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Coupling Types, Performance Requirements and Selection

Couplings, a mechanical component used to firmly connect the driving shaft and the driven shaft in different mechanisms to rotate together and transmit motion and torque. Sometimes it is also used to connect shafts and other parts (such as gears, pulleys, etc.). It is often composed of two halves, which are respectively connected by keys or tight fittings, and are fastened at the ends of the two shafts, and then the two halves are connected in some way. The coupling can also compensate for the offset (including axial offset, radial offset, angular offset or comprehensive offset) between the two shafts due to inaccurate manufacturing and installation, deformation during operation or thermal expansion, etc.; and shock mitigation and vibration absorption.

Most of the commonly used couplings have been standardized or standardized. Generally, it is only necessary to correctly select the type of coupling and determine the type and size of the coupling. When necessary, the load capacity can be checked and calculated for its vulnerable weak links; when the rotation speed is high, the centrifugal force of the outer edge and the deformation of the elastic element should also be checked, and the balance check should be carried out.


Couplings can be divided into two categories: rigid couplings and flexible couplings.
Rigid couplings do not have buffering properties and the ability to compensate for the relative displacement of the two axes, and require strict alignment of the two axes. However, this type of coupling has a simple structure, low manufacturing cost, convenient assembly and disassembly, and easy maintenance, which can ensure that the two axes are relatively stable. High neutrality, large transmission torque, and wide application. Commonly used are flange couplings, sleeve couplings and jacket couplings.
Flexible couplings can be divided into flexible couplings with no elastic elements and flexible couplings with elastic elements. The former type only has the ability to compensate for the relative displacement of the two axes, but it cannot buffer and reduce vibration. The common ones are slippery. Block couplings, gear couplings, universal couplings and chain couplings, etc.; the latter type contains elastic elements, in addition to the ability to compensate for the relative displacement of the two axes, it also has the functions of buffering and damping. However, due to the limitation of the strength of the elastic element, the transmitted torque is generally not as good as the flexible coupling without elastic element. The common elastic sleeve pin coupling, elastic pin coupling, plum-shaped coupling, tire type coupling Couplings, serpentine spring couplings and reed couplings, etc.

Performance requirements

According to different working conditions, the coupling needs to have the following properties:
(1) Portability. The mobility of the coupling refers to the ability to compensate for the relative displacement of the two rotating components. Factors such as manufacturing and installation errors between connected components, temperature changes during operation, and deformation under load all place requirements on portability. Movable performance compensates or relieves additional loads between shafts, bearings, couplings and other components due to relative displacement between rotating components.
(2) Buffering. For occasions where frequent load starts or working load changes, the coupling needs to have elastic elements for buffering and vibration damping to protect the prime mover and the working machine from being damaged or not damaged.
(3) Safe, reliable, with sufficient strength and service life.
(4) Simple structure, convenient assembly and disassembly and maintenance.


Selection of Coupling Type When selecting a coupling type, the following items should be considered.
① The size and nature of the required transmission torque, the requirements for buffering and vibration reduction functions, and whether resonance may occur.
② The relative displacement of the two shaft axes caused by manufacturing and assembly errors, shaft load and thermal expansion deformation, and relative movement between components.
③ The allowable dimensions and installation methods, and the necessary operating space for easy assembly, adjustment and maintenance. For large couplings, it should be possible to disassemble and assemble under the condition that the shaft does not need to move axially.
In addition, the working environment, service life and conditions such as lubrication, sealing and economy should also be considered, and then a suitable type of coupling should be selected with reference to the characteristics of various types of couplings.

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