When selecting a coupling, the designer should choose the coupling based on the needs of the shafting transmission system, and should avoid simply considering the coupling of the main and driven ends. 
　

　 (XNUMX) Mechanical characteristics of power machine
　　
　　Between the power machine and the working time, the main and driven ends are connected through one or several couplings of different varieties or different types and specifications to form a shaft transmission system.In mechanical transmission, power machines are nothing more than electric motors, internal combustion engines and steam turbines.Due to the different working principles and structures of the power machines, their mechanical characteristics are very different. Some run smoothly, and some have shocks during operation, which have unequal effects on the transmission system. 
　　The mechanical characteristics of the power machine have a certain impact on the entire transmission system. For different types of power machines, due to their different mechanical characteristics, the corresponding power machine coefficient KW should be selected and the best coupling suitable for the system should be selected.The type of power machine is the basic factor for selecting the type of coupling; the power of the power machine is one of the main basis for determining the size of the coupling, and it is proportional to the torque of the coupling. 
　　Most of the power machines in the transmission system of a fixed mechanical product are electric motors. The power machines in the transmission systems of the mechanical products (such as Bobo, various vehicles, etc.) are mostly internal combustion engines. When the power machine is an internal combustion engine with a different number of cylinders, torsional vibration must be considered. The influence on the transmission system is related to the number of cylinders of the internal combustion engine and whether each cylinder is working normally.In this case, flexible couplings should generally be selected to adjust the natural frequency of the shafting, reduce the torsional vibration amplitude, thereby damping, buffering, and protecting the transmission device components, improving the centering performance, and increasing the stability of the output power. 
　　 (XNUMX) Load category
　　
　　Due to different structures and materials, the couplings used in the transmission systems of various mechanical products have very different bearing capacities.The load category is mainly for the impact, vibration, forward and reverse rotation, braking, frequent start and other reasons of the working load of the working machine to form different types of loads.In order to facilitate selection and calculation, the load of the transmission system is divided into four categories. 
　　The load category of the traditional system is the basic basis for selecting the type of coupling.For working loads with large changes in shock, vibration and transfer knowledge, flexible couplings with elastic elements, that is, elastic couplings, should be selected to buffer, reduce vibration, compensate for axis deviation, and improve the performance of the transmission system.The torque during frequent starting, forward and reverse rotation, and braking is several times the torque during normal and stable operation. It is overload work, which will inevitably shorten the service life of the coupling elastic element. The coupling only allows short-term overload, generally short-term The overload shall not exceed 2~3 times of the nominal torque, ie [Tmax]≥2~3Tn. 
　　Low-speed and heavy-duty working conditions should avoid the use of couplings that are only suitable for small and medium power, such as: elastic sleeve pin coupling, core-type elastic coupling, polygonal rubber coupling, tire coupling, etc.; For shafting systems that control overload safety protection, safe couplings should be used; for shafting systems with large changes in load and impact and vibration, flexible couplings with elastic elements and better cushioning and damping effects should be selected.The load-bearing capacity of the metal elastic coupling is higher than that of the non-metal elastic element; the reliability of the elastic coupling with the elastic element being squeezed is higher than that of the elastic coupling with the elastic element being sheared. 
　　 (XNUMX) Allowable speed of coupling
　　
　　The allowable speed range of the coupling is determined by calculation according to the maximum outer edge size of the allowable linear speed of different materials of the coupling.The allowable speed range of couplings of different materials, varieties and specifications is different. Changing the material of the coupling can increase the allowable speed range of the coupling. The allowable speed for steel is greater than the allowable speed for cast iron.