Basic Knowledge of Diaphragm Couplings

Composition and Structure of Diaphragm Couplings
Couplings are mechanical components used to connect two shafts (driving and driven shafts) in different mechanisms to rotate together and transmit torque. In high-speed heavy-duty power transmission, some couplings also have the functions of buffering, damping, and improving the dynamic performance of the shaft system. Today, we will focus on introducing diaphragm couplings, which are a type of flexible coupling with elastic elements. This article specifically discusses its importance.
 
Diaphragm couplings belong to metal flexible couplings, which use metal elastic diaphragms as flexible elements to transmit torque. Its main characteristics include: high torque transmission capacity, absorption of misalignment by diaphragm deformation, no relative movement between parts leading to no wear, no noise, long vibration damping life, and no lubrication required. The torsional stiffness and critical speed can be adjusted by changing the outer diameter or wall thickness of the intermediate section, thereby improving the torsional vibration characteristics of the unit.
 
A diaphragm coupling consists of at least one diaphragm and two hubs. The diaphragm is fastened to the hub with pins and generally does not loosen or cause recoil between the diaphragm and the hub. Some manufacturers provide couplings with two diaphragms, and some provide three diaphragms with one or two rigid elements in between, connected to the hubs on both sides. The difference between single-diaphragm and double-diaphragm couplings lies in their ability to handle various deviations. Due to the need for complex bending of the diaphragm, single-diaphragm couplings are not suitable for eccentricity, while double-diaphragm couplings can bend in different directions simultaneously to compensate for eccentricity.
 
Main Characteristics of Diaphragm Couplings:

(1) Strong ability to compensate for misalignment of two shafts, with double the angular displacement compared to gear couplings, minimal reaction force during radial displacement, high flexibility, allowing for certain axial, radial, and angular displacement.

(2) Significant damping effect, no noise, no wear.

(3) Suitable for working in high temperatures (-80 to +300 degrees Celsius) and harsh environments, capable of safe operation under impact and vibration conditions.

(4) High transmission efficiency, up to 99.86%. Particularly suitable for medium and high-speed high-power transmission.

(5) Simple structure, lightweight, small size, easy installation and disassembly. Can be disassembled without moving the machinery (referring to the type with an intermediate shaft), no lubrication required.

(6) Accurate transmission of speed, no slippage during operation, suitable for precision mechanical transmission.
 
Currently known diaphragm couplings can manufacture maximum coupling transmission power of 50,000 kW, a maximum speed of 80,000 rpm, and a maximum length of 12 meters. Moreover, diaphragm couplings can undergo various types of modifications.
 
Applications of Diaphragm Couplings:
Diaphragm couplings are widely used in shaft drive of various mechanical devices, such as pumps (especially high-power, chemical pumps), fans, compressors, hydraulic machinery, petroleum machinery, printing machinery, textile machinery, chemical machinery, mining machinery, metallurgical machinery, aviation (helicopters), high-speed power transmission systems for ships, steam turbines, piston-powered mechanical transmission systems, tracked vehicles, and high-speed, high-power mechanical transmission systems for generator sets, which are commonly used in high-speed transmission shaft systems after dynamic balance.
 
Causes of Abnormal Noise in Diaphragm Couplings:

(1) The gap between the two halves of the coupling is too wide, causing the diaphragm to experience significant axial force, resulting in wear of the serration hole or serration bolt, leading to abnormal noise.

(2) Excessive axial offset or deflection angle of the two halves of the coupling can also cause vibration and abnormal noise during equipment operation.

(3) Differences in speed between the driving end and the driven end can also cause vibration and abnormal noise during equipment operation.

(4) Malfunction of the speed encoder of the motor, causing the motor's speed to fluctuate, resulting in abnormal noise in the diaphragm coupling.