Minimize torsional stress

During tightening, bolts are subjected to both tensile and torsional stress. The desired tensile stress (clamp load) is achieved when the bolt is stretched. Unwanted torsional stress (twisting) in bolts arises during tightening due to friction between the contact surfaces in the threads. High thread friction increases twisting of the bolts and causes yielding at lower clamp load levels than normal.

Applying an adhesive significantly increases thread friction during tightening. The graph to the right shows that when tightening bolts with adhesives on the threads, only half as much clamp load was obtained before reaching the yield points compared to when tightening similar lubricated bolts. Since NORD-LOCK’s unique wedge-locking technique is not affected by lubrication, the thread friction, and thereby also the torsional stress, can be minimized.

In addition, the diagram shows that at any given torque value the clamp load deviation for lubricated bolts is very low. Using NORD-LOCK washers together with a lubricant ensures that bolted joints will be safely locked at the highest possible clamp load level.

Example of a torque-load diagram
for M12 bolt (8.8)

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