines are followed. Nord-Lock’s guidelines are based on clamp load levels of between 62 and 75 percent of the bolt’s yield strength, depending on bolt quality and use of lubricant. To utilise more of the bolt capacity, further control of the tightening method and tightening tool is required to prevent the bolt from exceeding its yield point and starting to deform permanently.

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