Bolted Joint - Measurement of Frictional Torque of Threads in Bolt

Measurement of Frictional Torque of Threads in Bolt

The torque is applied by means of suspending the weights on one end of the rope and other end is wound around the head of the fastener and tied to the projection. The amount of load is increased gradually until the fastener starts rotating. The applied load is then calculated by adding up the weights. This is the load that is required to overcome the friction between the threads. Similarly, the net applied torque is calculated by multiplying the resultant load by the radius of the fastener's head.

In another method, the torque is applied to the nut by an electromagnetic force. A specially designed gripper is used to grip the nut. A bar magnet is mounted on the gripper, and the gripper is then surrounded by a coil of wire through which alternating current is passed. As the magnetic field from the permanent magnet interacts with the field created by the coil, the permanent magnet (and thus the nut) is subjected to a torque. This is quite similar to the construction of an electric motor, and hence a motor can be directly used to provide the torque. A stepper motor can be used so that the torque is provided in steps, each of which causes a small, measurable angular displacement in the nut from which the torque can be calculated. The discrete torques can be added to get the net torque consumed in displacing the nut from one end of the fastener to the desired location. This is the torque that is required to overcome the friction between the threads.