Flange coupling is a rigid coupling, which connects two semi-couplings with flanges with two shafts respectively by ordinary Ping Jian, and then connects the two semi-couplings into a whole by bolts to transmit motion and torque. There are two main structural forms of this kind of coupling: ① The shaft alignment is realized by reaming holes with bolts, and the torque is transmitted by the bolt rod bearing extrusion and shearing; (2) Centering is achieved by matching the shoulder on one half coupling with the groove on the other half coupling. The bolts connecting the two semi-couplings can be ordinary bolts of Grade A and Grade B, and the torque is transmitted by the friction torque of the joint surfaces of the two semi-couplings.