Because of the different structure and material, the bearing capacity of each mechanical product transmission system has a great difference. The load category is mainly based on the impact of working load, vibration, positive and negative rotation, braking, frequent start-up and other reasons to form different types of load. The load of the transmission system is divided into four categories for the convenience of calculation.

The load category of traditional system is the basic basis of choosing the coupling variety. Shock, vibration and the change of the larger work load, the flexible coupling should be selected with elastic components, namely, elastic coupling, to cushion, vibration, compensation axis offset, improve the transmission system performance. Starting frequent, positive and negative rotation, braking torque is the normal smooth working time of several times, is overloaded work, will inevitably shorten the coupling elastic components service life, coupling only allow short overload, generally short time overload should not exceed the nominal torque $number times, that is [Tmax]≥2~3tn.

The low speed heavy duty operation condition should avoid selecting the coupling which applies only to medium and small power, for example: elastic sleeve pin coupling, core-type elastic coupling, multi-angle rubber coupling, tire-type coupling, etc. need to control the overload protection of the shafting, it is appropriate to choose the safety coupling; It is advisable to select elastic couplings with elastic elements and good cushioning and damping effects. The bearing capacity of metal elastic couplings is higher than that of non-metallic elastic components; elastic coupling with elastic element being squeezed is more reliable than elastic coupling which is sheared by elastic element.