The use effect and selection of diaphragm coupling

Diaphragm coupling (also known as lamination, steel sheet coupling) is a new type of two-axis coupling device with broad development prospects that can replace gear couplings. It consists of two shafts at both ends and a diaphragm group. , Intermediate shaft and connecting bolts.Among them, the diaphragm set is made up of a number of thin stainless steel coated diaphragms, which are used to transmit torque and the two shafts connected by the Yunji coupling. Due to manufacturing and installation errors, load-bearing deformation, thermal deformation, and mechanical Due to the sinking of the seat, a certain degree of axial, angular, and radial deviation between the axes will cause additional loads on the shafts, bearings and couplings, which will worsen the working conditions of the unit. The coupling can absorb the three-way offset between the axes through the flexibility of the diaphragm. The diaphragm coupling can transmit large torque under working conditions, and has the advantages of simple structure, convenient processing, and no need for lubrication, so it is widely used Used in aviation, shipbuilding, petrochemical industry, machinery manufacturing and other fields.

The diaphragm is the key element of the diaphragm flexible coupling. Due to the offset between the axes, the transmission of torque, and the bearing of centrifugal force, the diaphragm is in a complex state of stress during operation. The diaphragm acts as an elastic element and bears the load.

The bolts of two adjacent holes on the diaphragm are respectively connected with the convex edges of the shafts at both ends and the intermediate shaft, that is, the bolts are arranged in opposite directions, resulting in a relative position between them through the flexibility of the diaphragm. When a hole is located When the position of is fixed, the normal force is caused by pre-deformation at the two adjacent holes, and the third hole that is separated by one hole can be fixed and restrained.

The diaphragm is a key component, and its fatigue life determines the normal service life of the diaphragm coupling.From the above finite element analysis, the stress state of the diaphragm can be obtained. Since the diaphragm is a notched part, its fatigue strength and life depend on the larger local stress and strain at the stress concentration (or strain concentration). Therefore, it is suitable The fatigue crack initiation life is calculated by the local stress-strain method.

Under normal circumstances, the transmission torque should be determined according to the actual transmission power and actual working speed of the unit. The diaphragm coupling selected in this way can not only meet the torque transmission requirements, but also has a light structure and additional force on the unit. And the bending moment is also small.In order to pursue safety, some users add layers when choosing couplings. The couplings selected in this way are often too bulky and the use effect is not good.The coupling is subjected to the combined action of steady-state load CAL torque, axial misalignment medium ring mouth alternating load CAL alternating torque, angular and radial misalignment during operation.Coupling manufacturers usually leave a fatigue coefficient when designing the product. The composite stress point of the key force component generally falls on the lower left of the modified Goodman curve (like a constant life curve), causing fatigue The coefficient is greater than 1.When selecting the coupling, the manufacturer will multiply a reasonable working condition coefficient according to the severity of torque fluctuations under different working conditions. The actual working point will be farther away from the Goodman curve.The actual compound stress point position when choosing different working condition coefficients.According to the working condition coefficient of the diaphragm coupling, the working condition coefficient should not be less than 1.5. When it is necessary to match the shafting system, the supply and demand parties can negotiate to reduce the working condition coefficient, but the value should not be less than 1.2.

The selection of the diaphragm coupling should be based on the machine type provided by the package supplier or the host manufacturer and the shaft power under normal conditions, and should not be over-coded.Of course, other working conditions should be considered in some occasions.

The correct choice of diaphragm coupling: 

1. The diaphragm coupling is composed of at least one diaphragm and two shaft sleeves.The diaphragm is fastened to the shaft sleeve with a pin and generally does not loosen or cause backlash between the diaphragm and the shaft sleeve.Some manufacturers provide two diaphragms, and others provide three diaphragms, with one or two rigid elements in the middle, and the two sides are connected to the shaft sleeve. 

2. The characteristic of diaphragm coupling is a bit like a bellows coupling. In fact, the way the coupling transmits torque is similar.The diaphragm itself is very thin, so it is easy to bend when the relative displacement load is generated, so it can withstand up to 1.5 degrees of deviation, while generating a lower bearing load in the servo system. 

3. Diaphragm couplings are often used in servo systems. Diaphragms have good torque rigidity, but are slightly inferior to bellows couplings. 

4. On the other hand, the diaphragm coupling is very delicate, and it is easy to be damaged if it is misused or not installed correctly during use.Therefore, it is very important to ensure that the deviation is within the tolerance range of the normal operation of the coupling.

The diaphragm coupling relies on the elastic deformation of the diaphragm to compensate for the relative displacement of the two shafts connected. It is a high-performance flexible coupling with metal elastic elements. It does not require lubrication, has a compact structure, high strength and long service life. There is no rotation gap, and it is not affected by temperature and oil pollution. It has the characteristics of acid resistance, alkali resistance, and is suitable for shaft transmission in high temperature, high speed, and corrosive medium conditions. It is widely used in shaft transmission of various mechanical devices.

The design of the diaphragm coupling should be able to operate continuously in the unit for more than 3 years, and the coupling and shaft connection should be able to withstand 175% of the large continuous torque during unit operation; when transmitting 175% of the large moment specified by the buyer The coupling does not break when torque is applied, but the connection is allowed to fail; when the displacement of the axis of the two shafts connected by the coupling reaches 125% of the rated value, it can operate normally and continuously.For couplings with spacer sleeves, the spacer sleeve should have sufficient length so that the coupling can be assembled and disassembled without moving the shaft.The coupling hub and shaft should adopt an interference fit.

Compared with the gear coupling, the diaphragm coupling has no relative sliding, no lubrication, sealing, no noise, basically no maintenance, more convenient to manufacture, and can partially replace the gear coupling.

Diaphragm couplings are widely used in shaft transmission of various mechanical devices, such as water pumps (especially high-power and chemical pumps), fans, compressors, hydraulic machinery, petroleum machinery, printing machinery, textile machinery, chemical machinery, mining Machinery, metallurgical machinery, aviation (helicopter), naval high-speed power transmission systems, steam turbines, piston-type power mechanical transmission systems, crawler vehicles, and generator sets high-speed, high-power mechanical transmission systems, which are applied to high-speed transmission after dynamic balance Shafting has become more common.