ABSTRACT
In addition to controlling the primary factors of torque or angle, it is usually advantageous to monitor a second (or third) variable. If you monitor and record torque data throughout the rundown sequence, you create a dynamic profile of the fastening process. This dynamic profile, or signature, can be recorded as torque versus time or torque versus angle. When comparing signatures from one rundown to another, normal differences occur because of friction, part variations, or tool speed. But the signature also reveals joint abnormalities that a peak torque reading alone cannot detect. For example, the profile of a cross-threaded nut compared to a normal signature may look like Figure 15. Defining a torque-time window as a secondary criterion for this joint prevents accepting a faulty rundown. Generally tightening sequences are programmed such that the signature must pass through various preset "windows" for the rundown to be acceptable.
