Method of tightening threaded fasteners

摘要

The invention is directed to a method for tightening threaded fasteners by means of a controlled fastener-driving tool. The tightening of the fasteners is controlled by the elastic limit thereof. The slope of the actual load-strain characteristic curve is continuously determined during the fastener-driving operation. This actual slope is compared with a predetermined slope determined with reference to a characteristic curve. When the predetermined slope is reached, a control signal is generated to switch off the fastener-driving tool. In practice, departures occur in the actual characteristic curve of an actual fastener-driving operation. In order to compensate for such departures from the characteristic reference characteristic curve, a comparison is made in the straight portion of the actual load-strain characteristic curve with the predetermined characteristic slope of the reference characteristic curve and a corrective value for transformation of one characteristic curve to the other is formed in the presence of a departure of the slopes. For this purpose, before the actual determined slope is compared with the predetermined switch-off slope one of the two quantities is transformed by means of a corrective value.