What Is the Impact of Loose Coupling Bolts?

When the coupling is in operation, if the coupling bolts become loose or slip out, the normal operation of the mechanical equipment will be affected. Next, let us introduce the effects of loose coupling bolts.

A coupling is a transmission component that firmly connects the drive and driven shafts of the equipment to rotate together. There are three ways for couplings to transmit torque: the first is through bolt transmission, the second is through frictional force transmission at the joint surface of the coupling, and the third is through the combination of bolt transmission and frictional force transmission at the joint surface. In the process of combining the transmission of bolts with the transmission of friction force on the joint surface using the third method, the torque received by each bolt should be uniform, so that during the load change process, the force transmitted by each bolt is also uniform.

If two bolts in relative positions within the same plane of the coupling are tightened, and the bolt shear force is equal, then the coupling only transmits torque; If the bolt looseness causes unequal shear forces, in addition to torque, there is also a force - F acting on the center of the rotor, which changes with the load of the unit. Therefore, the vibration of the unit changes with the load. Bolt loosening can also cause changes in the relative position of the two half hubs, deviation in the center of mass of the coupling, and the emergence of new additional unbalanced masses, resulting in additional unbalanced forces, manifested as vibration surges. The relative positions of the two half hubs change with the change of load, so the vibration of the unit also shows a sudden increase with the change of load.

In the coupling industry, premature damage to the coupling often occurs due to the loosening of fasteners, leading to significant economic losses. Therefore, coupling manufacturers will choose appropriate locking methods for the fasteners, which is an important guarantee for the long-term, reliable, and trouble-free operation of the coupling. So when choosing a coupling, we should pay attention to whether the locking method used by the coupling manufacturer is suitable. Nuts used on disc or diaphragm couplings generally use locking nuts, and at the same time, we should pay more attention to installation and use.

Fig.1 Disc coupling with spacer