Stainless Steel Diaphragm1

Structure of Stainless Steel Diaphragm

The structure of metal diaphragm flexible coupling is mainly composed of metal diaphragm group (diaphragm), half coupling, intermediate section, compression element, bolt, locknut, washer, etc. The working principle is: the torque is input from the half-coupling at the driving end, and the torque is transmitted to the diaphragm group through the main transmission torsion bolts arranged at intervals along the circumference, and then the diaphragm group is transmitted to the intermediate section through the bolts, and also output by the diaphragm group, bolts and half-coupling. The metal diaphragm is the key component of the flexible coupling. It consists of a number of thin metal diaphragms stacked to form a diaphragm group, through which torque and motion are transmitted.

The diaphragm of the coupling is mainly subjected to three forces, the axial thrust given to it by the main shaft of the unit, the film stress and the inertial centrifugal stress generated by the rotational torque of the steam turbine. The diaphragm is an elastic diaphragm, and the axial thrust will not have a destructive effect on it. Membrane stress and inertial centrifugal stress due to torque.

1. Membrane stress caused by torque. Let the transmitted torque be T, the total number of pieces be m, the number of bolt holes be n, and the diaphragm radius be r. From the simplified conditions, it is known that the force on each main bolt is F=T/nmr. It can be seen that under the same conditions, the force on the diaphragm is inversely proportional to the number of sheets and the number of bolt holes. The four-hole diaphragm coupling is much more stressed than the hole, and it is bound to be easily damaged.

2. The transverse stiffness of the coupling can be obtained by fitting the experimental data: four-bolt diaphragm: K=2000N/m; six-bolt diaphragm: K=3000N/mo. It can be seen that the stiffness of the six-bolt hole diaphragm is better than Four-bolt hole diaphragm, and stiffness is also an important factor affecting the long-term operation of the diaphragm coupling.

3. Centrifugal stress generated by inertia

The simplified mechanical model of the coupling is a spring-mass system with two degrees of freedom. Calculation of the first-order critical speed frequency of the coupling. There are two factors that affect the critical speed of the coupling, one is the stiffness of the diaphragm, and the other is the mass of the intermediate section, which is proportional to the stiffness of the diaphragm and inversely proportional to the mass of the intermediate section. In the implementation, the weight of the middle section of the coupling remains unchanged, which is 3kg. Substituting the obtained stiffness data into the formula, the critical speed of the four-bolt coupling is 50.3Hz, and the critical speed of the six-bolt coupling is 75.5Hz. Six-bolt couplings can withstand higher critical speeds than four-bolt couplings. The centrifugal stress can be loaded according to the radial force F=(2n/60)2rp. According to the previous calculation of the critical speed, the critical speed of the four-bolt diaphragm is 50.3Hz, that is, 3018r/min. Working at a speed of 4250r/min causes the inertial centrifugal stress to exceed the bearing capacity, resulting in excessive deformation of the diaphragm, which in turn intensifies the radial and angular Other stresses such as deflection force cause huge impact damage to the coupling diaphragm.