Reduction of relaxation induced tension scatter in fasteners

摘要

A method of reducing variations in the static torque of threaded fasteners (36), as measured after a relaxation period, uses an instrumented nutrunner (10) to "break" the joint (34). Breaking the joint (34) is done by monitoring the torque (T) and angle (α) of the fastener (36) during a torque recovery cycle. The angle (α) of the fastener (36) is advanced until a threshold torque (Tsp) is reached and then the fastener (36) is turned an additional predetermined number of degrees. A static audit may be simultaneously performed by storing torque and angle values. Static torque (Tso) is distinguished from break away torque (Tb) by detecting the point of minimum curvature of the subsequently produced torque angle curve.