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| HYDRAULIC TORQUING SERVICES - HOW IT WORKS |
Torque tightening utilizes the applied force to turn the nut, which reacts through the thread helix to elongate the bolt. It is the varying friction between the threads of the stud and nut and between the nut face and flange that causes inconsistency between the applied force and the Residual Bolt Load. Surface finish, lubrication and material type all change the effects of friction.
- Only 10% of applied torque effort results in useful bolt load;
- 50% is wasted in overcoming nut face friction; and
- 40% is wasted in overcoming friction between the bolt threads and the nut threads.
In addition to tighting variation in friction, torque tightening is also affected by cross talk. Cross talk is the elastic interaction in the flange by subsequent tightening of individual bolts. When torque is applied to a single stud the resultant residual load compresses the flange joint further. As bolts behave as springs, this joint compression results in loss of spring tension in adjacent bolts and even bolts across the flange. The result is a typical saw tooth pattern experienced by torque tightening.
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