Atlas Copco Industrial Technique Ab

Arne Torgny Roloff

Erik Vilhelm Persson

In an apparatus and a method of evaluating a clamp force (F) in a threaded joint between a bolt and a matching threaded piece during a tightening operation, a torque (T) provided to the joint is continuously measured and ultra-sonic pulses are simultaneously induced into the bolt such that a time of flight (TOF) of the pulses in the bolt is measured. In response to an increase of the measured torque (T) an increase rate (dT/d&#x3b1;) of the torque (T) is determined, from which an initial rotation angle (&#x3b1;) where the torque (T) starts to increase due to bolt deformation is determined. An increase rate (dTOF/d&#x3b1;) of the time of flight (TOF) is also determined. A total increase of the time of flight (&#x394;TOF) during the tightening operation is then determined based on the initial rotation angle (&#x3b1;) and the increase rate (dTOF/d&#x3b1;) of the time of flight (TOF).

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Arne Torgny Roloff